Abbe, T.B., and D.R. Montgomery, Large woody debris jams, channel hydraulics and habitat formation in large rivers, Regulated Rivers-Research & Management, 12 (2-3), 201-221, 1996.
Field surveys document the accumulation of large woody debris (LWD) into structurally distinctive jam types in the alluvial channel of the Queets River on the Olympic Peninsula of north west Washington. Calculations, field observations and historical evidence show that these jams can form stable structures controlling local channel hydraulics and providing refugia for riparian forest development over decades and possibly centuries. Distinctive spatial patterns of LWD, pools, bars and forested islands form in association with particular jam types. The deposition of 'key member' logs initiates the formation of stable bar apex and meander jams that alter the local flow hydraulics and thereby the spatial characteristics of scour and deposition leading to pool and bar formation. Historical evidence and the age structure of forest patches documents the temporal development of alluvial topography associated with these jam types. Bar apex jams, for example, are associated with a crescentic pool, an upstream arcuate bar and a downstream central bar that is the focus of forest patch development. Experimental and empirical studies in hydraulic engineering accurately predict channel scour associated with jams. Individual jams can be remarkably stable, providing long- term bank protection that creates local refugia for mature forest patches within a valley floor environment characterized by rapid channel migration and frequent disturbance. Processes controlling the formation, structure and stability of naturally occurring LWD jams are fundamental to the dynamics of forested river ecosystems and provide insights into the design of both habitat restoration structures and ecosystem-based watershed management.
Abernethy, B., and I.D. Rutherfurd, The effect of riparian tree roots on the mass-stability of riverbanks, Earth Surface Processes and Landforms, 25 (9), 921-937, 2000.
Abrahams, A.D., G. Li, and J.F. Atkinson, Step-Pool Streams - Adjustment to Maximum Flow Resistance, Water Resources Research, 31 (10), 2593-2602, 1995.
Steep headwater streams are often characterized by alternating steps and pools, which may be described by mean step height (H) over bar and mean step length (L) over bar. A conceptual model is developed based on the notion that the largest floods are just capable of moving the largest debris in the channel. The model suggests that step pools evolve toward a condition of maximum flow resistance because maximum resistance implies maximum stability and that this condition is achieved when steps are regularly spaced and the mean step steepness (H/L) over bar is slightly greater than the channel slope S. To test this conceptual model, four series of flume experiments were performed. These experiments show that the relation between resistance to flow and (L) over bar is convex upward with maximum flow resistance occurring when steps are regularly spaced and have (H/L) over bar/S values between 1 and 2. Field measurements reveal that 18 natural step-pool streams also satisfy the inequality 1 less than or equal to (H/L) over bar/S less than or equal to 2, strongly suggesting that the form of such streams is adjusted to maximize resistance to flow. The results of the flume experiments are inconsistent with the proposition that step pools form as antidunes, as Froude numbers for the flume step pools at which flow resistance was maximized fall well below those values usually associated with these bed forms.
Adams, R.S., and R.M. Bustin, The effects of surface area, grain size and mineralogy on organic matter sedimentation and preservation across the modern Squamish Delta, British Columbia: the potential role of sediment surface area in the formation of petroleum source rocks, International Journal of Coal Geology, 46 (2-4), 93-112, 2001.
Adenlof, K.A., and E.E. Wohl, Controls On Bedload Movement in a Sub-Alpine Stream of the Colorado Rocky-Mountains, Usa, Arctic and Alpine Research, 26 (1), 77-85, 1994.
Agrawal, Y.C., and H.C. Pottsmith, Instruments for particle size and settling velocity observations in sediment transport, Marine Geology, 168 (1-4), 89-114, 2000.
Akan, A.O., Tractive force channel design aid, Canadian Journal of Civil Engineering, 28 (5), 865-867, 2001.
The Manning formula and the tractive force equation are combined and written in terms of dimensionless parameters. Predetermined solutions to this equation have been obtained and presented in chart form. Also, a mathematical expression is obtained that approximates the chart to determine the channel width explicitly.
Allan, A.F., and L. Frostick, Framework dilation, winnowing, and matrix particle size: The behavior of some sand-gravel mixtures in a laboratory flume, Journal of Sedimentary Research, 69 (1), 21-26, 1999.
Allen, J.R.L., A Simplified Cascade Model For Transverse Stone-Ribs in Gravelly Streams, Proceedings of the Royal Society of London Series a- Mathematical Physical and Engineering Sciences, 385 (1789), 253-266, 1983.
Allen, P.M., J.G. Arnold, and B.W. Byars, Downstream Channel Geometry For Use in Planning-Level Models, Water Resources Bulletin, 30 (4), 663-671, 1994.
Alley, R.B., K.M. Cuffey, E.B. Evenson, J.C. Strasser, D.E. Lawson, and G.J. Larson, How glaciers entrain and transport basal sediment: Physical constraints, Quaternary Science Reviews, 16 (9), 1017-1038, 1997.
Allison, R.J., and D.L. Higgitt, Slope form and associations with ground boulder cover in arid environments, northeast Jordan, Catena, 33 (1), 47-74, 1998.
Anderson, R.S., Eolian Ripples As Examples of Self-Organization in Geomorphological Systems, Earth-Science Reviews, 29 (1-4), 77-96, 1990.
Anderson, M.J., and P. Legendre, An empirical comparison of permutation methods for tests of partial regression coefficients in a linear model, Journal of Statistical Computation and Simulation, 62 (3), 271-303, 1999.
This study compared empirical type I error and power of different permutation techniques for the test of significance of a single partial regression coefficient in a multiple regression model, using simulations. The methods compared were permutation of raw data values, two alternative methods proposed for permutation of residuals under the reduced model, and permutation of residuals under the full model. The normal- theory t-test was also included in simulations. We investigated effects of (1) the sample size, (2) the degree of collinearity between the predictor variables, (3) the size of the covariable's parameter, (4) the distribution of the added random error and (5) the presence of an outlier in the covariable on these methods. We found that two methods that had been identified as equivalent formulations of permutation under the reduced model were actually quite different. One of these methods resulted in consistently inflated type 1 error. In addition, when the covariable contained an extreme outlier, permutation of raw data resulted in unstable (often inflated) type 1 error. There were no significant differences in power among the three permutation methods (raw data permutation, reduced-model permutation and full-model permutation), but all had greater power than the normal-theory t-test when errors were non-normal. The reduced model permutation method had the most consistent and reliable results of the methods investigated here for the test of a partial regression coefficient. However, reasonably extreme situations needed to be simulated in order to distinguish methods from the normal- theory t-test and from one another. Permutation of raw data, permutation under the reduced model, and permutation under the full model are generally asymptotically equivalent.
Anderson, M.J., Effects of patch size on colonisation in estuaries: revisiting the species-area relationship, Oecologia, 118 (1), 87-98, 1999.
The effects of patch size on the colonisation and succession of intertidal invertebrates and algae were investigated in an estuary near Sydney, New South Wales, Australia. The specific aim was to test explicitly for the presence of a species-area relationship, and examine whether this could be explained by the random placement hypothesis (i.e. that the number of species per unit area was the same on patches of different sizes). In addition, I tested the extent to which differences in numbers of species reflected differences in the composition of assemblages. Wooden panels of three different sizes (10 x 10 cm, 20 x 20 cm and 40 x 40 cm) were placed in the field on intertidal oyster leases in each of two different experimental trials: spring (October 1994) and summer (January 1995). Independent replicate measures of the number of colonising species on panels were obtained after different periods of time, up to 25 months. I also obtained measures of abundance of individual species and composition of assemblages on panels of different sizes. This allowed specific tests of the hypothesis that the size of the patch being colonised is important in structuring these assemblages. The strength of the species-area relationship increased through time on panels submersed in October, but the trend was reversed for panels submersed in January. There was a significant interaction between factors of patch size and time of submersion for multivariate measures of differences in composition among replicates. The random placement hypothesis was supported in certain situations, but not in others. When rejected, it was far different reasons on panels submersed in the two different trials. Panels initiated in October tended to have proportionally greater numbers of species per unit area on larger panels, while the panels initiated in January tended to have more species per unit area on smaller panels. There was an identifiable relationship between differences in numbers of species and differences in species composition for panels submersed in October. This was not true, however, for panels submersed in January, where the species-area relationship did not hold after longer periods. The succession of organisms through time was, overall, more important in structuring the assemblages than was the size of the patch being colonised. The species-area relationship should not necessarily be regarded as a truism - it did not always hold in this system. The initial timing of experiments with respect to recruitment and succession influenced the results.
Anderson, S.P., K.M.H. Fernald, R.S. Anderson, and N.F. Humphrey, Physical and chemical characterization of a spring flood event, Bench Glacier, Alaska, USA: evidence for water storage, Journal of Glaciology, 45 (150), 177-189, 1999.
Anderson, M.J., and A. Clements, Resolving environmental disputes: A statistical method for choosing among competing cluster models, Ecological Applications, 10 (5), 1341-1355, 2000.
The protection of whole assemblages of species requires that such assemblages be identified in some nonarbitrary, quantitative manner. Clustering methods can be used to identify groups or clusters of observations (i.e., sites, transects, quadrats, etc.) on the basis of multivariate assemblage data, where each species is a variable. There are many kinds of cluster analyses, all potentially providing different outcomes, that is, different clusters of the multivariate observations. The wide choice of clustering methods and the necessarily subjective choice of which method and measure of similarity to use for a particular data set. is problematic. It can lead (and has led) to disputes about the way multivariate observations should be grouped, causing conflicts in making environmental decisions. We present a statistical test for choosing among competing cluster models and demonstrate its use with a case in point. The method provides an objective way to discriminate among competing models in order to determine the model that best fits the available data. Provided each party in a dispute identifies and articulates the cluster model it supports, the method can give a nonarbitrary judgment concerning the best model. This method provides an important tool for the resolution of environmental disputes concerning the presence of a particular community at a particular place and time, which may be impacted by a proposed development.
Andrefouet, S., L. Roux, Y. Chancerelle, and A. Bonneville, A fuzzy-possibilistic scheme of study for objects with indeterminate boundaries: Application to French Polynesian reefscapes, Ieee Transactions On Geoscience and Remote Sensing, 38 (1), 257-270, 2000.
This communication describes the study of an ecological system using remote-sensing data and image-analysis tools derived from possibility theory. Possibility theory enables the construction of membership functions using a multisource fusion algorithm. The sources of information are the sampled training stations. We test:to see if the possibilistic algorithm is able to provide results with an accuracy at least equal to that provided by traditional probabilistic-classification algorithms. Then, for each pixel,we analyze the hierarchy of membership degrees output by the fusion to study the spatial structure of an ecosystem composed of objects: that lack precise boundaries. We characterize patches or gradients,:boundary rates, and transition states. As an example, a scheme of analysis for underwater reefscapes at Moorea Island, French Polynesia, is proposed, The nonparametric multisource fusion method has an accuracy of 82% (overall normalized-percentage agreement), while a probabilistic maximum-likelihood classifier has an accuracy of 73%. The analysis of the hierarchy of membership degrees indicates that almost 25% of Moorea Island lagoon is heterogeneous, composed of real boundaries, transition states, and fragmented zones.
Andrews, E.D., Measurement and Computation of Bed-Material Discharge in a Shallow Sand-Bed Stream, Muddy Creek, Wyoming, Water Resources Research, 17 (1), 131-141, 1981.
Andrews, E.D., Bank Stability and Channel Width Adjustment, East Fork River, Wyoming, Water Resources Research, 18 (4), 1184-1192, 1982.
Andrews, E.D., Entrainment of Gravel From Naturally Sorted Riverbed Material, Geological Society of America Bulletin, 94 (10), 1225-1231, 1983.
Andrews, E.D., and D.C. Erman, Persistence in the Size Distribution of Surficial Bed Material During an Extreme Snowmelt Flood, Water Resources Research, 22 (2), 191-197, 1986.
Andrews, E.D., Marginal Bed-Load Transport in a Gravel-Bed Stream, Sagehen Creek, California, Water Resources Research, 30 (7), 2241-2250, 1994.
Andrews, E.D., Bed material transport in the Virgin River, Utah, Water Resources Research, 36 (2), 585-596, 2000.
Detailed information concerning the rate and particle size distribution of bed material transport by streamflows can be very difficult and expensive to obtain, especially where peak streamflows are brief and bed material is poorly sorted, including some very large boulders. Such streams, however, are common in steep, arid watersheds. Any computational approach must consider that (1) only the smaller particle sizes present on the streambed move even during large floods and (2) the largest bed particles exert a significant form drag on the flow. Conventional methods that rely on a single particle size to estimate the skin friction shear stress acting on the mobile fraction of the bed material perform pearly. Instead, for this study, the skin friction shear stress was calculated for the observed range of streamflows by calculating the form drag exerted on the reach-averaged flow field by all particle sizes. Suspended and bed load transported rates computed from reach- averaged skin friction shear stress are in excellent agreement with measured transport rates. The computed mean annual bed material load, including both bed load and suspended load, of the East Fork Virgin River for the water years 1992-1996 was approximately 1.3 x 10(5) t. A large portion of the bed material load consists of sand-sized particles, 0.062-1.0 mm in diameter, that are transported in suspension. Such particles, however, constituted only 10% of the surface bed material and less than 25% of the subsurface bed material. The mean annual quantity of bed load transported was 1060 t/yr with a median size of 15 mm.
Anthony, E.J., and M. Julian, Source-to-sink sediment transfers, environmental engineering and hazard mitigation in the steep Var River catchment, French Riviera, southeastern France, Geomorphology, 31 (1-4), 337-354, 1999.
Steep coastal margins are potentially subject to mass wasting processes involving notable landslide activity and sediment evacuation downstream by steep-gradient streams. Sediment transfer from short source-to-sink segments, coupled with mountain hydrological regimes, regulate patterns of river channel aggradation and coastal sediment supply in such geomorphic settings. On the steep French Riviera margin, sediment transfers from existing landslides or from various minor mass wasting processes to stream channels may result following bursts of heavy, concentrated rainfall. High- magnitude flooding and massive sediment transport downstream are generally related to unpredictable extreme rainfalls. Both mass movements and channel sediment storage pose serious hazards to downvalley settlements and infrastructure. A consideration of channel sediment storage patterns in the Var River catchment, the most important catchment in this area, highlights two important shortcomings relative to environmental engineering and hazard mitigation practices. In the first place, the appreciation of geomorphic processes is rather poor. This is illustrated by the undersized nature of engineering works constructed to mitigate hazards in the upstream bedload- dominated channels, and by the unforeseen effects that ten rock dams, constructed in the early 1970s, have had on downstream and coastal sediment storage and on sediment dispersal patterns and, consequently, valley flooding. Secondly, planners and environmental engineers have lacked foresight in valley and coastal management issues on this steep setting, notably as regards the reclaimed areas of the lower Var channel and delta liable to flooding. Urbanization and transport and environmental engineering works have progressively affected patterns of storage and transport of fine-grained sediments in the lower Var channel and delta. Meanwhile the problems raised by these changes have not been adequately addressed in terms of scientific research. A necessary future step in bettering the engineering solutions implemented to contain natural hazards or to harness water and sediment resources is that of fine-scale analysis of source-to-sink sediment transfer processes, of sediment budgets, of time-scales of storage in stream channels, and, finally, of high-magnitude hydrometeorological forcing events in this area. The way all these aspects have been modulated by engineering practices and socioeconomic development should also be an important part of such an analysis. (C) 1999 Elsevier Science B.V. All rights reserved.
Archibold, O.W., D.H. DeBoer, and L. Delanoy, A device for measuring gully headwall morphology, Earth Surface Processes and Landforms, 21 (11), 1001-1005, 1996.
Armanini, A., Nonuniform Sediment Transport - Dynamics of the Active Layer, Journal of Hydraulic Research, 33 (5), 611-622, 1995.
Arrowsmith, J.R., and D.D. Rhodes, Original Forms and Initial Modifications of the Galway Lake Road Scarp Formed Along the Emerson Fault During the 28 June 1992 Landers, California, Earthquake, Bulletin of the Seismological Society of America, 84 (3), 511-527, 1994.
Ashiq, M., and J.C. Bathurst, Comparison of bed load sampler and tracer data on initiation of motion, Journal of Hydraulic Engineering-Asce, 125 (6), 661-664, 1999.
Ashley, G.M., W.H. Renwick, and G.H. Haag, Channel Form and Processes in Bedrock and Alluvial Reaches of the Raritan River, New-Jersey, Geology, 16 (5), 436-439, 1988.
Ashmore, P.E., Bed-Load Transport in Braided Gravel-Bed Stream Models, Earth Surface Processes and Landforms, 13 (8), 677-695, 1988.
Ashmore, P.E., How Do Gravel-Bed Rivers Braid, Canadian Journal of Earth Sciences, 28 (3), 326-341, 1991.
Sedimentary processes and bed forms leading to the onset of braiding were observed in small-scale hydraulic models of grave-bed streams. The laboratory streams had a variety of combinations of (constant) discharge and slope but identical bed-material particle-size distributions. From initially straight channels, braiding occurred by four different processes: deposition and accumulation of a central bar, chute cutoff of point bars, conversion of single transverse unit bars to mid-channel braid bars, and dissection of multiple bars. In these experiments the chute cutoff mechanism was the most common, but the predominant braiding mechanism depends upon sediment mobility (excess bed shear stress) and the bed-form regime. At very low excess bed shear stress the central bar process dominates, but at higher excess bed shear stress slip- face unit bars are more common, bed scour at confluences is more pronounced, and propogation of alternate convergence (scour) and divergence (deposition) is more likely; thus chute cutoffs and bar conversion dominate. The multiple bar mechanism is restricted to channels with very high width/depth ratio. All of these processes, along with avulsion, are significant for maintenance of an established braided channel. The direct physical sedimentary cause of primary braiding is essentially the same in all these processes: local aggradation (often by stalling of bed-load sheets) and loss of competence in a lateral flow expansion. The chute cutoff process occurs in a morphologically distinctive setting and may be aided by other factors, but it is usually triggered by the local thalweg shoaling that is the fundamental physical mechanism causing the onset of braiding by the other processes. Local short-term pulses in bed-load supply are often the trigger for the initiation and maintenance of braiding, regardless of the exact braiding process.
Ashmore, P., Contemporary Erosion of the Canadian Landscape, Progress in Physical Geography, 17 (2), 190-204, 1993.
Studies of contemporary patterns of erosion in the glaciated and largely undisturbed Canadian landscape reveal spatial patterns that do not conform to the conventional concepts of drainage basin sediment delivery. In particular stream and valley side sediment sources dominate over erosion of the land surface, and specific (unit) sediment yield is often positively, rather than inversely, related to drainage area. Much of this is a legacy of glaciation that left large quantities of sediment in the landscape and disrupted regional drainage patterns. The absence of an integrated drainage network affects sediment delivery in many areas. To some extent unusual patterns of specific yield are to be expected in large drainage basins where environmental and geologic conditions may vary considerably within the basin. Only in the agricultural areas of the Great Lakes basin and St. Lawrence valley do more conventional patterns of erosion occur. Applied studies related to agricultural soil erosion and pollution have helped to illuminate the pathways and sources of sediment in particular cases and show the effects of landscape disturbance.
Ashmore, P., F.M. Conly, D. deBoer, Y. Martin, E. Petticrew, and A. Roy, Recent (1995-1998) Canadian research on contemporary processes of river erosion and sedimentation, and river mechanics, Hydrological Processes, 14 (9), 1687-1706, 2000.
Canadian research on contemporary erosion and sedimentation processes covers a wide range of scales, processes, approaches and environmental problems. This review of recent research focuses on the themes of sediment yield, land-use impact, fine- sediment transport, bed material transport and river morphology and numerical modelling of fluvial landscape development. Research on sediment yield and denudation has confirmed that Canadian rivers are often dominated by riparian sediment sources. Studies of the effects of forestry on erosion, in- stream sedimentation and habitat are prominent, including major field experimental studies in coastal and central British Columbia. Studies of fine-sediment transport mechanisms have focused on the composition of particles and the dynamics of flocculation. In fluvial dynamics there have been important contributions to problems of turbulence-scale flow structure and entrainment processes, and the characteristics of bedload transport in gravel-bed rivers. Although much of the work has been empirical and field-based, results of numerical modelling of denudational processes and landscape development also have begun to appear. The nature of research in Canada is driven by the progress of the science internationally, but also by the nature of the Canadian landscape, its history and resource exploitation. Yet knowledge of Canadian rivers is still limited, and problems of, for example, large pristine rivers or rivers in cold climates, remain unexplored. Research on larger scale issues of sediment transfer or the effects of hydrological change is now hampered by reductions in national monitoring programmes. This also will make it difficult to test theory and assess modelling results. Monitoring has been replaced by project- and issues-based research, which has yielded some valuable information on river system processes and opened opportunities for fluvial scientists. However, future contributions will depend on our ability to continue with fundamental fluvial science while fulfilling the management agenda. Copyright (C) 2000 John Wiley & Sons, Ltd.
Ashworth, P.J., and R.I. Ferguson, Size-Selective Entrainment of Bed-Load in Gravel Bed Streams, Water Resources Research, 25 (4), 627-634, 1989.
Ashworth, P.J., R.I. Ferguson, P.E. Ashmore, C. Paola, D.M. Powell, and K.L. Prestegaard, Measurements in a Braided River Chute and Lobe .2. Sorting of Bed-Load During Entrainment, Transport, and Deposition, Water Resources Research, 28 (7), 1887-1896, 1992.
Ashworth, P.J., Mid-channel bar growth and its relationship to local flow strength and direction, Earth Surface Processes and Landforms, 21 (2), 103-123, 1996.
Ashworth, P.J., J.L. Best, J.E. Roden, C.S. Bristow, and G.J. Klaassen, Morphological evolution and dynamics of a large, sand braid- bar, Jamuna River, Bangladesh, Sedimentology, 47 (3), 533-555, 2000.
The initiation and evolution of a kilometre-scale, sand braid- bar was monitored during a 28-month survey period from 1993 to 1996 in one of the world's largest braided rivers, the Jamuna River, Bangladesh. Repeated bathymetric surveys through two monsoon flood seasons, combined with bar-top surveys during exposure of the bar at low flow, provide the most detailed chronology of braid-bar growth yet compiled for a large sand- bed river. During rising and peak flow of the 1994 monsoon flood, a 1.5-km-long, 0.5-km-wide, 12-m-high, symmetrical mid- channel bar was deposited in the centre of a major channel downstream of a zone of flow convergence and significant bank erosion. Initial deposition and growth of the bar core were probably caused by amalgamation of dunes that are present in the Jamuna channels at all flow stages. Bar-top aggradation continued through downstream migration of an 'accretionary dune front', a 3-m-high, angle-of-repose slipface that was composed of amalgamated, 0.5- to 1-m-high dunes. At waning and low flow, the mid-channel bar widened by up to 1 km through the lateral accretion of dunes onto the margins of the initial bar core. A low-velocity zone in the sheltered wake region of the bar-tail led to the accumulation of substantial volumes of silts and clays. During the rising and peak flows of the next monsoon flood, the mid-channel bar extended its bar-tail by up to 1.5 km, as one of the anabranches became dominant, and flow was deflected across the bar-tail. Accretion at the bar-tail generated a lobate, transverse bar-front with a 10-m-high, angle-of-repose avalanche face. Emergence of several smaller bars along this depositional front produced an overall reach morphology that more closely resembled an alternate bar rather than several mid-channel bars. The conversion of a mid-channel bar to an alternate bar is contrary to many previous descriptions of the braiding process.
Aslan, A., and A.K. Behrensmeyer, Taphonomy and time resolution of bone assemblages in a contemporary fluvial system: The East Fork River, Wyoming, Palaios, 11 (5), 411-421, 1996.
Experiments that recorded the dispersal of 142 bones within a meandering, 2030 m-long reach of the East Fork River, Wyoming over a 13-year period provide a basis for interpreting distribution patterns and time averaging in. fossiliferous channel deposits. Results show that light and porous bones, (e.g., vertebrae, patellae, and phalanges) were transported farther than heavy bones (e.g., limb bones and mandibles). Dispersal patterns of bones from individual experimental sets representing point sources demonstrate that bones became sorted by size and shape within 1 to 2 years and that sorting patterns varied according to initial channel position. The combined distribution of bones from all the experimental sets, however was unsorted and generally random, suggesting that unsorted fluvial bone assemblages reflect multiple bone sources and differences in the time at which bones enter the channel. Estimates of time-averaging of potential and observed natural bone assemblages in. the East Fork River and the South Platte River range from 10(1)-10(4) years. The upper Limit for this estimate is controlled by both the age of fossiliferous floodplain deposits that border the rivers and by the ability of the rivers to rework these floodplain. deposits. The lower limit reflects either the scarcity of bones in the floodplain sediments or the inability of the rivers to rework these older bones; in this case channel bone assemblages should represent only remains from deaths in the channel or remains that were transported into the channel from adjoining land surfaces, resulting in. short intervals of time-averaging (10(1)-10(2) years). The East Fork study further suggests that sandstone geometry, paleosol development, and the sedimentary context of fossil occurrences cart be used to evaluate time-averaging in ancient fossiliferous channel deposits. Fossil bone assemblages that are present exclusively in ribbon-shaped channel deposits associated with weakly developed paleosols and unfossiliferous floodplain deposits should represent shorter time intervals than similar fossil assemblages associated with Sheet sandstones and moderately developed paleosols with abundant fossils.
Assani, A.A., and F. Petit, Log-Jam Effects On Bed-Load Mobility From Experiments Conducted in a Small Gravel-Bed Forest Ditch, Catena, 25 (1-4), 117-126, 1995.
Atanov, G.A., E.G. Evseeva, and P.A. Work, Variational problem of water-level stabilization in open channels, Journal of Hydraulic Engineering-Asce, 124 (1), 50-54, 1998.
A method is presented far minimization of water-level fluctuations in an open channel controlled by pumping stations at bath ends. The situation is posed as a variational problem to determine the optimum upstream flow control, given constraints at the opposite end. The method of indefinite Lagrangian multipliers is used. A global measure-integrated in space and time-of the water-level deviation away from some desired water level is defined. The problem involves minimizing this deviation while still satisfying the governing equations and the initial boundary conditions for the flow. The solution is obtained numerically. The equations governing gradually varied, unsteady open-channel flow are assumed to be valid. A horizontal, frictionless channel of constant trapezoidal cross section is assumed, although the method could readily be extended to more general conditions. The problem has many applications related to hydropower and water supply canals. An example is presented to illustrate the utility and effectiveness of the method.
Aubry, P., and D. Debouzie, Geostatistical estimation variance for the spatial mean in two- dimensional systematic sampling, Ecology, 81 (2), 543-553, 2000.
Many ecologists use two-dimensional systematic sampling to estimate mean density of individuals over the domain sampled. They usually calculate the variance of the mean as if the sample were a simple random sample, using the unbiased estimator under this sampling design, that is, sigma(2)/n. This practice leads to a selection bias, i.e., incorrect inclusion probabilities of population units in the sample are used in the estimator of variance of the mean. The magnitude of the bias varies with the underlying spatial autocorrelation structure. Design-based inference and model-based inference are two conceptual frameworks for tackling estimation of variance of the mean in a systematic sample. This paper reports use of the geostatistical estimation variance sigma(E)(2) with the model- based approach. This variance of the overall spatial mean depends on the spatial autocorrelation structure of the data. We illustrate the method by considering the density of acorns fallen under a sessile oak during one season. Acorns were numbered in square quadrats of 0.25 m(2); the data set was exhaustive. We drew nine one-start systematic samples from the whole population of quadrats. We computed semivariograms for the whole population and each sample and fitted them to exponential models without nugget. Using geostatistical theoretical results, we calculated a variance of the mean density of acorns by Monte Carlo integration. We show that our variance estimate depends on (1) the origin of the systematic sample, the central sample being the most accurate, (2) quadrat size, with a decrease in the variance when quadrat size increases, (3) the semivariogram model, (4) discretization of the domain used in Monte Carlo integration, and (5) the random number generator. Considering all sources of variation, the variance estimate we calculated ranged from similar to 2 to 36 in our example, for an overall mean equal to 95 acorns per quadrat. Geostatistical variance mainly reflects the locations and size of the sampled quadrats, and the spatial autocorrelation function. In our example, using the variance estimator of a simple random sample leads to a high selection bias. The bias can be neglected only in the absence of significant spatial autocorrelation in the sample. Otherwise, we advocate a geostatistical model-based approach that accounts for spatial autocorrelation.
Baas, J.H., An empirical model for the development and equilibrium morphology of current ripples in fine sand, Sedimentology, 46 (1), 123-138, 1999.
A flume study on the development and equilibrium morphology of current ripples in fine sand (D-50 = 0.238 mm) was performed to extend an empirical model for current ripple stability in 0.095 mm sand to larger grain sizes. The results of the flume experiments agree with the very fine sand model that current ripple development from a Mat bed is largely independent of flow velocity. At all flow velocities, ripples evolve from incipient, through straight, sinuous and non-equilibrium linguoid, to equilibrium linguoid plan morphology. The time needed to achieve an equilibrium linguoid plan form is related to an inverse power of flow velocity and ranges from several minutes to more than hundreds of hours. Average equilibrium height and length are 17.0 mm and 141.1 mm respectively. These values are about 20% larger than in very fine sand. Equilibrium ripple height and length are proportional to flow velocity near the stability field of dunes. In the same velocity range, a characteristic grouping of ripples with smaller ripples migrating on the upstream face of larger ripples was observed. Bed-form development shows a conspicuous two-phase behaviour at flow velocities < 0.49 m s(-1). In the first phase of development, ripple height and length increase along an exponential path, similar to that at higher flow velocities, thus reaching intermediate equilibrium values of 14.8 mm and 124.5 mm respectively. After some time, however, a second phase commences, that involves a rapid increase in bed-form size to the typical equilibrium values for 0.238 mm sand. A comparison with literature data shows that the results obtained for 0.238 mm sand agree reasonably well with other flume studies at similar grain size. Yet considerable variability in the relationships between ripple dimensions and flow strength ensues from, among others, underestimation of equilibrium time, shallow flow depths and differences in sediment texture.
Baddour, R.E., Stratified Cooling Channel For Thermal Discharges, Journal of Environmental Engineering-Asce, 120 (1), 242-253, 1994.
A method of designing a stratified cooling channel for managing the excess heat of a thermal discharge is presented. The cooling channel is connected to a larger body of water such as a river, lake, or ocean. A continuous exchange flow with a larger body of water allows mixing to play an important role in reducing the temperature of a discharge in the cooling channel. The equations governing the now and temperature in a deep cooling channel are derived from basic principles of momentum and heat balance. The numerical solutions show that most of the thermal impact of a heated discharge may be confined to within the boundaries of the cooling channel, minimizing the ecological impact on the natural environment. An example is used to demonstrate the method of designing a cooling channel. The example shows that cooling channels could operate under thermal loading conditions significantly higher than those required in cooling ponds.
Baecheler, J.V., and L.A. Riquelme, Estimation of longitudinal dispersion coefficient for wide rivers with shallow waters and mild slope. Application of the model at Bio Bio river, Chile, Ingenieria Hidraulica En Mexico, 16 (1), 5-13, 2001.
This paper presents the different simple methods to estimate the longitudinal dispersion coefficient (D-L) for wide rivers, with shallow waters and mild slope. The method proposed by Mc Quivey and Keefer (1974) gives the best estimations among all the reviewed methods. A hybrid model is proposed which combines the method proposed by Liu (1977), but estimating the parameter beta from a dimensionless shape coefficient (W/R). The real beta values are correlated with the corresponding (W/R) through a simple regression analysis of the form Y = aX(b). The proposed method has a standard average error 10% smaller than the method proposed by McQuivey and Keefer (1974). The proposed model was applied in a reach of the Bio Bio river, Central Chile.
Bajpai, V.N., T.K.S. Roy, and S.K. Tandon, Subsurface sediment accumulation patterns and their relationships with tectonic lineaments in the semi-arid Luni river basin, Rajasthan, Western India, Journal of Arid Environments, 48 (4), 603-621, 2001.
Bakke, P.D., P.O. Basdekas, D.R. Dawdy, and P.C. Klingeman, Calibrated Parker-Klingeman model for gravel transport, Journal of Hydraulic Engineering-Asce, 125 (6), 657-660, 1999.
Bakry, M.F., T.K. Gates, and A.F. Khattab, Field-Measured Hydraulic Resistance Characteristics in Vegetation-Infested Canals, Journal of Irrigation and Drainage Engineering-Asce, 118 (2), 256-274, 1992.
RealiStiC estimates of hydraulic resistance are essential to the proper design and analysis of irrigation canal networks. Extensive field studies in Egypt provide data on the magnitude and variability of hydraulic resistance in earthen irrigation canals infested with aquatic weeds. Values of Manning resistance coefficient, n, were calculated from 280 measurements at selected cross sections in 23 stable canals with emergent ditch-bank vegetation. The temporal sample mean of monthly, values of n estimated within a year ranged from 0.017-0.062 for cross sections where five or more measurements were made. The temporal sample coefficient of variation ranged from 0.03-0.42. Dependence of n on flow regime (hydraulic depth and product of average velocity and hydraulic radius) was explored. Studies also were conducted on nine canals containing submerged vegetation. These studies included 312 sonar measurements of vegetation density as well as 156 measurements to estimate n at selected cross sections. Regression analysis revealed that variability in flow regime and in vegetation density contribute significantly to variability in n. Temporal mean of monthly values of vegetation density within a year ranged from 0.06-0.25, with temporal coefficient of variation between 0.17 and 0.92. Vegetation density at measured cross sections showed a clear seasonal pattern. The spatial mean and coefficient of variation in vegetation density along a canal were found to range monthly from 0.06-0.36 and from 0.18-0.76, respectively. Temporal mean values of n in canals with submerged vegetation ranged from 0.028-0.074, with temporal coefficient of variation between 0.13 and 0.57.
Bartholdy, J., and J. KislingMoller, Bed-load sorting in an alluvial river, Journal of Sedimentary Research, 66 (1), 26-35, 1996.
Basha, H.A., Analytical model of two-dimensional dispersion in laterally nonuniform axial velocity distributions, Journal of Hydraulic Engineering-Asce, 123 (10), 853-862, 1997.
An analytical model of the advection-dispersion phenomenon in rivers with a laterally nonuniform axial velocity distribution is presented. The dispersion phenomenon is assumed to be governed by the two-dimensional advection-diffusion equation with constant but anisotropic turbulent diffusion coefficients. An infinitely long river with a prismatic cross section bounded laterally by parallel nondispersive banks is assumed. The velocity distribution is allowed to vary in an arbitrary functional form, but was restricted in this work to a family of power-law velocity distributions. The method of moments is used to derive the important statistical parameters of the concentration distribution. The concentration moment equations are solved analytically using the method of Greens function coupled with the method of images. The moments are then used to construct an approximate model of two-dimensional dispersion for an arbitrary velocity function, an initial distribution, and source injection scenarios. A one-dimensional simplification of the two-dimensional dispersion model with a time-dependent dispersion coefficient is also outlined. The dependence of the concentration moments on the velocity distribution and the shape of the source distribution is analyzed, and numerical results for a plane source and vertical line sources at the centerline and at the side are compared. The effect of the asymmetry of the velocity profile on the mixing length and time and on the skewness of the concentration distribution is shown to be significant, which might partly explain the persistence of the skewness observed in the field. However, the effect of the source injection scenario was not significant at large times. The analytical results can be used to model the fate and movement of pollutants and to better assess the effect of discharge siting on the dispersion of a contaminant. The model can be also used as a simple practical tool in simulating transport in a nearly prismatic river system.
Batalla, R.J., Evaluating bed-material transport equations using field measurements in a sandy gravel-bed stream, Arbucies River, NE Spain, Earth Surface Processes and Landforms, 22 (2), 121-130, 1997.
Batalla, R.J., and J.P. Martin-Vide, Thresholds of particle entrainment in a poorly sorted sandy gravel-bed river, Catena, 44 (3), 223-243, 2001.
A series of bedload samples and hydraulic measurements were made in the poorly sorted sandy-gravel bed of the Arbucies River to determine the threshold conditions for initiation of motion. Entrainment has been analysed using two different initial-motion methods: the largest-grain method and the reference or fractional transport rate method. Both methods yield different results in terms of the equal mobility hypothesis. The deviation between scaled and non-scaled initial motion relation?, are clear: (a) the largest-grain critical shear stress varies to the power -0.68 of D-i/D-50, indicating a tendency towards size-selective entrainment: but (b) computation of the critical shear stress based on the reference transport method indicates only a very weak dependence on grain size (power -0.91). The question is whether such divergent results are caused by real differences or methodological problems. On one hand. estimations of tau (c). from bedload maximum particle size are methodologically problematic. The systematic error associated with determining D-i makes it an unreliable estimator of dimensionless critical shear stress. Much of the observed variation between D-i and tau may he more shear-stress estimations or bedload sampling effects than a consequence of selective entrainment. Any conclusion following this method cannot be substantiated, at least until more hydraulic and bedload data is available. On the other hand, scaling problems are less important in the reference transport method, because fractional rates incorporate scaling considerations. Results indicate a strong tendency towards equal mobility, a relatively common situation described in many other transport data, although the coefficient still suggests weak particle dependence. Bedload does not become coarser as shear stress increases, but its grain-size distribution remains constant, as expected under prevailing equal mobility conditions. (C) 2001 Elsevier Science B.V. All rights reserved.
Bathurst, J.C., Flow Resistance Estimation in Mountain Rivers, Journal of Hydraulic Engineering-Asce, 111 (4), 625-643, 1985.
Bathurst, J.C., and H.H. Cao, Formation and Effects of Alternate Bars - Discussion, Journal of Hydraulic Engineering-Asce, 112 (11), 1101-1103, 1986.
Bathurst, J.C., and M. Ashiq, Dambreak flood impact on mountain stream bedload transport after 13 years, Earth Surface Processes and Landforms, 23 (7), 643-649, 1998.
Studies of the bedload transport regime of the Roaring River, Colorado, in 1984-88, following a dambreak flood in 1982, showed that bedload transport rates were an order of magnitude higher than under pre-flood conditions. A gorge eroded by the flood in glacial moraine acted as a major sediment supply source. Measurements in early June 1995 showed a continued potential for high sediment supply from the gorge and a bedload transport regime similar to that of 1984-88. A major snowmelt flood in mid-June flushed sediment supplies from the gorge and measurements in July showed a corresponding reduction in bedload transport. However, high sediment supply will continue until the gorge cliffs revegetate or erode to a stable slope. The measurements demonstrate both the control exercised by sediment supply on transport rates and the persistent long-term impact of major floods on mountain streams. (C) 1998 John Wiley & Sons, Ltd.
Battin, T.J., Hydrologic flow paths control dissolved organic carbon fluxes and metabolism in an alpine stream hyporheic zone, Water Resources Research, 35 (10), 3159-3169, 1999.
The objective of the present paper was to link reach-scale streambed reactive uptake of dissolved organic carbon (DOC) and dissolved oxygen (DO) to subsurface flow paths in an alpine stream (Oberer Seebach (OSB)). The topography adjacent to the stream channel largely determined flow paths, with shallow hillslope groundwater flowing beneath the stream and entering the alluvial groundwater at the opposite bank. As computed from hydrometric data, OSB consistently lost stream water to groundwater with fluxes out of the stream averaging 943 +/- 47 and 664 +/- 45 L m(-2) h(-1) at low (Q < 600 L s(-1)) and high (Q > 600 L s(-1)) flow, respectively. Hydrometric segregation of streambed fluxes and physicochemical mixing analysis indicated that stream water was the major input component to the streambed with average contributions of 70-80% to the hyporheic zone (i.e., the subsurface zone where shallow groundwater and stream water mix). Surface water was also the major source of DOC with 0.512 +/- 0.043 mg C m(-2) h(-1) to the streambed. The DOC flux from shallow riparian groundwater was lower (0.309 +/- 0.071 mg C m(-2) h(-1)) and peaked in autumn with 1.011 mg C m(-2) h(-1). I computed the relative proportion of downstream discharge through the streambed as the ratio of the downstream length (S-sw) a stream water parcel travels before entering the streambed to the downstream length (S-hyp) a streambed water parcel travels before returning to the stream water. The relative streambed DOC retention efficiency, calculated as (input-output)/input of interstitial DOG, correlated with the proportion (S-sw/S-hyp) of downstream discharge (r(2) = 0.76, p = 0.006), Also, did the streambed metabolism (calculated as DO uptake from mass balance) decrease with low subsurface downstream routing, whereas elevated downstream discharge through the streambed stimulated DO uptake (r(2) = 0.69, p = 0.019)? Despite the very short DOC turnover times (similar to 0.05 days, calculated as mean standing stock/annual input) within the streambed, the latter constitutes a net sink of DOC (similar to 14 mg C m(-2) h(-1)). Along with high standing stocks of sediment associated particulate organic carbon, these results suggest microbial biofilms as the major retention and storage site of DOC in an alpine stream where large hydrologic exchange controls DOC fluxes.
Baucom, P.C., and C.A. Rigsby, Climate and lake-level history of the northern Altiplano Bolivia, as recorded in Holocene sediments of the Rio Desaguadero, Journal of Sedimentary Research, 69 (3), 597-611, 1999.
Bauer, S.B., and S.C. Ralph, Strengthening the use of aquatic habitat indicators in Clean Water Act programs, Fisheries, 26 (6), 14-+, 2001.
The loss of freshwater fluvial habitats is generally regarded as a key factor in the precipitous decline of native salmonids in the northwestern United States. State and federal water quality regulations, under the authority of the Clean Water Act (CWA), could be more relevant to recovery of Pacific salmon if physical habitat quality was explicitly integrated into water quality standards. We examine the concept of incorporating instream habitat measures into water quality regulations since these standards are the foundation of CWA programs. Commonly measured instream habitat variables for salmonids (flow regime, habitat space, channel structure, substrate quality, streambank stability) were evaluated in terms of their suitability as water quality criteria. The basis for this evaluation focused on these indicators in light of their: (1) relevance to ecological requirements of salmonid fishes, (2) applicability to landscape processes and the stream network in which they occur, (3) responsiveness to human-caused stressors (linking cause v. effect), and (4) degree of measurement reliability and precision. Our evaluation suggests that most habitat indicators, as currently measured, do not meet these criteria due to the limitations in the state of the science as well as constraints imposed by the existing framework for water quality standards. There is general agreement on salmonid habitat requirements and the effects of land use on these habitats; there is less certainty on quantifying physical habitat quality and on the reliability of habitat assessment techniques. These obstacles can be overcome by applying the principles of landscape ecology and stream network classification to indicator development, identifying and quantifying reference area conditions at a regional scale, calibrating relevant indicators to specific locales, and developing systematic monitoring procedures that meet rigorous data quality objectives.
Beach, T., The Fate of Eroded Soil - Sediment Sinks and Sediment Budgets of Agrarian Landscapes in Southern Minnesota, 1851-1988, Annals of the Association of American Geographers, 84 (1), 5-28, 1994.
Human-induced soil erosion has produced real-world laboratories for studying the fates of eroded soil particles in watersheds all over the world. This article investigates the spatial distribution of historical sediment and the sediment budgets of three of these laboratories in medium-size watersheds of southern Minnesota. Sediment storage is measured in various geomorphic sites or sinks including colluvium, stream-order floodplains, and reservoirs. Two of these watersheds exhibit erosion histories and quantities and patterns of historical alluvium that are comparable with watersheds in Wisconsin's Driftless Area. In these watersheds, the patterns of historical sediment storage are two-tiered, with 47 to 61 percent of all sediment stored in the uplands (in low-order floodplains and colluvium) and 38 to 52 percent stored in the main lower floodplains. In one stream, backwater effects from the Mississippi River cause significantly greater alluviation in the lower floodplain; in another stream, the main floodplain is narrower and alluvial storage is thinner. In both, floodplain width is the major influence on alluvial storage. A third and smaller watershed in central Minnesota reports lower erosion and sedimentation rates and a different pattern of storage; 73 percent of the sediment is stored in colluvium and 27 percent in the lower main floodplain. Based on estimates of soil erosion, historical sediment yields and sediment budgets are estimated for each watershed. Historical sediment yields of about 13 to 36.5 percent are comparable to other estimates for these areas, which means that 63.5 to 87 percent or more of all historically eroded soil still resides within the basins and within 4 to 25 km of original points of detachment. Moreover, in the 137 years of European settlement, 38 to 73 percent of all eroded sediment has travelled no more than 4 km.
Bednarek, A.T., Undamming rivers: A review of the ecological impacts of dam removal, Environmental Management, 27 (6), 803-814, 2001.
Dam removal continues to garner attention as a potential river restoration tool. The increasing possibility of dam removal through the FERC relicensing process, as well as through federal and state agency actions, makes a critical examination of the ecological benefits and costs essential. This paper reviews the possible ecological impacts of dam removal using various case studies. Restoration of an unregulated flow regime has resulted in increased biotic diversity through the enhancement of preferred spawning grounds or other habitat. By returning riverine conditions and sediment transport to formerly impounded areas, riffle/pool sequences, gravel, and cobble have reappeared, along with increases in biotic diversity. Fish passage has been another benefit of dam removal. However, the disappearance of the reservoir may also affect certain publicly desirable fisheries. Short-term ecological impacts of dam removal include an increased sediment load that may cause suffocation and abrasion to various biota and habitats. However, several recorded dam removals have suggested that the increased sediment load caused by removal should be a short-term effect. Pre-removal studies for contaminated sediment may be effective at controlling toxic release problems. Although monitoring and dam removal studies are limited, a continued examination of the possible ecological impacts is important for quantifying the resistance and resilience of aquatic ecosystems. Dam removal, although controversial, is an important alternative for river restoration.
Beechie, T., and S. Bolton, An approach to restoring salmonid habitat-forming processes in Pacific Northwest watersheds, Fisheries, 24 (4), 6-15, 1999.
We present an approach to diagnosing salmonid habitat degradation and restoring habitat-forming processes that is focused on causes of habitat degradation rather than on effects of degradation. The approach is based on the understanding that salmonid Stocks are adapted to local freshwater conditions and that their environments are naturally temporally dynamic. In this context, we define a goal of restoring the natural rates and magnitudes of habitat-forming processes, and we allow for locally defined restoration priorities. The goal requires that historical reconstruction focus on diagnosing disruptions to processes rather than conditions. Historical reconstruction defines the suite of restoration tasks, which then may be prioritized based on local biological objectives, We illustrate the use of this approach for two habitat-forming processes: sediment supply and stream shading. We also briefly contrast this approach to several others that maybe used as components of a restoration strategy.
Beechie, T.J., Empirical predictors of annual bed load travel distance, and implications for salmonid habitat restoration and protection, Earth Surface Processes and Landforms, 26 (9), 1025-1034, 2001.
Measurements of annual travel distance (L-b) of bed load sediment at 16 locations in Alaska, the intermountain USA, west coast USA and Scotland are strongly correlated with bankfull channel width (r(2) = 0.86, p < 0.001). Travel distance of particles is probably limited by trapping in bars, which have a longitudinal spacing proportional to channel width. Increased abundance of woody debris reduces bar spacing and may reduce L- b. Longer cumulative duration of bed load transporting flows in a year appears to increase L-b. Other predictors of annual travel distance such as stream power per unit length, drainage area and bankfull discharge were less well correlated with L-b (r(2) ranging from 0.27 to 0.51). Stream power per unit bed area, basal shear stress and slope were not significantly related to L-b (r(2) < 0.05). Most correlations were improved when regressions were limited to data from the west coast USA. Travel distance estimates can be used to help identify reaches that may take longer to recover from large, short-term increases in sediment supply. Published in 2001 by John Wiley & Sons, Ltd.
Beeson, C.E., and P.F. Doyle, Comparison of Bank Erosion At Vegetated and Non-Vegetated Channel Bends, Water Resources Bulletin, 31 (6), 983-990, 1995.
Following major floods in 1990 which resulted in widespread bank erosion in southern British Columbia, four streams typical of the region were evaluated for the effect which riparian vegetation played in reducing erosion. A total of 748 bends in the four stream reaches were assessed by comparing pre- and post-flood aerial photography. Bends without riparian vegetation were found to be nearly five times as likely as vegetated bends to have undergone detectable erosion during the flood events. Major bank erosion was 30 times more prevalent on non-vegetated bends as on vegetated bends. The likelihood of erosion on semi-vegetated bends was between that of the vegetated and non-vegetated categories of bends.
Belleudy, P., Numerical simulation of sediment mixture deposition part 1: analysis of a flume experiment, Journal of Hydraulic Research, 38 (6), 417-425, 2000.
This paper reports the numerical simulation of previously published laboratory experiments concerning deposition of a sediment mixture in a flume. The results of the simulation are analyzed and their interdependencies are discussed with reference to flume observations and previously published analyses. Cross-comparison of different parameters of the system (deposition rate, Sediment transport, grain size) allows some validation of the system of equations of our modeling system. It may also give some clues and directions for further measurements and numerical experiments.
Belleudy, P., Numerical simulation of sediment mixture deposition part 2: a sensitivity analysis, Journal of Hydraulic Research, 39 (1), 25-31, 2001.
Belmonte, A.M.C., and F.S. Beltran, Flood events in Mediterranean ephemeral streams (ramblas) in Valencia region, Spain, Catena, 45 (3), 229-249, 2001.
Benda, L., and T. Dunne, Stochastic forcing of sediment supply to channel networks from landsliding and debris flow, Water Resources Research, 33 (12), 2849-2863, 1997.
Sediment influx to channel networks is stochastically driven by rainstorms and other perturbations, which are discrete in time and space and which occur on a landscape with its own spatial variability in topography, colluvium properties, and state of recovery from previous disturbances. The resulting stochastic field of sediment supply interacts with the topology of the channel network and with transport processes to generate spatial and temporal patterns of flux and storage that characterize the sedimentation regime of a drainage basin. The regime varies systematically with basin area. We describe how the stochastic sediment supply is generated by climatic, topographic, geotechnical, and biotic controls that vary between regions. The general principle is illustrated through application to a landscape where sediment is supplied by mass wasting, and the forcing variables are deterministic thickening of colluvium, random sequences of root-destroying wildfires, and random sequences of rainstorms that trigger failure in a population of landslide source areas with spatial variance in topography and colluvium strength. Landslides stop in channels or convert to scouring debris flows, depending on the nature of the low-order channel network. Sediment accumulates within these channels for centuries before being transferred downstream by debris flows. Time series of sediment supply, transport, and storage vary with basin scale for any combination of climatic, topographic, and geotechnical controls. In a companion paper [Benda and Dunne, this issue] we use simulations of timing, volumes, and locations of mass wasting to study the interaction between a stochastically forced sediment supply and systematic changes of storage and flux through channel networks.
Benda, L., and T. Dunne, Stochastic forcing of sediment routing and storage in channel networks, Water Resources Research, 33 (12), 2865-2880, 1997.
The stochastic field of sediment supply to the channel network of a drainage basin depends on the large-scale interactions among climatically driven processes such as forest fire and rainstorms, topography, channel network topology, and basin scale. During infrequent periods of intense erosion, large volumes of colluvium are concentrated in parts of a channel network, particularly near tributary junctions. The rivers carry bed material and wash load downstream from these storage sites at different rates. The bed material travels slowly, creating transient patterns of sediment transport, sediment storage, and channel morphology along the channel network. As the concentrations of bed material migrate along the network their waveforms can undergo changes by diffusion, interference at tributary junctions, and loss of mass through temporary sediment storage in fans and terraces and through particle abrasion, which converts bed material to wash load. We investigated how these processes might influence the sediment mass balance in channels of third and higher order in a 215- km(2) drainage basin within the Oregon Coast Range over a simulated 3000-year period with a climate typical of the late Holocene. We used field measurements and a simulation model to illustrate interactions between the major controls on large- scale processes functioning over long periods of time in complex drainage basins.
Bendix, J., Scale, Direction, and Pattern in Riparian Vegetation Environment Relationships, Annals of the Association of American Geographers, 84 (4), 652-665, 1994.
Bendix, J., Stream power influence on southern Californian riparian vegetation, Journal of Vegetation Science, 10 (2), 243-252, 1999.
Mechanical damage by floodwaters is frequently invoked to explain the distribution of riparian plant species, but data have been lacking to relate vegetation to specific estimates of flood damage potential. This research uses detailed estimates of unit stream power (an appropriate measure of the potential for mechanical damage) in conjunction with vegetation cover data to test this relationship at 37 valley-bottom sites in the Transverse Ranges of Southern California. A computer program, HEC-2, was used to model the slope and the variation in flow depth and velocity of the 20-yr flood across the sites. Regression models tested the influence of stream power (and of height above the water table) on the woody species composition of 393 4-m cross-section segments of the valley-bottom sites. Results indicate that unit stream power does have a significant effect on the riparian vegetation, but that the amount of that influence and its importance relative to the influence of height above the water table varies between watersheds. Some species are found primarily in locations of high stream power, while others are limited to portions of the valley bottom that experience only low stream power.
Bendix, J., and C.R. Hupp, Hydrological and geomorphological impacts on riparian plant communities, Hydrological Processes, 14 (16-17), 2977-2990, 2000.
Bennett, S.J., and J.L. Best, Particle size and velocity discrimination in a sediment-Laden turbulent flow using phase Doppler anemometry, Journal of Fluids Engineering-Transactions of the Asme, 117 (3), 505-511, 1995.
Bennett, S.J., and J.S. Bridge, An Experimental-Study of Flow, Bedload Transport and Bed Topography Under Conditions of Erosion and Deposition and Comparison With Theoretical-Models, Sedimentology, 42 (1), 117-146, 1995.
Bennett, S.J., and J.S. Bridge, The Geometry and Dynamics of Low-Relief Bed Forms in Heterogeneous Sediment in a Laboratory Channel, and Their Relationship to Water-Flow and Sediment Transport, Journal of Sedimentary Research Section a-Sedimentary Petrology and Processes, 65 (1), 29-39, 1995.
Bergeron, N.E., Scale-space analysis of stream-bed roughness in coarse gravel- bed streams, Mathematical Geology, 28 (5), 537-561, 1996.
This paper shows the usefulness of the scale-space filtering technique for the analysis of stream-bed roughness. In the first part of the paper, the scale-space filtering technique originally developed for signal analysis is adapted for the analysis of stream-bed microtopographic profiles. The modified technique provides a multiscale description of bed profiles, which allows the objective identification and measurement of individual roughness elements at all scales of observation. These bed elements then are classified as either grain or form roughness elements according to the roughness scales identified from a semivariogram analysis of the bed profile. Roughness indices describing each rough,less scale are obtained by calculating the mean height and spacing of the grain and form roughness elements. Because they measure directly the geometry of the bed, these indices provide a better description of stream-bed roughness than the traditional method based on a single grain index. in the second part of the paper, the technique is applied to the analysis of stream-bed roughness and resistance reflow of nine different gravel-bed stream reaches. The roughness indices calculated from this approach are used to obtain predicted values of resistance to pow which are in good agreement with the values observed in the field. The quality of this prediction is compared to the one obtained from a traditional description of bed roughness based on a single grain-size index. The results indicate that the values of resistance to flow calculated using the traditional approach are significantly less accurate than the values calculated using the new procedure which separates stream-bed roughness into a grain and a form component.
Best, J., S. Bennett, J. Bridge, and M. Leeder, Turbulence modulation and particle velocities over flat sand beds at low transport rates, Journal of Hydraulic Engineering-Asce, 123 (12), 1118-1129, 1997.
Beuselinck, L., G. Govers, A. Steegen, P.B. Hairsine, and J. Poesen, Evaluation of the simple settling theory for predicting sediment deposition by overland flow, Earth Surface Processes and Landforms, 24 (11), 993-1007, 1999.
Bhallamudi, S.M., and M.H. Chaudhry, Numerical Modeling of Aggradation and Degradation in Alluvial Channels, Journal of Hydraulic Engineering-Asce, 117 (9), 1145-1164, 1991.
The Saint-Venant equations describing unsteady flow in open channels and the continuity equation for the conservation of sediment mass are numerically solved to determine the aggradation and degradation of channel bottom due to an imbalance between water flow and sediment discharge. For this purpose, the MacCormack explicit finite-difference scheme is introduced. This scheme is second-order accurate, handles shocks and discontinuities in the solution without any special treatment, and allows simultaneous solution of the water and sediment equations, thereby obviating the need for iterations. The sediment transport relationship in any form may be included in the computations. Computational procedures are outlined for incorporating the typical boundaries for hydraulic engineering applications. The mathematical model presented here is applied to predict (1) Bed-level changes due to sediment overloading; (2) development of longitudinal profile due to base-level lowering; (3) and bed-level changes associated with the migration of knickpoints. The computed results are compared with the available experimental data obtained on laboratory flumes. The agreement between the computed and experimental results is satisfactory.
Biggs, B.J.F., M.J. Duncan, S.N. Francoeur, and W.D. Meyer, Physical characterisation of microform bed cluster refugia in 12 headwater streams, New Zealand, New Zealand Journal of Marine and Freshwater Research, 31 (4), 413-422, 1997.
Recent sediment transport research has demonstrated that microform bed clusters (MBC) are particularly resistant to entrainment during floods and preliminary biological surveys have shown that such structures could be providing important refugia for benthos in streams. We therefore surveyed MBC in a selection of headwater streams, South Island, New Zealand to determine how common such structures are and then related their occurrence to flow variability, relative armouring, reach gradient, and sediment geology/geometry to obtain a greater understanding of hydrological and hydraulic stream-scale factors affecting their density and composition. MBC were present in all streams and ranged in density from 0.067 to 0.279 m(-2). They occupied up to 4.4% of the surface area of the survey reaches, generally had 2-3 particles (a maximum of 7), and the average size for the largest particles ranged from 18.5 to 42.8 cm. MBC density and percentage site cover was significantly related to the relative armouring, but not to flow variability. The number of sediment particles per cluster was significantly correlated with reach gradient, although sediment geology, and associated geometry of particles, also appeared to be important. Thus, density and structure of MBC appeared to be primarily controlled by the interaction of relative armouring and reach gradient with highest densities and the largest number of cluster particles occurring in steep streams with high bed armouring. These structures were sufficiently common to be playing a significant role as flood refugia for benthos in some high gradient, headwater streams.
Biggs, B.J.F., R.A. Smith, and M.J. Duncan, Velocity and sediment disturbance of periphyton in headwater streams: biomass and metabolism, Journal of the North American Benthological Society, 18 (2), 222-241, 1999.
Disturbance by floods is believed to be 1 of the fundamental controllers of temporal and spatial patterns in stream periphyton. However, the exact causes of biomass losses are still poorly understood and discharge measures of disturbance often only explain limited variance in periphyton development. We investigated the effects of 2 of the main mechanisms of flood disturbance to periphyton-frequency of high-velocity events and frequency of bed sediment movement-in an effort to better understand disturbance processes and improve the quantification of flood disturbance regimes for studies of stream periphyton. Three sites were selected in headwater streams in each of 4 groups according to a 2-way factorial design of frequency of high-velocity events and sediment stability, giving a total of 12 sites. Periphyton were sampled monthly for 15 mo and analyzed for chlorophyll a. Maximum photosynthetic rates (P-max), chlorophyll-specific P-max, community respiration (CR), and P-max:CR ratios were determined seasonally. Nutrient concentrations were generally low and did not vary as a function of disturbance regime. Peaks in chlorophyll a were usually low reflecting the low nutrients. Chlorophyll was 2-10X higher where bed sediments moved <15X/y and with seasonal maxima most often in autumn. Frequency of bed movement, soluble reactive P, and the frequency of velocity perturbations were significant predictors of mean monthly chlorophyll a (r(2) = 0.88). Chlorophyll a and water temperature were major correlates of P-max, specific P-max, and CR, and thus the metabolic variables partly reflected changes in biomass among the disturbance regimes. With chlorophyll and temperature removed as covariates, the main factor influencing all metabolic parameters was season. P-max was 7X higher in summer than in spring when minima occurred, chlorophyll- specific P-max was 10X higher in summer than in spring, and CR was 4X higher in autumn than in spring. P-max:CR ratios indicated that the communities were generally autotrophic at times of maximum photosynthesis with the highest ratios in summer (3X higher than winter). The frequency of velocity perturbations also had a significant effect on P-max:CR ratios with highest ratios at sites where there was a low frequency of high-velocity events. Our results suggest that sediment instability greatly increases disturbance intensity for periphyton. It is therefore essential to assess not just the frequency of floods, but also the degree of bed movement when quantifying disturbance regimes for periphyton in headwater streams.
Birkeland, G.H., Riparian vegetation and sandbar morphology along the lower Little Colorado River, Arizona, Physical Geography, 17 (6), 534-553, 1996.
Birkhead, A.L., and C.S. James, Synthesis of rating curves from local stage and remote discharge monitoring using nonlinear muskingum routing, Journal of Hydrology, 205 (1-2), 52-65, 1998.
The specification of environmental water requirements in rivers requires the ability to relate discharge to local hydraulic conditions. Rating curves at locations of interest are a basic requirement. but are difficult and time-consuming to compile using conventional methods. River stage can be monitored relatively easily and can be related to discharge monitored at a different location on the same river by flood routing techniques. Simultaneous short-term records of local stage and remote discharge can be used through a nonlinear Muskingum model to optimize the parameters of a rating function at the local site. The approach is verified by resynthesizing a rating function used in rigorous routing in a hypothetical channel, and applied to a monitored site on the Sable River in South Africa, with account taken of dynamic bank storage. (C) 1998 Elsevier Science B.V.
Biron, P.M., S.N. Lane, A.G. Roy, K.F. Bradbrook, and K.S. Richards, Sensitivity of bed shear stress estimated from vertical velocity profiles: The problem of sampling resolution, Earth Surface Processes and Landforms, 23 (2), 133-139, 1998.
Blacknell, C., Morphology and Surface Sedimentary Features of Point Bars in Welsh Gravel-Bed Rivers, Geological Magazine, 119 (2), 181-&, 1982.
Blaustein, L., and J. Margalit, Priority effects in temporary pools: Nature and outcome of mosquito larva toad tadpole interactions depend on order of entrance, Journal of Animal Ecology, 65 (1), 77-84, 1996.
Bledsoe, B.P., and T.H. Shear, Vegetation along hydrologic and edaphic gradients in a North Carolina coastal plain creek bottom and implications for restoration, Wetlands, 20 (1), 126-147, 2000.
Bledsoe, B.P., and C.C. Watson, Effects of urbanization on channel instability, Journal of the American Water Resources Association, 37 (2), 255-270, 2001.
Channel instability and aquatic ecosystem degradation have been linked to watershed imperviousness in humid regions of the U.S. In an effort to provide a more process-based linkage between observed thresholds of aquatic ecosystem degradation and urbanization, standard single event approaches (U.S. Geological Survey Flood Regression Equations and rational) and continuous hydrologic models (HSPF and CASC2D) were used to examine potential changes in flow regime associated with varying levels of watershed imperviousness. The predicted changes in flow parameters were then interpreted in concert with risk-based models of channel form and instability. Although low levels of imperviousness (10 to 20 percent) clearly have the potential to destabilize streams, changes in discharge, and thus stream power, associated with increased impervious area are highly variable and dependent upon watershed-specific conditions. In addition to the storage characteristics of the pre-development watershed, the magnitude of change is sensitive to the connectivity and conveyance of impervious areas as well as the specific characteristics of the receiving channels. Different stream types are likely to exhibit varying degrees and types of instability, depending on entrenchment, relative erodibility of bed and banks, riparian condition, mode of sediment transport (bedload versus suspended load), and proximity to geomorphic thresholds. Nonetheless, simple risk-based analyses of the potential impacts of land use change on aquatic ecosystems have the potential to redirect and improve the effectiveness of watershed management strategies by facilitating the identification of channels that may be most sensitive to changes in stream power.
Bledsoe, B.P., and C.C. Watson, Logistic analysis of channel pattern thresholds: meandering, braiding, and incising, Geomorphology, 38 (3-4), 281-300, 2001.
A large and geographically diverse data set consisting of meandering, braiding, incising, and post-incision equilibrium streams was used in conjunction with logistic regression analysis to develop a probabilistic approach to predicting thresholds of channel pattern and instability. An energy-based index was developed for estimating the risk of channel instability associated with specific stream power relative to sedimentary characteristics. The strong significance of the 74 statistical models examined suggests that logistic regression analysis is an appropriate and effective technique for associating basic hydraulic data with Various channel forms. The probabilistic diagrams resulting from these analyses depict a more realistic assessment of the uncertainty associated with previously identified thresholds of channel form and instability and provide a means of gauging channel sensitivity to changes in controlling variables. (C) 2001 Elsevier Science B.V. All rights reserved.
Blizard, C.R., and E.E. Wohl, Relationships between hydraulic variables and bedload transport in a subalpine channel, Colorado Rocky Mountains, USA, Geomorphology, 22 (3-4), 359-371, 1998.
Blondeaux, P., and G. Seminara, A Unified Bar Bend Theory of River Meanders, Journal of Fluid Mechanics, 157 (AUG), 449-470, 1985.
Blott, S.J., and K. Pye, GRADISTAT: A grain size distribution and statistics package for the analysis of unconsolidated sediments, Earth Surface Processes and Landforms, 26 (11), 1237-1248, 2001.
Blum, M.D., and T.E. Tornqvist, Fluvial responses to climate and sea-level change: a review and look forward, Sedimentology, 47, 2-48, 2000.
Boadu, F.K., Hydraulic conductivity of soils from grain-size distribution: New models - Closure, Journal of Geotechnical and Geoenvironmental Engineering, 127 (10), 899-900, 2001.
Boardman, J., Classics in physical geography revisited - Trimble,S.W. 1983: A sediment budget for Coon Creek basin in the Driftless area, Wisconsin, 1983-1977. American Journal of Science 283, pg 454- 74, Progress in Physical Geography, 25 (2), 261-266, 2001.
Bolster, C.H., A.L. Mills, G.M. Hornberger, and J.S. Herman, Effect of surface coatings, grain size, and ionic strength on the maximum attainable coverage of bacteria on sand surfaces, Journal of Contaminant Hydrology, 50 (3-4), 287-305, 2001.
Bonner, J.S., R.L. Autenrieth, and L. Schreiber, Aquatic Sediments, Research Journal of the Water Pollution Control Federation, 62 (4), 593-614, 1990.
Boogerd, P., B. Scarlett, and R. Brouwer, Recent modelling of sedimentation of suspended particles: A survey, Irrigation and Drainage, 50 (2), 109-128, 2001.
Booth, D.B., and C.R. Jackson, Urbanization of aquatic systems: Degradation thresholds, stormwater detection, and the limits of mitigation, Journal of the American Water Resources Association, 33 (5), 1077-1090, 1997.
Bousmar, D., and Y. Zech, Momentum transfer for practical flow computation in compound channels, Journal of Hydraulic Engineering-Asce, 125 (7), 696-706, 1999.
A new theoretical 1D model of compound channels flows-the exchange discharge model-is presented. The interactions between main channel and floodplains are taken into account as a momentum transfer proportional to the product of the velocity gradient at the interface by the mass discharge exchanged through this interface due to turbulence. Geometrical changes in cross sections are also modeled; they generate a similar momentum transfer, proportional to the actual mass transfer. Both effects are incorporated into the flow equations as an additional head loss. This make the formulation suitable for stage-discharge computation but also enables practical water- profile simulations. The model is tested successfully against available experimental data for (1) stage-discharge relations; and (2) water-profile computation applied to a field case.
Bovis, M.J., Hillslope Geomorphology and Geotechnique, Progress in Physical Geography, 17 (2), 173-189, 1993.
This review focuses on recent Canadian contributions to hillslope geomorphology, and emphasizes geotechnical studies of mass movement phenomena in the Canadian Cordillera, including debris flows, rock avalanches, talus slopes, rock creep, and slow earthflows. A brief discussion is included of quick-clay flow slides in eastern Canada, and gelifluction phenomena in arctic and alpine areas. Comparisons are made with similar geotechnical work conducted in the Pacific-rim steeplands.
Bowersox, M.A., and D.G. Brown, Measuring the abruptness of patchy ecotones - A simulation- based comparison of landscape pattern statistics, Plant Ecology, 156 (1), 89-103, 2001.
The use of statistics of landscape pattern to infer ecological process at ecotones requires knowledge of the specific sensitivities of statistics to ecotone characteristics. In this study, sets of patch-based and boundary-based statistics were evaluated to assess their suitability as measures of abruptness on simulated ecotone landscapes. We generated 50 realizations each for 25 groups of ecotones that varied systematically in their degree of abruptness and patchiness. Factorial ANOVA was used to evaluate the sensitivity of statistics to the known differences among the simulated groups. Suitability of each index for measuring abruptness was evaluated using the ANOVA results. The statistics were then ranked in order of their suitability as abruptness statistics based on their sensitivity to abruptness, the consistency of the relationship, and their lack of sensitivity to patchiness. The two best statistics for quantifying abruptness were those we developed based on lattice delineation methods, and are called cumulative boundary elements and boundary element dispersion. The results of this research provide support for studies of ecotone process that rely on the interpretation of patch or boundary statistics.
Bradford, S.F., N.D. Katopodes, and G. Parker, Characteristic analysis of turbid underflows, Journal of Hydraulic Engineering-Asce, 123 (5), 420-431, 1997.
Bradford, S.F., and N.D. Katopodes, Hydrodynamics of turbid underflows. I: Formulation and numerical analysis, Journal of Hydraulic Engineering-Asce, 125 (10), 1006-1015, 1999.
Brandt, S.A., Classification of geomorphological effects downstream of dams, Catena, 40 (4), 375-401, 2000.
Brasington, J., B.T. Rumsby, and R.A. McVey, Monitoring and modelling morphological change in a braided gravel-bed river using high resolution GPS-based survey, Earth Surface Processes and Landforms, 25 (9), 973-990, 2000.
Braudrick, C.A., G.E. Grant, Y. Ishikawa, and H. Ikeda, Dynamics of wood transport in streams: A flume experiment, Earth Surface Processes and Landforms, 22 (7), 669-683, 1997.
The influence of woody debris on channel morphology and aquatic habitat has been recognized for many years. Unlike sediment, however, little is known about how wood moves through river systems. We examined some dynamics of wood transport in streams through a series of flume experiments and observed three distinct wood transport regimes: uncongested, congested and semi-congested. During uncongested transport, logs move without piece-to-piece interactions and generally occupy less than 10 per cent of the channel area. In congested transport, the logs move together as a single mass and occupy more than 33 per cent of the channel area. Semi-congested transport is intermediate between these two transport regimes. The type of transport regime was most sensitive to changes in a dimensionless input rate, defined as the ratio of log volume delivered to the channel per second (Q(log)) to discharge (Q(log)); this ratio varied between 0.015 for uncongested transport and 0.20 for congested transport. Depositional fabrics within stable log jams varied by transport type, with deposits derived from uncongested and semi-congested transport regimes having a higher proportion of pieces oriented normal to flow than those derived from congested transport. Because wood input rates are higher and channel dimensions decrease relative to piece size in low-order channels, we expect congested transport will be more common in low-order streams while uncongested transport will dominate higher-order streams. Single flotation models can be used to model the stability of individual pieces, especially in higher-order channels, but are insufficient for modelling the more complex interactions that occur in lower-order streams. (C) 1997 by John Wiley & Sons, Ltd.
Brayshaw, A.C., L.E. Frostick, and I. Reid, The Hydrodynamics of Particle Clusters and Sediment Entrainment in Coarse Alluvial Channels, Sedimentology, 30 (1), 137-143, 1983.
Bremen, R., and W.H. Hager, Experiments in Side-Channel Spillways, Journal of Hydraulic Engineering-Asce, 115 (5), 617-635, 1989.
Brenner, R.L., G.A. Ludvigson, B.J. Witzke, A.N. Zawistoski, E.P. Kvale, R.L. Ravn, and R.M. Joeckel, Late Albian Kiowa-skull creek marine transgression, lower Dakota formation, eastern margin of Western Interior Seaway, USA, Journal of Sedimentary Research, 70 (4), 868-878, 2000.
Brewer, P.A., and J. Lewin, Planform cyclicity in unstable reach: Complex fluvial response to environmental change, Earth Surface Processes and Landforms, 23 (11), 989-1008, 1998.
Long- and short-term channel changes are documented and analysed for a historically unstable reach of the River Severn at Llandinam, mid-Wales. Long-term changes (the last 150 years), reconstructed from 10 archival sources, are characterized by channel planform switching between meandering (1836-1840 and 1948-1963) and braided (1884-1903 and 1975- present) phases. Short-term changes, monitored by detailed planform surveys over a 2.5 year period, showed smaller-scale channel adjustments involving channel switching, bar accretion and channel expansion. Phases of braiding at Llandinam have been triggered by extrinsic controls, primarily flooding, but intrinsic controls (floodplain sediments, planform evolution and channel gradient) have been influential in priming the reach prior to destabilization. Flow regulation on the River Severn since 1968 has partly frozen the planform of the contemporary braid zone. Management of channel planform adjustments, where environmental change is phased in over time, must be informed by a knowledge of the potential for triggered planform switches. In addition, the effects of environmental change on fluvial systems are often historically contingent upon the state of the channel at the time of impact. (C) 1998 John Wiley & Sons, Ltd.
Bridge, J.S., Hydraulic Interpretation of Grain-Size Distributions Using a Physical Model For Bedload Transport, Journal of Sedimentary Petrology, 51 (4), 1109-1124, 1981.
Bridge, J.S., Paleochannel Patterns Inferred From Alluvial Deposits - a Critical-Evaluation, Journal of Sedimentary Petrology, 55 (4), 579-589, 1985.
Bridge, J.S., and S.J. Bennett, A Model For the Entrainment and Transport of Sediment Grains of Mixed Sizes, Shapes, and Densities, Water Resources Research, 28 (2), 337-363, 1992.
Bridge, J.S., and R.S. Tye, Interpreting the dimensions of ancient fluvial channel bars, channels, and channel belts from wireline-logs and cores, Aapg Bulletin-American Association of Petroleum Geologists, 84 (8), 1205-1228, 2000.
A primary objective in exploration for and development of fluvial reservoirs is determining the thickness and width of sandstone-conglomerate bodies (mainly channel-belt deposits). Most of the existing techniques for estimating the dimensions of fluvial reservoirs have major drawbacks. A fresh approach to the problem is made using recent theoretical, experimental, and field studies. This new approach involves (1) new models for the lateral and vertical variation of lithofacies and petrophysical-log response of river-channel deposits with explicit recognition of the different superimposed scales of strata, (2) distinction among single and superimposed channel bars, channels, and channel belts, (3) interpretation of maximum paleochannel depth from the thickness of channel bars and the thickness of sets of cross-strata formed by dunes, and (4) evaluation of various methods for estimation of widths of sandstone-conglomerate bodies that represent either single or connected channel belts (outcrop analogs; correlation of sandstone-conglomerate bodies between wells; use of empirical equations relating channel depth, channel width, and channel- belt width; theoretical models; and three-dimensional seismic data). Two fluvial reservoirs were reinterpreted using this new approach. In the first example from the Mesaverde Group, Colorado, maximum paleochannel depth had been underestimated because the degree of superposition of channel bars had been overestimated. As a result, channel-belt widths determined from empirical equations were underestimated. In the second example from the Travis Peak Formation, Texas, channel-belt width and connectivity of channel-belt sandstone bodies had been overestimated because of overzealous well-to-well correlation and inappropriate use of width and thickness data from supposed analogs. These examples demonstrate the potential value of this new approach in reservoir characterization and management.
Brierley, G.J., Bar Sedimentology of the Squamish River, British-Columbia - Definition and Application of Morphostratigraphic Units, Journal of Sedimentary Petrology, 61 (2), 211-225, 1991.
In a 20-km river reach of the Squamish River, British Columbia, in which channel planform changes progressively downstream from braided to meandering, there is a corresponding down-valley change in bar type from mid-channel compound bars to bank- attached compound bars to point bars. On each of 10 bars studied, within-bar facies and particle size trends relate directly to the spatial distribution of local-scale depositional environments on bar surfaces. Four fluvial morphostratigraphic units, defined in terms of their surface morphology and sedimentary characteristics, are differentiated: bar platform, chute channel, ridge, and remnant floodplain. The morphology, scale, and sedimentologic character of each morphostratigraphic unit are described. Compound bars are composed of extensive bar platform units dissected by chute channels, with remnants of other morphostratigraphic units. Within-bar facies and particle size trends are highly irregular, whether viewed down-bar, across-bar or vertically. Sediment sequences on point bars exhibit both around-the-bend and lateral trends. Bar platform units are transitional laterally to alternating ridge and chute features away from the main channel, with floodplain sequences beyond. Analysis of bar sedimentology using fluvial morphostratigraphic unit analysis provides a more reliable basis for palaeoenvironmental reconstruction than do existing procedures based on facies associations at the channel bedform scale.
Brierley, G.J., T. Cohen, K. Fryirs, and A. Brooks, Post-European changes to the fluvial geomorphology of Bega catchment, Australia: implications for river ecology, Freshwater Biology, 41 (4), 839-848, 1999.
1. Within a few decades of European disturbance in the mid- nineteenth century, river character and behaviour were transformed in Bega catchment on the south coast of New South Wales, Australia. Ecological impacts of geomorphic changes to river structure and function throughout the catchment are assessed. 2. At the time of European settlement, many water courses in Bega catchment were discontinuous, with extensive swamps along middle and upper courses. Following a series of direct and indirect human impacts, channels became continuous in the middle and upper parts of the catchment, as extensive valley fills at the base of the escarpment were incised. Along the lowland plain, the channel widened by over 300%, fundamentally altering the relationship between the channel and its adjacent floodplain. 3. Geomorphic changes to river structure have modified habitat availability throughout Bega catchment. The impacts have been least pronounced in headwater streams, but have been dramatic along virtually all river courses beyond the base of the escarpment. 4. Changes in river structure have been directly related to altered riparian vegetation cover, and vice versa. As a consequence of changes to river structure, bed substrate calibre (and supply volume/rate) has been modified along most streams. 5. A series of indirect, secondary impacts have modified habitat viability along river courses. Lateral, longitudinal and vertical linkages within the river system have been altered, affecting the transfer of water, sediment, organic matter, nutrients and other biotic interactions. 6. These direct and indirect consequences of geomorphic changes in river structure suggest that ecologists need to adopt a longer-term, catchment-framed view of human disturbance to river ecosystems. 7. Effective, sustainable ecological rehabilitation of river courses is dependent on an understanding of geomorphic processes and determination of appropriate river structure at differing positions in catchments.
Brookes, A., River Channelization - Traditional Engineering Methods, Physical Consequences and Alternative Practices, Progress in Physical Geography, 9 (1), 44-73, 1985.
Brookes, C.J., J.M. Hooke, and J. Mant, Modelling vegetation interactions with channel flow in river valleys of the Mediterranean region, Catena, 40 (1), 93-118, 2000.
Brown, L.J., D.D. Wilson, N.T. Moar, and D.C. Mildenhall, Stratigraphy of the Late Quaternary Deposits of the Northern Canterbury Plains, New-Zealand, New Zealand Journal of Geology and Geophysics, 31 (3), 305-335, 1988.
Browne, G.H., and J.T. Thomas, Clast size characteristics of gravel within rivers of the Waimea Plains, Nelson, New Zealand Journal of Geology and Geophysics, 44 (1), 89-96, 2001.
Gravel within rivers of the Waimea Plains near Nelson, New Zealand, was derived through the Wairoa Gorge from Paleozoic- Mesozoic basement rocks to the southeast, and to a lesser extent from Pleistocene gravels to the west. A downstream reduction of mean clast size and an increase in sorting occurs in three rivers of the Waimea Plains. Clast form is dominated by bladed clasts, with a slight tendency with transport distance to more elongate forms. Clast sizes are apparently larger in the modern rivers than in fluvial gravels of the Last Glacial period. The smaller clast size in the Last Glacial deposits may indicate more efficient clast-size reduction in glacial as opposed to modern-day rivers.
Brunke, M., Colmation and depth filtration within streambeds: Retention of particles in hyporheic interstices, International Review of Hydrobiology, 84 (2), 99-117, 1999.
Colmation refers to the retention processes that can lead to the clogging of the top layer of channel sediments and decolmation refers to the resuspension of deposited fine particles. Internal colmation, clogging of the interstices directly below the armor layer, may form a thin seal that disconnects surface water from hyporheic water by inhibiting exchange processes. The settling of particles under low flow conditions can cause external colmation. Colmated channel sediments are characterized by reduced porosity and hydraulic conductivity as well as by a consolidated texture. The term 'depth filtration' refers to the transport and storage of fine matrix sediments in interstitial layers. Depth filtration is of significance for the transport of colloidal and fine particulate inorganic as well as organic matter within the hyporheic interstices and into the alluvial aquifer. The role of depth filtration is assessed for the content (given in mg/per liter) of matrix fine particles retained in the coarse framework sediment of a gravel-bed;river in Switzerland. Sediment samples were taken by freeze-coring with liquid nitrogen down to 70 cm depth and by piezometers down to 150 cm depth. Seventy-two percent of the mobile matrix fine particles were smaller than 0.1 mm and 50% were smaller than 0.03 mm. The content of fines tended to increase with depth, although higher accumulations were found at intermediate depths in sediments influenced by 'exfiltrating ground water. Interstitial detrital particles >90 mu m showed vertical distribution patterns opposing those of total particles. These relationships revealed a differential significance of import, storage, and transport within three types of hydrological exchange zones (infiltration, horizontal advection, exfiltration) in the cross-section of the stream.
Bryan, R.B., Soil erodibility and processes of water erosion on hillslope, Geomorphology, 32 (3-4), 385-415, 2000.
The importance of the inherent resistance of soil to erosional processes, or soil erodibility, is generally recognized in hillslope and fluvial geomorphology, but the full implications of the dynamic soil properties that affect erodibility are seldom considered. In Canada, a wide spectrum of soils and erosional processes has stimulated much research related to soil erodibility. This paper aims to place this work in an international framework of research on water erosion processes, and to identify critical emerging research questions. It focuses particularly on experimental research on rill and interrill erosion using simulated rainfall and recently developed techniques that provide data at appropriate temporal and spatial scales, essential for event-based soil erosion prediction. Results show that many components of erosional response, such as partitioning between rill and interrill or surface and subsurface processes, threshold hydraulic conditions for rill incision, rill network configuration and hillslope sediment delivery, are strongly affected by spatially variable and temporally dynamic soil properties. This agrees with other recent studies, but contrasts markedly with long- held concepts of soil credibility as an essentially constant property for any soil type. Properties that determine erodibility, such as soil aggregation and shear strength, are strongly affected by climatic factors such as rainfall distribution and frost action, and show systematic seasonal variation. They can also change significantly over much shorter time scales with subtle variations in soil water conditions, organic composition, microbiological activity, age-hardening and the structural effect of applied stresses. Property changes between and during rainstorms can dramatically affect the incidence and intensity of rill and interrill erosion and, therefore, both short and long-term hillslope erosional response. Similar property changes, linked to climatic conditions, may also significantly influence the stability and resilience of plant species and vegetation systems. Full understanding of such changes is essential if current event- based soil erosion models such as WEPP and EUROSEM are to attain their full potential predictive precision. The complexity of the interacting processes involved may, however, ultimately make stochastic modelling more effective than physically based modelling in predicting hillslope response to erodibility dynamics. (C) 2000 Elsevier Science B.V. All rights reserved.
Bryant, M.D., and F.H. Everest, Management and condition of watersheds in southeast Alaska: The persistence of anadromous salmon, Northwest Science, 72 (4), 249-267, 1998.
In contrast to most of North America and Europe, numerous intact or lightly disturbed watersheds are present throughout southeast-Alaska These watersheds support abundant and diverse populations of anadromous salmonids. While the watersheds throughout the northern hemisphere have been exposed to human disturbance from millennia to centuries, significant human disturbance to the watersheds of southeast Alaska did not begin until the 1950's with the start of industrial logging. Although management of watersheds has evolved to reduce risks to aquatic habitat, the most intensive logging occurred during the first 20 years of limber harvest when few restraints were placed on timber harvest in watersheds. As a result, a legacy of streams with deteriorating habitat remains. While few salmon stocks in southeast Alaska appear to be in decline, escapement records on specific watersheds, particularly those most severely affected by management are non-existent or qualitative. The present status of salmon stocks may be attributed to abundant intact watersheds, high marine survival, and escapement levels that fully seed most watersheds. The numerous intact watersheds throughout southeast Alaska are a critical factor in maintaining sustainable salmon stocks in southeast Alaska.
Buffin-Belanger, T., A.G. Roy, and A.D. Kirkbride, On the integration of turbulent flow structures within the dynamics of a gravel-bed river reach, Geographie Physique Et Quaternaire, 54 (1), 105-117, 2000.
On the integration of turbulent flow structures within the dynamics of a gravel-bed river reach. Understanding the dynamics of a river involves knowledge on the interactions between flow, sediment transport and bedform development at a range of scales. This requires the characterisation of flow structures and of the flow organisation at the reach scale. Three types of flow structures have been commonly described in flows over gravel-bed rivers: the bursting motions in the near- bed region (ejections), the shedding motions from the larger protruding particles and the large-scale flow structures which develop in the outer region of the flow. We describe the processes that give birth to these flow structures along with the possible interactions between them. As an example, the passage of large-scale flow structures changes the dynamics of the separation of flow in the wake of an obstacle, thus affecting the manifestation of shedding motions. These processes and interactions are then combined into an illustration of the complex organisation of flow at the scale of a river reach. Although speculative, this illustration highlights that (1) the scales and locations in space of the structures are closely related to the scale and distribution of the roughness elements, (2) the flow is organized into clear zones of production and dissipation of flow structures, and (3) the organization of the flow presents a strong structural anisotropy with complex interactions between the flow structures. This essay outlines that the interactions between flow structures are as important as the presence of the structures themselves in the description of turbulent flows over gravel-bed rivers.
Buffington, J.M., W.E. Dietrich, and J.W. Kirchner, Friction Angle Measurements On a Naturally Formed Gravel Streambed - Implications For Critical Boundary Shear-Stress, Water Resources Research, 28 (2), 411-425, 1992.
We report the first measurements of friction angles for a naturally formed gravel streambed. For a given test grain size placed on a bed surface, friction angles varied from 10-degrees to over 100-degrees; friction angle distributions can be expressed as a function of test grain size, median bed grain size, and bed sorting parameter. Friction angles decrease with increasing grain size relative to the median bed grain size, and are a systematic function of sorting, with lower friction angles associated with poorer sorting. The probability distributions of critical shear stress for different grain sizes on a given bed surface, as calculated from our friction angle data, show a common origin, but otherwise diverge with larger grains having narrower and lower ranges of critical shear stresses. The potential mobility of a grain, as defined by its probability distribution of critical shear stress, may be overestimated for larger grains in this analysis, because our calculations do not take into account the effects of grain burial and altered near-bed flow fields.
Buffington, J.M., and D.R. Montgomery, A systematic analysis of eight decades of incipient motion studies, with special reference to gravel-bedded rivers, Water Resources Research, 33 (8), 1993-2029, 1997.
Buffington, J.M., and D.R. Montgomery, Effects of hydraulic roughness on surface textures of gravel- bed rivers, Water Resources Research, 35 (11), 3507-3521, 1999.
Field studies of forest gravel-bed rivers in northwestern Washington and southeastern Alaska demonstrate that bed-surface grain size is responsive to hydraulic roughness caused by bank irregularities, bars, and wood debris. We evaluate textural response by comparing reach-average median grain size (D-50) to that predicted from the total bank-full boundary shear stress (tau(0bf)), representing a hypothetical reference condition of low hydraulic roughness. For a given tau(0bf), channels with progressively greater hydraulic roughness have systematically finer bed surfaces, presumably due to reduced bed shear stress, resulting in lower channel competence and diminished bed load transport capacity, both of which promote textural fining. In channels with significant hydraulic roughness, observed values of D-50 can be up to 90% smaller than those predicted from tau(0bf). We find that wood debris plays an important role at our study sites, not only providing hydraulic roughness but also influencing pool spacing, frequency of textural patches, and the amplitude and wavelength of bank and bar topography and their consequent roughness. Our observations also have biological implications. We find that textural fining due to hydraulic roughness can create usable salmonid spawning gravels in channels that otherwise would be too coarse.
Buffington, J.M., and D.R. Montgomery, Effects of sediment supply on surface textures of gravel-bed rivers, Water Resources Research, 35 (11), 3523-3530, 1999.
Using previously published data from flume studies, we test a new approach for quantifying the effects of sediment supply (i.e., bed material supply) on surface grain size of equilibrium gravel channels. Textural response to sediment supply is evaluated relative to a theoretical prediction of competent median grain size (D-50'). We find that surface median grain size (D-50') varies inversely with sediment supply rate and systematically approaches the competent value (D-50') at low equilibrium transport rates. Furthermore, equilibrium transport rate is a power function of the difference between applied and critical shear stresses and is therefore a power function of the difference between competent and observed median grain sizes (D-50' and D-50'). Consequently, we propose that the difference between predicted and observed median grain sizes can be used to determine sediment supply rate in equilibrium channels. Our analysis framework collapses data from different studies toward a single relationship between sediment supply rate and surface grain size. While the approach appears promising, we caution that it has been tested only on a limited set of laboratory data and a narrow range of channel conditions.
Buffington, J.M., and D.R. Montgomery, A procedure for classifying textural facies in gravel-bed rivers, Water Resources Research, 35 (6), 1903-1914, 1999.
Textural patches (i.e., grain-size facies) are commonly observed in gravel-bed channels and are of significance for both physical and biological processes at subreach scales. We present a general framework for classifying textural patches that allows modification for particular study goals, while maintaining a basic degree of standardization. Textures are classified using a two-tier system of ternary diagrams that identifies the relative abundance of major size classes and subcategories of the dominant size. An iterative procedure of visual identification and quantitative grain-size measurement is used. A field test of our classification indicates that it affords reasonable statistical discrimination of median grain size and variance of bed-surface textures. We also explore the compromise between classification simplicity and accuracy. We find that statistically meaningful textural discrimination requires use of both tiers of our classification. Furthermore, we find that simplified variants of the two-tier scheme are less accurate but may be more practical for field studies which do not require a high level of textural discrimination or detailed description of grain-size distributions. Facies maps provide a natural template for stratifying other physical and biological measurements and produce a retrievable and versatile database that can be used as a component of channel monitoring efforts.
Buffington, J.M., The legend of A. F. Shields, Journal of Hydraulic Engineering-Asce, 125 (4), 376-387, 1999.
The well-known doctoral work of Shields is a tale that is frequently recounted by many authors and has spawned a large, continuing body of research over the last 60 years. Despite the success of Shields' work, the details of his experimental methods and results as reported by others are quite variable. Inconsistencies and misconceptions regarding Shields' work are identified and examined here. Incomplete descriptions by Shields, loss of his original data, and Shields' postgraduate absence from the hydraulic engineering community leave some of the identified inconsistencies open to debate.
Buffington, J.M., The legend of A.F. Shields - Closure, Journal of Hydraulic Engineering-Asce, 126 (9), 721-723, 2000.
Buffington, J.M., and D.R. Montgomery, Comment on "Effects of hydraulic roughness on surface textures of gravel-bed rivers" by John M. Buffington and David R. Montgomery - Reply, Water Resources Research, 37 (5), 1529-1533, 2001.
Bunte, K., and S.R. Abt, Sampling frame for improving pebble count accuracy in coarse gravel-bed streams, Journal of the American Water Resources Association, 37 (4), 1001-1014, 2001.
Improved sampling techniques are needed to increase the accuracy of pebble-count particle-size distributions used for stream studies in gravel-bed streams. However, pebble counts are prone to operator errors introduced through subjective particle selection, serial correlation, and inaccurate particle-size measurements. Errors in particle-size measurements can be minimized by using a gravel template. Operator influence on particle selection can be minimized by using a sampling frame, 60 by 60 cm, in which sampling points are identified by the cross points of thin elastic bands. Serial correlation can be minimized by adjusting the spacing between the cross points and setting it equal to the dominant large particle size (approximate toD(95)). In a field test in a cobble-bed stream, the sampling frame developed in this study produced slightly coarser size distributions, particularly in the cobble range, than the traditional heel-to-toe walk that selects particles with a blind touch at the tip of the boot. The sampling frame produced more similar sampling results between two operators than heel-to-toe walks. The difference between the two sampling methods is attributed to an unbiased selection of fine and coarse particles when using the sampling frame.
Burns, B.A., P.L. Heller, M. Marzo, and C. Paola, Fluvial response in a sequence stratigraphic framework: Example from the Montserrat fan delta, Spain, Journal of Sedimentary Research, 67 (2), 311-321, 1997.
Butler, J.B., S.N. Lane, and J.H. Chandler, Characterization of the structure of river-bed gravels using two-dimensional fractal analysis, Mathematical Geology, 33 (3), 301-330, 2001.
This paper is concerned with the application of fractal analysis to understand the structure of water-worked gravel-bed river surfaces. High resolution digital elevation models, acquired using digital photogrammetric methods, allowed the application of two-dimensional fractal methods. Previous gravel-bed river studies have been based upon sampled profiles and hence one-dimensional fractal characterisation. After basic testing that bed elevation increments are Gaussian, the paper uses two-dimensional variogram surfaces to derive directionally dependent estimates of fractal dimension. The results identify mixed fractal behavior with two characteristic fractal bands, one associated with the subgrain scale and one associated with the grain scale, The subgrain scale characteristics were isotropic and sensitive to decisions made during the data collection process. Thus, it was difficult to differentiate whether these characteristics were real facets of the surfaces studied. The second band was anisotropic and not sensitive to data collection issues. Fractal dimensions were greater in the downstream direction than in other directions suggesting that the effects of water working are to alter the level of surface organisation, by increasing surface irregularity and hence roughness. This is an important observation as it means that water-worked surfaces may have a distinct anisotropic signal, revealed when using a fractal type analysis.
Byrd, T.C., and D.J. Furbish, Magnitude of deviatoric terms in vertically averaged flow equations, Earth Surface Processes and Landforms, 25 (3), 319-328, 2000.
The depth-integrated momentum and kinetic energy equations contain velocity correlation terms that involve products of local deviations in velocity components about depth-averaged values. Based on velocity data obtained from North Boulder Creek, Colorado, a simple scaling analysis suggests that certain of these terms, which normally can be neglected in the case of smooth channels, can be significant parts of the momentum and energy balances in steep, rough channels owing to the occurrence of non-logarithmic velocity profiles. A linearized version of the kinetic energy equation suggests that, for flow accelerations over small-amplitude bed forms, the energy of the mean motion is spatially partitioned between a form involving the depth-averaged velocity and a form involving the deviatoric part of the velocity profile; this partitioning is associated with spatial variations in the uniformity of the vertical profile of the streamwise velocity. These points are consistent with published flume measurements involving flow over sand-roughened dunes, and with published field measurements of flow over a gravel bar. Copyright (C) 2000 John WiIey & Sons, Ltd.
Byrd, T.C., D.J. Furbish, and J. Warburton, Estimating depth-averaged velocities in rough channels, Earth Surface Processes and Landforms, 25 (2), 167-173, 2000.
Profiles of streamwise velocity obtained from North Boulder Creek, Colorado, typically are non-logarithmic in form and exhibit the strong influence of form drag associated with coarse bed roughness. The spatially averaged profile is consistent with recent theoretical profile forms suggested for rough channels that are based on a partitioning of the total stress between a fluid part and a part associated with form drag on bed particles. Estimates of local depth-averaged velocity using algorithms that are based on several measurements in the flow column improve with explicit Riemann averaging, versus simple averaging, of the measurements. Estimates based on a single-point measurement at 0.6 of the flow depth, assuming a logarithmic or approximately logarithmic velocity profile, are the least reliable. Copyright (C) 2000 John Wiley & Sons, Ltd.
Camarero, J.J., E. Gutierrez, and M.J. Fortin, Spatial pattern of subalpine forest-alpine grassland ecotones in the Spanish Central Pyrenees, Forest Ecology and Management, 134 (1-3), 1-16, 2000.
We describe the spatial structure of two contrasting subalpine Pinus uncinata forest-alpine grassland ecotones located in the Central Pyrenees (Ordesa and Tesso sites) as a preliminary step to infer the processes that produced their spatial patterns. All trees were mapped and measured within 4200 m(2) rectangular plots parallel to the maximum slope and encompassing timberline and treeline. The spatial description of the ecotones was accomplished using several methodologies. Point pattern analysis (Ripley's K) was first used to quantify the spatial pattern of trees using each stem x-y coordinates. Then, surface pattern analyses (Moran and Mantel spatial correlograms) were used to quantify the spatial pattern of tree characteristics across the ecotone (size, growth-form, estimated age). In the Ordesa site, krummholz individuals showed significant and positive spatial interaction with seedlings. In this site, P. unicinata individuals evolved from shrubby to vertical. growth- forms abruptly producing a steep spatial gradient. In the Tesso site, regeneration was concentrated near the treeline and the spatial gradient was gradual. Both ecotones formed similar to 45 m long zones of influence along the slope based on different variables. Wind and snow avalanches seem to be the main controlling factors of the spatial pattern of trees in the sites Ordesa and Tesso, respectively. Our results point out potential different responses of treeline populations to environmental changes according to the spatial pattern. (C) 2000 Elsevier Science B.V. All rights reserved.
Cao, S.Y., and D.W. Knight, Design for hydraulic geometry of alluvial channels, Journal of Hydraulic Engineering-Asce, 124 (5), 484-492, 1998.
Cao, Z.X., Equilibrium near-bed concentration of suspended sediment, Journal of Hydraulic Engineering-Asce, 125 (12), 1270-1278, 1999.
Carbonneau, P.E., and N.E. Bergeron, The effect of bedload transport on mean and turbulent flow properties, Geomorphology, 35 (3-4), 267-278, 2000.
This paper reports the results of a flume experiment that was designed to investigate the effect of bedload transport on mean and turbulent properties of the flow. The experiment consisted of varying the bedload transport rate for a given hydraulic condition, and of measuring the flow velocity profiles using an Acoustic Doppler Velocimeter (ADV) for each transport rate in order to allow for comparison. Bedload transport was produced by injecting gravel-size particles (D-50 = 7.4 mm) with a conveyer belt mounted at the upstream end of the flume. The results indicate that the effect of bedload on flow characteristics is complex. It is shown that bedload transport causes opposite effects on flow velocity depending on the roughness of the bed and the relative magnitude of flow and sediment transport variables. A better understanding of these conflicting results is obtained from the application of an energy budget approach to the analysis of velocity data. This approach demonstrates that bedload affects flow velocity by modifying the rate of dissipation of turbulent kinetic energy. However, the mechanisms responsible for the modification of turbulent dissipation are still unknown. (C) 2000 Elsevier Science B.V. All rights reserved.
Carling, P.A., The Noon Hill Flash Floods - July 17th 1983 - Hydrological and Geomorphological Aspects of a Major Formative Event in an Upland Landscape, Transactions of the Institute of British Geographers, 11 (1), 105-118, 1986.
Carling, P.A., Bedload Transport in 2 Gravel-Bedded Streams, Earth Surface Processes and Landforms, 14 (1), 27-39, 1989.
Carling, P.A., An Appraisal of the Velocity-Reversal Hypothesis For Stable Pool Riffle Sequences in the River Severn, England, Earth Surface Processes and Landforms, 16 (1), 19-31, 1991.
The 'velocity-reversal hypothesis' is the linchpin for a number of recent conceptual models pertaining to sediment sorting and the maintenance of pool-riffle sequences in gravel-bedded streams. The literature in support of the hypothesis together with published adverse criticism is reviewed. It is concluded that convincing evidence for the ubiquitous occurrence of such a reversal in a range of channel geometries is currently unavailable. Continuity considerations indicate that riffles need to be considerably wider than pools for a reversal in the mean velocity to occur under conditions of subcritical flow, high stage, and stable morphology. These observations are substantiated by a detailed study of the hydraulic geometry of stable pool-riffle sequences in the River Severn, England. Neither the sectionally-averaged velocity nor the near-bed shear velocity is sensibly greater in the pools than over the riffles during bankfull or near bankfull flow. Instead a tendency towards equalization of the values of average hydraulic variables is noted as discharge increases. A detailed investigation of the three-dimensional character of the flow is required to demonstrate whether the entrainment forces within pools can locally exceed those over neighbouring riffles. Unusual behaviour of the energy gradient over riffles during moderate discharges is related to backwater effects as mediated by the spacing of the riffles. The hydraulic data are used to comment on the stability of the test reaches in the context of the development of the River Severn in the vicinity of Shrewsbury.
Carling, P.A., and N. Wood, Simulation of Flow Over Pool-Riffle Topography - a Consideration of the Velocity Reversal Hypothesis, Earth Surface Processes and Landforms, 19 (4), 319-332, 1994.
Computer flow simulations using the HEC-2 step-backwater routine are used to demonstrate the effect of systematically varying river channel width, riffle spacing and channel roughness on the shear velocity, section-mean velocity and energy slope in fixed-bed pool-riffle sequences. Initial scaling is obtained by utilizing published information on hydraulic parameters within reaches of the River Severn. Subsequently this restriction is relaxed and the effect of varying parameter combinations within realistic limits is explored. The purpose of this exercise is to isolate those scenarios which may preclude or promote the occurrence of a competence reversal', such that pools scour at high flow whilst deposition occurs on riffles. It is concluded that rivers in which pools are hydraulically rougher than riffles are likely to demonstrate a competence reversal. For prescribed conditions, the critical discharge at which a reversal occurs is a negative function of riffle spacing and riffle width relative to pool width. Downstream variation in hydraulic roughness also has implications for the phase relationship of shear velocity maxima and minima in relation to the extremes in pool-riffle topography.
Carling, P.A., Flow-Separation Berms Downstream of a Hydraulic Jump in a Bedrock Channel, Geomorphology, 11 (3), 245-253, 1995.
The first direct observation of the development of lateral gravel berms associated with hydraulic jumps in bedrock channels is reported. Cobbles and pebbles were observed being swept through jumps and deposited in the tranquil flow immediately downstream and either side of the V-shaped shock- waves. Field measurements of jump geometry, current speed and water depth are found to be consistent both with laboratory data and theoretical considerations. The deposits have significance in constraining flood palaeoflow reconstructions as the presence of berms determines the former location of hydraulic jumps whilst the angle subtended by the berm crestline (with respect to a regular bankline) may be used to estimate the Froude number of the flow.
Carling, P.A., Subaqueous gravel dunes, Journal of Sedimentary Research, 69 (3), 534-545, 1999.
Gravel dunes are rarely reported owing to comparative rarity of occurrence and generic confusion with antidunes and classes of gravel bars. A compilation of data from the literature for sediments with a median size greater than 2 mm shows that dunes have been developed in the laboratory in median grain sizes up to 28.6 mm, For field conditions, there are data for grain sizes up to 60 mm, Equilibrium and non-equilibrium gravel dunes range in length from less than 0.6 m to greater than 100 m, Heights range from less than 0.1 m to 16 m. Height and length data for the steepest three dimensional (3-D) gravel dunes are consistent with the H:L function reported by Ashley (1990) for equilibrium dunes developed in sand. For a broad range of dune length, 3-D gravel dunes are steeper than two-dimensional (2-D) dunes, but for L > 100 m and H > 8 m there are too few data to draw any conclusion. Ashley's H:L function does not apply to a broad range of 2-D gravel dunes, A separate well defined function is proposed to describe the H:L relationship for 2-D gravel dunes of maximum steepness. There are few data on the hydrodynamic development of gravel dunes. As a guide, gravel dunes develop for a range of Froude numbers up to 0.75 given that the nondimensional mean bed shear stress (0) exceeds circa 0.1, Dunes reach their maximum height at 0 = 0.25 and have reduced in height when 0 = 0.3. Froude numbers of 0.84 and above lead to crestal flattening, dune diminution, and eventual replace ment by antidunes or upper stage plane beds. How ever, offing to lag effects, transitional bedforms have been recorded for Froude numbers near the critical value of 1. The development of gravel dune steepness from lo lower-stage plane bed through to upper-stage plane bed is well described in only one case, by Dinehart (1992a), Fredsoe's (1975) 8 function for equilibrium dune steepness applies reasonably web to Dinehart's steepest dunes. Alien's (1984) bedform existence field based on 0 and a characteristic grain size of the bed sediment has been extended from 5 mm to include bedstocks as coarse as 33 mm.
Carling, P.A., and H.G. Orr, Morphology of riffle-pool sequences in the River Severn, England, Earth Surface Processes and Landforms, 25 (4), 369-384, 2000.
Despite the occurrence of riffle-pool sequences in many rivers there are few data concerning riffle-pool unit morphology. Of many criteria proposed to identify riffle-pool units, only three methods can be regarded as objective and robust. These are the 'zero-crossing', the 'spectral analysis' and the 'control-point' methods. In this paper statistics are developed using the first two of these methods to describe the streamwise morphology of 275 riffles and 285 pools which forma continuous 32.1 lan reach of the bed of the River Severn in Shropshire, England. Yalin's theoretical relationship between the average riffle:pool unit length (lambda(p)) and channel width ((W) over bar), lambda(p) = 3 (W) over bar, applies to the River Severn. Reach-average riffle height ((H) over bar) is a constant proportion of bankfull depth ((h) over bar); typicaily (H) over bar congruent to 0.16h. Riffle height is a positive function of riffle length. Pool depth is a positive function of pool length. However, both riffle length and pool length increase more rapidly than the bed-level amplitude, such that long riffles or pools are relatively 'flat'. As channel gradient reduces, bedforms flatten and become more asymmetric as riffle stoss sides and the proximal slope of pools lengthen at the expense of riffle lee sides and pool distal slopes. The statistical relationships between riffle steepness (H/L) and water depth are similar to those for equilibrium subaqueous dunes. The Severn data are consistent with Yalin's theoretical analysis relating riffle bedform length (L-r) to water depth, i.e. L-r = alpha 2 pi h, wherein alpha congruent to 1 for steep near-equilibrium bedforms but alpha congruent to 2 to 3 as the relative depth decreases and riffles become long, low features. Theoretical consideration and turbulence data indicate that the frequency of coherent turbulent-flow structures associated with the riffle-pool mixing length in the Severn should be of the order of 50 to 100 s. The morphological similarity of the steepest River Severn riffles with dunes raises intriguing questions with respect to self-similar, convergent organization of periodic alluvial bedforms and to bedform dynamic classification particularly. Copyright (C) 2000 John Wiley & Sons, Ltd.
Carling, P.A., E. Golz, H.G. Orr, and A. Radecki-Pawlik, The morphodynamics of fluvial sand dunes in the River Rhine, near Mainz, Germany. I. Sedimentology and morphology, Sedimentology, 47 (1), 227-252, 2000.
The dynamics of large isolated sand dunes moving across a gravel lag layer were studied in a supply-limited reach of the River Rhine, Germany. Bed sediments, dune geometry, bedform migration rates and the internal structure of dunes are considered in this paper. Hydrodynamic and sediment transport data are considered in a companion paper. The pebbles and cobbles (D-50 of 10 mm) of the flat lag layer are rarely entrained. Dunes consist of well-sorted medium to coarse sand (D-50 of 0.9 mm). Small pebbles move over the dunes by 'overpassing', but there is a degree of size and shape selectivity. Populations of ripples in sand (D-50 < 0.6 mm), and small and large dunes are separated by distinct breaks in the bedform length data in the regions of 0.7-1 m and 5-10 m. Ripples and small dunes may have sinuous crestlines but primarily exhibit two-dimensional planforms. In contrast, large dunes are primarily three-dimensional barchanoid forms. Ripples on the backs of small dunes rarely develop to maximum steepness. Small dunes may achieve an equilibrium geometry, either on the gravel bed or as secondary dunes within the boundary layer on the stoss side of large dunes. Secondary dunes frequently develop a humpback profile as they migrate across the upper stoss slope of large dunes, diminishing in height but increasing in length as they traverse the crestal region. However, secondary dunes more than 5 m in length are rare. The dearth of equilibrium ripples and long secondary dunes is probably related to the limited excursion length available for bedform development on the parent bedforms. Large dunes with lengths between 20 m and 100 m do not approach an equilibrium geometry. A depth limitation rather than a sediment supply limitation is the primary control on dune height; dunes rarely exceed 1 m high in water depths of approximate to 4 m. Dune celerity increases as a function of the mean flow velocity squared, but this general relationship obscures more subtle morphodynamics. During rising river stage, dunes tend to grow in height owing to crestal accumulation, which slows downstream progression and steepens the dune form. During steady or falling stage, an extended crestal platform develops in association with a rapid downstream migration of the lee side and a reduction in dune height. These diminishing dunes actually increase in unit volume by a process of increased leeside accumulation fed by secondary dunes moving past a stalled stoss toe. A six-stage model of dune growth and diminution is proposed to explain variations in observed morphology. The model demonstrates how the development of an internal boundary layer and the interaction of the water surface with the crests of these bedload-dominated dunes can result in dunes characterized by gentle lee sides with weak flow separation. This finding is significant, as other studies of dunes in large rivers have attributed this morphological response to a predominance of suspended load transport.
Carlson, P.R., J.L. Chin, and F.L. Wong, Bedrock knobs, San Francisco Bay: Do navigation hazards outweigh other environmental problems?, Environmental & Engineering Geoscience, 6 (1), 41-55, 1999.
Three bedrock knobs (Arch, Harding, and Shag rocks) rise above the unconsolidated sediment of central San Francisco Bay to a water depth of less than -12 m (< -39.4 ft MLLW), These rocks are within the westbound vessel traffic area, and the northernmost, Harding Rock, is similar to 300 m (984 ft) from the two-way deep water traffic lane. The rocks pose a hazard to deep-draft vessels. Large ships with drafts deeper than -17 m (-55.8 ft) cross central San Francisco Bay bound for and returning from major port cities of the Bay estuary. Acoustic profiling data show that bedrock extends at a gentle to moderate slope away from the knobs. These data also show that two of the knobs, Harding and Shag, may be part of a bedrock ridge that extends to Alcatraz Island and perhaps southeast to Blossom Rock. The tops of these rocks should be lowered to a depth of -17 m (-55.8 ft), with a total volume of as much as 245,000 m(3) (320,460 yd(3)), at an estimated cost of nearly 27 million dollars, to eliminate the possibility that a tanker would strike one and rupture. A resulting large oil spill would likely cost many times more than the 10 million dollars needed to clean up a small 1996 spill. If the rocks were removed, local habitat for striped bass and other game fish would be altered, with potential negative impact on sport fishing. Currently, public officials are studying the benefits to the Bay environment of lowering the rock knobs.
Carmel, Y., and R. Kadmon, Effects of grazing and topography on long-term vegetation changes in a Mediterranean ecosystem in Israel, Plant Ecology, 145 (2), 243-254, 1999.
The dynamics of Mediterranean vegetation over 28 years was studied in the Northern Galilee Mountains, Israel, in order to identify and quantify the major factors affecting it at the landscape scale. Image analysis of historical and current aerial photographs was used to produce high resolution digital vegetation maps (pixel size = 30 cm) for an area of 4 km(2) in the Galilee Mountains, northern Israel. GIS tools were used to produce corresponding maps of grazing regime, topographic indices and other relevant environmental factors. The effects of those factors were quantified using a multiple regression analyses. Major changes in the vegetation occurred during the period studied (1964-1992); tree cover increased from 2% in 1964 to 41% in 1992, while herbaceous vegetation cover decreased from 56% in 1964 to 24% in 1992. Grazing, topography and initial vegetation cover were found to significantly affect present vegetation patterns. Both cattle grazing and goat grazing reduced the rate of increase in tree cover, yet even intensive grazing did not halt the process. Grazing affected also the woody-herbaceous vegetation dynamics, reducing the expansion of woody vegetation. Slope, aspect, and the interaction term between these two factors, significantly affected vegetation pattern. Altogether, 56% and 72% of the variability in herbaceous and tree cover, respectively, was explained by the regression models. This study indicates that spatially explicit Mediterranean vegetation dynamics can be predicted with fair accuracy using few biologically important environmental variables.
Carson, M.A., Characteristics of High-Energy Meandering Rivers - the Canterbury Plains, New-Zealand, Geological Society of America Bulletin, 97 (7), 886-895, 1986.
Carson, M.A., and G.A. Griffiths, Gravel Transport in the Braided Waimakariri River - Mechanisms, Measurements and Predictions, Journal of Hydrology, 109 (3-4), 201-220, 1989.
Cenderelli, D.A., and E.E. Wohl, Peak discharge estimates of glacial-lake outburst floods and "normal" climatic floods in the Mount Everest region, Nepal, Geomorphology, 40 (1-2), 57-90, 2001.
Glacial-lake outburst floods (GLOFs) in the Mount Everest region of Nepal on 3 September 1977 and 4 August 1985 dramatically modified channels and valleys in the region by eroding, transporting, and depositing large quantities of sediment for tens of kilometers along their flood routes. Prior to this research, the GLOF discharges had not been determined and the hydrology of "normal" climatic floods (SHFFs: seasonal high flow floods) was not known. A one-dimensional step- backwater flow model was utilized, in conjunction with paleostage indicators, to estimate the peak discharges of the GLOFs and SHFFs and to reconstruct the hydrology and hydraulic conditions of the GLOFs at 10 reaches and SHFFs at 18 reaches. The most reliable GLOF and SHFF peak discharge estimates were upstream from constrictions where there was critical-depth control. The peak discharge of the 1977 GLOF at 8.6 km from the breached moraine was approximately 1900 m(3)/s. At 7.1 km downstream from the breached moraine, the 1985 GLOF discharge was estimated at 2350 m(3)/s. At 27 km downstream from the breached moraine, the 1985 GLOF attenuated to an estimated discharge of 1375 m(3)/s. The peak discharges of SHFFs ranged from 7 to 205 m(3)/s and were positively correlated with increasing drainage area. The GLOF discharges were 7 to 60 times greater than the SHFF discharges with the greatest ratios occurring near the breached moraines. The downstream decline in the ratio between the GLOF discharge and SHFF discharge is the result of the downstream attenuation of the GLOF and the increased discharge of the SHFF because of increased contributing drainage area and the increased effects of monsoonal precipitation at lower elevations. (C) 2001 Elsevier Science B.V. All rights reserved.
Chandler, T.J., and R.A. Kostaschuk, Test of Selected Bed-Material Load Transport Models - Nottawasaga River, Ontario, Canadian Journal of Civil Engineering, 21 (5), 770-777, 1994.
Chang, H.H., Selection of Gravel-Transport Formula For Stream Modeling, Journal of Hydraulic Engineering-Asce, 120 (5), 646-651, 1994.
A method for selecting a sediment-transport formula for mathematical modeling of a specific gravel stream is described and illustrated with an example. This method is based on the measured changes in stream morphology instead of site-specific gravel transport data. In the approach, several transport formulas are tested based on their applicabilities in simulating stream-channel changes. It is the working hypothesis that a sediment formula suitable for mathematical application should generate stream-channel changes that can be substantiated by measurements. For Stony Creek in California, the Meyer-Peter Muller, Yang, Parker, and Engelund-Hanson formulas were tested separately. Sediment deliveries obtained using the Yang and Parker formulas are more or less similar. Simulated erosional and depositional changes are also similar and compare favorably with the measurements. The Meyer-Peter Muller formula predicted lower transport rates while the Engelund-Hanson formula produced higher transport rates. On the basis of the tests. the Yang formula and Parker formula were selected for Stony Creek applications.
Chang, H.H., L.L. Harrison, W. Lee, and S. Tu, Numerical modeling for sediment-pass-through reservoirs, Journal of Hydraulic Engineering-Asce, 122 (7), 381-388, 1996.
Sediment accumulation in reservoirs on the North Fork Feather River will soon affect hydroelectric power generation. For sediment control, low-level outlets through the dams have been considered to allow Sediment-Pass-Through (SPT) the reservoirs. The objective of SPT is to maintain sediment balance through the reservoirs with no net erosion or deposition over an extended operating cycle. The velocity required for bed sediment to pass through a reservoir will be achieved by reservoir level drawdown during large floods. A numerical modeling study, using FLUVIAL-12, was made to evaluate the feasibility and effectiveness of SPT for the system. The study developed the following features: (1) rating curves that specify the reservoir drawdown in relation to the changing discharge; and (2) reservoir operation rules that specify the operational procedure and settings for control gates. Simulated results are presented to demonstrate that mass balance for the river/reservoir system can be achieved, without adverse siltation in the river channel to affect fish spawning. This approach for reservoir sediment control should be useful for similar problems.
Chanson, H., Comment on "Critical flow constrains flow hydraulics in mobile- bed streams: A new hypothesis" by G. E. Grant, Water Resources Research, 35 (3), 903-905, 1999.
Chanson, H., Boundary shear stress measurements in undular flows: Application to standing wave bed forms, Water Resources Research, 36 (10), 3063-3076, 2000.
Waters flowing in natural streams and rivers have the ability to scour and to deposit materials, hence to change the bed topography. It is recognized that undular flows have great potential for sediment transport. In the present study, a fixed-bed model was used to investigate the spatial Variations of boundary shear stress under standing waves (i.e., undular flow). The results (Figure 8) highlight the nonuniformity of the boundary shear stress distributions. Minimum boundary shear stress is observed under the wave crests, and maximum shear stress is observed under the wave troughs. The experimental findings suggest the formation of three-dimensional standing waves bed forms. Overall, the study highlights large variations of boundary shear stress in response to free-surface undulations.
Chartrand, S.M., and P.J. Whiting, Alluvial architecture in headwater streams with special emphasis on step-pool topography, Earth Surface Processes and Landforms, 25 (6), 583-600, 2000.
Alluvial mountain streams exhibit a range of channel forms: pool-riffle, plane bed, step-pool and cascades. Previous work suggested that these forms exist within discrete, and progressively steeper slope classes. Measurements conducted at over 100 sites in west-central and central Idaho confirm that slope steepens progressively as one moves from pool-riffle, to plane bed, to step-pool, and finally to cascades. Median slope for pool-riffle topography is 0.0060, for plane beds 0.013, for step-pools 0.044, and for cascades 0.068. There is substantial overlap in the slopes associated with these channel forms. Pool-riffle topography was found at slopes behween 0.0010 and 0.015, plane beds between 0.0010 and 0.035, step-pools between 0.015 and 0.134, and cascades between 0.050 and 0.12. Step- pools are particularly striking features in headwater streams. They are characterized by alternating steep and gentle channel segments. The steep segments (step risers) are transverse accumulations of boulder and cobbles, while the gentle segments (pools) contain finer material. Step wavelength is best correlated to step height which is in turn best correlated to the median particle size found on step risers. This result differs from past studies that have reported channel slope to be the dominant control on step wavelength. The presumed geometry and Froude number associated with the features under formative conditions are consistent with the existence field for antidunes and by extension with the hypothesis that step- pools are formed by antidunes. Copyright (C) 2000 John Wiley & Sons, Ltd.
Chau, K.T., Onset of natural terrain landslides modelled by linear stability analysis of creeping slopes with a two-state variable friction law, International Journal For Numerical and Analytical Methods in Geomechanics, 23 (15), 1835-1855, 1999.
This paper further examines the possibility of modelling landslide as a consequence of the unstable slip in a steadily creeping slope when it is subject to perturbations, such as those induced by rainfall and earthquakes. In particular, the one-state variable friction law used in the landslide analysis by Chau is extended to a two-state variable friction law. According to this state variable friction law, the shear strength (tau) along the slip surface depends on the creeping velocity (V) as well as the two state variables (theta(1) and theta(2)), which evolve with the ongoing slip. For translational slides, a system of three coupled non-linear first-order ordinary differential equations is formulated, and a linear stability analysis is applied to study the stability in the neighbourhood of the equilibrium solution of the system. By employing the stability classification of Reyn for three- dimensional space, it is found that equilibrium state (or critical point) of a slope may change from a 'stable spiral' to a 'saddle spiral with unstable plane focus' through a transitional state called 'converging vortex spiral' (i.e. bifurcation occurs), as the non-linear parameters of the slip surface evolve with its environmental changes (such as those induced by rainfall or human activities). If the one-state variable friction law is used in landslide modelling, velocity strengthening (i.e. d tau(ss)/dV > 0, where tau(ss) is the steady-state shear stress) in the laboratory always implies the stability of a creeping slope containing the same slip surface under gravitational pull. This conclusion, however, does not apply if a two-state variable friction law is employed to model the sliding along the slip surface. In particular, neither the region of stable creeping slopes in the non-linear parameter space can be inferred by that of velocity strengthening, nor the unstable region by that of velocity weakening. Copyright (C) 1999 John Wiley & Sons, Ltd.
Chen, C., and R.J. Wagenet, Simulation of Water and Chemicals in Macropore Soils .1. Representation of the Equivalent Macropore Influence and Its Effect On Soilwater Flow, Journal of Hydrology, 130 (1-4), 105-126, 1992.
Macropores are a relatively small proportion of the soil volume. but they play an important role in the movement of water and chemicals owing to occasional rapid fluxes through them. The occurrence of macropore flow does not depend on the water content (or potential) of the bulk matrix unless the soil is close to saturation, but depends instead principally upon surface boundary conditions. Accordingly, three control situations of infiltration are recognized: macropore control, application control, and matrix control. These three situations indicate that the two-domain system may be a proper approach for the simulation of macropore soil. In this conceptualization, macropores are defined as channeling pores of different radii in which the flux density (with unit hydraulic gradient) occurring in the minimum sizes of such pores is greater than or equal to the saturated matrix hydraulic conductivity. Recognizing the two structural domains of the macropore and matrix, and possible water flow situations, three flow regions are suggested: matrix, macropore, and transaction. The matrix and the macropore are the two domains, and the transaction represents the exchange of water between the matrix and the macropore. The classic approach of the Richards equation is applicable to describe the flow in the matrix domain. The Hagen-Poiseuille and the Chezy- Manning equations for tube flow can be applied to represent the relationship between the hydraulic conductivity of the macroporosity and the total macroporosity, where the total macroporosity is defined as the ratio of the summed macropore cross-sectional area and the total soil cross-sectional area. An equation describing water flow in the macropore domain is then obtained.
Cheng, N.S., and Y.M. Chiew, Pickup probability for sediment entrainment, Journal of Hydraulic Engineering-Asce, 124 (2), 232-235, 1998.
Cheng, N.S., and Y.M. Chiew, Incipient sediment motion with upward seepage, Journal of Hydraulic Research, 37 (5), 665-681, 1999.
Chew, L.C., and P.E. Ashmore, Channel adjustment and a test of rational regime theory in a proglacial braided stream, Geomorphology, 37 (1-2), 43-63, 2001.
Chiew, Y.M., Bed Features in Nonuniform Sediments, Journal of Hydraulic Engineering-Asce, 117 (1), 116-120, 1991.
Chin, A., Step Pools in Stream Channels, Progress in Physical Geography, 13 (3), 390-407, 1989.
Chin, A., On the stability of step-pool mountain streams, Journal of Geology, 106 (1), 59-69, 1998.
Although step-pools are generally considered to be stable bedforms, stability is not absolute, but depends on size, scale, and perspective. Hydraulic analysis of the stability of step-pool sequences in the Santa Monica Mountains, California, indicates that they are active channel features that are generally restructured within 5 to 100 years. The degree of mobility depends on step particle size. Steps are stable within small temporal and spatial scales, where they function as independent variables that dissipate stream energy and regulate channel hydraulics, but stability decreases at larger scales, where step pools become dependent variables that respond to discharge and sediment load. Hence the role of step-pools changes from energy dissipation to one of channel adjustment. These results underscore the need to consider larger spatial and temporal scales in order to reveal the complete function and significance of step-pools in mountain fluvial systems.
Chin, A., The morphologic structure of step-pools in mountain streams, Geomorphology, 27 (3-4), 191-204, 1999.
Step-pool sequences in streams in the Santa Monica Mountains of southern California impart a characteristic morphologic structure that varies with slope. But despite the strong association with slope that suggests a direct process control, analysis of 464 step-pools in 13 study reaches reveals the relationship to reflect correlation, but not necessarily causality. The direct control on step height is particle size, whereas discharge is the probable causal process determining step wavelength. Because both particle size and discharge generally change with channel slope downstream, a slope variation with step wavelength and height is the apparent indirect geometric result. A conceptual model of process-form linkages is proposed based on these results, whereby the step- pool morphology is produced by positive relationships between wavelength and discharge, and between height and particle size. The model offers new insights for explaining the step-pool morphology, and it is potentially useful in channeling future efforts toward the appropriate scales and variables. (C) 1999 Elsevier Science B.V. All rights reserved.
Chin, A., On the origin of step-pool sequences in mountain streams, Geophysical Research Letters, 26 (2), 231-234, 1999.
This paper reports a field test of the prevailing antidune theory to explain the mechanisms of step-pool formation in steep mountain streams. The theory is supported by laboratory data but it has not received extensile field testing that would enable wide applicability to natural conditions. Data from the Santa Monica Mountains of California are used to test the antidune model where step wavelength and reconstructed hydraulic conditions are compared with the formation domain predicted by experimental and theoretical studies. Results show general agreement between field and laboratory data. Step wavelength and hydraulic requirements are consistent with those of the antidune process' of formation, but results also suggest that true antidunes may be difficult to achieve in the steep headwaters where channels may be dominated by large roughness elements. These findings strengthen the link between theory and observation in clarifying how step-pools form; they contribute to the basis for elucidating why step-pools form in mountain streams.
Cho, K.J., J.H. Lee, J.J. Park, J.K. Kim, and K.B. Uhm, Analysis of spatial pattern of Frankliniella occidentalis (Thysanoptera : Thripidae) on greenhouse cucumbers using dispersion index and spatial autocorrelation, Applied Entomology and Zoology, 36 (1), 25-32, 2001.
Studies were conducted in two commercial cucumber greenhouses to examine thrips' seasonal and spatial patterns on Cheju Island, Korea, in 1996. Leaf and flower samples were taken to determine the thrips species and stage complexes inhabiting cucumber plants. Adult thrips (54-55%) were the most dominant stage on flowers and the majority of adult species was Frankliniella occidentalis (Pergande), whereas immature (82- 84%) was the dominant stage on leaves. To determine the spatial distribution patterns of thrips, at least 63 leaf samples which were regularly spaced within a greenhouse were visually inspected from among the Ist, the 7th and the 15th leaves assigned from the top plant canopy. The leaf positions were located at 1.8, 1.0 and 0.3 m above ground level, respectively. Taylor's power law indicated that the counts of thrips on leaves were aggregated regardless of thrips stage and leaf position. Autocorrelation analysis, which is based on the relative position of samples revealed the different spatial distribution patterns among the leaf positions. In general, the counts of thrips were nonrandomly distributed on the 7th leaf position, whereas the counts were randomly distributed on the ist and 15th leaf positions. Correlograms suggested the presence of single or multiple gradients within the sample portion of the greenhouse, depending on thrips stage. Our results suggest that Taylor's power law cannot detect the spatial relationship in data sets accurately, and testing correlograms for significance is more accurate for describing the spatial distribution patterns of thrips.
Choi, S.U., Layer-averaged modeling of two-dimensional turbidity currents with a dissipative-Galerkin finite element method - Part I: Formulation and application example, Journal of Hydraulic Research, 36 (3), 339-362, 1998.
Choi, S.U., Layer-averaged modeling of two-dimensional turbidity currents with a dissipative-Galerkin finite element method Part II: Sensitivity analysis and experimental verification, Journal of Hydraulic Research, 37 (2), 257-271, 1999.
Church, M., J.F. Wolcott, and W.K. Fletcher, A Test of Equal Mobility in Fluvial Sediment Transport - Behavior of the Sand Fraction, Water Resources Research, 27 (11), 2941-2951, 1991.
Church, M., M.A. Hassan, and J.F. Wolcott, Stabilizing self-organized structures in gravel-bed stream channels: Field and experimental observations, Water Resources Research, 34 (11), 3169-3179, 1998.
Stable reticulate structures, which we call "stone cells," have been observed in cobble-gravel channel beds with low bed material transport rates. Experiments show that such structures develop simultaneously with the armor layer during an extended period when flows do not exceed the Shields threshold by more than similar to 2 times, so that bed material transport is low. They are constructed by particles moving from less stable positions into more stable configurations against each other. Intermediate developments include clusters and stone lines. They reduce sediment transport by orders of magnitude and are evidently a major stability-promoting mechanism in gravel channels. The timescale for their development suggests that the boundaries of many gravel-bed channels are not in equilibrium with recent competent flows but reflect the history of recent "dominant" flows.
Ciampalini, R., and D. Torri, Detachment of soil particles by shallow flow: Sampling methodology and observations, Catena, 32 (1), 37-53, 1998.
Clague, J.J., and O. Slaymaker, Canadian geomorphology 2000 - Introduction, Geomorphology, 32 (3-4), 203-211, 2000.
Clark, J.J., and P.R. Wilcock, Effects of land-use change on channel morphology in northeastern Puerto Rico, Geological Society of America Bulletin, 112 (12), 1763-1777, 2000.
Between 1830 and 1950 much of northeastern Puerto Rico was cleared for agriculture. Runoff increased by similar to 50% and sediment supply to the river channels increased by more than an order of magnitude. Much of the land clearance extended to steep valley slopes, resulting in widespread gullying and landslides and a large load of coarse sediments delivered to the stream channels. A shift from agriculture to industrial and residential land uses over the past 50 yr has maintained the elevated runoff while sediment supply has decreased, allowing the rivers to begin removing coarse sediment stored within their channels. The size, abundance, and stratigraphic elevation of in-channel gravel bar deposits increases, channel depth decreases, and the frequency of overbank flooding in creases downstream along these channels. This is presumed to be a transient state and continued transport will lead to degradation of the bed in downstream sections as the channel adjusts to the modern supply of water and sediment. A downstream decrease in channel size is contrary to the expected geometry of self-adjusted channels, but is consistent with the presence of partially evacuated sediment remaining from the earlier agricultural period. Reverse (downstream decreasing) channel morphology is not often cited in the literature, although consistent observations are available from areas with similar land-use history. Identification of reverse channel morphology along individual watercourses may be obscured in multiwatershed compilations in which other factors produce a consistent, but scattered downstream trend. Identification of reverse channel morphology along individual streams in areas with similar land-use history would be useful for identifying channel disequilibrium and anticipating future channel adjustments.
Clifford, N.J., A. Robert, and K.S. Richards, Estimation of Flow Resistance in Gravel-Bedded Rivers - a Physical Explanation of the Multiplier of Roughness Length, Earth Surface Processes and Landforms, 17 (2), 111-126, 1992.
The need to estimate velocity and discharge indirectly in gravel-bedded rivers is a commonly-encountered problem. Semilogarithmic friction equations are used to estimate mean velocity using a friction factor obtained from depth and grain size information. Although such equations have a semi- theoretical basis, in natural gravel-bed channels, an empirical constant (6.8 or 3.5) has to be introduced to scale-up the characteristic grain size (D50 or D84) to represent the effective roughness length. In this paper, two contrasting approaches are used to suggest that the multiplier of characteristic grain size is attributable to the effect of small-scale form resistance, reflecting the occurrence of microtopographic bedforms in gravel-bedded environments. First, spatial elevation dependence in short, detailed bed profiles from a single gravel-bedded river is investigated using semivariogram and zero-crossing analyses. This leads to objective identification of two discrete scales of bed roughness, associated with grain and microtopographic roughness elements. Second, the autocorrelation structure of the three- dimensional near-bed velocity field is examined to identify regularities associated with eddy shedding and energy losses from larger grains and microtopographic bedforms. Apart from improving the capacity to determine friction factors for velocity and discharge estimation, the findings have implications in general for the initial motion of gravelly bed material.
Clifford, N.J., Differential Bed Sedimentology and the Maintenance of Riffle- Pool Sequences, Catena, 20 (5), 447-468, 1993.
Riffle-pools are the characteristic reach-scale bedforms of gravel- and mixed-bedded channels of low to moderate slope. The purpose of this paper is to clarify several aspects of the sedimentology of riffle-pool sequences, and to suggest how these both reflect and control riffle-pool stability in the presence of spatial differences in the turbulent near-bed flow field. High-frequency velocity measurements obtained using an array of electromagnetic current meters, are combined with results from grid and transect sampling of bed sediments from 9 sites on 3 small upland rivers in N. Ex-moor, U.K. Riffle sediments are shown to possess greater development of microtopographic structuring than adjacent pools, which enhances riffle stability, and which may reflect greater turbulent kinetic energy there over most of the flow range. Data on surface sediment arrangement and turbulent flow characteristics can be combined with different transport threshold equations to explain the maintenance of riffle-pool sequences with respect to a particle queuing ('kinematic wave') model, without recourse to a competence reversal, as conventionally assumed.
Clifford, N.J., Formation of Riffle Pool Sequences - Field Evidence For an Autogenetic Process, Sedimentary Geology, 85 (1-4), 39-51, 1993.
Riffle-pool sequences are the characteristic reach-scale bedforms of mixed- and gravel-bedded rivers. While most research has been directed to the quantitative description of these sequences and to their maintenance, comparatively little attention has been given to the processes responsible for their formation. In this paper, field results from quasi-continuous velocity records obtained with an array of electro-magnetic current meters are analysed with respect to a model of macro- scale structure in the turbulent velocity field of natural channels. This model has been suggested as the most plausible basis for riffle-pool formation. The results demonstrate the occurrence of a variety of coherent flow structures, some of which scale on channel dimensions as predicted by the model, but which also suggest that some revision of the association between flow structure and riffle-pool formation is necessary. It is suggested that riffle-pool units are initiated with the generation of roller eddies upstream and downstream from a major flow obstacle corresponding to engineering criteria for scour around bridge piers. The obstacle persists long enough to fix the flow pattern and hence account for significant modification of channel form, but is ultimately removed as part of the process of bed modification via the extension of scour. Three distinct stages in the process are involved: local scour of a single pool creates deposition downstream, which then generates the next-downstream flow irregularity. A riffle-pool sequence is thus created autogenetically as the summation of a sequence of irregularities, each unit of which is formed and maintained only by flow dynamics operating at the local scale. The process is essentially both deterministic and statistical in character. It is further suggested that spatial differences in the near-bed turbulence field arising from incipient riffle- pool topography themselves create differences in surface sediment entrainment which enhance and maintain the sequence in a form-process feedback mechanism. Similar reasoning might possibly be extended to the entire range of bedform sizes.
Clifford, N.J., Classics in physical geography revisited - Leopold,LB and Maddock,TM jr 1953: The hydraulic geometry of stream channels and some physiographic implications. USGS Professional Paper 252, Progress in Physical Geography, 20 (1), 81-87, 1996.
Clifford, N., Fluvial forms and processes: a new perspective, Area, 31 (3), 303-304, 1999.
Coco, G., D.A. Huntley, and T.J. O'Hare, Regularity and randomness in the formation of beach cusps, Marine Geology, 178 (1-4), 1-9, 2001.
Controversy still exists on whether rhythmic features such as beach cusps are the result of the presence of standing edge wave motions in the hydrodynamics or if they are the result of self-organising processes. The compatibility between the two mechanisms is here investigated through the use of a numerical model simulating the formation and development of beach cusps. Simulations characterised by different forcing conditions have been performed. A series of 'random' simulations, each individual run simply differing from the others in the seed used in the random number generator, showed the typical self- organisation behaviour with the features appearing at different locations and even with slightly different spacing. 'Regular' series of simulations have been run by changing the wavelength of the template superimposed by the hydrodynamic forcing and the number of cycles when the template was present. Results surprisingly indicate that even a minimum number of cycles with a regular forcing can deterministically induce the final shoreline configuration. Furthermore, if the forcing template has the same wavelength as the one resulting from purely random simulations, growth rates are much faster than those obtained with random conditions. Implications for the kind of field measurements necessary to discern which of the two mechanisms is responsible for beach cusp formation have also been considered. (C) 2001 Elsevier Science B.V. All rights reserved.
Cole, R.G., T.R. Healy, M.L. Wood, and D.M. Foster, Statistical analysis of spatial pattern: A comparison of grid and hierarchical sampling approaches, Environmental Monitoring and Assessment, 69 (1), 85-99, 2001.
Previous studies have combined random-site hierarchical sampling designs with analysis of variance techniques, and grid sampling with spatial autocorrelation analysis. We illustrate that analysis techniques and sampling designs are interchangeable using densities of an infaunal bivalve from a study in Poverty Bay, New Zealand. Hierarchical designs allow the estimation of variances associated with each level, but high-level factors are imprecisely estimated, and they are inefficient for describing spatial pattern. Grid designs are efficient for describing spatial pattern, and are amenable to conventional analysis. Our example deals with a continuous spatial habitat, but our conclusions also apply in disjunct or patchy habitats. The influence of errors in positioning is also assessed. The advantages of systematic sampling are reviewed, and more efficient hierarchical approaches are identified. The distinction between biological and statistical significance in all analyses is emphasised.
Coleman, S.E., and J.D. Fenton, Potential-flow instability theory and alluvial stream bed forms, Journal of Fluid Mechanics, 418, 101-117, 2000.
The present work constitutes a reassessment of the role of potential-flow analyses in describing alluvial-bed instability. To facilitate the analyses, a new potential-flow description of unsteady alluvial flow is presented, with arbitrary phase lags between local flow conditions and sediment transport permitted implicitly in the flow model Based on the present model, the explicit phase lag between local sediment transport rate and local flow conditions adopted for previous potential-flow models is shown to be an artificial measure that results in model predictions that are not consistent with observed flow system behaviour. Previous potential-flow models thus do not provide correct descriptions of alluvial flows, and the understanding of bed-wave mechanics inferred based upon these models needs to be reassessed. In contrast to previous potential-flow models, the present one, without the use of an explicit phase lag, predicts instability of flow systems of rippled or dune-covered equilibrium beds. Instability is shown to occur at finite growth rates for a range of wavelengths via a resonance mechanism occurring for surface waves and bed waves travelling at the same celerity. In addition, bed-wave speeds are predicted to decrease with increasing wavelength, and bed waves are predicted to grow and move at faster rates for flows of larger Froude numbers. All predictions of the present potential-flow model are consistent with observations of physical flow systems. Based on the predicted unstable wavelengths for a given alluvial flow, it is concluded that bed waves are not generated from plane bed conditions by any potential-flow instability mechanism. The predictions of instability are nevertheless consistent with instances of accelerated wave growth occurring for flow systems of larger finite developing waves. Potential-flow description of alluvial flows should, however, no longer form the basis of instability analyses describing bed-form (sand-wavelet) generation from flat bed conditions.
Collins, B.D., and G.R. Pess, Evaluation of forest practices prescriptions from Washington's watershed analysis program, Journal of the American Water Resources Association, 33 (5), 969-996, 1997.
In Washington's watershed analysis program, scientific analysts identify watershed areas that are sensitive to forest practices. Land managers then develop watershed-specific rules or ''prescriptions'' that condition forestry activities in those sensitive areas. Prescriptions are intended to provide greater protection than existing, or ''standard,'' roles where necessary to avoid cumulative effects on public aquatic resources (fish habitat and public works). To assess strengths and opportunities for improving Washington's watershed analysis, we evaluate prescriptions from 20 analyses conducted from 1993 to 1995. We ask: (1) Are prescriptions watershed specific, compared to the general, or ''standard'' forest practices rules? (2) Are prescriptions scientifically sound? (3) What promotes or limits development of watershed-specific and scientifically sound prescriptions? We find: (I) Prescriptions tend to be similar to standard rules. One reason is that some components of the scientific assessment methodology incorporate approaches or assumptions from the standard rules, some of which are untested or unsupported. Another reason is that while other assessment methods are not patterned after the standard rules, resulting prescriptions do not necessarily integrate assessment information. (2) Many prescriptions lack a scientific rationale and are unproved in meeting their stated objectives. Despite the experimental nature of many prescriptions, they generally lack an evaluation component. (3) Washington's watershed analysis can be strengthened by: testing assumptions of some scientific assessment methods; basing prescriptions more rigorously on scientific assessment data and published scientific literature; and addressing uncertainty in whether prescriptions meet their objectives.
Colombini, M., and G. Parker, Longitudinal streaks, Journal of Fluid Mechanics, 304, 161-183, 1995.
A commonly observed bedform in wide erodible-bed channels consists of rows of streaks or stripes parallel to the flow. These stripes can be manifested in terms of transverse variation of bed elevation, characteristic grain size (and thus roughness) or both. The former case is manifested most strongly in sediment with a nearly uniform size distribution and the latter most strongly in sediment with substantial heterogeneity in size. The amplitude of stripes is rarely larger than one or two grain diameters, and the transverse spacing is invariably of the order of the flow depth. They are closely linked to a pattern of paired cells of secondary flow in the flow cross- section. An existing theory of streak formation for the case of uniform sediment relies on a second-order turbulence closure which explicitly links the streamwise flow to transverse variations in bed elevation. The theory successfully predicts the formation of streaks, but only at rather high values of the Shields stress, i.e. rather strong sediment transport. Streaks are commonly observed, however, at Shields stresses as low as only slightly above the threshold of motion. In the present analysis the previous flow model is adapted to the case of transverse variation of roughness as well as elevation, and the constraint of uniform sediment is removed. The theory indicates that allowance for even slight heterogeneity of bed sediment results in the formation of streaks at any Shields stress above the threshold of motion. The resulting streaks are hybrid in the sense that they show transverse variation in both elevation and roughness. The model thus provides a general theory of streak formation.
Cookman, J.L., and P.B. Flemings, STORMSED1.0: hydrodynamics and sediment transport in a 2-D, steady-state, wind- and wave-driven coastal circulation model, Computers & Geosciences, 27 (6), 647-674, 2001.
Costa, J.E., Paleohydraulic Reconstruction of Flash-Flood Peaks From Boulder Deposits in the Colorado Front Range, Geological Society of America Bulletin, 94 (8), 986-1004, 1983.
Coulthard, T.J., M.J. Kirkby, and M.G. Macklin, Non-linearity and spatial resolution in a cellular automaton model of a small upland basin, Hydrology and Earth System Sciences, 2 (2-3), 257-264, 1998.
The continuing development of computational fluid dynamics is allowing the high resolution study of hydraulic and sediment transport processes but, due to computational complexities, these are rarely applied to areas larger than a reach. Existing approaches, based upon linked cross sections, can give a quasi two-dimensional view, effectively simulating sediment transport for a single river reach. However, a basin represents a whole discrete dynamic system within which channel, floodplain and slope processes operate over a wide range of space and time scales. Here, a cellular automaton (CA) approach has been used to overcome some of these difficulties, in which the landscape is represented as a series of fixed size cells. For every model iteration, each cell acts only in relation to the influence of its immediate neighbours in accordance with appropriate rules. The model presented here takes approximations of existing how and sediment transport equations, and integrates them, together with slope and floodplain approximations, within a cellular automaton framework. This method has been applied to the basin of Cam Gill Beck (4.2 km(2)) above Starbotton, upper Wharfedale, a tributary of the River Wharfe, North Yorkshire, UK. This approach provides, for the first time, a workable model of the whole basin at a 1 m resolution. Preliminary results show the evolution of bars, braids, terraces and alluvial fans which are similar to those observed in the field, and examples of large and small scale non-linear behaviour which may have considerable implications for future models.
Coulthard, T.J., M.J. Kirkby, and M.G. Macklin, Modelling geomorphic response to environmental change in an upland catchment, Hydrological Processes, 14 (11-12), 2031-2045, 2000.
Coulthard, T.J., and M.G. Macklin, How sensitive are river systems to climate and land-use changes? A model-based evaluation, Journal of Quaternary Science, 16 (4), 347-351, 2001.
Simulated Holocene sediment discharges from a high-resolution cellular model of river evolution in northern England, driven by a peat-bog proxy climate and palynological based land-cover record, show a very close similarity to alluviation phases evident in British river valleys. Independent validation of the model indicates that British river systems have been surprisingly sensitive to short term (ca. 10(2) yr) climate fluctuations, although river dynamics also have been modulated by land-use change and sediment supply. This has important implications for understanding alluvial system evolution, establishing controlling factors and, most importantly, forecasting river response to future climate and land-use changes. Copyright (C) 2001 John Wiley & Sons, Ltd.
Crave, A., and P. Davy, A stochastic "precipiton" model for simulating erosion/sedimentation dynamics, Computers & Geosciences, 27 (7), 815-827, 2001.
We present a stochastic modelling of erosion-sedimentation processes. based on cellular automata, which mimics the natural variability of climatic events with deterministic transport processes, The numerical procedure calculates the runoff water discharge as a function of the return period of elementary walking elements. This procedure generates water flux distributions at each point of the system, that depends on the local drainage area. and on the walker rainfall, and that are statistically analogous to natural river discharge distributions. It happens that a wide range of non-linear transport processes can be directly simulated in a intuitive way, relating the water flux and the local slope to the sediment transport activity. The present version of the code encompasses the main characteristics of erosion-sedimentation processes, from the simple hillslope diffusive law to the more complex nonlinear fluvial transport. To illustrate the versatility of the model to reproduce complex natural dynamics, we calculate several geomorphological instabilities which are crucial in relief dynamics. (C) 2001 Elsevier Science Ltd. All rights reserved.
Crews, S.G., and F.G. Ethridge, Laramide Tectonics and Humid Alluvial-Fan Sedimentation, Ne Uinta Uplift, Utah and Wyoming, Journal of Sedimentary Petrology, 63 (3), 420-436, 1993.
Laramide uplift and erosion of the Uinta Mountains are recorded in a 10-km-long outcrop of the Lower Eocene Wasatch Formation, on the Utah-Wyoming border. This 750-m-thick package of interbedded sandstones and conglomerates is dominated by a coarsening then fining-upward megasequence 650 m thick that records the growth and abandonment of a humid alluvial fan system during a major cycle of uplift and unroofing of the thrust-bounded northern flank of the Uinta mountains. Grain size, thickness, and lateral extent of channel-complex deposits increase upward in the lower 400 m of the sequence, reflecting construction and northward progradation of the fan. Grain size and channel-complex thickness decrease upward in the upper 250 m of the sequence, reflecting gradual reduction of both sediment yield and sediment caliber during postorogenic lowering of source-area relief. Within the megasequence, coarsening-up sequences 10-100 m thick built mainly of channel- complex deposits reflect progradation of fan lobes, punctuated by periodic fan-head avulsions. These medium-scale sequences in turn comprise small-scale fining-up cycles 1-10 m thick that reflect such fluvial processes on the fan as bar building, discrete flood events, and the filling and lateral migration of braided-stream channels. Both the medium-scale and small-scale sequences are commonly underlain by paleosols. Evidence of debris flows or other mass-movement processes is conspicuously lacking. Above the main megasequence a second, thinner megasequence containing lacustrine mudstones and wave-reworked conglomerates indicates that the fan persisted as a locus of coarse clastic deposition during the first of a series of lacustrine transgressions that began as ratios of sediment flux to subsidence rate decreased toward the end of the Early Eocene. Partial inundation of the fan during this transgression transformed it into a fan delta.
Croad, R.N., Analysis and Comparisons of Degradation Models - Discussion, Journal of Hydraulic Engineering-Asce, 113 (11), 1471-1474, 1987.
Cui, Y.T., G. Parker, and C. Paola, Numerical simulation of aggradation and downstream fining, Journal of Hydraulic Research, 34 (2), 185-204, 1996.
Cui, Y.T., and G. Parker, The arrested gravel front: stable gravel-sand transitions in rivers - Part 2: General numerical solution, Journal of Hydraulic Research, 36 (2), 159-182, 1998.
Cushing, C.E., G.W. Minshall, and J.D. Newbold, Transport Dynamics of Fine Particulate Organic-Matter in 2 Idaho Streams, Limnology and Oceanography, 38 (6), 1101-1115, 1993.
D'Agostino, V., and M.A. Lenzi, Bedload transport in the instrumented catchment of the Rio Cordon Part II: Analysis of the bedload rate, Catena, 36 (3), 191-204, 1999.
Sediment transport is monitored by a specially designed instrumentation installed on a steep mountain streams (the Rio Cordon). The variability of bedload rate and yield reflects the variability in flow discharge. Bedload and flow data for 'ordinary' (low peak flow floods) and 'exceptional' sediment transport events are used to test the range of application of the bedload equations proposed for high gradient streams. Such equations overestimate bedload rate for ordinary events while their reliability increases when used to predict high bedload transport rates like those recorded during the exceptional flood that affected Rio Cordon on September 14, 1994. The best agreement between computed and measured values of cumulated bedload volumes is found by using the Bagnold [Bagnold, R.A., 1956. The flow of cohesionless grains in fluids. Philos. Trans. R. Sec. London 249A, 235-297.], Smart and Jaeggi [Smart, J.M., Jaeggi, M.N.R., 1983. Sediment transport on steep slopes. Mitteil. 64, Versuchsanstalt fur Wasserbau, Hydrologie und Glaziologie, ETH-Zurich, Switzerland, 191 pp.] and Rickenmann [Rickenmann, D., 1991. Hyperconcentrated flow and sediment transport at steep slopes. J. Hydraul. Eng., Zurig 117 (11) 1419-1439.] formulas. The Schoklitsch equation [Schoklitsch, A., 1962. Handbuch des Wasserbaues, 3rd edn. Springer, Wien.] also provides good estimations for instantaneous bedload rates at high-sediment transport intensity and unlimited sediment supply conditions. The formal type of the last equation is still valid and can be calibrated for low intensity bedload rates. (C) 1999 Elsevier Science B.V. All rights reserved.
D'Andrea, R., Hydraulic conductivity of soils from grain-size distribution: New models - Discussion, Journal of Geotechnical and Geoenvironmental Engineering, 127 (10), 899-899, 2001.
Dabney, S.M., L.D. Meyer, W.C. Harmon, C.V. Alonso, and G.R. Foster, Depositional patterns of sediment trapped by grass hedges, Transactions of the Asae, 38 (6), 1719-1729, 1995.
Dade, W.B., and P.F. Friend, Grain-size, sediment-transport regime, and channel slope in alluvial rivers, Journal of Geology, 106 (6), 661-675, 1998.
Dade, W.B., Grain size, sediment transport and alluvial channel pattern, Geomorphology, 35 (1-2), 119-126, 2000.
Dalby, C.E., "Assessing stream channel stability thresholds using flow competence estimates at bankfull stage," by D. S. Olsen, A. C. Whitaker, and D. F. Potts - Discussion, Journal of the American Water Resources Association, 35 (1), 185-186, 1999.
Danehy, R.J., N.H. Ringler, and R.J. Ruby, Hydraulic and geomorphic influence on macroinvertebrate distribution in the headwaters of a small watershed, Journal of Freshwater Ecology, 14 (1), 79-91, 1999.
Spatial variability of aquatic macroinvertebrates was examined in riffles of second to fourth order streams in Onondaga Creek, in central New York, USA. Even with only small differences in stream sizes, aquatic macroinvertebrates were distributed primarily by a headwater-to-valley gradient as defined by mean stream width and water surface slope. Secondary and tertiary gradients were based on hydraulic character. Direct gradient analysis using canonical correspondence analysis (CCA) examined the common and rare (respectively, < 5 - 0.5% and 0.5 - 0.001% of total) macroinvertebrate assemblage among sites. The variables used in the analysis were mean wetted width, water surface slope, mean Froude number and Froude number variance. The first CCA axis explained 43.1% of the variability. Froude number variance and Froude number affected the second and third CCA axes most strongly. The gradients revealed by the second and third CCA axes did not influence lower gradient valley sites, but did separate the headwater sites based on hydraulic character. Taxa were also distributed by functional feeding groups (i.e., collector-gatherer). The headwater-to-valley gradient did separate taxa slightly by functional feeding groups; however, the hydraulic gradient clearly separated scrapers and shredders from collector filterers.
Darby, S.E., and C.R. Thorne, Modelling the sensitivity of channel adjustments in destabilized sand-bed rivers, Earth Surface Processes and Landforms, 21 (12), 1109-1125, 1996.
Darby, S.E., and C.R. Thorne, Numerical simulation of widening and bed deformation of straight sand-bed rivers .1. Model development, Journal of Hydraulic Engineering-Asce, 122 (4), 184-193, 1996.
Darby, S.E., Modelling width adjustment in straight alluvial channels, Hydrological Processes, 12 (8), 1299-1321, 1998.
Darby, S.E., Effect of riparian vegetation on flow resistance and flood potential, Journal of Hydraulic Engineering-Asce, 125 (5), 443-454, 1999.
Darby, S.E., and C.R. Thorne, A river runs through it: morphological and landowner sensitivities along the Upper Missouri River, Montana, USA, Transactions of the Institute of British Geographers, 25 (1), 91-107, 2000.
Landowners along the Missouri River in Montana believe that the operation of Fort Peck Dam has initiated bank erosion, thus threatening agricultural development within the region. Their concerns have been heightened by proposals to increase discharge in order to enhance fisheries and wildlife interests. Geomorphological evaluation indicates that bed degradation and bank erosion have declined since construction of the dam, and the channel is now approaching dynamic equilibrium; public sensitivity to the proposed change is greater than the morphological sensitivity of the river. Sustainable management of the Missouri is now based on strategies that place more emphasis on partnership with local citizens.
Darnell, S.J., L.T. Meinke, L.J. Young, and C.A. Gotway, Geostatistical investigation of the small-scale spatial variation of western corn rootworm (Coleoptera : Chrysomelidae) adults, Environmental Entomology, 28 (2), 266-274, 1999.
Field studies were conducted in 1994 and 1995 to characterize the spatial distribution of western corn rootworm, Diabrotica virgifera virgifera LeConte, adults in field corn using whole- plant counts as the sampling tool. Geostatistical methods were used to determine the small-scale spatial, relationships of adults within fields during different corn phenology periods and as beetle population densities changed. Because the focus was on small-scale spatial variation, trend surface regression methods were used to remove large-scale variation. Geostatistical analysis of whole-plant count data indicated that no small-scale spatial correlation was present among samples taken > 5.3 m apart in 5 of 55 semivariograms that were plotted. The 3 significant small-scale spatial relationships occurred around peak pollination periods, and during this time, samples were spatially dependent at distances of <30-40 m apart. Nc small-scale spatial correlation was detected during other growth stages. The small-scale spatial patterns detected also appeared to be independent of beetle density within the range of densities (0.1-5.0 beetles per plant) that were sampled. Data suggest that beetle spatial patterns can be affected by changes in crop phenology. Contrasts in corn phenology within and among fields should be considered when developing sampling programs based on visual beetle counts.
Dauble, D.D., and D.R. Geist, Comparison of mainstem spawning habitats for two populations of fall chinook salmon in the Columbia River basin, Regulated Rivers-Research & Management, 16 (4), 345-361, 2000.
Extensive hydroelectric development in the Columbia River system has eliminated most mainstem riverine habitat available for spawning by fall chinook salmon (Oncorhynchus tshawytscha). The two remaining populations, Hanford Reach, Columbia River and Hells Canyon Reach, Snake River, are separated geographically and their status is markedly different. Annual escapements to Hanford Reach have averaged approximately 80000 adults, while the Snake River run size has declined to < 1500 adults over the past 10 years. We compared their spawning habitat characteristics over a range of measurement scales, as a means to identify strategies for rebuilding the weak Snake River population. Physical habitat characteristics of redds were similar for both study areas. Redd locations were correlated with channel characteristics, such as braiding and sinuosity. Several differences between the two spawning areas were identified at the watershed scale: the Hells Canyon Reach had a much steeper longitudinal gradient, was largely confined by bedrock, and had a more variable flow regime. These features are controlling variables that operate at the reach-scale to limit the availability and size of substrate and other conditions that influence egg deposition and incubation survival. Geomorphological characteristics of the two study sites are sufficiently different to indicate that the production potential of the Hells Canyon Reach population is markedly lower than that of the Hanford Reach population. Copyright (C) 2000 John Wiley & Sons, Ltd.
Dawdy, D.R., and V.A. Vanoni, Modeling Alluvial Channels, Water Resources Research, 22 (9), S71-S81, 1986.
Day, S.J., and W.K. Fletcher, Concentration of Magnetite and Gold At Bar and Reach Scales in a Gravel-Bed Stream, British-Columbia, Canada, Journal of Sedimentary Petrology, 61 (6), 871-882, 1991.
de Blois, S., G. Domon, and A. Bouchard, Environmental, historical, and contextual determinants of vegetation cover: a landscape perspective, Landscape Ecology, 16 (5), 421-436, 2001.
We formulated and tested models of relationships among determinants of vegetation cover in two agroforested landscapes of eastern North America (Haut Saint-Laurent, Quebec, Canada) that differed by the spatial arrangement of their geomorphic features and intensity of agricultural activities. Our landscape model compared the woody plots of each landscape in terms of the relative influence of environmental attributes, land use history (1958 - 1997), and spatial context (i.e., proximity of similar or contrasting land cover). Our vegetation model evaluated the relative contribution of the same sets of variables to the distributions of herbs, trees, and shrubs. Relationships were assessed using partial Mantel tests and path analyses. Significant environmental and contextual differences were found between the vegetation plots of the two landscapes, but disturbance history was similar. Our vegetation model confirms the dominant effect of historical factors on vegetation patterns. Whereas land-use history overrides environmental and contextual control for trees, herbaceous and shrub species are more sensitive to environmental conditions. Context is determinant only for understory species in older, less-disturbed plots. Results are discussed in relevance to vegetation dynamics in a landscape perspective that integrates interactions between environmental and human influences.
de Scally, F., O. Slaymaker, and I. Owens, Morphometric controls and basin response in the Cascade Mountains, Geografiska Annaler Series a-Physical Geography, 83A (3), 117-130, 2001.
Densmore, A.L., M.A. Ellis, and R.S. Anderson, Landsliding and the evolution of normal-fault-bounded mountains, Journal of Geophysical Research-Solid Earth, 103 (B7), 15203-15219, 1998.
Much of the tectonic and climatic history in high-relief regions, such as the mountains of the western U.S. Basin and Range province, is contained in the morphology of hillslopes, drainage networks, and other landforms that range in scale from 10(-1) to 10(1) km. To understand how these landforms evolve, we have developed a numerical landscape evolution model that combines a detailed tectonic displacement field with a set of physically based geomorphic rules. Bedrock landsliding, long recognized as a significant geomorphic process in mountainous topography, is for the first time explicitly included in the rule set. In a series of numerical experiments, we generate synthetic landscapes that closely resemble mountainous topography observed in the Basin and Range. The production of realistic landscapes depends critically on the presence of bedrock landslides, and landsliding yields rates of long-term erosion that are comparable in magnitude to those of fluvial erosion. The erosive efficiency of bedrock landsliding implies that hillslopes may respond very quickly to changes in local base lever and that fluvial erosion is the rate-limiting process in steady state experimental landscapes. Our experiments generate power law distributions of landslide sizes, somewhat similar to both field and laboratory observations. Thus even a simple model of bedrock landsliding is capable of quantitatively reproducing mountainous topography and landslide distributions and represents a significant step forward in our understanding of the evolution of normal-fault- bounded ranges.
DeVries, P., and D.J. Goold, Leveling rod base required for surveying gravel river bed surface elevations, Water Resources Research, 35 (9), 2877-2879, 1999.
Consistent surveying of bed elevations in natural channels containing gravel and cobble substrates is subject to measurement error if a leveling rod is placed indiscriminately between or on top of individual particles. The influence of surface microtopography decreases with increasing leveling rod base diameter, while the influence of bed form topography increases. Field tests were performed to identify a rod base diameter that minimizes these survey errors. A leveling rod base diameter of 127 mm (5 inches) is suggested to be most appropriate for consistent bed surveys.
Dey, S., Chebyshev solution as aid in computing GVF by standard step method, Journal of Irrigation and Drainage Engineering-Asce, 126 (4), 271-274, 2000.
The standard step method is commonly used to compute free surface profiles in gradually varied flow (GVF) through open channels. In this study, generalized numerical solutions in the Chebyshev form are presented for the standard step method to compute the free surface profiles in GVF without using look-up tables, interpolation procedures, or simplified assumptions concerning the cross-section geometry. The solutions are obtained using the flow resistance equations of Manning, Chezy, and Colebrook-White. The necessary parameters of some particular cases, namely rectangular, triangular, trapezoidal, circular, and exponential channels, are furnished. The use of the Chebyshev approximation has the advantage of requiring less iteration than the Newton-Raphson approximation.
Dey, S., Bank profile of threshold channels: A simplified approach, Journal of Irrigation and Drainage Engineering-Asce, 127 (3), 184-187, 2001.
Dinehart, R.L., Dune Migration in a Steep, Coarse-Bedded Stream, Water Resources Research, 25 (5), 911-923, 1989.
Dinehart, R.L., Evolution of Coarse Gravel Bed Forms - Field-Measurements At Flood Stage, Water Resources Research, 28 (10), 2667-2689, 1992.
Field measurements to investigate the origin and growth of mesoscale gravel bed forms in deep flows were made in the North Fork Toutle River, Washington. Sonar observations of the gravel streambed at a stationary point were recorded during two storm flows in December 1989 and January 1990 with concurrent bed load sampling and continuous velocity measurements. Mean diameter of bed load was about 3 cm, flow depths were 1.4-2.4 m, and bed shear stresses were 2-5 times the critical stress of mean bed load diameter, as computed from the depth-slope product. These records document the hydrodynamic conditions under which dunelike coarse gravel bed forms were observed. Coarse gravel dunes (height, 20 cm; length, 6-15 m) evolved more than 24 hours after peak stage, primarily by accretion, as inferred from bed form changes revealed in dual sonar records. Dune heights increased to 40 cm as mean trough elevation rose about 50 cm over several hours. Smaller dunes (wavelength, 1-3 m), transitional from bed load sheets, migrated on the backs of the large dunes. The superposed dunes finally became indistinguishable from the large dunes, which diminished in height by increasing the mean level of troughs. Gravel deposition occurred at the observation point in conjunction with migration of gravel dunes. The direct comparison of known bed form regimes and gravel bar facies provides alternative interpretations of gravelly deposits.
Dingman, S.L., and K.P. Sharma, Statistical development and validation of discharge equations for natural channels, Journal of Hydrology, 199 (1-2), 13-35, 1997.
Although the Manning equation is widely accepted as the empirical flow law for rough turbulent open-channel flow, using the equation in practical situations such as slope-area computations is fraught with uncertainty because of the difficulty in specifying the value of the reach resistance, Manning's n. Riggs (1976, J. Res. US Geol. Surv., 4: 285-291) found that n was correlated with water-surface slope, and proposed a multiple-regression equation that obviates the need for estimating n in slope-area estimates of discharge, Because his relation was developed from a relatively small sample (N = 62), had potential flaws owing to multicollinearity, and was not thoroughly validated, we used an expanded data base (N = 520) and objective methods to develop a new relation for the same purpose: Q=1.564A(1.173)R(0.400)S(-0.0543logS) when Q is discharge (m(3) s(-1)), A is cross-sectional area (m(2)), R is hydraulic radius (m), and S is water-surface slope, We validated Riggs's model and our model using 100 measurements not included in model development and found that both give similar results. Riggs's model is somewhat better in terms of actual (m(3) s(-1)) error, but ours is better in terms of relative (log Q) error. We conclude that either Riggs's or our model can be used in place of Manning's equation in slope-area computations, but that our model is preferable because it has less bias, minimizes multicollinearity, and performs better when applied to discharge changes in individual reaches, We also found that our model performs better than those of Jarrett (1984, J. Hydraul. Eng., 110: 1519-1539) or Riggs in the range of applicability of Jarrett's equation (0.15 m less than or equal to R less than or equal to 2.13 m; 0.002 less than or equal to S less than or equal to 0.052), Both Riggs' s and our models significantly overestimate Q in flows satisfying both of the following conditions: e < 3 m(3) s(-1) and Froude number less than 0.2. For other in-bank Bows in relatively straight reaches, our model can be recommended for use in slope-area computations and other applications of the Chezy or Manning equations over a wide range of channel sizes (0.41 m(2) less than or equal to A less than or equal to 8520 m(2)) and slopes (0.00001 less than or equal to S less than or equal to 0.0418), thus obviating the difficulty of a priori determination of the resistance factor.
Diplas, P., and J.B. Fripp, Properties of Various Sediment Sampling Procedures, Journal of Hydraulic Engineering-Asce, 118 (7), 955-970, 1992.
Several issues regarding the sampling and analysis of bed material from gravel bed streams are addressed in this paper. The need to convert surface samples into volumetric equivalents, and methods to do so, are explained. It is found that most surface samples are unique and, thus, are not directly comparable. Particular attention is paid to areal sampling with clay and with wax. The areal-to-volumetric conversion of samples removed from different sediment structures is also considered. Criteria are proposed for determining the minimum dimensions of unbiased volumetric samples. These criteria can be used to determine the minimum area of an areal sample. The minimum depth of a volumetric sample is shown to be larger than the depth of most surface layers. Thus, a surface layer can not be sampled volumetrically. A technique is presented for sampling a wide size range of underwater surface particles. This technique has been tested in the field and found to provide good results.
Diplas, P., Modeling of Fine and Coarse Sediment Interaction Over Alternate Bars, Journal of Hydrology, 159 (1-4), 335-351, 1994.
Diplas, P., and V.K. Lohani, "Application of the pebble count: Notes on purpose, method, and Variants," by G. Mathias Kondolf - Discussion, Journal of the American Water Resources Association, 33 (6), 1397-1399, 1997.
Dollar, E.S.J., Fluvial geomorphology, Progress in Physical Geography, 24 (3), 385-406, 2000.
Doyle, M.W., J.M. Harbor, C.F. Rich, and A. Spacie, Examining the effects of urbanization on streams using indicators of geomorphic stability, Physical Geography, 21 (2), 155-181, 2000.
Duck, R.W., and J. McManus, A Long-Term Estimate of Bedload and Suspended Sediment Yield Derived From Reservoir Deposits, Journal of Hydrology, 159 (1-4), 365-373, 1994.
Duckson, D.W., and L.J. Duckson, Morphology of Bedrock Step Pool Systems, Water Resources Bulletin, 31 (1), 43-51, 1995.
One-hundred-and-sixty step pools were examined that have developed in andesitic, basaltic, or dacitic lavas or in glacio-fluvial sediments along several reaches of Soda Creek in the Three Sisters Wilderness of the Oregon High Cascades to determine whether such systems exhibit similar morphology. Pool shapes, sizes, and spacing were measured, and the hydraulic head loss calculated for each pool surface. Lithologic variations among 15 shape categories were not significant, but size attributes - length, depth, and area - of pools were systematically different by rock type. The energy lost at hydraulic jumps did not differ significantly among the four lithologies, suggesting that perhaps step pools represent similar stream channel adjustments in steep terrain.
Duckson, D.W., and L.J. Duckson, Channel bed steps and pool shapes along Soda Creek, Three Sisters Wilderness, Oregon, Geomorphology, 38 (3-4), 267-279, 2001.
Field study of bedrock step-pool systems along the upper reaches of Soda Creek in the Three Sisters Wilderness of Oregon shows strong correlation between several form variables (shape) and channel slope. Although step height and step length showed no regular spacing and variable correlation with channel slope, length to height ratios demonstrated strong negative correlations: steep slopes (20% to 80%) featured greater step height and shorter pool lengths than did flatter channel slopes. Correlations between step height to length ratios and channel slope varied between three lithologies. Explained variations ranged from 0.984 for the oldest channel steps developed in basalt, to 0.982 for steps of intermediate age developed in andesite, to 0.964 fur the youngest steps developed in dacite. Sample size was 57, 40, and 33, respectively. The frequency of pool shape classes did not vary by lithology, but specific shape classes developed under differing slope conditions by rock type. All pool classes have adjusted (developed) their form to maximize resistance to flow H/L/S, and they have done so in remarkably uniform fashion. (C) 2001 Elsevier Science B.V. All rights reserved.
Dunkerley, D.L., Bulk Sampling of Coarse Clastic Sediments For Particle-Size Analysis - Discussion, Earth Surface Processes and Landforms, 19 (3), 255-261, 1994.
Dunkerley, D.L., Stone cover on desert hillslopes: Extent of bias in diameters estimated from grid samples and procedures for bias correction, Earth Surface Processes and Landforms, 21 (6), 573-580, 1996.
Dunkerley, D., and K. Brown, Flow behaviour, suspended sediment transport and transmission losses in a small (sub-bank-full) flow event in an Australian desert stream, Hydrological Processes, 13 (11), 1577-1588, 1999.
Durand, J.D., B. Guinand, and Y. Bouvet, Local and global multivariate analysis of geographical mitochondrial DNA variation in Leuciscus cephalus L-1758 (Pisces : Cyprinidae) in the Balkan Peninsula, Biological Journal of the Linnean Society, 67 (1), 19-42, 1999.
Geographical variation of cytochrome b mitochondrial DNA (mtDNA) in chub (Leuciscus cephalus L.) was analysed in 31 samples from 20 different river basins in the Balkan Peninsula and Danube catchment. Multivariate methods of ordination were used to analyse variation of the data sets. The results were interpreted in the context of the proposed ichthyogeographic districts separating the Balkan Peninsula into two main ichthyogeographic divisions (Eastern Greece/Ponto-Aegean and Western Greece/South Adriatic-Tonian). Boundary detection supported these two ichthyogeographic districts for L. cephalus, revealing a boundary that ran from north to south through the Balkan Peninsula and the middle of Greece. The results also revealed the existence of a third division in Central Greece. The results of ordination techniques on homogeneous zones and analysis of the molecular variance confirmed the results obtained in studying local variability (boundaries). They also allowed us to test the existence of possible subdivisions proposed by different authors inside the two main ichthyogeographic districts. These subdivisions were not supported. The multivariate methods used in this study allowed us to propose a coherent picture of chub ichthyogeographic districts in terms of boundary detection and maximal autocorrelation between populations and to explain the patterns of chub mtDNA variation. A complete interpretation of results concerning L. cephalus requires careful consideration of both boundary analysis and autocorrelative approach. Results from an the autocorrelative approach alone could lead to substantial misinterpretations. (C) 1999 The Linnean Society of London.
Easa, S.M., Probabilistic Design of Open Drainage Channels, Journal of Irrigation and Drainage Engineering-Asce, 118 (6), 868-881, 1992.
A method for designing open drainage channels that incorporates the uncertainty associated with various design variables is presented. The design involves two random components: runoff (demand) and channel capacity (supply). The runoff Is formulated conSidering the uncertainties of rainfall intensity, drainage area, and other watershed characteristics. The channel capacity is formulated considering the uncertainties of channel friction factor, longitudinal slope, channel width, side slope, and water-flow depth. The probabilistic characteristics of the runoff and channel capacity are established based on the first-order principle of probability theory. A reliability index that can he used to design an open channel to convey runoff for a given probability of failure is developed. This probabilistic approach Should be valuable in the design of open drainage channels whose runoff and capacity variables are generally uncertain.
Eaton, B.C., and M.F. Lapointe, Effects of large floods on sediment transport and reach morphology in the cobble-bed Sainte Marguerite River, Geomorphology, 40 (3-4), 291-309, 2001.
Sediment transport rates were estimated for two flood events on the cobble-bed Sainte Marguerite River in the Saguenay region, Canada. Morphologic methods were used to derive one set of estimates, and a combination of the Meyer-Peter and Muller equation with a dimensionless sediment transport ratio (after Dietrich et al. [Nature 340 (1989) 215]) was used to derive another set of estimates. Both sets of estimates give consistent results for the first event (which had a decade- scale return period), and for the second event (which was the largest flood on record and had a century-scale return period). The transport occurring during the second event was an order of magnitude greater than that occurring during the first event: despite this disparity in the transport intensity of the two events, the channel morphology remained qualitatively similar. The observed degree of channel stability is attributed to a change of channel pattern and the initiation of bed degradation following channel rectification in the 1960s. (C) 2001 Elsevier Science B.V. All rights reserved.
Ebisemiju, F.S., The Sinuosity of Alluvial River Channels in the Seasonally Wet Tropical Environment - Case-Study of River Elemi, Southwestern Nigeria, Catena, 21 (1), 13-25, 1994.
Einsele, G., and M. Hinderer, Terrestrial sediment yield and the lifetimes of reservoirs, lakes, and larger basins, Geologische Rundschau, 86 (2), 288-310, 1997.
Elliott, J.G., and R.S. Parker, Altered streamflow and sediment entrainment in the Gunnison gorge, Journal of the American Water Resources Association, 33 (5), 1041-1054, 1997.
Elliott, J.G., and L.A. Hammack, Entrainment of riparian gravel and cobbles in an alluvial reach of a regulated Canyon river, Regulated Rivers-Research & Management, 16 (1), 37-50, 2000.
Ellis, J., and W. Mualla, Wave Action in Pumping Station Storm Overflow, Journal of Hydraulic Engineering-Asce, 113 (3), 342-369, 1987.
Erskine, W.D., P.M. Geary, and D.N. Outhet, Potential Impacts of Sand and Gravel Extraction On the Hunter River, New-South-Wales, Australian Geographical Studies, 23 (1), 71-86, 1985.
Erskine, W.D., Response and recovery of a sand-bed stream to a catastrophic flood, Zeitschrift Fur Geomorphologie, 40 (3), 359-383, 1996.
Between 17 and 18 June 1949 up to 508 mm of rainfall occurred over the 2000 km(2) Wollombi Brook drainage basin in south- eastern Australia. The resultant flood peak was almost 27 times greater than the mean annual flood but had a return period of only 87 years on the annual maximum series. Wollombi Brook is characterised by one of the steepest annual series flood frequency curves in the World and this results in relatively low return periods for large events. Furthermore, the catastrophic flood was followed by a series of large events over the succeeding 5 years. River response to the flood varied in direct proportion to the degree of lateral confinement by materials of limited erodibility. At the storm centre on the upper reaches of the river, the channel is unconfined and did not respond to the flood. In the middle reaches, the channel is closely confined by bedrock and responded to the flood by widening up to 100% and by up to 4m of bed aggradation. In the lower reaches, the channel is partially confined by bedrock and terrace sediments and responded in the same way but to a slightly lesser degree than the middle reaches. Since the late 1950s partial channel recovery has occurred by bed degradation excavating the flood-deposited sand and by in-channel bench formation contracting the channel. Nevertheless, the recovery time is likely to be greater than the return period of the 1949 flood. Therefore, the channel is likely to be unstable in the long term because the frequency of perturbing events is greater than the channel recovery time.
Ettema, R., F. Braileanu, and M. Muste, Method for estimating sediment transport in ice-covered channels, Journal of Cold Regions Engineering, 14 (3), 130-144, 2000.
Falconer, R.A., and P.H. Owens, Numerical Modeling of Suspended Sediment Fluxes in Estuarine Waters, Estuarine Coastal and Shelf Science, 31 (6), 745-762, 1990.
Fan, X.S., and J. Masliyah, Laboratory Investigation of Beach Profiles in Tailings Disposal, Journal of Hydraulic Engineering-Asce, 116 (11), 1357-1373, 1990.
Felton, E.A., K.A.W. Crook, and B.H. Keating, The Hulopoe Gravel, Lanai, Hawaii: New sedimentological data and their bearing on the "giant wave" (mega-tsunami) emplacement hypothesis, Pure and Applied Geophysics, 157 (6-8), 1257-1284, 2000.
Recognition that many oceanic islands are shaped by giant landslides has highlighted claims that the Hulopoe Gravel on south Lanai, Hawaii, was deposited by giant waves (mega- tsunami) generated by such a landslide. This interpretation is controversial. Resolution of the controversy has global implications because mass wasting of oceanic islands has been a common process for as long as hot spot volcanism has affected the ocean basins. Thus, if mega-tsunami are attendant upon the mass wasting process, their effect on earth surface processes should be discernible for much of geological time and may be comparable to that resulting from bolide impacts that form astroblemes. Detailed facies analysis of the pebble, cobble and boulder gravels that form the Hulopoe Gravel type section shows that the gravels are composed predominantly of basalt clasts with appreciable amounts of limestone clasts in 8 of the 14 beds present. Deposition was not continuous: eight disconformities are recognized in the 9.2 m type section, three of which are associated with truncated paleosols. The Hulopoe Gravel was not deposited by a single tsunami at 105 ka, as has been proposed. One bed is clearly an alluvial deposit. The origins of others are unclear but the facies data do not exclude tsunami as one of the processes that deposited individual beds within the Hulopoe Gravel, either above or below sea level.
Ferguson, R.I., Hydraulics and Hydraulic Geometry, Progress in Physical Geography, 10 (1), 1-31, 1986.
Ferguson, R.I., K.L. Prestegaard, and P.J. Ashworth, Influence of Sand On Hydraulics and Gravel Transport in a Braided Gravel Bed River, Water Resources Research, 25 (4), 635-643, 1989.
Ferguson, R., and P. Ashworth, Slope-Induced Changes in Channel Character Along a Gravel-Bed Stream - the Allt Dubhaig, Scotland, Earth Surface Processes and Landforms, 16 (1), 65-82, 1991.
Ferguson, R.I., P.E. Ashmore, P.J. Ashworth, C. Paola, and K.L. Prestegaard, Measurements in a Braided River Chute and Lobe .1. Flow Pattern, Sediment Transport, and Channel Change, Water Resources Research, 28 (7), 1877-1886, 1992.
Ferguson, R.I., Critical Discharge For Entrainment of Poorly Sorted Gravel, Earth Surface Processes and Landforms, 19 (2), 179-186, 1994.
Ferguson, R., T. Hoey, S. Wathen, and A. Werritty, Field evidence for rapid downstream fining of river gravels through selective transport, Geology, 24 (2), 179-182, 1996.
Ferguson, R.I., and C. Paola, Blas and precision of percentiles of bulk grain size distributions, Earth Surface Processes and Landforms, 22 (11), 1061-1077, 1997.
Ferguson, R.I., and S.J. Wathen, Tracer-pebble movement along a concave river profile: Virtual velocity in relation to grain size and shear stress, Water Resources Research, 34 (8), 2031-2038, 1998.
Fetherston, K.L., R.J. Naiman, and R.E. Bilby, Large Woody Debris, Physical Process, and Riparian Forest Development in Montane River Networks of the Pacific-Northwest, Geomorphology, 13 (1-4), 133-144, 1995.
We present a conceptual biogeomorphic model of riparian forest development in montane river networks. The role of physical process in driving the structure, composition, and spatial distribution of riparian forests is examined. We classify the drainage network into disturbance process-based segments including: (1) debris-flow and avalanche channels, (2) fluvial and debris-flow channels, and (3) fluvial channels. Riparian forests are shown to be significant in the development of channel morphology through the stabilization of active floodplains and as sources of large woody debris (OLWD). LWD is operationally defined as wood > 0.1 m diameter and > 1 m length. LWD plays a key role in the development of montane riparian forests. LWD deposited in the active channel and floodplain provides sites for vegetation colonization, forest island growth and coalescence, and forest floodplain development. Riparian forest patterns parallel the distribution of hillslope and fluvial processes through the network. Riparian forest structure, composition, and spatial distribution through the network are driven by the major disturbance processes including: (1) avalanches, (2) debris- flows, and (3) flooding. Riparian forest patterns also reflect the action of LWD in the organization and development of forested floodplains in gravel bedded montane river networks. The focus of our examples are montane river networks of the Pacific Northwest, USA.
Field, W.G., M.F. Lambert, and B.J. Williams, Energy and momentum in one dimensional open channel flow, Journal of Hydraulic Research, 38 (3), 233-234, 2000.
Field, J., Channel avulsion on alluvial fans in southern Arizona, Geomorphology, 37 (1-2), 93-104, 2001.
Historical aerial photographs and field observations on five fluvially dominated alluvial fans in southern Arizona demonstrate that channel avulsion invariably occurs where bank heights are low and often at channel bends. Channel abandonment occurs through stream capture when overland flow from the main channel accelerates and directs headward erosion of smaller channels heading on the fan surface. Five distinct channel morphologies observed on the fans are related to different stages of the avulsion process and can be used to identify areas on a fan surface that are prone to avulsion. A descriptive model of channel avulsion illustrates how the morphology of a single channel reach will evolve through time as it captures the main flow path and is itself eventually abandoned. Immediately following avulsions. small preexisting channels that capture flow from the main channel will typically experience three fold or greater increases in channel width. Subsequent large floods can be stably conveyed through these high-capacity reaches. An uninterrupted sequence of sediment- charged small flows, however, will eventually begin to back- fill the wide channels as vegetation growth stabilizes the banks. The stabilized and back-filled channels are now prone to abandonment during large floods because the decrease in the channel's capacity leads to the generation of overland flow beyond the margins of the shallowed channels. The action of the small aggrading floods is critical in the avulsion process since the greatest amount of overland flow is generated where bank heights are lowest. As a result. both small and large floods are effective agents of landscape change on the fans. Channel avulsions on the five fans are not completely random events in space and time because their occurrence is controlled by the relative positioning of low banks along the main channel and smaller channels draining the fan surface. Consequently, the location and timing of future channel avulsions can potentially be anticipated in an effort to improve flood hazard assessment on fluvial fans in the rapidly urbanizing southwestern United States. (C) 2001 Elsevier Science B.V. All rights reserved.
Fielding, C.R., A Review of Recent Research in Fluvial Sedimentology, Sedimentary Geology, 85 (1-4), 3-14, 1993.
Fitzpatrick, F.A., and J.C. Knox, Spatial and temporal sensitivity of hydrogeomorphic response and recovery to deforestation, agriculture, and floods, Physical Geography, 21 (2), 89-108, 2000.
Clear-cut logging followed by agricultural activity caused hydrologic and geomorphic changes in North Fish Creek, a Wisconsin tributary to Lake Superior. Hydrogeomorphic responses to changes in land use were sensitive to the location of reaches along the main stem and to the relative timing of large floods. Hydrologic and sediment-load modeling indicates that flood peaks were three times larger and sediment loads were five times larger during maximum agricultural activity in the 1920s and 1930s than prior to about 1890, when forest cover was dominant. Following logging, overbank sedimentation rates in the lower main stem increased four to six times above pre- settlement rates. Accelerated streambank and channel erosion in the upper main stem have been and continue to be primary sources of sediment to downstream reaches. Extreme floods in 1941 and 1946, followed by frequent moderate floods through 1954, caused extensive geomorphic changes along the entire main stem. Sedimentation Fates in the lower main stem may have decreased in the last several decades as agricultural activity declined. However, geomorphic recovery is slow, as incised channels in the upper main stem function as efficient conveyors of watershed surface runoff and thereby continue to promote flooding and sedimentation problems downstream.
Fletcher, W.K., and C.H. Loh, Transport and deposition of cassiterite by a Malaysian stream, Journal of Sedimentary Research, 67 (5), 763-775, 1997.
Flippin, S.J., and R.H. French, Comparison of Results From Alluvial-Fan Design Methodology With Historical Data, Journal of Irrigation and Drainage Engineering-Asce, 120 (1), 195-210, 1994.
The Federal Emergency Management Agency (FEMA) method for delineating flood plains on alluvial fans was modified by French in 1992 to estimate design peak flow rates of specified return periods at transportation alignments crossing alluvial fans. The hydraulic engineer can use these estimates to size the drainage facilities required to protect an alignment from flood damage. The focus of this paper is an examination of the validity of the estimates derived from this modified methodology. The strategy adopted in the study was to identify a limited number of existing transportation alignments that cross alluvial fans and use the design methodology to solve for the return periods associated with the maximum capacities of the drainage structures that adopted the alignment from damage. The probability that one or more events would exceed the estimated capacity of each structure in the period of time the structure has been in place can then be estimated in accordance with the U.S. Water Resources Council's 1981 guidelines and compared with the recorded history of flood damage to the alignment. This study showed that for a number of reasons the methodology likely yields conservative estimates.
Fossati, J., G. Pautou, and J.P. Peltier, Water as resource and disturbance for wadi vegetation in a hyperarid area (Wadi Sannur, Eastern Desert, Egypt), Journal of Arid Environments, 43 (1), 63-77, 1999.
Foufoula-Georgiou, E., and V. Sapozhnikov, Scale invariances in the morphology and evolution of braided rivers, Mathematical Geology, 33 (3), 273-291, 2001.
This paper presents an overview and synthesis of an extensive research effort to characterize and quantify scale invariances in the morphology and evolution of braided rivers. Braided rivers were shown to exhibit anisotropic spatial scaling (self- affinity) in their morphology, implying a statistical scale invariance tinder appropriate resealing of the axes along and perpendicular to the main direction of flow. The scaling exponents were found similar in rivers of diverse flow regimes, slopes, types of bed material and braid plain widths, indicating the presence of universal features in the underlying mechanisms responsible for the formation of their spatial structure. In regions where predominant geologic controls or predominant flow paths were present, no spatial scaling was found. Regarding their spatiotemporal evolution, braided rivers were found to exhibit dynamic scaling, implying that a smaller part of a braided river evolves identically to a larger one provided that space and time are appropriately normalized. Based on these findings, and some additional analysis of experimental rivers as they approach equilibrium, it was concluded that the mechanism bringing braided rivers to a state where they show spatial and temporal scaling is self-organized criticality and inferences about the physical mechanisms of self-organization were suggested.
Fraccarollo, L., and A. Marion, Statistical Approach to Bed-Material Surface Sampling, Journal of Hydraulic Engineering-Asce, 121 (7), 540-545, 1995.
Fraccarollo, L., and M. Papa, Numerical simulation of real debris-flow events, Physics and Chemistry of the Earth Part B-Hydrology Oceans and Atmosphere, 25 (9), 757-763, 2000.
A one-dimensional model is presented to predict debris-flow runouts. The model is based on shallow water type assumptions. The fluid is assumed to be homogeneous and the original bed of the flow domain to be unerodible. The fluid is characterized by a rheology of Bingham type. A numerical tool able to cope with the nature of debris flows has been worked out. It represents an extension of a second order accurate and conservative method of Godunov type. Special care has been devoted to the influence of the source terms and of the geometrical representation of the natural cross sections, which play a fundamental role. The application concerns a monitored event in the Dolomites in Italy, where field analyses allowed characterization of the behavior of solid-liquid mixture as a yield stress material. The comparison between numerical simulations and field observations highlights the impossibility of representing all phases of the flow with constant values of the rheological parameters. Nevertheless the results show that it is possible to separately represent the phase of the flow in the upstream reach and the phase of the deposition in the alluvial fan, with a good agreement with field observations. (C) 2000 Elsevier Science Ltd. All rights reserved.
Franklin, S.E., E.E. Dickson, D.R. Farr, M.J. Hansen, and L.M. Moskal, Quantification of landscape change from satellite remote sensing, Forestry Chronicle, 76 (6), 877-886, 2000.
Satellite remote sensing data and methods can be used to develop maps of large areas at different times in order to assess changes in forest ecosystem patterns and processes. Such maps are useful in understanding wildlife populations and habitat, forest biodiversity, and forest productivity. They may be important in ecological monitoring programs at multiple spatial and temporal scales, and could include assessment of structural aspects of the landscape, such as forest or habitat fragmentation. Quantification and measurement of landscape structure depend on the definition of landscape classes or patches, defined on the basis of more or less homogeneous elements, which differ in some measurable way from neighbouring patches. In this paper, we review some of the issues, and provide examples using satellite remote sensing data, in the quantification of landscape structure in two Canadian forests. The link between landscape structure and biodiversity is provided through the emergence of ecological understanding of species richness, species-habitat or niches, and metapopulation dynamics.
Friedman, J.M., and G.T. Auble, Mortality of riparian box elder from sediment mobilization and extended inundation, Regulated Rivers-Research & Management, 15 (5), 463-476, 1999.
Fripp, J.B., and P. Diplas, Surface Sampling in Gravel Streams, Journal of Hydraulic Engineering-Asce, 119 (4), 473-490, 1993.
The accuracy of studies concerning the characteristics of gravel-bed waterways is often dependent upon the techniques used to sample and quantify the material found on the channel boundary. Due to the vertical stratification present in the riverbed, the use of sampling techniques that remove only the particles within a thin surface layer is often necessary. Attributes of clay and grid sampling are considered in the present work. Criteria for determining the minimum sample size for a desirable level of accuracy are also presented. Many of the current surface sampling techniques truncate either the upper or lower size range of particles. Truncation of part of a size distribution not only limits the available information, but can also bias the rest of the distribution. The present work rectifies this problem by proposing the use of a hybrid technique that can sample the entire size range of either dry or submerged bed material. Results of field tests that utilize this new method are described in detail.
Froehlich, D.C., Armor-Limited Clear-Water Contraction Scour At Bridges, Journal of Hydraulic Engineering-Asce, 121 (6), 490-493, 1995.
Fryirs, K., and G.J. Brierley, Slope-channel decoupling in Wolumla catchment, New South Wales, Australia: the changing nature of sediment sources following European settlement, Catena, 35 (1), 41-63, 1999.
Within a few decades of European settlement, channel incision transformed discontinuous river courses throughout Wolumla catchment, on the south coast of New South Wales, Australia. The development of continuous channels greatly increased sediment delivery from the catchment. This paper documents the character, timing and proportion of sediment sourced from upland valley fills, channel expansion sites, and gully networks. Volumes of material transferred from these sources are compared with estimates of sediment eroded from hillslopes, and the movement of sediment off the slopes to the valley floor is assessed. Although disturbance of slopes resulted in significant movement of materials, most of this material has been stored on-slope, in trapped tributary fills and along lower order drainage lines. The slopes are effectively decoupled from the channel. Sediment accumulation in farm dams over the past few decades has been negligible. Around 75% of the total volume of material released from creeks in Wolumla catchment since 1865, i.e., 5500 x 10(3) m(3), has been derived from channel incision into valley fills at the base of the escarpment. Sediment flushing occurred within a few decades of catchment disturbance. Bedrock confinement in the middle and lower catchment resulted in very efficient downstream transfer of materials. Although gully networks and channel expansion sites have released a relatively small volume of material, these sources are the greatest contemporary source of sediment in Wolumla catchment. (C) 1999 Elsevier Science B.V. All rights reserved.
Fryirs, K., and G.J. Brierley, Variability in sediment delivery and storage along river courses in Bega catchment, NSW, Australia: implications for geomorphic river recovery, Geomorphology, 38 (3-4), 237-265, 2001.
In many catchments in southeastern Australia, alluvial stores have been the dominant source of sediments mobilised in the period since European settlement. In Bega catchment, on the South Coast of New South Wales (NSW), this has been reflected by dramatic changes to river morphology. Extensive volumes of material have been released and efficiently flushed to the lowland plain, with a sediment delivery ratio of almost 70%. However, only 16% of these alluvial sediments have been flushed through to the estuary, as antecedent controls on Valley width have resulted in the lowland plain acting as a large sediment sink. The changing nature of sediment source, transfer and accumulation zones has varied markedly from subcatchment to subcatchment, The volume of material supplied to the lowland plain from differing subcatchments is not related to subcatchment area. Rather, the pattern of river types dictates the spatial variability in storage and transfer. Over 67% of sediment released has been sourced from just 25% of the catchment, from subcatchments characterised by large valley fills (cut and All River Style) that previously stored extensive volumes of material at the base of the escarpment. These parts of Bega catchment were especially sensitive to disturbance. Sediment exhaustion from these parts of the catchment, and from river courses elsewhere, has major implications for the geomorphic recovery potential of rivers, constraining what can be realistically achieved in terms of river rehabilitation. (C) 2001 Elsevier Science B.V. All rights reserved.
Fukushima, M., Salmonid habitat-geomorphology relationships in low-gradient streams, Ecology, 82 (5), 1238-1246, 2001.
A link between stream geomorphology and lotic ecosystems was demonstrated by quantitatively examining the precise locations of salmonid redds with respect to the planform geometry of streams using a differential global positioning system. A total stream distance of 59 km was surveyed in 17 streams, in which a total of 309 redds of Sakhalin taimen (Hucho perryi) were recorded. The average size (+/- SD) of these redds was 227 +/- 60 cm in length and 122 +/- 42 cm in width. A meta-analysis of these data showed that channel sinuosity was significantly greater at sites where Sakhalin taimen redds were constructed than,the average stream sinuosity. This salmonid preference for highly sinuous reaches was detected when the sinuosity index was calculated at 50-m increments and became insignificant at greater distance increments. This habitat-sinuosity relationship will be more pronounced in streams with only moderately sinuous channels, less abundant large woody debris, and higher spawner densities.
Fuller, I.C., M.G. Macklin, J. Lewin, D.G. Passmore, and A.G. Wintle, River response to high-frequency climate oscillations in southern Europe over the past 200 ky, Geology, 26 (3), 275-278, 1998.
A 200 k.y. chronology of river response to climate-related environmental change has been established for northeast Spain using newly developed luminescence dating techniques. This constitutes the best-documented record of late Quaternary river behavior currently available for the North Atlantic region and enables fluvial stratigraphies to be compared with high- resolution ice core and marine oxygen isotope climate series. Pleistocene and Holocene river aggradational episodes coincide with stadial or neoglacial events, while phases of river incision occur during interstadial or interglacial periods. Alluviation and erosion cycles would appear to track variations in sediment supply controlled by vegetation cover and winter storm frequency.
Furbish, D.J., Conditions For Geometric Similarity of Coarse Stream-Bed Roughness, Mathematical Geology, 19 (4), 291-307, 1987.
Furbish, D.J., Spatial Autoregressive Structure in Meander Evolution, Geological Society of America Bulletin, 103 (12), 1576-1589, 1991.
The migration of a river bend depends in part on the high flow velocities that characteristically impinge on its outside bank. Recent models have treated this in terms of a spatial convolution, whereby local bend migration is mathematically a weighted aggregate of upstream curvature and bed topography. The convolution model can be tested using river migration data after it is discretized and recast into a finite autoregressive form. Published isochrones marking former positions of bends on the Beatton River, Canada, support the hypothesis that rates of bend migration follow a convolutional relation. In addition, a comparison of the underlying flow model with published flume experiments involving constant-curvature bends illustrates how it predicts the near-bank depth-averaged velocity associated with a forced-bar topography in absence of free bars. The autoregressive form of the model is equivalent to a stochastic linear-difference equation; this allows bend curvature to be treated as a random process. Cast in the frequency domain, the convolution model predicts that big bends to grow at the expense of little bends and curvature irregularities in complex trains; there exists no tendency for preferential growth of an intermediate bend size. The model also predicts the well-known shift of maximum migration rates to positions down-stream of curvature apexes and implies that the magnitude of this shift increases with decreasing bend size. Predicted shifts compare well with published, measured shifts on the Nishnabotna River, Iowa. The sensitivity of the meandering process to initial bend geometries and entrance flow conditions ensures that diverse bend shapes arise along freely migrating rivers independently of factors such as unsteady flow and nonuniform erodibility. No single geometrical form serves as an asymptotic, evolutionary state for individual bends.
Furbish, D.J., Flow Structure in a Bouldery Mountain Stream With Complex Bed Topography, Water Resources Research, 29 (7), 2249-2263, 1993.
Bouldery, mountain streams often possess highly irregular banks and beds composed of bedrock outcrops and immobile clasts mingled with alluvial bed forms. This complex morphology can induce locally strong flow accelerations and distortions of the water surface. Despite the complexity of flow at a scale of one or two channel widths and smaller, it is possible to identify a filament of high streamwise velocity that exhibits a near- oscillatory structure, albeit noisy, as it threads back and forth across the channel over tens of channel widths; and transverse water surface slopes locally mimic transverse bed slopes. These features are responses to shoaling of flow over an irregular, nearly random, bed topography. To clarify the mechanisms leading to this structure, linearized forms of the depth-averaged equations of momentum and continuity are solved in the wavenumber domain, for the case of a straight channel with uniform width, using a doubly periodic description of bed topography as a forcing term. Systematic changes in the strength and phase of velocity and water surface responses with varying wavenumber of bed undulations reflect mutual interaction of streamwise and transverse flow accelerations and transverse water surface slopes. These results are cast in terms of spectral responses to a bed composed of many superimposed waveforms. Then the shapes of spectra describing transverse water surface slopes and the transverse coordinate of the high-velocity filament, as measured from 100 equally spaced sections along North Boulder Creek, Colorado, are predicted by the analysis. The levels of the spectra are underestimated, however, due to factors not taken into account by the linear analysis, notably variations in width, and form drag associated with coarse roughness.
Furbish, D.J., Irregular bed forms in steep, rough channels - 1. Stability analysis, Water Resources Research, 34 (12), 3635-3648, 1998.
A scaling analysis of the depth-integrated momentum equations tailored to the rough bed conditions of mountain streams suggests that certain velocity correlation terms that arise from depth integration, and which normally can be neglected in the case of smoother alluvial channels, can be a significant part of the momentum balance in these steep channels. By introducing the kinetic energy equation of the time-averaged motion to treat these correlation terms, which involve products of local deviations in velocity components about depth-averaged values, a flow model that suitably characterizes streamwise accelerations is obtained. A linear stability analysis using a flow model that retains the streamwise correlation terms suggests that their effect is to strengthen the initial selection of bed form wavelengths, as reflected by sharpened peaks in curves of growth rate versus bed form wavelength. Wavelengths with zero migration rate are close to wavelengths having the large;st growth rate; thus selection of fixed bars is strong. Critical width-depth ratios necessary for bed form growth are significantly less than the critical ratios that are predicted when correlation terms are neglected. Moreover, a broader band of wavenumbers can be activated at a given width- depth ratio, and bed form modes representing midchannel bars can be activated in a narrower channel than would otherwise be predicted. Thus alternate bars can initially "compete" with midchannel bars, particularly at low sediment transport rates. This competition probably contributes to the complexity of bed topography that is typical of rough, mountain channels.
Furbish, D.J., S.D. Thorne, T.C. Byrd, J. Warburton, J.J. Cudney, and R.W. Handel, Irregular bed forms in steep, rough channels - 2. Field observations, Water Resources Research, 34 (12), 3649-3659, 1998.
A linear stability analysis using a flow model appropriate for steep, rough channels suggests that initial wavelength selection of alternate bars is strong for extant flow conditions in North Boulder Creek, Colorado. This is due in part to effects of velocity correlation terms in the streamwise momentum balance that involve deviations in velocity components about depth-averaged values. The analysis also suggests that alternate bars and midchannel bars can "compete" during initial bed form growth at low sediment transport rates. These points are consistent with the observation that alternate and midchannel bar forms in North Boulder Creek have comparable topographic relief, as revealed by spectral analysis of the bed topography. Moreover, the dominant wavelengths of these bar forms match the fastest growing wavelengths predicted by the stability analysis. However, whereas the alternate bar topography can be attributed to free-bar growth, much of the midchannel bar topography probably is a forced-bar topography that is related to flow accelerations associated with variations in channel width. The complex bed topography of North Boulder Creek thus consists of a decipherable mixture of bed forms that have evolved as free alternate bars together with forced bars whose positions and geometries are fixed in relation to variations in channel width or to large immobile boulders.
Gabriel, A.O., and R.D. Kreutzwiser, Conceptualizing environmental stress: A stress-response model of coastal sandy barriers, Environmental Management, 25 (1), 53-69, 2000.
The purpose of this paper is to develop and apply a conceptual framework of environmental stress-response for a geomorphic system. Constructs and methods generated from the literature were applied in the development of an integrative stress- response framework using existing environmental assessment techniques: interaction matrices and a systems diagram. Emphasis is on the interaction between environmental stress and the geomorphic environment of a sandy barrier system. The model illustrates a number of stress concepts pertinent to modeling environmental stress-response, including those related to stress-dependency, frequency-recovery relationships, environmental heterogeneity, spatial hierarchies and linkages, and temporal change. Sandy barrier stress-response and recovery are greatly impacted by fluctuating water levels, stress intensity and frequency, as well as environmental gradients such as differences in sediment storage and supply. Aspects of these stress-response variables are articulated in terms of three main challenges to management: dynamic stability spatial integrity, and temporal variability. These in turn form the framework for evaluative principles that may be applied to assess how policies and management practices reflect key biophysical processes and human stresses identified by the model.
Gaillot, S., and H. Piegay, Impact of gravel-mining on stream channel and coastal sediment supply: Example of the Calvi Bay in Corsica (France), Journal of Coastal Research, 15 (3), 774-788, 1999.
Beach erosion during the last three decades in Calvi Bay, Corsica, is described and linked to a reduction of gravel and sand delivery from the Figarella and Flume Seccu coastal streams. Recent assessment of bedload transport during a 1 in 2 year flood and stream bed changes; evaluated from aerial photographs and field measurements (cross-sections, long profiles, sediment size analysis) show these streams deliver less and less sediment to the beach, thereby explaining its erosion. Two main causes explain this trend: (1) in-channel gravel-mining has been operated on these streams since the 1970's and (2) significant land-use changes have taken place in their watershed since the end of the 19(th) century. The gravel pits trap sediments and induce adjustments in channel geometry. An alder forest that colonized the gravel pit on the Flume Seccu traps most of the sand delivered by the watershed and represents a major flood risk because vegetation encroachment has increased hydraulic roughness. The excavation in the Figarella measures 600 000 m(3), corresponding to a channel degradation of 3 m. Channel degradation and armoring are also observed upstream and downstream of the excavation due to progressive and regressive erosion as a result of bedload transport disruption and downstream winnowing. The winnowing process has been very effective because bed material is heterogeneous. Field measurements demonstrate that less than 50% of the beach sediment deficit results directly from mining. Beach erosion is also linked to decreases in sediment delivery from the watersheds. Channel patterns have simplified even in the reaches which are not affected by mining. Braided channels have been replaced by single-bed channels and most of the channels observed in aerial photographs from the 1950's are now vegetated. Late 19(th) c. agricultural decline has led to land- use changes, croplands and pasture being replaced by spontaneous undergrowth and woods, reducing erosion and run- off. Beach erosion, due initially to watershed land-use and channel changes on coastal streams occuring since the Late 19(th) century, and worstened by gravel-mining, is far hom under control. As gravel pits will continue to trap sediments for several decades, decision-makers should favor natural or artificial solutions to increasing sediment delivery if they want to maintain the beach, essential to the local tourist industry.
Garbrecht, J., R. Kuhnle, and C. Alonso, A Sediment Transport Capacity Formulation For Application to Large Channel Networks, Journal of Soil and Water Conservation, 50 (5), 527-529, 1995.
Garcia, M., and G. Parker, Entrainment of Bed Sediment Into Suspension, Journal of Hydraulic Engineering-Asce, 117 (4), 414-435, 1991.
The literature abounds with apparently conflicting relations for predicting the reference near-bed concentration of suspended sediment or the entrainment rate of noncohesive bed sediment into suspension. Most of these relations have been developed for uniform material. In this paper, seven such relations are compared against a common set of experimental data for which direct measurements of near-bed concentration are available. The relations put forward by Van Rijn and by Smith and McLean are found to perform best. A new relation for uniform material, having similar predictive capabilities, is developed using the same experimental data. The new relation is generalized to handle sediment mixtures with the aid of field data. The generalization accounts for the hiding effect due to the presence of grains of different sizes. A test against an independent field data set indicates that the empirical fit can provide reasonable of the sediment entrainment coefficient for beds covered with nonuniform material.
Garcia, C., J.B. Laronne, and M. Sala, Variable source areas of bedload in a gravel-bed stream, Journal of Sedimentary Research, 69 (1), 27-31, 1999.
Garcia, C., J.B. Laronne, and M. Sala, Continuous monitoring of bedload flux in a mountain gravel-bed river, Geomorphology, 34 (1-2), 23-31, 2000.
An automatic bedload monitoring station has been established on the perennial Tordera River, a Mediterranean mountain gravel- bed stream located in NE Spain. Bedload fluxes were obtained automatically at 1-min intervals using two Birkbeck-type pit bedload samplers aligned across the width of the channel. Flow depth and water-surface slope were both measured continuously and synchronously with bedload. Data for five flow events show that bedload flux varies considerably. Bedload flux is high when it is compared with other perennial streams. For a 15-min interval, maximum channel-average bedload flux was 0.83 kg m(- 1) s(-1). Bedload records also show that there is no direct relationship between bedload flux and grain shear stress. The low correlation between bedload flux and hydraulics arises due to the different thresholds of initiation of motion for each flow event and the variable character of the bed between events. For two individual floods, there is a reasonable relationship between bedload flux and grain shear stress, in part, as a consequence of individual particle entrainment and patch movement over a stable coarse gravel-bed during moderately high discharges. These results demonstrate that the Birkbeck system functions well in a Mediterranean mountain gravel-bed stream with a longitudinal slope of 2%. (C) 2000 Elsevier Science B.V. All rights reserved.
Garcianavarro, P., F. Alcrudo, and J.M. Saviron, 1-D Open-Channel Flow Simulation Using Tvd-Mccormack Scheme, Journal of Hydraulic Engineering-Asce, 118 (10), 1359-1372, 1992.
The addition of a dissipation step to the widely used McCormack numerical scheme is proposed for solving one-dimensional open- channel flow equations. The extra step is devised according to the theory of total variation diminishing (TVD) schemes that are capable of capturing sharp discontinuities without generating the spurious oscillations that more classical methods do. At the same time, the extra step does not introduce any additional difficulty for the treatment of the source terms of the equations. Results from several computations arc presented and comparison with the analytical solution for some test problems is shown. The overall performance of the method can be considered verv good, and it allows for accurate open- channel flow computations involving hydraulic jumps and bores.
Garcianavarro, P., and V. Zorraquino, Numerical Modeling of Flood Propagation Through System of Reservoirs, Journal of Hydraulic Engineering-Asce, 119 (3), 380-389, 1993.
An explicit numerical flow-routing model is developed based on the second order McCormack scheme. This paper describes the use of the finite difference scheme for the solution of the St. Venant equations of the one-dimensional unsteady open channel flow, and the treatment of the boundary problem by the method of characteristics. A case study is presented using the system of reservoirs and the fluvial network of tributaries of the left-hand side of the Ebro River valley in Spain. To get an estimate of the regulating action provided by those reservoirs during the strong rainfall of the first days of November 1982, the registered inflow and outflow hydrographs are used for the simulation of the propagation of the waves along the watercourses. Results of flow computations are presented and compared with field measurements to show that this model can be considered a suitable technique for hydraulic studies involving rapidly varying flows.
Garton, L.S., R.L. Autenrieth, J.S. Bonner, and B.A. Sylvester, Aquatic Sediments, Water Environment Research, 64 (4), 610-625, 1992.
Garton, L.S., B.A. Sylvester, R.L. Autenrieth, and J.S. Bonner, Aquatic Sediments, Water Environment Research, 65 (4), 534-547, 1993.
Gasparini, N.M., G.E. Tucker, and R.L. Bras, Downstream fining through selective particle sorting in an equilibrium drainage network, Geology, 27 (12), 1079-1082, 1999.
The phenomenon of downstream fining has been attributed to both particle abrasion and selective particle sorting; the latter is generally considered to play the dominant role within resistant lithologies. It has been recognized that tributaries can disrupt lining patterns; however, few downstream-fining studies have considered the entire fluvial network structure. Here we combine a theory for selective transport with a model of river- basin evolution in order to simulate the dynamics of selective sorting throughout a drainage network. Previous numerical modeling studies of single-thread or braided channels have treated downstream lining as a phenomenon driven by differential deposition rates. We show, however, that in an eroding drainage network, downstream fining emerges as a natural dynamic adjustment to variable water, sediment, and energy inputs, even under conditions of uniform size distribution in sediment flux. Thus, although selective deposition and abrasion clearly can and do play a role in some fluvial systems, neither is necessary to produce downstream fining within a drainage network.
Gates, T.K., A.A. Alshaikh, S.I. Ahmed, and D.J. Molden, Optimal Irrigation Delivery System-Design Under Uncertainty, Journal of Irrigation and Drainage Engineering-Asce, 118 (3), 433-449, 1992.
The effects of various types of uncertainty in the design of hydraulic structures in an open-channel system for irrigation water delivery are investigated. Uncertainty due to ambiguity in the values of system physical and management characteristics is addressed by modeling selected parameters (temporally varying water-supply level; spatially varying canal geometry, bed slope and hydraulic resistance; and spatially and temporally varying irrigation demand and irrigation patterns) as stochastic processes. Vagueness in the specification of system performance objectives (adequacy, efficiency. dependability, and equity) is modeled using postulated fuzzy set membership functions. An optimal design criterion is formulated that incorporates quantitative measures of water delivery system performance. Two design objectives, high technical performance and low cost, are considered in a simple illustrative example. A model of spatially varied flow in an open channel delivering water to farm turnouts is used to analyze design scenarios under two different operating schemes. Monte Carlo simulation allows analysis of system behavior in a stochastic setting. Response surface methodology is used to derive optimal design solutions for sizing of diversion and regulating structures. Implications for design and analysis of large-scale delivery networks in an uncertain environment are discussed.
Gates, T.K., and A.A. Alshaikh, Stochastic Design of Hydraulic Structures in Irrigation Canal Networks, Journal of Irrigation and Drainage Engineering-Asce, 119 (2), 346-363, 1993.
A methodology is presented for optimal design of hydraulic structures in a branched irrigation canal network subject to parametric and objective uncertainty. Monte Carlo simulation of steady spatially varied flow is incorporated into the Hooke and Jeeves direct-search method to determine a high-performance, low-cost solution. Fuzzy membership functions address subjectivity associated with interpreting expected values of performance measures in light of water delivery objectives. Solution of an example problem yields an optimal design for 10 pipe diversion structures in a lined canal network. Water supply level, potential crop evapotranspiration, canal hydraulic resistance, and irrigation application efficiency were modeled as random variables. Results indicated that predicted performance for a given design can be subject to significant variability. Coefficients of variation in system performance measures for adequacy, efficiency, dependability, and equity of water delivery were 0. 13, 0.04, 0.17, and 0.20, respectively, at the optimal design. The method describes variability in system performance and relative cost for non- optimal designs as well. Such information is valuable for assessing the anticipated impact of alternative designs on overall system performance.
Gates, T.K., and S.I. Ahmed, Sensitivity of Predicted Irrigation-Delivery Performance to Hydraulic and Hydrologic Uncertainty, Agricultural Water Management, 27 (3-4), 267-282, 1995.
A stochastic simulation model is developed which treats selected hydraulic and hydrologic input parameters as random variables in predicting the performance of an irrigation-water- delivery system. The model is applied to a hypothetical earthen canal network representative of field conditions in the upper Nile valley in Egypt to investigate the sensitivity of the relative variability in predicted system performance to the relative variability in the input parameters. The methodology combines a model of steady spatially-varied canal network flow with statistical models that generate possible realizations of the random hydraulic and hydrologic parameters through Monte Carlo simulation. System performance is assessed by statistical analysis of predicted performance measures for adequacy, efficiency, dependability and equity of water delivery. Though the magnitude of the relative variability will vary for the particular system conditions, results from this study indicate the degree to which the coefficient of variation, CVomega, in predicted system performance is sensitive to changes in the CVomega of the respective input parameters. Results show that sensitivity to the CVomega in Manning hydraulic resistance and channel bed slope was low; sensitivity to the CVomega, in irrigation application efficiency was low to moderate; sensitivity to the CV in upstream water supply level was moderate to high; and sensitivity to the CV, in channel cross- section geometry and potential crop evapotranspiration was high. These results provide insight into the stochastic nature of irrigation canal network flows and indicate the comparative value of data describing the statistical space-time variability of selected parameters.
Geist, D.R., and D.D. Dauble, Redd site selection and spawning habitat use by fall chinook salmon: The importance of geomorphic features in large rivers, Environmental Management, 22 (5), 655-669, 1998.
Knowledge of the three-dimensional connectivity between rivers and groundwater within the hyporheic zone can be used to improve the definition of fall chinook salmon (Oncorhynchus tshawytscha) spawning habitat. Information exists on the microhabitat characteristics that define suitable salmon spawning habitat. However, traditional spawning habitat models that use these characteristics to predict available spawning habitat are restricted because they can not account for the heterogeneous nature of rivers. We present a conceptual spawning habitat model for fall chinook salmon that describes how geomorphic features of river channels create hydraulic processes, including hyporheic flows, that influence where salmon spawn in unconstrained reaches of large mainstem alluvial rivers. Two case studies based on empirical data from fall chinook salmon spawning areas in the Hanford Reach of the Columbia River are presented to illustrate important aspects of our conceptual model. We suggest that traditional habitat models and our conceptual model be combined to predict the limits of suitable fail chinook salmon spawning habitat. This approach can incorporate quantitative measures of river channel morphology, including general descriptors of geomorphic features at different spatial scales, in order to understand the processes influencing redd site selection and spawning habitat use. This information is needed in order to protect existing salmon spawning habitat in large rivers, as well as to recover habitat already lost.
Germanoski, D., and S.A. Schumm, Changes in Braided River Morphology Resulting From Aggradation and Degradation, Journal of Geology, 101 (4), 451-466, 1993.
Gill, M.A., Nonlinear Solution of Aggradation and Degradation in Channels, Journal of Hydraulic Research, 25 (5), 537-547, 1987.
Gill, M.A., Hyperbolic Model For Aggrading Channels, Journal of Engineering Mechanics-Asce, 114 (7), 1245-1255, 1988.
Gill, M.A., Study of Open-Channel Dynamics As Controlled Process - Discussion, Journal of Hydraulic Engineering-Asce, 119 (4), 543-545, 1993.
Gill, M.A., Hydrodynamics of Mining Pits in Erodible Bed Under Steady Flow, Journal of Hydraulic Engineering-Asce, 120 (11), 1337-1348, 1994.
Gillespie, B.M., and J.R. Giardino, The nature of channel planform change: Brazos river, Texas, Texas Journal of Science, 49 (2), 109-142, 1997.
Gilvear, D., and S. Bradley, Geomorphological adjustment of a newly engineered upland sinuous gravel-bed river diversion: Evan Water, Scotland, Regulated Rivers-Research & Management, 13 (4), 377-389, 1997.
Gimenez, R., and G. Govers, Interaction between bed roughness and flow hydraulics in eroding rills, Water Resources Research, 37 (3), 791-799, 2001.
Govers [1992] showed that the flow velocity in rills eroding loose, nonlayered materials could be predicted from knowledge of discharge only (without significant slope or soil effect). The objective of this paper is to investigate to what extent the observed slope independence of flow velocity in eroding rills can be explained by the interaction between rill bed roughness and flow hydraulics. In a laboratory study, two situations were compared: (1) rills which can freely erode a uniform soil layer and (2) rills with a fixed bed geometry. During the experiments, rill discharge and flow velocity were recorded. After each experiment, a detailed topographic survey of the rill bed was carried out using a laser scanner. From these data the main hydraulic variables (mean values of flow depth, wetted perimeter, and hydraulic radius) were estimated. The experiments confirmed the slope independence of rill flow velocities on mobile beds. When the bed is fixed, the flow velocity in rills is clearly slope-dependent. The slope independence of flow velocity on mobile beds is due to a feedback between rill bed morphology and flow conditions. The roughness amplitude (which was assessed from the standard deviation of corrected height values) and the frequency of macroroughness elements (which was assessed by counting the number of peaks per unit length in a previously simplified longitudinal profiles) both increase and tend to counteract the effect of the increase in slope gradient on rill flow velocity. The final rill flow velocity appears to be characterized by a constant average Froude number.
Gippel, C., Changes in Stream Channel Morphology At Tributary Junctions, Lower Hunter Valley, New-South-Wales, Australian Geographical Studies, 23 (2), 291-307, 1985.
Goedhart, M.L., and N.D. Smith, Braided stream aggradation on an alluvial fan margin: Emerald Lake fan, British Columbia, Canadian Journal of Earth Sciences, 35 (5), 534-545, 1998.
Goff, J.R., and P. Ashmore, Gravel Transport and Morphological Change in Braided Sunwapta River, Alberta, Canada, Earth Surface Processes and Landforms, 19 (3), 195-212, 1994.
The relation between morphological change and patterns of variation in bedload transport rate in braided streams was observed by repeated, daily topographic surveys over a 25 day study period in a 60 m reach of the proglacial Sunwapta River, Alberta, Canada. There are two major periods of morphological change, each lasting several days and each involving the complete destruction and reconstruction of bar complexes. Bar complex destruction was caused by redirection of the flow and by downstream extension of the confluence scour zone upstream. Reconstruction involved accretion of unit bars on bar head, flank and tail and in one case was initiated by disection of a large, lobate unit bar. High rates of sediment movement, measured from net scour and fill of the cross-sections, coincided with these morphological changes. Sediment was supplied from both bed and bank erosion, and patterns and distances of transfer were highly variable. Rates of transport estimated by matching upstream erosional volumes with downstream deposition were much greater than those estimated from either a step-length approach or a sediment budget. Measurements of scour and fill and observations of morphological change indicate that step lengths (virtual transport distances) were typically 40-100 m during a diurnal discharge cycle. Shorter step lengths occurred when transfer was confined to a single anabranch and longer steps involved channel changes at the scale of the entire reach. Sediment budgeting was used to describe the spatial patterns of sediment transport associated with the morphological changes and to estimate minimum daily reach-averaged transport rates. Mean bedload transport rates correlate with discharge, but with considerable scatter. The largest deviations from the mean relation can be tied to phases of channel incision, bank erosion, scour hole migration, bar deposition and channel filling apparently controlled by changes and fluctuations in sediment supply from upstream, independent of discharge. These are interpreted as field evidence of 'autopulses' or 'macropulses' in bedload transport, previously observed only in laboratory models of braided streams.
Gomez, B., Temporal Variations in Bedload Transport Rates - the Effect of Progressive Bed Armouring, Earth Surface Processes and Landforms, 8 (1), 41-54, 1983.
Gomez, B., and M. Church, An Assessment of Bed-Load Sediment Transport Formulas For Gravel Bed Rivers, Water Resources Research, 25 (6), 1161-1186, 1989.
Gomez, B., R.L. Naff, and D.W. Hubbell, Temporal Variations in Bedload Transport Rates Associated With the Migration of Bedforms, Earth Surface Processes and Landforms, 14 (2), 135-156, 1989.
Gomez, B., D.W. Hubbell, and H.H. Stevens, At-a-Point Bed-Load Sampling in the Presence of Dunes, Water Resources Research, 26 (11), 2717-2731, 1990.
Gomez, B., Bedload Transport, Earth-Science Reviews, 31 (2), 89-132, 1991.
The complete understanding of bedload transport requires the development of reliable apparatus and techniques for predicting, measuring, and sampling bedload in rivers. This review presents an overview of the development of knowledge and research into bedload transport during the past century. Particular emphasis is placed on the development of methods of predicting and estimating bedload discharge. Problems involved in using field data to calibrate bedload transport formulae and bedload samplers, and factors that affect the design of sampling programmes are specifically addressed. Reluctance to acknowledge the inherently unstable nature of bedload transport has been a principal factor in limiting progress. Some causes of temporal and spatial instability in bedload transport are isolated, and their effect upon the transport process elucidated.
Gomez, B., Roughness of Stable, Armored Gravel Beds, Water Resources Research, 29 (11), 3631-3642, 1993.
The grain roughness of stable armored beds that formed in a laboratory flume under a range of steady flow conditions on rounded, flat and angular gravel is analyzed. Gravel roughness geometry is determined from bed surface profiles and vertical photographs. These techniques have been employed in field situations. Thus the methodology is potentially applicable to the analysis of grain roughness in natural gravel bed channels. The description of representative roughness geometry is also analogous to that used to characterize artificial roughness arrays. Armor roughness increases with increasing flow. Armored surfaces composed of angular gravel are roughest, and surfaces formed of flat gravel offer least resistance to the flow. Stable armored beds may exhibit a tendency to maximize the ratio of the shear due to drag on representative roughness elements to total shear. Roughness concentration is strongly correlated with the energy slope, and there is a linear increase in equivalent roughness height with increasing roughness concentration. The friction factor for an armored surface varies in a linear manner with representative roughness geometry. The equation defining this relation is probably similar to that used to characterize variations in the friction factor with artificial roughness geometry at low roughness concentrations. However, to reconcile the relations for artificial and natural roughness completely, it may be necessary to explicitly consider the contribution to flow resistance made by roughness shape, background roughness, and blocking in shallow flows.
Gomez, B., Effects of Particle-Shape and Mobility On Stable Armor Development, Water Resources Research, 30 (7), 2229-2239, 1994.
Gomez, B., and B.M. Troutman, Evaluation of process errors in bed load sampling using a dune model, Water Resources Research, 33 (10), 2387-2398, 1997.
Gomez, B., B.J. Rosser, D.H. Peacock, D.M. Hicks, and J.A. Palmer, Downstream fining in a rapidly aggrading gravel bed river, Water Resources Research, 37 (6), 1813-1823, 2001.
Downstream changes in particle size that occur in the Waipaoa River, a 104km-long gravel bed river in which rapid aggradation in the historic (post-1800) period was triggered by the conversion of native forest to pasture, are summarized in this paper. The textural data presented are unique for a field situation, not only because of the spatial resolution and extent of the sampling program but also because they provide information about the pattern of fining at different points in time. They are supported by equally comprehensive topographic survey data from which local rates of aggradation can be derived, Despite variability induced by lateral sediment inputs, there is an essentially continuous pattern of fining along the entire length of the river. Fining occurs in both the fine and coarse size fractions of the bed material. The highest rates of fining occur in the larger percentiles of the subsurface bed material and in the surface bed material. Downstream fining in the Waipaoa River appears to be a response to changes in flow hydraulics that are regulated by the concave configuration of the long profile. The fining gradient developed rapidly tin < 45 years). It does not appear to be influenced by the rate of aggradation (nor the overall rate of sediment supply to the channel system), because, in the short term, aggradation has a negligible impact on the inherited form of the long profile.
Gomi, T., R.C. Sidle, M.D. Bryant, and R.D. Woodsmith, The characteristics of woody debris and sediment distribution in headwater streams, southeastern Alaska, Canadian Journal of Forest Research-Revue Canadienne De Recherche Forestiere, 31 (8), 1386-1399, 2001.
Large woody debris (LWD), fine woody debris (FWD), fine organic debris (FOD), and sediment deposition were measured in 15 steep headwater streams with five management and disturbance regimes. Clear-cut channels logged in 1995 contained large accumulations of logging residue that initially provided sites for sediment storage. Half of the LWD in clear-cut channels was recruited during and immediately after logging. Woody debris from logging activities remains in young growth conifer channels 37 years after logging. Numbers of LWD in clear-cut and young conifer channels were significantly higher than in old-growth channels, although numbers of FWD pieces were not significantly different because of higher recruitment from old-growth stands. Channels that experienced recent (1979 and (or) 1993) and earlier (1961 and (or) 1979) scour and runout of landslides and debris flows contained less LWD and FWD, although large volumes of LWD and FWD were found in deposition zones. The volumes of sediment stored in young alder and recent landslide channels were higher than in the other channels. Because of the recruitment of LWD and FWD from young alder stands, the ratio of sediment stored behind woody debris to total sediment volume was higher in young alder channels compared with recent landslide channels. Numbers of LWD and FWD pieces in all streams were significantly correlated with the volumes of sediment stored behind woody debris. Timber harvesting and soil mass movement influence the recruitment, distribution, and accumulation of woody debris in headwater streams; this modifies sediment storage and transport in headwater channels.
Gonzalez, M.A., Recent formation of arroyos in the Little Missouri Badlands of southwestern North Dakota, Geomorphology, 38 (1-2), 63-84, 2001.
Goossens, D., Effect of Rock Fragment Eccentricity On Eolian Deposition of Atmospheric Dust, Catena, 23 (3-4), 227-251, 1994.
Goossens, D., Field Experiments of Aeolian Dust Accumulation On Rock Fragment Substrata, Sedimentology, 42 (3), 391-402, 1995.
Graf, W.L., Transport and deposition of plutonium-contaminated sediments by fluvial processes, Los Alamos Canyon, New Mexico, Geological Society of America Bulletin, 108 (10), 1342-1355, 1996.
Graf, W.L., Locational probability for a dammed, urbanizing stream: Salt River, Arizona, USA, Environmental Management, 25 (3), 321-335, 2000.
Grant, G.E., F.J. Swanson, and M.G. Wolman, Pattern and Origin of Stepped-Bed Morphology in High-Gradient Streams, Western Cascades, Oregon, Geological Society of America Bulletin, 102 (3), 340-352, 1990.
Grant, G.E., Critical flow constrains flow hydraulics in mobile-bed streams: A new hypothesis, Water Resources Research, 33 (2), 349-358, 1997.
A new hypothesis predicts that in mobile-bed river channels, interactions between the channel hydraulics and bed configuration prevent the Froude number (Fr) from exceeding 1 for more than short distances or periods of time. Flow conditions in many steep, competent streams appear to be close to critical. Froude numbers of steep (slope approximate to 0.01) sand-bed streams with considerable freedom to adjust boundaries oscillate between 0.7 and 1.3 over 20- to 30-s cycles, with an average of 1.0 at the channel thalweg. Critical flow in these streams is maintained by the interaction between the mobile bed and free water surface at high Fr, which results in a cyclical pattern of creation and destruction of bed forms. Field observations support that a similar mechanism of flow-bed form interaction constrains Fr less than or equal to 1 in active-bed braided gravel rivers, step-pool streams, laboratory rills, lahar-runout channels, and even some bedrock channels. Empirical and analytical results show that as slope increases, competent flows tend to asymptotically approach critical flow. An assumption of critical flow would dramatically simplify paleohydraulic flow reconstructions and modeling of flow hydraulics in high gradient streams.
Grant, G.E., Comment on "Critical flow constrains flow hydraulics in mobile- bed streams: A new hypothesis" by G.E. Grant - Reply, Water Resources Research, 35 (3), 907-907, 1999.
Greenbaum, N., A. Margalit, A.P. Schick, D. Sharon, and V.R. Baker, A high magnitude storm and flood in a hyperarid catchment, Nahal Zin, Negev Desert, Israel, Hydrological Processes, 12 (1), 1-+, 1998.
Gregory, K.J., Fluvial Geomorphology, Progress in Physical Geography, 7 (3), 385-396, 1983.
Griffiths, G.A., Stochastic Estimation of Bed-Load Yield in Pool-and-Riffle Mountain Streams, Water Resources Research, 16 (5), 931-937, 1980.
Griffiths, G.A., Form Resistance in Gravel Channels With Mobile Beds, Journal of Hydraulic Engineering-Asce, 115 (3), 340-355, 1989.
Griffiths, G.A., Sediment Translation Waves in Braided Gravel-Bed Rivers, Journal of Hydraulic Engineering-Asce, 119 (8), 924-935, 1993.
Bed-load transport capacity in braided gravel-bed rivers varies as hydraulic geometry changes downstream. Differences in capacity lead to variations in bed-material storage as a consequence of bed-load transport during floods. In turn, storage changes produce irregular fluctuations in bed-level or sediment translation waves in the bed material. These waves are the mechanism by which bed load is transported in braided and, in fact, all alluvial rivers with variable downstream hydraulic geometry. An approximate expression for wave velocity indicates that annual wave travel distance can be hundreds of meters or more per year for waves up to 0.5 m high. Although sediment waves cause shifts in bed-load rating at a cross section, bed- load yield may still be estimated using bed-load ratings based on depth-discharge relations defined for periods between rating changes. A procedure is given for stable channel design in the presence of sediment waves based on equivalence of yield for some period in the design reach and a stable reference reach. The condition that the bed-load ratings for the two reaches must intersect either aids or allows solutions of the design problem.
Groeneveld, D.P., and R.H. French, Hydrodynamic Control of an Emergent Aquatic Plant (Scirpus- Acutus) in Open Channels, Water Resources Bulletin, 31 (3), 505-514, 1995.
Control of emergent aquatic plants such as tule (Scirpus acutus Muhl.; Bigel.) is of direct interest to managers of surface waters in Western North America. Where conditions of water velocity and depth occur that permit this and similar species to colonize and grow, their clonal habit may restrict, or even block, open channels within several seasons after their establishment. Fortunately, sufficient flow depth and velocity naturally prevent these plants from growing into and blocking channels. We investigated physical constraints for tule stem growth with the ultimate intent to apply this knowledge in rehabilitating 60 miles of the diverted Owens River in Eastern California, presently choked with emergent growth. Bending stress resulting from hydrodynamic drag on tule stems was found to induce lodging; permanent deformation and consequent loss of function. The depth-velocity envelope describing this process (at 95 percent confidence) is uD/d = 12.8 where u = average velocity acting upon the stem (m/s), D = local depth of flow (m), and d = tule stem diameter at the point of attach ment (m). Maintaining a discharge or reconfiguring a channel so this critical depth-velocity-stem diameter envelope is exceeded (predictable using flow models) through the summer growing period should prevent encroachment into an active channel.
Groves, J.R., and D.W. Moody, A Survey of Hydrology Course Content in North-American Universities, Water Resources Bulletin, 28 (3), 615-621, 1992.
This report presents the results of a survey of hydrology faculties of colleges and universities in the United States and Canada. Information is presented on topics covered in classes, allocation of class periods to individual topics, textbooks, prerequisites, computer use, and accreditation categories for hydrology courses offered by engineering departments. Hydrology courses generally require courses in fluid mechanics, mathematics, statistics, and computer science as prerequisites. Topics that receive the largest allocation of time in both introductory and advanced courses include rainfall-runoff relations, the hydrologic cycle, routing and open channel flow, and statistics. Advanced courses place greater emphasis on watershed models than do the introductory courses. Hydrology courses at both levels allocate the smallest amounts of time to snow hydrology, ground-water hydrology, and "other topics." Very few courses include field or experimental work. In a discipline where computer modeling is a major tool, this lack of field and data-collection experience may lead students to underestimate the uncertainties associated with data used to calibrate models and the modeling results themselves. Survey responses on hydrology courses taught in departments other than civil engineering were too few to permit detailed analysis. Most of these courses spend approximately two-thirds of available class time on the same topics as presented in engineering hydrology courses. The balance of class time is spent on topics that emphasize the specialized interest of the particular discipline, such as soil physics and soil moisture in agricultural engineering.
Grunwald, S., and L.D. Norton, An AGNPS-based runoff and sediment yield model for two small watersheds in Germany, Transactions of the Asae, 42 (6), 1723-1731, 1999.
Guo, Q.C., and Y.C. Jin, Modeling sediment transport using depth-averaged and moment equations, Journal of Hydraulic Engineering-Asce, 125 (12), 1262-1269, 1999.
Guo, J.C.Y., Roll waves in high gradient channels, Water International, 24 (1), 65-69, 1999.
Vedernikov's number quantifies the allowable capacity that can be sustained as a stable uniform flow in a high gradient channel, but it does not provide any guidance to the design of freeboard when roll waves exist. Without considering roll waves, high gradient channels are undersized using the uniform flow approach and fail to maintain design integrity. This paper presents revised design curves to determine the stability of flow in high gradient channels. When the design condition exceeds the limiting condition roll waves should be considered in design. This study applies the model of moving hydraulic jump to simulate roll waves. It provides estimations for wave heights when Froude number is greater than 1.50.
Guo, J.C.Y., Critical flow section in collector channel, Journal of Hydraulic Engineering-Asce, 125 (4), 422-425, 1999.
This paper shows how the critical flow section in a collector channel can be located by solving the dynamic equation of spatially varied flow, Manning's equation, and making use of the singular-point concept. In addition to channel length and tailwater elevation, the occurrence of a critical flow section in a spatially varied flow also depends on the combination of channel cross-sectional geometry, roughness, slope, and inflow rate. When the critical flow section is necessary to be developed in a collector channel, the two dimensionless parameters (F-q/S-0 representing the design capacity and N/S-0 representing the channel roughness) derived in this study guide selection of channel cross-sectional parameters. A set of design charts is provided for trapezoidal channels with a side slope of 1V:1H, 0.5V:1H, or 0V:1H.
Gurnell, A.M., Adjustments in river channel geometry associated with hydraulic discontinuities across the fluvial-tidal transition of a regulated river, Earth Surface Processes and Landforms, 22 (10), 967-985, 1997.
Gurnell, A.M., G.E. Petts, N. Harris, J.V. Ward, K. Tockner, P.J. Edwards, and J. Kollmann, Large wood retention in river channels: The case of the Fiume Tagliamento, Italy, Earth Surface Processes and Landforms, 25 (3), 255-275, 2000.
After more than 300 years of widespread and intensive river management, few examples of complex, unmanaged river systems remain within Europe. An exception is the Flume Tagliamento, Italy, which retains a riparian woodland margin and unconfined river channel system throughout almost the entire 170 km length of its river corridor. A research programme is underway focusing on a range of related aspects of the hydrology, fluvial geomorphology and ecology of the Tagliamento. This paper contributes to that programme by focusing on large wood retention. The paper adopts a simple force:resistance approach at the scale of the entire river corridor in order to identify reaches of the river with a high wood retention potential. Information on the character of the river corridor is derived from 1:10 000 scale topographic maps. A range of indices measured at 330 transects across the river corridor supports a classification of the geomorphological style of the river which reflects the presence and abundance of properties previously identified in the literature as large wood retention sites. This classification provides a qualitative representation of the 'resistance' of the corridor to wood movement and thus its overall wood-retention potential. The map-derived indices are also used to extrapolate estimates of the ten year return period flood to each of the 330 transects so that the downstream pattern of unit stream power can be quantified as an index representing 'force' in the analysis. Although input of wood is an important factor in many river systems, it is assumed not to be a limiting factor along the Tagliamento, where riparian woodland is abundant. Field observations of large wood storage illustrate that wood retention at eight sites along the river reflects the presence and abundance of the features incorporated in the classification of geomorphological style, including the complexity of the channel network, the availability of exposed gravel areas, and the presence of islands. In general at the time of survey in August 1998, open gravel areas were estimated to store approximately 1 t ha-(1) of wood in single-thread reaches and 6 t ha(-1) in multiple-thread reaches. Established islands were estimated to store an average of 80 t ha(-1) of wood. Nevertheless, there was considerable variability between sites, and pioneer islands, which are not represented on maps or readily identified from air photographs because of their small size, were estimated to store an order of magnitude more wood than established islands. Furthermore, the wood storage from this sample of eight sites did not reflect variability in estimated unit stream power. A series of areas for further research are identified, which can be explored using field data, and which will throw more light on the processes of wood retention in this extremely dynamic fluvial environment. Copyright (C) 2000 John Wiley & Sons, Ltd.
Gurnell, A.M., P.J. Edwards, G.E. Petts, and J.V. Ward, A conceptual model for alpine proglacial river channel evolution under changing climatic conditions, Catena, 38 (3), 223-242, 2000.
This paper integrates concepts derived from the literature to focus upon interactions between riparian vegetation and river channel dynamics in alpine glacier basins. Discussion of the nature and variability of discharge and sediment regimes of alpine glacier-fed rivers; downstream variations in the physical character of the river channel and corridor; consequent downstream variations in lateral processes; and regional variations in alpine glacier dynamics, lead to the proposal of a conceptual model of proglacial river channel- riparian vegetation interactions under changing climatic conditions. (C) 1999 Elsevier Science B.V. All rights reserved.
Gurnell, A.M., G.E. Petts, D.M. Hannah, B.P.G. Smith, P.J. Edwards, J. Kollmann, J.V. Ward, and K. Tockner, Riparian vegetation and island formation along the gravel-bed Fiume Tagliamento, Italy, Earth Surface Processes and Landforms, 26 (1), 31-62, 2001.
Guzzetti, F., M. Marchetti, and P. Reichenbach, Large alluvial fans in the north-central Po Plain (Northern Italy), Geomorphology, 18 (2), 119-136, 1997.
Habersack, H.M., The river-scaling concept (RSC): a basis for ecological assessments, Hydrobiologia, 422, 49-60, 2000.
Habersack, H.M., H.P. Nachtnebel, and J.B. Laronne, The continuous measurement of bedload discharge in a large alpine gravel bed river, Journal of Hydraulic Research, 39 (2), 125-133, 2001.
Habersack, H.M., Radio-tracking gravel particles in a large braided river in New Zealand: a field test of the stochastic theory of bed load transport proposed by Einstein, Hydrological Processes, 15 (3), 377-391, 2001.
Hall, A.J., Hydrology in Tropical Australia and Papua-New-Guinea, Hydrological Sciences Journal-Journal Des Sciences Hydrologiques, 29 (4), 399-423, 1984.
Hall, R.O., C.L. Peredney, and J.L. Meyer, The effect of invertebrate consumption on bacterial transport in a mountain stream, Limnology and Oceanography, 41 (6), 1180-1187, 1996.
Hall, K.R., and S.L. Maruca, Mapping a forest mosaic - A comparison of vegetation and bird distributions using geographic boundary analysis, Plant Ecology, 156 (1), 105-120, 2001.
Many areas of ecological inquiry require the ability to detect and characterize change in ecological variables across both space and time. The purpose of this study was to investigate ways in which geographic boundary analysis techniques could be used to characterize the pattern of change over space in plant distributions in a forested wetland mosaic. With vegetation maps created using spatially constrained clustering and difference boundary delineation, we examined similarities between the identified boundaries in plant distributions and the occurrence of six species of songbirds. We found that vegetation boundaries were significantly cohesive, suggesting one or more crisp vegetation transition zones exist in the study site. Smaller, less cohesive boundary areas also provided important information about patterns of treefall gaps and dense patches of understory within the study area. Boundaries for songbird abundance were not cohesive, and bird and vegetation difference boundaries did not show significant overlap. However, bird boundaries did overlap significantly with vegetation cluster boundaries. Vegetation clusters delineated using constrained clustering techniques have the potential to be very useful for stratifying bird abundance data collected in different sections of the study site, which could be used to improve the efficiency of monitoring efforts for rare bird species.
Hallet, B., Self-Organization in Freezing Soils - From Microscopic Ice Lenses to Patterned-Ground, Canadian Journal of Physics, 68 (9), 842-852, 1990.
Hallisey, J.E., and G.H. Belt, Relationships between particle movement and channel morphology in some northern Idaho streams, Water Resources Bulletin, 32 (2), 383-391, 1996.
Ham, D.G., and M. Church, Bed-material transport estimated from channel morphodynamics: Chilliwack River, British Columbia, Earth Surface Processes and Landforms, 25 (10), 1123-1142, 2000.
Harbor, D.J., Dynamic equilibrium between an active uplift and the Sevier River, Utah, Journal of Geology, 106 (2), 181-194, 1998.
In a zone of active tectonic uplift, one expects a river to change morphology simply because valley slope deforms. But by cutting through a transverse uplift, the Sevier River in southern Utah also adapts to the tectonics by eroding and depositing. These localized changes of transport are caused by varying channel geometry, pattern, sedimentology, and slope. In the uplift, the river is narrow, efficiently shaped, coarser- grained, and expends a greater proportion of energy on bed particles. It deposits sediments downstream in exaggerated meandering reaches with wider; less efficient channels. Localized erosion and deposition create a dynamic equilibrium with the structural growth, but this equilibrium includes nonlinear responses like knickpoints and depositional lobes. In response to the required erosion and deposition, the river so dramatically alters channel grain size and channel geometry that the increase of sinuosity expected in the tectonically steepened valley does not occur.
Harding, K.A., and D.C. Ford, Impacts of Primary Deforestation Upon Limestone Slopes in Northern Vancouver-Island, British-Columbia, Environmental Geology, 21 (3), 137-143, 1993.
Effects of deforestation upon slopes in limestones and in volcanic rocks in the Benson River valley, northern Vancouver Island, have been investigated quantitatively. Postlogging soil erosion and vegetal regeneration success were assessed by measuring soil depth, percent bare rock and moss cover, and the numbers and diversity of trees, shrubs, and plants on 25 sampling sites, each containing ten measuring quadrats selected at random. Sixteen sites were on the Quatsino Formation, a well-karstified limestone, and nine on the Karmutsen Formation of basaltic lavas. Eight sites were of virgin forest, 16 were logged between 1970 and 1983, and one (on limestone) was logged in 1911. Both bedrock types were significantly affected by the cutting. There was greater loss of soil and an increase in bare rock on the limestones. Erosion was increased significantly by burning on the limestones but not on the volcanics. Within- group comparisons on the limestones determined that steeper slopes and harder burned areas suffered the most and are slowest to regenerate. Volume of timber on the 1911 site was 19 percent of that in similar uncut forest sites. It appears that complete recovery on the barren limestone slopes will require at least some centuries.
Harris, T., and K.S. Richards, Design and calibration of a recording bedload trap, Earth Surface Processes and Landforms, 20 (8), 711-720, 1995.
Harris, C.K., and P.L. Wiberg, Approaches to quantifying long-term continental shelf sediment transport with an example from the Northern California STRESS mid-shelf site, Continental Shelf Research, 17 (11), 1389-1418, 1997.
Harvey, J.W., and K.E. Bencala, The Effect of Streambed Topography On Surface-Subsurface Water Exchange in Mountain Catchments, Water Resources Research, 29 (1), 89-98, 1993.
A numerical hydrological simulation suggested that water exchange between stream channels and adjacent aquifers is enhanced by convexities and concavities in streambed topography. At St. Kevin Gulch, an effluent stream in the Rocky Mountains of Colorado, subsurface hydraulic gradients and movement of ionic tracers indicated that stream water was locally recharged into well-defined flow paths through the alluvium. Stream water-filled flow paths in the alluvium (referred to as substream flow paths) returned to the stream a short distance downstream (1 to 10 m). Recharge to the substream flow paths occurred where stream water slope increased, at the transition from pools (<1%) to steeper channel units (5-20%). Return of substream flow paths to the stream occurred where stream water slope decreased, at the transition from steeper channel units to pools. A net water flux calculation is typically used to characterize water and solute fluxes between surface and subsurface zones of catchments. Along our study reach at St. Kevin Gulch the net inflow of water from subsurface to stream (1.6 mL s-1 m-1) underestimated the gross inflow (2.7 mL s-1 m-1) by 40%. The influence of streambed topography is to enhance hydrological fluxes between stream water and subsurface zones and to prolong water-sediment contact times; these effects could have important consequences for solute transport, retention. and transformation in catchments.
Harvey, B.C., and T.E. Lisle, Effects of suction dredging on streams: A review and an evaluation strategy, Fisheries, 23 (8), 8-17, 1998.
Suction dredging for gold in river channels is a small-scale mining practice whereby streambed material is sucked up a pipe, passed over a sluice box to sort out the gold, and discarded as tailings over another area of bed. Natural resource managers should be concerned about suction dredging because it is common in streams in western North America that contain populations of sensitive aquatic species. It also is subject to both state and federal regulations, and has provided the basis for litigation. The scientific literature contains few peer-reviewed studies of the effects of dredging, but knowledge of dredging practices, and the biology and physics of streams suggests a variety of mechanisms linking dredging to aquatic resources. Effects of dredging commonly appear to be minor and local, but natural resource professionals should expect effects to vary widely among stream systems and reaches within systems. Fishery managers should be especially concerned when dredging coincides with the incubation of embryos in stream gravels or precedes spawning runs soon followed by high flows. We recommend that managers carefully analyze each watershed so regulations can be tailored to particular issues and effects. Such analyses are part of a strategy to (1) evaluate interactions between suction dredging and other activities and resources; (2) use this information to regulate dredging and other activities; (3) monitor implementation of regulations and on- and off-site effects of dredging; and (4) adapt management strategies and regulations according to new information. Given the current level of uncertainty about the effects of dredging, where threatened or endangered aquatic species inhabit dredged areas, fisheries managers would be prudent to suspect that dredging is harmful to aquatic resources.
Harvey, B.C., R.J. Nakamoto, and J.L. White, Influence of large woody debris and a bankfull flood on movement of adult resident coastal cutthroat trout (Oncorhynchus clarki) during fall and winter, Canadian Journal of Fisheries and Aquatic Sciences, 56 (11), 2161-2166, 1999.
To improve understanding of the significance of large woody debris to stream fishes, we examined the influence of woody debris on fall and winter movement by adult coastal cutthroat trout (Oncorhynchus clarki) using radiotelemetry. Fish captured in stream pools containing large woody debris moved less than fish captured in pools lacking large woody debris or other cover. Fish from pools lacking cover commonly moved to habitats with large boulders or brush, particularly during the day. Movements by fish over 1-day periods were strongly influenced by large woody debris or other elements providing cover. Fish initially found in habitats lacking large woody debris, large boulders, or brush cover moved the most extensively, while fish initially found in pools with large woody debris moved the least. Fish did not move extensively in response to a bankfull flood, although some moved to habitat downstream of large woody debris in tributaries or secondary channels. Habitat downstream of woody debris in the main channel was not used during the flood, apparently because of extreme turbulence. Overall, these observations provide additional evidence for the value of habitat complexity to some stream fishes and support previous observations of minimal effects of flooding on adult fish.
Harvey, A.M., Coupling between hillslopes and channels in upland fluvial systems: implications for landscape sensitivity, illustrated from the Howgill Fells, northwest England, Catena, 42 (2-4), 225-250, 2001.
The sensitivity of upland fluvial systems depends on the magnitude and frequency of sediment and flood producing events, modified by the internal coupling characteristics of the system. This paper assesses the role of hillslope/channel coupling for the sensitivity of upland geomorphic systems, using evidence from a 30-year monitoring programme of geomorphic change in the Carlingill valley, Howgill Fells, northwest England. In the hillslope zone, there is little sediment supply to the stream system. Locally, slope failures occur in response to extreme events (six such events in 30 years within the ca. 6 km(2) Carlingill valley). In the footslope coupling zone, basally induced gullies are major sediment sources to the stream. Sediment-production events occur ca. 30 times per year, feeding sediment to basal debris cones. Stream floods which can entrain these sediments occur once every ca. 2-5 years. Stream channel morphology is adjusted to this regime. Downstream of gullies, channels are wide and braided; elsewhere they are narrow and single-thread. As the gullies develop, however, this coupling weakens and the eroding slopes eventually stabilise by revegetation. Over the 30-year monitoring period, there has been a progressive trend towards gully stabilisation, and an associated reduction in channel instability. Massive destabilisation may occur in response to rare extreme flood events. Such an event (return period > 100 years) occurred in neighbouring Langdale and Bowderdale valleys in June 1982. That event destabilised the system, causing slope failures, fan deposition, and in some places, a switch in channel style to wide braided channels. Since 1982 there has been a progressive recovery by slope stabilisation and single- thread sinuous channels have become reestablished. A different style of extreme event occurred in Carlingill in October 1998, in response to the wettest week in the 30-year period. A slope failure fed debris flows 400 m downslope, almost coupling with the channel system. Future climatic change could render the system prone to destabilisation, through either extreme flood events or through major slope failures. (C) 2001 Elsevier Science B.V. All rights reserved.
Haschenburger, J.K., and M. Church, Bed material transport estimated from the virtual velocity of sediment, Earth Surface Processes and Landforms, 23 (9), 791-808, 1998.
Haschenburger, J.K., A probability model of scour and fill depths in gravel-bed channels, Water Resources Research, 35 (9), 2857-2869, 1999.
Hassan, M.A., and I. Reid, The Influence of Microform Bed Roughness Elements On Flow and Sediment Transport in Gravel Bed Rivers, Earth Surface Processes and Landforms, 15 (8), 739-750, 1990.
Pebble clusters are reported widely as characteristic of gravel river beds and are known to influence the initial entrainment of bedload. A field assessment suggests that their distribution is not ubiquitous, favouring channel bars, but also reveals a tendency towards a preferred streamwise spacing. A series of laboratory flume experiments shows that flow resistance rises to, and falls from, a peak value as the longitudinal spacing of pebble clusters decreases, in a manner similar to that shown by others for strip roughness, isolated blocks, and simulated ripples and dunes. The experiments also reveal a strong inverse relationship between bedload flux rates and the flow resistance induced by the concentration of pebble clusters. It is concluded that pebble cluster spacing tends towards an equilibrium that is regulated by a feedback process involving sediment transport rates and that the spatial concentration of these microforms will adjust to the point where they induce maximum flow resistance.
Hassan, M.A., and M. Church, Experiments on surface structure and partial sediment transport on a gravel bed, Water Resources Research, 36 (7), 1885-1895, 2000.
Eight flume experiments were conducted to study the development of bed surface texture and structure in the presence of partial bed material transport. The experiments have two phases, a no- feed degradational phase followed by a feeding phase. A surface structure of irregular, reticulate stone nets and clusters was developed before sediment feeding commenced. Bed load transport equaled or slightly exceeded the fed supply, except at the highest feed rate. The bed structure was maintained, but bed surface texture fined with increasing sediment load. The two phenomena may coexist because the largest grains on the bed moved only very sporadically. The actual sediment transport rates were much less than the expected rate calculated from the ratio of bed surface grain size to transported grain size. The difference reflects the increase in bed stability introduced by the bed structure. Between 17% and 47% of the bed shear stress is estimated to be carried by the structure, <4% being absorbed by the load, while the bed grains carried the balance of the stress. Bed material transport is exceedingly sensitive to bed surface structure and grain size, which raises concerns about the realizable precision of grain size measurements and characterization of the structure.
Hassan, M.A., and M. Church, Sensitivity of bed load transport in Harris Creek: Seasonal and spatial variation over a cobble-gravel bar, Water Resources Research, 37 (3), 813-825, 2001.
Bed load sediment was caught in pit traps at several locations on a bar in Harris Creek, a cobble-gravel stream with a nivally dominated hydrograph, a structurally highly organized bed, and very low rates of bed material transport. Observations were made during two spring freshets. In order to obtain representative grain size distributions of the material in transport, the traps were left for periods of up to 24 hours, so that samples of up to 30 kg were recovered. We examine the sensitivity of bedload flux to flow variations via trap- specific ratings for narrowly defined textural subranges. All the ratings are very sensitive, indicating that bed load flux remains in the regime of "partial transport." The ratings also exhibited seasonal hysteresis and varied from trap to trap and from year to year. At one trap the ratings for large material are distinctly segmented, with no strong correlation for the highest flows. Significant transport for material >8 mm in size begins at similar to7 m(3) s(-1), considerably higher than for sand. At flows competent to move the local bed gravel the portion of the sand load between 0.25 and 0.50 mm goes into suspension (finer material being dominantly suspended at all flows). Most of the sand transported at <7 m(3) s(-1) is washed in from upstream while the local bed remains stable. Auxiliary tracer studies demonstrate that at no observed stage (up to mean annual flood level) was the local bed generally mobilized.
Hattingh, J., and W.K. Illenberger, Shape Sorting of Flood-Transported Synthetic Clasts in a Gravel-Bed River, Sedimentary Geology, 96 (3-4), 181-190, 1995.
An experiment was set up in a gravel-bed river to test shape- sorting of gravel-size clasts. Synthetic clasts representing four shape types were used. Spheres were entrained in larger numbers than the other shapes, and travelled furthest. Rods and blades were intermediate in mobility. Discs moved the shortest distance, and in the least numbers. The angle of repose, and therefore the pivotability of clasts in combination with lift and drag forces exerted on the clast, will determine if a clast will be entrained or not as well as the shear stress needed for the clast to maintain motion. A sphere projects relatively higher than the other shape types of equal volume and will induce a higher degree of flow separation in its wake than other shape types. Therefore larger components of lift and drag forces exerted by water flow will be present to set this shape type in motion or to maintain motion. The prolate clasts have a small angle of repose compared to discoid clasts and will roll much more readily. The imbricated orientation assumed by discoid and sometimes blade-shaped clasts is a very stable position. Very high applied shear stress will be needed to dislodge imbricated discs.
Heimsath, A.M., W.E. Dietrich, K. Nishiizumi, and R.C. Finkel, Stochastic processes of soil production and transport: Erosion rates, topographic variation and cosmogenic nuclides in the Oregon Coast Range, Earth Surface Processes and Landforms, 26 (5), 531-552, 2001.
Landscapes in areas of active uplift and erosion can only remain soil-mantled if the local production of soil equals or exceeds the local erosion rate. The soil production rate varies with soil depth, hence local variation in soil depth may provide clues about spatial variation in erosion rates. If uplift and the consequent erosion rates are sufficiently uniform in space and time, then there will be tendency toward equilibrium landforms shaped by the erosional processes. Soil mantle thickness would adjust such that soil production matched the erosion. Previous work in the Oregon Coast Range suggested that there may be a tendency locally toward equilibrium between hillslope erosion and sediment yield. Here results from a new methodology based on cosmogenic radionuclide accumulation in bedrock minerals at the base of the soil column are reported. We quantify how soil production varies with soil thickness in the southern Oregon Coast Range and explore further the issue of landscape equilibrium. Apparent soil production is determined to be an inverse exponential function of soil depth, with a maximum inferred production rate of 268 m Ma(-1) occurring under zero soil depth. This rate depends, however, on the degree of weathering of the underlying bedrock. The stochastic and large-scale nature of soil production by biogenic processes leads to large temporal and spatial variations in soil depth; the spatial variation of soil depth neither supports nor rejects equilibrium morphology. Our observed catchment-averaged erosion rate of 117 m Ma(-1) is, however, similar to that estimated for the region by others, and to soil production rates under thin and intermediate soils typical for the steep ridges. We suggest that portions of the Oregon Coast Range may be eroding at roughly the same rate, but that local competition between drainage networks and episodic erosional events leads to landforms that are out of equilibrium locally and have a spatially varying soil mantle. Copyright (C) 2001 John Wiley & Sons, Ltd.
Heller, P.L., C. Paola, I.G. Hwang, B. John, and R. Steel, Geomorphology and sequence stratigraphy due to slow and rapid base-level changes in an experimental subsiding basin (XES 96- 1), Aapg Bulletin, 85 (5), 817-838, 2001.
Subsidence is a major factor in the accumulation and architecture of natural basin fills. A recently built experimental facility (Experimental Earthscape Facility [XES]) at St. Anthony Falls Laboratory of the University of Minnesota incorporates, for the first time, a flexible subsiding floor in its design. Thus the experimental basin can model erosion and deposition associated with independent variations in sediment supply, absolute base-level change, and rates and geometries of subsidence. The results of the first experiment in a prototype basin (1 x 1.6 x 0.8 m) are described here, wherein the stratigraphic development associated with first slow and then rapid base-level cycles in a basin that has a sag geometry has been analyzed. A videotape of the experiment and subsequent serial slicing of the dried strata in the basin allow interpretation of the sequence development under conditions of precisely known changes of absolute base level, subsidence, and sedimentation. Relative base-level changes, which strongly varied in the basin owing to the sag geometry of subsidence, seem to exert primary control on sedimentary patterns, although autocyclic changes were also important. Style of sequence boundaries differed between slow and fast base-level falls. During the slow base-level fall, an incised valley developed once the shoreline prograded out of the zone of maximum subsidence, suggesting that incision at the shoreline may be very sensitive to changes in relative base level. Once started, however, the valley quickly widened, by knickpoint retreat, into a broad, low-relief erosion surface that stretched across the entire basin. As erosion took place at the knickpoint, deposition occurred immediately downflow, so both the knickpoint and the upstream limit of deposition migrated landward together, producing a strong time-transgressive erosion and onlap sequence. The stratigraphic record of this sequence boundary is a single yet Very subtle widespread unconformity that becomes conformable downstream, which is difficult to trace in stratigraphic cross section. In contrast, the incised valley that formed during the rapid baselevel fall was relatively narrow, deep, and lengthened over time as deposits at the mouth of the valley were gradually exposed and incised through. Wholesale backfilling of the incised valley did not begin until the rapid base-level rise started. As a result, the rapid base-level, change produced a more easily recognized incised valley in the stratigraphic record than did the slow base-level change. Potential reservoir development within the strata is evaluated by means of a gray-scale proxy for porosity. Four distinctive zones of enhanced reservoir quality occurred in the basin: the most proximal part of the basin; the upper part of growth-fault-bounded sedimentary wedges; deep-water forced regressive systems tract composed of grainflow deposits; and transgressive systems tract formed during the rapid base-level rise. This distribution of relatively porous units suggests that, for a variety of reasons, rapid sea level cycles may produce the best reservoir units.
Helmer, E.H., The landscape ecology of tropical secondary forest in montane Costa Rica, Ecosystems, 3 (1), 98-114, 2000.
Multinomial logistic models of land use/land cover in montane Costa Rica and landscape pattern analysis showed that relative to agriculture, secondary forest occurred closer to old-growth forest, further from roads, in forest reserves, and at higher elevations. Collinearity between explanatory variables yielded simple multivariate models; proportion of surrounding old growth predicted secondary forest most accurately. An old- growth matrix [mean patch size (MPS) 24.5 ha], located mainly within protected areas, dominated elevations greater than 2500 m. A matrix of agriculture (MPS 23.5 ha), with smaller patches (approximately 9 ha) of secondary forest and old growth, dominated elevations from 1500 to 2500 m. Combining secondary forest with old growth decreased forest parch number and increased MPS from 7.3 to 37.1 ha. I concluded that: (a) secondary forest pattern is nonrandom, so ancillary data will aid its mapping with satellite imagery. The variables elevation, agriculture distance, road distance, and population density distinguished secondary forest from old growth with 74% accuracy; (b) socioeconomic and biological forces probably interact to create these secondary forest patterns; and (c) the strong association between secondary forest and old growth supports the concept that tropical forest recovery depends on the landscape structure of remnant forest.
Henshaw, P.C., and D.B. Booth, Natural restabilization of stream channels in urban watersheds, Journal of the American Water Resources Association, 36 (6), 1219-1236, 2000.
Stream channels are known tb change their form as a result of watershed urbanization, but do they restabilize under subsequent conditions of constant urban land use? Streams in seven developed and developing watersheds (drainage areas 5-35 km(2)) in the Puget Sound lowlands were evaluated for their channel stability and degree of urbanization, using geld and historical data. Protocols for determining channel stability by visual assessment, calculated bed mobility at bankfull flows, and resurveyed cross-sections were compared and yielded nearly identical results. We found that channel restabilization generally does occur within one or two decades of constant watershed land use, but it is not universal. When (or if) an individual stream will restabilize depends on specific hydrologic and geomorphic characteristics of the channel and its watershed; observed stability is not well predicted by simply the magnitude of urban development or the rate of ongoing land-use change. The tendency for channel restabilization suggests that management efforts focused primarily on maintaining stability, particularly in a still- urbanizing watershed, may not always be necessary. Yet physical stability alone is not a sufficient condition for a biologically healthy stream, and additional rehabilitation measures will almost certainly be required to restore biological conditions in urban systems.
Herget, J., Holocene development of the River Lippe Valley, Germany: A case study of anthropogenic influence, Earth Surface Processes and Landforms, 25 (3), 293-305, 2000.
Heritage, G.L., L.J. Broadhurst, and A.L. Birkhead, The influence of contemporary flow regime on the geomorphology of the Sabie River, South Africa, Geomorphology, 38 (3-4), 197-211, 2001.
The existence of a channel-funning, 'dominant' or 'bankfull' discharge has been applied, with some success, to a variety of alluvial river systems in temperate areas. This paper presents the results of an investigation into the relationship between flow magnitude and frequency, and the geomorphological units of the Sable River in the Mpumalanga Province, South Africa. The river is perennial, however, it exhibits an extreme seasonal flow regime. The river has been subject to incision (100,000- 10,000 years ago), which exposed bedrock areas as topographic highs within a wide macro-channel. Zones of deposition have created alluvial sections resulting in a morphologically diverse river system. Stage-discharge relationships have been observed and constructed for 23 monitoring sites on the Sable River. These have been used in conjunction with a 62-year calibrated simulated daily discharge record, to generate inundation frequencies for the morphological units present at each site. This includes results using annual maximum series data and time spans for activation, using the continuous daily flow data. The results reveal that the overall form of the cross-section is not related to a single channel-forming discharge, instead, a complex relationship exists whereby the section is influenced by the entire flow regime. The results do however suggest a poorly defined division of morphological units within the incised macro-channel, namely, those influenced by perennial, seasonal and infrequent flows. This relationship is best demonstrated by the morphological units associated with the perennial, active channels in alluvial sections. which correlate with the low flow regime (1-2-year return period on the annual maximum series), and larger macro- channel deposits which are related to rarer higher flows. Climatic wet and dry cycles, human influences and the physical effect of bedrock in the macro-channel further complicate the inundation pattern, resulting in disequilibrium conditions between channel form and contemporary flow regime on the Sable River. Macro-channel sedimentary deposits, ill particular, show no consistent relationship with a particular segment of the flow regime, being inundated by flows of between a 10- and 50- year return period. (C) 2001 Elsevier Science B.V. All rights reserved.
Heritage, G.L., M.E. Charlton, and S. O'Regan, Morphological classification of fluvial environments: An investigation of the continuum of channel types, Journal of Geology, 109 (1), 21-33, 2001.
Bedrock-controlled channel systems exhibit considerable morphological variation. Both bedrock-influenced and alluvial morphological units coexist to forma system of changing channel patterns in response to changes in the relative influence of the controlling process variables. This article investigates the morphological composition of the bedrock-influenced Sabie River, Mpumalanga Province, South Africa, mapping 25 km of river channel at the scale of individual morphological units. Cluster and discriminant analyses define objective reach-scale "channel type" assemblages based on morphological unit composition. A number of robust clusters emerged that could be broadly classified into five channel types, namely, bedrock anastomosed, mixed anastomosed, pool-rapid, braided, and alluvial single-thread. The cluster analysis revealed that these channel types fit on a continuum from bedrock-dominated channels to fully alluvial systems. Each channel type could also be characterized by a certain set of "dominant" morphological units, which changed from bedrock-influenced at one end of the continuum (bedrock anastomosed, pool-rapid) to alluvial deposits at the other (braided, alluvial single- thread). An investigation of the role of controlling process variables in defining these channel types revealed a broad link between the degree of bedrock influence and the amount of available energy within the system as defined by indices such as the flow regime and water-surface slope variation. It is clear that the bedrock-dominated channel types are characterized by energy levels in excess of those accepted for alluvial systems, and an extended river classification is presented for the Sabie River that includes these bedrock channels. The mixed anastomosing channel type on the Sabie River is characterized by higher available energy levels than braided or alluvial single-thread reaches. As such, it appears to be a higher-energy example of an anabranched system, probably formed as a result of sediment accumulation on top of a high-energy bedrock anastomosed channel template.
Hey, R.D., and C.R. Thorne, Stable Channels With Mobile Gravel Beds, Journal of Hydraulic Engineering-Asce, 112 (8), 671-689, 1986.
Hey, R.D., Bar Form Resistance in Gravel-Bed Rivers, Journal of Hydraulic Engineering-Asce, 114 (12), 1498-1508, 1988.
Heyerdahl, E.K., L.B. Brubaker, and J.K. Agee, Spatial controls of historical fire regimes: A multiscale example from the interior west, USA, Ecology, 82 (3), 660-678, 2001.
Our objective was to infer the controls of spatial variation in historical fire regimes. We reconstructed a multicentury history of fire frequency, size, season, and severity from fire scars and establishment dates of 1426 trees sampled on grids in four watersheds (similar to 64 plots, over similar to 1620 ha each) representative of the Blue Mountains, Oregon and Washington, USA. The influence of regional climate, a top-down control, was inferred from among-watershed variation in fire regimes, while the influence of local topography, a bottom-up control, was inferred from within-watershed variation. Before about 1900, fire regimes varied among and within watersheds, suggesting that both top-down and bottom-up controls were important. At the regional scale, dry forests (dominated by ponderosa pine), burned twice as frequently and earlier in the growing season in southern watersheds than in northern watersheds, consistent with longer and drier fire seasons to the south. Mesic forests (dominated by subalpine fir or grand fir) probably also burned more frequently to the south. At the local scale, fire frequency varied with different parameters of topography in watersheds with steep terrain, but not in the watershed with gentle terrain. Frequency varied with aspect in watersheds where topographic facets are separated by significant barriers to fire spread, but not in watersheds where such facets interfinger without fire barriers. Frequency varied with elevation where elevation and aspect interact to create gradients in snow-cover duration and also where steep talus interrupts fuel continuity. Frequency did not vary with slope within any watershed. The presence of both regional-scale and local-scale variation in the Blue Mountains suggests that top-down and bottom-up controls were both important and acted simultaneously to influence fire regimes in the past. However, an abrupt decline in fire frequency around 1900 was much greater than any regional or local variation in the previous several centuries and indicates that 20th-century fire regimes in these watersheds were dramatically affected by additional controls such as livestock grazing and fire suppression. Our results demonstrate the usefulness of examining spatial variation in historical fire regimes across scales as a means for inferring their controls.
Hill, D., P. Coquillard, and J. de Vaugelas, Discrete-event simulation of alga expansion, Simulation, 68 (5), 269-277, 1997.
In the middle of the eighties, the French coast of the Mediterranean Sea (in the vicinity of Monaco) had been the initial site of the development of Caulerpa taxifolia, a tropical alga introduced by mistake. At the present time, this species has colonized several thousand acres of the French coast and has been detected at numerous points of the north- Mediterranean coast from Messina (Italy) to the Baleares Islands (Spain). Since the colonization of the French coast presented an impressive growth rate, and in order to forecast the development of Caulerpa, a simulation study was engaged. The purpose of the study is to evaluate Caulerpa propagation by means of an algorithmic computer model involving less restrictions than a mathematical model. This paper proposes the coupling of a Geographical Information System with a discrete- event simulation model that has to cope with incomplete data and sampling difficulties encountered in the hostile environment of the sea. This paper also presents an effort of collaboration between scientists of different disciplines.
Hilmes, M.M., and E.E. Wohl, Changes in Channel Morphology Associated With Placer Mining, Physical Geography, 16 (3), 223-242, 1995.
Channel morphology along the Middle Fork of the South Platte River near Fairplay, Colorado has changed from 1859 to the present in association with placer gold mining. Based on the premise that mining destabilized channel-bed and bank sediments, we hypothesize that there will be a relation between mining and channel morphologic and sedimentologic characteristics. To quantify differences in channel morphology between mined and unmined reaches, four primary channel characteristics (shape, bed material, migration, and sinuosity) were examined. A discriminant function analysis showed no statistical difference in channel shape between mined and unmined reaches. Bed material in reaches where mining occurred in the channel can be distinguished from unmined reaches on the basis of mean grain-size, sorting, and skewness. Mean grain- size and sorting increase and the skewness of the distribution is nearly symmetrical in mined areas. Statistical differences in planimetric form also were observed. The channel has been more mobile and has a lower sinuosity in mined areas than in unmined areas. The loss of fines during mining decreases bank cohesion because vegetation is removed and cannot reestablish on the coarse tailing piles. The channel still has not recovered from the mining disturbance in 67-82 years. To be reclaimed, the tailing piles may have to be stabilized and the channel bed may need to reflect that of an undisturbed area.
Hodgson, R., and K.L. Young, Preferential groundwater flow through a sorted net landscape, Arctic Canada, Earth Surface Processes and Landforms, 26 (3), 319-328, 2001.
preferential suprapermafrost groundwater Row was observed in deepened channels lying between raised frost mounds. Here, saturated hydraulic conductivity, k, ranged from 90 to 1000 m/day but was only 0.1-1.0 m/day in the mound centres. A high proportion of fines occurs in the frost mound centre due to particle sorting, while channels contain gravels. Three approaches of areal weighting of k and groundwater flow, Q(s), across a wetland-upland boundary were explored. When percentage area covered by channels, mounds or gravel was considered, estimates of water flow on a daily and seasonal basis fell by 30 to 50 per cent. This study is of relevance to northern scientists who require reliable estimates of groundwater now across patterned ground landscapes. Copyright (C) 2001 John Wiley & Sons, Ltd.
Hoey, T.B., and A.J. Sutherland, Channel Morphology and Bedload Pulses in Braided Rivers - a Laboratory Study, Earth Surface Processes and Landforms, 16 (5), 447-462, 1991.
Bedload pulses in gravel-bed rivers have been widely reported in recent years and attempts have been made to relate them to channel morphology. Bedload transport and channel morphology were measured in a small-scale generic model of braided gravel- bed streams. Two experiments are described in which braided channels developed in a 14 m x 3 m sand tray. Total bedload output from the tray was weighed every 15 minutes. Stream bed geometry was surveyed every four hours. Pulses were observed in the bedload output time series, and were qualitatively related to the channel morphology immediately upstream of the measuring section. The Bagnold (1980) bedload equation generally overpredicts measured bedload transport rates when applied to channels that were in equilibrium or aggrading. Underprediction occurred when applied to degrading channels. Aggradation was associated with channel multiplication and bar deposition. Channel pattern simplification occurred when degradation took place, and bars emerged from the water flow. Development of phases of aggradation and degradation is dependent upon the three-dimensional geometry of the stream beds. Spatial and temporal feedback loops can be identified, enabling links between channel morphology and bedload transport rate to be directly identified.
Hoey, T., Temporal Variations in Bedload Transport Rates and Sediment Storage in Gravel-Bed Rivers, Progress in Physical Geography, 16 (3), 319-338, 1992.
Temporal variability in bedload transport rates and spatial variability in sediment storage have been reported with increasing frequency in recent years. A spatial and temporal classification for these features is suggested based on the gravel bedform classification of Church and Jones (1982). The identified scales, meso-, macro-, and mega- are each broad, and within each there is a wide range of processes acting to produce bedload fluctuations. Sampling the same data set with different sampling intervals yields a near linear relationship between sampling interval and pulse period. A range of modelling strategies has been applied to bed waves. The most successful have been those which allow for the three- dimensional nature of sediment storage processes, and which allow changes in the width and depth of stored sediment. The existence of bed waves makes equilibrium in gravel-bed rivers necessarily dynamic. Bedload pulses and bed waves can be regarded as equilibrium forms at sufficiently long timescales.
Hoey, T.B., and R. Ferguson, Numerical-Simulation of Downstream Fining By Selective Transport in Gravel-Bed Rivers - Model Development and Illustration, Water Resources Research, 30 (7), 2251-2260, 1994.
Hoey, T.B., and R.I. Ferguson, Controls of strength and rate of downstream fining above a river base level, Water Resources Research, 33 (11), 2601-2608, 1997.
Hoey, T.B., and B.J. Bluck, Identifying the controls over downstream fining of river gravels, Journal of Sedimentary Research, 69 (1), 40-50, 1999.
Holder, K., R. Montgomerie, and V.L. Friesen, A test of the glacial refugium hypothesis using patterns of mitochondrial and nuclear dna sequence variation in rock ptarmigan (Lagopus mutus), Evolution, 53 (6), 1936-1950, 1999.
The glacial refugium hypothesis (GRH) proposes that glaciers promoted differentiation and generation of intraspecific diversity by isolating populations in ice-free refugia. We tested three predictions of this hypothesis for the evolutionary divergence of rock ptarmigan (Lagopus mutus) during the Wisconsin glaciation of the late Pleistocene, To do this, we examined subspecies distributions, population genetic structure, and phylogenetic relationships in 26 populations across North America and the Bering Sea region. First, we analyzed sequence variation in the mitochondrial control region, in a nuclear intron (Gapdh), and in an internal transcribed spacer (ITS1). Control region sequences of 154 rock ptarmigan revealed strong population and phylogeographic structure. Variation in intron sequences of 114 rock ptarmigan also revealed significant population structure compatible with results for the control region. Rock ptarmigan were invariant for ITS1. Second, we show that five known Nearctic refugia and an Icelandic refugium are concordant with the current distribution of morphologically distinct subspecies; five of these six refugia are geographically concordant with the distribution of closely related control region haplotypes. Third, our estimates of the time since phylogenetic lineages diverged predated the last glacial maximum for all but two lineages. In addition, all lines of evidence suggest that two unknown refugia in the Bering Sea region supported rock ptarmigan during the Wisconsin,glaciation. Overall, our results are most consistent with the hypothesis that isolated populations of rock ptarmigan diverged in multiple refugia during the Wisconsin and that geographic variation reflects patterns of recolonization of the Nearctic after the ice receded. The GRH may therefore offer the most plausible explanation for similar biogeographic patterns in a variety of Nearctic vertebrates.
Holder, K., R. Montgomerie, and V.L. Friesen, Glacial vicariance and historical biogeography of rock ptarmigan (Lagopus mutus) in the Bering region, Molecular Ecology, 9 (9), 1265-1278, 2000.
In this paper, we address alternative hypotheses for the evolution of subspecies of rock ptarmigan (Lagopus mutus) endemic to the Aleutian Archipelago. To do this we examined patterns of genetic differentiation among populations of rock ptarmigan in the Aleutian Islands and parts of both Alaska and Siberia. Variation in mitochondrial control region sequences of 105 rock ptarmigan from 10 subspecies within the Bering region revealed three major phylogenetic lineages, two of which are endemic to the Aleutian Islands. Accordingly, haplotype and nucleotide diversities of rock ptarmigan within the archipelago are much higher than within mainland Alaska or Siberia. For Aleutian rock ptarmigan, analyses of molecular variance indicated significant genetic structuring and low estimates of gene flow among populations, despite small interisland distances within the archipelago. However; isolation by distance did not describe the pattern of gene flow or differentiation at this scale. Our estimates of divergence times of lineages suggest that Aleutian rock ptarmigan became isolated prior to the most recent Pleistocene glaciation event (late Wisconsin Stade) and that current patterns of genetic variation reflect the postglacial redistribution of divergent lineages and subsequent limited gene flow In addition, genetic divergence among lineages was concordant with the distribution of plumage types among subspecies. The patterns of genetic variation described here for rock ptarmigan provide evidence for the role of glacial vicariance in contributing to genetic diversity within this and other Bering region species.
Holmes, R.M., J.B. Jones, S.G. Fisher, and N.B. Grimm, Denitrification in a nitrogen-limited stream ecosystem, Biogeochemistry, 33 (2), 125-146, 1996.
Hooke, J.M., The Significance of Mid-Channel Bars in an Active Meandering River, Sedimentology, 33 (6), 839-850, 1986.
Hooke, J.M., and C.E. Redmond, River-Channel Changes in England and Wales, Journal of the Institution of Water and Environmental Management, 3 (4), 328-335, 1989.
Hooke, J.M., and J.M. Mant, Geomorphological impacts of a flood event on ephemeral channels in SE Spain, Geomorphology, 34 (3-4), 163-180, 2000.
A flood event occurred on 30 September 1997, in three catchments, Torrealvilla, Salada and Nogalte, in SE Spain which were being monitored for morphological change. Peak discharges were high in the Torrealvilla catchment, moderate in the Salada and low in the Nogalte. Detailed topographic surveys were made before and after the flood and from these DEMs of difference were constructed. The two sites with highest flow both underwent significant incision of the channel. At other sites, both scour and aggradation of the channel took place, with scour holes of up to 1 m depth eroded. Elsewhere, within the channels major erosion took place downstream of tracks and structures such as check dams that impeded sediment movement. The pattern and amounts of change show little relationship to independent factors, other than a scale effect of peak discharge. Behaviour of channels is closely related to local sediment supply. Sediment flux calculated from changes in volumes at the site is comparable with the other figures produced for ephemeral channels and much higher than for perennially flowing streams. (C) 2000 Elsevier Science B.V. All rights reserved.
Hornberger, M.I., S.N. Luoma, A. van Geen, C. Fuller, and R. Anima, Historical trends of metals in the sediments of San Francisco Bay, California, Marine Chemistry, 64 (1-2), 39-55, 1999.
Concentrations of Ag, Al, Cr, Cu, Fe, Hg, Mn, Ni, Pb, V and Zn were determined in six sediment cores from San Francisco Bay (SFB) and one sediment core in Tomales Bay (TB), a reference estuary. SFB cores were collected from between the head of the estuary and its mouth (Grizzly Bay, GB; San Pablo Bay, SP; Central Bay, CB; Richardson Bay, RE, respectively) and ranged in length from 150 to 250 cm. Concentrations of Cr, V and Ni are greater than mean crustal content in SEE and TB sediments, and greater than found in many other coastal sediments. However, erosion of ultramafic rock formations in the watershed appears to be the predominant source. Baseline concentrations of other metals were determined from horizons deposited before sediments were influenced by human activities and by comparing concentrations to those in TB. Baseline concentrations of Cu co-varied with Al in the SFB sediments and ranged from 23.7 +/- 1.2 mu g/g to 41.4 +/- 2.4 mu g/g. Baseline concentrations of other metals were less variable: Ag, 0.09 +/- 0.02 mu g/g; Pb, 5.2 +/- 0.7 mu g/g; Hg, 0.06 +/- 0.01 mu g/g; Zn, 78 +/- 7 mu g/g. The earliest anthropogenic influence on metal concentrations appeared as Hg contamination (0.3-0.4 mu g/g) in sediments deposited at SP between 1850 and 1880, apparently associated with debris from hydraulic gold mining. Maximum concentrations of Hg within the cores were 20 times baseline. Greater inventories of Hg at SP and GB than at RE verified the importance of mining in the watershed as a source. Enrichment of Ag, Pb, Cu and Zn first appeared after 1910 in the RE core, later than is observed in Europe or eastern North America. Maximum concentrations of Ag and Pb were 5-10 times baseline and Cu and Zn concentrations were less than three times baseline. Large inventories of Pb to the sediments in the GB and SP cores appeared to be the result of the proximity to a large Pb smelter. Inventories of Pb at RE are similar to those typical of atmospheric inputs, although influence from the Pb smelter is also suspected. Concentrations of Hg and Pb have decreased since the 1970s (to 0.30 mu g/g and 25 mu g/g, respectively) and were similar among all cores in 1990. Early Ag contamination was perhaps a byproduct of the Pb smelting process, but a modern source of Ag is also indicated, especially at RE and CB. (C) 1999 Elsevier Science B.V. All rights reserved.
Horne, G.S., and P.C. Patton, Bedload-Sediment Transport Through the Connecticut River Estuary, Geological Society of America Bulletin, 101 (6), 805-819, 1989.
Horvath, T.G., K.M. Martin, and G.A. Lamberti, Effect of zebra mussels, Dreissena polymorpha, on macroinvertebrates in a lake-outlet stream, American Midland Naturalist, 142 (2), 340-347, 1999.
Zebra mussels, Dreissena polymorpha, increase macroinvertebrate abundance on hard substrata in lakes and large rivers because they enhance surface area, substratum heterogeneity and the accumulation of benthic organic matter (BOM). We tested the hypothesis that zebra mussel colonization of hard substrata in a lake-outlet stream would similarly increase macroinvertebrate abundance. Zebra mussels were attached to artificial rocks (0.05 m(2)) in a crossed factorial design with two states of mussels (live or dead) and three densities [low (200.m(-2)), medium (500.m(-2)) or high (1000.m(-2))] plus a noncrossed control (no attached mussels). Rocks were placed in an erosional zone of a lake-outlet stream in southwestern Michigan that contained low densities of zebra mussels. After 28 d total macroinvertebrate abundance was significantly higher on rocks with high densities of zebra mussels, bur live or dead treatment had no effect on macroinvertebrate abundance. Family richness differed significantly among density treatments (high = medium > low = control), but Simpson's diversity index did not differ among treatments. We conclude that changes in macroinvertebrate community structure probably were related to the increased substrate complexity provided by zebra mussels.
Hotchkiss, R.H., and G. Parker, Shock Fitting of Aggradational Profiles Due to Backwater, Journal of Hydraulic Engineering-Asce, 117 (9), 1129-1144, 1991.
Depositional deltas form in the headwaters of most reservoirs. The deltas are characterized by a developing foreset slope that eventually approaches the submerged angle of repose. Deltas extend both upstream and downstream; downstream growth seriously depletes reservoir storage, while upstream evolution raises local ground-water levels and increases flood frequency. Flow separates as it passes downstream over the delta lip into the deeper part of the reservoir. Because of this flow separation and attendant recirculation, traditional finite difference modeling approaches are invalid near the steep foreset slope and cannot model delta growth accurately. A method of numerically fitting a vertical shock face to the evolving delta is developed and illustrated. Conditions upstream of the shock are described with the traditional St. Venant equations; downstream conditions are constant. A one- dimensional mobile-bed computer model is developed and compared to a simulated reservoir in a laboratory flume. The simulated delta closely matches the growth and propagation rate of the observed delta.
Houle, G., M.F. McKenna, and L. Lapointe, Spatiotemporal dynamics of Floerkea proserpinacoides (Limnanthaceae), an annual plant of the deciduous forest of eastern North America, American Journal of Botany, 88 (4), 594-607, 2001.
Because environmental filters are temporally and spatially heterogeneous, there often is a lack of significant relationship between the spatial patterns of successive life stages in plant populations. In this study, we determined the spatiotemporal relationships between different life stages in two populations of an annual plant of the deciduous forests of eastern North America. Floerkea proserpinacoides. Demographic surveys were done over a 4-yr period, and experiments were performed in the field and under controlled conditions to test for the effects of various environmental factors on population dynamics. There was a general lock of relationship between the spatial patterns of seed bank and seedling density, and a lack of similarity between their spatial correlograms. This was related mostly to the effects of spatially variable environmental filters operating on germination and emergence. However, environmental tilters acting on plant survival were stable through time and contributed to stabilize the density and spatial patterns of the populations. Despite density- dependent presenescence mortality, spatial patterns of seedlings and mature individuals were similar and their correlograms were alike, suggesting that mortality did not fully compensate for density. Estimated fecundity was negatively correlated with population density over the study period. Although flower production started only 2-3 wk after emergence, seed maturation mostly occurred at the end of the life cycle, just before the onset of plant senescence. Yet, individual fecundity was low for an annual plant, i.e., 3.0 +/- 0.5 mature seeds/plant (mean +/- 1 SE). Seed predation by vertebrates was not significant. Low soil moisture had little effect on the total number of seeds germinating, although it slowed down the germination process. In quadrats where leaf litter was experimentally doubled, seedling emergence was lower than in control quadrats: in quadrats where leaf litter was completely removed, emergence did not differ from that in control quadrats. Susceptibility to drought stress was higher for seedlings than for mature plants. Although the species does not maintain a long-term persistent soil seed bank, other factors, such as density-dependent fecundity and autogamy, may temper population fluctuations through time and reduce the probability of local extinction.
Houston, W.S., J.E. Huntoon, and D.L. Kamola, Modeling of Cretaceous foreland-basin parasequences, Utah, with implications for timing of Sevier thrusting, Geology, 28 (3), 267-270, 2000.
Hovius, N., C.P. Stark, H.T. Chu, and J.C. Lin, Supply and removal of sediment in a landslide-dominated mountain belt: Central Range, Taiwan, Journal of Geology, 108 (1), 73-89, 2000.
A strong coupling between hillslope and valley systems is often inferred for mountain landscapes dominated by bedrock landsliding. We reveal the nature of this link using data sets on landsliding and sediment transport from two montane catchments draining the eastern Central Range of Taiwan. Here, the magnitude-frequency distribution of landslides can be modeled by a robust power law, but this scale invariance is not mirrored in the sediment discharge at the mountain front. Instead, downstream sediment loads reflect a complex response to both sediment supply and ambient hydraulic conditions. The rivers do not transport significant amounts of sediment unless it is provided by hillslope mass wasting in the catchment. Removal of landslide debris is a function of the transport capacity of the stream at the site of entry; thus, there is a dual supply and transport control on sediment loads in bedrock- floored streams. Over a monitoring period of >25 yr, the bulk of the sediment leaving the mountain belt was supplied by climate-triggered mass wasting. Peaks in water discharge were always closely followed by sediment load maxima, and the rapid decay of the latter indicates an effective removal of most supply Where an important part of a catchment's sediment yield is derived from interfluves, sediment transport cannot simply be estimated from known water discharge time series, using a sediment rating curve, but requires instead a detailed knowledge of the spatial and temporal patterns of hillslope mass wasting and sediment transfer into the fluvial system.
Howard, A.D., and T.R. Knutson, Sufficient Conditions For River Meandering - a Simulation Approach, Water Resources Research, 20 (11), 1659-1667, 1984.
Howard, A.D., W.E. Dietrich, and M.A. Seidl, Modeling Fluvial Erosion On Regional to Continental Scales, Journal of Geophysical Research-Solid Earth, 99 (B7), 13971-13986, 1994.
Hsieh, M.L., and P.L.K. Knuepfer, Middle-late Holocene river terraces in the Erhjen River Basin, southwestern Taiwan - implications of river response to climate change and active tectonic uplift, Geomorphology, 38 (3-4), 337-372, 2001.
We reconstruct the Holocene river history of the Erhjen River(area: 140 km(2)) by correlating river terraces aided by 28 radiocarbon dates. Multiple terraces developed in the lower Erhjen River since the middle Holocene; they converge downstream to the Coastal Plain. The rates of channel incision into bedrock calculated from these terraces at Yuehshihchieh are 7-8 mm/year during ca, 5.7-2.5 ka, 5 cm/year during 1.5-1.3 ka, and 1 cm/year since 1 ka; the last is close to the average incision rate since middle Holocene. Meanwhile, only a single but wide middle-late Holocene paleo-floodplain was developed in the upper Erhjen River; it was completely abandoned only after 0.8 ka, likely following an episode of base-level fall starting from the Coastal Plain. Based on the apparent downstream and upstream convergence of these dated terraces, we identify a doming structure or anticline within the basin, which results in a tilt rate of 10(-6) to 10(-7) per year in the lower Erhjen River valley. The major terraces here had different initial long profiles, which implies that a critical (graded) long profile may not be a prerequisite for formation of a wide erosional terrace surface. Instead, we propose that these terraces were initiated by a series of catastrophic rainfall events, probably climatic-related, which brought a large amount of bedload from hillslopes to prevent the channel from incising when valley widening was facilitated by high-discharge runoff. We find that not only terrace-surface formation but also channel incision can be strongly controlled by climatic-driven discharge and bedload conditions, as suggested by the contrast of bedrock incision rates we observe at Yuehshihchieh. Apparently, the climate and its effects on the landscape cannot be regarded as constant during the Holocene even in a humid tropical area like Taiwan. However, such a fluctuation of climate could only be recorded in a setting where rivers have a high tendency to incise so that multiple terraces can be created. The lower Erhjen River that is characterized by active tectonic tilting is an example of this setting. (C) 2001 Elsevier Science B.V. All rights reserved.
Huang, H.Q., and R.F. Warner, The Multivariate Controls of Hydraulic Geometry - a Causal Investigation in Terms of Boundary Shear Distribution, Earth Surface Processes and Landforms, 20 (2), 115-130, 1995.
Huang, H.Q., and G.C. Nanson, Vegetation and channel variation; A case study of four small streams in southeastern Australia, Geomorphology, 18 (3-4), 237-249, 1997.
Huang, H.Q., and G.C. Nanson, The influence of bank strength on channel geometry: An integrated analysis of some observations, Earth Surface Processes and Landforms, 23 (10), 865-876, 1998.
Huang, H.Q., and G.C. Nanson, Hydraulic geometry and maximum flow efficiency as products of the principle of least action, Earth Surface Processes and Landforms, 25 (1), 1-16, 2000.
Hubbell, D.W., H.H. Stevens, J.V. Skinner, and J.P. Beverage, New Approach to Calibrating Bed-Load Samplers, Journal of Hydraulic Engineering-Asce, 111 (4), 677-694, 1985.
Hudson, P.F., and J. Mossa, Suspended sediment transport effectiveness of three large impounded rivers, US Gulf Coastal Plain, Environmental Geology, 32 (4), 263-273, 1997.
Hugot, A., S. Zaleski, and P. Joseph, Phenomenological modeling of catastrophic dilute gravity flows, Oil & Gas Science and Technology-Revue De L Institut Francais Du Petrole, 55 (5), 471-483, 2000.
Hunt, A.G., A probabilistic treatment of fluvial entrainment of cohesionless particles, Journal of Geophysical Research-Solid Earth, 104 (B7), 15409-15413, 1999.
Hurtrez, J.E., F. Lucazeau, J. Lave, and J.P. Avouac, Investigation of the relationships between basin morphology, tectonic uplift, and denudation from the study of an active fold belt in the Siwalik Hills, central Nepal, Journal of Geophysical Research-Solid Earth, 104 (B6), 12779-12796, 1999.
The present study investigates correlations between an extensive range of geomorphic properties that can be estimated from a digital elevation model and the uplift rate on geological timescales. The analysis focuses on an area in the Siwalik Hills (central Nepal), where lithology and climate can be considered as uniform. This area undergoes rapid tectonic uplift at rates of up to 15 mm yr(-1), which are derived from the geometric pattern of a fault-bend model of fold growth. The selected geomorphic properties can be divided in two categories, depending on whether or not the vertical dimension is taken into account. None of the planar properties are significantly correlated to uplift rate, unlike those that include the vertical dimension, such as the: mean elevation of basins, hypsometric curve, and hypsometric integral, and relief defined by the amplitude factor of length scaling analysis. Correlation between relief and uplift rate is observed for all length scales of topography shorter than 600 m, which suggests that all orders of the streams are able to adjust to the tectonic signal. Simple mass balance considerations imply that the average elevation is only 10% of surface uplift, suggesting that a dynamic equilibrium has been reached quite rapidly. Using a simple two-process model for erosion, we find that fairly high diffusion coefficients (order of 10 m(2) yr(-1)) and efficient transport of the material by rivers are required. This unusually high value for mass diffusivity at small length scales may be obtained by either a very efficient linear diffusion or by landsliding. Actually, both processes may be active, which appears likely given the nature of the unconsolidated substratum and the favorable climatic conditions. Local relief in the study area may therefore be used to predict either uplift or denudation, but the prediction is calibrated only for that specific climatic and lithologic conditions and cannot be systematically applied to other contexts.
Ikeda, S., and N. Izumi, Width and Depth of Self-Formed Straight Gravel Rivers With Bank Vegetation, Water Resources Research, 26 (10), 2353-2364, 1990.
Inbar, M., and A.P. Schick, Bedload Transport Associated With High Stream Power, Jordan River, Israel, Proceedings of the National Academy of Sciences of the United States of America, 76 (6), 2515-2517, 1979.
Ingram, B.L., and P.K. Weber, Salmon origin in California's Sacramento-San Joaquin river system as determined by otolith strontium isotopic composition, Geology, 27 (9), 851-854, 1999.
Geochemical methods for distinguishing salmon of different runs would improve management practices designed to mitigate for declines in salmon populations in California's Sacramento-San Joaquin river system, Strontium isotopic measurements show a strong relationship between the Sr-87/Sr-86 ratio in hatchery water and the Sr-87/Sr-86 Patio in the otoliths (aragonitic ear bones) of juvenile chinook salmon (Oncorhynchus tshawytscha) raised in those waters. As a result of differences in basin geology from north to south along the western slope of the Sierra Nevada, important salmon spawning rivers within the Sacramento-San Joaquin river system have distinct Sr-87/Sr-86 ratios. Of the 10 rivers in this study, those in the Sacramento River drainage have lower Sr-87/Sr-86 ratios (0.7039-0.7063) than those in the San Joaquin River basin (0.7068-0.7092), with the exception of the American River, which has the highest Sr- 87/Sr-86 ratios in this study (average 0.7100), The combination of distinct river Sr-87/Sr-86 ratios and the relationship between water and otolith Sr isotope ratios indicates that this geochemical method can be used to identify the origin (and potentially the migration history) of juvenile, out-migrating salmon in the Sacramento-San Joaquin system.
Inoue, M., and S. Nakano, Effects of woody debris on the habitat of juvenile masu salmon (Oncorhynchus masou) in northern Japanese streams, Freshwater Biology, 40 (1), 1-16, 1998.
1. The effects of woody debris on stream habitat of juvenile masu salmon (Oncorhynchus masou) were examined at two spatial scales, stream reach and channel unit, for first- to third- order tributaries of the Teshio River in northern Hokkaido, Japan. The forty-eight study reaches were classified into three distinct types: coarse-substrate step-pool (CSP), coarse- substrate pool-riffle (CPR) and fine-substrate pool-riffle (FPR) reaches. Each reach type included reaches with different riparian settings, broadly classified as forest (relatively undisturbed forest and secondary forest after fires) or grassland (bamboo bushland and pasture). 2. The reach-scale analyses showed that neither total pool volume nor pool-to-pool spacing was correlated with woody debris abundance in any of the three reach types. Masu salmon density was positively correlated with both woody-debris cover area and total cover area, but not with total pool volume in the reaches. 3. Channel-unit-scale analyses revealed that woody debris reduced non-pool velocity, increased pool depth and retained fine sediment in pools in FPR reaches, where the size of woody debris was very large relative to the substrate material size. However, woody debris did not influence any of the hydraulic variables (depth, velocity, substrate) in either non-pools or pools of CSP and CPR reaches. Habitat use by masu salmon in non-pools or pools was affected by woody-debris cover area or total cover area rather than by hydraulic variables in any of the reach types. 4. The effects of woody debris on habitat at the reach- and channel-unit scales in the study area were less than those indicated by previous work in the Pacific Northwest, North America, owing to the relatively small size of the riparian trees. However, the overall results suggested that woody debris in the study area contributed to masu salmon habitat by providing cover at the smaller, microhabitat scale.
Inoue, M., and S. Nakano, Habitat structure along channel-unit sequences for juvenile salmon: a subunit-based analysis of in-stream landscapes, Freshwater Biology, 42 (4), 597-608, 1999.
1. Habitat structure and habitat use by juvenile masu salmon, Oncorhynchus masou Brevoort, in small streams in northern Hokkaido, Japan, were examined by considering 'subunits' (patches within channel units) as structural elements of stream reaches. 2. Whole wetted channel surfaces of three study reaches were divided into 0.5 x 0.5 m quadrats, which were grouped into eight subunit types according to water depth and velocity, and substratum conditions by a cluster analysis. The subunit distribution showed a regular mosaic pattern corresponding to the channel-unit sequence in each of the three reaches. 3. Juvenile masu salmon exhibited a strong preference for a subunit type characterized by greater depth and moderate current velocity (deep-moderate subunit; mean depth = 0.29 m; mean velocity = 0.19 m s(--1)). This subunit type usually occurred downstream of stretches with fast current. The preference of masu salmon for the deep-moderate subunit could be because of its usual spatial position in relation to other subunit types as well as to the characteristics of the subunit itself. 4. The results suggest that the value of a habitat is determined not only by the characteristics of the habitat itself, but also by those of adjacent habitats. Therefore, habitat use by stream fish should be studied in the context of the whole 'in-stream landscapes'.
Inoue, M., and S. Nakano, Fish abundance and habitat relationships in forest and grassland streams, northern Hokkaido, Japan, Ecological Research, 16 (2), 233-247, 2001.
The relationships between habitat variables and population densities of masu salmon (Oncorhynchus masou), rosyface dace (Leuciscus ezoe), Siberian stone leach (Noemacheilus barbatulus) and wrinklehead sculpin (Cottus nozawae) were examined by data collected at 55 reaches in forest and grassland streams in northern Hokkaido, Japan. Regression analysis suggested that salmon and dace densities were affected by water temperature (negative for salmon, positive for dace) and structural habitat factors (woody debris for salmon, pools for dace). Salmon density was higher in forest reaches than in grassland reaches, whereas dace density was higher in grassland reaches, suggesting that the removal of riparian forest had raised water temperature and allowed upstream invasions by dace. In contrast to salmon and dace, neither the density of leach nor sculpin differed between the forest and grassland reaches. For their densities, a negative effect of each on the other was most important, suggesting a strong effect of interspecific competition between leach and sculpin on their distributions. However, regression models also suggested that substrate heterogeneity mediated the outcome of their interspecific competition. On the basis of the results, a scenario is predicted for a fish-assemblage change with a typical land-development process in Hokkaido, and the importance of leaving or restoring riparian buffer for conservation and restoration of stream habitat is emphasized.
Isaak, D.J., and W.A. Hubert, Are trout populations affected by reach-scale stream slope?, Canadian Journal of Fisheries and Aquatic Sciences, 57 (2), 468-477, 2000.
Reach-scale stream slope and the structure of associated physical habitats are thought to affect trout populations, yet previous studies confound the effect of stream slope with other factors that influence trout populations. We isolated the effect of stream slope on trout populations by sampling reaches immediately upstream and downstream of 23 marked changes in stream slope on 18 streams across Wyoming and Idaho. No effect of stream slope on areal trout density was observed, but when trout density was expressed volumetrically to control for differences in channel cross sections among reaches in different slope classes, the highest densities of trout occurred in medium-slope reaches, intermediate densities occurred in high-slope reaches, and the lowest densities occurred in low-slope reaches. The relative abundance of large trout was reciprocal to the pattern in volumetric trout density. Trout biomass and species composition were not affected by stream slope. Our results suggest that an assumption made by many fish-habitat models, that populations are affected by the structure of physical habitats, is at times untenable for trout populations in Rocky Mountain streams and is contingent upon the spatial scale of investigation and the population metric(s) used to describe populations.
Isaak, D.J., and W.A. Hubert, Production of stream habitat gradients by montane watersheds: hypothesis tests based on spatially explicit path analyses, Canadian Journal of Fisheries and Aquatic Sciences, 58 (6), 1089-1103, 2001.
We studied how the features of mountain watersheds interact to cause gradients in three stream attributes: baseflow stream widths, total alkalinity, and stream slope. A priori hypotheses were developed before being tested in a series of path analyses using data from 90 stream reaches on 24 second- to fourth-order streams across a fifth-order Rocky Mountain watershed. Because most of the conventional least squares regressions initially calculated for the path analyses had spatially correlated residuals (13 of 15 regressions), spatially explicit regressions were often used to derive more accurate parameter estimates and significance tests. Our final working hypotheses accounted for most of the variation in baseflow stream width (73%), total alkalinity (74%), and stream slope (78%) and provide systemic views of watershed function by depicting interactions that occur between geomorphology, land surface features, and stream attributes. Stream gradients originated mainly from the unidirectional changes in geomorphic features that occur over the lengths of streams. Land surface features were of secondary importance and, because they change less predictably relative to the stream, appear to modify the rate at which stream gradients change.
Jackson, W.L., and R.L. Beschta, Influences of Increased Sand Delivery On the Morphology of Sand and Gravel Channels, Water Resources Bulletin, 20 (4), 527-533, 1984.
Jacobson, R.B., and K.B. Gran, Gravel sediment routing from widespread, low-intensity landscape disturbance, Current River basin, Missouri, Earth Surface Processes and Landforms, 24 (10), 897-917, 1999.
During the last 160 years, land-use changes in the Ozarks have had the potential to cause widespread, low-intensity delivery of excess amounts of gravel-sized sediment to stream channels. Previous studies have indicated that this excess gravel bedload is moving in wave-like forms through Ozarks drainage basins. The longitudinal, areal distribution of gravel bars along 160 km of the Current River, Missouri, was evaluated to determine the relative effects of valley-scale controls, tributary basin characteristics, and lagged sediment transport in creating areas of gravel accumulations. The longitudinal distribution of gravel-bar area shows a broad scale wave-like form with increases in gravel-bar area weakly associated with tributary junctions. Secondary peaks of gravel area with 1.8-4.1 km spacing (disturbance reaches) are superimposed on the broad form. Variations in valley width explain some, but not all, of the short-spacing variation in gravel-bar area. Among variables describing tributary drainage basin morphometry, present-day land use and geologic characteristics, only drainage area and road density relate even weakly to gravel-bar areal inventories. A simple, channel network-based sediment routing model shows that many of the features of the observed longitudinal gravel distribution can be replicated by uniform transport of sediment from widespread disturbances through a channel network. These results indicate that lagged sediment transport may have a dominant effect on the synoptic spatial distribution of gravel in Ozarks streams; present-day land uses are only weakly associated with present-day gravel inventories; and valley-scale characteristics have secondary controls on gravel accumulations in disturbance reaches. Copyright (C) 1999 John Wiley & Sons, Ltd.
Jacobson, P.J., K.M. Jacobson, P.L. Angermeier, and D.S. Cherry, Transport, retention, and ecological significance of woody debris within a large ephemeral river, Journal of the North American Benthological Society, 18 (4), 429-444, 1999.
Jacobson, P.J., K.M. Jacobson, P.L. Angermeier, and D.S. Cherry, Variation in material transport and water chemistry along a large ephemeral river in the Namib Desert, Freshwater Biology, 44 (3), 481-491, 2000.
Jacobson, P.J., K.M. Jacobson, P.L. Angermeier, and D.S. Cherry, Hydrologic influences on soil properties along ephemeral rivers in the Namib Desert, Journal of Arid Environments, 45 (1), 21-34, 2000.
Jacovkis, P.M., One-Dimensional Hydrodynamic Flow in Complex Networks and Some Generalizations, Siam Journal On Applied Mathematics, 51 (4), 948-966, 1991.
The one-dimensional hydrodynamic flow in complex networks that include many branches, junction points, and open boundary points is studied. The shallow-water equations are linearized, and the compatibility conditions at junction points and the boundary conditions at some or all of the open boundary points are analysed. Existence and uniqueness of smooth solutions is discussed and, under certain assumptions, proved. The necessary compatibility conditions depend on whether the flow is subcritical or super-critical. The results are extended to linear hyperbolic systems of more than two equations in networks. In particular, the flow over a network of channels with mobile (erodible) beds, modelled by means of a system of three equations, is analysed.
James, A., Time and the persistence of alluvium: River engineering, fluvial geomorphology, and mining sediment in California, Geomorphology, 31 (1-4), 265-290, 1999.
River managers need to understand fluvial systems as they change through time. Many river systems are presently in a state of flux as a result of substantial anthropogenic changes to water and sediment regimes and channel hydraulics. Yet, historical approaches to understanding river systems rarely receive adequate attention because historical methodologies are not conducive to the application of quantitative analysis. While there is limited precision in most historical reconstructions, the information derived from these studies constrains other interpretations and is essential to a full understanding of the behavior of fluvial systems. Geomorphology provides a perspective on river systems in which time - at various scales is interwoven into practical and theoretical aspects of scientific inquiry. Thus, geomorphology is important to our understanding of not only physical systems but also fundamental concepts of time. This study examines channel morphological changes in the Bear and American basins brought about by two episodes of sedimentation from hydraulic gold mining. The primary event was the production of more than 1 billion m(3) of sediment throughout the northern Sierra Nevada from 1853 to 1884 which caused aggradation in many channels across the Sierra foothills and Sacramento Valley. Assumptions by both engineers and geomorphologists that morphologic responses to this event were ephemeral, that sediment loads have returned to previous levels, and that deposits have stabilized, are not borne out by field and historical data in the Sacramento Valley. A secondary sedimentation event, not previously studied, was the production of at least 24 million m(3) of sediment during a period of licensed mining from 1893 to 1953. This episode of sedimentation has been largely overlooked as a geomorphic, hydrologic, or water quality event. Yet, channel morphologic responses in phase with mining during this period are demonstrated. Systematic changes in stage- discharge relationships reflect channel morphological changes that are relevant to flood risk assessments, stability of engineering structures on floodplains, and geomorphic interpretations. (C) 1999 Elsevier Science B.V. All rights reserved.
James, C.S., and W.E.L. Minter, Experimental flume study of the deposition of heavy minerals in a simulated witwatersrand sandstone unconformity, Economic Geology and the Bulletin of the Society of Economic Geologists, 94 (5), 671-688, 1999.
James, C.S., W. Liu, and W.R.C. Myers, Conveyance of meandering channels with marginal vegetation, Proceedings of the Institution of Civil Engineers-Water Maritime and Energy, 148 (2), 97-106, 2001.
Vegetation along the margins of meandering channels affects conveyance under both inbank and overbank flow conditions. Experiments using simulated vegetation with different channel and floodplain geometries have shown that vegetation increases resistance by introducing stem drag, but may also decrease it by reducing separation at tight bends. For inbank flows, bend resistance (including vegetation effects) is better accounted for by a bend curvature parameter than by sinuosity alone. Conveyance for overbank flows with marginal vegetation and straight floodplains can be predicted satisfactorily using the James and Wark method with adjustment for vegetation density.
Jimenez, O.F., and M.H. Chaudhry, Computation of Supercritical Free-Surface Flows, Journal of Hydraulic Engineering-Asce, 114 (4), 377-395, 1988.
Jin, Y.C., and P.M. Steffler, Predicting Flow in Curved Open Channels By Depth-Averaged Method, Journal of Hydraulic Engineering-Asce, 119 (1), 109-124, 1993.
A depth-averaged model formulated in the Cartesian coordinate system is introduced for simulating the velocity distribution in curved open channels. The finite element method is used to simplify the geometry problems in practical cases such as irregular cross sections and channels of varying plan curvature. The mathematical model consists of the depth- averaged continuity equation, the momentum equations, and two moment-of-momentum equations for closure purposes. The numerical analysis predicts satisfactory depth-averaged longitudinal and transverse velocities as well as reasonable secondary flows. The comparison of the numerical predication and the experimental results is included. The mathematical model discussed here can be applied to other channel flow problems where secondary flow and its effects are important.
Jin, Y.C., and B.Z. Li, The use of a one-dimensional depth-averaged moment of momentum equation for the nonhydrostatic pressure condition, Canadian Journal of Civil Engineering, 23 (1), 150-156, 1996.
A depth-averaged model formulated in the Cartesian coordinate system for curved open-channel flows is extended to solve problems where the effects of nonhydrostatic pressure distribution and nonuniform velocity distribution are significant. The nonhydrostatic pressure condition is added to the z-direction momentum equation assuming that the pressure deviation from the hydrostatic condition at the channel bed decreases linearly to the water surface. The pressure-effect terms are modified in both the moment of momentum and momentum equations. The resulting system of nonlinear equations is solved by a finite-element method. The derived model is then applied to four sophisticated nonuniform flow experiments from the literature. A comparison of the actual experimental results with their numerical prediction results, as calculated with the model, is presented. Generally speaking, a fairly good agreement for the depth-averaged velocities as well as reasonable perturbation profiles were obtained from this comparison. Therefore, it can be said that the depth-averaged model for open-channel flow is reasonably accurate under the given conditions.
Johnson, P.A., G.L. Gleason, and R.D. Hey, Rapid assessment of channel stability in vicinity of road crossing, Journal of Hydraulic Engineering-Asce, 125 (6), 645-651, 1999.
Johnson, S.L., F.J. Swanson, G.E. Grant, and S.M. Wondzell, Riparian forest disturbances by a mountain flood - the influence of floated wood, Hydrological Processes, 14 (16-17), 3031-3050, 2000.
Large floods can have major impacts on riparian forests. Here we examine the variability and spatial distribution of riparian forest responses along eight third- to fifth-order streams following a large flood ( similar to 100 year recurrence interval) in the Cascade Mountain Range of Oregon, We categorized disturbance intensity (physical force) exerted on riparian trees during floods into three classes: (i) purely fluvial (high water flow only); (ii) fluvial supplemented by dispersed pieces of floating wood (uncongested wood transport); (iii) fluvial with movement of batches of wood (congested wood transport). These types of material transport and associated classes of disturbance intensity resulted in a gradient of biotic responses of disturbance severity ranging from standing riparian trees inundated by high water, to trees toppled but still partially rooted, to complete removal of trees. High within-stream and among stream responses were influenced by pre-flood stream and riparian conditions as well as flood dynamics, especially the availability of individual pieces or congested batches of wood. Fluvial disturbance alone toppled fewer riparian trees than in reaches where floodwaters transported substantial amounts of wood. Debris flows delivered additional wood and sediment to parts of reaches of four of these study streams; riparian trees were removed and toppled for up to 1.5 km downstream of the debris flow tributary channel. Congested wood transport resulted in higher frequency of toppled trees and greater deposition of new wood levees along channel margins. The condition of the landscape at the time of a major flood strongly influenced responses of riparian forests. Recent and historic land-use practices, as well as the time since the previous large flood, influenced not only the structure and age of the riparian forests, but also the availability of agents of disturbance, such as large pieces of floating wood, that contribute to disturbance of riparian forests during floods. Copyright (C) 2000 John Wiley & Sons, Ltd.
Johnson, A.C., D.N. Swanston, and K.E. McGee, Landslide initiation, runout, and deposition within clearcuts and old-growth forests of Alaska, Journal of the American Water Resources Association, 36 (1), 17-30, 2000.
More than 300 landslides and debris flows were triggered by an October 1993 storm on Prince of Wales Island, southeast Alaska. Initiation, runout, and deposition patterns of landslides that occurred within clearcuts, second-growth, and old-growth forests were examined. Blowdown and snags, associated with cedar decline and "normal" rates of mortality, were found adjacent to at least 75 percent of all failures regardless of land use, Nearly 50 percent of the landslides within clearcuts occurred within one year following timber harvest; more than 70 percent of these sites had hydrophytic vegetation directly above failures. In following the runout paths of failures, significantly more erosion per unit area occurred within clearcuts than in old-growth forests on slopes with gradients from 9 to 28 degrees (16 to 54 percent). Runout length, controlled by hillslope position within deglaciated valleys, was typically longer in old-growth forests than in second growth and clearcuts (median values were 334, 201, and 153 m, respectively). Most landslides and debris flows deposited in first- and second-order channels before reaching the main stem channels used by anadromous fish. Slide deposits in old-growth forests were composed of a higher proportion of woody debris than deposits derived from slides in second growth or clearcuts.
Johnsson, M.J., R.F. Stallard, and N. Lundberg, Controls On the Composition of Fluvial Sands From a Tropical Weathering Environment - Sands of the Orinoco River Drainage- Basin, Venezuela and Colombia, Geological Society of America Bulletin, 103 (12), 1622-1647, 1991.
Fluvial sands in the Orinoco River drainage basin fall into three main compositional groupings: (1) sands of subarkose and arkose composition, from high-relief parts of the Guayana Shield, where crystalline rocks are exposed; (2) sands of litharenite and sublitharenite composition from the active orogenic belt at the western and northwestern margins of the drainage basin, and in those parts of the Llanos (Andean foreland basin) proximal to the mountain belt; and (3) sands of quartz-arenite composition, widespread throughout the remainder of the basin. Multicycle sand of quartz-arenite composition are produced from platform cover on parts of the elevated shield and from uplifted foreland-basin fill in the eastern Llanos. First-cycle sands of quartz-arenite composition are produced from granitic rocks on low-relief regions of the Guayana Shield and from reworked Holocene alluvium in parts of the western Llanos distal to the orogenic terranes. Erosion in the Orinoco River drainage basin may be described in terms of transport-limited and weathering-limited denudation regimes. In active orogenic terranes and in parts of the elevated shield, transport processes can remove weathered material as rapidly as it is produced by chemical weathering. Thin soils and short soil-mineral residence time result in sands that are incompletely chemically weathered and accurately reflect source-rock composition. In the orogenic terranes, subtle variations in source-rock lithology are preserved in sand composition. In contrast, in low-relief parts of the Guayana Shield and on flat erosion surfaces of the upland shield, weathering exceeds the rate at which transport processes can remove weathered material. Thick soils accumulate, soil- mineral residence time is long, and detritus is highly altered chemically. On much of the lowland Guayana Shield, upper soil layers consist of nearly pure quartz sand that erodes to produce first-cycle fluvial sand of quartz-arenite composition. On the alluvial plains of the western Llanos, storage of orogenically derived sediment allows time for substantial chemical weathering. Through reworking of the alluvial sequences, freshly eroded sediment is exchanged for older, compositionally more mature material. The chemically weathered component increases as rivers cross the Llanos, resulting in an increase in overall compositional maturity of bed-load sand away from the orogenic terranes. Rivers that rework the stored alluvium carry sands of quartz-arenite composition. Eolian recycling of sands between the exposed bed of the Orinoco mainstem and dune fields on the Llanos may also extend the duration of chemical weathering. Chemically weathered orogenically derived sand enters the Orinoco River on the left bank, while feldspathic shield-derived sand enters on the right bank. This geometry is responsible for the nearly total lack of longitudinal variation in sand composition along the 1,400- km length of the Orinoco River mainstem. Except in the upper 100 km of the Orinoco River mainstem, cross-channel heterogeneity in sand composition is also modest. Nevertheless, a weighted linear least-squares modeling approach suggests that sand moves down the Orinoco River mainstem in distinct pulses, perhaps corresponding to times of accelerated erosion in headwater regions. Because rivers that head in the orogenic terranes and traverse the Llanos contribute more than 99% of the sand in the lower Orinoco River mainstem, the composition of this sand is dominated by chemically weathered sands from the Llanos. The Orinoco River-the third largest river in the world-delivers first-cycle sands of quartz-arenite composition to its delta.
Johnston, C.E., E.D. Andrews, and J. Pitlick, In situ determination of particle friction angles of fluvial gravels, Water Resources Research, 34 (8), 2017-2030, 1998.
Jones, J.B., R.M. Holmes, S.G. Fisher, N.B. Grimm, and D.M. Greene, Methanogenesis in Arizona, USA dryland streams, Biogeochemistry, 31 (3), 155-173, 1995.
Jones, M.L., R.G. Randall, D. Hayes, W. Dunlop, J. Imhof, G. Lacroix, and N.J.R. Ward, Assessing the ecological effects of habitat change: Moving beyond productive capacity, Canadian Journal of Fisheries and Aquatic Sciences, 53, 446-457, 1996.
Jones, L.S., and N.F. Humphrey, Weathering-controlled abrasion in a coarse-grained, meandering reach of the Rio Grande: Implications for the rock record, Geological Society of America Bulletin, 109 (9), 1080-1088, 1997.
Jones, S.J., L.E. Frostick, and T.R. Astin, Climatic and tectonic controls on fluvial incision and aggradation in the Spanish Pyrenees, Journal of the Geological Society, 156, 761-769, 1999.
Jones, J.A., F.J. Swanson, B.C. Wemple, and K.U. Snyder, Effects of roads on hydrology, geomorphology, and disturbance patches in stream networks, Conservation Biology, 14 (1), 76-85, 2000.
We outline a view of how road networks interact with stream networks at the landscape scale and, based on examples from recent and current research, illustrate how these interactions might affect biological and ecological processes in stream and riparian systems. At the landscape scale, certain definable geometric interactions involving peak flows (floods) and debris flows (rapid movements of soil, sediment, and large wood down steep stream channels) are influences by the arrangement of the road network relative to the stream network. Although disturbance patches are created by peak-flow and debris-flow disturbances in mountain landscapes without roads, roads can alter the landscape distributions of the starting and stopping points of debris flows, and they can alter the balance between the intensity of flood peaks and the stream network's resistance to change. We examined this conceptual model of interactions between road networks and stream networks based on observations from a number of studies in the H. J. Andrews Experimental Forest, Oregan (U.S.A.). Road networks appear to affect floods and debris flows and thus modify disturbance patch dynamics in stream and riparian networks in mountain landscapes. We speculate that these changes may influence the rates and patterns of survival and recovery of disturbed patches in stream networks, affecting ecosystem resilience, and we outline an approach for detecting such effects based on a patch dynamics perspective. A field sampling scheme for detecting the magnitude of various road effects on stream and riparian ecology could involve (1) landscape stratification of inherent stream network susceptibility to floods or debris flows, (2) overlay of road and stream networks and creation of areas with various densities of road-stream crossings, and (3) designations of expected high- and low-impact stream segments based on numbers of upstream road-stream crossings where sampling of selected biological variables would be conducted.
Jones, A.P., Late quaternary sediment sources, storage and transfers within mountain basins using clast lithological analysis: Pineta Basin, central Pyrenees, Spain, Geomorphology, 34 (3-4), 145-161, 2000.
Understanding basin-wide sediment dynamics, both spatially and temporally, is an important antecedent to eventual quantitative interpretation of sediment transfer within mountain fluvial systems. This paper describes an attempt to trace sediment transfer modes and pathways using clast lithological analysis in a small mountain basin strongly influenced by glaciation: the Pineta Basin in the central Pyrenees of Spain. The paper interprets slope-channel interaction by encompassing the whole basin, enabling staged sedimentary pathways to be revealed. Additionally, bed-material textures of the modem rivers and youngest La Sarra Terrace were investigated to provide further information on the geomorphic coupling of the system. Relatively few studies have taken this approach. Glacial and later, fluvial systems transferred the sediments creating laterally extensive, polylithological sediment stores. Local depositional systems overprint this inherited signature. To what extent depends on the size and energy of the local system. Significant impacts are made by conduits, such as large-scale fluvially dominated fans and waterfalls, which deliver local lithologies to the main river. Conduits may be part of the main river system or part of the tributary system. Conduits are the most important elements when considering provenance studies and theoretical modelling. (C) 2000 Elsevier Science B.V. All rights reserved.
Jowett, I.G., Hydraulic geometry of New Zealand rivers and its use as a preliminary method of habitat assessment, Regulated Rivers-Research & Management, 14 (5), 451-466, 1998.
Julien, P.Y., Sediment Transport in Shallow Flows - Discussion, Journal of Hydraulic Engineering-Asce, 113 (9), 1214-1215, 1987.
Julien, P.Y., and J. Wargadalam, Alluvial Channel Geometry - Theory and Applications, Journal of Hydraulic Engineering-Asce, 121 (4), 312-325, 1995.
Juracek, K.E., Channel stability downstream from a dam assessed using aerial photographs and stream-gage information, Journal of the American Water Resources Association, 36 (3), 633-645, 2000.
Jurmu, M.C., and R. Andrle, Morphology of a wetland stream, Environmental Management, 21 (6), 921-941, 1997.
Little attention has been paid to wetland stream morphology in the geomorphological and environmental literature, and in the recently expanding wetland reconstruction field, stream design has been based primarily on stream morphologies typical of nonwetland alluvial environments. Field investigation of a wetland reach of Roaring Brook, Stafford, Connecticut, USA, revealed several significant differences between the morphology of this stream and the typical morphology of nonwetland alluvial streams. Six morphological features of the study reach were examined: bankfull flow, meanders, pools and riffles, thalweg location, straight reaches, and cross-sectional shape. It was found that bankfull flow definitions originating from streams in nonwetland environments did not apply. Unusual features observed in the wetland reach include tight bends and a large axial wavelength to width ratio. A lengthy straight reach exists that exceeds what is typically found in nonwetland alluvial streams. The lack of convex bank point bars in the bends, a greater channel width al riffle locations, an unusual thalweg location, and small form ratios (a deep and narrow channel) were also differences identified. Further study is needed on wetland streams of various regions to determine if differences in morphology between alluvial and wetland environments can be applied in order to improve future designs of wetland channels.
Juyal, N., R. Raj, D.M. Maurya, L.S. Chamyal, and A.K. Singhvi, Chronology of Late Pleistocene environmental changes in the lower Mahi basin, western India, Journal of Quaternary Science, 15 (5), 501-508, 2000.
Kadlec, R.H., Overland-Flow in Wetlands - Vegetation Resistance, Journal of Hydraulic Engineering-Asce, 116 (5), 691-706, 1990.
Kadlec, R.H., Detention and Mixing in Free-Water Wetlands, Ecological Engineering, 3 (4), 345-380, 1994.
Mixing was studied in a free water surface wetland receiving pumped river water, by measurement of the non-interacting tracer lithium. The flow pattern was found to be intermediate between plug flow and well-mixed. The nominal detention time, calculated from volume and flow, was 50% larger than the mean tracer detention time. The peak time was found to be one-half the tracer detention time. Three models were constructed: plug flow with dispersion, tanks in series, and a series-parallel network of tanks. All proved capable of fitting the exit tracer concentration curves but the network model provided a better fit to internal measurements. Pumping frequency was high enough to allow use of an average flowrate. The degree of mixing, as characterized by the variance of the exit tracer response curve, was comparable to that found by other researchers for wetlands, ponds and rivers.
Kahler, T.H., P. Roni, and T.P. Quinn, Summer movement and growth of juvenile anadromous salmonids in small western Washington streams, Canadian Journal of Fisheries and Aquatic Sciences, 58 (10), 1947-1956, 2001.
Movements of juvenile coho salmon (Oncorhynchus kisutch), cutthroat trout (Oncorhynchus clarki clarki), and steelhead trout (Oncorhynchus mykiss) were studied by observations and recapture of marked individuals in three western Washington streams to test the hypotheses that few fish would move, downstream movement would predominate, movers would be initially smaller and grow slower after movement than residents, and habitat quality would influence movement. Contrary to predictions, from 28 to 60% of marked fish moved at least one habitat unit, and immigration of unmarked fish also indicated considerable movement. Upstream movement predominated but the stream with the step-pool/cascade channel type had fewer upstream movers and greater distances moved downstream. Coho movers were not smaller than nonmovers, as predicted based on assumptions that movement results from competitive exclusion. Habitat units that coho left were smaller and shallower but lower in density than units where coho remained. Thus, movement is a common phenomenon rather than an aberration, and may reflect habitat choice rather than territorial eviction. Moreover, movers grew faster than nonmovers, so the "mobile fraction" of the population was not composed of competitively inferior fish but rather individuals that thrived. The phenomenon of small-scale habitat- and growth-related movements should be considered when planning and interpreting studies of juvenile salmonid ecology in streams.
Kaitala, V., and E. Ranta, Travelling wave dynamics and self-organization in a spatio- temporally structured population, Ecology Letters, 1 (3), 186-192, 1998.
We analyse spatial population dynamics showing that periodic or period-like chaotic dynamics produce self-organization structures, such as travelling waves. We suggest that self- organized patterns are associated with spatial synchrony patterns that often depend on geographical distance between subpopulations. The population dynamics also show statistical spatial autocorrelation patterns. We contrast our theoretical simulations with empirical data on annual damages in young sapling stands caused by voles. We conclude, an the basis of the periodicity, synchrony, and spatial autocorrelation patterns, and our simulation results, that vole dynamics represent travelling waves in population dynamics. We suggest that because such synchrony patterns are frequently observed in natural populations, spatial self-organization may be more common in population dynamics than reported in the literature.
Kalikhman, I., Distribution fields for aquatic ecosystem components: determination of significance of correlation zones, Hydrobiologia, 400, 1-11, 1999.
A method for identification of correlation zones was applied to test the spatial relationship of Peridinium cell density, chlorophyll concentration and cellular chlorophyll content, using data of sampling surveys carried out on the subtropical Lake Kinneret, Israel. Zones of correlation and correlation disturbance were observed. A method is suggested for determining the significance of the correlation zones, taking into account the values of the variables at sampling points where the correlation was actually measured. The method used was expedient for the description of spatial lake homogeneity/heterogeneity with regard to the examined variables. Heterogeneities, their spatial extent and intensity are defined by the method of identifying correlation zones and determining the significance of the zones while pinpointing the areas of interest in the lake.
Kassem, A.A., and M.H. Chaudhry, Comparison of coupled and semicoupled numerical models for alluvial channels, Journal of Hydraulic Engineering-Asce, 124 (8), 794-802, 1998.
Contrary to general statements in the literature, the investigations reported in this paper show that semicoupled models are not necessarily unstable and give results comparable to those of coupled models. For this purpose, a two-dimensional model is developed to calculate bed variations in alluvial channels. Vertically averaged Navier-Stokes equations in transformed coordinates are numerically solved in conjunction with the sediment transport equation for the bed load. These equations are solved simultaneously in a fully coupled model and separately in a semicoupled model using the Beam and Warming alternating-direction implicit scheme. Both models are applied to predict bed-level changes due to sediment overloading and sediment shut-off. The computed results compare satisfactorily with the experimental results obtained in a laboratory flume. The results obtained by the semicoupled model are relatively close to that of the fully coupled model. Because the former algorithm permits any sediment formula and armoring effect to be easily incorporated, the semicoupled model appears to be more attractive for general applications to real-life systems than the coupled model.
Kastler, J.A., and P.L. Wiberg, Sedimentation and boundary changes of Virginia salt marshes, Estuarine Coastal and Shelf Science, 42 (6), 683-700, 1996.
Kaufmann, R., Invertebrate succession on an alpine glacier foreland, Ecology, 82 (8), 2261-2278, 2001.
Since there is little known about invertebrates in glacier foreland succession, the aim of this study was (1) to characterize succession patterns of the epigean fauna, (2) to analyze how these are related to plant succession,, and (3) to investigate the influence of locally varying environmental conditions. The Central Alpine glacier foreland of the Rotmoostal (Obergurgl, Tyrol, Austria) was selected as an example situated above the treeline (2280-2450 in above sea level) where a 2 km long deglaciated area covers a chronosequence of 140 yr. The epigean fauna was sampled in 70 plots of all ages and in nearby sites outside the foreland by pitfall trapping over the entire growing season in 1996 (June- October). Abiotic characterization and vegetation recordings were available for all plots. Rapid development of pioneer communities over 50 yr was followed by little change in older stages. Further development towards the mature invertebrate communities characteristic of areas outside the foreland only occurred on the sunny slopes near the terminal moraine and proceeded in a qualitatively different way. Sites in the alluvial outwash plain or otherwise physically disturbed were clearly successionally younger than adjacent undisturbed sites. The first colonizers were almost exclusively predators. Herbivores and decomposers appeared later. Similarities and differences between faunal and floral succession patterns are discussed. The major factors affecting faunal succession as identified by canonical correspondence analysis were soil formation and vegetation development along the chronosequence. In addition, favorable sun and light conditions may facilitate successional progress. Fauna communities also react to local conditions, most notably to the moisture/snow cover regime, Abiotic environment, architecture of plants, and plant species composition interact strongly as explanatory factors, but all three aspects also contribute significant unique correlations. There were no hints of random colonization patterns at the youngest sites. Pioneer invertebrate communities had the same small-scale spatial heterogeneity and equally strong correlations with environmental conditions as did the well- established communities at older sites. This leads to the conclusion that faunal colonization and succession in Alpine glacier forelands, to a large extent, follow predictable and deterministic assembly rules and that stochastic effects are of minor importance.
Keefer, D.K., Earthquake-induced landslides and their effects on alluvial fans, Journal of Sedimentary Research, 69 (1), 84-104, 1999.
Earthquakes as small as magnitude 4.0 may dislodge landslides from susceptible slopes, and larger earthquakes can generate tens of thousands of landslides throughout areas of hundreds of thousands of square kilometers, producing billions of cubic meters of loose, surficial sediment. These landslides can have significant geomorphic effects that vary depending on the landslide characteristics and materials, and on the settings in which the landslides occur. A review of data from historical earthquakes indicates that the landslides they generated can be classified into 14 different types. These include highly disaggregated and fast-moving falls, disrupted slides, and avalanches; more coherent and slower-moving slumps, block slides, and earth slides; and lateral spreads and flows that involve partly to completely liquefied material. Rock falls, disrupted rock slides, and disrupted slides of earth and debris are the most abundant types of earthquake-induced landslides, whereas earth hows, debris flows, and avalanches of rock, earth, or debris typically transport material the farthest, Because of their abundance or long distances of transport, these landslides generally have the greatest effects on the landscape during and after earthquakes. Landslide effects on alluvial fans include direct deposition of material on fan surfaces; fissuring and displacement of fan materials; alterations in drainage basins such as devegetation, denudation, and changes in channel networks; and generation of large amounts of sediment that may be transported to fans by post-earthquake water flows or debris flows.
Keim, R.F., A.E. Skaugset, and D.S. Bateman, Dynamics of coarse woody debris placed in three Oregon streams, Forest Science, 46 (1), 13-22, 2000.
Many streams of the North American west coast are deficient in coarse woody debris (CWD) and have been subjected to aquatic habitat restoration by adding CWD, The ready availability of alder (Alnus rubra Bong.) CWD makes it attractive for such uses, but the dynamics of this relatively small debris are poorly understood. We placed CWD in three third-order streams in western Oregon either as large, key pieces (pulled-over streamside alders or bucked conifer logs) or as smaller logging debris (mostly alder), This treatment immediately increased CWD in the streams by 86% to 155%. We used chronosequences of surveys to evaluate whether the increased loadings of CWD persisted for more than a year, and whether the key pieces trapped smaller debris to create accumulations. Although there was more CWD in all three streams during the 3 yr after treatment than there had been before treatment, rates of movement were high. Aggregation of CWD increased in all three streams for at least 1 yr, and accumulations of CWD associated with key pieces were larger after 3 yr than immediately after treatment. Pulled-over alders were more stable and more effective in forming accumulations than bucked conifers but were subject to rapid decay.
Keller, E.A., and J.L. Florsheim, Velocity-Reversal Hypothesis - a Model Approach, Earth Surface Processes and Landforms, 18 (8), 733-740, 1993.
Hydraulic modelling of a riffle-pool-riffle sequence in a straight reach of Dry Creek near Winters, California, indicates that while at low flow the mean (section average) velocity at riffles exceeds that of an adjacent pool, during high flow the mean velocity of the pool exceeds that of adjacent riffles. This supports the velocity-reversal hypothesis which is based on limited field measurements of near-bed flow velocity. A velocity reversal does not occur at the same discharge in both riffle-pool sequences modelled, and a more detailed explanation is necessary to account for complex aspects of channel form and process in riffle-pool sequences. Nevertheless, the velocity- reversal hypothesis helps to explain many of the observations and processes that operate in the riffle-pool environment.
Keller, E.A., L. Gurrola, and T.E. Tierney, Geomorphic criteria to determine direction of lateral propagation of reverse faulting and folding, Geology, 27 (6), 515-518, 1999.
Kells, J.A., R. Balachandar, and K.P. Hagel, Effect of grain size on local channel scour below a sluice gate, Canadian Journal of Civil Engineering, 28 (3), 440-451, 2001.
Kench, P.S., and R.F. McLean, Hydraulic characteristics of bioclastic deposits: New possibilities for environmental interpretation using settling velocity fractions, Sedimentology, 43 (3), 561-570, 1996.
Kench, P.S., A currents of removal approach for interpreting carbonate sedimentary processes, Marine Geology, 145 (3-4), 197-223, 1998.
Kern, J.W., and K.O. Coyle, Global block kriging to estimate biomass from acoustic surveys for zooplankton in the western Aleutian Islands, Canadian Journal of Fisheries and Aquatic Sciences, 57 (10), 2112-2121, 2000.
Because of patchy distributions and the expense of collecting and processing net samples, zooplankton population data are often characterized by broad confidence intervals, with little detailed information on vertical and horizontal distributions. Although acoustic techniques and optical plankton counters combined with nets can supply much more detailed information on plankton distributions, application of classical statistical procedures to such data may be effected by pseudoreplication from autocorrelation in closely spaced samples. We apply two- dimensional kriging for population mapping and global estimation. The technique utilizes a computational estimator of the global block kriging mean, which can be applied to large data sets common to hydroacoustic surveys. The techniques are outlined using examples from acoustic data taken in the western Aleutian Islands. This technique has two fundamental advantages: (i) it minimizes pseudoreplication by accounting for autocorrelation, permitting rigorous statistical inferences, and (ii) it provides an effective technique for visualizing the results. These advantages may make this a useful technique for identifying changes in the size and distribution of populations.
Kerssens, P.J.M., and A. Vanurk, Experimental Studies On Sedimentation Due to Water Withdrawal, Journal of Hydraulic Engineering-Asce, 112 (7), 641-656, 1986.
Kiersch, G.A., Development of engineering geology in western United States, Engineering Geology, 59 (1-2), 1-49, 2001.
Geologic concepts and scientific-technical guidance for the planning-design and construction of engineered works was recognized in Europe by the 1800s and by the early 1900s in North America. This early geologic knowledge and experience provided the rudimentary principles that guided practitioners of the 19th century in serving the emerging projects in western United States. Case studies review the scientific-technical lessons learned and the legacy of geologic principles established in the planning and construction of major civil, mining, and military engineered works in the western states. These contributions to GeoScience knowledge and engineering geology practice include: Tunnels and aqueducts across active fault zones, beneath young volcanic features, groundwater- charged faults, and land subsidence mitigation. Controversial foundation design, Folsom and Auburn dams, Golden Gate Bridge. Protective underground construction chambers, safety dependent geologic setting. Geologic mapping as database management leasing, maintenance railroad trackway. Causeway Great Salt Lake, geo-risks calculated, mitigated 'as-constructed'. Nuclear powerplants seismic design. Urban Land-Use, on-going processes, acceptable geo-risks. Dwelling Insurance, insuree's responsibilities. Selecting technique/method to mitigate risk, preferably based on extensive database, evaluation of characteristics and historical origin adverse features/conditions that constitute a geo-risk. (C) 2001 Elsevier Science B.V. All rights reserved.
King, K.W., J.G. Arnold, and R.L. Bingner, Comparison of Green-Ampt and curve number methods on Goodwin Creek Watershed using SWAT, Transactions of the Asae, 42 (4), 919-925, 1999.
Kirby, E., K.X. Whipple, B.C. Burchfiel, W.Q. Tang, G. Berger, Z.M. Sun, and Z.L. Chen, Neotectonics of the Min Shan, China: Implications for mechanisms driving Quaternary deformation along the eastern margin of the Tibetan Plateau, Geological Society of America Bulletin, 112 (3), 375-393, 2000.
Kirchner, J.W., W.E. Dietrich, F. Iseya, and H. Ikeda, The Variability of Critical Shear-Stress, Friction Angle, and Grain Protrusion in Water-Worked Sediments, Sedimentology, 37 (4), 647-672, 1990.
Kirchner, J.W., R.C. Finkel, C.S. Riebe, D.E. Granger, J.L. Clayton, J.G. King, and W.F. Megahan, Mountain erosion over 10 yr, 10 k.y., and 10 m.y. time scales, Geology, 29 (7), 591-594, 2001.
We used cosmogenic Be-10 to measure erosion rates over 10 k.y. time scales at 32 Idaho mountain catchments, ranging from small experimental watersheds (0.2 km(2)) to large river basins (35 000 km(2)), These long-term sediment yields are, on average, 17 times higher than stream sediment fluxes measured over 10-84 yr, but are consistent with 10 m.y. erosion rates measured by apatite fission tracks. Our results imply that conventional sediment-yield measurements - even those made over decades - can greatly underestimate long-term average rates of sediment delivery and thus overestimate the life spans of engineered reservoirs. Our observations also suggest that sediment delivery from mountainous terrain is extremely episodic, sporadically subjecting mountain stream ecosystems to extensive disturbance.
Kitsiou, D., G. Tsirtsis, and M. Karydis, Developing an optimal sampling design. A case study in a coastal marine ecosystem, Environmental Monitoring and Assessment, 71 (1), 1-12, 2001.
The development of a sampling design for optimising sampling site locations collected from a coastal marine environment has been the purpose of the present work; application of statistical analysis and spatial autocorrelation methods have been carried out. The dataset included data collected from 34 sampling sites spaced out in the Strait of Lesbos, Greece, arranged in a 1x1 NM grid. The coastal shallow ecosystem was subdivided into three zones, an inner one (7 stations), a middle one (16 stations) and an offshore zone (11 stations). The standard error of the chlorophyll-a concentrations in each zone has been used as the criterion for the sampling design optimisation, resulting into reallocation of the sampling sites into the three zones. The positions of the reallocated stations have been assessed by estimation of the spatial heterogeneity and anisotropy of chlorophyll-a concentrations using variograms. Study of the variance of the initial dataset of the inner zone taking into account spatial heterogeneity, revealed two different sub-areas and therefore, the number of the inner stations has been reassessed. The proposed methodology eliminates the number of sampling sites and maximises the information of spatial data from marine ecosystems. It is described as a step-by-step procedure and could be widely applied in sampling design concerning coastal pollution problems.
Kitsiou, D., and M. Karydis, Marine eutrophication: A proposed data analysis procedure for assessing spatial trends, Environmental Monitoring and Assessment, 68 (3), 297-312, 2001.
A methodology for the discrimination of the different trophic levels at a spatial scale in the marine environment is proposed using spatial analysis methods and non-parametric statistics. Phytoplankton cell number, being a representative parameter to express trophic trends in the marine ecosystem is selected for the methodology development; Saronicos Gulf, Greece is used for the case study. The proposed stepwise methodology includes interpolation for assessing the spatial distribution of phytoplankton cell number, division of the Gulf into a number of quadrates, development of a scale characterising trophic levels and finally characterisation of the trophic state of each quadrate using non-parametric statistics. The advantages of this methodology and the potential applications in coastal management studies are also discussed.
Kling, G.W., G.W. Kipphut, M.M. Miller, and W.J. O'Brien, Integration of lakes and streams in a landscape perspective: the importance of material processing on spatial patterns and temporal coherence, Freshwater Biology, 43 (3), 477-497, 2000.
1. We studied the spatial and temporal patterns of change in a suite of twenty-one chemical and biological variables in a lake district in arctic Alaska, U.S.A. The study included fourteen stream sites and ten lake sites, nine of which were in a direct series of surface drainage. All twenty-four sites were sampled between one and five times a year from 1991 to 1997. 2. Stream sites tended to have higher values of major anions and cations than the lake sites, while the lake sites had higher values of particulate carbon, nitrogen, phosphorous and chlorophyll a. There were consistent and statistically significant differences in concentrations of variables measured at the inlet versus the outlet of lakes, and in variables measured at upstream versus downstream sites in the stream reaches which connect the lakes. In-lake processing tended ro consume alkalinity, conductivity, H+, DIC, Ca2+, Mg2+, CO2, CH4, and NO3-, and produce K+ and dissolved organic carbon (DOC). In-stream processing resulted in the opposite trends (e.g. consumption of K+ and DOC), and the magnitudes of change were often similar to those measured in the lakes but with the opposite sign. 3. Observed spatial patterns in the study lakes included mean concentrations of variables which increased, decreased or were constant along the lake chain from high to low altitude in the catchment (stream sites showed no spatial patterns with any variables). The strongest spatial patterns were of increasing conductivity, Ca2+, Mg2+, alkalinity, dissolved inorganic carbon and pH with lake chain number (high to low altitude in the basin). These patterns were partly determined by the effect of increasing catchment area feeding into lakes further downslope, and partly by the systematic processing of materials in lakes and in the stream segments between lakes. 4. Synchrony (the temporal coherence or correlation of response) of variables across all lakes ranged from 0.18 for particulate phosphorus to 0.90 for Mg2+; the average synchrony for all twenty-one variables was 0.50. The synchronous behaviour of lake pairs was primarily related to the spatial location or proximity of the lakes for all variables taken together and for many individual variables, and secondarily, to the catchment to lake area ratio and the water residence time. 5. These results illustrate that, over small geographic areas, and somewhat independent of lake or stream morphometry, the consistent and directional (downslope) processing of materials helps produce spatial patterns which are coherent over time for many limnological variables. We combine concepts from stream, lake and landscape ecology, and develop a conceptual view of landscape mass balance. This view highlights that the integration of material processing in both lakes and rivers is critical for understanding the structure and function of surface waters, especially from a landscape perspective.
Kneller, B.C., S.J. Bennett, and W.D. McCaffrey, Velocity and turbulence structure of density currents and internal solitary waves: potential sediment transport and the formation of wave ripples in deep water, Sedimentary Geology, 112 (3-4), 235-250, 1997.
Knight, D.W., and J.B. Abril, Refined calibration of a depth-averaged model for turbulent flow in a compound channel, Proceedings of the Institution of Civil Engineers-Water Maritime and Energy, 118 (3), 151-159, 1996.
Knight, D.W., F. Brown, E. Valentine, C. Nalluri, J. Bathurst, I. Benson, R. Myers, J. Lyness, and J. Cassells, The response of straight mobile bed channels to inbank and overbank flows, Proceedings of the Institution of Civil Engineers-Water Maritime and Energy, 136 (4), 211-224, 1999.
Knight, D.W., and M. Sterling, Boundary shear in circular pipes running partially full, Journal of Hydraulic Engineering-Asce, 126 (4), 263-275, 2000.
Knight, D.W., and F.A. Brown, Resistance studies of overbank flow in rivers with sediment using the flood channel facility, Journal of Hydraulic Research, 39 (3), 283-301, 2001.
Knighton, A.D., Channel Form and Flow Characteristics of Supraglacial Streams, Austre-Okstindbreen, Norway, Arctic and Alpine Research, 13 (3), 295-306, 1981.
Knighton, A.D., Asymmetry of River Channel Cross-Sections .2. Mode of Development and Local Variation, Earth Surface Processes and Landforms, 7 (2), 117-131, 1982.
Knighton, A.D., Models of Stream Bed Topography At the Reach Scale, Journal of Hydrology, 60 (1-4), 105-121, 1983.
Knighton, A.D., Indexes of Flow Asymmetry in Natural Streams - Definition and Performance, Journal of Hydrology, 73 (1-2), 1-19, 1984.
Knighton, A.D., Channel Form Adjustment in Supraglacial Streams, Austre Okstindbreen, Norway, Arctic and Alpine Research, 17 (4), 451-466, 1985.
Knighton, A.D., River Adjustment to Changes in Sediment Load - the Effects of Tin Mining On the Ringarooma River, Tasmania, 1875-1984, Earth Surface Processes and Landforms, 14 (4), 333-359, 1989.
Kodama, Y., Downstream Changes in the Lithology and Grain-Size of Fluvial Gravels, the Watarase River, Japan - Evidence of the Role of Abrasion in Downstream Fining, Journal of Sedimentary Research Section a-Sedimentary Petrology and Processes, 64 (1), 68-75, 1994.
Kodama, Y., Experimental-Study of Abrasion and Its Role in Producing Downstream Fining in Gravel-Bed Rivers, Journal of Sedimentary Research Section a-Sedimentary Petrology and Processes, 64 (1), 76-85, 1994.
Koenig, W.D., and J.M.H. Knops, Patterns of annual seed production by northern hemisphere trees: A global perspective, American Naturalist, 155 (1), 59-69, 2000.
We tested whether annual seed production (masting or mast fruiting) in Northern Hemisphere trees is an evolved strategy or a consequence of resource tracking by comparing masting patterns with those of annual rainfall and mean summer temperatures, two environmental variables likely to correlate with available resources. There were generally significant negative autocorrelations between the seed crop in year x and year x + 1 (year x + 2 in species of Quercus requiring 2 yr to mature acorns), as expected if resources are depleted in mast years in part by switching resources from growth to reproduction. Spatial autocorrelation in annual seed production generally declined with distance but was statistically significant over large geographic areas. Variability in annual seed production was relatively high and inversely correlated with latitude and generally not bimodally distributed. Patterns of spatial autocorrelation in annual rainfall and summer temperatures are generally similar to those exhibited by annual seed production, and relative variability in annual rainfall is also inversely correlated with latitude. However, these environmental variables exhibit distinctly different patterns of temporal autocorrelation, are much less variable, and are more normally distributed than annual seed production. Combined with the inverse relationship between growth and reproduction previously documented, these results support the hypothesis that variability in annual seed production is an evolved strategy and that annual seed production is more or less normally distributed rather than an all-or-none phenomenon.
Komar, P.D., and P.A. Carling, Grain Sorting in Gravel-Bed Streams and the Choice of Particle Sizes For Flow-Competence Evaluations, Sedimentology, 38 (3), 489-502, 1991.
Kondolf, G.M., Geomorphic and Environmental-Effects of Instream Gravel Mining, Landscape and Urban Planning, 28 (2-3), 225-243, 1994.
Instream gravel mining involves the mechanical removal of gravel and sand directly from the active channel of rivers and streams. Active channel deposits are desirable as construction aggregate because they are typically durable (weak materials having been eliminated in river transport), well-sorted, and frequently located near markets or on transportation routes. Instream gravel mining commonly causes incision of the channel bed, which can propagate upstream and downstream for kilometers. As a result, bridges and other structures may be undermined, spawning gravels lost and alluvial water tables lowered. In analyzing the effects of instream gravel mining, a sediment budget analysis sheds light on the relative magnitude of gravel supply, transport and extraction. Computer models of sediment transport are simplifications of complex natural processes; they can be useful components of a sediment budget analysis but should not be relied upon alone. A historical analysis of channel change and sediment supply is needed to understand the underlying processes responsible for present conditions. While instream gravel mining can be a useful tool in flood control and river stabilization in aggrading rivers, most rivers in the developed world (certainly the vast majority below reservoirs) are not aggrading and are more prone to incision-related effects of instream gravel mining.
Kondolf, G.M., and P.R. Wilcock, The flushing flow problem: Defining and evaluating objectives, Water Resources Research, 32 (8), 2589-2599, 1996.
Kondolf, G.M., Hungry water: Effects of dams and gravel mining on river channels, Environmental Management, 21 (4), 533-551, 1997.
Rivers transport sediment from eroding uplands to depositional areas near sea level. ii the continuity of sediment transport is interrupted by dams or removal of sediment from the channel by gravel mining, the flow may become sediment-starved (hungry water) and prone to erode the channel bed and banks, producing channel incision (downcutting), coarsening of bed material, and loss of spawning gravels for salmon and trout (as smaller gravels are transported without replacement from upstream). Gravel is artificially added to the River Rhine to prevent further incision and to many other rivers in attempts to restore spawning habitat. It is possible to pass incoming sediment through some smalt reservoirs, thereby maintaining the continuity of sediment transport through the system. Damming and mining have reduced sediment delivery from rivers to many coastal areas, leading to accelerated beach erosion. Sand and gravel are mined for construction aggregate from river channel and floodplains. In-channel mining commonly causes incision, which may propagate up- and downstream of the mine, undermining bridges, inducing channel instability, and lowering alluvial water tables. Floodplain gravel pits have the potential to become wildlife habitat upon reclamation, but may be captured by the active channel and thereby become instream pits. Management of sand and gravel in rivers must be done on a regional basis, restoring the continuity of sediment transport where possible and encouraging alternatives to river-derived aggregate sources.
Kondolf, G.M., Application of the pebble count: Notes on purpose, method, and variants, Journal of the American Water Resources Association, 33 (1), 79-87, 1997.
The pebble count procedure (Wolman, 1954) is the measurement of 100 randomly selected stones from a homogeneous population on a river bed or bar, which yields reproducible size distribution curves for surficial deposits of gravel and cobbles. The pebble count is widely used in geomorphology (and increasingly in river engineering) to characterize surficial grain size distributions in lieu of bulk samples, for which adequate sample sizes become enormous for gravels. Variants on the original method have been proposed, one of which, the so-called 'zig-zag' method (Bevenger and King, 1995), involves sampling along a diagonal line and drawing data points from many different geomorphic units. The method is not reproducible, probably because it incorporates stones from many different populations, and because an inadequate number of grains is sampled from any given population. Sampling of coarse bed material should be geomorphically stratified based on the natural sorting of grain sizes into distinct channel features. If a composite grain size is desired, the areas of the bed occupied by different populations can be mapped, pebble counts conducted on each, and a weighted average distribution computed.
Kondolf, G.M., Lessons learned from river restoration projects in California, Aquatic Conservation-Marine and Freshwater Ecosystems, 8 (1), 39-52, 1998.
Kondolf, G.M., M.W. Smeltzer, and S.F. Railsback, Design and performance of a channel reconstruction project in a coastal California gravel-bed stream, Environmental Management, 28 (6), 761-776, 2001.
A 0.9 km-reach of Uvas Creek, California, was reconstructed as a sinuous, meandering channel in November 1995. In February 1996, this new channel washed out. We reviewed project documents to determine the basis for the project design and conducted our own historical geomorphological study to understand the processes operating in the catchment and project reach. The project was designed using a popular stream classification system, based on which the designers assumed that a "C4" channel (a meandering gravel-bed channel) would be stable at the site. Our historical geomorphological analysis showed that the reach had been braided historically, typical of streams draining the Franciscan Formation in the California Coast Ranges, with episodic flows and high sand and gravel transport. After the project washed out, Uvas Creek reestablished an irregular, braided sand-and-gravel channel, although the channel here was narrower than it had been historically, probably due to such factors as incision caused by gravel mining. Our study casts doubt on several assumptions common in many stream restoration projects: that channel stability is always an appropriate goal; that channel forms are determined by flows with return periods of about 1.5 years; that a channel classification system is an easy, appropriate basis for channel design; and that a new channel form can be imposed without addressing the processes that determine channel form.
Kostylev, V., and J. Erlandsson, A fractal approach for detecting spatial hierarchy and structure on mussel beds, Marine Biology, 139 (3), 497-506, 2001.
Within beds of blue mussel (Mytilus edulis L.), individuals are aggregated into small patches, which in turn are incorporated into bigger patches, revealing a complex hierarchy of spatial structure. The present study was done to find the different scales of variation in the distribution of mussel biomass, and to describe the spatial heterogeneity on these scales. The three approaches compared for this purpose were fractal analysis, spatial autocorrelation and hierarchical (or nested) analysis of variances (ANOVA). The complexity (i.e. patchiness) of mussel aggregations was described with fractal dimension, calculated with the semivariogram method. Three intertidal mussel beds were studied on the west coast of Sweden. The distribution of wet biomass was studied along transects up to 128 in. The average biomasses of blue mussels on the three mussel beds were 1825 +/- 210, 179 +/- 21 and 576 +/- 66 g per 0.1 m(2), respectively, and the fractal dimensions of the mussel distribution were 1.726 +/- 0.010, 1.842 +/- 0.014 and 1.939 +/- 0.029 on transects 1-3, respectively. Distributions of mussels revealed multiscaling behaviour. The fractal dimension significantly changed twice on different scales on the first bed (thus showing three scaling regions), the second and third beds revealed two and three scaling regions, respectively. High fractal dimension was followed by significant spatial autocorrelation on smaller scales. The fractal analysis detects the multiple scaling regions of spatial variance even when the spatial structure may not be distinguished significantly by conventional statistical inference. The study shows that the fractal analysis, the spatial autocorrelation analysis and the hierarchical ANOVA give complementary information about the spatial variability in mussel populations.
Kotrechko, S.A., Y. Meshkov, and I. Dlouhy, Computer simulation of effect of grain size distribution on Weibull parameters, Theoretical and Applied Fracture Mechanics, 35 (3), 255-260, 2001.
Kracker, L.M., The geography of fish: The use of remote sensing and spatial analysis tools in fisheries research, Professional Geographer, 51 (3), 440-450, 1999.
Rather than seeing the oceans as an expansive void, researchers using acoustic technologies can detect the heterogeneity of biological resources and view the marine environment as a three-dimensional landscape. Underwater remote sensing, using acoustics, provides high resolution maps of the spatial distribution of organisms in aquatic ecosystems. Analyzing the spatial pattern of species distribution within the water column and the impact of that organization on ecological processes bridges the fields of fisheries and spatial analysis. Tools and concepts familiar to geographers, such as remote sensing, GIS, and landscape ecology, contribute to the investigation of large lake and marine ecosystems.
Krishnaswamy, J., M. Lavine, D.D. Richter, and K. Korfmacher, Dynamic modeling of long-term sedimentation in the Yadkin River basin, Advances in Water Resources, 23 (8), 881-892, 2000.
Modeling of sediment transport in relation to changing land- surface conditions against a background of considerable natural variability is a challenging area in hydrology. Bayesian dynamic linear models (DLMs) however, offer opportunities to account for non-stationarity in relationships between hydrologic input and basin response variables. Hydrologic data are from a 40 years long record (1951-1990) from the 5905 km(2) Yadkin River basin in North Carolina, USA. DLM regressions were estimated between log-transformed volume-weighted sediment concentration as a response and log-transformed rainfall erosivity and river flow, respectively, as input variables. A similar regression between log-transformed river flow and log- transformed basin averaged rainfall was also analyzed. The dynamic regression coefficient which reflects the erodibility of the basin decreased significantly between 1951 and 1970, followed by a slowly rising trend. These trends are consistent with observed land-use shifts in the basin. Bayesian DLMs represent a substantial improvement over traditional monotonic trend analysis. Extensions to incorporate multiple regression and seasonality are recommended for future applications in hydrology. (C) 2000 Elsevier Science Ltd. All rights reserved.
Kruse, C.G., W.A. Hugert, and F.J. Rahel, An assessment of headwater isolation as a conservation strategy for cutthroat trout in the Absaroka Mountains of Wyoming, Northwest Science, 75 (1), 1-11, 2001.
Isolation of native cutthroat trout (Oncorhynchus clarki) populations in headwater tributaries (by means of human-made barriers that prevent upstream movement of exotic Salmonidae) has been used (as an approach) to preserve extant populations from hybridization and competition. We evaluated this conservation strategy for Yellowstone cutthroat trout (O. c. bouvieri) in the Absaroka Mountains of northwestern Wyoming. We surveyed four existing populations to assess the potential for isolating Yellowstone cutthroat trout populations in 23 individual headwater tributary streams. It appeared that 21 of the populations would be large enough to minimize demographic risks of extinction, but only seven populations may be large enough (effective population size > 500) to lower the risk of extinction due to genetic limitations. Additionally, there is high potential for unpredictable environmental events to cause severe reductions in population size or local extinctions of Yellowstone cutthroat trout populations above barriers due to the unstable flow and habitat conditions. Isolation of Yellowstone cutthroat trout populations in headwater tributaries upstream from barriers appears to have a low probability of preserving sustainable populations of Yellowstone cut-throat trout in the Absaroka Mountains in the long term.
Kuhnle, R.A., and J.B. Southard, Bed-Load Transport Fluctuations in a Gravel Bed Laboratory Channel, Water Resources Research, 24 (2), 247-260, 1988.
Kuhnle, R.A., and J.C. Willis, Mean Size Distribution of Bed-Load On Goodwin Creek, Journal of Hydraulic Engineering-Asce, 118 (10), 1443-1446, 1992.
Kuhnle, R.A., Bed-Load Transport During Rising and Falling Stages On 2 Small Streams, Earth Surface Processes and Landforms, 17 (2), 191-197, 1992.
Kuhnle, R.A., Incipient Motion of Sand-Gravel Sediment Mixtures, Journal of Hydraulic Engineering-Asce, 119 (12), 1400-1415, 1993.
Kuhnle, R.A., Fluvial Transport of Sand and Gravel Mixtures With Bimodal Size Distributions, Sedimentary Geology, 85 (1-4), 17-24, 1993.
Kuhnle, R.A., R.L. Bingner, G.R. Foster, and E.H. Grissinger, Effect of land use changes on sediment transport in Goodwin Creek, Water Resources Research, 32 (10), 3189-3196, 1996.
Kuhnle, R.A., and J.C. Willis, Statistics of sediment transport in Goodwin Creek, Journal of Hydraulic Engineering-Asce, 124 (11), 1109-1114, 1998.
Kusky, T., and F. El-Baz, Neotectonics and fluvial geomorphology of the northern Sinai Peninsula, Journal of African Earth Sciences, 31 (2), 213-235, 2000.
Ladd, S.C., W.A. Marcus, and S. Cherry, Differences in trace metal concentrations among fluvial morphologic units and implications for sampling, Environmental Geology, 36 (3-4), 259-270, 1998.
This study examines the segregation of trace metals within and between fluvial morphologic units in sand-sized and finer bed sediments a cobble bed stream. The types of fluvial morphologic units sampled are low gradient riffles, high gradient riffles, glides, eddy drop zones, lateral scour pools, attached bars, and detached bars. Three to nine samples were collected from ten of each type of morphologic unit. All 12 metals show significantly different concentrations between some morphologic units in sediments smaller than 2 mm. Eddy drop zones and attached bars consistently have the highest metal concentrations, while low gradient riffles, high gradient riffles, and glides typically have the lowest concentrations. Metals showing the greatest between-unit variability are Al, Cr, Fe, Cu, and Ti, followed by Co, Mn, and Pb, while Mg, Mn, V, and Zn display relatively few differences between units. Lateral and longitudinal variations of metals within units are not significant, and there was no consistent, predictable variation in metal concentrations with distance downstream. Results indicate that metal studies in other gravel- and cobble-bed streams should include a reconnaissance survey to determine variations between morphologic units, stratify sampling by morphologic unit, and analyze spatial autocorrelation to determine sample spacing.
Lai, C.T., Multicomponent-Flow Analyses By Multimode Method of Characteristics, Journal of Hydraulic Engineering-Asce, 120 (3), 378-395, 1994.
For unsteady open-channel flows having N interacting unknown variables, a system of N mutually independent, partial differential equations can be used to describe the flow-field. The system generally belongs to marching-type problems and permits transformation into characteristic equations that are associated with N distinct characteristic directions. Because characteristics can be considered ''wave'' or ''disturbance'' propagation, a fluvial system so described can be viewed as adequately definable using these N component waves. A numerical algorithm to solve the N families of characteristics can then be introduced for formulation of an N-component flow-simulation model. The multimode method of characteristics (MMOC), a new numerical scheme that has a combined capacity of several specified-time-interval (STI) schemes of the method of characteristics, makes numerical modeling of such N-component riverine flows feasible and attainable. Merging different STI schemes yields different kinds of MMOC schemes, for which two kinds are displayed herein. With the MMOC, each characteristic is dynamically treated by an appropriate numerical mode, which should lead to an effective and suitable global simulation, covering various types of unsteady flow. The scheme is always linearly stable and its numerical accuracy can be systematically analyzed. By increasing the N value, one can develop a progressively sophisticated model that addresses increasingly complex river-mechanics problems.
Lane, S., The Dynamics of Dynamic River Channels, Geography, 80 (347), 147-162, 1995.
Lane, S.N., K.S. Richards, and J.H. Chandler, Morphological Estimation of the Time-Integrated Bed-Load Transport Rate, Water Resources Research, 31 (3), 761-772, 1995.
Lane, S.N., K.S. Richards, and J.H. Chandler, Discharge and sediment supply controls on erosion and deposition in a dynamic alluvial channel, Geomorphology, 15 (1), 1-15, 1996.
Lane, S.N., The reconstruction of bed material yield and supply histories in gravel-bed streams, Catena, 30 (2-3), 183-196, 1997.
This paper details a basic method for estimation of both bed material yield and supply rates for a glaciated catchment. Recent research has illustrated the potential of morphological methods for the estimation of bed material transport rates, but also raised important methodological issues, notably regarding the requisite spatio-temporal resolution of morphological data and the need for either information on upstream sediment supply or assumptions about typical distances of particle movement during transport. Both of the latter have proved problematic. This paper provides an additional means of estimating bed material transport rates and yields through the combination of a simple process-based relationship with morphological information. For a short reach of gravel-bed stream, in a glaciated catchment with a characteristic diurnal discharge hydrograph, a strong positive relationship was found between the volume of water passing through the reach and the volume of erosion in the reach, for points early on the rising limb of the hydrograph. This relationship broke down later in the hydrograph, notably after the discharge peak, associated with the advent of sediment supply from upstream. Thus, early in the hydrograph, this relationship provides an indication of the capacity of this reach to move sediment, either locally eroded material or sediment supplied from upstream, and this paper applies this relationship to a six week discharge hydrograph to predict the potential transport volumes. From these predictions, it calculates the minimum volume of bed material that must have been supplied to the reach from upstream, per hour, to maintain its observed elevation. The results are used to illustrate and discuss some of the problems associated with the use of morphological information for the estimation of bed material transfer rates. (C) 1997 Elsevier Science B.V.
Lane, S.N., Hydraulic modelling in hydrology and geomorphology: A review of high resolution approaches, Hydrological Processes, 12 (8), 1131-1150, 1998.
This paper will introduce the basic principles associated with hydraulic modelling of surface waters for geomorphological and hydrological purposes and illustrate how these have been applied to specific problems. The basic principles governing fluid flow are derived from the principles of conservation of mass and momentum. In the case of the shallow flow problems that typify most geomorphological and hydrological contexts, these equations involve some modifications: (i) as the boundary layer is likely to extend throughout the flow depth, it is possible to assume a hydrostatic pressure distribution; (ii) special conditions need to be determined for both the bottom and water surface, including the possibility of horizontal gradients of atmospheric pressure for large-scale applications, and wind stress; and (iii) it is generally permissible to ignore the Coriolis terms. Direct application of the resultant equations is complicated by the need to Reynolds-average, which introduces additional terms but no additional equations. These terms have to be determined through empirical or semi-empirical transport equations, usually termed turbulence models. Current applications of these equations to geomorphological and hydrological applications are reviewed. Applications to river channels have generally not made use of the full three- dimensional form of the governing equations, and have either been one-dimensional, or, more commonly, two-dimensional. The latter involves depth averaging of the governing equations but requires parameterization of the effects of secondary circulation upon the transport of momentum. This has emphasized secondary circulation generated by curvature of the depth- averaged streamlines, but has yet to address secondary circulation associated with topographic discordance at river channel confluences or diffluences or owing to anisotropic turbulence. Applications to unsteady flows require special attention to be given to the effects of spatial and temporal variation in the depth of inundation, and the associated treatments are reviewed. (C) 1998 John Wiley Sons, Ltd.
Lane, S.N., The measurement of river channel morphology using digital photogrammetry, Photogrammetric Record, 16 (96), 937-957, 2000.
This paper seeks to review the progress that is being achieved by fluvial geomorphologists in making use of digital photogrammetry for river channel research. Fluvial geomorphology is first placed in a basic historical context from which the failure to make full use of the potential of photogrammetry is noted. A review is then given of the ways in which fluvial geomorphologists are now making use of photogrammetry, recognizing that the development of digital approaches has both made photogrammetry a more cost-effective tool and also introduced a range of new research questions. The main objective of this paper is to demonstrate the importance of these questions and to illustrate some of the ways in which they are being addressed. Special attention is given to the issue of data quality, which is frequently (and perhaps conveniently) ignored.
Langedal, M., The influence of a large anthropogenic sediment source on the fluvial geomorphology of the Knabeana-Kvina rivers, Norway, Geomorphology, 19 (1-2), 117-132, 1997.
Molybdenum mining at Knaben discharged more than eight million tonnes of tailings into two lakes in the upstream end of the Knabeana river, southern Norway, during the period 1918-1973. A dam was built downstream of the lakes in 1976 to stop the fluvial dispersion of tailings. Bulk samples were collected from the tailings pond (n = 30), natural sediment sources (n = 7), sandbars (n = 98), and overbank sediments (0-25 cm depth, n = 79) along the 55-km river reach downstream of the mining area. In addition, overbank sediment samples of 1 cm thickness were collected at depth intervals of 1-5 cm in 19 vertical profiles (n = 497). Sedimentological properties were recorded in 17 of the profiles. Chemical analysis (ICP-AES after hot nitric acid or aqua regia extraction) has shown that a minimum of 420000 tonnes of tailings with a median molybdenum content of 80 ppm are presently stored in the fluvial sediments. The major volumes are present in sandbars in a 6 km long, low- gradient reach that acts as a bedload trap under normal flood conditions. However, bedload may be flushed into the steeper reaches by repeated major events. On the floodplains, C-14- dating has shown that the average sedimentation rate in one profile has increased from 0.5 to 4.3 mm/year due to deposition of tailings. Since lateral channel instability has only been detected in a few locations, the floodplains are regarded as semi-permanent sinks for tailings. However, extreme floods that strip off vegetation or undercut the floodplains may increase the availability of tailings from these deposits. The results from the Knabeana-Kvina rivers indicate that construction of weirs may stop the dispersion of bedload-sized contaminated sediments, while construction of dams may be necessary to trap contaminated sediments transported in suspension. In each case the benefit and disadvantages of such constructions must be evaluated according to the local conditions.
Lanzoni, S., and M. Tubino, Grain sorting and bar instability, Journal of Fluid Mechanics, 393, 149-174, 1999.
Lanzoni, S., Experiments on bar formation in a straight flume 1. Uniform sediment, Water Resources Research, 36 (11), 3337-3349, 2000.
Lanzoni, S., Experiments on bar formation in a straight flume 2. Graded sediment, Water Resources Research, 36 (11), 3351-3363, 2000.
Lapointe, M.F., Y. Secretan, S.N. Driscoll, N. Bergeron, and M. Leclerc, Response of the Ha! Ha! River to the flood of July 1996 in the Saguenay Region of Quebec: Large-scale avulsion in a glaciated valley, Water Resources Research, 34 (9), 2383-2392, 1998.
Modifications to valley form due to extreme flooding in the lower 34 km of the Ha! Ha! River were analyzed. Heavy regional precipitation in July 1996 triggered extreme runoff and the catastrophic drainage of Ha! Ha! Lake, producing discharges of 1100 m(3)/s, 8 times the 100-year flood. Dominant valley modifications, revealed by comparing preflood and postflood topographies derived photogrammetrically, were related to two large-scale avulsions; in particular, a deep retrogressive incision which bypassed the 30-m-high Perron Falls, exporting 6 x 10(6) m(3) of glacial stratified drift from a 2-km section of valley and producing massive sedimentation in the reach downstream. Reconstructed maximum flow power values support the existence of a 300 W/m(2) threshold for major scouring of the alluvial valley bottom. The evidence highlights the potential for massive scour and fill and reorganization of the long profile, with potentially catastrophic effects on infrastructure, during extreme floods in glaciated valley settings.
Lapointe, M., B. Eaton, S. Driscoll, and C. Latulippe, Modelling the probability of salmonid egg pocket scour due to floods, Canadian Journal of Fisheries and Aquatic Sciences, 57 (6), 1120-1130, 2000.
Laronne, J.B., and I. Reid, Very High-Rates of Bedload Sediment Transport By Ephemeral Desert Rivers, Nature, 366 (6451), 148-150, 1993.
Laronne, J.B., I. Reid, Y. Yitshak, and L.E. Frostick, The Non-Layering of Gravel Streambeds Under Ephemeral Flood Regimes, Journal of Hydrology, 159 (1-4), 353-363, 1994.
Laronne, J.B., I. Reid, L. Meerovich, and D.M. Powell, Selection of Gravel-Transport Formula For Stream Modeling - Discussion, Journal of Hydraulic Engineering-Asce, 121 (7), 567-568, 1995.
Latulippe, C., M.F. Lapointe, and T. Talbot, Visual characterization technique for gravel-cobble river bed surface sediments; Validation and environmental applications contribution to the Programme of CIRSA (Centre Interuniversitaire de Recherche sur le Saumon Atlantique), Earth Surface Processes and Landforms, 26 (3), 307-318, 2001.
Lavallee, D., C. Marche, and Y. Dastous, Turbulent Distribution of Granular Material in Open Water .2. a Mathematical-Model, Canadian Journal of Civil Engineering, 22 (3), 488-499, 1995.
Lawler, D.M., The Measurement of River Bank Erosion and Lateral Channel Change - a Review, Earth Surface Processes and Landforms, 18 (9), 777-821, 1993.
Lawless, M., and A. Robert, Scales of boundary resistance in coarse-grained channels: turbulent velocity profiles and implications, Geomorphology, 39 (3-4), 221-238, 2001.
Gravel-bed surfaces are characterized by morphological features occurring at different roughness scales. The total shear stress generated by the flow above such surfaces is balanced by the sum of friction drag (grain stress) and form drag components (created by bed forms). To facilitate a better understanding of total resistance and bed load transport processes, there is a need to mathematically separate shear stress into its component parts. One way to do so is to examine the properties of vertical velocity profiles above such surfaces. These profiles are characterized by an inner layer that reflects grain resistance and an outer layer that reflects total resistance. A flume-based project was conducted to address these concerns through systematically comparing different roughness scales to ascertain how increased roughness affects the properties of vertical velocity profiles. Great care was taken to create natural roughness features and to obtain flow data at a high spatial and temporal resolution using an Acoustic Doppler Velocimeter. Average vertical velocity profiles above each roughness scale were clearly segmented. The vertical extent of the inner flow region was directly related to the scale of roughness present on the bed (and independent of flow depth), increasing with increased roughness. On a rough but rather uniform "plane" bed made of heterogeneous coarse sediments (with no bed forms), the shape of the velocity profile was clearly dominated by the local variations in grain characteristics. When pebble clusters were superimposed, the average shear stress in the outer flow region increased by 100% from the plane bed conditions. The ratio of inner grain shear stress to outer total shear stress for this pebble cluster experiment was 0.18 under shallow flow conditions and 0.3 under deep flow conditions. The grain stress component that should be used in bed load transport equations therefore appears to vary in these experiments between 15% and 30% of the total channel stress, increasing with decreased resistance. Roughness height (K-s/D-50) values at the grain scale for the plane bed and pebble cluster experiments were 0.73 and 0.63, respectively. These are values that should be used in flow resistance equations to predict grain resistance and grain stress for bed load transport modeling. (C) 2001 Elsevier Science B.V. All rights reserved.
Lawless, M., and A. Robert, Three-dimensional flow structure around small-scale bedforms in a simulated gravel-bed environment, Earth Surface Processes and Landforms, 26 (5), 507-522, 2001.
Pebble clusters are common small-scale morphological features in gravel-bed rivers, occupying as much as 10 per cent of the bed surface. Important links exist between the presence of pebble clusters and the development of flow structures. These links are poorly understood at the three-dimensional level. Particularly neglected has been the effect of clusters on the lateral flow characteristics. A laboratory study was conducted using a hydraulic flume, within which simulated pebble clusters were superimposed onto a plane bed of gravel material. High- resolution three-dimensional flow data were collected above the bed at two different flow depths using an acoustic Doppler velocimeter. The results present evidence of the importance of lateral flow in the development of turbulent flow structure. Narrow regions of high lateral and downstream turbulence intensity exist to both sides of clusters and in a three- dimensional separation zone in their lee. This may indicate the presence of horseshoe-type vortical structures analogous to those identified in less hydraulically rough environments. However, it is likely that these structures are more complicated given the mutual interference of the surrounding medium. The lateral flow was also identified as a key component in the upwelling identified by other authors in the lee of pebble clusters. The results of the vertical flow analysis confirm the hypothesis that six regions with distinct vertical flow characteristics exist above clusters: flow acceleration up the stoss-side of the cluster; recirculation behind the cluster in the wake region; vortex shedding from the pebble crest and shear layer; flow reattachment downstream of the cluster; upwelling of flow downstream of the point of reattachment; and recovery of flow. Copyright (C) 2001 John Wiley & Sons, Ltd.
Lawrence, D.S.L., Macroscale surface roughness and frictional resistance in overland flow - Reply, Earth Surface Processes and Landforms, 23 (9), 861-863, 1998.
Lawrie, S.M., D.G. Raffaelli, and C.H. Emes, Small-scale patterns in the distribution of the amphipod Corophium volutator on the Ythan estuary, Aberdeenshire, Scotland, Sarsia, 85 (4), 321-327, 2000.
The small-scale patterns of spatial distribution of Corophium volutator (Pallas) were investigated in winter and summer by intensive, high spatial resolution surveys. Spatial analysis techniques (dispersion indices and spatial autocorrelation) were used to describe the patterns. In winter there was a strong pattern of high-density patches, 0-6 cm in size, distributed at random over the mud flat. A similar pattern was indicated during the summer, although it was less clear. Interactions between individuals seems the most likely mechanism for the formation and maintenance of this small-scale pattern in Corophium.
Leaf, C.F., An analytical framework for evaluating channel maintenance flows in Colorado, Journal of the American Water Resources Association, 34 (4), 865-876, 1998.
An accounting procedure is developed which determines a flow regime that is capable of transporting an amount of bedload sediment necessary to ensure channel stability downstream. The method allows for sediment buildup in the channel within geomorphic threshold limits during low now periods. During periods of high runoff, enough water is bypassed to transport the stored sediment. The procedure utilizes only those flows of sufficient magnitude to maintain channel stability over the long run (25-50+ years). An example is presented which determines the volume of water and frequency of release for channel maintenance purposes downstream from a hypothetical water diversion project. Of some 1,200,000 acre feet generated during a 59-year period, 86,500 acre feet was required for channel maintenance flows. Bypass flows were not required each year, but only during those years when average daily flow reached bankfull or greater. Such releases were made on 202 of the 411 days when average flows either equalled or exceeded bankfull discharge.
Lecce, S.A., Nonlinear downstream changes in stream power on Wisconsin's Blue River, Annals of the Association of American Geographers, 87 (3), 471-486, 1997.
Leckie, D.A., Canterbury Plains, New-Zealand - Implications For Sequence Stratigraphic Models, Aapg Bulletin-American Association of Petroleum Geologists, 78 (8), 1240-1256, 1994.
The Canterbury Plains, New Zealand, bounded by the Southern Alps and the Pacific Ocean, are traversed by four large gravel rivers. The coastline is wave dominated and microtidal (<2 m) with high rates of longshore sediment transport. The Canterbury coast is subdivided into southern and northern portions separated by the Banks Peninsula. The southern coastline, which is subjected to large oceanic swell originating as far away as 2000 km, is retrogradational and has wave-cut cliffs up to 25 m high. Coastal erosion at about 1 m/yr steepens the gradient, causing the rivers to incise 1.5-4.2 mm/yr during the present sea level highstand and accompanying transgression. Coastal erosion is caused by the extreme wave energy and efficient longshore sediment transport. River mouths are incising into the regional flood plain, with the amount of incision decreasing inland from the coast. The fluvial headwaters in the Southern Alps are rising tectonically and isostatically, causing incision that decreases seaward. Thus, fluvial incision takes place in the west due to mountain uplift and in the east, along the coast, due to a retreating shoreline during marine transgression. A zone of minimal valley incision occurs 8-15 km from the coast. In contrast to this observation, sequence stratigraphic models suggest that downcutting should occur during falling sea level, not during transgression. The northern coastline progrades about 1 m/yr and is largely sandy in its southern reaches. Thus, the Canterbury coastline is at one locale progradational and elsewhere retrogradational. The thickness of material being removed by erosional shoreface retreat during the present transgression is about 40 m. Although sea level plays a role, more important controls on progradation, retrogradation, and valley incision on the Canterbury Plains are the extreme wave energy and longshore drift.
Lee, H.Y., and S.T. Hwang, Migration of Backward-Facing Step, Journal of Hydraulic Engineering-Asce, 120 (6), 693-705, 1994.
A backward-facing step sometimes forms in an alluvial river. The step deforms and migrates when the inflow sediment and flow conditions change. A series of experiments were conducted to investigate the migration behavior of a backward-facing step composed of uniform sediment. According to the experimental observations, the phenomena observed were that the bed material picked up from the upstream reach was deposited in the separation zone at the step and caused the step to migrate downstream. Due to contraction of the flow cross section in the vicinity of the knickpoint, the bed-shear stress increased locally, which caused scouring. The scouring propagated either upstream or downstream depending on step height, flow conditions, and sediment characteristics. A linear-wave model was proposed to simulate the process. The model was calibrated and verified with experimental data. Due to the nonuniformity of the flow conditions in the vicinity of the step, the model can only provide qualitative information in this region. Fortunately, the nonuniform-flow conditions last at most 60 s, and hence the overall simulation results arc quite satisfactory.
Lee, H.Y., Y.H. Chen, J.Y. You, and Y.T. Lin, Investigations of continuous bed load saltating process, Journal of Hydraulic Engineering-Asce, 126 (9), 691-700, 2000.
Legendre, P., and M.J. Anderson, Distance-based redundancy analysis: Testing multispecies responses in multifactorial ecological experiments, Ecological Monographs, 69 (1), 1-24, 1999.
We present a new multivariate technique for testing the significance of individual terms in a multifactorial analysis- of-variance model for multispecies response variables. The technique will allow researchers to base analyses on measures of association (distance measures) that are ecologically relevant. In addition, unlike other distance-based hypothesis- testing techniques, this method allows tests of significance of interaction terms in a linear model. The technique uses the existing method of redundancy analysis (RDA) but allows the analysis to be based on Bray-Curtis or other ecologically meaningful measures through the use of principal coordinate analysis (PCoA). Steps in the procedure include: (1) calculating a matrix of distances among replicates using a distance measure of choice (e.g,, Bray-Curtis); (2) determining the principal coordinates (including a correction for negative eigenvalues if necessary), which preserve these distances (3) creating a matrix of dummy variables corresponding to the design of the experiment (i.e., individual terms in a linear model); (4) analyzing thr relationship between thp principal coordinates (species data) and the dummy variables (model) using RDA; and (5) implementing a test by permutation for particular statistics corresponding to the particular terms in the model. This method has certain advantages not shared by other multivariate testing procedures. We demonstrate the use of this technique with experimental ecological data from intertidal assemblages and show how the presence of significant multivariate interactions can be interpreted. It is our view that distance-based RDA will be extremely useful to ecologists measuring multispecies responses to structured multifactorial experimental designs.
Lekach, J., and A.P. Schick, Evidence For Transport of Bedload in Waves - Analysis of Fluvial Sediment Samples in a Small Upland Stream Channel, Catena, 10 (3), 267-279, 1983.
Lekach, J., R. Amit, T. Grodek, and A.P. Schick, Fluvio-pedogenic processes in an ephemeral stream channel, Nahal Yael, southern Negev, Israel, Geomorphology, 23 (2-4), 353-369, 1998.
Lenau, C.W., and A.T. Hjelmfelt, River Bed Degradation Due to Abrupt Outfall Lowering, Journal of Hydraulic Engineering-Asce, 118 (6), 918-933, 1992.
Lower reaches of tributaries to the Missouri River were straightened in the late 19th and early 20th century. Channel degradation has progressed upstream as a result, Channel deepening and widening have caused problems at stream crossings and have resulted in gully encroachment into cultivated fields. A diffusion model and an hyperbolic model, each describing channel degradation, are solved using a Laplace transform approach. A closed-form solution is obtained for the diffusion model. but numerical methods are necessary for evaluation of the inverse transform of the hyperbolic model. A closed-form asymptotic solution is found for the hyperbolic case. This asymptotic solution is shown to contain the solution to the diffusion model as a special case. The asymptotic solution is compared with observed degradation of West Tarkio Creek, a small river in northwestern Missouri and southwestern Iowa, with good results.
Lenzi, M.A., V. D'Agostino, and P. Billi, Bedload transport in the instrumented catchment of the Rio Cordon Part I: Analysis of bedload records, conditions and threshold of bedload entrainment, Catena, 36 (3), 171-190, 1999.
The paper illustrates the results of 10 years of research conducted on the Rio Cordon catchment (5 km(2)), where an experimental station has been operating for the integral and continuous automatic recording of water discharge and coarse sediment transport, The device operates by separating bedload from water discharge and fine sediment and subsequently measuring the two solid components. The recorded floods are grouped in two distinct categories according to the bedload transport rates, 'ordinary' and 'exceptional' floods (with return times exceeding 30-50 years). Based on data collected and field studies, the aspects characterising threshold conditions of bedload transport at flood initiation and cessation are illustrated. Then, a description is given of the conditions which are necessary for two distinct mechanisms of incipient motion of bed particles to occur: selective transport and equal mobility of stream bed material. (C) 1999 Elsevier Science B.V. All rights reserved.
Lenzi, M.A., and L. Marchi, Suspended sediment load during floods in a small stream of the Dolomites (northeastern Italy), Catena, 39 (4), 267-282, 2000.
Suspended sediment load was analyzed in a small, high-gradient stream of the Eastern Italian Alps which was instrumented to measure discharge and sediment transport. The ratio of suspended to total sediment yield and the relations between sediment concentration and water discharge were analyzed for seven floods which occurred from 1991 to 1996 in summer and autumn (from June to October). Different patterns of hysteresis in the relation between suspended sediment and discharge were related to types and locations of active sediment sources. The within-storm variation of particle size of suspended sediment during a major flood indicates a coarsening of transported material for increasing discharge. An analysis of grain size has shown that erosion areas on hillslopes were the main sources of suspended load. (C) 2000 Elsevier Science B.V. All rights reserved.
Lenzi, M.A., Step-pool evolution in the Rio Cordon, northeastern Italy, Earth Surface Processes and Landforms, 26 (9), 991-1008, 2001.
The principle that formative events, punctuated by periods of evolution, recovery or temporary periods of steady-state conditions, control the development of the step-pool morphology, has been applied to the evolution of the Rio Cordon stream bed. The Rio Cordon is a small catchment (5 km(2)) within the Dolomites wherein hydraulic parameters of floods and the coarse bedload are recorded. Detailed field surveys of the step-pool structures carried out before and after the September 1994 and October 1998 floods have served to illustrate the control on step-pool changes by these floods. Floods were grouped into two categories. The first includes 'ordinary' events which are characterized by peak discharges with a return time of one to five years (1.8-5.15 m(3) s(-1)) and by an hourly bedload rate not exceeding 20 m(3) h(-1). The second refers to 'exceptional' events with a return time of 30-50 years. A flood of this latter type occurred on 14 September 1994, with a peak discharge of 10.4 m(3) s(-1) and average hourly bedload rate of 324 m(3) h(-1). Step-pool features were characterized primarily by a steepness parameter c = (H/L-s)/S. The evolution of the steepness parameter was measured in the field from 1992 to 1998. The results indicate that maximum resistance conditions are gradually reached at the end of a series of ordinary flood events. During this period, bed armouring dominate the sediment transport response. However, following an extraordinary flood and unlimited sediment supply conditions, the steepness factor can suddenly decrease as a result of sediment trapped in the pools and a lengthening of step spacing. The analogy of step spacing with antidune wavelength and the main destruction and transformation mechanism of the steps are also discussed. Copyright (C) 2001 John Wiley & Sons, Ltd.
leRoux, J.P., Relationship between aerodynamic entrainment threshold and hydrodynamic settling velocity of particles, Sedimentary Geology, 109 (1-2), 199-205, 1997.
Lewin, J., and P.A. Brewer, Predicting channel patterns, Geomorphology, 40 (3-4), 329-339, 2001.
Li, S.G., L. Venkataraman, and D. McLaughlin, Stochastic-Theory For Irregular Stream Modeling .1. Flow Resistance, Journal of Hydraulic Engineering-Asce, 118 (8), 1079-1090, 1992.
A stochastic theory is developed for predicting flow resistance in natural rivers. Irregularly varying river width and bed elevation are represented as one-dimensional spatial random fields. Large-scale random flow acceleration and deceleration in response to boundary variations are described by the stochastic differential flow equation. Analytical stochastic flow solutions are developed for the case when boundary variations are small and statistically homogeneous. In particular, closed-form expressions for the effective flow resistance coefficient and flow variance are obtained. The results indicate that flow resistance in natural rivers is strongly influenced by cross-sectional nonuniformity and mean flow condition, in addition to relative boundary roughness and mean cross-sectional shape. The results also show that effective resistance is always greater than uniform resistance in a corresponding mean straight channel. This difference increases as the mean Froude number increases for a given mean bed slope or as mean bed slope decreases for a given mean Froude number. Part II of this paper will be published in the future.
Liebault, F., P. Clement, H. Piegay, and N. Landon, Assessment of bedload delivery from tributaries: The Drome River case, France, Arctic Antarctic and Alpine Research, 31 (1), 108-117, 1999.
Liggett, J.A., Critical Depth, Velocity Profiles, and Averaging, Journal of Irrigation and Drainage Engineering-Asce, 119 (2), 416-422, 1993.
Lisle, T.E., Effects of Aggradation and Degradation On Riffle-Pool Morphology in Natural Gravel Channels, Northwestern California, Water Resources Research, 18 (6), 1643-1651, 1982.
Lisle, T.E., Stabilization of a Gravel Channel By Large Streamside Obstructions and Bedrock Bends, Jacoby Creek, Northwestern California, Geological Society of America Bulletin, 97 (8), 999-1011, 1986.
Lisle, T.E., H. Ikeda, and F. Iseya, Formation of Stationary Alternate Bars in a Steep Channel With Mixed-Size Sediment - a Flume Experiment, Earth Surface Processes and Landforms, 16 (5), 463-469, 1991.
Alternate bars were formed by sediment transport in a flume with Froude-modelled flow and relative roughness characteristic of gravel-boulder channels with steep slopes. The flume (0.3 m wide x 7.5 m long) was filled with a sand-gravel mixture, which was also fed into the top of the flume at a constant rate under constant discharge. Channel slope was set at 0.03. Initially, coarse particles accumulated on incipient bar heads near one side of the flume and diverted flow and bedload transport across the flume toward a pool scoured against the opposite flume wall downstream. Sorting in the pool directed coarse particles onto the next bar head downstream. Alternate sequences of pools and coarse bar heads were thereby linked down the entire flume by interactions of sediment sorting, flow, and channel morphology. During episodes of bar construction, unsorted bedload invaded interior bar surfaces and was deposited. Persistent deposition of coarse particles on bar heads prevented downstream migration of bars by inhibiting bar-head erosion and bedload transport over bars. Likely factors leading to bar-head stabilization in modelled gravel-bed channels are coarse mixed-size sediment, steep channel gradients, and shallow depths.
Lisle, T.E., and S. Hilton, The Volume of Fine Sediment in Pools - an Index of Sediment Supply in Gravel-Bed Streams, Water Resources Bulletin, 28 (2), 371-383, 1992.
During waning flood flows in gravel-bed streams, fine-grained bedload sediment (sand and fine gravel) is commonly winnowed from zones of high shear stress, such as riffles, and deposited in pools, where it mantles an underlying coarse layer. As sediment load increases, more fine sediment becomes available to fill pools. The volume of fine sediment in pools can be measured by probing with a metal rod, and, when expressed as the fraction (V*) of scoured residual pool volume (residual pool volume with fine sediment removed), can be used as an index of the supply of mobile sediment in a stream channel. Mean values of V* were as high as 0.5 and correlated with qualitative evaluations of sediment supply in eight tributaries of the Trinity River, northwestern California. Fine-sediment volume correlated strongly with scoured pool volume in individual channels, but plots of V* versus pool volume and water surface slope revealed secondary variations in fines volume. In sediment-rich channels, V* correlated positively with scoured pool volume; in sediment-poor channels, V* correlated negatively with water-surface slope. Measuring fine sediment in pools can be a practical method to evaluate and monitor the supply of mobile sediment in gravel-bed streams and to detect and evaluate sediment inputs along a channel network.
Lisle, T.E., F. Iseya, and H. Ikeda, Response of a Channel With Alternate Bars to a Decrease in Supply of Mixed-Size Bed-Load - a Flume Experiment, Water Resources Research, 29 (11), 3623-3629, 1993.
Lisle, T.E., Effects of Coarse Woody Debris and Its Removal On a Channel Affected By the 1980 Eruption of Mount-St-Helens, Washington, Water Resources Research, 31 (7), 1797-1808, 1995.
During the May 18, 1980, eruption of Mount St. Helens, Washington, a pyroclastic surge introduced large volumes of coarse woody debris (CWD) and fine-grained sediment to Clearwater Creek, approximately 15 km northeast of the summit. Effects of controlled CWD removal on sediment storage, substrate, and pool frequency and volume were measured in four reaches, each with three 200-m segments, from 1982 to 1990. In each reach the-upstream segment served as a control with no debris removal, and CWD was totally and selectively removed from the other two segments. Unique among similar experiments are the large size and volume of CWD and the large inputs of fine-grained sediment. Except for segments of two reaches that received debris torrents, the Clearwater channel thalweg scoured until 1985. In three reaches, total debris removal caused additional scour and coarsening of the bed surface compared to segments with no or partial debris removal. Pools contracted from 1982 to 1985 and expanded afterward, especially in control segments. Total debris removal apparently caused pools to become shallower and, in segments of low sinuosity, decreased the frequency of major pools. Habitat complexity decreased after total debris removal, as indicated by a decrease in the standard deviation of residual depth and an increase in the size of substrate patches.
Lisle, T.E., Particle-Size Variations Between Bed-Load and Bed Material in Natural Gravel-Bed Channels, Water Resources Research, 31 (4), 1107-1118, 1995.
Lisle, T.E., J.E. Pizzuto, H. Ikeda, F. Iseya, and Y. Kodama, Evolution of a sediment wave in an experimental channel, Water Resources Research, 33 (8), 1971-1981, 1997.
The routing of bed material through channels is poorly understood. We approach the problem by observing and modeling the fate of a low-amplitude sediment wave of poorly sorted sand that we introduced into an experimental channel transporting sediment identical to that of the introduced wave. The wave essentially dispersed upstream and downstream without translation, although there was inconclusive evidence of translation late in the experiment when the wave was only 10-20 grain diameters high. Alternate bars migrated through zones of differing bed load transport rate without varying systematically in volume, celerity, or transport rate. Sediment that overpassed migrating bars was apparently responsible for dispersion of the wave. The evolution of the wave was well predicted by a one-dimensional model that contains no adjusted empirical constants. Numerical experiments demonstrate, however, that the theory does not predict sediment waves that migrate long distances downstream. Such waves can only be explained by the following processes not represented by the theory: selective bed load transport, spatial variations in bar and other form roughness, the mechanics of mobile armor, and perhaps other mechanisms.
Lisle, T.E., and S. Hilton, Fine bed material in pools of natural gravel bed channels, Water Resources Research, 35 (4), 1291-1304, 1999.
Natural gravel bed channels commonly contain a fine mode of sand and fine gravel that fills voids of the bed framework of coarser gravel. If the supply of fine bed material exceeds the storage capacity of framework voids, excess fine material forms surficial patches, which can be voluminous in pools during low flow. Data collected in 34 natural channels in northern California and southern Oregon indicate the following. (1) Fine material on the bed surface can be readily winnowed and transported at high particle velocities, much of it in intermittent suspension. Fine material can dominate the bed material load in gravel bed channels, but its abundance on the bed surface is limited by its increasing mobility as hiding places among prominent particles are filled. (2) Fine material in pools is typically replaced many times per year. (3) The proportion V* of residual pool volume filled with fine bed material correlates with annual sediment yield in channels whose parent material produces abundant sandy sediment. (4) Temporal and spatial changes in V* appear to correspond to variations in the balance between sediment inputs and water discharge. These results suggest that V* can be used to monitor and evaluate the supply of excess fine material in gravel bed channels and that samples of fine material in pools can characterize the fine, mobile mode of bed material load.
Lisle, T.E., J.M. Nelson, J. Pitlick, M.A. Madej, and B.L. Barkett, Variability of bed mobility in natural, gravel-bed channels and adjustments to sediment load at local and reach scales, Water Resources Research, 36 (12), 3743-3755, 2000.
Local variations in boundary shear stress acting on bed-surface particles control patterns of bed load transport and channel evolution during varying stream discharges. At the reach scale a channel adjusts to imposed water and sediment supply through mutual interactions among channel form, local grain size, and local flow dynamics that govern bed mobility. In order to explore these adjustments, we used a numerical flow model to examine relations between model-predicted local boundary shear stress (tau (j)) and measured surface particle size (D-50) at bank-full discharge in six gravel-bed, alternate-bar channels with widely differing annual sediment yields. Values of tau (j) and D-50 were pearly correlated such that small areas conveyed large proportions of the total bed load, especially in sediment-poor channels with low mobility. Sediment-rich channels had greater areas of full mobility; sediment-poor channels had greater areas of partial mobility; and both types had significant areas that were essentially immobiIe. Two reach-mean mobility parameters (Shields stress and Q*) correlated reasonably well with sediment supply. Values which can be practicably obtained from carefully measured mean hydraulic variables and particle size would provide first-order assessments of bed mobility that would broadly distinguish the channels in this study according to their sediment yield and bed mobility.
Lobo, J.M., I. Castro, and J.C. Moreno, Spatial and environmental determinants of vascular plant species richness distribution in the Iberian Peninsula and Balearic Islands, Biological Journal of the Linnean Society, 73 (2), 233-253, 2001.
Using an exhaustive data compilation, Iberian vascular plant species richness in 50 x 50 UTM grid cells was regressed against 24 explanatory variables (spatial, geographical, topographical, geological, climatic, Wand use and environmental diversity variables) using Generalized. Linear Models and partial regression analysis in order to ascertain the relative contribution of primary, heterogeneous and spatially structured variables. The species richness variation accounted for by these variables is reasonably high (65% of total deviance). Little less than half of this variation is accounted for spatially structured variables. A purely spatial component of variation is hardly significant. The most significant variables are those related to altitude, and particularly maximum altitude, whose cubic response reflects the occurrence of the maximum number of species at the highest altitudes. This result highlighted the importance of Iberian mountains as hotspots of diversity and the relevance of large and small scale historical factors in contemporary plant distribution patterns. Climatic or energy-related variables contributed little, whereas geological (calcareous and acid rocks) and, to a lesser extent, environmental heterogeneity variables (land use diversity and altitude range) seem to be more important. (C) 2001 The Linnean Society of London.
Logli, F., and R. Joffre, Individual variability as related to stand structure and soil condition in a Mediterranean oak coppice, Forest Ecology and Management, 142 (1-3), 53-63, 2001.
Knowledge of spatial variability of coppices, and of factors that determine them, is essential to adapt silvicultural practices to heterogeneous stands. Mediterranean oak coppices offer a good example of highly spatially variable ecosystem. We examined here the detailed structure of a Quercus pubescens coppice stand growing on a Mediterranean habit. The objectives were (1) to document the individual variability of stools measuring environmental and morphological parameters, (2) to define coppice types using this information and (3) to explore possible silvicultural implications. Exhaustive sampling of a 30 mx30 m plot was conducted. Stool basal area, height, crown area, and number of shoots per stool were measured. Distances between all stools located in the plot were recorded allowing the calculation of individual polygon area and crowding index. A principal component analysis (PCA) showed that the spatial pattern of the stand could be related to soil heterogeneity and to population parameters. Based on this analysis, we defined five types of individual-coppice-stool. These types reflected both the variability of the site (soil resource) and the structure of the stand (neighbourhood influences). Advanced silvicultural criteria based of a better knowledge of stand structure variability and taking into account spatial and environmental heterogeneity may be introduced in the management of these coppices. (C) 2001 Elsevier Science B.V. All rights reserved.
Lopez, J.L., and M.A. Falcon, Calculation of bed changes in mountain streams, Journal of Hydraulic Engineering-Asce, 125 (3), 263-270, 1999.
Lopezbermudez, F., Soil-Erosion By Water On the Desertification of a Semiarid Mediterranean Fluvial Basin - the Segura Basin, Spain, Agriculture Ecosystems & Environment, 33 (2), 129-145, 1990.
Soil erosion is a complex and dynamic conjunction of processes that work on all natural systems, but which are particularly serious and problematical in semi-arid environments subject to strong human pressure. The Segura basin finds itself in this situation. The loss of soil in this area of SE Spain is one of the highest and most serious of the whole Iberian peninsula; in some parts it reaches 200 Tm ha-1 year-1 and in others up to 300 Tm ha-1 year-1, which amounts to a soil thickness of approximately 12 and 20 mm, respectively. These irreversible soil losses imply the reduction and destruction of the biological or productive potential of the earth and lead to desertification.
Lowewenherz, D.S., Stability and the Initiation of Channelized Surface Drainage - a Reassessment of the Short Wavelength Limit, Journal of Geophysical Research-Solid Earth and Planets, 96 (B5), 8453-8464, 1991.
Instability leading to channel initiation occurs when advective processes dominate diffusive processes in the transport of surface material. Smith and Bretherton's (1972) linear treatment of this stability/instability phenomenon is here reexamined. Slopes of finite length are considered and a turning point analysis is used to construct a full asymptotic solution for the short wavelength limit. The analysis shows that the initial longitudinal profiles of marginally unstable surface incisions are deepest at a point corresponding to the convex/concave boundary in the base state profile and may actually extend upslope some distance from that point. The extent of the upslope incision is dependent upon the diffusion coefficient for the surface material and the wave number of the disturbance. In the original stability model, the growth rate of the short wavelength instability increases with decreasing wavelength, so that the shortest wavelengths are the most unstable. By introducing a surface material transport function which accounts for microscale nonlocal transfer, the shortest wavelengths are damped and the unstable growth rates are largest at moderate values of the wave number. The lengthscale set by nonlocal material transport represents the spatial scale at which the continuum description underlying the stability model breaks down. The neutral stability diagram for slope length-wave number space illustrates that when the very shortest wavelengths are damped, concave slope segments may exhibit stability, at least while the system is within a linear regime. The most promising field application of the linear model lies in the characterization of shallow surface incisions, such as rills, which are in initial stages of development.
Lu, J.Y., and H.W. Shen, Analysis and Comparisons of Degradation Models, Journal of Hydraulic Engineering-Asce, 112 (4), 281-299, 1986.
Lundquist, J.E., L.R. Lindner, and J. Popp, Using landscape metrics to measure suitability of a forested watershed: a case study for old growth, Canadian Journal of Forest Research-Revue Canadienne De Recherche Forestiere, 31 (10), 1786-1792, 2001.
Several metrics for spatial heterogeneity based on distribution of stands suitable for old growth were calculated for the actual and optimal conditions of a watershed in the Medicine Bow National Forest in Wyoming. Optimal conditions were based on expert opinions. The actual condition was compared with target conditions using a multivariate method called profiling, which develops profiles based on various spatial statistics and examines the similarity of these profiles using a multidimensional scaling (MDS) procedure. Profiles for various target landscapes clustered together in MDS space, and this space could be defined and quantified using a kernel density estimator. The distance from the centroid of the target space to the position of the actual stand is used as a measure of dissimilarity. By comparing the condition of a given watershed to that of what experts envisioned would be optimal, we argue that the relative condition of the watershed can be characterized. We make a distinction between stand-scale metrics and landscape-scale metrics. We propose that this method may be useful in quantifying changes in landscape conditions and could be useful as a monitoring method in forest plans.
Lundquist, J.E., and N.B. Klopfenstein, Integrating concepts of landscape ecology with the molecular biology of forest pathogens, Forest Ecology and Management, 150 (3), 213-222, 2001.
Increasingly more research has focused on characterizing diversity within forest pathogen populations using molecular markers but few studies have characterized features of the landscape that help created or maintain this diversity. Forest diseases commonly occur in patchy distributions across natural landscapes which can be reflected in the genetic composition of the fragmented pathogen populations. This metapopulation structure has seldom been, examined by forest pathologists but we believe it offers a potential means to understand the genetic ecology of pathogens in natural landscapes. Molecular markers can be used to detect, identify, and measure detailed differences among subpopulations of forest pathogens. Geographical information systems, spatial analysis and modeling, digital imagery of remotely sensed images, and other tools of landscape ecology provide the means to detect and interpret patterns associated with genotypic asymmetry. Integrating the tools and concepts of molecular biology and landscape ecology by focusing on metapopulation disease phenomena offers a way of conceptually linking molecules and ecosystems. Published by Elsevier Science B.V.
Lykke, A.M., and A. Goudiaby, Structure, floristic composition, and conservation potentials of a remnant gallery forest at 'Mare du Dragon', Senegal, Nordic Journal of Botany, 19 (5), 561-574, 1999.
Woody plants in the last existing fragment of closed gallery forest in Delta du Saloum National Park, Senegal, were investigated by use of a 0.6 ha transect covering the main part of the gallery forest. There were 24 species and 369 individuals greater than or equal to 5 cm dbh with a basal area of 12.6 m(2), 1062 individuals greater than or equal to 1 cm dbh in 31 species, and 1730 individuals < 1 cm dbh in 29 species. Constrained clustering revealed six floristically distinct sections along the transect, and these sections coincided with structural differences. The Vegetation in the study area is marked by degradation caused by frequent and intense fires coming from the surrounding savanna and by declining precipitation However, the gallery forest is unique to the area and of crucial importance for conserving biodiversity. It can in the future be important as a resource- base for restoration of the gallery forest system by means of natural regeneration.
MacDonald, L.H., Evaluating and managing cumulative effects: Process and constraints, Environmental Management, 26 (3), 299-315, 2000.
Cumulative effects (CEs) result from the combined effect of multiple activities over space or time. This implies a persistence through time and often a transmittal mechanism through space. Environmental legislation often requires a broader CE assessment in addition to the more direct. project- specific impacts. Current efforts to evaluate and manage CEs are hampered by the conceptual problems of defining the key issues. specifying the appropriate spatial and temporal scales, and determining the numerous interactions and indirect effects. These problems can be greatly alleviated by following an explicit process. The process proposed in this paper includes a scoping phase, an analysis phase, and a planning and management phase, with each phase consisting of two to five discrete but interrelated tasks. Numerous approaches have been developed to assess CEs, and these range from simple checklists to complex, physically based models. The utility of each approach depends on the resource of concern, relative risk to those resources, information available, and time frame for the evaluation. in nearly all cases the assessment and regulation of CEs is severely hampered by the variability in site conditions and management effects, inability to predict secondary or indirect effects, lack of data on recovery rates, difficulty of validating predictive models, and uncertainty of future events. Since any proposed activity could contribute to a wide range of potential CEs at different spatial and temporal scales, a tiered or nested approach should be followed to assess CEs. The difficulty of assessing and predicting CEs also suggests that in many cases the most efficient approach is to focus on minimizing on-site impacts. Under some circumstances adaptive management can also be a viable alternative to detailed CE assessments. Regular monitoring and feedback is critical to the successful management and regulation of CEs.
Macklin, M.G., and J. Lewin, Sediment Transfer and Transformation of an Alluvial Valley Floor - the River South Tyne, Northumbria, Uk, Earth Surface Processes and Landforms, 14 (3), 233-246, 1989.
Macklin, M.G., Holocene river environments in prehistoric Britain: Human interaction and impact, Journal of Quaternary Science, 14 (6), 521-530, 1999.
This paper presents a review of alluvial geoarchaeolgical research in Britain and considers some of the key conceptual and methodological issues that currently confront the subdiscipline. Three major themes are discussed. 1. The influence of Late Pleistocene inheritance on Holocene river development and river basin sensitivity to natural and anthropogenic perturbations. 2. Establishing correlations between river alluviation and erosion episodes with climate and prehistoric landuse change. 3. The effects of Holocene river development on the preservation and visibility of the alluvial archaeological record. It is concluded that only when adequate temporal and spatial resolution is achieved in both the archaeological and geomorphological records of river valleys, will a true synergy develop and a full understanding of long term human-river environment interaction emerge.
Maddock, I., The importance of physical habitat assessment for evaluating river health, Freshwater Biology, 41 (2), 373-391, 1999.
1. Physical habitat is the living space of instream biota; it is a spatially and temporally dynamic entity determined by the interaction of the structural features of the channel and the hydrological regime. 2. This paper reviews the need for physical habitat assessment and the range of physical habitat assessment methods that have been developed in recent years. These methods are needed for assessing improvements made by fishery enhancement and river restoration procedures, and as an intrinsic element of setting environmental flows using instream flow methods. Consequently, the assessment methods must be able to evaluate physical habitat over a range of scales varying from the broad river segment scale (up to hundreds of kilometres) down to the microhabitat level (a few centimetres). 3. Rapid assessment methods involve reconnaissance level surveys (such as the habitat mapping approach) identifying, mapping and, measuring key habitat features over long stretches of river in a relatively short space of time. More complex appraisals, such as the Physical Habitat Simulation System (PHABSIM), require more detailed information on microhabitat variations with flow. 4. Key research issues relating to physical habitat evaluation lie in deciding which levels of detail are appropriate for worthwhile yet cost-effective assessment, and in determining those features that are biologically important and hence can be considered habitat features rather than simple geomorphic features. 5. The development of new technologies particularly relating to survey methods should help improve the speed and level of detail attainable by physical habitat assessments. These methods will provide the necessary information required for the development of the two-and three-dimensional physical and hydraulic habitat models. 6. A better understanding of the ways in which the spatial and temporal dynamics of physical habitat determine stream health, and how these elements can be incorporated into assessment methods, remains a key research goal.
Madej, M.A., and V. Ozaki, Channel response to sediment wave propagation and movement, Redwood Creek, California, USA, Earth Surface Processes and Landforms, 21 (10), 911-927, 1996.
Redwood Creek, north coastal California, USA, has experienced dramatic changes in channel configuration since the 1950s. A series of large floods (in 1955, 1964, 1972 and 1975) combined with the advent of widespread commercial timber harvest and road building resulted in extensive erosion in the basin and contributed high sediment loads to Redwood Creek. Since 1975, no peak hows have exceeded a 5 year recurrence interval. Twenty years of cross-sectional survey data document the downstream movement of a 'sediment wave' in the lower 26 km of this gravel-bedded river at a rate of 800 to 1600 m a(-1) during this period of moderately low flows. Higher transit rates are associated with reaches of higher unit stream power. The wave was initially deposited at a site with an abrupt decrease in channel gradient and increase in channel width. The amplitude of the wave has attenuated more than 1 m as it moved downstream, and the duration of the wave increased from eight years upstream to more than 20 years downstream. Channel aggradation and subsequent degradation have been accommodated across the entire channel bed. Channel width has not decreased significantly after initial channel widening from large (> 25 year recurrence interval) hoods. Three sets of longitudinal surveys of the streambed showed the highest increase in pool depths and frequency in a degrading reach, but even the aggrading reach exhibited some pool development through time. The aggraded channel bed switched from functioning as a sediment sink to a significant sediment source as the channel adjusted to high sediment loads. From 1980 to 1990, sediment eroded from temporary channel storage represented about 25 per cent of the total sediment load and 95 per cent of the bedload exported from the basin.
Madej, M.A., Temporal and spatial variability in thalweg profiles of a gravel-bed river, Earth Surface Processes and Landforms, 24 (12), 1153-1169, 1999.
This study used successive longitudinal thalweg profiles in gravel-bed rivers to monitor changes in bed topography following floods and associated large sediment inputs. Variations in channel bed elevations, distributions of residual water depths, percentage of channel length occupied by riffles, and a spatial autocorrelation coefficient (Moran's I) were used to quantify changes in morphological diversity and spatial structure in Redwood Creek basin, northwestern California. Bed topography in Redwood Creek and its major tributaries consists primarily of a series of pools and riffles. The size, frequency and spatial distribution of the pools and riffles have changed significantly during the past 20 years. Following large floods and high sediment input in Redwood Creek and its tributaries in 1975, variation in channel bed elevations was low and the percentage of the channel length occupied by riffles was high. Over the next 20 years, variation in bed elevations increased while the length of channel occupied by riffles decreased. An index [(standard deviation of residual water depth/bankfull depth) x 100] was developed to compare variations in bed elevation over a range of stream sizes, with a higher index being indicative of greater morphological diversity. Spatial autocorrelation in the bed elevation data was apparent at both fine and coarse scales in many of the thalweg profiles and the observed spatial pattern of bed elevations was found to be related to the dominant channel material and the time since disturbance. River reaches in which forced pools dominated, and in which large woody debris and bed particles could not be easily mobilized, exhibited a random distribution of bed elevations. In contrast, in reaches where alternate bars dominated, and both wood and gravel were readily transported, regularly spaced bed topography developed at a spacing that increased with time since disturbance. This pattern of regularly spaced bed features was reversed following a 12-year flood when bed elevations became more randomly arranged. Copyright (C) 1999 John Wiley & Sons, Ltd.
Madej, M.A., Development of channel organization and roughness following sediment pulses in single-thread, gravel bed rivers, Water Resources Research, 37 (8), 2259-2272, 2001.
Large, episodic inputs of coarse sediment (sediment pulses) in forested, mountain streams may result in changes in the size and arrangement of bed forms and in channel roughness. A conceptual model of channel organization delineates trajectories of response to sediment pulses for many types of gravel bed channels. Channels exhibited self-organizing behavior to various degrees based on channel gradient, presence of large in-channel wood or other forcing elements, the size of the sediment pulse, and the number of bed-mobilizing flows since disturbance. Typical channel changes following a sediment pulse were initial decreases in water depth, in variability of bed elevations, and in the regularity of bed form spacing. Trajectories of change subsequently showed increased average water depth, more variable and complex bed topography, and increased uniformity of bed form spacing. Bed form spacing in streams with abundant forcing elements developed at a shorter spatial scale (two to five channel widths) than in streams without such forcing mechanisms (five to 10 channel widths). Channel roughness increased as bed forms developed.
Magilligan, F.J., and M.L. Stamp, Historical land-cover changes and hydrogeomorphic adjustment in a small Georgia watershed, Annals of the Association of American Geographers, 87 (4), 614-635, 1997.
This study utilizes hydrologic modeling (HEC-1) for discrete episodes of land use in a Georgia watershed to portray the hydrologic adjustments that occur during a period of intensive land clearing and subsequent revegetation. It then compares these hydrologic shifts to field based geomorphic adjustments such as gullying and valley aggradation. The Turner Creek watershed, settled in the mid-1830s, experienced a period of rapid land clearing with intensive cotton production (similar to 90 years) and then an extended period of reforestation (similar to 70 years), which generated hydrologic and geomorphic adjustments. Deep canyon formation in the poorly consolidated Coastal Plain lithologies occurred rapidly (similar to 30 years), causing upwards of 50 m of dissection. Results indicate that a new hydrologic regime has been established relative to both the prehistorical period (ca. 1800) and the period of maximum land clearing (ca. 1880), and that this hydrologic stability was achieved relatively quickly. Some geomorphic adjustments have coincided with the temporal pattern of hydrologic shifts. Aggradation rates, as determined by dendrochronology, have been a little slower to adjust but indicate an overall attenuation since 1948. Current sedimentation, unlike previous periods, is now most likely linked to the magnitude of spring storms. On the other hand, valley-side gully formation and stabilization are strongly linked to the pattern of hydrologic adjustments, as controlled by land-use patterns. Thus, this research indicates that watershed recovery and stability may be achieved, but it map differ from predisturbance conditions, and that not all hydrogeomorphic components respond similarly.
Magilligan, F.J., and P.F. McDowell, Stream channel adjustments following elimination of cattle grazing, Journal of the American Water Resources Association, 33 (4), 867-878, 1997.
Cattle grazing practices in the western United States have contributed to widespread riparian degradation resulting in unstable channel morphologies and the loss of fish habitat. Because of prolonged disturbance, numerous riparian areas oil both public and private lands have been fenced to exclude cattle in order to promote vegetation establishment and riparian improvement. We selected four gravel-bedded, steep alluvial streams in eastern Oregon with cattle exclosures greater than 14 years old for an analysis of geomorphic adjustments following the removal of cattle grazing. We compare channels inside exclosures and in adjacent grazed reaches to identify the salient stream channel properties that respond to the removal of riparian stresses and to document the magnitude of these changes. Results indicate that significant changes occur, with reductions in bankfull dimensions and increases in pool area being the most common and identifiable changes. At all four sites, bankfull widths are narrower by 10 to 20 percent, and the percentage of channel area occupied by pools is higher in the exclosure by 8 to 15 percent. The increase in pool area is primarily offset by a reduction in the percent glide area. Not all of the channel properties demonstrate adjustment, indicating that perhaps 14 years is an insufficient duration for these variables to adjust.
Magilligan, F., Fluvial forms and processes: A new perspective, Professional Geographer, 52 (3), 581-582, 2000.
Malvarez, G.C., J.A.G. Cooper, and D.W.T. Jackson, Relationships between wave-induced currents and sediment grain size on a sandy tidal-flat, Journal of Sedimentary Research, 71 (5), 705-712, 2001.
Manson, R.H., Spatial autocorrelation and the interpretation of patterns of tree seed and seedling predation by rodents in old-fields, Oikos, 91 (1), 162-174, 2000.
Spatial autocorrelation is ubiquitous in ecological systems. However, consideration of this phenomenon in seed and seedling predation studies has been limited, perhaps explaining some of the variation observed between studies and the difficulty in generalizing about the impacts of herbivores on successional processes. I examined the prevalence and patterns of spatial autocorrelation in seed and seedling survival between neighboring tree propagules in old-fields. All experiments were conducted within enclosures in which I manipulated the density of meadow voles (Microtus pennsylvanicus). Voles, and competitively inferior white-footed mice (Peromyscus leucopus), are the dominant consumers of tree seedlings and seeds in old- fields in the northeastern United States, respectively. An intermediate level of spatial autocorrelation was present in seed and seedling predation trials. Furthermore. the frequency of spatial autocorrelation increased under low-vole density conditions and in study sites with greater heterogeneity in vegetation cover. Survival of neighboring tree propagules was generally positively autocorrelated, suggesting that foraging by mice and voles contributes to a clumped pattern of tree propagule establishment in old-fields. A review of published predation studies found that only 8.3% attempted to test for spatial autocorrelation and that the minimum average spacing used between replicates is well below the average autocorrelation distance of 8.1 +/- 6.3 m observed in the current study. Patterns of autocorrelation appear somewhat predictable based on knowledge of the ecology of mice and voles and to provide insights into the factors influencing their foraging behavior and potential impacts on old-field succession.
Manville, V., J.D.L. White, B.F. Houghton, and C.J.N. Wilson, Paleohydrology and sedimentology of a post-1.8 ka breakout flood from intracaldera Lake Taupo, North Island, New Zealand, Geological Society of America Bulletin, 111 (10), 1435-1447, 1999.
Sudden releases of impounded water from lakes in volcanic regions constitute a major and frequently repeated hazard. An outburst flood from Taupo caldera, New Zealand, released similar to 20 kin(3) of water, within decades following an ignimbrite-emplacing eruption, ca. 1.8 ka. Paleohydrologic reconstruction of the Taupo flood provides estimates of peak discharge at the outlet in the range 17000-35000 m(3)/s. Dimensionless analysis demonstrates that (1) failure of the barrier was essentially instantaneous, (2) the event may be treated hydraulically as a dam break, and (3) the peak discharge was a function of outlet geometry rather than lake volume or breach formation rate. Paleohydraulic reconstructions based on empirical relations derived from historic dam breaches yield only order of magnitude estimates of peak discharge. Calculations based on the physical dimensions of the outlet channel and hydraulic principles are likely to be more accurate and are in close agreement with computer-implemented dynamic- flow-routing models. The latter give peak discharges and maximum stage levels similar to constraints imposed by field evidence and estimates of flow depth and velocity. The long duration of the Taupo flood and the relatively narrow, confined flood route resulted in minimal attenuation of the flood wave compared with modern dam breach events, and flood deposits can be traced as far as 232 km downstream. Caldera lake breakout floods may be among the most far-reaching hazards associated with volcanism.
Marek, D.W., M.K. Ali, and A.N. Ernest, Aquatic sediments, Water Environment Research, 68 (4), 629-662, 1996.
Marion, A., and L. Fraccarollo, New conversion model for areal sampling of fluvial sediments, Journal of Hydraulic Engineering-Asce, 123 (12), 1148-1151, 1997.
Marion, A., and L. Fraccarollo, Experimental investigation of mobile armoring development, Water Resources Research, 33 (6), 1447-1453, 1997.
Marr, J.G., J.B. Swenson, C. Paola, and V.R. Voller, A two-diffusion model of fluvial stratigraphy in closed depositional basins, Basin Research, 12 (3-4), 381-398, 2000.
Fundamental to interpreting the stratigraphic architecture within a basin is understanding the relationship between a basin's external conditions and its stratigraphic response. Here we present a model of fluvial basin filling that is based on two field observations. Firstly, natural fluvial systems commonly have an upstream region dominated by gravel transport and a downstream region dominated by sand transport with the transition between the two,being relatively abrupt. Second, gravel bed and sand bed systems operate at nearly constant but different mean Shields stresses. Our model is based on a single, linear diffusion equation but is unique in that we use distinct transport (diffusion) coefficients for the two dominant fluvial regimes: a proximal gravel region and a distal sand region. This problem is complicated by the existence of two moving boundaries: the position of the distal fluvial toe and the position of the gravel-sand transition. We present a rigorous numerical treatment of both of these moving boundaries and verify our numerical formulation by comparing the model results to a semi-analytical solution technique. We use the model to examine the stratigraphic response to perturbations in four external boundary conditions: sediment supply, water supply, rate of subsidence and gravel fraction. The response is analysed in terms of the phase relation between forcing and the position of the gravel front, the position of the fluvial toe, proximal accumulation rate and distal accumulation rate. The model supports the results of earlier single-diffusion models suggesting that the form of the response is dependent on the period of the perturbation relative to the intrinsic basin response time. For forcing periods less than the intrinsic basin response time, basin response is nearly constant and independent of the forcing period, suggesting that the transport system controls basin response. For forcing periods greater than the intrinsic response time of the basin the response time of the basin increases directly with the forcing period, suggesting that the transport system plays no role in limiting basin response. For gravel-sand systems we show that the intrinsic response time is a function of the ratio of gravel to sand entering the basin. Forcing of the above external boundaries, both slowly and rapidly relative to the basin response time, produces both distal and proximal unconformities. We present a nondimensional 'unconformity number' that constrains the amplitude and period of forcing necessary to generate proximal unconformities.
Marsalek, J., T.O. Barnwell, W. Geiger, M. Grottker, W.C. Huber, A.J. Saul, W. Schilling, and H.C. Torno, Urban Drainage Systems - Design and Operation, Water Science and Technology, 27 (12), 31-70, 1993.
Design and operation of urban drainage systems are addressed in the context of the urban water system comprising drainage, sewage treatment plants and receiving waters. The planning and design of storm sewers are reviewed with reference to planning objectives, design objectives, flows and pollutant loads, sewer system structures and urban runoff control and treatment. The discussion of combined sewers focuses on hydraulic design of combined sewer systems, including combined sewer overflow (CSO) structures, and the use of CSO structures and storage in control of CSOs. The section on operation of sewer systems focuses on real time control, its feasibility, planning, design, operation and applications. Sewer system planning and design are generally conducted using computer modelling tools and procedures which are reviewed in the last section. A brief listing of selected models focuses on internationally used models. Finally, it was concluded that further improvements in environmental and ecological protection of urban waters is feasible only by consideration of urban drainage systems in conjunctions with sewage treatment and water quality in the receiving waters.
Marsalek, P.M., W.E. Watt, J. Marsalek, and B.C. Anderson, Winter flow dynamics of an on-stream stormwater management pond, Water Quality Research Journal of Canada, 35 (3), 505-523, 2000.
The winter operation of an on-stream stormwater management pond, located in Kingston, Ontario, Canada, was studied with respect to ice cover formation and breakup, density stratification, velocity field under the ice cover, and the risk of sediment washout The pond freezes over in late November, with the ice thickness reaching up to 0.5 m. During the first half of the winter period, the ice thickness was well described by Stefan's formula with empirical coefficients appropriate for shallow water bodies. The pond was chemically stratified, with total dissolved solids concentrations up to 1200 mg . L-1 observed close to the bottom. The meromictic stability of this stratification was calculated as 882 g . cm . cm(-2). Measurements of the velocity field under the ice cover indicated a flow pattern comprising a fast flow region, a small dead zone and a large recirculation zone to the north and south of the fast flow trajectory, respectively. Such a pattern agreed well with that simulated by a CFD model (PHOENICS(TM)). During a snowmelt event, the near-bottom velocities reached up to 0.05 m . s(-1), but were not sufficient to scour the bottom sediment.
Martin, Y., and M. Church, Bed-Material Transport Estimated From Channel Surveys - Vedder River, British-Columbia, Earth Surface Processes and Landforms, 20 (4), 347-361, 1995.
Martin, Y., and M. Church, Re-examination of Bagnold's empirical bedload formulae, Earth Surface Processes and Landforms, 25 (9), 1011-1024, 2000.
Bagnold developed his formula for bedload transport over several decades, with the final form of the relation given in his 1980 paper. In this formula, bedload transport rate is a function of stream power above some threshold value, depth and grain size. In 1986, he presented a graph which illustrated the strength of his relation. A double-log graph of bedload transport rate, adjusted for depth and grain size, versus excess stream power was shown to collapse along a line having a slope of 1.5. However, Bagnold based his analyses on limited data. In this paper, the formula is re-examined using a large data set in order to define the most consistent empirical representation, and dimensional analysis is performed to seek a rationalization of the formula. Functional analysis is performed for the final version of the equation defined by Bagnold to determine if the slope of 1.5 is preserved and to assess the strength of the relation. Finally, relations between excess stream power and bedload transport are examined for a fixed slope of 1.5 to assess the performance of various depth and grain size adjustment factors. The rational scaling is found to provide the best result. Copyright (C) 2000 John Wiley & Sons, Ltd.
Martin, D.J., and L.E. Benda, Patterns of instream wood recruitment and transport at the watershed scale, Transactions of the American Fisheries Society, 130 (5), 940-958, 2001.
A wood budget was constructed for the Game Creek basin (132 km(2)) in southeast Alaska to identify spatial and temporal controls on the abundance and distribution of large woody debris (LWD). Field measurements of wood storage, size, and age were used to estimate volumetric rates of LWD recruitment and transport. Mortality recruitment did not follow a spatial pattern and ranged from 0.1 to 8.1 m(3.)km(-1.)year(-1) (recruitment corresponded to forest mortality rates of 0.1-2.6% per year). Wood recruitment by bank erosion increased with increasing drainage area and ranged from 1 m(3.)km(-1.)year(-1) at the smallest drainage areas to about 16 m(3.)km(-1.)year(-1) at 60 km(2). Bank erosion recruitment exceeded the maximum mortality recruitment at a drainage area of approximately 20 km(2) (about 10-m-wide channel). Recruitment from land-sliding was only locally significant. The contribution of fluvial transport (flux) to total LWD storage increased with drainage area to an asymptotic maximum of 50% at about 50 km(2) (about 20-m-wide channel). Mean predicted transport distances for mobile LWD over the lifetime of individual pieces ranged from about 200 m in small, jam-rich streams to about 2,500 m in larger channels with fewer jams. Fluvial transport of LWD increased interjam spacing and jam size and decreased jam age with increasing distance downstream. Constructing LWD budgets at the watershed scale has numerous geomorphic and ecological implications, including identifying spatial controls on the abundance and diversity of aquatic habitats. In addition, information on LWD budgets may be useful for determining how and where to protect LWD sources to streams.
Martin-Vide, J.P., D. Ninerola, A. Bateman, A. Navarro, and E. Velasco, Runoff and sediment transport in a torrential ephemeral stream of the Mediterranean coast, Journal of Hydrology, 225 (3-4), 118-129, 1999.
Marutani, T., M. Kasai, L.M. Reid, and N.A. Trustrum, Influence of storm-related sediment storage on the sediment delivery from tributary catchments in the upper Waipaoa River, New Zealand, Earth Surface Processes and Landforms, 24 (10), 881-896, 1999.
Although much is known about overall sediment delivery ratios for catchments as components of sediment production and sediment yield, little is known about the component of temporary sediment storage. Sediment delivery ratios focused on the influence of storm-related sediment storage are measured at Matakonekone and Oil Springs tributaries of the Waipaoa River basin, east coast of New Zealand. The terrace deposits of both tributaries show abundant evidence of storm-related sedimentation, especially sediment delivered from Cyclone Bola, a 50 year return rainfall event which occurred in 1988. The sediment delivery ratio is calculated by dividing the volume of sediment transported from a tributary to the main stream by the volume of sediment generated at erosion sites in the tributary catchment. Because the sediment delivery volume is unknown, it can be calculated as the difference between sediment generation volume and sediment storage volume in the channel reach of the tributary. The volume of sediment generated from erosion sites in each tributary catchment was calculated from measurements made on aerial photographs dating from 1960(1:44 000) and 1988 (1 :27 000). The volume of sediment stored in the tributary can be calculated from measurements of cross-sections located along the tributary channel, which are accompanied by terrace deposits dated by counting annual growth rings of trees on terrace surfaces. Sediment delivery ratios are 0.93 for both Matakonekone catchment and Oil Springs catchment. Results indicate that Oil Springs catchment has contributed more than twice the volume of sediment to the Waipaoa River than the Matakonekone catchment (2.75 x 10(6) m(3) vs 1.22 x 10(6) m(3)). Although large volumes of sediment are initially deposited during floods, subsequent smaller flows scour away much of these deposits. The sediment scouring rate from storage is 1.25 x 10(4) m(3) a(-1) for Matakonekone stream and 0.83 x 10(4) m(3) a(-1) for Oil Springs stream. Matakonekone and Oil Springs channels respond to extreme storms by instantaneously aggrading, then gradually excavating the temporarily stored sediment. Results from Matakonekone and Oil Springs streams suggest a mechanism by which event recurrence interval can strongly influence the magnitude of a geomorphic change. Matakonekone stream with its higher stream power is expected to excavate sediment deposits more rapidly and allow more rapid re-establishment of storage capacity. Copyright (C) 1999 John Wiley & Sons, Ltd.
Mason, T., and T.T. Coates, Sediment transport processes on mixed beaches: A review for shoreline management, Journal of Coastal Research, 17 (3), 645-657, 2001.
Massong, T.M., and D.R. Montgomery, Influence of sediment supply, lithology, and wood debris on the distribution of bedrock and alluvial channels, Geological Society of America Bulletin, 112 (4), 591-599, 2000.
Field surveys in the Willapa River basin, Washington State, indicate that the drainage area-channel slope threshold describing the distribution of bedrock and alluvial channels is influenced by the underlying lithology and that local variations in sediment supply can overwhelm basinwide trends. Field data from 90 short-reach surveys indicate that about one- eighth of the surveyed reaches do not conform to a threshold defined by data from free-formed alluvial and bedrock reaches due to the effects of logjams or local sediment sources or sinks. Mapping of channel type distributions in 18 extended reconnaissance surveys of >100 channel widths in channel length show that similar to 75% of the channel network was alluvial, but that the proportion of forced alluvial channels varies from 0% to 84%, Using the drainage area-slope thresholds defined by bedrock and alluvial data from the short-reach surveys, only 40% of the total channel length mapped in the longer reconnaissance surveys was correctly classified from a 10 m grid digital elevation model. Of the misclassified reaches, 80% of the alluvial channels predicted to be bedrock had forced alluvial morphologies, while almost half of the bedrock channels predicted to be alluvial were forced by low sediment supply, typically due to their location immediately downstream of large channel-spanning logjams, Poor representation of reach-scale slope in the digital topography and/or a stochastic influence of sediment wave propagation likely account for the remaining misclassified channels, which together compose 7% of the total surveyed channel length. Although variations in sediment supply can locally overwhelm the channel type predicted by the threshold model, the effect of logjams masks any influence of propagating sediment waves on the distribution of bedrock and alluvial channels in the Willapa River basin.
Mast, J.N., and T.T. Veblen, Tree spatial patterns and stand development along the pine- grassland ecotone in the Colorado Front Range, Canadian Journal of Forest Research-Revue Canadienne De Recherche Forestiere, 29 (5), 575-584, 1999.
Patterns of stand development may be interpreted from spatial analyses, based on variables such as tree age and size, together with past records of climate and disturbance. In the present study, our objective is to examine spatial patterns of tree age and size to determine if they are consistent with the episodic pattern of tree regeneration proposed for ponderosa pine (Pinus ponderosa Dougl. ex P. & C. Laws.) and expected changes in tree spatial patterns as cohort patches age. According to our hypothesis, internal patch structure should become less clumped as single cohort patches age due to self- thinning, with few trees attaining dominance in a small patch. In this study, tree spatial patterns in 16 stands of P. ponderosa in the Colorado Front Range are described and related to patterns of stand development. Analytical methods included Ripley's K(t) (a univariate statistic of tree spatial distribution), Ripley's K-12(t) (a bivariate statistic of spatial association), and Moran's I (a measure of spatial autocorrelation). Spatial patterns imply establishment of patches of pines followed by self-thinning. Continued stand development results in strong size hierarchies as manifested by stronger spatial autocorrelation of tree age than tree size. Hence, pines exhibit a strong size class hierarchy developed within an even-aged patch.
Matthaei, C.D., K.A. Peacock, and C.R. Townsend, Patchy surface stone movement during disturbance in a New Zealand stream and its potential significance for the fauna, Limnology and Oceanography, 44 (4), 1091-1102, 1999.
A patchy movement of surface stones during disturbance in streams has been proposed from held observations, but few attempts have been made to quantify this phenomenon. If spates produce a mosaic of stable and disturbed areas, the former could serve as refugia for benthic invertebrates. We monitored the stability of surface stones at three geomorphically contrasting sites in a river with an unstable bed during three spates and one large flood. Stones were marked in situ by drilling holes in them or by scraping them with a chisel. For each stone, we determined visible surface area, embeddedness in the substratum, water depth, size of surrounding stones, and presence or absence of large stones upstream. During the first monitoring period, which covered one spate and the large flood, we marked 400 stones at each 20-m-long site in a systematic grid with 40 to 60 cm between stones. Stones were relocated after each disturbance, but each stone set was used to monitor both subsequent events. After the large flood, few marked stones were left. Therefore, additional sets of 200 stones were marked for a second monitoring period covering the remaining two spates; these stones were located at the same sites, but the distance between transects was doubled. Patchy bed movement occurred during all four disturbances, especially during the three smaller ones, which moved only 33 to 72% of marked stones. Stability of individual stones was mainly influenced by their size and embeddedness and sometimes by the water depth above the stone. Larger-scale parameters (e.g., the position of the stone across the transect) were less important. Whole-site stability differed little among sites. During the three smaller events, many stable surface stones were available as potential invertebrate refugia. In contrast, invertebrate refugia may have been restricted to the hyporheic zone and inundated hood- plain gravels during the large flood. Because patchy stone movement was observed in a river with an unstable bed, it is likely to be a feature of most rivers. Therefore, small-scale experiments may be able to simulate the effects of disturbance on the benthic community more effectively than previously thought.
Matthaei, C.D., C.J. Arbuckle, and C.R. Townsend, Stable surface stones as refugia for invertebrates during disturbance in a New Zealand stream, Journal of the North American Benthological Society, 19 (1), 82-93, 2000.
We tested whether stable surface stones serve as invertebrate refugia in a New Zealand gravel-bed stream. Two-hundred stones were marked in situ in a systematic grid across 20 transects 40-60 cm between stones, 1 m between transects). Six days prior to a spate, ive sampled invertebrates on 24 unmarked stones. Twelve were randomly chosen among well-embedded stones, the others among stones of similar size lying loosely on top of the bed. (Previous work had shown the former to be more stable than the latter during high-flow events.) As soon as possible after the spate, we sampled another set of stones. Ten were marked stones that had remained stable during the spate, whereas 12 were chosen at random among loose stones. Nineteen days after the spate, we sampled a final set of 8 stable and 12 unstable stones in the same way. Taxon richness, area-standardized total densities of invertebrates, and densities of Chironomidae, Deleatidium spp., Austrosimulium spp., Zelandoperla spp., and Oligochaeta were similar on both stone categories before the spate. Shortly after the spate, their densities land taxon richness) were all significantly higher on stable than on unstable stones, and values on the former exceeded pre- disturbance levels in several cases. By day 19, most of these differences had disappeared, although densities of 3 of the 5 taxa on unstable stones had not vet recovered to pre- disturbance levels. We concluded that stable surface stones were important invertebrate refugia during the spate. The higher densities of several taxa relative to pre-disturbance levels implied that invertebrates may actively seek stable refugium stones, whereas many leave or are dislodged from unstable stones. It remains to be determined how invertebrates can identify stones that remain stable during high-flow events.
Matthews, B.W., C.A.J. Fletcher, A.C. Partridge, and S. Vasquez, Computations of curved free surface water flow on spiral concentrators, Journal of Hydraulic Engineering-Asce, 125 (11), 1126-1139, 1999.
Spiral concentrators, consisting of an open trough that twists vertically downward about a central axis, are used to separate radially a thin-film slurry of mineral and waste material on the basis of particle density and size. This paper reports the derailed steady and uniform flow results of a computational fluid dynamics model for the water phase. The flow is characterized by a free surface, shallow (1-14 mm) depths, radial transition to fully turbulent flow, and superimposed secondary motion. Validated results are presented for depths and primary and secondary velocity components, both internally and on the free surface. A detailed understanding of the flow behavior beyond that readily available by experimentation on the concentrator has been gleaned. More importantly, an efficient and fully predictive computational fluid dynamics methodology is demonstrated for the class of problems represented by the example, having wider relevance for hydraulic open channel applications. The model solves the Reynolds-averaged Navier-Stokes equations and employs the volume of fluid free surface method, isotropic k-epsilon and Renormalization Group k-epsilon turbulence formulations, and the wall function approach.
McDowell, D.M., A General Formula For Estimation of the Rate of Transport of Non-Cohesive Bed-Load, Journal of Hydraulic Research, 27 (3), 355-361, 1989.
McEwan, I.K., B.J. Jefcoate, and B.B. Willetts, The grain-fluid interaction as a self-stabilizing mechanism in fluvial bed load transport, Sedimentology, 46 (3), 407-416, 1999.
A grain-scale model of fluvial bed load transport is described, with particular emphasis on the equilibrium between the saltating grains and the near bed flow, and its role in determining transport rate. The model calculates, explicitly, the modification of the velocity profile by the moving grains, together with the consequential reduction in surface fluid shear stress. As the surface fluid shear stress is reduced by the moving grains, so the entrainment rate decreases and the model reaches a steady state. The results provide insight into two important questions at a macroscopic level. First, they show that, in the absence of large static roughness, the dynamic roughness caused by the moving grains may be a significant contributor to flow resistance. Secondly, the model indicates the manner in which transport may be limited by a combination of the transport capacity of the flow and the availability of sediment for entrainment. Only in the case of high sediment availability does the fluid shear stress acting at the surface approach the critical entrainment value, reproducing the behaviour suggested by Bagnold (1956) and Owen (1964). This suggests that prediction formulae based on this assumption only describe the bed load transport system under particular conditions.
McEwan, I., and J. Heald, Discrete particle modeling of entrainment from flat uniformly sized sediment beds, Journal of Hydraulic Engineering-Asce, 127 (7), 588-597, 2001.
McGlone, M.S., The Polynesian Settlement of New-Zealand in Relation to Environmental and Biotic Changes, New Zealand Journal of Ecology, 12, 115-129, 1989.
McIntosh, B.A., J.R. Sedell, R.F. Thurow, S.E. Clarke, and G.L. Chandler, Historical changes in pool habitats in the Columbia River Basin, Ecological Applications, 10 (5), 1478-1496, 2000.
An historical stream survey (1934-1945) was compared with current surveys (1987-1997) to assess changes in pool frequencies in the Columbia River Basin. We surveyed 2267 km of 122 streams across the basin, representing a wide range of lithologies, stream sizes, land use histories, ownerships, and ecoregions. Based on pool classes inherited from the historical surveys, the frequencies of large (greater than or equal to 20 m(2) and greater than or equal to 0.9 m depth) and deep (greater than or equal to 20 m(2) and greater than or equal to 1.8 m depth) pools have decreased significantly (P < 0.01) since the 1930s. We classified streams as natural or commodity based on their watershed management and land use histories. Natural streams were in watersheds minimally affected by human activities (e.g., wilderness or roadless designation, limited entry), with only 12% having roads in riparian areas. Commodity streams were defined as having watersheds managed predominantly for extraction of resources via timber harvest, livestock grazing, and other human activities. Ninety percent of these streams had roads in the riparian areas. In natural streams, large-pool frequencies increased or remained the same in 96% of the streams (88% for deep pools). In commodity streams. large- and deep-pool frequencies decreased in 52% and 54% of the streams, respectively. Despite differences in stream size and the level of human activities, the magnitude and direction of these changes were consistent. Land ownership did not influence trends; pools decreased significantly on both private and public lands. Only where entire watersheds or headwaters were designated as wilderness or roadless areas did pools consistently remain unchanged or increase. Pool frequencies decreased in all ecoregions except the North Cascades ecoregion. We developed regional histories of human activities for the Columbia River Basin. Human activity histories were typically of low spatial resolution and available for broad geographic areas only; we rarely were able to obtain information at the scale of individual watersheds. Consequently, we were unable to test the relationship between temporal and spatial patterns in human activities and their influence on site-specific trends in pools. Despite our inability to isolate causal mechanisms, management emphasis and human activities clearly influenced trends in pools. We conclude that the persistent effects of human activities have simplified stream channels and reduced large- and deep-pool frequencies in watersheds outside of designated wilderness and roadless areas in the Columbia River Basin.
McIver, J., and L. Starr, Restoration of degraded lands in the interior Columbia River basin: passive vs. active approaches, Forest Ecology and Management, 153 (1-3), 15-28, 2001.
Evidence for success of passive and active restoration is presented for interior conifer forest, sagebrush steppe, and riparian ecosystems, with a focus on the Columbia River basin. Passive restoration, defined as removal of the stresses that cause degradation, may be most appropriate for higher elevation forests, low-order riparian ecosystems, and for sagebrush steppe communities that are only slightly impaired. More active approaches, in which management techniques such as planting, weeding, burning, and thinning are applied, have been successful in forests with excessive fuels and in some riparian systems, and may be necessary in highly degraded sagebrush steppe communities. There is general agreement that true restoration requires not only reestablishment of more desirable structure or composition, but of the processes needed to sustain these for the long term. The challenge for the restorationist is to find a way to restore more desirable conditions within the context of social constraints that limit how processes are allowed to operate, and economic constraints that determine how much effort will be invested in restoration. Published by Elsevier Science B.V.
McLean, D.G., M. Church, and B. Tassone, Sediment transport along lower Fraser River - 1. Measurements and hydraulic computations, Water Resources Research, 35 (8), 2533-2548, 1999.
A comprehensive program of sediment transport measurements was conducted along lower Fraser River, British Columbia, between 1966 and 1986. The data yield a detailed sediment budget. Annual total suspended loads at three stations are virtually identical, averaging 17 x 10(6) tonnes/year (t yr(-1)). The suspended sand load is about 5.5 x 10(6) t yr(-1), about one third of the total. In the gravel bed reach of the river the sand behaves as wash load. Significant transport of gravel begins at Agassiz at a discharge of about 5000 m(3) s(-1). The annual gravel transport was estimated to be about 0.23 x 10(6) t yr(-1), only 1% of the total load. All of this material is deposited in the reach upstream of Mission. At Mission, sands finer than 0.177 mm make up more than 50% of the suspended sand load but are virtually absent from the sand bed. Therefore a portion of the sand load at Mission is wash load. The total bed material load here was estimated to be 3.0 x 10(6) t yr(-1), about 18% of the total sediment load. Virtually all of the bed material load was transported in intermittent suspension near the bed, less than 5% occurring as bed load. In the long term the suspended sand load upstream is approximately equal to the total sand load at Mission. However, within individual years some of the sand is stored within the reach temporarily and then reentrained later.
McLelland, S.J., P.J. Ashworth, J.L. Best, and J.R. Livesey, Turbulence and secondary flow over sediment stripes in weakly bimodal bed material, Journal of Hydraulic Engineering-Asce, 125 (5), 463-473, 1999.
Meade, R.H., Wavelike Movement of Bedload Sediment, East Fork River, Wyoming, Environmental Geology and Water Sciences, 7 (4), 215-225, 1985.
Meigs, A., N. Brozovic, and M.L. Johnson, Steady, balanced rates of uplift and erosion of the Santa Monica Mountains, California, Basin Research, 11 (1), 59-73, 1999.
Topographic change in regions of active deformation is a function of rates of uplift and denudation. The rate of topographic development acid change of an actively uplifting mountain range, the Santa Monica Mountains, southern California, was assessed using landscape attributes of the present topography, uplift rates and denudation rates. Landscape features were characterized through analysis of a digital elevation model (DEM). Uplift rates at time scales ranging from 10(4) to 10(6) years were constrained with geological cross-sections and published estimates. Denudation rate was determined from sediment yield data from debris basins in southern California and from the relief of rivers set into geomorphic surfaces of known age. First-order morphology of the Santa Monica Mountains is set by large-scale along-strike variations in structural geometry. Drainage spacing, drainage geometry and to a lesser extent relief are controlled by bedrock strength. Dissection of the range flanks and position of the principal drainage divide are modulated by structural asymmetry and differences in structural relief across the range. Topographic and catchment-scale relief are approximate to 300-900 m. Mean denudation rate derived from the sediment yield data and river incision is 0.5 +/- 0.3 mm yr(-1). Uplift rate across the south flank of the range is approximate to 0.5 +/- 0.4 mm yr(-1) and across the north flank is 0.24 +/- 0.12 mm yr(-1). At least 1.6-2.7 Mgr is required to create either the present topographic or the catchment-scale relief based on either the mean rates of denudation or uplift. Although the landscape has had sufficient time to achieve a steady-state form, comparison of the time-scale of uplift and denudation rate variation with probable landscape response times implies the present topography does not represent the steady-state form.
Meirovich, L., J.B. Laronne, and I. Reid, The variation of water-surface slope and its significance for bedload transport during floods in gravel-bed streams, Journal of Hydraulic Research, 36 (2), 147-157, 1998.
Merigliano, M.F., Cottonwood and willow demography on a young island, Salmon River, Idaho, Wetlands, 18 (4), 571-576, 1998.
Woody colonizers of stream deposits are often aged to reconstruct flow and sedimentation history. Precise work requires knowledge of age structure of putatively even-aged stands or cohorts of colonizers. The demography of cottonwood and sandbar willow on a young island along the largely unregulated stream indicates that there: can be 4 years of age variance between individuals that established within 2 meters of each other. Size of individuals indicates their relative ages, but sediment composition can also influence size.
Merritt, D.M., and D.J. Cooper, Riparian vegetation and channel change in response to river regulation: A comparative study of regulated and unregulated streams in the Green River Basin, USA, Regulated Rivers-Research & Management, 16 (6), 543-564, 2000.
Meyer, G.A., Recent large-magnitude floods and their impact on valley-floor environments of northeastern Yellowstone, Geomorphology, 40 (3-4), 271-290, 2001.
The Lamar River watershed of northeastern Yellowstone contains some of the most diverse and important habitat in the national park. Broad glacial valley floors feature grassland winter range for ungulates, riparian vegetation that provides food and cover for a variety of species, and alluvial channels that are requisite habitat for native fish. Rapid Neogene uplift and Quaternary climatic change have created a dynamic modern environment in which catastrophic processes exert a major influence on riverine-riparian ecosystems. Uplift and glacial erosion have generated high local relief and extensive cliffs of friable volcaniclastic bedrock. As a result, steep tributary basins produce voluminous runoff and sediment during intense precipitation and rapid snowmelt. Recent major floods on trunk streams deposited extensive overbank gravels that replaced loamy soils on flood plains and allowed conifers to colonize valley-floor meadows. Tree-ring dating identifies major floods in 1918, ca. 1873, and possibly ca. 1790. In 1996 and 1997, discharge during snowmelt runoff on Soda Butte Creek approached the 100-year flood estimated by regional techniques, with substantial local bank erosion and channel widening. Indirect estimates show that peak discharges in 1918 were approximately three times greater than in 1996, with similar duration and much greater flood plain impact. Nonetheless, 1918 peak discharge reconstructions fall well within the range of maximum recorded discharges in relation to basin area in the upper Yellowstone region. The similar to 1873 and 1918 floods produced lasting impacts on the channel form and flood plain of Soda Butte Creek. Channels may still be locally enlarged from flood erosion, and net downcutting has occurred in some reaches, leaving the pre-1790 flood plain abandoned as a terrace. Gravelly overbank deposits raise flood-plain surfaces above levels of frequent inundation and are well drained, therefore flood-plain soils are drier. Noncohesive gravels also reduce bank stability and may have persistent effects on channel form. Overall, floods are part of a suite of catastrophic geomorphic processes that exert a very strong influence on landscape patterns and valley-floor ecosystems in northeastern Yellowstone. (C) 2001 Elsevier Science B.V. All rights reserved.
Miao, T.D., Q.S. Mu, and S.Z. Wu, Computer simulation of aeolian sand ripples and dunes, Physics Letters a, 288 (1), 16-22, 2001.
A discrete computer method, which considers the principal characteristics of the motion of discrete particles caused by the airflow over the aeolian bedforms using a set of simple rules, is suggested to simulate the initiation and evolution of wind blown sand ripples and dunes. The results indicate that, if the grain-bed impacting and surface creep are taken into account, the model is capable of reproducing sand ripples vividly, and describing the reparation of any destroy to rippled surface, a phenomenon observed in field. lf the saltation driven by the main flow and the secondary flow, the surface creep due to gravity, and the slide occurring when the slope of sand surface is larger than the angle of repose are considered, the model can simulate the formation and development of sand dunes whose shape and arrangement in space are in accordance with the landscape of typical deserts. After a further investigation into the simulation process, we draw the conclusion that the aeolian bedforms is a system of self- organization and hierarchy with a fractal character. (C) 2001 Published by Elsevier Science B.V.
Michels, K.H., Inferring maximum geostrophic current velocities in the Norwegian-Greenland Sea from settling-velocity measurements of sediment surface samples: Methods, application, and results, Journal of Sedimentary Research, 70 (5), 1036-1050, 2000.
Middleton, B., Hydrochory, seed banks, and regeneration dynamics along the landscape boundaries of a forested wetland, Plant Ecology, 146 (2), 169-184, 2000.
Following the environmental sieve concept, the setting in which the recruitment of Taxodium distichum occurs in, becomes increasingly restrictive from the seed to seedling stage in an impounded forested wetland. Although a wide elevational band of dispersing seed moves across the boundary of a swamp-field in the water sheet, the zone of germination is relegated to that portion of the forested wetland that draws down during the growing season. Seedling recruitment is further restricted to the uppermost zone of the winter water sheet. These patterns are likely applicable to other species of dominant swamp species, e.g., Cephalanthus occidentalis crossed the boundary of a forested wetland and abandonded field in winter flooding (November-December and November-March, respectively) in Buttonland Swamp. The elevation of the boundary was 101.3 m NGVD. While the seeds of at least 40 swamp species were dispersed across the boundary, few viable seeds were dispersed after the winter season. Kriged maps showed seeds of T. distichum and C. occidentalis dispersed in patches in the water depending on the position of the water sheet. Most species of both water- and gravity-dispersed species had a localized pattern of seed distribution (either spherical or exponential) and this indicated that seeds may not be dispersed for great distances in the swamp. Water-dispersed T. distichum and C. occidentalis had larger dispersal ranges (A(0)=225 and 195 m, respectively) than Bidens frondosa and B. discoidea (A(0)=14 and 16 m, respectively). Seed dispersal varied with season depending on the availability of seeds. In Buttonland Swamp, viable seeds typically were dispersed for T. distichum in November-June, and for C. occidentalis in November-July. Low water occurred in August 1993 and high in February 1994 (99.8 and 101.6 m NGVD, respectively). The seed banks along the landscape boundary varied in species composition according to elevation (r(2)=0.996). While the similarity of species richness between water-dispersed seeds and the seed bank at elevations that flooded (during June 1993 through May 1995) was high (10-17%), it was low between water-dispersed seeds and the seed bank at elevations that did not flood (5%). T. distichum seeds had a short germination window in that seeds germinated within a year following their production in zones that were flooded in the winter followed by drawdown during the next growing season. After 1 year, less than 5% of the T. distichum seeds remained viable on the surface of the soil. Germination of T. distichum was confined to specific elevations (above 99.3 but below 101.6 m NGVD) during this study with 4.1% of the seedlings surviving for more than 2 years at a mean of 101.4 m NGVD. All seedlings below this elevation died. To maximize natural regeneration along the boundaries of swamps in abandoned farm fields targeted for restoration, this study suggests a flood pulse regime consisting of high water in the winter to maximize dispersal of live seeds followed by low water in the summer to facilitate seed germination and seedling recruitment. Hydrologic restoration could assist in the natural recovery of damaged wetlands if a seed source exists nearby.
Milan, D.J., G.L. Heritage, A.R.G. Large, and M.E. Charlton, Stage dependent variability in tractive force distribution through a riffle-pool sequence, Catena, 44 (2), 85-109, 2001.
High resolution data on spatial and temporal variability in flow hydraulics and sediment transport within riffle-pool sequences are required to improve understanding of how fluvial processes maintain these meso-scale bedforms. This paper addresses this issue by providing velocity and boundary shear stress data over a range of discharges from base flow (0.07 m(3) s(-1)) to just over bankfull (8.52 m(3) s(-1)), fl om a sequence of four pools and three riffles in the River Rede, Northumberland. The data supports the reversal hypothesis of Keller [Geol. Sec. Am. Bull. 87 (1971) 753.] as the primary explanation for the maintenance of the riffle-pool sequence, although they also indicate that spatial variability in tractive force is highly stage dependent and complex. Section- averaged velocity data indicate reversal to be evident at four our of six riffle-pool units. An equalisation in velocity was: found for the other two riffle-pool units close to bankfull stage. The spatial patterns of tractive force exhibited in the study reach as a result of increased discharge demonstrate that riffle-pool units operate independently of one another. Shear stress reversals were observed in individual riffle-pool units at different river stages during a flood hydrograph. and in some instances, two occurred in the same riffle-pool unit during a single flow event. Pools were characterised by coarser bed sediments and narrower channel widths in comparison to riffles, increasing the likelihood of tractive force reversal in the River Rede. Areas of predicted bed sediment entrainment obtained from tau (o) - tau (c), matched observed channel changes in the upper part of the study reach, but over- estimated change in the middle portion of the reach. (C) 2001 Elsevier Science B.V. All rights reserved.
Millar, R.G., and M.C. Quick, Effect of Bank Stability On Geometry of Gravel Rivers, Journal of Hydraulic Engineering-Asce, 119 (12), 1343-1363, 1993.
Millar, R.G., Grain and form resistance in gravel-bed rivers, Journal of Hydraulic Research, 37 (3), 303-312, 1999.
Grain and form resistances for bankfull and near bankfull flows have been determined for 176 gravel reaches using data compiled from several published sources. Partitioning grain and form resistance is based on the original definition of k(s) adopted by Nikuradse (1933). Grain resistance is calculated with the Keulegan equation assuming a grain roughness height equal to D- 50. This defines a lower bound to the observed flow resistance. Form resistance, which includes grain protrusion, pebble clusters, dunes, bars and pool-riffle sequences, is shown to be significant at bankfull flow. Computed form resistance comprises up to 90% of the total. No predictive relation for form resistance has yet been developed. The results have implications for river restoration efforts that include the reintroduction of pool-riffle sequences into degraded or channelised rivers, and indicate that constructed pool-riffle sequences would have a significant effect on flood levels.
Millar, R.G., Influence of bank vegetation on alluvial channel patterns, Water Resources Research, 36 (4), 1109-1118, 2000.
Miller, J.R., and J.B. Ritter, An examination of the Rosgen classification of natural rivers, Catena, 27 (3-4), 295-299, 1996.
Miller, J.R., The role of fluvial geomorphic processes in the dispersal of heavy metals from mine sites, Journal of Geochemical Exploration, 58 (2-3), 101-118, 1997.
It is not uncommon for more than 90% of the total metal load in rivers to be transported in the solid phase, either sorbed onto particle surfaces and coatings, or incorporated into mineral grains. Fluvial geomorphic processes are therefore of fundamental importance in the transport and fate of heavy metals derived from mine sites. In this paper, the role of physical processes in the dispersal of heavy metals in river systems are reviewed for channels that have (1) remained relatively unchanged in terms of process and form following the introduction of mine wastes, and (2) exhibited a significant metamorphosis in channel form in response to the influx of mining and milling debris. In general, all processes responsible for the variations in metal concentrations within sediments moving through stable channels also operate in channels undergoing metamorphosis. However, downstream, lateral, and vertical patterns in metal values tend to be more complex where channel transformations have occurred. This complexity results, in part, because temporal and spatial changes in the types, rates, and magnitudes of erosional and depositional processes lead to highly variable stratigraphic sequences of post-mining age, and because greater quantities of contaminated debris is stored along the channel margins where it can be eroded and sporadically redistributed during times of flood.
Miller, D.J., and L.E. Benda, Effects of punctuated sediment supply on valley-floor landforms and sediment transport, Geological Society of America Bulletin, 112 (12), 1814-1824, 2000.
Large, infrequent fluxes of sediment to streams by mass wasting are intrinsic to the erosion regime of mountain drainage basins. To elucidate the role of mass wasting in the construction and evolution of steep land channel environments, it is crucial that me identify the processes involved and recognize their legacy on the valley floor. In the winter of 1996, nine storm-triggered debris flows carried similar to 18 000 m(3) of coarse debris into the upper reaches of the South Fork of Gate Creek (Oregon Cascade Range) during flood how. Analysis of resulting channel morphologies and bed textures shows that the sediment moved downstream as a wave-like pulse or pulses, overwhelming the channel and causing it to braid, with flooding and alluvial deposition over the valley poor. Downstream progression of the sediment wave resulted in vertical accretion of the valley floor with sediment carried as bedload, the maximum depth of valley-poor burial being set by the amplitude of the mwe. Passage of the wave left a channel incised to bedrock, inset between coarse-grained alluvial terraces. This study examines the genesis of these features at Gate Creek and points to such terraces as held indicators of massive episodic influxes of sediment and the associated formation of fluvially transported sediment waves.
Milne, J.A., Bed Forms and Bend-Arc Spacings of Some Coarse-Bedload Channels in Upland Britain, Earth Surface Processes and Landforms, 7 (3), 227-240, 1982.
Milne, J.A., and D.A. Sear, Modelling river channel topography using GIS, International Journal of Geographical Information Science, 11 (5), 499-519, 1997.
The modelling of environmental processes based on catchment elevation surfaces is well-established, but the use of TIN and grid surface models as three-dimensional representations of river channel topography at the reach scale is much less common. In this paper, surface modelling facilities in ARC/INFO GIS have been used to model the geometry of seven short sections of gravel-bed river channels in upland Britain from held surveys taken in 1976 and 1994. The methods used in converting field survey data and implementing bed-topography models as TIN and grid data structures are described. The use of derived surface models to define pool-riffle bedforms, estimate sediment budgets and assess channel change between surfaces of different dates are discussed and evaluated.
Minshall, G.W., S.A. Thomas, J.D. Newbold, M.T. Monaghan, and C.E. Cushing, Physical factors influencing fine organic particle transport and deposition in streams, Journal of the North American Benthological Society, 19 (1), 1-16, 2000.
Mishra, S.K., and V.P. Singh, On the Seddon speed formula, Hydrological Sciences Journal-Journal Des Sciences Hydrologiques, 46 (3), 333-347, 2001.
The Seddon speed formula expressed mathematically as c = dQ/dA (or alternatively, as c = (1 + m)u(0); where Q is the discharge, A is the area of cross-section, c is the wave speed, u(0) is the normal flow velocity, and m is a dimensionless parameter) is revisited in the context of elasticity and thermodynamics. Its link with the linearized solution of St Venant's equations for wave celerity, which does not appear to have been reported in the hydrological literature, is established. The rating exponent m is shown to be equivalent to the dimensionless relative celerity and is found to be the ratio of two specific heats, viz. c(p) and c(v) which are the specific heats at constant pressure and volume, respectively. The use of the parameter m as a complex variable helps describe shallow wave characteristics, the damping capacity of a wave, and the mechanism of occurrence of the hysteretic phenomenon. The damping capacity is found to describe the magnitude of wave subsidence, whereas the hysteresis also describes the speed of subsidence.
Mohrig, D., and J.D. Smith, Predicting the migration rates of subaqueous dunes, Water Resources Research, 32 (10), 3207-3217, 1996.
Molinas, A., and B.S. Wu, Comparison of fractional bed-material load computation methods in sand-bed channels, Earth Surface Processes and Landforms, 25 (10), 1045-1068, 2000.
Molnar, P., and J.A. Ramirez, Energy dissipation theories and optimal channel characteristics of river networks, Water Resources Research, 34 (7), 1809-1818, 1998.
Molnar, P., and J.A. Ramirez, An analysis of energy expenditure in Goodwin Creek, Water Resources Research, 34 (7), 1819-1829, 1998.
Montgomery, D.R., J.M. Buffington, R.D. Smith, K.M. Schmidt, and G. Pess, Pool Spacing in Forest Channels, Water Resources Research, 31 (4), 1097-1105, 1995.
Field surveys of stream channels in forested mountain drainage basins in southeast Alaska and Washington reveal that pool spacing depends on large woody debris (LWD) loading and channel type, slope, and width. Mean pool spacing in pool-riffle, plane-bed, and forced pool-riffle channels systematically decreases from greater than 13 channel widths per pool to less than 1 channel width with increasing LWD loading, whereas pool spacing in generally steeper, step-pool channels is independent of LWD loading. Although plane-bed and pool-riffle channels occur at similar low LWD loading, they exhibit typical pool spacings of greater than 9 and 2-4 channel widths, respectively. Forced pool-riffle channels have high LWD loading, typical pool spacing of <2 channel widths, and slopes that overlap the ranges of free-formed pool-riffle and plane- bed channel types. While a forced pool-riffle morphology may mask either of these low-LWD-loading morphologies, channel slope provides an indicator of probable morphologic response to wood loss in forced pool-riffle reaches. At all study sites, less than 40% of the LWD pieces force the formation of a pool. We also find that channel width strongly influences pool spacing in forest streams with similar debris loading and that reaches flowing through previously clear-cut forests have lower LWD loading and hence fewer pools than reaches in pristine forests.
Montgomery, D.R., J.M. Buffington, N.P. Peterson, D. SchuettHames, and T.P. Quinn, Stream-bed scour, egg burial depths, and the influence of salmonid spawning on bed surface mobility and embryo survival, Canadian Journal of Fisheries and Aquatic Sciences, 53 (5), 1061-1070, 1996.
Bed scour, egg pocket depths, and alteration of stream-bed surfaces by spawning chum salmon (Onchorhynchus keta) were measured in two Pacific Northwest gravel-bedded streams. Close correspondence between egg burial depths and scour depths during the incubation period suggests an adaptation to typical depths of bed scour and indicates that even minor increases in the depth of scour could significantly reduce embryo survival. Where egg burial depths are known, expressing scour depth in terms of bed-load transport rate provides a means for predicting embryo mortality resulting from changes in watershed processes that alter shear stress or sediment supply. Stream- bed alteration caused by mass spawning also may influence embryo survival. Theoretical calculations indicate that spawning-related bed surface coarsening, sorting, and form drag reduce grain mobility and lessen the probability of stream-bed scour and excavation of buried salmon embryos. This potential feedback between salmon spawning and bed mobility implies that it could become increasingly difficult to reverse declines in mass-spawning populations because decreased spawning activity would increase the potential for bed scour, favoring higher embryo mortality. Further analysis of this effect is warranted, however, as the degree to which spawning-related bed loosening counteracts reduced grain mobility caused by surface coarsening, sorting, and redd form drag remains uncertain.
Montgomery, D.R., T.B. Abbe, J.M. Buffington, N.P. Peterson, K.M. Schmidt, and J.D. Stock, Distribution of bedrock and alluvial channels in forested mountain drainage basins, Nature, 381 (6583), 587-589, 1996.
MOUNTAIN river networks often consist of both bedrock and alluvial channel(1-5), the spatial distribution of which controls several fundamental geomorphological and ecological processes(6,7). The nature of river channels can influence the rates of river incision and landscape evolution(1,2), as well as the stream habitat characteristics affecting species abundance and aquatic ecosystem structure(8-11), Studies of the factors controlling the distribution of bedrock and alluvial channels have hitherto been limited to anthropogenic badlands(12), Here we investigate the distribution of channel types in forested mountain drainage basins, and show that the occurrence of bedrock and alluvial channels can be described by a threshold model relating local sediment transport capacity to sediment supply. In addition, we find that valley-spanning log jams create alluvial channels-hospitable to aquatic life-in what would otherwise be bedrock reaches, The formation of such jams depends critically on the stabilizing presence of logs derived from the largest trees in the riverside forests, suggesting that management strategies that allow harvesting of such trees can have a devastating influence on alluvial habitats in mountain drainage basins.
Montgomery, D.R., River management - What's best on the banks?, Nature, 388 (6640), 328-329, 1997.
Montgomery, D.R., and J.M. Buffington, Channel-reach morphology in mountain drainage basins, Geological Society of America Bulletin, 109 (5), 596-611, 1997.
A classification of channel-reach morphology in mountain drainage basins synthesizes stream morphologies into seven distinct reach types: colluvial, bedrock, and five alluvial channel types (cascade, step pool, plane bed, pool riffle, and dune ripple), Coupling reach-level channel processes with the spatial arrangement of reach morphologies, their links to hillslope processes, and external forcing by confinement, riparian vegetation, and woody debris defines a process-based framework within which to assess channel condition and response potential in mountain drainage basins, Field investigations demonstrate characteristic slope, grain size, shear stress, and roughness ranges for different reach types, observations consistent with our hypothesis that alluvial channel morphologies reflect specific roughness configurations adjusted to the relative magnitudes of sediment supply and transport capacity, Steep alluvial channels (cascade and step pool) have high ratios of transport capacity to sediment supply and are resilient to changes in discharge and sediment supply, whereas low-gradient alluvial channels (pool riffle and dune ripple) have lower transport capacity to supply ratios and thus exhibit significant and prolonged response to changes in sediment supply and discharge, General differences in the ratio of transport capacity to supply between channel types allow aggregation of reaches into source, transport, and response segments, the spatial distribution of which provides a watershed-level conceptual model linking reach morphology and channel processes, These two scales of channel network classification define a framework within which to investigate spatial and temporal patterns of channel response in mountain drainage basins.
Montgomery, D.R., E.M. Beamer, G.R. Pess, and T.P. Quinn, Channel type and salmonid spawning distribution and abundance, Canadian Journal of Fisheries and Aquatic Sciences, 56 (3), 377-387, 1999.
Consideration of fundamental channel processes, together with map-based and field investigations, indicates that stream channel type influences salmonid spawning distributions across entire channel networks and salmonid abundance within channel reaches. Our analysis suggests that salmonid spawning patterns in mountain drainage basins of the Pacific Northwest are adapted to, among other things, the timing and depth of channel bed mobility. We hypothesize that because the bed of pool- riffle and plane-bed reaches scours to a variable fraction of the thickness of alluvium, survival to emergence is favored by either burying eggs below the annual scour depth or avoiding egg burial during times of likely bed mobility. Conversely, annual mobility of all available spawning gravel in steeper step-pool and cascade channels favors either adaptations that avoid egg burial during times of likely bed mobility or selection of protected microhabitats. Consistent with these expectations, we find that salmonid spawning distributions track channel slope distributions in several west-slope Pacific Northwest watersheds, implying that spatial differences in channel processes influence community structure in these rainfall-dominated drainage basins. More detailed field surveys confirm that different channel types host differential use by spawning salmonids and reveal finer-scale influences of pool spacing on salmonid abundance.
Montgomery, D.R., Process domains and the river continuum, Journal of the American Water Resources Association, 35 (2), 397-410, 1999.
The concept of process domains is proposed as an alternative to the River Continuum Concept for the influence of geomorphic processes on aquatic ecosystems. Broadly defined, the Process Domain Concept is a multi-scale hypothesis that spatial variability in geomorphic processes governs temporal patterns of disturbances that influence ecosystem structure and dynamics. At a coarse scale, regional climate, geology, vegetation, and topography control the suite of geomorphic processes that are distributed over a landscape. Within the broad context so defined, stream channel classification can guide identification of functionally similar portions of a channel network, but the response of otherwise similar reaches can depend upon their geologic and geomorphic context. Within geomorphic provinces defined by differences in topography, climate history, and tectonic setting, areas with generally similar geology and topography define lithotopo units, which are useful for stratifying different suites of dominant geomorphic processes. Process domains are spatially identifiable areas characterized by distinct suites of geomorphic processes, and the Process Domain Concept implies that channel networks can be divided into discrete regions in which community structure and dynamics respond to distinctly different disturbance regimes. The concepts of process domains and lithotopo units provide both a framework for the application of patch dynamics concepts to complex landscapes and a context for addressing the effects of watershed processes on the ecology of mountain drainage basins.
Montgomery, D.R., M.S. Panfil, and S.K. Hayes, Channel-bed mobility response to extreme sediment loading at Mount Pinatubo, Geology, 27 (3), 271-274, 1999.
Since the 1991 eruption of Mount Pinatubo, the specific sediment yields from watersheds draining its slopes have been the highest ever recorded. In spite of this overwhelming sediment load, rivers inundated by pyroclastic-flow deposits delivered almost half of the initial deposits to downslope alluvial and/or debris fans by 1996, Although most of this transport occurred by hyperconcentrated flows and debris flows (lahars), very high sediment transport rates also characterize low flow Measured flow velocities and depths, channel properties, and the size of both mobile and stable clasts in the Sacobia and Pasig-Potrero Rivers indicate median bed- surface grain sizes of 2 to 8 mm, grain-size-independent dimensionless critical shear stresses (tau(c)*) of 0.016 to 0.041 and Manning's n values of 0.017 to 0.024, values well below those previously reported for steep mountain channels. The dramatic bed-surface fining, bed mobility, and selective transport in these extremely sediment-rich channels indicate that changes in grain size, tau(c)* values, and bed roughness can increase transport capacity in response to high sediment supply. Our observations also suggest viewing the apparently contradictory concepts of an equal threshold of bed mobility and grain-size-dependent selective transport as end-member concepts that apply to channels with low (or intermittent) and high (or continuous) sediment supply, respectively.
Montgomery, D.R., Slope distributions, threshold hillslopes, and steady-state topography, American Journal of Science, 301 (4-5), 432-454, 2001.
Digital elevation models of two "steady-state" mountain ranges, the Olympic Mountains (OM) and Oregon Coast Range (OCR), are used to examine relationships between slope distributions, the development of threshold hillslopes, and steady-state topography. Plots of drainage area versus slope for these mountain ranges exhibit substantial scatter that complicates comparison of range form to analytical theories and landscape evolution models. Contour plots of the density of such data reveal an attractor at the scale of the transition from hillslope processes to channel processes, and log-bin averaging reveals trends that parallel predictions of steady-state erosion laws but with different rate laws for five distinct process domains: hillslopes, valley heads, and colluvial, bedrock, and alluvial valley segments. Slope histograms computed for 100 km(2) areas (defined by a 10 X 10 km grid) throughout the OM exhibit approximately normal or exponential distributions in areas of active rock uplift and depositional topography, respectively. Local slope distributions in the OCR also tend to be normally distributed, but some are left-skewed in areas with gentler slopes. Mean slopes determined both over the above referenced grid and a 10-km diam moving window are relatively invariant in the core of the OM in spite of strong contrasts in bedrock erodibility and gradients in long-term rock uplift rates. In contrast, the mean slopes in the OCR parallel latitudinal gradients in rock uplift rates and bedrock erodibility. Hence, the slope distributions in the OM and OCR reflect distinct relationships between development of threshold bedrock and soil-mantled hillslopes and steady-state topography.
Montgomery, D.R., and K.B. Gran, Downstream variations in the width of bedrock channels, Water Resources Research, 37 (6), 1841-1846, 2001.
Field surveys of channel width w and drainage area A in bedrock channel reaches reveal relationships where w = CA(b), Similar to the classic hydraulic geometry of alluvial channels. Data from five mountain channel networks support the assumption used in many landscape evolution models that an alluvial hydraulic geometry relationship where b = 0.3-0.5 holds for bedrock channel systems. Although there is substantial local variability in channel width in bedrock channel systems, there is no systematic difference in width versus drainage area relations for the surveyed bedrock and alluvial reaches in sedimentary lithologies in coastal Oregon and Washington. In contrast, bedrock channels were narrower, and therefore had deeper flow, than alluvial channels with equal drainage areas in the granite and limestone terrain of the Yuba River, California. in addition, data from the Mokelumne River show that bedrock channel width decreases substantially downstream at the contact between relatively weak limestone and more erosion-resistant granite, but that channel slope does not change appreciably across contacts between these two lithologies. Data from coastal Oregon drainage basins further show systematic channel widening after flood flows and debris flow impacts. We conclude that downstream Variations in the width of bedrock channels generally follow traditional hydraulic geometry relations but also reflect the local influence of longitudinal patterns of bedrock erosivity and disturbance history.
Moody, J.A., and B.M. Troutman, Quantitative model of the growth of floodplains by vertical accretion, Earth Surface Processes and Landforms, 25 (2), 115-133, 2000.
A simple one-dimensional model is developed to quantitatively predict the change in elevation, over a period of decades, for vertically accreting floodplains. This unsteady model approximates the monotonic growth of a floodplain as an incremental but constant increase of net sediment deposition per flood for those floods of a partial duration series that exceed a threshold discharge corresponding to the elevation of the floodplain. Sediment deposition from each flood increases the elevation of the floodplain and consequently the magnitude of the threshold discharge resulting in a decrease in the number of floods and growth rate of the floodplain. Floodplain growth curves predicted by this model are compared to empirical growth curves based on dendrochronology and to direct field measurements at five floodplain sites. The model was used to predict the value of net sediment deposition per flood which best fits (in a least squares sense) the empirical and field measurements; these values fall within the range of independent estimates of the net sediment deposition per flood based on empirical equations. These empirical equations permit the application of the model to estimate of floodplain growth for other floodplains throughout the world which do not have detailed data of sediment deposition during individual floods. Copyright (C) 2000 John Wiley & Sons, Ltd.
Moody, J.A., and D.A. Martin, Initial hydrologic and geomorphic response following a wildfire in the Colorado Front Range, Earth Surface Processes and Landforms, 26 (10), 1049-1070, 2001.
A wildfire in May 1996 burned 4690 hectares in two watersheds forested by ponderosa pine and Douglas fir in a steep, mountainous landscape with a summer, convective thunderstorm precipitation regime. The wildfire lowered the erosion threshold in the watersheds, and consequently amplified the subsequent erosional response to shorter time interval episodic rainfall and created both erosional and depositional features in a complex pattern throughout the watersheds. The initial response during the first four years was an increase in runoff and erosion rates followed by decreases toward pre-fire rates. The maximum unit-area peak discharge was 24 m(3) s(-1) km(-2) for a rainstorm in 1996 with a rain intensity of 90 min h(-1). Recovery to pre-fire conditions seems to have occurred by 2000 because for a maximum 30-min rainfall intensity of 50 mm. h(- 1), the unit-area peak discharge in 1997 was 6.6 m(3) s(-1) km(-2), while in 2000 a similar intensity produced only 0.11 m(3) s(-1) km(-2). Rill erosion accounted for 6 per cent, interrill erosion for 14 per cent, and drainage erosion for 80 per cent of the initial erosion in 1996. This represents about a 200-fold increase in erosion rates on hillslopes which had a recovery or relaxation time of about three years. About 67 per cent of the initially eroded sediment is still stored in the watersheds after four years with an estimated residence time greater than 300 years. This residence time is much greater than the fire recurrence interval so erosional and depositional features may become legacies from the wildfire and may affect landscape evolution by acting as a new set of initial conditions for subsequent wildfire and flood sequences. Published in 2001 by John Wiley & Sons, Ltd.
Moog, D.B., and P.J. Whiting, Annual hysteresis in bed load rating curves, Water Resources Research, 34 (9), 2393-2399, 1998.
The relationship between flow and bed load transport measured for 10 years in six: gravel-bed streams in Idaho exhibits annual hysteresis. At a given flow rate, more bed load is carried by discharges preceding the first annual occurrence of a "threshold" rate, which is characteristic of each stream. Incorporating the effect of hysteresis leads to a small improvement in the fit of the bed load-flow regression. As the turning point for hysteresis, a constant threshold discharge is found to work better than the annual peak discharge. This bimodal hysteresis model is also found to out perform one with a more gradual transition, based on cumulative discharge. These results are interpreted to reflect a buildup of readily moved sediment supplies during the low-how periods from late summer to early spring, supplies which are then exhausted by rising springtime discharges up to the threshold. The threshold is greater than mean annual discharge and about one-half bank-full discharge.
Morelseytoux, H.J., H. Fahmy, and J.P. Lamagat, A Composite Hydraulic and Statistical Flow-Routing Method, Water Resources Research, 29 (2), 413-418, 1993.
A simple and efficient method for flow routing, combining the kinematic wave equation with a statistical procedure, is introduced. It accounts for the nonlinearity and the dispersion of the flood wave propagation phenomenon and for lateral flow. The method is flexible, because it can be used to simulate a variety of flow variables, for example, water stage or discharge. Its calibration is based on historical records at both ends of the reach, and does not require geometric cross- section or longitudinal data. An application to the White Nile in Sudan demonstrates the practicality and accuracy of the method.
Morisawa, M., The Geological-Society-of-America-Bulletin and the Development of Quantitative Geomorphology, Geological Society of America Bulletin, 100 (7), 1016-1022, 1988.
Morris, S.E., Geomorphic aspects of stream-channel restoration, Physical Geography, 16 (5), 444-459, 1995.
Stream restoration is fundamentally a geomorphic activity, inasmuch as quasi-equilibrium stream channels and functional floodplains promote the greatest aquatic and terrestrial habitat diversity and represent the natural conditions under which riparian ecosystems develop. The vast body of hydraulic geometry research as well as existing physical models of threshold conditions provide guidance for stream-channel restorations. These methods provide approximate channel cross- section dimensions as well as estimates of plan-form characteristics. Although it is difficult to defend the rigid application of any specific method, two examples of restoration problems illustrate the general utility of these geomorphic assessments. In many cases nongeomorphic constraints on the restoration goals and scope preclude the reestablishment of true historic channel and floodplain geometry. These design compromises are further complicated by the placement of in- stream structures to the degree that restorations often include a variety of bank stabilization treatments to discourage excessive channel migration.
Morris, P.H., and D.J. Williams, Relative celerities of mobile bed flows with finite solids concentrations, Journal of Hydraulic Engineering-Asce, 122 (6), 311-315, 1996.
The relative magnitudes of the celerities at which disturbances on the water surface and the bed are propagated play a key role in the mathematical modeling of mobile bed flow. Earlier analyses assumed that the solids concentration of the how was negligible. This assumption is inappropriate both for some natural streams and for many aqueous mine-waste disposal applications. Here, the relative celerities of mobile bed flow are determined for flows with finite solids concentrations. The solids concentration is assumed to be a function of the velocity and depth of dow The analysis confirms and extends the results of earlier analyses. It is shown that the movement of the sediment and the water can be considered to be mathematically independent of each other only within very limited ranges of solids concentration and Froude number. This severely constrains the application of numerous existing mathematical models to mobile bed hows with relatively high solids concentrations.
Morris, P.H., and D.J. Williams, Exponential longitudinal profiles of streams, Earth Surface Processes and Landforms, 22 (2), 143-163, 1997.
Morris, P.H., and D.J. Williams, Worldwide correlations for subaerial aqueous flows with exponential longitudinal profiles, Earth Surface Processes and Landforms, 24 (10), 867-879, 1999.
It is shown that very strong, worldwide correlations exist between the bed concavity coefficients of a wide range of subaerial aqueous flows with exponential longitudinal profiles and both the corresponding stream segment lengths and exponential bed particle size diminution coefficients. The former correlation is complementary to an existing similar correlation for the exponential size diminution coefficients, while the latter is consistent with earlier theoretical correlations based on very limited data. The data supporting the correlations extend over virtually the whole range of stream lengths, solids concentrations, and bed sediment particle sizes found on Earth. This universality strongly suggests that there are underlying mechanisms common to all kinds of mobile bed subaerial aqueous flows. However, the scatter of the data for the correlations is significant and is mostly attributable to variations in hydraulic conditions and sediment properties rather than measurement errors. Some of the conditions and properties have been identified, but others remain obscure. Copyright (C) 1999 John Wiley & Sons, Ltd.
Morris, P.H., and D.J. Williams, A worldwide correlation for exponential bed particle size variation in subaerial aqueous flows, Earth Surface Processes and Landforms, 24 (9), 835-847, 1999.
The particle size of the bed sediments in or on many natural streams, alluvial fans, laboratory flumes, irrigation canals and mine waste deltas varies exponentially with distance along the stream. A plot of the available worldwide exponential bed particle size diminution coefficient data against stream length is presented which shows that all the data lie within a single narrow band extending over virtually the whole range of stream lengths and bed sediment particle sizes found on Earth. This correlation applies to both natural and artificial flows with both sand and gravel beds, irrespective of either the solids concentration or whether normal or reverse sorting occurs. This strongly suggests that there are common mechanisms underlying the exponential diminution of bed particles in subaerial aqueous flows of all kinds. Thus existing models of sorting and abrasion applicable to some such flows may be applicable to others. A comparison of exponential laboratory abrasion and field diminution coefficients suggests that abrasion is unlikely to be significant in gravel and sand bed streams shorter than about 10 km to 100 km, and about 500 km, respectively. Copyright (C) 1999 John Wiley & Sons, Ltd.
Morse, B., and R.D. Townsend, Modeling Channel Bed Transients Using Explicit F-D Schemes, Journal of Hydraulic Engineering-Asce, 116 (11), 1345-1356, 1990.
Morse, B., R.D. Townsend, and M. Sydor, Mathematical-Modeling of Riverbed Dynamics - a Canadian Case- Study, Canadian Journal of Civil Engineering, 18 (5), 772-780, 1991.
A new mobile-bed mathematical model for simulating sediment transport in river networks under unsteady flow conditions is presented. The new model, ONE-D-SED, is an extended version of the extensively validated fixed-bed, one-dimensional hydrodynamic model ONE-D. This paper reports the results of an application of ONE-D-SED to Simulate bed profile development along a 43-km-long tidal channel network of the Lower Fraser River in British Columbia. The sand-bed study reach has been undergoing degradation caused by navigational dredging and river training works in lower channel reaches and by borrow dredging within the study reach itself. ONE-D-SED was used to simulate bed degradation in the study reach during the 1979- 1984 period. The simulated annual change in bed elevation at the downstream end of the study reach showed good agreement with that observed during 1968, the data year used to calibrate the model. The predicted cumulative change in bed profile from 1979 to 1984 also compared favourably with the overall degradation pattern observed during that same period.
Mosley, M.P., and D.S. Tindale, Sediment Variability and Bed Material Sampling in Gravel-Bed Rivers, Earth Surface Processes and Landforms, 10 (5), 465-482, 1985.
Mosley, M.P., Bedload Transport and Sediment Yield in the Onyx River, Antarctica, Earth Surface Processes and Landforms, 13 (1), 51-67, 1988.
Murray, A.B., and C. Paola, A Cellular-Model of Braided Rivers, Nature, 371 (6492), 54-57, 1994.
A BROAD Sheet of water flowing over non-cohesive sediment typ- ically breaks up into a network of interconnected channels called a braided stream (Fig. 1). The dynamics of such networks are complex; channels migrate laterally, split, rejoin and develop bars, with the flow shifting unpredictably from one part of the network to another. Many processes are known to operate in a braided river(1-3), but it is unclear which of these are essential to explain the observed dynamics. We describe here a simple, deterministic numerical model of water flow over a cohesionless bed that captures the main spatial and temporal features of real braided rivers. The patterns arise from local scour and deposition caused by a nonlinear dependence of bedload sediment flux on water discharge. Although the morphology of the resulting network depends in detail on the sediment-transport rule used in the model, our results suggest that the only factors essential for braiding are bedload sediment transport and laterally unconstrained free-surface flow.
Murray, A.B., and C. Paola, A new quantitative test of geomorphic models, applied to a model of braided streams, Water Resources Research, 32 (8), 2579-2587, 1996.
Recent simple cellular models of self-organized geomorphic patterns embody a new understanding of complex, spatially extended systems. Such models can be difficult to test quantitatively because the statistics traditionally used can be insensitive even to visually obvious variations in a complex pattern. Here we develop a new approach to evaluating such models. We begin by applying to spatial patterns the state- space reconstruction techniques developed for dynamical systems, producing plots that summarize the patterns in a way that preserves more information than do the statistics usually used in geomorphology. Methods exist for characterizing some aspects of such plots. Here we develop a complementary method for quantitatively comparing state-space plots in a way that more directly evaluates the similarity between the typical features of spatial patterns. An application of this method to the patterns produced by a cellular braided-stream model and real braided streams indicates that this approach provides a relatively sensitive way of comparing model-generated and real spatial patterns.
Murray, A.B., and C. Paola, Properties of a cellular braided-stream model, Earth Surface Processes and Landforms, 22 (11), 1001-1025, 1997.
We have shown in a previous paper that many of the main features of braided streams can be captured in a relatively simple cellular computer model. Here we examine some of the detailed characteristics of this model. We show the qualitative form of the braiding produced by the model is generally insensitive to changes in most of the numerical parameters used in the model. The most crucial parameter choice is the use of a non-linear exponent (>1) to describe the relation between sediment flux and local stream power. Use of water discharge instead of stream power to parameterize sediment flux produces braiding, but also unrealistically high-amplitude topography variations in the long term. Introduction of a threshold transport condition causes no noticeable change in the model's behaviour. Inclusion of lateral sediment transport due to gravitational effects on lateral slopes is not crucial to produce braiding, but is needed to provide reasonable lateral channel shifting, and to maintain a continuing dynamic behaviour. As long as lateral sediment transport is included, altering the initial topography for a run has no effect, other than a transient period of regrading. In addition, we show that there is a simple and apparently fundamental connection between braided-stream channel networks and erosional (dendritic) networks that has not been previously recognized. All that is needed to switch the model from braided to dendritic patterns is either to remove redeposition from the rules, simulating entrainment of cohesive sediment, or to add a cliff to the initial topography, making local redeposition unimportant. This result suggests that the presence or absence of significant local redeposition, which causes bar formation, channel division, and avulsion, determines whether a braided or dendritic pattern will form. (C) 1997 John Wiley & Sons, Ltd.
Mutz, M., Influences of woody debris on flow patterns and channel morphology in a low energy, sand-bed stream reach, International Review of Hydrobiology, 85 (1), 107-121, 2000.
In lowland areas, such as the glacial landscapes of eastern Germany, sand-bed streams are the most common stream type. They have low gradients and their hydrological regime is often subdued due to the frequent interruption by lakes. Very few is known about the influence of woody debris in these streams, since nearly all previous studies are from high-gradient conditions, where streams have coarse bed sediments and harsh hydrological regimes. The research objectives of this study were first to assess the quasi-natural quantity and quality of wood in a lowland sand-bed stream and second to understand the influence of wood on the channel morphology and the flow patterns at base-flow. The three-dimensional stream bed relief was surveyed by electronic distance measurement. The position and the size of large woody debris was assessed by close-up photography. An acoustic Doppler velocimeter was used to record the patterns of flow velocity and turbulence. Overlay and analysis of the spatial data was done using a Geographic Information System. The standing stock of wood was 1.9 m(3) and 39 woody elements per 100 m(2) of stream bed. The flow pattern was clearly controlled by the wood. Woody elements elevated above the stream bed deflected flow and locally caused strong secondary current, high turbulence, and scour of the stream bed at baseflow. Wood resting directly on the stream bed, which contributed the majority of the wood inside the bank-full channel, determined the roughness of the stream bed. Near-bed flow patterns observed were isolated roughness flow and wake interference flow, which was registered inside the accumulations of wood. 68% of the stream bed had shear stress above critical. Hence, the secondary morphological structures of the sand-bed were controlled at base-flow by the flow which was determined by the woody debris distribution.
Myers, W.R.C., Flow Resistance in Compound Channels, Journal of Hydraulic Research, 28 (2), 141-155, 1990.
Myers, T., and S. Swanson, Variability of pool characteristics with pool type and formative feature on small Great Basin rangeland streams, Journal of Hydrology, 201 (1-4), 62-81, 1997.
Land managers and stream restorationists often set goals or complete designs including specifications for pools that are unrealistic because of a lack of knowledge of the potential conditions of the stream. Using 36 study sites on 17 rangeland streams in Nevada in the western United States, we determined relationships among pool and nonpool length, gradient, pool spacing, pool type and formative feature and stream type. Step pools primarily were formed by boulders while backwater pools were formed by coarse woody debris, This led to most pools being randomly located because structural pool-forming features are too large to move by the flows on these small streams. Montgomery and Buffington (1993) stream type associated with pool type and feature because of the direct linkage between the stream type definitions and pool features, Pool spacing varied only with Montgomery-Buffington stream type presumably because of its linkage with pool type and formative feature. Pool length varied with both Rosgen (1994) and Montgomery-Buffington stream type because of the relations between stream type and pool type and feature. Meander bend pools tended to be deeper because they form in erosive, fine substrate and because the spacing of forced pools may not be optimal which leads to sedimentation. Pool area did not vary with stream type but did with various formative features and pool and nonpool length, Variation of pool area with gradient and ln(gradient) was significant but explained much less variation than did other parameters. Meander bend dominated reaches had the highest pool area. The variability of results and the dependence of pool measures on pool type and formative feature indicates that strict adherence to published equations or expectations due to stream type should be avoided. Land managers should set goals for pool measures based on site specific conditions rather than perceived aquatic species needs or stream type. (C) 1997 Elsevier Science B.V.
Myers, T.J., and S. Swanson, Precision of channel width and pool area measurements, Journal of the American Water Resources Association, 33 (3), 647-659, 1997.
The precision of width and pool area measurements has rarely been considered in relation to downstream or at section hydraulic geometry, fisheries studies, long-term or along a continuum research studies, or agency monitoring techniques. We assessed this precision and related it to other stream morphologic characteristics. Confidence limits (95 percent) around mean estimates with four transects (cross-sections perpendicular to the channel centerline) ranged from +/- 0.4 to 1.8 m on streams with a width of only 2.2 m. To avoid autocorrelation, transects should be spaced about three channel widths apart. To avoid stochastic inhomogeneity, reach length should be about 30 channel widths or ten transects to optimize sampling efficiency. Precision of width measurements decreased with decreased depth and increased with stream size. Both observations reflect variability caused by features such as boulders or coarse woody debris. Pool area precision increased with pool area reflecting increased precision for flat, wide streams with regular pool-rime sequences. The least precision occurred on small, steep streams with random, boulder or coarse woody debris formed pools.
Myers, T.J., and S. Swanson, Stochastic modeling of pool-to-pool structure in small Nevada rangeland streams, Water Resources Research, 33 (4), 877-889, 1997.
We developed, calibrated, and verified a compound Poisson process model of pool-to-pool spacing and size using an exponential distribution for spacing and gamma distributions for length and width on 12 rangeland streams in Nevada. Neither distribution parameter varied with simple stream morphologic or vegetation characteristics. We verified the model by comparing the first three moments and distributions of stream simulations with observed streams using two transect-based sampling schemes. Very small errors stemmed from an inability to reproduce autocorrelation of width at short distances, pool cyclicity, and additional density at the tails. We conclude that the presented model is accurate for small, Nevada, rangeland streams and for pools located randomly on small streams with forced pool-riffle or step-pool sequences and regularly on larger, pool-riffle systems. Simulated streams may be used for testing stream survey procedures and hypotheses regarding pool habitat, spacing, and length.
Myers, W.R.C., D.W. Knight, J.F. Lyness, J.B. Cassells, and F. Brown, Resistance coefficients for inbank and overbank flows, Proceedings of the Institution of Civil Engineers-Water Maritime and Energy, 136 (2), 105-115, 1999.
Myers, W.R.C., J.F. Lyness, J.B. Cassells, and J.J. O'Sullivan, Geometrical and roughness effects on compound channel resistance, Proceedings of the Institution of Civil Engineers-Water Maritime and Energy, 142 (3), 157-166, 2000.
This paper presents an analysis of resistance coefficients derived from measurements taken in phases A, B and C of the research programme of the UK Flood Channel Facility (FCF). The FCF is a large-scale compound channel facility and the programme has included straight and meandering planforms, smooth and mobile main channel roughnesses and smooth and rod- roughened floodplain boundaries. Floodplain roughness consisted of 25 mm surface-penetrating dowel rods. Data were also obtained for straight trapezoidal channels for comparison by confining flow to the main channels. Stage-discharge relationships were derived which enabled calculation of Manning's roughness coefficient values for a range of selected relative depths for each geometry, planform and roughness case. Graphs are presented of the variation with depth of Manning's coefficient for each geometry and roughness expressed as a ratio of smooth straight compound, or straight trapezoidal channel data, These presentations quantify the increase or decrease of roughness coefficient resulting form cross- sectional geometry, planform and boundary roughness. It is suggested that this represents a possible valid approach to the estimation of Manning's roughness coefficient in compound channels and rivers.
Naden, P., Modeling Gravel-Bed Topography From Sediment Transport, Earth Surface Processes and Landforms, 12 (4), 353-367, 1987.
Nakamura, F., F.J. Swanson, and S.M. Wondzell, Disturbance regimes of stream and riparian systems - a disturbance-cascade perspective, Hydrological Processes, 14 (16-17), 2849-2860, 2000.
Geomorphological processes that commonly transport soil down hillslopes and sediment and woody debris through stream systems in steep, mountainous, forest landscapes can operate in sequence down gravitational flowpaths, forming a cascade of disturbance processes that alters stream and riparian ecosystems. The affected stream and riparian landscape can be viewed through time as a network containing a shifting mosaic of disturbance patches - linear zones of disturbance created by the cascading geomorphological processes. Ecological disturbances range in severity from effects of debris flows, which completely remove alluvium, riparian soil and vegetation along steep, narrow, low-order channels, to localized patches of trees toppled by floating logs along the margins of larger channels. Land-use practices can affect the cascade of geomorphological processes that function as disturbance agents by changing the frequency and spatial pattern of events and the quantity and size distribution of material moved. A characterization of the disturbance regime in a stream network has important implications for ecological analysis. The network structure of stream and riparian systems, for example, may lend resilience in response to major disturbances by providing widely distributed refuges. An understanding of disturbance regime is a foundation for designing management systems. Copyright (C) 2000 John Wiley & Sons, Ltd.
Nash, D.B., Effective Sediment-Transporting Discharge From Magnitude- Frequency Analysis, Journal of Geology, 102 (1), 79-95, 1994.
Nash, D.J., The dry valleys of the Kalahari: Documentary evidence of environmental change in central southern Africa, Geographical Journal, 162, 154-168, 1996.
Nash, C.H., J.S. Richardson, and S.G. Hinch, Spatial autocorrelation and fish production in freshwaters: a comment on Randall et al. (1995), Canadian Journal of Fisheries and Aquatic Sciences, 56 (9), 1696-1699, 1999.
Nash, D.J., Arid geomorphology, Progress in Physical Geography, 23 (3), 429-439, 1999.
Nash, D.J., Arid geomorphology, Progress in Physical Geography, 24 (3), 425-443, 2000.
Nathan, R., U.N. Safriel, I. Noy-Meir, and G. Schiller, Spatiotemporal variation in seed dispersal and recruitment near and far from Pinus halepensis trees, Ecology, 81 (8), 2156-2169, 2000.
Spatiotemporal variation in the wind-generated dispersion pattern of Aleppo pine (Pinus halepensis) seeds was examined by placing seed traps up to 110 m away from a small. isolated stand in Israel during six successive dispersal seasons. Subsequent recruitment was surveyed two years later. Of the 5487 seeds, 97% were trapped 120 m from the nearest adult tree. Seasonal dispersal curves were consistently right-skewed and leptokurtic. The inverse power law and the negative exponential model accounted for a similar fraction of the variation in the number of dispersed seeds at different distances (79-86% and 76-88%, respectively). Seed dispersal rates varied significantly among seasons. Eighty saplings (3-5 yr old) became established during the three years of the study, most within 15 m of the nearest canopy, some farther away, and none directly under the tree canopies. The estimated probability of seed survival to sapling stage increased significantly with increasing distance from adults, as predicted by the escape hypothesis. Winds varied significantly between seasons. generating significant interseasonal variation in seed deposition patterns far from, but not near to, adult trees. Coefficients of variation of seed dispersal rates were lower near adult trees than farther away. Both Moran's I correlograms and partial Mantel tests revealed interseasonal consistency in seed deposition patterns for the total study area and for the area near adult trees but showed considerable variation farther away. We suggest that the low spatiotemporal variation near adults and the high variation far away act to intensify the effects of predation (by increasing the efficiency of predators near adults and reducing it far away) and competition (by increasing the intensity of seedling competition near adults and reducing it far away) in structuring the observed survivorship curve predicted by the escape hypothesis.
Nathan, R., and H.C. Muller-Landau, Spatial patterns of seed dispersal, their determinants and consequences for recruitment, Trends in Ecology & Evolution, 15 (7), 278-285, 2000.
Growing interest in spatial ecology is promoting new approaches to the study of seed dispersal, one of the key processes determining the spatial structure of plant populations. Seed- dispersion patterns vary among plant species, populations and individuals, at different distances from parents, different microsites and different times. Recent field studies have made progress in elucidating the mechanisms behind these patterns and the implications of these patterns for recruitment success. Together with the development and refinement of mathematical models, this promises a deeper, more mechanistic understanding of dispersal processes and their consequences.
Needham, D.J., The Development of a Bedform Disturbance in an Alluvial River or Channel, Zeitschrift Fur Angewandte Mathematik Und Physik, 39 (1), 28-49, 1988.
Needham, D.J., Wave Hierarchies in Alluvial River Flows, Geophysical and Astrophysical Fluid Dynamics, 51 (1-4), 167-194, 1990.
Needham, D.J., and D.D.L. Zanre, On the alluvial hydraulics of steady flow around a bridge pier, Geophysical and Astrophysical Fluid Dynamics, 84 (3-4), 205-243, 1997.
In the paper we develop an alluvial hydraulic theory for the Bow of an alluvial river around the base of a bridge pier. General results are established and then the cases of particular pier geometries are considered, Finally, the effects of Bow separation on the hydraulic theory are assessed.
Nel, R., A. McLachlan, and D.P.E. Winter, The effect of grain size on the burrowing of two Donax species, Journal of Experimental Marine Biology and Ecology, 265 (2), 219-238, 2001.
Nelson, J.M., The Initial Instability and Finite-Amplitude Stability of Alternate Bars in Straight Channels, Earth-Science Reviews, 29 (1-4), 97-115, 1990.
Nelson, J.M., Predictive techniques for river channel evolution and maintenance, Water Air and Soil Pollution, 90 (1-2), 321-333, 1996.
Nemec, W., and G. Postma, Quaternary Alluvial Fans in Southwestern Crete - Sedimentation Processes and Geomorphic Evolution - Reply, Sedimentology, 42 (3), 535-549, 1995.
Ney-Nifle, M., and M. Mangel, Species-area curves based on geographic range and occupancy, Journal of Theoretical Biology, 196 (3), 327-342, 1999.
The species-area relationship (SPAR) is one of the cornerstones of ecological science. We use information about the geographic distribution of species to deduce the SPAR from a new model; our results complement existing ones that explain SPARs on the basis of equilibrium theory or species-abundance relationships. We assume that each species is characterized by a geographic range and level of abundance (occupancy). We use a mixture of analytical tin one dimension) and numerical (in two dimensions) methods to create SPARs that are concave and can often be parametrized by a power law with exponent less than 1. We show that the main features of the SPAR depend upon the way that one censuses patches and on the characteristics (range and occupancy) of the species. Our approach identifies the key field variables that need to be measured and have implication for conservation, particularly when one estimates the number of species lost after habitat destruction. (C) 1999 Academic Press.
Nezu, I., A. Kadota, and H. Nakagawa, Turbulent structure in unsteady depth-varying open-channel flows, Journal of Hydraulic Engineering-Asce, 123 (9), 752-763, 1997.
Turbulence measurements over a smooth wall in unsteady depth- varying open-channel flows were conducted by the simultaneous use of a two-component laser Doppler anemometer (LDA) and a water-wave gauge. In the present study, velocity measurements in the viscous sublayer of highly unsteady flow have been first conducted to evaluate the friction velocity independently of the log-law. The von Karman constant kappa was calculated using this friction velocity. It was proven then that the value of kappa was really a constant of 0.41 even in unsteady open- channel flows. Next, statistical structures of mean velocity and turbulence characteristics were investigated across the whole flow from the near-wall region up to the free surface. In particular, turbulence measurements near the depth-varying water-surface zone of flood flow were conducted successfully for the first time with the LDA; such measurements have been impossible with conventional velocity instruments such as hot- film anemometers. Mean velocity profiles and turbulence characteristics were revealed in both the rising and the falling stages of the flood period.
Nicholas, A.P., P.J. Ashworth, M.J. Kirkby, M.G. Macklin, and T. Murray, Sediment slugs: Large-scale fluctuations in fluvial sediment transport rates and storage volumes, Progress in Physical Geography, 19 (4), 500-519, 1995.
Variations in fluvial sediment transport rates and storage volumes have been described previously as sediment waves or pulses. These features have been identified over a wide range of temporal and spatial scales and have been categorized using existing bedform classifications. Here we describe the factors controlling the generation and propagation of what we term sediment slugs. These can be defined as bodies of elastic material associated with disequilibrium conditions in fluvial systems over time periods above the event scale. Slugs range in magnitude from unit bars (Smith, 1974) up to sedimentary features generated by basin-scale sediment supply disturbances (Trimble, 1981). At lower slug magnitudes, perturbations in sediment transport are generated by local riverbank and/or bed erosion. Larger-scale features result from the occurrence of rare high-magnitude geomorphic events, and the impacts on water and sediment production of tectonics, glaciation, climate change and anthropogenic influences. Simple sediment routing functions are presented which may be used to describe the propagation of sediment slugs in fluvial systems. Attention is drawn to components of the fluvial system where future research is urgently required to improve our quantitative understanding of drainage-basin sediment dynamics.
Nicholas, A.P., and G.H.S. Smith, Relationships between flow hydraulics, sediment supply, bedload transport and channel stability in the proglacial Virkisa River, Iceland, Geografiska Annaler Series a-Physical Geography, 80A (2), 111-122, 1998.
We present data from a proglacial river in Iceland that exhibits very different sedimentological characteristics when compared to its alpine counterparts. The braidplain is characterised by coarse outburst gravels that inhibit sediment transport and channel change. Bedload transport is restricted to the movement of fine-grained gravels that pass through the channel system without promoting significant changes in channel geometry. Bar forms are erosional features, inherited from the last major peak flow, rather than depositional in nature. On the basis of our observations we conclude that braidplain morphology is controlled by low frequency, high magnitude flow events, possibly associated with glacial outburst floods. This is in marked contrast to process-form relationships in more dynamic alpine proglacial channels that are characterised by high rates of sediment transport and channel change.
Nicholas, A.P., and G.H.S. Smith, Numerical simulation of three-dimensional flow hydraulics in a braided channel, Hydrological Processes, 13 (6), 913-929, 1999.
Results are presented from a numerical simulation of three- dimensional flow hydraulics around a mid-channel bar carried out using the FLUENT/UNS computational fluid dynamics (CFD) software package. FLUENT/ UNS solves the three-dimensional Reynolds-averaged form of the Navier-Stokes equations. Turbulence closure is achieved using a RNG k-epsilon model. Simulated flow velocities are compared with measured two- dimensional velocities (downstream and cross-stream) obtained using an electromagnetic current meter (ECM). The results of the simulation are qualitatively consistent with the flow structures observed in the field. Quantitative comparison of the simulated and measured velocity magnitudes indicates a strong positive correlation between the two (r = 0.88) and a mean difference of 0.09 m s(-1). Deviations between simulated and measured velocities may be identified that are both random and systematic. The former may reflect a number of factors including subgrid-scale natural spatial variability in flow velocities associated with local bed structures and measurement uncertainty resulting from problems of ECM orientation. Model mesh configuration, roughness parameterization and inlet boundary condition uncertainty may each contribute to systematic differences between simulated and measured flow velocities. These results illustrate the potential for using CFD software to simulate flow hydraulics in natural channels with complex configurations. They also highlight the need for detailed spatially distributed datasets of three-dimensional flow variables to establish the accuracy and applicability of CFD software. Copyright (C) 1999 John Wiley & Sons, Ltd.
Nicholas, A.P., Modelling bedload yield in braided gravel bed rivers, Geomorphology, 36 (1-2), 89-106, 2000.
This paper outlines an approach for estimating the annual bedload yield of a braided channel. This procedure is based on the extension of theory of flow and sediment transport in braided rivers recently presented by Paola (1996). The revised approach accounts explicitly for the relationship between increasing discharge and varying channel hydraulics, and is suitable for use in obtaining bedload transport rate estimates over a range of discharges. integration of such estimates using flow-duration data allows annual bedload yield to be determined. Model parameterisation is achieved using topographic survey data for the Waimakarili River, New Zealand. Comparison of modelled bedload yield with values estimated from repeated topographic surveys indicates that the model is able to accurately predict both the medium-term (c. 30 years) mean annual bedload yield of the Waimakariri at Crossbank (the section 17.8 km upstream of the river mouth), and also short- term fluctuations in bedload yield associated with varying annual flow statistics. Streamwise patterns of volumetric erosion and deposition determined for a 45-km length of the Waimakariri using the model are also in broad agreement with trends identified in topographic survey data for the period 1961-1997. However, significant deviations between modelled and surveyed volumes of cut and fill are evident at some locations. Comparison of model performance with conventional applications of bedload transport equations, which tend to underestimate transport rates for braided channels, suggests that the approach presented here may represent a significant improvement. This is the case because the model quantifies the relationship between braid intensity and spatial variability in flow hydraulics at a cross-section. Output from the model suggests that braided rivers may transport a significant proportion of their annual bedload at lower discharges than those indicated by earlier theoretical approaches. Results also provide quantitative support for the argument that increased intensity of braiding may promote higher rates of bedload transport in gravel bed rivers. (C) 2000 Elsevier Science B.V. All rights reserved.
Nicholas, A.P., Computational fluid dynamics modelling of boundary roughness in gravel-bed rivers: An investigation of the effects of random variability in bed elevation, Earth Surface Processes and Landforms, 26 (4), 345-362, 2001.
Results from a series of numerical simulations of two- dimensional open-channel flow, conducted using the computational fluid dynamics (CFD) code FLUENT, are compared with data quantifying the mean and turbulent characteristics of open-channel flow over two contrasting gravel beds. Boundary roughness effects are represented using both the conventional wall function approach and a random elevation model that simulates the effects of supra-grid-scale roughness elements (e.g. particle clusters and small bedforms). Results obtained using the random elevation model are characterized by a peak in turbulent kinetic energy located well above the bed (typically at y/h = 0.1-0.3). This is consistent with the field data and in contrast to the results obtained using the wall function approach for which maximum turbulent kinetic energy levels occur at the bed. Use of the random elevation model to represent supra-grid-scale roughness also allows a reduction in the height of the near-bed mesh cell and therefore offers some potential to overcome problems experienced by the wall function approach in flows characterized by high relative roughness. Despite these benefits, the results of simulations conducted using the random elevation model are sensitive to the horizontal and vertical mesh resolution. increasing the horizontal mesh resolution results in an increase in the near- bed velocity gradient and turbulent kinetic energy, effectively roughening the bed. Varying the vertical resolution of the mesh has little effect on simulated mean velocity profiles, but results in substantial changes to the shape of the turbulent kinetic energy profile. These findings have significant implications for the application of CFD within natural gravel- bed channels, particularly with regard to issues of topographic data collection, roughness parameterization and the derivation of mesh-independent solutions. Copyright (C) 2001 John Wiley & Sons, Ltd.
Nicotra, A.B., R.L. Chazdon, and S.V.B. Iriarte, Spatial heterogeneity of light and woody seedling regeneration in tropical wet forests, Ecology, 80 (6), 1908-1926, 1999.
Variation in forest canopy structure influences both understory light availability and its spatial distribution. Because light is a major environmental factor limiting growth and survival of many forest species, its distribution may affect stand-level regeneration patterns. We examined spatial patterning in light availability and seedling regeneration in old-growth, second- growth, and selectively logged stands of tropical moist forest in northeastern Costa Rica. Our objectives were to determine how the frequency distribution and spatial pattern of understory light "microsites" differ among tropical wet forests; whether patterns of seedling regeneration are linked to spatial patterning of light availability; and whether these relationships differ among old-growth, second-growth, and selectively logged forest stands. We used both sensor-based and hemispherical photograph-based methods to measure light availability along three 130-160 m long transects in each of eight stands (three old-growth, three second-growth, and two selectively logged). Woody seedling abundance was assessed at 4 m(2), 25 m(2), and full-stand scales (430 m(2)), and species richness was computed at the 25-m(2) and full-stand levels. Data were analyzed using both conventional parametric approaches and spatial statistics. Mean light availability did not differ markedly among stand types, but variance and frequency distributions of light availability did. Second- growth stands had significantly higher unweighted canopy openness along solar tracks and a higher frequency of microsites at intermediate light levels. Old-growth stands had greater representation of both low- and high-light microsites, and greater overall variance in light availability. Old-growth stands also had slightly higher abundance and species richness of woody seedlings. Light availability was significantly spatially autocorrelated in all stand types, but patch size (analogous to gap size) was twice as large in old-growth stands, based on sensor data. Seedling abundance was also spatially autocorrelated over greater distances in old-growth than in second-growth stands, often at similar spatial scales to light distribution. The selectively logged stands demonstrated spatial autocorrelation of light and seedling abundance over distances intermediate to the other two stand types. Despite the similarities in patterns of light and seedling distributions, relationships between woody seedling abundance, species richness, and the three light availability measures were not strong or consistently positive, regardless of whether standard regressions or partial Mantel tests were applied. Although seedling abundance is likely to be affected by a wide variety of factors, the similarities in the scales of spatial autocorrelation of light and seedling abundance suggest that current seedling abundance distributions may reflect past patterns of light distribution within the stands. Our results confirm the importance of examining spatial dependence of resource availability in studies of forest dynamics, but they also underscore the limitations of a single period of data collection. Long-term studies as well as experimental manipulations of resource availability are needed to establish causal relationships between resource availability and stand- level patterns of seedling regeneration.
Niemann, J.D., R.L. Bras, D. Veneziano, and A. Rinaldo, Impacts of surface elevation on the growth and scaling properties of simulated river networks, Geomorphology, 40 (1-2), 37-55, 2001.
We investigate the connection between surface elevation and the growth and scaling of river networks. Three planar models (Scheidegger, Eden, and invasion percolation) are first considered. These models develop aggregating networks according to stochastic rules but do not simulate erosion because the network growth is independent of the surface elevation. We show that none of these planar growth models produces scaling results consistent with observations for natural river basins. We then modify the models to include elevation, simulating the effects of fluvial erosion by enforcing the slope-area relationship. The resulting configurations have scaling properties that still depend on the model (Scheidegger, Eden, or invasion percolation) but are closer to natural river networks when compared with those from the planar growth rules. We conclude that inclusion of the vertical dimension in these three models is critical for explaining the formation and regularities of fluvial networks. (C) 2001 Elsevier Science BN. All rights reserved.
Nikora, V.I., A.N. Sukhodolov, and P.M. Rowinski, Statistical sand wave dynamics in one-directional water flows, Journal of Fluid Mechanics, 351, 17-39, 1997.
Moving sand waves and the overlying tubulent flow were measured on the Wilga River in Poland, and the Tirnava Mica and Buzau Rivers in Romania. Bottom elevations and how velocities were measured at six points simultaneously by multi-channel measuring systems. From these data, the linear and two- dimensional sections of the three-dimensional correlation and structure functions and various projections of sand wave three- dimensional spectra were investigated. It was found that the longitudinal wavenumber spectra of the sand waves in the region of large wavenumbers followed Hino's -3 law (S(K-x) proportional to K-x(-3)) quite satisfactorily, confirming the theoretical predictions of Hino (1968) and Jain & Kennedy (1974). However, in contrast to Hino (1968), the sand wave frequency spectrum in the high-frequency region was approximated by a power function with the exponent -2, while in the lower-frequency region this exponent is close to -3. A dispersion relation for sand waves has been investigated from analysis of structure functions, frequency spectra and the cross-correlation functions method. For wavelengths less than 0.15-0.25 of the flow depth, their propagation velocity C is inversely proportional to the wavelength lambda. When the wavelengths of spectral components are as large as 3-4 times the flow depth, no dispersion occurs. These results proved to be in good qualitative agreement with the theoretical dispersion relation derived from the potential-flow-based analytical models (Kennedy 1969; Jain & Kennedy 1974). We also present another, physically-based, explanation of this phenomenon, introducing two types of sand movement in the form of sand waves. The first type (I) is for the region of large wavenumbers (small wavelengths) and the second one (II) is for the region of small wavenumbers (large wavelengths). The small sand waves move due to the motion of individual sand particles (type I, C proportional to lambda(-1)) while larger sand waves propagate as a result of the motion of smaller waves on their upstream slopes (type II, C proportional to lambda(0)). Like the sand particles in the first type, these smaller waves redistribute sand from upstream slopes to downstream ones. Both types result in sand wave movement downstream but with a different propagation velocity. The main characteristics of turbulence, as well as the quantitative values characterizing the modulation of turbulence by sand waves, are also presented.
Nikora, V.I., D.G. Goring, and B.J.F. Biggs, On gravel-bed roughness characterization, Water Resources Research, 34 (3), 517-527, 1998.
The random field approach for gravel-bed roughness characterization, which is based on the presentation of bed elevations as a three-dimensional random field, is justified as an alternative to the characteristic particle size approach. We first show that the bed elevation distribution is close to Gaussian and then investigate gravel-bed roughness using the second-order structure function. The latter reveals two distinct regions: a scaling region at small spatial lags and a saturation region at large scales. The scaling exponent H (a form of Hurst exponent) appears to be isotropic and universal for both manually created "unworked" gravel beds (H = 0.5) and natural water-worked gravel beds (H = 0.79). However, the gravel-bed roughness, in general, is not isotropic and should be characterized by three independent characteristic scales. A simple model of gravel-bed roughness based on the structure function parameterization is developed and compared with the characteristic particle size approach.
Nikora, V., and D. Goring, Flow turbulence over fixed and weakly mobile gravel beds, Journal of Hydraulic Engineering-Asce, 126 (9), 679-690, 2000.
Characteristics of turbulence structure in quasi-2D flows with static and weakly mobile gravel beds are presented. Three sets of measurements with acoustic Doppler velocimeters in an irrigation canal were used: two with subcritical bed shear stress (static beds) and one with the bed shear stress tau(o) close to critical tau(oc) (weakly mobile bed). The analyses included vertical distributions of local mean velocities, turbulence intensities, turbulent shear stresses, velocity auto- and cross-spectra, the quadrant method, and high-order velocity moments. A number of properties of turbulence intensities, high-order moments, streamwise bursting parameters, and velocity spectra appeared to be similar fur all three flows, but some properties were different. The most important one was an observed reduction in the von Karman constant for the flow with weakly mobile bed. Comparison of these results with other studies and analogies with drag- reducing flows suggest that at tau(o)/tau(oc) approximate to 1 the drag on the bed for a given granular material should be minimized.
Noel, J.R., and R.C. Sidle, A Program to Calculate Channel Scour and Fill, Water Resources Bulletin, 25 (4), 733-741, 1989.
O'Driscoll, R.L., D.C. Schneider, G.A. Rose, and G.R. Lilly, Potential contact statistics for measuring scale-dependent spatial pattern and association: an example of northern cod (Gadus morhua) and capelin (Mallotus villosus), Canadian Journal of Fisheries and Aquatic Sciences, 57 (7), 1355-1368, 2000.
Analysis of simulated data showed that potential contact statistics could be used to describe spatial pattern in sample density data. Potential contact is a new method, analogous to Ripley's K function for mapped point pattern analysis. Potential contact can be used to describe spatial pattern and association over a range of scales without grouping data and is robust against the presence of zeros. The statistical output is ecologically interpretable, as a measure of the degree of contact between individuals. This new technique was applied to examine changes in the spatial distribution of Atlantic cod (Gadus morhua) off Newfoundland, Canada, from 1985 to 1994, a period that encompassed a collapse of the cod stock. Sample data from bottom-trawl surveys indicated that cod were aggregated in patches with dimensions of 100-250 km. During the period of cod decline in the 1990s, spatial structure changed in three ways: the number of patches decreased, patch size shrank, and contact with conspecifics at small (10-20 km) scales fell. Cod were broadly associated with capelin (Mallotus villosus), a major prey species. Spatial distribution of capelin changed over the same time period as changes in cod distribution, and there was no evidence that contact between cod and capelin decreased.
Ogden, R., N. Spooner, M. Reid, and J. Head, Sediment dates with implications for the age of the conversion from palaeochannel to modern fluvial activity on the Murray River and tributaries, Quaternary International, 83-5, 195-209, 2001.
Oguchi, T., and H. Ohmori, Analysis of Relationships Among Alluvial-Fan Area, Source Basin Area, Basin Slope, and Sediment Yield, Zeitschrift Fur Geomorphologie, 38 (4), 405-420, 1994.
Olley, J.M., A. Murray, and R.G. Roberts, The effects of disequilibria in the uranium and thorium decay chains on burial dose rates in fluvial sediments, Quaternary Science Reviews, 15 (7), 751-760, 1996.
Buried sediments receive about 53% of their annual dose of ionising radiation from radionuclides in the uranium and thorium decay chains. In luminescence dating of sediment samples, it is usually assumed that the dose rate does not change over the period of burial, implying that the uranium and thorium decay series are in secular equilibrium. For the Th-232 decay chain there is little iterature available on the equilibrium conditions in sediments, but given the short half- lives of the longer-lived daughters in the series, Ra-228 (5.75 years) and Th-228 (1.91 years), the decay chain is expected to be in secular equilibrium in most natural materials. However, for the U-238 decay chain, disequilibrium is commonplace in the surficial environment and the half-lives of several members of this decay chain (U-234, Th-230, Ra-226) are sufficiently long that any disequilibrium, once established, may persist for millennia. In these circumstances, the dose rate will vary with time unless the decay rate is matched by the transport and deposition of the relevant (unsupported) nuclide. We present data from a variety of fluvial and lacustrine depositional environments, and demonstrate that disequilibria is common in these Australian surficial sediments. The origins of the disequilibria and their likely evolution in time are discussed. The effect on the dose rate is assessed and, in the majority of cases, is found to be comparable with other luminescence dating uncertainties of typically 5-10%. Copyright (C) 1996 Elsevier Science Ltd
Olley, J.M., R.G. Roberts, and A.S. Murray, A novel method fdr determining residence times of river and lake sediments based on disequilibrium in the thorium decay series, Water Resources Research, 33 (6), 1319-1326, 1997.
Sediment fluxes in rivers have proved difficult to measure or model at timescales relevant to land and water resource management decisions. Determining transport rates and residence times is complicated by the intermittent movement and temporary storage of sediments in natural streams. This paper presents a new tool for estimating the residence times of river-borne sediments, based on the observed disequilibria between the naturally occurring radionuclides Ra-228 and Th-232 in the thorium decay series. Disequilibrium between concentrations of Ra-228 (half-life 5.75 years) and its long-lived parent Th-232 has been observed in marine environments and in terrestrial freshwaters but has not been previously reported in fluvial sediments or soils. Here we report Ra-228 excesses in sandy stream and silty lake sediments from southeastern Australia. The excess is developed in hillslope soils in the catchment headwaters and begins to decay back to secular equilibrium once the sediment is finally removed from contact with the sail water. The short half-life of Ra-228 enables this process to be used to investigate fluvial sediment transfers, and alluvial and lacustrine sediment storages, over the past 30 years. When combined with indicators of sediment source, such as Ra-226/Th- 232 and Th-230/Th-232 ratios, observation of this excess should provide a useful new tool for examining the residence and transit times of bed load and suspended load sediments in streams and lakes.
Olsen, D.S., A.C. Whitaker, and D.F. Potts, Assessing stream channel stability thresholds using flow competence estimates at bankfull stage, Journal of the American Water Resources Association, 33 (6), 1197-1207, 1997.
Olsen, D.S., A.C. Whitaker, and D.F. Potts, "Assessing stream channel stability thresholds using flow competence estimates at bankfull stage" - Reply to discussion by Charles E. Dalby, Journal of the American Water Resources Association, 35 (1), 187-188, 1999.
Oneill, M.P., and A.D. Abrahams, Objective Identification of Pools and Riffles, Water Resources Research, 20 (7), 921-926, 1984.
Oneill, M.P., and A.D. Abrahams, Objective Identification of Meanders and Bends, Journal of Hydrology, 83 (3-4), 337-353, 1986.
Orndorff, R.L., and P.J. Whiting, Computing effective discharge with S-PLUS, Computers & Geosciences, 25 (5), 559-565, 1999.
Osterkamp, W.R., Processes of fluvial island formation, with examples from Plum Creek, Colorado and Snake River, Idaho, Wetlands, 18 (4), 530-545, 1998.
Osterkamp, W.R., and J.M. Friedman, The disparity between extreme rainfall events and rare floods - with emphasis on the semi-arid American West, Hydrological Processes, 14 (16-17), 2817-2829, 2000.
Research beginning 40 years ago suggested that semi-arid lands of the USA have higher unit discharges for a given recurrence interval than occur in other areas. Convincing documentation and Br arguments for this suspicion, however, were not presented. Thus, records of measured rainfall intensities for specified durations and recurrence intervals, and theoretical depths of probable maximum precipitation for specified recurrence intervals and areal scales an considered here for comparing extreme rainfalls of semi-arid areas with those of other climatic areas. Runoff from semi-arid lands, as peaks of rare floods, is compared with that of other areas using various published records. Relative to humid areas, semi-arid parts of the conterminous USA have lower 100-year, 6-h rainfall intensities and smaller depths of 100-year probable maximum precipitation for 26-km(2) areas. Nonetheless, maximum flood peaks, flash-flood potentials, and runoff potentials are generally larger in semi-arid areas than in more humid parts of the nation. Causes of this disparity between rainfall and runoff appear to be results of soil and vegetation that in humid areas absorb and intercept rainfall and attenuate runoff, but in semi-arid areas limit infiltration and enhance runoff from bare, crusted surfaces. These differences in soil and vegetation conditions are indicated by the relatively high curve numbers and drainage densities that are typical of semi- arid areas. Owing to soil and vegetation conditions, rare floods in semi-arid areas are more likely to cause landform change than are floods of similar magnitude elsewhere.
Owens, P.N., D.E. Walling, Q.P. He, J. Shanahan, and I.D.L. Foster, The use of caesium-137 measurements to establish a sediment budget for the Start catchment, Devon, UK, Hydrological Sciences Journal-Journal Des Sciences Hydrologiques, 42 (3), 405-423, 1997.
Caesium-137 (Cs-137) measurements have been used to investigate the delivery of sediment from the hillslopes to a lake which marks the downstream limit of the small agricultural Start basin in Devon, UK. Total Cs-137 inventories and Cs-137 depth distributions in sediment cores were used to estimate that the eroded sediment stored within the fields and on the flood plain of the main river was equivalent to sediment yields of ca. 21 and 30 t km(-2) year(-1), respectively. Based on published information on sediment accumulation in the lake, the minerogenic sediment yield from the basin was estimated to be ca. 29 t km(-2) year. The erosion rate on the hillslopes in the basin, calculated as the sum of the sediment yield to the lake and the two storage components, is ca. 80 t km(2) year(-1). Of the soil eroded from the slopes more than 60% is stored at intermediate locations and the sediment delivery to the lake is less than 40%. The calculated soil erosion rare for the Start basin is consistent with an estimate of the erosion rate for the basin of the nearby Old Mill Reservoir of ca. 63 t km(-2) year(-1).
Owens, P.N., D.E. Walling, and G.J.L. Leeks, Deposition and storage of fine-grained sediment within the main channel system of the River Tweed, Scotland, Earth Surface Processes and Landforms, 24 (12), 1061-1076, 1999.
This paper assesses the importance of deposition and storage of fine grained (c. < 150 mu m) sediment on the floodplains and beds of the main (non-tidal) channels of the River Tweed (4390 km(2)), Scotland, and two of its tributaries (River Teviot and Ettrick Water). Caesium-137 analysis of floodplain sediment cores has been used to estimate average rates of overbank sedimentation during the last 30 to 40 years. Average values for individual transects ranged from 0.16 to 2.18 kg m(-2) a(- 1) (0.13 to 2.2 mm a(-1)). The mean for the 10 transects investigated was 1.29 kg m(-2) a(-1) (1.3 mm a(-1)). The total amount of fine sediment deposited was estimated to be about 44 000 t a(-1). The fine-grained sediment stored in the channel bed was quantified using resuspension techniques. Average values for individual sites ranged from 0.12 to 0.96 kg m(-2). The mean for the 10 sites investigated was 0.56 kg m(-2). The total amount of sediment stored on the channel bed of the main channel system at the time of sampling was estimated to be about 4300 t. Comparison of these estimates of floodplain and channel storage with the estimated suspended sediment load for the River Tweed at the downstream gauging site at Norham, indicates that floodplain sedimentation and channel bed storage represent about 40 and 4 per cent, respectively, of the annual load of fine sediment delivered to the main channel system. Erosion of channel banks will reintroduce the equivalent of about 30 per cent of the floodplain-deposited sediment back into the channel. The residence time of the fine-grained sediment stored on the channel bed is probably less than one year, but that of sediment deposited on the floodplain is likely to be considerably longer. Conveyance losses associated with overbank deposition have important implications for the routing of sediment through fluvial systems and the interpretation of downstream sediment yields. Copyright (C) 1999 John Wiley & Sons, Ltd.
Paige, A.D., and E.J. Hickin, Annual bed-elevation regime in the alluvial channel of Squamish River, southwestern British Columbia, Canada, Earth Surface Processes and Landforms, 25 (9), 991-1009, 2000.
The aim of this study is to examine the annual regime of channel scour and fill by monitoring bed-elevation changes in a reach of Squamish River in southwestern British Columbia, Canada. Sonar surveys of 13 river cross-sections in a sandy gravel-bed single-channel study reach were repeated biweekly over a full hydrologic year (1995/6). The survey results show that bedload movement occurs as waves or pulses forming bedwaves that appear to maintain an overall coherence with movement downstream. These bedwaves propagate downstream by a mode here termed pulse scour and pulse fill, a process distinguished from the conventional mode of scour and fill commonly associated with flood events there termed local scour and local fill). Bedwave celerity was estimated to be about 15.5 m d(-1) corresponding to a bedwave residence time in the study reach of almost one hydrologic year. The total amount of local bed-elevation change ranged between 0.22 m and 2-41 m during the period of study. Analysis of the bed-elevation and flow data reveals that, because of the bedwave phenomenon, there is no simple relation between the mean bed-elevation and discharge nor any strong linear correlation among cross- sectional behaviour. The bed-elevation data also suggest that complex changes to the bed within a cross-section are masked when the bed is viewed in one dimension, although no definitive trends in bed behaviour were found in the two-dimensional analysis. Although a weak seasonal effect is evident in this study, the bed-elevation regime is dominated by sediment supply driven fluctuations in bedload transport occurring at timescales shorter than the seasonal fluctuation in discharge. The study also indicates that bed-elevation monitoring on Squamish River, and others like it, for purposes of detecting and measuring aggradation/degradation must take into account very considerable and normal channel-bed variability operating at timescales from hours to months. Copyright (C) 2000 John Wiley & Sons, Ltd.
Paine, J.N., Open-Channel Flow Algorithm in Newton-Raphson Form, Journal of Irrigation and Drainage Engineering-Asce, 118 (2), 306-319, 1992.
The standard step method is one of the most widely accepted procedures for computing open-channel water surface profiles. Conventional computer models that use the standard step method often have cumbersome data requirements for routine drainage analyses. An algorithm has been developed that executes the standard step method in prismatic open channels. This algorithm, presented in Newton-Raphson form, is suitable for subcritical, supercritical, critical, adverse, and horizontal flow regimes. Transition channel sections having linearly variable bottom widths are easily accommodated. Numerical solution of the standard step equations, without using look-up tables and interpolation procedures, results in fast execution times. A steady flow computer program that uses the algorithm has been developed to perform some "smart" checking of hydraulic profile logic and to facilitate simple data entry. The program is available to interested persons free of charge, upon receipt of a self-addressed stamped envelope, disk mailer, and diskette.
Palomo, C., J. Acosta, J.L. Sanz, P. Herranz, A. Munoz, E. Uchupi, and J. Escartin, Morphometric interpretation of the northwest and southeast slopes of Tenerife, Canary Islands, Journal of Geophysical Research-Solid Earth, 102 (B9), 20325-20342, 1997.
Pan, D.Y., A. Bouchard, P. Legendre, and G. Domon, Influence of edaphic factors on the spatial structure of inland halophytic communities: a case study in China, Journal of Vegetation Science, 9 (6), 797-804, 1998.
In order to understand the influence of edaphic factors on the spatial structure of inland halophytic plant communities, a 2.6 km(2) study site, located on the lower fringe of the alluvial fan of the Hutubi River, in an arid region of China, was sampled and mapped. 105 patches were found to be homogeneous in species composition. Plant species and their coverage were recorded in each patch. 45 patches were randomly selected for the measurement of edaphic variables. A map with quadrat locations and boundaries of patches was digitized into a GIS and related to the vegetation and edaphic data matrices. CCA was used to evaluate the relative importance of edaphic factors in explaining the variation of the species assemblages and to identify the ecological preferences of species. The spatial structure of the communities and the main edaphic factors were analyzed using correlograms, Mantel correlograms and clustering under constraint of spatial contiguity. Gradient analysis showed that there are two distinct vegetation gradients in the study area, one of which is determined mainly by soil moisture (determined by depth to the water table), and the other by soil salinity (determined by electrical conductivity and hydrolytic alkalinity of the first soil layer). However, spatial analyses showed that at the sampling scale the halophytic communities in the study area are structured along one main spatial gradient determined by the water table level. Similar spatial autocorrelation structures between the factors related to the first soil layer and the communities, given our sampling scale, could not be detected. Our results suggest that the relative importance of the effects of different edaphic factors on the spatial structure of halophytic communities is scale-dependent. The partitioning of species variation indicates that in addition to edaphic factors, other factors, such as biotic interactions, may play an important role in structuring these communities.
Paola, C., G. Parker, R. Seal, S.K. Sinha, J.B. Southard, and P.R. Wilcock, Downstream Fining By Selective Deposition in a Laboratory Flume, Science, 258 (5089), 1757-1760, 1992.
Paola, C., and R. Seal, Grain-Size Patchiness As a Cause of Selective Deposition and Downstream Fining, Water Resources Research, 31 (5), 1395-1407, 1995.
Paola, C., and D. Mohrig, Palaeohydraulics revisited: Palaeoslope estimation in coarse- grained braided rivers, Basin Research, 8 (3), 243-254, 1996.
Methods for estimating palaeoslope from fluvial deposits have been available for some time, but new data and improved understanding of the relevant physical processes afford the possibility of improving existing methods, and the emerging field of quantitative stratigraphy provides a new context for the results. Here we focus on deriving palaeoslope estimates for coarse-grained fluvial deposits. These estimates can be used in basin analyses to constrain the magnitude of the slope change necessary for a given deflection of palaeocurrents, to constrain temporal and spatial variation in basin subsidence rate, and to provide a surface datum for use in sediment- backstripping calculations. The algorithm we derive to estimate palaeoslope applies to rivers that self-adjust through variations in channel width to maintain a temporally and spatially averaged bed shear stress equal to some constant multiple of the critical shear stress for initial motion of bed sediment. Data from modern coarse-grained rivers with minimal bank cohesion and form resistance suggest that this boundary shear stress is equal to about 1.4 times the critical shear stress for movement of the median-sized clast of the surface layer. The key sedimentological criteria for recognition of systems appropriate for this type of analysis are: (1) field relations suggesting that channel banks formed in effectively noncohesive gravel (i.e. free of clay-size sediment and plant roots); (2) absence of significant volumes of dune-derived cross-stratification and (3) absence of indicators of extremely rapid, flash-flood-type deposition. The basic input data for a palaeoslope calculation are spatially averaged estimates of palaeodepth and median grain size. The most important aspect of data collection is that the depth and grain-size estimates should be determined independently by random sampling over the whole outcrop. Joint analysis of data from appropriate modern rivers and of errors associated with palaeodepth and grain-size estimates indicates that in coarse-grained braided-river deposits, palaeoslope can be estimated to within a factor of 2.
Paola, C., Quantitative models of sedimentary basin filling, Sedimentology, 47, 121-178, 2000.
Quantitative modelling of the filling of sedimentary basins was begun in earnest in the 1960s. Dozens of themes and variations have been proposed since then, and have yielded an abundance of idealized stratigraphic patterns as functions of both imposed changes and basin properties. Post-plate-tectonic modelling began with 'rigid-lid' models, which show the stratigraphic signature of subsidence variation. This work introduced the connection between stratigraphy and the rheology of the lithosphere. Rigid-lid models are the simplest type of geometric model, in which the sediment surface is assigned prescribed geometries, usually corresponding to different depositional environments. These can reproduce many aspects of overall stratal geometry but are formally restricted to relatively long timescales, for which quasi-steady surface topography can be assumed. So-called dynamic models attempt to represent the morphodynamics of the sediment surface by abstracting and averaging short-term transport processes. Most of the dynamic models proposed to date can be seen as special cases of a single general morphodynamic equation. The most important result of the first wave of quantitative basin- filling models is that even relatively simple models can produce reasonable stratal patterns. We now have a wide array of tools for exploring scenarios, searching for general behaviours and effects, and making initial quantitative predictions. We have also learned that basin response to external forcing as recorded in stratigraphy can be as sensitive to the characteristics of the basin as to the forcing. The main brake on the development of basin modelling is not computing power but lack of methods and data for testing the models we have already developed. Physical experiments, which are only just beginning, are one means of doing this. Experimental stratigraphy is a bridge to quantitative field tests, which will require collaboration among academic researchers from a wide range of areas, and between academia and industry, on projects of greater scale and degree of integration than we have seen so far. The advancement of quantitative sedimentary geology will also require significant changes in the way the subject is taught, at all levels.
Paphitis, D., Sediment movement under unidirectional flows: an assessment of empirical threshold curves, Coastal Engineering, 43 (3-4), 227-245, 2001.
Pardo, I., Patterns of community assembly in a fourth order stream, Archiv Fur Hydrobiologie, 148 (2), 301-320, 2000.
Spatial patterns in community structure were studied for one year along a fourth order stream in NW Spain, the Tea Stream. Differences were observed for most biological variables examined between upper-middle lotic reaches and downstream reaches in autumn, a season characterised by occurrence of high and frequent spates. Diversity and richness values were high at the upper stream reaches throughout the year, even when discharge was high. Downstream sites were inhabited by species- poor communities during autumn and winter. In spring and summer, however, richness and diversity values increased, and invertebrate abundance was higher at these sites than at the upper reaches. Observed spatial patterns in community structure were mainly correlated with physical variables, such as a combination of morphological channel features, dissolved salts and oxygen concentration, and surface water velocities. The spatio-temporal differences in community structure observed in this study are greater than expected for a fourth-order stream. The greatest discontinuity in community composition occurred between high and low gradient sites during periods of high flow. The flow conditions during autumn-winter seemed to exert a strong abiotic influence on communities inhabiting downstream reaches, when species richness and abundances remained low. The upper-middle reaches of the Tea supported high richness throughout the year, with more resilience to high flows than downstream communities.
Park, I., and S.C. Jain, Riverbed Profiles With Imposed Sediment Load, Journal of Hydraulic Engineering-Asce, 112 (4), 267-280, 1986.
Parker, G., and P.C. Klingeman, On Why Gravel Bed Streams Are Paved, Water Resources Research, 18 (5), 1409-1423, 1982.
Parker, G., P. Diplas, and J. Akiyama, Meander Bends of High Amplitude - Closure, Journal of Hydraulic Engineering-Asce, 110 (12), 1881-1887, 1984.
Parker, G., Surface-Based Bedload Transport Relation For Gravel Rivers, Journal of Hydraulic Research, 28 (4), 417-436, 1990.
Parker, G., and A.J. Sutherland, Fluvial Armor, Journal of Hydraulic Research, 28 (5), 529-544, 1990.
Mobile armor layers which form during bed load transport of non-uniform sediments are shown to be closely related to the static armor layers that form by selective erosion as a result of the action of clear water flows. Two previously published numerical models of the transport of non-uniform sediments are used as a basis for the discussion. Each model is inverted, so that it predicts surface layer compositions given the imposed flow conditions and bed load transport rate and composition. Static armor is then obtained in the limit of vanishing sediment transport, under the constraint that the bedload and substrate size distributions are identical. Good agreement is obtained between measured and calculated static armor compositions over the entire grain size distribution.
Parker, G., and P.R. Wilcock, Sediment Feed and Recirculating Flumes - Fundamental Difference, Journal of Hydraulic Engineering-Asce, 119 (11), 1193-1204, 1993.
Parker, K.C., Effects of Complex Geomorphic History On Soil and Vegetation Patterns On and Alluvial Fans, Journal of Arid Environments, 30 (1), 19-39, 1995.
Parker, G., and P.R. Wilcock, Sediment Feed and Recirculating Flumes - Fundamental Difference - Closure, Journal of Hydraulic Engineering-Asce, 121 (3), 293-294, 1995.
Parker, K.C., and J. Bendix, Landscape-scale geomorphic influences on vegetation patterns in four environments, Physical Geography, 17 (2), 113-141, 1996.
Parker, G., Interaction between basic research and applied engineering: A personal perspective, Journal of Hydraulic Research, 34 (3), 291-316, 1996.
Examples from the personal experience of the author are used to illustrate the synergistic ways in which basic and applied research can interact in the field of hydraulics. While maintaining such a joint effort is not always easy, the intellectual rewards can be substantial.
Parker, G., C. Paola, K.X. Whipple, and D. Mohrig, Alluvial fans formed by channelized fluvial and sheet flow. I: Theory, Journal of Hydraulic Engineering-Asce, 124 (10), 985-995, 1998.
Alluvial fans and fan-deltas are of three basic types: those built up primarily by the action of constantly avulsing river and stream channels, those constructed by sheet flows, and those resulting from the successive deposition of debris flows. The present analysis is directed toward the first two types. A mechanistic formulation of flow and sediment transport through river channels is combined with a simple quantification of the overall effect of frequent avulsion to derive relations describing the temporal and spatial evolution of mean (i.e., averaged over many avulsions) bed slope and elevation in an axially symmetric fan. An example of a fan formed predominantly by the deposition of sand is compared to a similar one formed predominantly by the deposition of gravel. In each example the case of channelized flow is compared to the case of sheet flow. The model is applied to the tailings basin of a mine in the companion paper.
Parker, G., and Y.T. Cui, The arrested gravel front: stable gravel-sand transitions in rivers - Part 1: Simplified analytical solution, Journal of Hydraulic Research, 36 (1), 75-100, 1998.
Most rivers exhibit a tendency for the characteristic size of the bed material to become finer in the downstream direction. In addition, most river sediments also exhibit a paucity of material in the pea gravel range. Because of this paucity the transition in the downstream direction from a gravel-bed stream to a sand-bed stream is usually rather abrupt, and is often marked by a discontinuity in bed slope and stream morphology as well. If the front marking the gravel-sand transition is not to prograde continuously in the direction of the point at which base level is established, e.g. the ocean, then some mechanism must operate to arrest it in place. Here two such mechanisms are examined; abrasion of gravel and basin subsidence (or alternatively base level rise). It is found that either one or a combination of the two can act to stabilize the spatial location of the gravel-sand transition. The present paper is devoted to a simplified analytical solution to the problem that renders the structure of the formulation relatively transparent. A complete numerical solution that more realistically describes the field manifestation is presented in a companion paper.
Parker, G., and N. Izumi, Purely erosional cyclic and solitary steps created by flow over a cohesive bed, Journal of Fluid Mechanics, 419, 203-238, 2000.
An erodible surface exposed to supercritical flow often devolves into a series of steps that migrate slowly upstream. Each step delineates a headcut with an associated hydraulic jump. These steps can form in a bed of cohesive material which, once eroded, is carried downstream as washload without redeposition. Here the case of purely erosional, one- dimensional periodic, or cyclic steps in cohesive material is considered. The St. Venant shallow-water equations combined with a formulation for sediment erosion are used to construct a complete theory of the erosional case. The solution allows wavelength, wave height, migration speed and bed and water surface profiles to be determined as functions of imposed parameters. The analysis also admits a solution for a solitary step, or single headcut of self-preserving form.
Parker, G., C. Paola, and S. Leclair, Probabilistic Exner sediment continuity equation for mixtures with no active layer, Journal of Hydraulic Engineering-Asce, 126 (11), 818-826, 2000.
The Exner equation of sediment continuity is the foundation of river morphodynamics. Generalization of this equation to mixtures of grain sizes has required the introduction of an active layer (i.e., a buffer layer between the sediment moving in the water column and the immobile substrate below). The active layer is defined to be a well-mixed layer, with no vertical structure, that encompasses those grains available to exchange directly with the moving sediment. The sediment in the substrate below exchanges with the active layer only as the bed aggrades or degrades. The active layer concept is a useful one that has served the research community well for 3 decades. However, the division of the erodible bed into a discrete active layer and substrate must represent only an approximation of a more general formulation that contains no active layer and in which parameters pertaining to the entrainment from and deposition to the bed vary continuously with depth below the sediment-water interface. Here the probability density function of bed elevation is used to derive a general Exner equation of sediment continuity with no discrete layers. The formulation is applicable to both sediment mixtures and tracers in uniform sediment. Although the treatment requires more information than that of the active layer approach, it offers the prospect of a better understanding of how streams create a stratigraphic record of their activities through deposition.
Parsons, A.J., and S.G.L. Stromberg, Experimental analysis of size and distance of travel of unconstrained particles in interrill flow, Water Resources Research, 34 (9), 2377-2381, 1998.
Passmore, D.G., and M.G. Macklin, Late Holocene channel and floodplain development in a wandering gravel-bed river: The River South Tyne at Lambley, northern England, Earth Surface Processes and Landforms, 25 (11), 1237-1256, 2000.
Geomorphological analyses of the morphology, lithostratigraphy and chronology of Holocene alluvial fills in a 2.75 km long piedmont reach of the wandering gravel-bed River South Tyne at Lambley in Northumberland, northern England, have identified spatial and temporal patterns of late Holocene channel and floodplain development and elucidated the relationship between reach- and subreach-scale channel transformation and terrace formation. Five terraced alluvial fills have been dated to periods sometime between c. 1400 BC-AD 1100, AD 1100-1300, AD 1300-1700, AD 1700-1850 and from AD 1850 to the present. Palaeochannel morphology and lithofacies architecture of alluvial deposits indicate that the past 3000 years has been characterized by episodic channel and floodplain change associated with development and subsequent recovery of subreach-scale zones of instability which have been fixed in neither time nor space. Cartographic and photographic evidence spanning the past 130 years suggests channel transformation can be accomplished in as little as 50 years. The localized and episodic nature of fluvial adjustment at Lambley points to the operation of subreach-scale controls of coarse sediment transfers. These include downstream propagation of sediment waves, as well as internal controls imposed by differing valley floor morphology, gradient and boundary materials. However, the preservation of correlated terrace levels indicates that major phases of floodplain construction and entrenchment have been superimposed over locally complex patterns of sediment transfer. Reach-scale lateral and vertical channel adjustments at Lambley appear to be closely related to climatically driven changes in flood frequency and magnitude, with clusters of extreme floods being particularly important for accomplishing entrenchment and reconfiguring the pattern of localized instability zones. Confinement of flood flows by valley entrenchment, and contamination of catchment river courses by metal-rich fine sediments following recent historic mining operations, have combined to render the South Tyne at Lambley increasingly sensitive to changes in flood regimes over the past 1000 years. Copyright (C) 2000 John Wiley & Sons, Ltd.
Patel, P.L., and K.G.R. Raju, Fractionwise calculation of bed load transport, Journal of Hydraulic Research, 34 (3), 363-379, 1996.
Patel, P.L., and K.G.R. Raju, Critical tractive stress of nonuniform sediments, Journal of Hydraulic Research, 37 (1), 39-58, 1999.
Patten, D.T., Riparian ecosystems of semi-arid North America: Diversity and human impacts, Wetlands, 18 (4), 498-512, 1998.
Patton, T.M., and W.A. Hubert, Reservoirs On a Great-Plains Stream Affect Downstream Habitat and Fish Assemblages, Journal of Freshwater Ecology, 8 (4), 279-286, 1993.
Payne, B.A., and M.F. Lapointe, Channel morphology and lateral stability: effects on distribution of spawning and rearing habitat for Atlantic salmon in a wandering cobble-bed river, Canadian Journal of Fisheries and Aquatic Sciences, 54 (11), 2627-2636, 1997.
Peakall, J., B. McCaffrey, and B. Kneller, A process model for the evolution, morphology, and architecture of sinuous submarine channels, Journal of Sedimentary Research, 70 (3), 434-448, 2000.
Although analogies have been drawn between some types of meandering rivers and medium- to high-sinuosity, aggradational, leveed submarine channels, a number of different or additional processes operate in submarine channels. Analysis of several individual submarine channels suggests that they undergo much slower bend growth than alluvial rivers and may reach a planform equilibrium, in contrast to meandering rivers, in which bends progressively migrate downstream. Sinuous leveed submarine channels should therefore aggrade to produce isolated ribbons of thalweg deposits (of predictable 3D geometry), in contrast to the stacked channel belts characteristic of most alluvial meandering rivers. A simple model of the flow structure and flow evolution of turbidity currents traversing submarine channels is proposed, based on theoretical, experimental, and field-derived concepts. It predicts that submarine channel hows are highly stratified, have significant supra-levee thicknesses, and form broad overbank bodies of low- concentration fluid moling along the entire channel length. The interaction between the broad body of overbank fluid and within-channel how is controlled by the processes of tolling and angular shear, whose possible effects on channel sedimentation and planform stability are explored.
Pelletier, B., J.W. Fyles, and P. Dutilleul, Tree species control and spatial structure of forest floor properties in a mixed-species stand, Ecoscience, 6 (1), 79-91, 1999.
The influence of tree species on forest floor properties (total N, P, K, Ca, and Mg, extractable K, Ca, and Mg, pH, basal respiration, potentially-mineralizable N, horizon thickness, bulk density, and loss on ignition) of microsites of a mixed- species stand was examined using a variation-paritioning method and redundancy analysis (RDA). The influence of eastern hemlock (Tsuga canadensis), American beech (Fagus grandifolia), red maple (Acer rubrum), striped maple (Acer pensylvanicum), red oak (Quercus rubra), paper birch (Betula papyrifera), yellow birch (Betula alleghaniensis), and uncommon species was expressed with a tree species influence index (TSII) based on the size of the individual trees of each species and their distance from a microsite. Maps and Mantel correlograms were used to describe and quantify the spatial structure of forest floor and TSII variables. Trend surface analysis (TSA) and a neighbourhood matrix (NM), based on the mean values of forest floor properties at neighbouring microsites, were used to incorporate a spatial component in the partitioning of the forest floor variation. TSII explained 29.6% of the forest floor variation of which about half was spatially structured and jointly expressed by the trend surface polynomial and the NM. The NM proved to be more efficient in capturing small-scale spatial patterns than the TSA. The main ecological trends observed for both the local and the total TSII effect were the influence of the beech-hemlock gradient on calcium, and the differential effect of striped maple and red maple on the amount of organic matter and associated nutrients. The relevance of the incorporation of a spatial component in the variation-partitioning of forest floor data and the potential of this technique to deal with the complexity of natural mixed- forests are verified and discussed.
Pelletier, J.D., Self-organization and scaling relationships of evolving river networks, Journal of Geophysical Research-Solid Earth, 104 (B4), 7359-7375, 1999.
The power spectra S of linear transects of Earth's topography is often observed to be a power law function of wave number k with exponent close to -2: S(k) proportional to k(-2). In addition, river networks are fractal trees that satisfy several power law relationships between their morphologic components. A model equation for the evolution of Earth's topography by transport-limited erosional processes which produces fractal topography and fractal river networks is presented, and its solutions are compared in detail to real topography. The model is the diffusion equation for sediment transport on hillslopes and channels with the diffusivity constant on hillslopes and proportional to the three-halves power of discharge in channels. The dependence of diffusivity on discharge is consistent with sediment rating curves. We study the model in two ways. In the first analysis the diffusivity is parameterized as a function of elevation, and a Taylor expansion procedure is carried out to obtain a differential equation for the landform elevation which includes the spatially variable diffusivity to first order in the elevation. The solution to this equation is a self-affine or fractal surface with linear transects that have power spectra S(k) proportional to k(-1.8), independent of the age of the topography, consistent with observations of real topography. The hypsometry produced by the model equation is skewed such that lowlands make up a larger fraction of the total area than highlands as observed in real topography. In the second analysis we include fiver networks explicitly in a numerical simulation by calculating the discharge at every point. We characterize the morphology of real river basins with five independent scaling relations between six morphometric variables. Scaling exponents are calculated for seven river networks from a variety of tectonic environments using high- quality digital elevation models. River networks formed in the model match the observed scaling laws and satisfy Tokunaga side-branching statistics.
Pender, G., and Q. Li, Numerical prediction of graded sediment transport, Proceedings of the Institution of Civil Engineers-Water Maritime and Energy, 118 (4), 237-245, 1996.
This paper reports on the development and testing of a comprehensive unsteady how, non-equilibrium, graded sediment transport mobile bed model for predicting river channel changes in response to engineering intervention. The theoretical background of the model is discussed and results indicating the model's performance in predicting graded sediment transport for hypothetical and flume data are presented. The hypothetical data is a slot infilling test adopted as a benchmark by other workers, whereas the flume data provides the opportunity to compare model performance with detailed measurements of bed load transport rate and size fraction mobility. Conclusions are drawn regarding the applicability of the model and the suitability of hiding functions based on statistical regression for simulating short time scale variation in observed sediment transport rate.
Pender, G., T.B. Hoey, C. Fuller, and I.K. McEwan, Selective bedload transport during the degradation of a well sorted graded sediment bed, Journal of Hydraulic Research, 39 (3), 269-277, 2001.
The paper presents an analysis of the composition of bedload transport and changes to bed structure and topography during three graded sediment degradation experiments. The analysis suggests that variations in channel hydraulics and active layer composition alone may not explain the observed reductions in sediment transport. Further, the experiments appear to cover a crucial range of mean bed shear stresses for armouring studies, ranging between a condition of passive winnowing, to one of more active armour development in which the coarse grains play a role in determining bed structure. This indicates that the active layer concept, commonly applied in computer models of graded sediment transport, may be Limited in its application.
Perrusquia, G.S., An Experimental-Study On the Transport of Sediment in Sewer Pipes With a Permanent Deposit, Water Science and Technology, 25 (8), 115-122, 1992.
An experimental study of the transport of sediment in a part- full pipe was carried out in a concrete pipe. The experiments were confined to bedload transport. The purpose of this study was to analyze the flow conditions that characterize the stream traction in pipe channels and their relationship to flow resistance and sediment transport rate. Three procedures used in this kind of experimental study were tested and found valid: 1) the vertical velocity distribution near the sediment bed can be described by the velocity-defect law, 2) the side wall elimination procedure can be used to compute the hydraulic radius of the sediment bed, and 3) the critical shear stress of the sediment particles can be obtained by using Shields' diagram. A relationship to estimate bedload transport, based on dimensional analysis, was proposed. This was expressed in terms of both flow and particle parameters as well as geometric factors. Further experimental work is recommended before this relationship can be fully incorporated in a simulation model for the analysis of storm sewers.
Pethick, J.S., and S. Crooks, Development of a coastal vulnerability index: a geomorphological perspective, Environmental Conservation, 27 (4), 359-367, 2000.
Petit, F., Dimensionless Critical Shear-Stress Evaluation From Flume Experiments Using Different Gravel Beds, Earth Surface Processes and Landforms, 19 (6), 565-576, 1994.
Petit, F., D. Poinsart, and J.P. Bravard, Channel incision, gravel mining and bedload transport in the Rhone river upstream of Lyon, France (''canal de Miribel''), Catena, 26 (3-4), 209-226, 1996.
Petrie, J., and P. Diplas, Statistical approach to sediment sampling accuracy, Water Resources Research, 36 (2), 597-605, 2000.
Petts, G.E., and M.C. Thoms, Morphology and Sedimentology of a Tributary Confluence Bar in a Regulated River - North Tyne, Uk, Earth Surface Processes and Landforms, 12 (4), 433-440, 1987.
Petts, G.E., A.M. Gurnell, A.J. Gerrard, D.M. Hannah, B. Hansford, I. Morrissey, P.J. Edwards, J. Kollmann, J.V. Ward, K. Tockner, and B.P.G. Smith, Longitudinal variations in exposed riverine sediments: a context for the ecology of the Fiume Tagliamento, Italy, Aquatic Conservation-Marine and Freshwater Ecosystems, 10 (4), 249-266, 2000.
Phillips, B.C., and A.J. Sutherland, Diffusion-Models Applied to Channel Degradation, Journal of Hydraulic Research, 24 (3), 179-191, 1986.
Phillips, B.C., and A.J. Sutherland, Spatial Lag Effects in Bed-Load Sediment Transport, Journal of Hydraulic Research, 27 (1), 115-133, 1989.
Phillips, J.D., Self-Organization and Landscape Evolution, Progress in Physical Geography, 19 (3), 309-321, 1995.
Self-organization is common in earth surface systems, and related principles have been proposed as general principles applicable to geomorphic systems. Non-self-organizing behaviour is also observed in geomorphic systems, however. If a reasonable box-and-arrow diagram and associated qualitative interaction matrix can be devised for a geomorphic system, one can determine whether or not (or under what conditions) the system is self-organizing, Both self-organizing (at-a-station hydraulic geometry) and non-self-organizing (soil landscape evolution) geomorphic systems are illustrated. The development of topographic relief demonstrates the principle that landscape evolution may be characterized by both modes at different times or under different circumstances. Increasing relief, involving a mean divergence of elevations, may be self-organizing. Topographic development by decreasing relief, where elevations generally converge, is always non-self-organizing Self- organization in geomorphology may be similar to steady-state equilibrium, in that its explanatory value lies not in general applicability, but in distinguishing between fundamentally different modes of landscape development.
Phillips, J.D., Divergence, convergence, and self-organization in landscapes, Annals of the Association of American Geographers, 89 (3), 466-488, 1999.
sMany theories, old and new, of landscape and earth-surface system development involve concepts of self-organization. There are at least eleven distinct definitions of self-organization in the literature that are relevant to landscapes. Some have profoundly different implications with respect to the nature and trajectories of landscape evolution and earth-surface system behavior, including whether evolution is convergent or divergent, whether entropy or energy dissipation is maximized or minimized, the role of chaos, and the mechanisms by which self-organized patterns are generated. Despite these differences, most self-organization concepts can be broadly aggregated into two categories: those concerned with the evolution of order and regularity in the aggregate or ensemble properties of the landscape, and those concerned with the differentiation of landscapes into more diverse spatial units. This paper presents a theory of spatially divergent self- organization related to the latter, showing that autogenic differentiation is directly linked to dynamical instability and chaos. The determination of the self-organization properties of a landscape should be a starting point rather than a goal of geographic explanation. The extent to which field-testable hypotheses are generated, or explanations provided based on process mechanics or landscape history, will ultimately determine the utility of self-organization concepts and methods in physical geography.
Phillips, J.D., P.A. Gares, and M.C. Slattery, Agricultural soil redistribution and landscape complexity, Landscape Ecology, 14 (2), 197-211, 1999.
A number of hypotheses and conceptual models, particularly those emphasizing nonlinear dynamics and self-organization, postulate increases or decreases in complexity in the evolution of drainage basins, topography, soils, ecosystems, and other earth surface systems. Accordingly, it is important to determine under what circumstances and at what scales either trend might occur. This paper is concerned with changes in soil landscape complexity due to redistribution of sediment by fluvial, aeolian, and tillage processes at historical time scales in an agricultural field system near Grifton, North Carolina. Soil mapping and soil stratigraphic investigations were used to identify and map soil changes associated with erosion and deposition by water, wind, and tillage; reconstruct the pre-agricultural soil pattern; and identify transformations between soil types. The Kolmogorov entropy of the pre- and post-agricultural landscapes was then compared. The soil transformations associated with erosion and deposition coated four distinct new soils and made possible new transformations among soil series, increasing the number of soil types from seven to 11 and the number of possible transformations from 14 to 22. However, the entropy and complexity of the soil landscape decreased, with associated increases in information and redundancy. The mass redistributions created a lower- entropy landscape by concentrating particular soils and soil transformations in specific landscape settings. This result is contrary to studies showing a trend toward increasing pedological complexity at comparable spatial scales, but over much longer time scales. These results point to the importance of temporal scale, and to the fact that environmental complexity is influenced by factors other than the number of different landscape units present.
Phillips, J.D., Signatures of divergence and self-organization in soils and weathering profiles, Journal of Geology, 108 (1), 91-102, 2000.
Complex system behaviors such as self-organization are difficult to address in geology. System evolution often cannot be directly observed and, in geology models and theory, must be reconciled with field evidence. However, self-organization can be addressed within the historical-interpretive paradigm by applying a measure of the degree of self-organization of geologic features, using standard interpretive methods to determine the nature of changes, and determining whether those changes result in an increase or decrease in organization. In this way, stable non-self-organizing convergent development can be distinguished from unstable chaotic self-organizing divergent development. Kolmogorov entropy (K-entropy) was used as a measure of the self-organization of soil profiles in eastern North Carolina. In general, the profiles are low in K- entropy, indicating a generally high level of predictability and information in the vertical arrangement of pedogenetic horizons. As a broad generality, the study profiles appear to be decreasing in entropy if or when surface erosion is minimal and increasing in entropy otherwise. However, results show that whether the profiles demonstrate evidence of convergent or divergent behavior is deter-mined by the relative rates or magnitudes of three main processes: (1) horizon differentiation in surficial horizons by the formation of transitional AE or A&E horizons due to secondary podzolization, (2) thickening of the solum at the weathering front, and (3) surface erosion. There is no direct relationship between the degree of pedogenic development and self-organization. The results suggest that complex system behaviors are controlled by, and can be linked to, specific pedologic and geomorphic processes and that soils and regoliths may be characterized by both convergent and divergent developmental pathways.
Pickup, G., and V.H. Chewings, Random Field Modeling of Spatial Variations in Erosion and Deposition in Flat Alluvial Landscapes in Arid Central Australia, Ecological Modelling, 33 (2-4), 269-296, 1986.
Pickup, G., and V.H. Chewings, Forecasting Patterns of Soil-Erosion in Arid Lands From Landsat Mss Data, International Journal of Remote Sensing, 9 (1), 69-84, 1988.
Piegay, H., A. Thevenet, G.M. Kondolf, and N. Landon, Physical and human factors influencing potential fish habitat distribution along a Mountain River, France, Geografiska Annaler Series a-Physical Geography, 82A (1), 121-136, 2000.
Potential fish habitat along the Drome River, France, is a function of the distribution of large woody debris, boulders, undercut banks, gravel substrate, and pools. The distribution of these features is, in turn, a function or channel geomorphology, watershed and riparian forest characteristics. We conducted field work;Ind analysed aerial photographs for 190 elementary segments of 500 m length along the Drome River's 95 km course from the Alps westward to its confluence with the Rhone River near Loriol. The Drome River dues not follow the classic pattern of a monotone downstream decrease in gradient and change in channel characteristics. Although channel gradient, braided index and channel incision all decrease downstream, stream power is independent of longitudinal distance. These variables are largely controlled by geomorphic, human or hydrologic factors at the reach scale. Potential fish habit;lr richness decreases downstream bur individual habitat variables affecting habitat richness do not necessarily decrease downstream, many being controlled by local factors rather than by position along the continuum. Large woody debris is more abundant in braided reaches located directly downstream of confluences with main tributaries or downstream input sites, Boulders are most abundant downstream of failed bank protection works or in gorges. To improve fish habitat in the Drome River, rye recommend taking a longterm and large-scale perspective. Because structures placed in this unstable channel are likely to be washed downstream we propose to emulate natural river dynamics and to permit large woody debris to enter the channel in unstable reaches via bank erosion, and that this debris not be removed (as is routinely done now) but permitted to migrate downstream through the system, creating fish habitat en route.
Pinca, S., and M.E. Huntley, Spatial organization of particle size composition in an eddy- jet system off California, Deep-Sea Research Part I-Oceanographic Research Papers, 47 (6), 973-996, 2000.
We describe here the results of an interdisciplinary study conducted off the coast of northern and central California during September 1993 in which we deployed an Optical Plankton Counter. This instrument counted and measured particles in the size range between 0.27 and 9.8 mm equivalent spheric diameter (ESD) occurring between the surface and 240 m depth. The survey region was characterized by the presence of the California Current jet and a cyclonic and an anticyclonic eddy. We analyzed the spatial (horizontal and vertical) distribution of planktonic particles and their relation to this hydrodynamic structure. We used specific analytical methods that take into account spatial constraints, i.e. autocorrelation analysis, constrained agglomerative clustering and contiguity constraints permutation analysis of variance. Horizontal spatial organization of particles was revealed at three different spatial scales (5, 18 and 100 km), while vertical patterns were described at a much smaller scale (20 m). We could detect some degree of similarity between particle size category spatial organization and hydrodynamic structure both by size category association independent of current movements and by comparison of dynamically differentiated areas. Five groups of similar size composition were detected that had some relation to the dynamic structure. Four sub-regions were determined a priori by their different hydrodynamic heights. We could describe a variability of particle abundance among these regions, both for total particles and for some size categories. Particles were more abundant inside the cyclonic eddy and less abundant inside the anticyclonic eddy. We also found deep concentration maxima inside the anticyclonic eddy and shallower concentration maxima inside the cyclonic eddy, with particles > 2 mm ESD at deeper levels, for both daytime and nighttime sampling. No systematic difference was detected between daytime and nighttime samples in 0-240 m integrated total particle abundance. However, at night particles appeared to be concentrated into three depth strata (10-50, 70-90 and 90-230 m) of different size-abundance composition, while during the day particles were distributed into one shallow (10-50 m) and one deeper stratum (70-240 m). Smaller particles always occupied the most shallow depths (C) 2000 Elsevier Science Ltd. All rights reserved.
Pinell-Alloul, B., C. Guay, N. Angeli, P. Legendre, P. Dutilleul, G. Balvay, D. Gerdeaux, and J. Guillard, Large-scale spatial heterogeneity of macrozooplankton in Lake of Geneva, Canadian Journal of Fisheries and Aquatic Sciences, 56 (8), 1437-1451, 1999.
Spatial distribution of macrozooplankton was studied during spring in Lake of Geneva to evaluate the influence of abiotic (water temperature and stability, nutrients) and biotic (bacteria, chlorophyll a, fish biomass) factors on macrozooplankton distribution. Mapping and spatial analyses revealed that abiotic factors, as well as crustacean abundances, were structured along a gradient in the great lake basin. Chlorophyll a biomass, bacteria density, cyclopoid abundance, and fish biomass showed more patchy or inshore- offshore distribution patterns. Using canonical analyses, we determined the relative contribution of the spatial and environmental factors to the distribution of macrozooplankton species and of trophic groups based on herbivory and omnivory/carnivory. The distribution of macrozooplankton can be explained by small-scale variations and lake gradients in abiotic and biotic factors, with a dominant contribution of the abiotic factors. Water temperature and stability, as well as ammonium, are the main factors related to macrozooplankton distribution in Lake of Geneva during spring. Chlorophyll a biomass was also related to the distribution of cyclopoids. The canonical models explained 35-72% of the variance in the distribution of total crustaceans, species, and trophic groups. However, 28-65% of the macrozooplankton variance remained unexplained, which may be due to fine-scale variations in other environmental factors.
Pitlick, J., Variability of Bed-Load Measurement, Water Resources Research, 24 (1), 173-177, 1988.
Pitlick, J., Flow Resistance Under Conditions of Intense Gravel Transport, Water Resources Research, 28 (3), 891-903, 1992.
A study of flow resistance was undertaken in a channelized reach of the North Fork Toutle River, downstream of Mount St. Helens, Washington. Hydraulic and sediment transport data were collected in flows with velocities up to 3 m/s and shear stresses up to 7 times the critical value needed for bed load transport. Details of the flow structure as revealed in vertical velocity profiles indicate that weak bed load transport over a plane gravel bed has little effect on flow resistance. The plane gravel bed persists up to stresses approximately 3 times critical, at which point, irregular bed forms appear. Bed forms greatly increase flow resistance and cause velocity profiles to become distorted. The latter arises as an effect of flows becoming depth-limited as bed form amplitude increases. At very high rates of bed load transport, an upper stage plane bed appeared. Velocity profiles measured in these flows match the law of the wall closely, with the equivalent roughness being well represented by k(s) = 3D84 of the bed load. The effects noted here will be important in very large floods or in rivers that are not free to widen, such as those cut into bedrock.
Pitlick, J., Response and Recovery of a Sub-Alpine Stream Following a Catastrophic Flood, Geological Society of America Bulletin, 105 (5), 657-670, 1993.
The July 15, 1982, Lawn Lake flood in Rocky Mountain National Park, Colorado, was caused by the failure of a 79-yr-old earthen dam. Peak discharges of the flood far exceeded naturally occurring flows, and it caused severe channel disturbance along most of Roaring River and some parts of Fall River. This study documents the geomorphic response of a 5-km reach of Fall River in the 5 yr following the flood. In 1983, the first year after the Lawn Lake flood, snowmelt flows were well above average. These high flows together with very high sediment yields from Roaring River resulted in significant geomorphic changes on reaches of Fall River downstream. During the 1983 snowmelt runoff, approximately 15.5 X 10(6) kg of bed- load sediment was eroded from the upper part of the study area. These loads were at least 1,000 times higher than before the Lawn Lake flood. Most of this sediment was then deposited in a highly sinuous reach of Fall River in the lower part of the study area. This reach had not been much affected by the Lawn Lake flood, but sedimentation during the period of high flow in 1983 completely filled in the channel, resulting in the formation of a continuous 2.3-km-long depositional zone. In 1984, sediment yield from Roaring River declined dramatically, and this trend continued for the next 3 yr. By 1987, the bed- load sediment yield in the upper reaches of Fall River was only about 0.4 X 10(6) kg/yr. The decline in sediment loads resulted in progressive erosion and recovery of the original channel of Fall River in the depositional zone reach. Recovery in the upstream part of the depositional zone was complete by 1985. Recovery in the downstream part of the depositional zone took longer because of the continued supply of sediment and because the sediment was mobile less of the time. As of 1987, about 80% of the material initially stored in the sedimentation zone had been eroded. Bed-load sediment yields at a sampling site 1 km downstream of the terminus of the depositional zone ranged from 5 X 10(6) to 11 X 10(6) kg/yr, but showed no significant decline over the 5-yr study period. The average rate of bed- load transport through this reach was at least 100 times greater than before the Lawn Lake flood, but few discernible channel changes resulted from the higher loads.
Pitlick, J., and M.M. Van Steeter, Geomorphology and endangered fish habitats of the upper Colorado River 2. Linking sediment transport to habitat maintenance, Water Resources Research, 34 (2), 303-316, 1998.
Pitsch, H., Grain size distribution: A quality characteristic of bulk material, American Laboratory, 33 (17), 48-+, 2001.
Pizzuto, J.E., Numerical-Simulation of Gravel River Widening, Water Resources Research, 26 (9), 1971-1980, 1990.
Pizzuto, J.E., Downstream Lining in a Network of Gravel-Bedded Rivers, Water Resources Research, 31 (3), 753-759, 1995.
A network-based routing model is used to determine how spatial variations in sediment supply influence rates of downstream fining in a small watershed in central Pennsylvania. Gravel of a specified size distribution and lithology is supplied to the network at zero-order basins. Once in transport, the total sample weight and moments of the grain-size distribution are modified according to empirical functions of transport distance. Contributions from each zero-order basin are summed to determine the total population of sizes and lithologies at any location. In the study area, resistant quartz sandstone ridges supply sediment an order of magnitude larger than other lithologies. Because these ridges occur primarily in the basin headwaters, spatial variations in supply strongly influence rates of downstream fining. Model calculations indicate that spatial variations in supply alone account for over 80% of the decrease in mean grain size along the main channel.
Pizzuto, J.E., W.C. Hession, and M. McBride, Comparing gravel-bed rivers in paired urban and rural catchments of southeastern Pennsylvania, Geology, 28 (1), 79-82, 2000.
Surveys in eight paired urban and rural watersheds illustrate how urbanization changes fluvial morphology and processes. Our data also provide quantitative criteria for evaluating stream- restoration projects in urban areas. Bankfull depth, reach- averaged bed slope, and median grain size are similar in urban and rural watersheds. The median width of urban channels is 26% larger than the median width of rural channels. The median sinuosity is 8% lower in urban channels and pools are 31% shallower, The median composite Manning's n based on median grain diameter, pool depth, and channel sinuosity is 10% lower in urban streams, while the median bankfull discharge per unit drainage basin area is 131% higher in urban channels. Histograms of bed sediment-size distributions in urban channels lack a secondary mode in the size range 2-64 mm characteristic of rural channels, indicating that these sizes tend to be selectively removed from urban channels. However, bankfull Shields stresses in urban and rural channels exceed typical threshold values at most sites, indicating significant bedload transport at bankfull stage. Apparently, increased peak discharges caused by decades of urbanization have not removed all the transportable sediment from these urban stream channels. We speculate that the supply of sediment to urban channels from hillslope processes and channel erosion remains significant, even though much of the upland surfaces of these urban catchments are covered with nonerodible impervious surfaces.
Poesen, J.W.A., and J.M. Hooke, Erosion, flooding and channel management in Mediterranean environments of southern Europe, Progress in Physical Geography, 21 (2), 157-199, 1997.
Pohl, M.M., Radiocarbon Ages On Organics From Piedmont Alluvium, Ajo Mountains, Arizona, Physical Geography, 16 (4), 339-353, 1995.
Porto, P., and J. Gessler, Ultimate bed slope in calabrian streams upstream of check dams: Field study, Journal of Hydraulic Engineering-Asce, 125 (12), 1231-1242, 1999.
Powell, D.M., and P.J. Ashworth, Spatial Pattern of Flow Competence and Bed-Load Transport in a Divided Gravel-Bed River, Water Resources Research, 31 (3), 741-752, 1995.
Powell, D.M., Patterns and processes of sediment sorting in gravel-bed rivers, Progress in Physical Geography, 22 (1), 1-32, 1998.
Sedimentological studies of coarse-grained alluvial rivers reveal patterns of bed material sorting at a variety of spatial scales ranging from downstream fining over the length of the long profile to the vertical segregation of a coarse surface layer at the scale of individual particles. This article reviews the mechanisms that sort bed material by size during sediment entrainment, transport and deposition and discusses some of the inter-relationships that exist between patterns and processes of sediment sorting at different spatial and temporal scales. At initiation of motion, sorting can arise from the preferential entrainment of the finer fractions from the heterogeneous bed sediments. Bedload grain-size distributions are modified during transport as different size fractions are routed along different transport pathways under the influence of nonuniform bed topography and associated flow patterns, and during deposition as the variable pocket geometry of the rough bed surface and turbulence intensity of the flow control the size of the particles that deposit. The review highlights the poor understanding of the many feedback linkages that exist between patterns and processes of sediment sorting at different scales and the need for a greater awareness of the spatial and temporal bounds of these linkages.
Powell, D.M., I. Reid, and J.B. Laronne, Hydraulic interpretation of cross-stream variations in bed-load transport, Journal of Hydraulic Engineering-Asce, 125 (12), 1243-1252, 1999.
Powell, D.M., I. Reid, and J.B. Laronne, Evolution of bed load grain size distribution with increasing flow strength and the effect of flow duration on the caliber of bed load sediment yield in ephemeral gravel bed rivers, Water Resources Research, 37 (5), 1463-1474, 2001.
Power, M.E., Habitat Heterogeneity and the Functional-Significance of Fish in River Food Webs, Ecology, 73 (5), 1675-1688, 1992.
Predation by fish (roach, Hesperoleucas symmetricus, and steelhead Oncorhynchus mykiss) produced strong cascading effects on biota associated with boulder-bedrock substrates in pools of a northern California river, but not on gravel- dwelling biota. Enclosure-exclosure experiments in the South Fork Eel River of northern California (39-degrees 44' N, 123- degrees 39' W) showed that fish, by suppressing densities of damselfly nymphs and other small predators, released algivorous chironomids (Pseudochironomus richardsoni) from predation. Chironomids in tum dramatically reduced algal standing crops. In contrast, fish had little effect on algae or invertebrates associated with gravel. Gravel-dwelling heptageniid mayflies were behaviorally inhibited from using tops of stones in fish enclosures, and stone surfaces had more chironomid tubes in fish enclosures than in fish exclosures. However, no effects on epilithic algae or densities of invertebrates comparable to those of biota on boulder-bedrock substrates were detected. These spatially varying predator effects in a river parallel results from marine benthic systems, where strong effects of large predators documented for rocky intertidal habitats and unvegetated soft bottoms are not conspicuous in seagrass beds.
Prager, E.J., J.B. Southard, and E.R. VivoniGallart, Experiments on the entrainment threshold of well-sorted and poorly sorted carbonate sands, Sedimentology, 43 (1), 33-40, 1996.
Pratson, L.F., J. Imran, E.W.H. Hutton, G. Parker, and J.P.M. Syvitski, BANG1D: a one-dimensional, Lagrangian model of subaqueous turbid surges, Computers & Geosciences, 27 (6), 701-716, 2001.
Prestegaard, K.L., Progress in Understanding Fluvial Processes, Journal of Geological Education, 32 (4), 254-260, 1984.
Prosser, I.P., A.O. Hughes, and I.D. Rutherfurd, Bank erosion of an incised upland channel by subaerial processes: Tasmania, Australia, Earth Surface Processes and Landforms, 25 (10), 1085-1101, 2000.
The headwaters of many rivers are characterized by gullies and incised streams that generate significant volumes of sediment and degrade downstream water quality. These systems are characterized by harsh climates, ephemeral flows that do not reach bank top, and bare cohesive banks of clay and weathered bedrock. We investigated the rates and processes of bank erosion in an incised canal that has such characteristics. Detailed measurements of bank position were made over two years with a purpose-built groundprofiler and photo-electronic erosion pins (PEEPs). Stage height and turbidity were also monitored. The bare banks eroded at 13 +/- 2 mm a(-1). Erosion is controlled by subaerial processes that loosen bank material. Observations show that needle-ice growth is important in winter and desiccation of clays predominates in summer. Flows are unable to erode firm cohesive clays from the banks, and erosion is generally limited by the availability of loosened material. This produces strong hysteresis in turbidity during events. Peak turbidity is related to the number of days with low flow between events, and not peak stage. Rehabilitation with a moderate cover of grass is able to prevent bank erosion by limiting the subaerial erosion processes. Projections of current erosion suggest that without vegetation cover the banks are unlikely to stabilize for many years. Copyright (C) 2000 John Wiley & Sons, Ltd.
Prosser, I.P., I.D. Rutherfurd, J.M. Olley, W.J. Young, P.J. Wallbrink, and C.J. Moran, Large-scale patterns of erosion and sediment transport in river networks, with examples from Australia (vol 52, pg 91, 2001), Marine and Freshwater Research, 52 (5), 817-U20, 2001.
This paper examines the patterns of sediment transport in rivers in terms of the sources of sediment and its transport and deposition through the river network. The analysis is in the context of dramatic human influences on river sediment transport and how they might influence freshwater ecosystems. The review of Australian work shows that erosion of hillslopes and stream banks has greatly increased in historical times, supplying vast quantities of sediment to rivers, much of which is still stored within the river system. The stored sediment will continue to effect in-stream and estuarine ecosystems for many decades. In most Australian catchments the dominant source of sediment is streambank erosion. An analysis of historical channel widening suggests that a conceptual framework of relative stream power can explain the diversity of behaviour observed in the numerous case studies. Sediment delivery through catchments is considered first in a generic whole network sense, which emphasizes the crucial role played by riverine deposition in determining catchment sediment budgets. A method is then presented for analysing the diverse spatial patterns of sediment storage in any river network. Finally, the paper considers the temporal changes to channel morphology in response to a human-induced pulse of sediment.
Prosser, I.P., I.D. Rutherfurd, J.M. Olley, W.J. Young, P.J. Wallbrink, and C.J. Moran, Large-scale patterns of erosion and sediment transport in river networks, with examples from Australia, Marine and Freshwater Research, 52 (1), 81-99, 2001.
This paper examines the patterns of sediment transport in rivers in terms of the sources of sediment and its transport and deposition through the river network. The analysis is in the context of dramatic human influences on river sediment transport and how they might influence freshwater ecosystems. The review of Australian work shows that erosion of hillslopes and stream banks has greatly increased in historical times, supplying vast quantities of sediment to rivers, much of which is still stored within the river system. The stored sediment will continue to effect in-stream and estuarine ecosystems for many decades. In most Australian catchments the dominant source of sediment is streambank erosion. An analysis of historical channel widening suggests that a conceptual framework of relative stream power can explain the diversity of behaviour observed in the numerous case studies. Sediment delivery through catchments is considered first in a generic whole network sense, which emphasizes the crucial role played by riverine deposition in determining catchment sediment budgets. A method is then presented for analysing the diverse spatial patterns of sediment storage in any river network. Finally, the paper considers the temporal changes to channel morphology in response to a human-induced pulse of sediment.
Pugh, S.A., and R.G. Congalton, Applying spatial autocorrelation analysis to evaluate error in new England forest-cover-type maps derived from Landsat Thematic Mapper data, Photogrammetric Engineering and Remote Sensing, 67 (5), 613-620, 2001.
A spatial autocorrelation of error analysis was performed to compare the patterns of error in a classified Landsat Thematic Mapper (TM) forest-cover-type image for two forested areas-one public and one private. TM data were classified to generate a derailed forest type map, and intensive ground reference data covering approximately 3600 ha were collected for both study areas. Two difference images were produced by comparing the reference inventory with the classified data, pixel by pixel. The subsequent spatial autocorrelation analysis indicated that concentrated blocks of error rr ere more pronounced in the public lands study area than in the private lands study area, where error was more evenly distributed. The results indicated that systematic sampling is not always suitable for assessing error in TM data.
Radeloff, V.C., T.F. Miller, H.S. He, and D.J. Mladenoff, Periodicity in spatial data and geostatistical models: autocorrelation between patches, Ecography, 23 (1), 81-91, 2000.
Several recent studies in landscape ecology have found periodicity in correlograms or semi-variograms calculated, for instance, from spatial data of soils, forests, or animal populations. Some of the studies interpreted this as an indication of regular or periodic landscape patterns. This interpretation is in disagreement with other studies that doubt whether such analysis is valid. The objective of our study was to explore the relationship between periodicity in landscape patterns and geostatistical models. We were especially interested in the validity of the assumption that periodicity in geostatistical models indicates periodicity in landscape pattern, and whether the former can characterize frequency and magnitude of the latter. We created maps containing various periodic spatial patterns, derived correlograms from these, and examined periodicity in the correlograms. We also created non- regular maps that we suspected would cause periodicity in correlograms. Our results demonstrate that a) Various periodic spatial patterns produce periodicity in correlograms derived from them, b) the distance-lags at which correlograms peak correspond to the average distances between patch centers, c) periodicity is strongest when the diameter of patches is equal to the distance between patch edges, d) periodicity in omni- directional correlograms of complex spatial patterns (such as checkerboards) are combinations of several waves because inter- patch distances differ with direction; multiple directional correlograms can decompose such complexity, and e) periodicity in correlograms can also be caused when the number bf patches in a study site is small. These results highlight that correlograms can be used to detect and describe regular spatial patterns. However, it is crucial to ensure that the assumption of stationarity is not violated, i.e., that the study area contains a sufficiently large number of patches to avoid incorrect conclusions.
Ramamurthy, A.S., S.F. Saghravani, and R. Balachandar, A direct integration method for computation of gradually varied flow profiles, Canadian Journal of Civil Engineering, 27 (6), 1300-1305, 2000.
A simple procedure to compute the length of gradually varied flow profiles is presented. It is based on the direct integration of the dynamic equation for gradually varied flow, which forms the bases for existing methods of computing flow profiles. In these methods, a long reach for which the profile length is needed gets divided into several subsections, to ensure that the hydraulic exponents do not vary very much in the subsections. Since the proposed analytical method does not use the hydraulic exponent in its development, the flow profiles can be computed in one step and one can still get accurate results. The results of the profile computations based on existing methods are compared with the corresponding results of the present method. The results find direct application in hydraulic engineering practice, where flow profile lengths are needed for design purposes.
Rathburn, S.L., and E.E. Wohl, One-dimensional sediment transport modeling of pool recovery along a mountain channel after a reservoir sediment release, Regulated Rivers-Research & Management, 17 (3), 251-273, 2001.
Reheis, M.C., J.L. Slate, C.K. Throckmorton, J.P. McGeehin, A.M. SarnaWojcicki, and L. Dengler, Late quaternary sedimentation on the Leidy Creek fan, Nevada- California: Geomorphic responses to climate change, Basin Research, 8 (3), 279-299, 1996.
Reid, I., L.E. Frostick, and J.T. Layman, The Incidence and Nature of Bedload Transport During Flood Flows in Coarse-Grained Alluvial Channels, Earth Surface Processes and Landforms, 10 (1), 33-44, 1985.
Reid, I., and L.E. Frostick, Dynamics of Bedload Transport in Turkey Brook, a Coarse-Grained Alluvial Channel, Earth Surface Processes and Landforms, 11 (2), 143-155, 1986.
Reid, I., J.B. Laronne, and D.M. Powell, The Nahal Yatir bedload database: Sediment dynamics in a gravel-bed ephemeral stream, Earth Surface Processes and Landforms, 20 (9), 845-857, 1995.
Reid, I., and J.B. Laronne, Bed-Load Sediment Transport in an Ephemeral Stream and a Comparison With Seasonal and Perennial Counterparts (Vol 31, Pg 773, 1995), Water Resources Research, 31 (8), 2125-2125, 1995.
Reid, I., and J.B. Laronne, Bed-Load Sediment Transport in an Ephemeral Stream and a Comparison With Seasonal and Perennial Counterparts, Water Resources Research, 31 (3), 773-781, 1995.
Reid, I., D.M. Powell, and J.B. Laronne, Prediction of bed-load transport by desert flash floods, Journal of Hydraulic Engineering-Asce, 122 (3), 170-173, 1996.
Reid, I., J.B. Laronne, and D.M. Powell, Flash-flood and bedload dynamics of desert gravel-bed streams, Hydrological Processes, 12 (4), 543-557, 1998.
Reinfelds, I., and G. Nanson, Formation of Braided River Floodplains, Waimakariri River, New- Zealand, Sedimentology, 40 (6), 1113-1127, 1993.
Floodplains along the braided gravel-bed Waimakariri River are discontinuous although generally extensive landforms composed predominantly of gravel bars capped with vertically accreted fines. In order of importance, three mechanisms lead to floodplain formation. River bed abandonment by lateral migration of the braid-train initiates the formation of the largest floodplains, which usually occur downstream of tributary fans and valley bedrock spurs. In the headwater reaches, localized river bed aggradation during high magnitude events leads to floodplain formation by producing a surface resistant to erosion by lesser events due to either the coarse nature of the deposit, or by its elevation over the river bed, or both. The least important mechanism initiating floodplain development is localized river or channel incision. A six stage model is proposed for the sequential development of floodplains on the Waimakariri River from: (i) active river bed: (ii) stabilizing bar; (iii) incipient floodplain; (iv) established floodplain; (v) mature floodplain; and to (vi) terrace. Two mechanisms, lateral migration by the braid-train and reactivation of abandoned channels within floodplains, operating separately or in combination, are responsible for floodplain reworking and their relatively young age (< 250 years). Clearly, braided rivers can construct substantial areas of well developed floodplain.
Rennie, C.D., and R.G. Millar, Estimation of gravel-bed river flow resistance - Discussion, Journal of Hydraulic Engineering-Asce, 125 (12), 1317-1319, 1999.
Rennie, C.D., and R.G. Millar, Spatial variability of stream bed scour and fill: a comparison of scour depth in chum salmon (Oncorhynchus keta) redds and adjacent bed, Canadian Journal of Fisheries and Aquatic Sciences, 57 (5), 928-938, 2000.
Rhee, C.W., H.R. Jo, and S.K. Chough, An allostratigraphic approach to a non-marine basin: the north- western part of Cretaceous Kyongsang basin, SE Korea, Sedimentology, 45 (3), 449-472, 1998.
The north-western part of the Cretaceous Kyongsang Basin, south-east Korea, comprises alluvial deposits of conglomerate, gravelly sandstone, sandstone and mudstone which can be grouped into four allomembers bounded by stratigraphic discontinuities. The discontinuities trend NW-SE and are marked by distinct facies transitions, abrupt emplacement of conglomerate and thin but persistent mudstone beds. Sedimentary facies and architectural analyses reveal that each allomember formed a depositional system of fluvial channel networks draining toward the southeast with alluvial fans on the northern margin. Each allomember can be characterized by distinctive architecture of channel-fills, clast composition of conglomerate and sandstone/mudstone ratio, Successive units show an eastward shift in the locus of deposition, suggesting basinward relocations of alluvial systems. Such variations with time and space are interpreted to reflect changes in accommodation space and sediment supply during basin evolution, probably caused by fault movements. This study shows that detailed mapping, combined with architectural analysis, and the establishment of alluvial allostratigraphy can help assess changes in alluvial systems and structural development of the basin.
Rhoads, B.L., Stream Power Terminology, Professional Geographer, 39 (2), 189-195, 1987.
Rhoads, B.L., Mutual Adjustments Between Process and Form in a Desert Mountain Fluvial System, Annals of the Association of American Geographers, 78 (2), 271-287, 1988.
Rhoads, B.L., Hydrologic Characteristics of a Small Desert Mountain Stream - Implications For Short-Term Magnitude and Frequency of Bedload Transport, Journal of Arid Environments, 18 (2), 151-163, 1990.
Rhoads, B.L., and M.R. Welford, Initiation of River Meandering, Progress in Physical Geography, 15 (2), 127-156, 1991.
Rhoads, B.L., Fluvial Geomorphology, Progress in Physical Geography, 16 (4), 456-477, 1992.
Rhoads, B.L., Fluvial Geomorphology, Progress in Physical Geography, 18 (4), 588-608, 1994.
Rice, S., and M. Church, Bed material texture in low order streams on the Queen Charlotte Islands, British Columbia, Earth Surface Processes and Landforms, 21 (1), 1-18, 1996.
Low order channels comprise a large proportion of the links of every drainage basin, and are often at the centre of land management concerns. They exhibit hydrological and geomorphological characteristics atypical of higher order links. This paper examines the nature and causes of variations in the bed material texture of two streams on the Queen Charlotte Islands, British Columbia. The extant, functional exponential model is found to be inadequate for explaining observed changes in grain size parameters with distance downstream. Recurrent disruption of sediment transport by large organic debris jams, and the sporadic contamination of the fluvial sediment population by colluvial inputs, preclude the development of longitudinal structure. Rather, grain size varies erratically over short distances. A stochastic model best describes the observed variations, and should be adopted as an alternative to the exponential model in low order links. Characteristic variances are controlled by the degree of hillslope-channel coupling, and the extent and characteristics of non-alluvial storage mechanisms.
Rice, S., and M. Church, Grain size along two gravel-bed rivers: Statistical variation, spatial pattern and sedimentary links, Earth Surface Processes and Landforms, 23 (4), 345-363, 1998.
A new set of field data facilitates a detailed analysis of variations in bed material grain size within two confluent gravel-bed rivers in northeastern British Columbia, Canada. A preliminary assessment of grain-size variability establishes a basis for examination of the spatial pattern of grain-size change. Standard ANOVA techniques are inappropriate because individual samples have unequal variances and are not normally distributed. Alternative tests for homoscedasticity and comparison of means are therefore utilized. Within-site, between-sample variability is not significant. The grain-size distributions that were obtained at individual sites are therefore representative of the depositional environments that were sampled. In both rivers mean grain size does vary significantly between sites and there is therefore a basis for examining the data for spatial patterns such as downstream fining. Textural variations along the two rivers studied here are complex and show negligible overall fining (in over 100km). This is the consequence of a large number of tributary inputs and non-alluvial sediment sources which an the legacy of Late Pleistocene glaciation. The identification of lateral sources like these is fundamental for understanding textural changes within rivers. The sedimentary link (a channel reach between significant lateral sediment inputs) provides a means of isolating fluvial maturation processes (abrasion and sorting) from contingent lateral inputs. Strong fining trends are apparent in most links and classification of grain-size measurements according to their location within particular links greatly improves the statistical explanation of textural variation. Identification of sedimentary links provides a means of applying models of fluvial fining processes, so isolation of link networks will aid the development of basin-scale models of textural variation. (C) 1998 John Wiley & Sons, Ltd.
Rice, S., Which tributaries disrupt downstream fining along gravel-bed rivers?, Geomorphology, 22 (1), 39-56, 1998.
Tributaries and other lateral sediment sources can have a significant impact on river bed sediment texture and, in turn, on channel form. Sufficiently voluminous or distinct sediment inputs redefine the mainstem grain-size distribution, punctuating downstream maturation and isolating a sequence of discrete sedimentary links. Within these links fining processes usually dominate, such that models of sorting and abrasion, when applied to individual links, provide reasonable predictions of grain-size change. Links represent the fundamental natural unit within which fining models can be tested, developed and applied. Identification of significant lateral sources is therefore important, yet, beyond vague references to relative tributary size, sediment load, and sediment calibre, no criteria exist for the a priori discrimination of such sources. In this paper a procedure for identifying significant lateral (tributary) sources, without the benefit of grain-size information, is outlined. A high- resolution characterisation of bed material texture along two Canadian gravel-bed rivers facilitated classification of all their perennial tributaries as either significant or insignificant. Three absolute tributary basin parameters and their relative counterparts, chosen to reflect the likely controls on tributary significance, are then used to develop a discriminant function which isolates a large proportion of significant tributaries while minimising incorrect classifications. Examination of consistently misclassified (anomalous) tributaries reveals the importance of lateral source spacing and of inconsistencies in the geomorphic history of the contributing basins. In turn, a general tributary categorisation procedure is suggested which includes a logistic regression model for attaching probability statements to individual classifications. The generality of the discriminant and logistic functions cannot be assessed because of the lack of other suitable data sets. (C) 1998 Elsevier Science B.V.
Rice, S., The nature and controls on downstream fining within sedimentary links, Journal of Sedimentary Research, 69 (1), 32-39, 1999.
At scales of 10(0) to 10(2) km, grain size change in gravelly, alluvial systems is characterized by punctuated downstream fining, Significant lateral sediment inputs define a sequence of sedimentary links within which fluvial processes produce fining trends, Using a new set of surface grain-size data, eighteen such links along two Canadian gravel-bed rivers are examined. Negative exponential functions are found to be most appropriate for describing within-link grain size changes. Development of a pragmatic means of predicting grain size is then pursued by searching for a means to relate model diminution coefficients to link attributes, Consideration of lithologically differentiated fining trends indicates that lithology plays an insignificant role in controlling fining rate. Examination of within-link longitudinal profiles indicates a reasonable relation between fining rate and the rate of change of channel slope. The predictive value of this relation is Limited by the regional nature of the data upon which it is based and the relative difficulty of obtaining accurate gradient information. However, as previously noted for alluvial fans (although for different reasons), channel gradient is correlated with link length and a reasonable predictive tool is apparent in a relation between Link length and diminution rate. The validity of the derived relation cannot be tested for want of a suitable data set. Several lines of evidence indicate that abrasion is unimportant as a fining mechanism on these rivers, and it is argued that this may be typical of sedimentary links. Fining rate must then be a function of the efficiency with which sorting processes operate, and it is suggested that this efficiency is dependent on aggradation rates associated with the lateral sediment influxes at the head and terminus of individual links.
Rice, S.P., and M. Church, Longitudinal profiles in simple alluvial systems, Water Resources Research, 37 (2), 417-426, 2001.
Theoretical considerations suggest that exponential or quadratic functions are apt for describing the longitudinal profiles of aggrading, alluvial systems that are unaffected by significant lateral inputs of water or sediment. A new set of field data confirms this for individual sedimentary links along a wandering gravel-bed river in British Columbia, Canada. Each link is viewed as a simple alluvial system, without major water or sediment inputs, within which grain size typically fines downstream in a relatively systematic manner. Such homogeneous reaches are suitable for the investigation of simple profile form. It is found that quadratic approximations are the most flexible descriptor for link longitudinal profiles. Overall, the river forms an irregularly cuspate long profile structured by these fundamental length-scale units. Both link gradients and link fining rate reflect size-selective aggradation associated with the bounding lateral inputs.
Richard, M., T. Bernhardt, and G. Bell, Environmental heterogeneity and the spatial structure of fern species diversity in one hectare of old-growth forest, Ecography, 23 (2), 231-245, 2000.
The precise relationship between species diversity and spatial heterogeneity has not often been investigated using quantitative and repeatable measures of environmental variation. In this study, we map the metre-level distribution of fern species in one hectare of old-growth forest and test for a relationship between diversity and heterogeneity of physical features and soil conditions. The nineteen species recorded in the hectare were non-randomly distributed and varied greatly in abundance and spatial aggregation. Different species distributions were not independent of one another; three groups were formed with species which occurred together significantly more often than random expectation. Physical and soil conditions were highly variable and spatially autocorrelated from the 5 m scale up to the extent of the whole hectare. Based on the sites where they grew, species differed in their preferences for soil moisture, fertility and pH. Fern diversity was highest at sites with high soil moisture and low soil fertility; however, there was no relationship between diversity and the environmental variance within quadrats. Unpredictable spatial distribution patterns produced by processes of dispersal and immigration may obscure any relationship between diversity and spatial heterogeneity at this fine scale.
Richards, K.S., and L.M. Milne, Problems in the Calibration of an Acoustic Device For the Observation of Bedload Transport, Earth Surface Processes and Landforms, 4 (4), 335-346, 1979.
Richards, K., Fluvial Geomorphology, Progress in Physical Geography, 11 (3), 432-457, 1987.
Richards, K., Fluvial Geomorphology - Initial Motion of Bed Material in Gravel-Bed Rivers, Progress in Physical Geography, 14 (3), 395-415, 1990.
Richards, K., and N. Clifford, Fluvial Geomorphology - Structured Beds in Gravelly Rivers, Progress in Physical Geography, 15 (4), 407-422, 1991.
Rickenmann, D., Sediment transport in Swiss torrents, Earth Surface Processes and Landforms, 22 (10), 937-951, 1997.
Ridenour, G.S., and J.R. Giardino, Logratio Linear Modeling of Hydraulic Geometry Using Indexes of Flow Resistance As Covariates, Geomorphology, 14 (1), 65-72, 1995.
Ritter, D.F., R.C. Kochel, and J.R. Miller, The disruption of Grassy Creek: implications concerning catastrophic events and thresholds, Geomorphology, 29 (3-4), 323-338, 1999.
Two catastrophic events, occurring simultaneously in the valley of Little Grassy Creek, IL, allow for an examination of the threshold concept in geomorphology. Movement of debris associated with failure and sliding of valley-side material, caused damming and avulsion of Little Grassy Creek. Slope and river disruptions, both severe in character, were linked because the effect of one event (slope failure) was the cause of the second event (fluvial avulsion). The slope failure represents a true threshold-crossing event because the results are irreversible on a graded-time scale. In contrast, the fluvial disruption was not a threshold crossing, although the event was catastrophic and short-term instability occurred. In the fluvial case, a new channel developed, and the re- establishment of equilibrium, as estimated by channel characteristics, occurred within 10 years. The river system functions as it did before the slope failure/avulsion, though the channel reach is now in a different location. Criteria needed to employ thresholds to explain geomorphic events are suggested, and a definition of thresholds as time-dependent phenomena is presented as a means of reducing confusion over the use of the threshold concept. (C) 1999 Elsevier Science B.V. All rights reserved.
Robert, A., Statistical Properties of Sediment Bed Profiles in Alluvial Channels, Mathematical Geology, 20 (3), 205-225, 1988.
Robert, A., Boundary Roughness in Coarse-Grained Channels, Progress in Physical Geography, 14 (1), 42-70, 1990.
Robert, A., Fractal Properties of Simulated Bed Profiles in Coarse-Grained Channels, Mathematical Geology, 23 (3), 367-382, 1991.
Bed roughness characteristics in coarse-grained channels are fairly complex. A hierarchy of roughness elements can be observed, ranging from variable particle sizes and shapes and small-scale sedimentary structures, to large-scale bedforms such as riffle-pool sequences. The effects of these scales of roughness on the flow geometry still remain to be thoroughly investigated. The semivariogram has been suggested in the past as a means of quantifying bed roughness effects on streamflow, as well as for distinguishing between scales of roughness. However, field measurements are rather time-consuming. The low number of bed profiles measured in the field precludes the identification of generally applicable relationships between the statistical properties derived from the semivariograms (such as the Hausdorff dimensions and the scale of autocorrelation corresponding to each fractal band) and the bed configuration itself (geometrical and sedimentological properties). Simulation results of gravel-bed profiles are, therefore, presented in order to complement the original investigation of Robert (1988a). The simulation experiments, based on grain characteristics of sizes and shapes and on morphological properties of small-scale bedforms, yield very significant information on boundary roughness at the microscale and give insight into the interpretation of empirical semivariograms (derived from field measurements). Bed-material sorting, variable grain shapes, and height and spacing of cluster bedforms control the fractal dimensions obtained from the semivariograms, as well as the location of the break of slope and the range of the process.
Robert, A., A.G. Roy, and B. Deserres, Changes in Velocity Profiles At Roughness Transitions in Coarse-Grained Channels, Sedimentology, 39 (5), 725-735, 1992.
Robert, A., Bed Configuration and Microscale Processes in Alluvial Channels, Progress in Physical Geography, 17 (2), 123-136, 1993.
Numerous recent studies on fluvial processes, both in Canada and internationally, have focused on small-scale phenomena. Investigations on the characterization of surface roughness in coarse-grained channels and its links with flow resistance and sediment transport processes have been a dominant field of research. Closely related is a second major area of investigation on turbulent flow structures in boundary layers over both sand and gravel beds and their relations with the transport of bed material. Phenomena potentially related to 'bursting' have been shown to control bedload transport processes and the concentration of sediment in suspension. Detailed investigations have also been conducted on the links between flow turbulence, bed material movement, and bed morphology at channel junctions. Finally, selective entrainment and transport of individual coarse particles have been studied from field measurements and laboratory experiments. Emphasis has been put on bed microtopography, surface structure and texture, and on a probabilistic approach to bedload transport.
Robert, A., A.G. Roy, and B. DeSerres, Turbulence at a roughness transition in a depth limited flow over a gravel bed, Geomorphology, 16 (2), 175-187, 1996.
Robert, A., Characteristics of velocity profiles along riffle-pool sequences and estimates of bed shear stress, Geomorphology, 19 (1-2), 89-98, 1997.
Numerous velocity profiles were measured along a riffle-pool sequence for three different flow conditions. For each flow condition (ranging from baseflow to about 2/3 of bankfull depth), ten to fifteen velocity profiles were measured along the same transect. The objectives of the study were: (i) to differentiate between components of bed roughness and shear stress attributed to surface friction and large-scale bed undulations, and (ii) to investigate the effects of fluctuating discharges on the mean vertical flow structure in pools and riffles. No previous attempts have been made to investigate scales of bed roughness from velocity profiles along riffle- pool sequences and to determine how near-bed velocity gradients change with increasing flow discharge. At low flows (and as expected), riffles are characterized by higher near-bed velocity gradients than pools. Similarly, average bed shear stresses, as determined from measurements of flow depth and energy gradient, indicate a greater resistance and bed shear stress in riffle sections. Invariably, however, local shear stresses as determined from near-bed velocity gradients in pools and in riffles are much smaller than reach averages estimated from measurements of depth and slope. The shape of spatially averaged velocity profiles changes as discharges increases. The difference in terms of near-bed velocities between pools and riffles decreases as discharge increases which suggests that a velocity reversal may occur at or near bankfull. Further away from the bed surface, velocity differences between pools and riffles do remain significant. Finally, the curvature of the velocity profiles is more significant at high flows and surface roughness is maximized when flow conditions are intermediate, perhaps a result of increasing density of small-scale sedimentary structures.
Robinson, R.A.J., and R.L. Slingerland, Origin of fluvial grain-size trends in a foreland basin: Pocono Formation on the central Appalachian basin, Journal of Sedimentary Research, 68 (3), 473-486, 1998.
Robinson, R.A.J., and R.L. Slingerland, Grain-size trends, basin subsidence and sediment supply in the Campanian Castlegate Sandstone and equivalent conglomerates of central Utah, Basin Research, 10 (1), 109-127, 1998.
Reconstructions of grain-size trends in alluvial deposits can be used to understand the dominant controls on stratal architecture in a foreland basin. Different initial values of sediment supply, tectonic subsidence and base-level rise are investigated to constrain their influence on stratal geometry using the observed grain-size trends as a proxy of the goodness of fit of the numerical results to the observed data. Detailed measurements of grain-size trends, palaeocurrent indicators, facies and thickness trends, channel geometries and palynological analyses were compiled for the middle Campanian Castlegate Sandstone of the Book Cliffs and its conglomerate units in the Gunnison and Wasatch plateaus of central Utah. They define the initial conditions for a numerical study of the interactions between large-scale foreland basin and small-scale sediment transport processes. From previous studies, the proximal foreland deposits are interpreted as recording a middle Campanian thrusting event along the Sevier orogenic belt, while the stratal architecture in the Book Cliffs region is interpreted to be controlled by eustatic fluctuation with local tectonic influence. Model results of stratal geometry, using a subsidence curve with a maximum rate of approximate to 45 m Myr(-1) for the northern Wasatch Plateau region predict the observed grain-size trends through the northern Book Cliffs. A subsidence curve with a maximum rate of approximate to 30 m Myr(-1) in the Gunnison-Wasatch Plateaus best reproduces the observed grain-size trends in the southern transect through the southern Wasatch Plateau. Eustasy is commonly cited as controlling Castlegate deposition east of the Book Cliffs region. A eustatic rise of 45 m Myr(-1) produces grain-size patterns that are similar to the observed, but a rate of eustatic rise based on Haq et nl. (1988) will not produce the observed stratal architecture or grain-size trends. Tectonic subsidence alone, or a combined rate of tectonic subsidence and a Haq er nl. (1988) eustatic rise, can explain the stratal and grain-size variations in the proximal and downstream regions.
Roering, J.J., J.W. Kirchner, and W.E. Dietrich, Evidence for nonlinear, diffusive sediment transport on hillslopes and implications for landscape morphology, Water Resources Research, 35 (3), 853-870, 1999.
Steep, soil-mantled hillslopes evolve through the downslope movement of soil, driven largely by slope-dependent transport processes. Most landscape evolution models represent hillslope transport by linear diffusion, in which rates of sediment transport are proportional to slope, such that equilibrium hillslopes should have constant curvature between divides and channels. On many soil-mantled hillslopes, however, curvature appears to vary systematically, such that slopes are typically convex near the divide and become increasingly planar downslope. This suggests that linear diffusion is not an adequate model to describe the entire morphology of soil- mantled hillslopes. Here we show that the interaction between local disturbances (such as rainsplash and biogenic activity) and frictional and gravitational forces results in a diffusive transport law that depends nonlinearly on hillslope gradient. Our proposed transport law (1) approximates linear diffusion at low gradients and (2) indicates that sediment Aux increases rapidly as gradient approaches a critical value. We calibrated and tested this transport law using high-resolution topographic data from the Oregon Coast Range. These data, obtained by airborne laser altimetry, allow us to characterize hillslope morphology at approximate to 2 m scale. At five small basins in our study area, hillslope curvature approaches zero with increasing gradient, consistent with our proposed nonlinear diffusive transport law. Hillslope gradients tend to cluster near values for which sediment flux increases rapidly with slope, such that large changes in erosion rate will correspond to small changes in gradient. Therefore average hillslope gradient is unlikely to be a reliable indicator of rates of tectonic forcing or baselevel lowering. Where hillslope erosion is dominated by nonlinear diffusion, rates of tectonic forcing will be more reliably reflected in hillslope curvature near the divide rather than average hillslope gradient.
Roering, J.J., J.W. Kirchner, and W.E. Dietrich, Hillslope evolution by nonlinear, slope-dependent transport: Steady state morphology and equilibrium adjustment timescales, Journal of Geophysical Research-Solid Earth, 106 (B8), 16499-16513, 2001.
Soil-mantled hillslopes are typically convex near the crest and become increasingly planar downslope, consistent with nonlinear, slope-dependent sediment transport models. In contrast to the widely used linear transport model (in which sediment flux is proportional to slope angle), nonlinear models imply that sediment flux should increase rapidly as hillslope gradient approaches a critical value. Here we explore how nonlinear transport influences hillslope evolution and introduce a dimensionless parameter TL to express the relative importance of nonlinear transport. For steady state hillslopes, with increasing YL (i.e., as slope angles approach the threshold angle and the relative magnitude of nonlinear transport increases), the zone of hillslope convexity becomes focused at the hilltop and side slopes become increasingly planar. On steep slopes, rapid increases in sediment flux near the critical gradient limit further steepening, such that hillslope relief and slope angle are not sensitive indicators of erosion rate. Using a one-dimensional finite difference model, we quantify hillslope response to changes in baselevel lowering and/or climate-related transport efficiency and use an exponential decay function to describe how rapidly sediment flux and erosion rate approach equilibrium. The exponential timescale for hillslope adjustment decreases rapidly with increasing TL. Our results demonstrate that the adjustment timescale for hillslopes characteristic of the Oregon Coast Range and similar steep, soil-mantled landscapes is relatively rapid (less than or equal to 50 kyr), less than one quarter of the timescale predicted by the linear transport model.
Rogers, H.M., Stand dynamics of Dacrydium cupressinum dominated forest on glacial terraces, south Westland, New Zealand, Forest Ecology and Management, 117 (1-3), 111-128, 1999.
Stand structure, disturbance histories, and patterns of tree replacement of three conifer-dominated stands growing on glacial terraces, differing in age, were investigated. Regeneration patterns of the conifers Dacrydium cupressinum, Manoao colensoi, Prumnopitys ferruginea and Phyllocladus alpinus were inferred from age and size (diameter) distributions, the spatial distribution of tree ages, and tree locations. Disturbance histories and patterns of tree replacement were reconstructed from age distributions, the spatial distribution of tree ages, and tree locations. Disturbance histories were related to soil drainage which was inferred from the depth of rusting on mild steel rods inserted across each stand. Stands differed in structure and composition, reflecting different patterns of disturbance. Manoao colensoi and Dacrydium cupressinum were established in response to catastrophic disturbance on extremely poorly drained soils on the oldest terrace. On less poorly drained soils, Dacrydium cupressinum, Prumnopitys ferruginea and Phyllocladus alpinus were established in response to smaller canopy gap formation from intermittent windthrow and synchronous canopy collapse. A secular model of stand dynamics is envisaged across the glacial terraces, reflecting an even long-term soil development, where the chance of catastrophic disturbance will increase as soils become increasingly poorly drained over millennia. The implications of these findings for sustainable forest management are discussed. (C) 1999 Elsevier Science B.V. All rights reserved.
Rosgen, D.L., A Classification of Natural Rivers, Catena, 22 (3), 169-199, 1994.
Rosgen, D.L., A classification of natural rivers: Reply, Catena, 27 (3-4), 301-307, 1996.
Rot, B.W., R.J. Naiman, and R.E. Bilby, Stream channel configuration, landform, and riparian forest structure in the Cascade Mountains, Washington, Canadian Journal of Fisheries and Aquatic Sciences, 57 (4), 699-707, 2000.
The hierarchical relationship of five key elements, valley constraint, riparian landform, riparian plant community, channel type, and channel configuration, are described for 21 sites in mature to old-growth riparian forests of the western Cascades Mountains, Washington, U.S.A. Channel type (bedrock, plane-bed, and forced pool-riffle) was closely related to channel configuration (especially large woody debris (LWD) volume, density, and LWD-formed pools) at the smallest spatial scale and valley constraint at the largest. Valley constraint significantly influenced off-channel habitat (r(2) = 0.71) and LWD volume within forced pool-riffle channels (r(2) = 0.58). Riparian plant community composition was differentiated by four landform classes: three alluvial landforms based on height above the channel and one based on hillslope. Just above the active channel, floodplain landforms contained more deciduous stems than conifer and greater conifer basal area than deciduous. Conifers dominated other landforms. The diameter of in-channel LWD increased with the age of the riparian forest (r(2) = 0.34). In old-growth forests, LWD diameter was equivalent to or greater than the average riparian tree diameter for all sites. In younger forests, the mixed relationship between LWD and riparian tree diameter may reflect a combination of LWD input from the previous old-growth stand and LWD input from the existing stand.
Rowntree, K.M., and E.S.J. Dollar, Vegetation controls on channel stability in the Bell River, Eastern Cape, South Africa, Earth Surface Processes and Landforms, 24 (2), 127-134, 1999.
Royall, D., Lake-sediment-based evaluation of recent sediment yield from a small appalachian watershed, Thompson Lake, Virginia, Physical Geography, 21 (1), 68-88, 2000.
Rubin, D.M., and D.J. Topping, Quantifying the relative importance of flow regulation and grain size regulation of suspended sediment transport alpha and tracking changes in grain size of bed sediment beta, Water Resources Research, 37 (1), 133-146, 2001.
Ryan, S.E., and G.E. Grant, Downstream Effects of Timber Harvesting On Channel Morphology in Elk River Basin, Oregon, Journal of Environmental Quality, 20 (1), 60-72, 1991.
Downstream effects, a type of cumulative watershed effect, were identified using changes in the width and distribution of open riparian canopies measured from aerial photography taken between 1956 and 1979 in Elk River basin, southwest Oregon. Open canopies appear on aerial photographs of densely forested basins as unvegetated areas bordering stream channels. Opening occurs when large disturbances, such as landslides, debris flows, large floods, and excessive sedimentation, disrupt the vegetation in the riparian corridor. Downstream changes in channel morphology, inferred by the changing pattern of open reaches were linked to upslope forestry activities; a causal link was assumed where: (i) open reaches extended continuously downstream from clearcuts and roads or (ii) the timing and pattern of opening downstream varied in direct relation to the intensity of upslope forestry activities. Open riparian canopies were observed in first- through fifth-order channels, though only 11% of open reaches in low-order channels were spatially connected to open reaches in higher order channels. Open reaches on low-order tributaries were attributed to landslides and surface erosion generated from clearcuts and roads; the total length of open reaches in low-order channels increased 30-fold during the study period. Open reaches occurred on higher-order channels throughout the study period but did not increase in size or change location in relation to upslope harvest activities. Instead, open canopies were restricted mainly to wide and low gradient channel reaches, which comprised approximately one-third of the length of higher-order channels. Limited downstream change in riparian canopies associated with upslope forestry activity during the study period, which included a 100-yr storm, was attributed to three physical factors: (i) lack of debris flows in most parts of the basin; (ii) channels constrained by competent hillslopes limiting the potential for opening; and (iii) low harvest levels over much of the basin at the time of the 100-yr storm. While air photo interpretation proved useful in deciphering the gross disturbance history of the basin and in distinguishing the general processes which generate downstream effects, sedimentation processes that do not distrub the riparian canopy may also be active in Elk River basin but were not detected due to the coarseness of the techniques used.
Ryan, S., Morphologic response of subalpine streams to transbasin flow diversion, Journal of the American Water Resources Association, 33 (4), 839-854, 1997.
Ryan, S.E., and L.S. Porth, A field comparison of three pressure-difference bedload samplers, Geomorphology, 30 (4), 307-322, 1999.
Sablik, M.J., Modeling the effect of grain size and dislocation density on hysteretic magnetic properties in steels (vol 89, pg 5610, 2001), Journal of Applied Physics, 90 (4), 2051-2051, 2001.
Sadatomi, M., M. Kawaji, C.M. Lorencez, and T. Chang, Prediction of Liquid-Level Distribution in Horizontal Gas- Liquid Stratified Flows With Interfacial Level Gradient, International Journal of Multiphase Flow, 19 (6), 987-997, 1993.
A one-dimensional momentum equation has been derived based on a two-fluid model and used to predict the axial distribution of liquid level or void fraction in steady, cocurrent, gas-liquid stratified flows in horizontal circular pipes and rectangular channels. The equation is carefully formulated to incorporate the effect of interfacial level gradient. Two different critical liquid levels are found from the momentum equation and are adopted as a boundary condition to calculate the liquid level or void fraction distribution upstream of the channel exit. The predicted void fraction distributions are compared with the experimental data obtained in a rectangular channel in this work and other data reported for large-diameter pipes. Good agreement is shown for air-kerosene, air-water and stream- water stratified flows with a smooth gas-liquid interface.
Saiedi, S., Coupled modeling of alluvial flows, Journal of Hydraulic Engineering-Asce, 123 (5), 440-446, 1997.
Saint-Laurent, D., and P. Guimont, Fluvial dynamic and bank evolution of Nottaway, Broadback and Rupert rivers, James Bay area (Quebec), Geographie Physique Et Quaternaire, 53 (3), 389-399, 1999.
Saint-Laurent, D., Canadian Landform Examples. 38. River bank erosion at the mouth of Rupert River (James Bay, Quebec), Canadian Geographer-Geographe Canadien, 43 (4), 439-446, 1999.
Salaheldin, T.M., J. Imran, M.H. Chaudhry, and C. Reed, Role of fine-grained sediment in turbidity current flow dynamics and resulting deposits, Marine Geology, 171 (1-4), 21-38, 2000.
Salem, H.S., Application of the Kozeny-Carman equation to permeability determination for a glacial outwash aquifer, using grain-size analysis, Energy Sources, 23 (5), 461-473, 2001.
Salinas, M.J., G. Blanca, and A.T. Romero, Riparian vegetation and water chemistry in a basin under semiarid Mediterranean climate, Andarax River, Spain, Environmental Management, 26 (5), 539-552, 2000.
Samuels, P.G., Backwater Lengths in Rivers, Proceedings of the Institution of Civil Engineers Part 2- Research and Theory, 87, 571-582, 1989.
Saunderson, H.C., D.J. Smith, and M.K. Woo, Progress in Canadian geomorphology and hydrology 1996-2000, Canadian Geographer-Geographe Canadien, 44 (1), 67-86, 2000.
Since 1996 a broad range of publications has been produced by Canadian geomorphologists and hydrologists. These publications have been distributed in journals with national and international circulations. Although there remains a major focus on the study of observable processes in pluvial, aeolian, coastal and slope environments there is also a strong, historical component to explanations of landforms, landform assemblages and sedimentary sequences. Some of these histories have incorporated the effects of high-magnitude (catastrophic) events, some of which may have no modern analogues. Perspectives on the interactions among microclimatic variables, including changes induced by human actions, continue to evolve. Forest clearance and its effects on evaporation rates, water- table levels and timing of snowmelt, the human use of wetlands and release of methane and carbon dioxide, will continue to demand the attention of scholars interested in explaining future climatic scenarios.
Saxl, I., and P. Ponizil, Grain size estimation: w-s diagram, Materials Characterization, 46 (2-3), 113-118, 2001.
Scarsbrook, M.R., and C.R. Townsend, Stream Community Structure in Relation to Spatial and Temporal Variation - a Habitat Templet Study of 2 Contrasting New- Zealand Streams, Freshwater Biology, 29 (3), 395-410, 1993.
1. The physical characteristics of two contrasting streams, and habitat types within these streams, are described in terms of a two-dimensional physical habitat templet in which disturbance frequency and the availability of spatial refugia are the temporal and spatial axes. 2. It is predicted that habitats experiencing a high disturbance frequency and low refuge availability will be characterized by a low invertebrate species diversity, a low biomass of epilithic algae and particulate organic matter and a community made up of mobile, weedy species. Habitats having a low disturbance frequency and high refuge availability will be characterized by a diverse community containing sedentary and specialist species, with high algal and particulate organic matter levels. 3. A lower median substrate particle size and higher shear stress regime in Timber Creek were indicative of a higher disturbance frequency than in the Kyeburn. Substrate diversity was lower in Timber Creek than in the Kyeburn and indicated that the availability of refugia was lower in Timber Creek. In both streams, pools were found to have a higher disturbance frequency and lower availability of refugia than riffles. 4. Invertebrate species diversity, the biomass of epilithic algae and particulate organic matter and the representation of sedentary species, filter feeders and shredders were higher in the more temporally stable and spatially heterogeneous Kyeburn. The community of Timber Creek, frequently disturbed and having low refuge availability, had a high proportion of mobile and weedy species, with the highly mobile, generalist-feeding Deleatidium spp. (Ephemeroptera; Leptophlebiidae) being the most dominant organisms. 5. The predictions made about stream community structure and species characteristics in relation to disturbance frequency and the availability of spatial refugia are generally supported. Now a larger scale investigation is required to test the generality of the predictions. We conclude that the habitat templet approach offers a sound framework within which to pose questions in stream ecology.
Schick, A.P., T. Grodek, and M.G. Wolman, Hydrologic processes and geomorphic constraints on urbanization of alluvial fan slopes, Geomorphology, 31 (1-4), 325-335, 1999.
Schlesinger, W.H., T.J. Ward, and J. Anderson, Nutrient losses in runoff from grassland and shrubland habitats in southern New Mexico: II. Field plots, Biogeochemistry, 49 (1), 69-86, 2000.
Schmidt, K.H., and P. Ergenzinger, Bedload Entrainment, Travel Lengths, Step Lengths, Rest Periods - Studied With Passive (Iron, Magnetic) and Active (Radio) Tracer Techniques, Earth Surface Processes and Landforms, 17 (2), 147-165, 1992.
Schmidt, J.C., R.H. Webb, R.A. Valdez, G.R. Marzolf, and L.E. Stevens, Science and values in river restoration in the Grand Canyon - There is no restoration or rehabilitation strategy that will improve the status of every riverine resource, Bioscience, 48 (9), 735-747, 1998.
Schmidt, J.C., R.A. Parnell, P.E. Grams, J.E. Hazel, M.A. Kaplinski, L.E. Stevens, and T.L. Hoffnagle, The 1996 controlled flood in Grand Canyon: Flow, sediment transport, and geomorphic change, Ecological Applications, 11 (3), 657-671, 2001.
The 1996 controlled flood released from Glen Canyon Dam into the Colorado River was a small magnitude, short duration event compared to pre-dam floods. The controlled flood was of lesser magnitude than a 1.25-yr recurrence, and only 10% of the pre dam spring snowmelt floods during the period 1922-1962 were of lower magnitude. The flood occurred unusually early: 36-38 d prior to any previous annual flood since 1922. The stage difference between the flood's peak and the recessional baseflow was smaller than in those pre-dam years of similar magnitude or annual volume. However, the controlled flood was large from the perspective of the post-dam flood regime. The hood had a recurrence of 5.1 yr for the period between 1963 and 1999 and a similar magnitude flood had not occurred in 10 yr. The sediment flux of the flood was small in relation to pre-dam hoods, and the suspended sand concentration was within the historical variance for flows of similar magnitude. This flood reworked fine-grained deposits that are primarily composed of sand, but the flood caused much less reworking of coarser grained deposits. Scour primarily occurred in the offshore parts of eddies, in many eddy return-current channels, and in some parts of the main channel. Return-current channels constitute important nursery habitats for, the native fishery when baseflows are low, because these channels become areas of stagnant and warmer water. The number and area of these backwaters increased greatly after the flood. Fluvial marshes were extensively scoured because these habitats occur in the low elevation centers of eddies where velocities during the flood were large. Riparian shrubs that were inundated along the banks were not scoured, however, because these shrubs occur where flood velocities were very low and where deposition of suspended sediment occurred. Some physical changes persisted for several years, but other changes, such as the area of newly formed backwaters decreased quickly. Thus, the lasting effect of this flood varied among different small-scale fluvial environments.
Schnackenberg, E.S., and L.H. MacDonald, Detecting cumulative effects on headwater streams in the Routt National Forest, Colorado, Journal of the American Water Resources Association, 34 (5), 1163-1177, 1998.
This study evaluated the use of a modified pebble count procedure (Bevenger and King, 1995) to detect cumulative watershed effects on headwater streams in the Routt National Forest in northcentral Colorado. The 42 sample reaches were stratified by disturbance (reference or disturbed) and geologic terrane (granitic or mixed sedimentary-volcanic). Water surface slope was a significant control on the number of fine particles in the reference reaches in both terranes, and the data from the disturbed reaches were adjusted accordingly. The disturbed reaches in the granitic terrane generally had a higher percentage of fine particles, and the adjusted number of fine particles was significantly correlated with the number of road crossings. Disturbed reaches in the sedimentary-volcanic (s-v) terrane generally did not have significantly more fine particles, nor were the adjusted numbers of fine particles significantly correlated with any management index. The lack of significant trends in the s-v streams is probably due to differences in weathering between the two rock types, and the location of the sample reach relative to sedimentary outcrops. Two other procedures were also used to assess cumulative watershed effects, with the Pfankuch channel stability rating yielding stronger and more consistent differences between the reference and the disturbed streams than the Tarzwell substrate ratio. We conclude that it may be difficult to define a standard reference condition, and that the number of mad crossings is more strongly correlated with the number of fine particles than equivalent clearcut area.
Scholz, J.G., and D.B. Booth, Monitoring urban streams: Strategies and protocols for humid- region lowland systems, Environmental Monitoring and Assessment, 71 (2), 143-164, 2001.
Governmental mandates and public awareness have forced progressively smaller and less sophisticated agencies and organizations to initiate stream monitoring programs, particularly in urban and urbanizing areas. Yet many of these monitoring efforts lack either a coherent conceptual framework or appropriately chosen methods, and they rely on monitoring techniques that are simply infeasible for these institutional settings. We propose a monitoring strategy, and specific existing monitoring protocols, that will be useful for the management and rehabilitation of streams in urbanizing watersheds. A monitoring strategy must be developed by 1) identifying the management question(s) being addressed, 2) determining the institional level of effort required (and available) to effectively make particular kinds of measurements, and 3) identifying what specific parameters should and can be measured. Only a limited set of parameters show much utility or feasibility in addressing the most common management questions being faced by municipalities in urbanizing, humid-area regions of the United States. These include measures of riparian canopy, bank erosion and bank hardening, and in-stream large woody debris. With some additional expertise useful data can also be included on channel gradient, substrate composition, and pools. Nearly all of the other myriad parameters that have been measured historically on rivers and streams show little apparent value in these watershed and institutional settings.
Schropp, M., and H.L. Fontijn, Flow Profiles For Steady Spatially Varied Flow - an Explorative Analysis, Journal of Hydraulic Research, 27 (1), 135-147, 1989.
Seal, R., and C. Paola, Observations of Downstream Fining On the North Fork Toutle River Near Mount St-Helens, Washington, Water Resources Research, 31 (5), 1409-1419, 1995.
Seal, R., C. Paola, G. Parker, J.B. Southard, and P.R. Wilcock, Experiments on downstream fining of gravel .1. Narrow-channel runs, Journal of Hydraulic Engineering-Asce, 123 (10), 874-884, 1997.
Sear, D.A., Sediment transport processes in pool-riffle sequences, Earth Surface Processes and Landforms, 21 (3), 241-262, 1996.
Sear, D.A., A. Briggs, and A. Brookes, A preliminary analysis of the morphological adjustment within and downstream of a lowland river subject to river restoration, Aquatic Conservation-Marine and Freshwater Ecosystems, 8 (1), 167-183, 1998.
Sear, D.A., and J.A. Milne, Surface modelling of upland river channel topography and sedimentology using GIS, Physics and Chemistry of the Earth Part B-Hydrology Oceans and Atmosphere, 25 (4), 399-406, 2000.
This paper outlines the use of GIS surface modelling to reconstruct the 3-D geometry of sinuous upland gravel-bed rivers. The opportunities afforded by the use of surface models for the analysis of geomorphological data is assessed using case studies from Northern Britain. Topographic data were collected using different survey techniques. These datasets were transformed using custom software from which surface models of bed topography, bedforms and bed material grainsize were constructed using ARC/INFO A method for the objective identification of meso-scale bedforms in these rivers is presented and the resultant bedform polygons used to sample surfaces of bed material grainsize. River channel adjustment over a twenty year period is assessed using surface differencing techniques from which sediment budgets can be calculated. (C) 2000 Elsevier Science Ltd. All rights reserved.
Sear, D.A., W. Damon, D.J. Booker, and D.G. Anderson, A load cell based continuous recording bedload trap, Earth Surface Processes and Landforms, 25 (6), 659-672, 2000.
Seminara, G., M. Colombini, and G. Parker, Nearly pure sorting waves and formation of bedload sheets, Journal of Fluid Mechanics, 312, 253-278, 1996.
Bedload sheets are coherent migrating patterns of bed material recently observed both in flume studies and in held streams with beds of coarse sand and fine gravel. This newly recognized feature is inherently associated with the heterogeneous character of the sediment and consists of sorting waves with distinct coarse fronts only one or two coarse grains high. The question of the formation of bedload sheets poses an interesting and peculiar stability problem for the grain size distribution. Sorting waves are essentially two-dimensional migrating perturbations associated with variations of this distribution. We show that their growth is strictly associated with grain sorting. In fact the latter gives rise to perturbations of bedload transport which drive small perturbations of bottom elevation the amplitude of which scales with grain size. The sorting wave also induces spatial variations of bottom roughness, and consequently alters the fluid motion, which conversely exerts a spatially varying stress on the bed. The feature of bedload sheets which allows them to be distinguished from dunes over beds with coarse sand or fine gravel is then the fact that sorting is the dominant effect controlling their growth, rather than being a relatively small perturbation of the mechanism which gives rise to dunes in the case of uniform sediment. The requirement that perturbations should not alter the sediment budget leads to an integral condition which gives rise to an integro-differential mathematical problem. With the help of recently developed bedload relationships suitable for mixtures, as well as appropriate modelling of turbulent channel flow over a bed with spatially periodic perturbations of bottom elevation and roughness we are able to derive a general dispersion relation which can be readily solved in terms of undisturbed size densities in the form of sums of Dirac distributions. Perturbations are found to be unstable within a range of wavenumbers depending on the relative roughness and Froude number. We show that when the effects of perturbations of bottom elevation are neglected the unstable region corresponds to the range of conditions where the bottom stress leads bottom roughness, a range distinct from that which characterizes the formation of dunes. This result is given a physical explanation which depends crucially on the deviation from equal mobility of different grain sizes in the surface layer. The effect of perturbations of bottom elevation is however not negligible when the bottom roughness is fairly large compared to depth. In the latter case perturbations of bottom elevation and of bottom roughness are equally important, and gravel sheets are not easily distinguished from small-amplitude dunes. Comparison with the field observations of Whiting et al. (1985, 1988) is satisfactory insofar as the bedload sheet mode is unstable under the conditions of the experiments, and the predicted wavelengths fall within the experimental range. The laboratory observations of Kuhnle & Southard (1988), on the other hand, appear to fall within a range of bottom roughness where the observed bedforms do not exhibit features unambiguously distinct from those of small-amplitude dunes.
Shanahan, P., and S.C. Gaudet, Mixing and Transport, Research Journal of the Water Pollution Control Federation, 62 (4), 546-555, 1990.
Shanahan, P., Mixing and Transport, Water Environment Research, 64 (4), 514-523, 1992.
Sherwood, C.R., Numerical model of frazil ice and suspended sediment concentrations and formation of sediment laden ice in the Kara Sea, Journal of Geophysical Research-Oceans, 105 (C6), 14061-14080, 2000.
Shields, F.D., S.S. Knight, and C.M. Cooper, Rehabilitation of Watersheds With Incising Channels, Water Resources Bulletin, 31 (6), 971-982, 1995.
Shields, F.D., S.S. Knight, and C.M. Cooper, Cyclic perturbation of lowland river channels and ecological response, Regulated Rivers-Research & Management, 16 (4), 307-325, 2000.
Certain lowland streams have experienced prehistorical and historical cycles of aggradation, occlusion, degradation, headward incision, and renewed aggradation. Historical cycles appear to be related to human activities. A case study is presented of the Yalobusha River in Mississippi with emphasis on the effects of blockage and removal on aquatic habitats and fish. The adjacent Skuna River, which was channelized;and unblocked, was used in space for time substitution to infer effects of blockage removal on the Yalobusha. Variables describing physical aquatic habitat and fish were sampled from three groups of river reaches: unblocked channelized, channelized and blocked, and naturally sinuous. Fish collections were used to compute six indicators of ecological integrity. At baseflow, mean water depths were an order of magnitude lower in the unblocked channelized stream than for the others. In-channel aquatic habitat volume per unit valley length was 5, 85, and 283 m(3)/m for the channelized, blocked channelized, and natural reaches, respectively. Mean values for all six ecological indicators were lowest for the channelized group. Species richness was greatest for the channelized blocked reach. The ecological indicators displayed gradients in response to the range of observed physical conditions. Management of corridors susceptible to the cycle described above should involve a blend of measures designed to conserve higher quality habitats.
Shimeta, J., and P.A. Jumars, Physical-Mechanisms and Rates of Particle Capture By Suspension-Feeders, Oceanography and Marine Biology, 29, 191-257, 1991.
Shvidchenko, A.B., and G. Pender, Initial motion of streambeds composed of coarse uniform sediments, Proceedings of the Institution of Civil Engineers-Water Maritime and Energy, 142 (4), 217-227, 2000.
Shvidchenko, A.B., and G. Pender, Flume study of the effect of relative depth on the incipient motion of coarse uniform sediments, Water Resources Research, 36 (2), 619-628, 2000.
Shvidchenko, A.B., G. Pender, and T.B. Hoey, Critical shear stress for incipient motion of sand/gravel streambeds, Water Resources Research, 37 (8), 2273-2283, 2001.
Sibanda, E., I. McEwan, and A. Marion, Measuring the structure of mixed-grain-size sediment beds, Journal of Hydraulic Engineering-Asce, 126 (5), 347-353, 2000.
Sichingabula, H.M., Magnitude-frequency characteristics of effective discharge for suspended sediment transport, Fraser River, British Columbia, Canada, Hydrological Processes, 13 (9), 1361-1380, 1999.
This study analyses archival discharge and sediment concentration data (1965-1988), monitored by Water Survey of Canada, to examine suspended sediment transport rates and their relationship to effective discharge (Q(eff)) based on daily discharge duration curves. Effective discharge was determined as the mid-point of the discharge class transporting the greatest portion of the suspended sediment load (hence class- based Q(eff)). Results showed that the concept of effective discharge was applicable to the Fraser River basin where the average class-based Q(eff) occurred during 8.4% of the study period with individual values ranging from 0.03% to 16.1%. The durations of effective discharge classes ranged from 0.02% to 19.6% while the transport of 50% of total sediment loads ranged from 3% to 22% with an average of 14% of the time. Equations for predicting the class-based Q(eff) in the Fraser River basin from bankfull discharge and drainage area are presented. The observed variations among stations in sediment-discharge regimes based on subjectively selected 20 discharge classes, seem to reflect the influence of sediment controlling factors such as geology, physiography. catchment size and land use practice in the basin. Future directions of research on applications of the effective discharge concept are explored. As a solution to the problem of lack of an objective method for determining the effective discharge, the effective discharge should be determined from event based assessments of sediment transport (event-based Q(eff)), avoiding any subjectivity in the selection of number of discharge classes used for its determination. In conclusion, it is proposed that continued use of the conventional method of determining Q(eff) should cease. Copyright (C) 1999 John Wiley & Sons, Ltd.
Sieben, J., A theoretical analysis of discontinuous flow with mobile bed, Journal of Hydraulic Research, 37 (2), 199-212, 1999.
The nonlinear mathematical model for depth-averaged flow allows for discontinuous solutions that correspond with the dynamic behaviour of rapid changes in flow. Such discontinuities, that can fundamentally affect the predicted morphological response of a river, are analyzed theoretically and numerically. Hereto, the entropy conditions as defined by Lax and the Rankine- Hugoniot or shock relations are used to analyze propagation rates and stability. Apart from subcritical and supercritical flows, a transition regime can be identified for flows with mobile beds.
Simon, A., and C.R. Thorne, Channel adjustment of an unstable coarse-grained stream: Opposing trends of boundary and critical shear stress, and the applicability of extremal hypotheses, Earth Surface Processes and Landforms, 21 (2), 155-180, 1996.
Singh, V.P., Kinematic wave modelling in water resources: a historical perspective, Hydrological Processes, 15 (4), 671-706, 2001.
Since its development by Lighthill and Whitham (1955a,b), the kinematic wave theory has found widespread application in environmental and water sciences, It took nearly 15 years before the theory was accepted as a sound scientific concept for modelling of a variety of hydrological processes. The debate as to its validity, however, still continues in some quarters and is not likely to end any time soon. Irrespective of the merits of the argument for or against the theory, new areas of its application continue to unfold and its scope is expanding considerably. These days the kinematic wave theory is being applied to a variety of hydrological processes (Singh, 1996a, 1997a,b). Examples of its application span overland and channel flow, baseflow, unsaturated flow, macropore flow, flow in furrows and borders, river hydraulics, movement of glaciers, erosion and sediment transport, sedimentation, solute transport, microbial. transport and chromatographic transport, to name but a few. These and other applications of the kinematic wave theory can be pooled together under different branches of hydrology, including surface water hydrology, vadose zone hydrology, river and coastal hydrology, irrigation hydrology, subsurface hydrology, snow and glacier hydrology, and water quality hydlology. The discussion in what follows is organized according to these areas of application. The objective of this paper is to trace the history of evolution of the kinematic wave theory and its application in hydrology and water resources. This historical essay attempts to put the theory in I,roper perspective and should serve as a guide to decide when and where to use the theory. The essay points to areas where further advances in applying the theory can be made.
Sinha, S.K., and G. Parker, Causes of concavity in longitudinal profiles of rivers, Water Resources Research, 32 (5), 1417-1428, 1996.
A smooth concave configuration represents the most common quasiequilibrium profile of alluvial rivers. In the present paper a generalized, unified set of models for the longitudinal profile of rivers is presented. Various independent effects that drive concavity in longitudinal rivers are considered and classified. The driving mechanisms considered here are (1) horizontal wavelike progradation of the river profile, (2) abrasion of bed particles, (3) aggradation of the river profile balancing subsidence at a constant speed, and (4) the effect of tributaries adding sediment and water to the main stem of the river. For simplicity it is assumed that the long-term supply of water and sediment is constant; hence a single discharge, that is, bank-full discharge, is used as an approximate characterization of the hydrologic regime for each point along the river. Sediment sorting has been studied elsewhere and is excluded from this analysis. The river is assumed to have uniform bed material, although the mean size may vary downstream. It is concluded that the quasi-equilibrium longitudinal profile created by each of the first three driving mechanisms mentioned above is concave. The degree of concavity varies, however, depending on a set of physical conditions that can be identified by a set of dimensionless numbers. A comparison of these numbers reveals the relative importance of the driving mechanisms for concavity. A condition for concavity driven by the fourth mechanism, that is, tributary input, is delineated.
Slaymaker, O., Climate Change and Erosion Processes in Mountain Regions of Western Canada, Mountain Research and Development, 10 (2), 171-182, 1990.
Slaymaker, O., Mountain Geomorphology - a Theoretical Framework For Measurement Programs, Catena, 18 (5), 427-437, 1991.
Ten distinctive mountain geomorphic systems, identified on the basis of structural elements and spatial scale, are considered. Questions and approaches to measurement programmes that are most appropriate to each system are discussed with the aid of illustrative examples from the literature.
Slaymaker, O., Natural hazards in British Columbia: an interdisciplinary and inter-institutional challenge, International Journal of Earth Sciences, 88 (2), 317-324, 1999.
Although British Columbia experiences many natural hazards, there is as yet no unified policy to promote natural hazard management in the province. The problem is not in the quantity and quality of geoscience assessment of natural hazards, but instead, it is suggested, in the isolation of that work from broader risk perspectives and in the lack of clarity of division of responsibilities between various levels of government. The example of recent changes in perception of the terrain stability problem illustrates how natural hazard problems are driven by social and political priorities rather than by geoscience priorities.
Slaymaker, O., Assessment of the geomorphic impacts of forestry in British Columbia, Ambio, 29 (7), 381-387, 2000.
Timber harvesting in British Columbia influences (a) forest hydrology; (b) fluvial geomorphology; (c) terrain stability; and (d) integrated watershed behavior. Impacts on forest hydrology are well understood and include increased average runoff, total water yield, increased storm runoff and advances in timing of floods. Stream channels and valley floors are impacted differently by fine sediment, coarse sediment and large woody debris transport. Terrain stability is influenced through gully and mass movement processes that are accelerated by timber harvesting. Impacts on integrated watershed behavior are assessed through disturbed sediment budgets and lake sediments. The Forest Practices Code (1995) is a significant step towards sustainable management of the land in so far as it attempts to minimize these geomorphic impacts of forest in B. C.
Sloan, J., J.R. Miller, and N. Lancaster, Response and recovery of the Eel River, California, and its tributaries to floods in 1955, 1964, and 1997, Geomorphology, 36 (3-4), 129-154, 2001.
Northwestern California is prone to regional. high magnitude winter rainstorms. which repeatedly produce catastrophic floods in the basins of the northern Coast Ranges. Major floods on the Eel River in 1955 and 1964 resulted in substantial geomorphic changes to the channel, adjacent terraces, and tributaries. This study evaluated the changes and the effects of a moderate flood in 1997 through field observations and examination of aerial photographs that spanned from 1954 to 1996. The purpose was to document the nature and magnitude of geomorphic responses to these three floods and assess the rates and controls on the recovery of the Eel River and its tributaries. Channel widening from extensive bank erosion was the dominant geomorphic change along the lower Eel River during major floods. As a result of the 1964 flood. the largest amount of widening was 195 m and represented an 80% change in channel width. Channel narrowing characterized the periods after the 1955 and 1964 floods. More than 30 years after the 1964 flood, however, the river had not returned to pre-flood width, which suggests that channel recovery required decades to complete. A long recovery time is unusual given that the Eel River is located in an area with a "superhumid" climate and has an exceptionally high sediment yield, This long recovery time may reflect highly seasonal precipitation and runoff, which are concentrated in 3-5 months each winter. In contrast to the main stem of the Eel River, the dominant effects of floods on the tributaries of the Eel River were rapid aggradation of channel bed and valley floor followed by immediate downcutting. Dendrogeomorphic data, aerial photographs, and field observations indicate that thick wedges of gravel, derived largely from hillslope failures in upper reaches of the tributaries, are deposited at and immediately upstream of the mouths of tributaries as the stage of the Eel River exceeded that of the tributaries during major floods. In the waning stages of the flood, the tributaries cut through the gravel at a rate equal to the lowering of the Eel and generated unpaired terraces and nickpoints. The complete process of deposition acid incision can occur within a few days of peak discharge. Although reworking of some sediment on the valley floor may continue for years after large floods, channel morphology in the tributaries appears to be a product of infrequent, high magnitude events. The morphology of the tributary channel also appears to be greatly influenced by the frequency and magnitude of mass wasting in headwater areas of small basins. (C) 2001 Elsevier Science B.V. All rights reserved.
Smart, G.M., Turbulent velocity profiles and boundary shear in gravel bed rivers, Journal of Hydraulic Engineering-Asce, 125 (2), 106-116, 1999.
Vertical profiles of turbulent streamwise velocities in gravel bed rivers are investigated. Field measurements made at high and low flows with electronic pitot tubes show logarithmic velocity profiles to extend over much of the flow depth. For the gravel bed rivers studied the velocity at 0.6 of the total depth was generally a good indicator of depth-averaged flow velocity. An unambiguous definition of flow depth is adopted to deal with situations where the bed is uneven or moving. When hydraulic roughness Z(0) is defined as a fitted parameter of a logarithmic velocity profile, the river data indicate that the profile origin displacement below the tops of roughness elements scales with Z(0). No direct relation between Z(0) and bed material size is evident under mobile bed conditions. For these conditions a relation between hydraulic roughness and U*(2) is identified (with U* also derived as a log profile parameter). A flow resistance equation using this relation is verified by comparison with mobile bed laboratory measurements in which U* is not fitted from velocity profiles.
Smith, S.A., Sedimentation in a Meandering Gravel-Bed River - the River Tywi, South-Wales, Geological Journal, 24 (3), 193-204, 1989.
Smith, S.A., The Sedimentology and Accretionary Styles of an Ancient Gravel- Bed Stream - the Budleigh Salterton Pebble Beds (Lower Triassic), Southwest England, Sedimentary Geology, 67 (3-4), 199-219, 1990.
Smith, S.A., and R.A. Edwards, Regional Sedimentological Variations in Lower Triassic Fluvial Conglomerates (Budleigh Salterton Pebble Beds), Southwest England - Some Implications For Paleogeography and Basin Evolution, Geological Journal, 26 (1), 65-83, 1991.
The Budleigh Salterton Pebble Beds (BSPD) are a 20-30 m thick formation of conglomerates and subordinate sandstones which crop out along the western margin of the Wessex Basin. The formation has previously been interpreted as representing a major conduit for southerly-derived (Armorican) detritus and as signalling the start of early Triassic rifting. In this paper the role of the BSPB in the evolution of the Wessex Basin is reassessed. In the south of the outcrop, the lower portions of the BSPB are dominated by extensive (> 50 m) sheets or narrow lenses of planar cross-bedded conglomerate (sets 1-3 m thick). This reflects deposition from linguoid-shaped bars whose downstream margins were bounded by slipfaces. These accreted at anabranch confluences and as bank-attached bars in relatively confined and channelized gravel-bed streams. Most of the rest of the BSPB consists of couplets of horizontally- bedded conglomerate overlain by large-scale trough cross-bedded sandstone. This style of accretion represents deposition from relatively low-relief gravel bars and large sand dunes in substantial but poorly confined channels. Towards the top of the BSPB in the central parts of the outcrop, there is a change to thinner-bedded units with more lenticular and ribbon-like geometries. This represents deposition in smaller and more flashy streams. The BSPB was deposited either on a braidplain or by an antecedent 'wet' alluvial fan. In both settings, the BSPB streams were exotic, draining basins to the south of the Wessex Basin. This implies that the BSPB did not necessarily develop in response to differential subsidence and rifting within the Wessex Basin.
Smith, R.D., R.C. Sidle, P.E. Porter, and J.R. Noel, Effects of Experimental Removal of Woody Debris On the Channel Morphology of a Forest, Gravel-Bed Stream, Journal of Hydrology, 152 (1-4), 153-178, 1993.
Experimental removal of woody debris from a small, gravel-bed stream in a forested basin resulted in dramatic redistribution of bed sediment and changes in bed topography. Removal of debris changed the primary flow path, thereby altering the size and location of bars and pools and causing local bank erosion and channel widening. Marked bed adjustments occurred almost immediately following experimental treatment in May 1987 and continued through to the end of the study period in 1991. Increased bed material mobility was attributable to destabilization of sediment storage sites by removal of debris but-tresses, elimination of low-energy, backwater environments related to debris, and an inferred increase in boundary shear stress resulting from the removal of debris-related flow resistance. In contrast to these changes, which favored sediment mobilization, deposition was favored by the elimination of debris-related scouring turbulence and by increased flow resistance from a developing sequence of alternate bars. A more regularly spaced sequence of alternate bars replaced the pretreatment bar sequence, whose location, size, and shape had been strongly influenced by large woody debris as well as by bank projections and channel curvature. Following initial readjustment of the stream bed during the first posttreatment year, loss of scouring turbulence and increased flow resistance from alternate bars resulted in deposition of approximately 44 m3 of sediment within the 96 m study reach. The loss of 5.2 m3 to bank erosion left a net increase in sediment storage of 39 m3. Mean spacing of thalweg cross-overs and pools did not change measurably following debris removal, although variability of spacing between thalweg cross-overs tended to decrease with time as the location of bars stabilized. No consistent pattern of change in mean residual depth of pools or in distribution of depths occurred within the first 4 years following debris removal.
Smith, R.D., R.C. Sidle, and P.E. Porter, Effects On Bedload Transport of Experimental Removal of Woody Debris From a Forest Gravel-Bed Stream, Earth Surface Processes and Landforms, 18 (5), 455-468, 1993.
Experimental removal of woody debris from a small, gravel-bed stream in a forested area resulted in a four-fold increase in bedload transport at bankfull discharge. This was caused by increased transportability of sediment previously stored upslope of debris buttresses or in low-energy hydraulic environments related to debris. Bank erosion delivered additional sediment to the channel, and transport energy was increased by an inferred increase in the component of total boundary shear stress affecting grains on the bed. Increased transport following debris removal in May 1987 continued throughout the entire autumn storm season through late November 1987, indicating persistent adjustment of the stream bed and banks despite marked response to earlier flows as large as bankfull. Stream bed adjustments included development of a semi-regular sequence of alternate bars and pools, many of which were spaced independently of former pool locations.
Smith, G.A., Climatic Influences On Continental Deposition During Late-Stage Filling of an Extensional Basin, Southeastern Arizona, Geological Society of America Bulletin, 106 (9), 1212-1228, 1994.
Smith, G.H.S., and R.I. Ferguson, The Gravel Sand Transition Along River Channels, Journal of Sedimentary Research Section a-Sedimentary Petrology and Processes, 65 (2), 423-430, 1995.
Smith, G.H.S., Bimodal fluvial bed sediments: Origin, spatial extent and processes, Progress in Physical Geography, 20 (4), 402-417, 1996.
Smith, G.H.S., and R.I. Ferguson, The gravel-sand transition: Flume study of channel response to reduced slope, Geomorphology, 16 (2), 147-159, 1996.
Smith, G.H.S., A.P. Nicholas, and R.I. Ferguson, Measuring and defining bimodal sediments: Problems and implications, Water Resources Research, 33 (5), 1179-1185, 1997.
Smith, G.A., Recognition and significance of streamflow-dominated piedmont facies in extensional basins, Basin Research, 12 (3-4), 399-411, 2000.
Smith, G.H.S., Small-scale cyclicity in alpine proglacial fluvial sedimentation, Sedimentary Geology, 132 (3-4), 217-231, 2000.
Smith, T.R., G.E. Merchant, and B. Birnir, Transient attractors: towards a theory of the graded stream for alluvial and bedrock channels, Computers & Geosciences, 26 (5), 541-580, 2000.
Snyder, N.P., K.X. Whipple, G.E. Tucker, and D.J. Merritts, Landscape response to tectonic forcing: Digital elevation model analysis of stream profiles in the Mendocino triple junction region, northern California, Geological Society of America Bulletin, 112 (8), 1250-1263, 2000.
The topographic evolution of orogens is fundamentally dictated by rates and patterns of bedrock-channel incision. Quantitative held assessments of process-based laws are needed to accurately describe landscape uplift and denudation in response to tectonics and climate. We evaluate and calibrate the shear stress (or similar unit stream-power) bedrock-incision model by studying stream profiles in a tectonically active mountain range. Previous work on emergent marine terraces in the Mendocino triple junction region of northern California provides spatial and temporal control on rock-uplift rates. Digital elevation models and field data are used to quantify differences in landscape morphology associated with along- strike northwest to southeast changes in tectonic and climatic conditions. Analysis of longitudinal profiles supports the hypothesis that the study-area channels are in equilibrium with current uplift and climatic conditions, consistent with theoretical calculations of system response time based on the sheer-stress model. Within uncertainty, the profile concavity (theta) of the trunk streams is constant throughout the study area (theta approximate to 0.43), as predicted by the model. Channel steepness correlates with uplift rate. These data help constrain the two key unknown model parameters, the coefficient of erosion (K) and the exponent associated with channel gradient (n). This analysis shows that K cannot be treated as a constant throughout the study area, despite generally homogeneous substrate properties. For a reasonable range of slope-exponent values (n), best-fit values of K are positively correlated with uplift rate. This correlation has important implications for landscape-evolution models and likely reflects dynamic adjustment of K to tectonic changes, due to variations in orographic precipitation, and perhaps channel width, sediment load, and frequency of debris flows. The apparent variation in K makes a unique value of n impossible to constrain with present data.
Sobocinski, R.W., T.E. Cerling, S.J. Morrison, and I.L. Larsen, Sediment Transport in a Small Stream Based On Cs-137 Inventories of the Bed-Load Fraction, Water Resources Research, 26 (6), 1177-1187, 1990.
Solari, L., and G. Parker, The curious case of mobility reversal in sediment mixtures, Journal of Hydraulic Engineering-Asce, 126 (3), 185-197, 2000.
Songfack, P., and R. Rajamani, Hold-up studies in a pilot scale continuous ball mill: dynamic variations due to changes in operating variables, International Journal of Mineral Processing, 57 (2), 105-123, 1999.
In the past experimental studies on mill hold-up were done using tracers and residence time distribution analysis (RTD). In one or two studies the entire content of the mill was weighed after the experimental run. Either as a result of inflexible experimental setup or difficulties in measuring hold-up in closed-circuit industrial mills via the RTD approach, the published correlation between hold-up measurements and mill feed rate disagree with each other. In this study a carefully constructed pilot mill enabled hold-up measurements in real time while the mill was operating. Therefore, extremely accurate hold-up data and transient hold- up data were obtained. In light of this data the correct trends in hold-up as a function of operating conditions are established. Explanations for the observed trends are provided throwing much light on anomalies on previously published data. (C) 1999 Elsevier Science B.V. All rights reserved.
Sorrisovalvo, M., and A.G. Sylvester, The Relationship Between Geology and Landforms Along a Coastal Mountain Front, Northern Calabria, Italy, Earth Surface Processes and Landforms, 18 (3), 257-273, 1993.
The geomorphology of the central Coastal Range, a north south trending horst along the west coast of northern Calabria, is governed largely by major faults, fault scarps and the distribution of principal rock types, as well as by a variety of slope processes operative in a Mediterranean climate. Segments of the major rivers and streams have three principal orientations parallel to major faults in the study area: northwest right-oblique slip faults (oldest); E-W oblique slip faults; NE left-oblique slip faults; and north-south right oblique normal faults (youngest), all of which cut pre-Tertiary metamorphic rocks, Mesozoic limestone, Miocene molasse and calcarenite. Small, underfit alluvial fans, composed chiefly of locally derived debris flow detritus, are present at the mouths of large, west-flowing canyons, some of which reach eastward to the crest of the mountain range. Not only do the north-south normal faults displace rocks and structures of all orientations, but they also make steep scarps in the small alluvial fans and in sediments of the coastal plain. Locally, some of the scarps are buried by recent debris flow deposits. Incipient young rivers utilized the weaknesses along the major faults and cracks as avenues of erosion. Smaller streams and gullies generally flowed westward downflank of the north- trending horst and incised, thereby, deep, V-shaped canyons; some of them have captured older, SW-flowing canyons. Locally, they were guided in other directions where they encountered faults or tectonic fractures. The rocks present a varied resistance to erosion, depending upon the degree of cementation by groundwater salts, upon the orientation of the foliation, and upon the rocks themselves. Thus, mica schist with a relatively flat foliation forms nearly vertical sea cliffs, but the sea cliffs are more gentle where the foliation is steep or dips towards the sea. Therefore, downslope movements are facilitated by seaward slip on foliation, schistosity, bedding and fault surfaces, and are evinced especially by large and deep pre-Holocene landslides (Sackung) in phyllite having areal dimensions up to 2 Km2. Other downslope processes include surficial creep and soil slip, particularly of highly fractured phyllite and schist, block sliding and rock falls.
Springer, G.S., H.S. Dowdy, and L.S. Eaton, Sediment budgets for two mountainous basins affected by a catastrophic storm: Blue Ridge Mountains, Virginia, Geomorphology, 37 (1-2), 135-148, 2001.
On June 27th, 1995, a catastrophic storm generated thousands of slope failures in mountainous portions of Madison County, VA, USA. Within a 129-km(2) area, 16-h rainfall totals reached 775 mm. Using direct field measurements, sediment budgets were constructed for two drainage basins impacted by the event, Teal and Jenkins Hollows. Lengthwise distributions of channel erosion and deposition were examined by taking measurements within incremental 30-m-long channel segments. Comparison of sediment budgets reveals that the two hollows responded very differently to the storm event. These differences are largely due to differences in soil types, failure volumes. and natures of the resulting flows. Within Jenkins Hollow, the kinetic energy of a 4200-m(3). liquefied slope failure scoured the channel of virtually all sediment and vegetation and resulted in a sediment retention rate of 5%. In contrast, slope failures that reached the central channel of Teal Hollow failed to generate a large flow track and erosion features are coupled with deposition features. The sediment retention rate in Teal Hollow was 27%. Single storm denudation rates for the basins exceed the regional 1 ka area-normalized denudation rate of 25.5 mm ka(-1); denudation was 27 mm in Teal Hollow and > 38 mm in Jenkins Hollow. Following catastrophic events, considerable attention has been paid to those channels dramatically modified by debris flows. The high denudation rate for Teal Hollow, attributed to liquefaction of fine-grained soils easily transported as washload, suggests that extremely high denudation rates are possible even in low-order mountainous basins that appear relatively undisturbed by catastrophic storms. (C) 2001 Elsevier Science B.V. All rights reserved.
Stanley, E.H., S.G. Fisher, and N.B. Grimm, Ecosystem expansion and contraction in streams, Bioscience, 47 (7), 427-435, 1997.
Stansby, P.K., and M.A.O. Awang, Response time analysis for suspended sediment transport, Journal of Hydraulic Research, 36 (3), 327-338, 1998.
Stark, C.P., and N. Hovius, The characterization of landslide size distributions, Geophysical Research Letters, 28 (6), 1091-1094, 2001.
Landslide size distributions generally exhibit power-law scaling over a limited scale range. The range is set by the mapping resolution, by the number of observed events, and by the slope failure process itself. This property of self- similarity is an important insight into the physics of hillslope failure. Typically, however, a large proportion of the landslide data does not fit a simple power law. These data are always ignored in order to characterize the scaling. We show that landslide data sets from New Zealand and Taiwan exhibit two scaling regimes, separated by a crossover scale that is purely an artefact of mapping resolution. Below this scale the landslide data are undersampled. We propose a general model for the size distribution of observed landslides which can account for the whole population of mapped slope failures. The model quantifies the undersampling of smaller landslides and provides an improved estimation of the power-la cv scaling of larger landslides. Estimates of this scaling suggest that the area disturbed by landsliding, and perhaps the landslide sediment yield, are essentially dependent on the frequency of smaller landslides. Higher resolution landslide maps will be required in order to quantify these fluxes. Our results also indicate that the probability of extreme landslide events is less than previous studies would predict.
Statzner, B., M.F. Arens, J.Y. Champagne, R. Morel, and E. Herouin, Silk-producing stream insects and gravel erosion: Significant biological effects on critical shear stress, Water Resources Research, 35 (11), 3495-3506, 1999.
Steegen, A., and G. Govers, Correction factors for estimating suspended sediment export from loess catchments, Earth Surface Processes and Landforms, 26 (4), 441-449, 2001.
Sterling, M., and D.W. Knight, Resistance and boundary shear in circular conduits with flat beds running part full, Proceedings of the Institution of Civil Engineers-Water Maritime and Energy, 142 (4), 229-240, 2000.
Stolum, H.H., Planform geometry and dynamics of meandering rivers, Geological Society of America Bulletin, 110 (11), 1485-1498, 1998.
Stover, S.C., and D.R. Montgomery, Channel change and flooding, Skokomish River, Washington, Journal of Hydrology, 243 (3-4), 272-286, 2001.
Analysis of 35 years of cross-section data documents changes in channel width and bed elevation along the Skokomish River, Washington. The bed of the South Fork Skokomish incised over 1 m between 1940 and 1964, although both prior and subsequent to this period the mean bed elevation oscillated as much as 0.8 m with almost no cumulative change. In contrast, the mainstem Skokomish channel bed aggraded nearly 0.5 m between 1939 and 1944, oscillated at amplitudes up to 1 m with little net change from 1945 to 1964, and aggraded over 1.3 m between 1965 and 1997. In the late 1920s, prior to the onset of gaging station records, damming of the North Fork significantly reduced flow in the mainstem Skokomish. From the 1930s to the 1990s, peak discharge data for both the South Fork and the mainstem indicate no net increase in peak flows. Despite the reduced discharge from darn construction in the 1930s and no increase in peak flows during the following years, the frequency of overbank flooding in recent decades has increased on the floodplain of the mainstem. Systematic written descriptions and aerial photographs of the catchment from 1929 to 1992 document land use, including timber harvesting, road construction, and in-channel debris removal. The timing of changes in channel width and elevation imply that debris removal may have triggered periods of degradation and that near-channel and headwater land use potentially elevated the sediment supply to both reaches. Although direct land use causality is difficult to constrain, progressive reduction of channel conveyance in the mainstem as observed in USGS gage height trends does indicate that increased flooding on the mainstem Skokomish River resulted from aggradation, without an increase in peak discharges. (C) 2001 Elsevier Science B.V. All lights reserved.
Sun, Z.L., and J. Donahue, Statistically derived bedload formula for any fraction of nonuniform sediment, Journal of Hydraulic Engineering-Asce, 126 (2), 105-111, 2000.
Sun, T., P. Meakin, and T. Jossang, A computer model for meandering rivers with multiple bed load sediment sizes 1. Theory, Water Resources Research, 37 (8), 2227-2241, 2001.
Surian, N., and E.D. Andrews, Estimation of geomorphically significant flows in alpine streams of the Rocky Mountains, Colorado (USA), Regulated Rivers-Research & Management, 15 (4), 273-288, 1999.
Sutherland, R.A., and R.B. Bryan, Sediment Budgeting - a Case-Study in the Katiorin Drainage- Basin, Kenya, Earth Surface Processes and Landforms, 16 (5), 383-398, 1991.
The primary objective of this study was to compute a detailed budget for a small semiarid tropical drainage basin in Kenya. Results indicated that transfer of sediments ('inputs') from primary source areas was minor in comparison to changes in storage. The major sediment source area within the Katiorin drainage basin was the colluvial hillslope zone. The net change in storage within this zone was approximately 2100 Mg yr-1. Surface wash and rilling were the dominant transport processes responsible for the remobilization of colluvial sediments. Sediment storage within the in-channel reservoir increased by 60 Mg yr-1, which was minor when compared to the total store of sediment in this reservoir. During 1986, the channel network stored only a small fraction (< 3 per cent) of the sediment delivered from the hillslope subsystem. Therefore, the in-channel reservoir had limited influence on sediment conveyance to the basin outlet. These data indicate that a static equilibrium condition cannot be assumed within the Katiorin drainage basin. Such an assumption would result in erosion estimates of approximately 5.5 mm yr-1 for the entire basin (based on a sediment output of 7430 Mg km-2 yr-1 and a measured bulk density of 1.35 Mg m-3). However, this masked the actual rates of 1.2 to 7.1 mm yr-1 in subbasin primary source areas, and rates of 0.6 to 17 mm yr-1 for colluvial material in the various subbasins. The extreme accelerated erosion rates resulted from minimal ground vegetation, steep slopes, soil crust formation, an erodible substrate, and a well-integrated drainage network for rapid conveyance of sediments from the hillslope subsystem to the basin outlet.
Sutherland, R.A., Loss-on-ignition estimates of organic matter and relationships to organic carbon in fluvial bed sediments, Hydrobiologia, 389 (1-3), 153-167, 1998.
Fluvial bed sediments represent an important sink and source for a variety of organic and inorganic compounds. Their most important constituent is organic matter (OM) and its primary component organic carbon (OC). Few studies have been conducted in fluvial environments examining bed-associated OM or OC. This is surprising given the recent interest in global carbon cycling and the importance of bed-associated organics as ecosystem energy sources. The objective of this study was to examine the relationship between OM, determined by loss-on- ignition (LOI), and OC in fluvial bed sediments determined by a dry combustion analyzer. The wide adoption of the LOI method in soil science reflects its ease of use, it is inexpensive, it is rapid, requires no specialized training, and strong statistical relationships commonly exist between OM and OC estimated by standard dry combustion procedures. Regression models were developed between OC and OM for six bed sediment size fractions (less than or equal to 2.0 mm) for 113 sample sites in a tropical stream on Oahu, Hawaii. All models were highly significant (p < 0.0001), with coefficients of determination ranging from 35 to 79%. Measurement of LOI explained 64% of the variation in OC for all grouped data. The black-box LOI approach may be useful for rapid reconnaissance surveys of drainage systems. Examination of OM to OC conversion factors for Manoa bed sediments indicates that values typically observed in the soils literature (1.7-2.2) are far too low. Values of OM/OC were found to increase with increasing grain size, and decrease with increasing LOI percentage. Conversion factors obtained for grouped data had a mean of 14.9, a coefficient of variation of 21%, and a range of values between 6.2 and 27.4. It is suggested that these high conversion factors reflect significant water loss by dehydration of Fe, Al, and Mn oxides at a muffle furnace temperature of 450 degrees C. Therefore, the blind application of conversion factors developed from soils should be avoided when converting from OM to OC for fluvial bed sediments.
Sutherland, R.A., Distribution of organic carbon in bed sediments of Manoa Stream, Oahu, Hawaii, Earth Surface Processes and Landforms, 24 (7), 571-583, 1999.
Organic carbon (OC) associated with fluvial bed sediment plays an important role in biotic and abiotic processes operating within drainage basins. Increasingly, there is a need to characterize storage and spatial distributions of OC in aquatic sediments, particularly under-sampled areas like tropical streams. The objectives of this study were to examine in detail the variation of OC concentration with bed sediment grain size, to characterize the influence of grain size variation on relative OC mass storage, and to compare weighted OC values to those in other aquatic sediments worldwide. The study area selected was a third-order dendritic drainage basin developed in a basaltic complex. Bed sediments along a 6 km section of Manoa Stream were systematically sampled every 50 m for a total of 113 sample site locations. Sediments were partitioned into six size fractions (< 2.0 mm) and OC was determined by dry combustion. Data indicate that the OC concentration increases with decreasing grain size, with the greatest values in the < 0.063 mm (silt + clay) fraction, approximately 4.6 times greater than the very coarse sand fraction (1.00-2.00 mm). Robust smoothing techniques illustrated a general decrease in OC concentration downstream for the size fractions < 0.25 mm. Bed sediments were dominated by size fractions coarser than 0.5 mm (80 per cent of the total distribution) and only about 2 per cent in the fractions less than 0.13 mm. Combining information on OC concentration per size fraction and the mass contribution of each fraction to the whole sample, it was observed that fractions coarser than 0.5 mm had eight to 12 times the storage of OC per kilogram of bed sediments than the fractions finer than 0.13 mm. Weighted OC values for Manoa Stream were on average 6.7 g-OC kg(-1), and these were similar to those reported in the literature for a variety of sediments in aquatic environments, both freshwater and marine. These data provide important information on the relative mass storage of OC in bed sediments and their longitudinal patterns in a tropical fluvial environment. Copyright (C) 1999 John Wiley & Sons, Ltd.
Sutherland, R.A., Bed sediment-associated trace metals in an urban stream, Oahu, Hawaii, Environmental Geology, 39 (6), 611-627, 2000.
act Of the 117 stream and lake systems sampled nationwide, fish from Manoa Stream on Oahu, Hawaii, have consistently shown the highest Pb concentrations. Therefore a detailed study was conducted to examine total metal contents in bed sediments from a 5.8-km stretch of Manoa Stream. A of 123 samples (< 63 mu m) were examined for elements and 14 samples for 21 elements. Selected samples were also examined using different solutions to examine metal phase associations. All trace metal data, computations of enrichment ratios and the modified index of geoaccumulation point to mineralogical control for Cr and Ni; minor anthropogenic contamination for Ba, Cd, Cu, Hg and Zn; and a very strong contamination signal Pb. Maximum Pb contents (up to 1080 mg kg-l) associated with anthropogenic material dumping minor tributaries, storm sewer sediments sediments in the "lower" section of the basin.,Proportionally Pb had the highest non-residual component of elements examined; dominantly in reducible phase associated with Mn and amors Fe oxyhydroxides. The contamination signal typically lowest in the "undisturbed" headwater of the basin (above 5.1 km) with significant increases throughout the "residential" and "comercial-institutional" zones of the mid-basin. The spatial pattern of bed sediment contamination and evidence from storm sewer-outlet sediments strongly indicates that Pb, and to a lesser degree some metals, is still being transported to the stream and the primary agent is soil erosion and port of metals sorbed to sediments. The primary source of sediment-associated metals is coned to be the automobile, though other minor :es can not be ruled out. Abstract Of the 117 stream and lake systems sampled nationwide, fish from Manoa Stream on Oahu, Hawaii, have consistently shown the highest Pb concentrations. Therefore a detailed study was conducted to examine total metal contents in bed sediments from a 5.8-km stretch of Manoa Stream. A total of 123 samples (< 63 mu m) were examined for 18 elements and 14 samples for 21 elements. Selected samples were also examined using different leach solutions to examine metal phase associations. All trace metal data, computations of enrichment ratios and the modified index of geoaccumulation point to mineralogical control for Cr and Ni; minor anthropogenic contamination for Ba, Cd, Cu, Hg and Zn; and a very strong contamination signal for Pb. Maximum Pb contents (up to 1080 mg kg-l) were associated with anthropogenic material dumping in minor tributaries, storm sewer sediments and sediments in the "lower" section of the basin. Proportionally Pb had the highest non-residual component of elements examined; dominantly in the reducible phase associated with Mn and amorphous Fe oxyhydroxides. The contamination signal was typically lowest in the "undisturbed" headwater reach of the basin (above 5.1 km) with significant increases throughout the "residential" and "commercial-institutional" zones of the mid-basin. The spatial pattern of bed sediment contamination and evidence from storm sewer-outlet sediments strongly indicates that Pb, and to a lesser degree some other metals, is still being transported to the stream and the primary agent is soil erosion and transport of metals sorbed to sediments. The primary source of sediment-associated metals is considered to be the automobile, though other minor sources can not be ruled out.
Swan, C.M., and M.A. Palmer, What drives small-scale spatial patterns in lotic meiofauna communities?, Freshwater Biology, 44 (1), 109-121, 2000.
1. Lotic meiofaunal communities demonstrate extremely variable dynamics, especially when viewed at small spatial scales (less than or equal to metres). Given the limited amount of research on lotic meiofauna, we chose to organise our discussion of their small-scale spatial patterns around the dominant factors we believe drive their spatial distributions in streams. We separate scale-dependent effects that structure lotic meiofauna into biotic factors (e.g. predation, food quantity/quality, dispersal) and abiotic factors (e.g. local flow dynamics and substratum characteristics). 2. The impact of predation on the distribution of meiofauna varies with the scale over which predators forage (e.g, fish predation influences meiofauna in different ways and at broader spatial scales than do invertebrate predators), the type of streambed substrata in which the predator-prey interactions occur, and the dispersal ability of different meiofauna. The latter is greatly influenced by predator and prey (meiofauna) interactions with the flow envrironment. 3. Organic matter influences the small- scale distribution of meiofauna in streams. Both its quality as food (as indicated by C:N content, ATP content, or microbial biomass) and its spatial distribution on the streambed, influence meiofauna patchiness, community structure and life history characteristics. As a habitat, the structure that organic matter provides (e.g. wood or leaves) can influence predator-prey interactions, offer materials for case-building and offer refugia during disturbance events - all of which influence the small-scale spatial distribution of meiofauna. 4. Stream flow influences the distribution of meiofauna at broad scales (10s-100s of metres), primarily because of the high susceptibility of meiofauna to passive drift; small-scale interactions between flow and substrata are also important, however, particularly at more localised (less than or equal to metre) scales. At both scales, substratum particle size is important to interstitial-dwelling fauna, influencing the probability of passive drift by meiofauna as well as local microhabitat conditions (e.g. dissolved oxygen; upwelling/ downwelling in the hyporheic zone) and, thus, the small-scale distribution among microhabitats. 5. In general, the processes governing the distribution of meiofauna at small scales cannot be separated entirely from those processes working at larger scales. A conceptual diagram is presented illustrating the relative importance of various factors in influencing the spatial patterns of meiofauna and over what scales these factors act.
Swenson, J.B., V.R. Voller, C. Paola, G. Parker, and J.G. Marr, Fluvio-deltaic sedimentation: A generalized Stefan problem, European Journal of Applied Mathematics, 11, 433-452, 2000.
We present a model of sedimentation in a subsiding fluvio- deltaic basin with steady sediment supply and unsteady base level. We demonstrate that mass transfer in a fluvio-deltaic basin is analogous to heat transfer in a generalized Stefan problem, where the basin's shoreline represents the phase front. We obtain a numerical solution to the governing equations for sediment transport and deposition in this system via an extension of a deforming-grid technique from the phase- change literature. Through modification of the heat-balance integral method, we also develop a semi-analytical solution, which agrees well with the numerical solution, We construct a space of dimensionless groups for the basin and perform a systematic exploration of this space to illustrate the influence of each group on the shoreline trajectory. Our model results suggest that all subsiding fluvio-deltaic basins exhibit a standard autoretreat shoreline trajectory in which a brief period of shoreline advance is followed by an extended period of shoreline retreat. Base-level cycling produces a shoreline response that varies relative to the autoretreat signal. Contrary to previous studies, we fail to observe either a strong phase shift between shoreline and base level or a pronounced attenuation of the amplitude of shoreline response as the frequency of base-level cycling decreases. However, the amplitude of shoreline response to base-level cycling is a function of the basin's age.
Sylvester, B.A., L.S. Garton, and R.L. Autenrieth, Aquatic Sediments, Water Environment Research, 66 (4), 496-531, 1994.
Talling, P.J., and M.J. Sowter, Erosion, deposition and basin-wide variations in stream power and bed shear stress, Basin Research, 10 (1), 87-108, 1998.
Talling, P.J., Self-organization of river networks to threshold states, Water Resources Research, 36 (4), 1119-1128, 2000.
Numerical models in which grid-cells self-organize, so that the shear stress in each cell equals a predetermined threshold value, are remarkably successful in producing the fundamental structure of river networks. Such models are a reasonable approximation of networks characterized by near-constant dimensionless shear stress (tau(*) alpha bed shear stress/bed grain size), with each cell's threshold value being proportional to median-bed grain size. Previous work has shown that this is the case for channels cut into alluvium, and that the characteristic narrow range of tau(*) is different for gravel- and sand-bed channels. Channels in the Italian Apennines that are slowly incising into weak bedrock, but which are covered by a Veneer of gravel for most of the time, are shown to be characterized by the same tau(*) as alluvial gravel-bed channels. Thus threshold models capture the fundamental behavior of many river networks, even in areas of long-term bedrock incision.
Tandon, S.K., B.K. Sareen, M.S. Rao, and A.K. Singhvi, Aggradation history and luminescence chronology of Late Quaternary semi-arid sequences of the Sabarmati basin, Gujarat, Western India, Palaeogeography Palaeoclimatology Palaeoecology, 128 (1-4), 339-357, 1997.
Tate, E.L., and F.A.K. Farquharson, Simulating reservoir management under the threat of sedimentation: The case of Tarbela dam on the River Indus, Water Resources Management, 14 (3), 191-208, 2000.
Tenschert, J., Hdr Test Series-E33.1/2 For Investigation of Contact Condensation Processes in Horizontal Pipes During Emergency Core Cooling Injection, Nuclear Engineering and Design, 154 (1), 1-16, 1995.
Within the framework of phase III of the Germany HDR Safety Program, an experimental facility was planned and built to investigate and simulate contact condensation processes during emergency core cooling injection during loss-of-coolant accidents. In the pressurized water reactors of the Siemens/UB KWU, the emergency core cooling system is based on a simultaneous cold water injection into the cold leg (nozzle inlet) and into the hot leg (so called 'Hutze'). The HDR- E33.1/2 test facility is a single-effect test facility with a pipe 8 m long and 187 mm in diameter, as well as a horizontal cold water inlet via nozzle (diameter, 65 mm). The test series E33.0/1 and E33.2 were carried out in May and September 1990, with large variation of the test parameters, water and steam mass flow rates and the system pressure. Two basically different flow patterns predominated during the tests: stratified flow and plug flow. The immediate area surrounding the nozzle region functioned as the zone of the greatest interaction between the steam and cold water, irrespective of the actual flow pattern. This paper is based on a systematization and first physical evaluation, and reviews the significant results from about 170 HDR tests.
Tewari, A., and A.M. Gokhale, Estimation of three-dimensional grain size distribution from microstructural serial sections, Materials Characterization, 46 (4), 329-335, 2001.
Thompson, A., Secondary Flows and the Pool-Riffle Unit - a Case-Study of the Processes of Meander Development, Earth Surface Processes and Landforms, 11 (6), 631-641, 1986.
Thompson, D.M., E.E. Wohl, and R.D. Jarrett, Revised velocity-reversal and sediment-sorting model for a high-gradient, pool-riffle stream, Physical Geography, 17 (2), 142-156, 1996.
Sediment-sorting processes related to varying channel-bed morphology were investigated from April to November 1993 along a 1-km pool-riffle and step-pool reach of North Saint Vrain Creek, a small mountain stream in the Rocky Mountains of northern Colorado. Measured cross-sectional areas of flow were used to suggest higher velocities in pools than in riffles at high flow. Three hundred and sixteen tracer particles, ranging in size from 16 mm to 256 mm, were placed in two separate pool- riffle-pool sequences and used to assess sediment-sorting patterns and sediment-transport competence variations. Tracer- particle depositional evidence indicated higher sediment- transport competence in pools than in riffles at high flow. Pool-riffle sediment sorting may be created by velocity reversals, and more localized sorting results from gravitational forces along the upstream sloping portion of the channel bed located at the downstream end of pools.
Thompson, D.M., J.M. Nelson, and E.E. Wohl, Interactions between pool geometry and hydraulics, Water Resources Research, 34 (12), 3673-3681, 1998.
An experimental and computational research approach was used to determine interactions between pool geometry and hydraulics. A 20-m-long, 1.8-m-wide flume was used to investigate the effect of four different geometric aspects of pool shape on flow velocity. Plywood sections were used to systematically alter constriction width, pool depth, pool length, and pool exit- slope gradient, each at two separate levels. Using the resulting 16 unique geometries with mea:jured pool velocities in four-way factorial analyses produced an empirical assessment of the role of the four geometric aspects on the pool flow patterns and hence the stability of the pool. To complement the conclusions of these analyses, a two-dimensional computational flow model was used to investigate the relationships between pool geometry and flow patterns over a wider range of conditions. Both experimental and computational results show that constriction and depth effects dominate in the jet section of the pool and that pool length exhibits an increasing effect within the recirculating-eddy system. The pool exit slope appears to force flow reattachment. Pool length controls recirculating-eddy length and vena contracta strength. In turn, the vena contracta and recirculating eddy control velocities throughout the pool.
Thompson, D.M., E.E. Wohl, and R.D. Jarrett, Velocity reversals and sediment sorting in pools and riffles controlled by channel constrictions, Geomorphology, 27 (3-4), 229-241, 1999.
Keller [Keller, E.A,, 1971. Areal sorting of bed-load material: the hypothesis of velocity reversal. Geological Society of America Bulletin 82, 753-756] hypothesized that at high flow, near-bed velocities in pools exceed velocities in riffles and create pool scour. Pools, however, typically have larger cross- sectional areas of flow at bankfull discharge. This condition raises an inconsistency with Keller's velocity reversal hypothesis and the one-dimensional continuity of mass equation. To address this problem, a model of pool maintenance and sediment sorting is proposed that relies on constriction of flow by recirculating eddies and flow divergence over the exit- slopes of pools. According to the model, a narrow zone of high velocity occurs in the center of pools, creating scour. Along the downstream end of pools, an uphill climb of particles up the pool exit-slope promotes sediment deposition. The model is tested with field and flume measurements of velocity, water- surface elevation, and size of bed sediments in recirculating- eddy influenced pools. Local reversals of the water-surface gradient were measured in the field and a velocity reversal was created in the flume. The reversals that were measured indicate higher gradients of the water surface over the upstream portions of pools and higher velocities in pools at high flow. The distribution of bed sediments collected in the field also support the proposed model of pool maintenance. (C) 1999 Elsevier Science B.V. All rights reserved.
Thompson, D.M., Random controls on semi-rhythmic spacing of pools and riffles in constriction-dominated rivers, Earth Surface Processes and Landforms, 26 (11), 1195-1212, 2001.
Average pool spacing between five and seven bankfull widths has been documented in environments throughout the world, but has limited theoretical justification in coarse-bedded and bedrock environments. Pool formation in coarse-bedded and bedrock channels has been attributed to bedrock and boulder constrictions. Because the spacing of these constrictions may be irregular in nature, it is difficult to reconcile pool- formation processes with the supposedly rhythmic spacing of pools and riffles. To address these issues, a simulation model for pool and riffle formation is used to demonstrate that semi- rhythmic spacing of pools with an approximate spacing of five to seven bankfull. widths can be recreated from a random distribution of obstructions and minimum pool- and riffle- length criteria. It is assumed that a pool-riffle couplet will achieve a minimum length based on dominant-discharge conditions. Values for the minimum-length assumption are based on field data collected in New England and California, while the theoretical basis relies on the demonstrated hydraulic response of individual pools to elongation. Results from the simulations show that the location of pools can be primarily random in character, but still assume an average spacing between four and eight bankfull widths for a variety of conditions. Field verification data generally support the model but highlight a highly skewed distribution of pool-forming elements and pool spacing. The relation between pool spacing and bankfull widths is attributed to the common geometric response of these features to dominant-discharge conditions. Copyright (C) 2001 John Wiley & Sons, Ltd.
Thompson, D.M., and K.S. Hoffman, Equilibrium pool dimensions and sediment-sorting patterns in coarse-grained, New England channels, Geomorphology, 38 (3-4), 301-316, 2001.
Pools and riffles are natural bedforms that produce variations in width and depth along channels deemed critical for aquatic habitat. An understanding of this morphology is necessary for the successful design of a reconstructed or restored channel. To better understand pool geometry and sorting characteristics of New England channels, characterizations of pool geometry were performed on 145 different pools strongly influenced by channel constrictions. Characterizations of channel-bed sediments were also performed at 34 of these locations. Data from 120 pools were used in least-squares, multiple-regression analysis with 19 different independent variables to develop prediction equations for pool depth, length, and exit-slope gradient. These equations were then tested using the 25 remaining pools. Eighteen different geometric variables were then used to predict sediment phi (50) values in pool centers, pool exit slopes, and riffles for the subset of 34 samples. The regression analyses for pool geometry indicate that pool depth is significantly influenced to a decreasing degree by pool exit-slope width, constriction gradient, constriction width, drainage area, upstream channel width, and the exit-slope expansion ratio, with an R-2 value of 0.53. Similarly, pool length is influenced by channel gradient, location of the channel constriction, pool width, drainage area and constriction length, with an R-2 value of 0.72. The gradient of pool exit slope is influenced by drainage area, channel gradient, and constriction gradient, with an R-2 value of 0.34. However, R-2 values for exit slope increased to 0.65 when sediment d(50) data were utilized. Using the resulting regression equations to predict dimensions fur the 25 verification pools yields average residuals near zero, although moderate variations do exist. A Tukey-Kramer HSD comparison of the means for sediment phi (50) values indicates pool sediments are significantly coarser than pool exit-slops and riffle sediments for the subset of 34 pools. Regression analyses also suggest significant relations between the size of sediments in pools and riffles and a combination of geometric variables with R-2 values that range from 0.45 to 0.62. The results suggest that pool dimensions are related to basin-wide variability and local hydraulic conditions. The findings also suggest that the characteristics of constrictions and the downstream section of pools provide an important control on scouring and sorting characteristics throughout the pool-riffle morphology. (C) 2001 Elsevier Science B.V. All rights reserved.
Thoms, M.C., A Comparison of Grab-Sampling and Freeze-Sampling Techniques in the Collection of Gravel-Bed River Sediment, Sedimentary Geology, 78 (3-4), 191-200, 1992.
Freeze- and grab-sampling techniques for the collection of bulk sub-surface sediments in gravelly rivers are compared. Data obtained from sampling a substratum of known composition and at over 300 field locations, indicate that grab-sampling underestimates the proportion, by weight, of the fine sediment component but collects representative samples of the coarser gravel component. As a consequence of this sampling bias, the textural characteristics of the composite grab-sample means were significantly different (p < 0.01) from the population means. Grab-samples were coarser, better sorted, had a stronger negative skew and were more leptokurtic by comparison. In contrast, freeze-sampling was shown to be a more accurate and precise technique for collecting bulk sub-surface sediments. One third the number of freeze-samples is required at-a-site in order to obtain representative estimates of all the true textural characteristics of the sediment. All sample estimates were within 10% of population mean values.
Thoms, M.C., and F. Sheldon, Water resource development and hydrological change in a large dryland river: the Barwon-Darling River, Australia, Journal of Hydrology, 228 (1-2), 10-21, 2000.
Thorne, S.D., and D.J. Furbish, Influences of Coarse Bank Roughness On Flow Within a Sharply Curved River Bend, Geomorphology, 12 (3), 241-257, 1995.
Thorne, C.R., C. Alonso, R. Bettess, D. Borah, S. Darby, P. Diplas, P. Julien, D. Knight, L.G. Li, J. Pizzuto, M. Quick, A. Simon, M. Stevens, S. Wang, and C. Watson, River width adjustment. I: Processes and mechanisms, Journal of Hydraulic Engineering-Asce, 124 (9), 881-902, 1998.
Thorne, C.R., C. Alonso, R. Bettess, D. Borah, S. Darby, P. Diplas, P. Julien, D. Knight, L.G. Li, J. Pizzuto, M. Quick, A. Simon, M. Stevens, S. Wang, C. Watson, A. Kovacs, E. Mosselman, L. Schippa, and S. Wiele, River width adjustment. II: modeling, Journal of Hydraulic Engineering-Asce, 124 (9), 903-917, 1998.
Thrift, N., and D. Walling, Geography in the United Kingdom 1996-2000, Geographical Journal, 166, 96-124, 2000.
Tinkler, K.J., Critical flow in rockbed streams with estimated values for Manning's n - Reply, Geomorphology, 25 (3-4), 283-285, 1998.
Tooth, S., and G.C. Nanson, The Geomorphology of Australia Fluvial Systems - Retrospect, Perspect and Prospect, Progress in Physical Geography, 19 (1), 35-60, 1995.
Tooth, S., and G.C. Nanson, Anabranching rivers on the Northern Plains of arid central Australia, Geomorphology, 29 (3-4), 211-233, 1999.
Tooth, S., and G.C. Nanson, The role of vegetation in the formation of anabranching channels in an ephemeral river, Northern plains, arid central Australia, Hydrological Processes, 14 (16-17), 3099-3117, 2000.
As the distribution and abundance of vegetation in drylands is often controlled by the greater availability of water along river channels, riparian vegetation has the potential to influence significantly dryland river form, process and behaviour, This paper demonstrates how a small indigenous shrub, the inland teatree (Melaleuca glomerata), influences the formation and maintenance of anabranching channels in a reach of the ephemeral Marshall River, Northern Plains, arid central Australia. Here, the Marshall is characterized by ridge-form anabranching, where water and sediment are routed through subparallel, multiple channels of variable size which occur within a typically straight channel-train. Channels are separated by channel-train ridges - narrow, flow-aligned, vegetated features - or by wider islands. By providing a substantial element of boundary roughness, dense stands of teatrees growing on channel beds or atop the ridges and islands influence flow velocities, flow depths and sediment transport, resulting in how diversion, bank and floodplain erosion, and especially sediment deposition. Ridges and islands represent a continuum of forms, and their formation and development can be divided into a three-stage sequence involving teatree growth and alluvial sedimentation. (1) Teatrees colonize a flat, sandy channel bed, initiating the formation of ridges by lee-side accretion. Individual ridges grow laterally, vertically and longitudinally and maintain a geometrically similar streamlined (lemniscate) form that presents minimum drag. (2) Individual ridges grow in size, and interact with neighbouring ridges, causing the lemniscate forms to become distorted. Ridges in the lee of other ridges tend to be protected from the erosive effects of floods and survive, whereas individual teatrees or small ridges exposed to flow concentrated between larger ridges, lend to be removed. (3) Ridges lengthen, and coalesce with downstream ridges, eventually subdividing the channel- train into well-defined anabranches. This sequence turns a channel, initially obstructed with dense and chaotic stands of teatrees, into a well-organized system of ridge-form anabranches. In the moderate- to low-gradient Marshall River, which is colonized by an abundance of within-channel vegetation and subject to declining downstream discharges, this helps to minimize flow resistance, thereby maintaining an efficient water and sediment flux. Copyright (C) 2000 John Wiley & Sons, Ltd.
Tooth, S., and G.C. Nanson, Equilibrium and nonequilibrium conditions in dryland rivers, Physical Geography, 21 (3), 183-211, 2000.
Rivers in drylands typically are characterized by extreme flow variability with long periods of little or no flow interspersed with occasional large, sometimes extreme, floods. Complete adjustment of river form and process is sometimes inhibited, resulting in a common assumption that equilibrium conditions may rarely, if ever, exist in dryland rivers, and that transient and unstable (nonequilibrium) behavior is the norm. Examples from the Channel Country and the Northern Plains in central Australia challenge that notion. Along the middle reaches of these intermediate and large, low-gradient rivers, where long duration floods generate moderate to low unit stream powers and boundary resistance is high as a result of indurated alluvial terraces, cohesive muds or riparian vegetation, there is evidence that: (1) channels have remained essentially stable despite large floods; (21 sediment transport discontinuities, while present at a catchment scale, are largely insignificant for channel form and process in individual reaches; (3) there are strong correlations between many channel form and process variables; and (4) many rivers appear to be adjusted to maximum sediment transport efficiency under conditions of low gradient, abundant within-channel vegetation and declining downstream discharge. In these middle reaches, rivers are characterized by equilibrium conditions. However, in the aggradational lower reaches of rivers on the Northern Plains, where upstream terraces are buried by younger sediments and channels are less confined, nonequilibrium conditions prevail. Here, channels sometimes undergo sudden and substantial changes in form during large floods, sediment transport discontinuities are readily apparent, and landforms such as splays remain out-of-balance with normal flows. Hence, dryland rivers can exhibit both equilibrium and nonequilibrium conditions, depending on factors such as catchment size, channel gradient, flood duration, unit stream power, channel confinement, sediment cohesion, and bank strength.
Tooth, S., Process, form and change in dryland rivers: a review of recent research, Earth-Science Reviews, 51 (1-4), 67-107, 2000.
Many of the world's extensive warm dryland regions support numerous, albeit often infrequently flowing, rivers. Dryland rivers are increasingly a focus of scientific and applied interest but empirical research and fluvial theory for drylands need to be strengthened. Recent research in arid central Australia indicates greater diversity in dryland river process, form and change than has hitherto been appreciated, and highlights the need for a global review assessing the present state of knowledge. This review outlines the distinctive characteristics of dryland fluvial environments (hillslope and channel hydrological and sediment transport processes, river pattern and geometry, temporal and spatial aspects of channel change, sedimentary structures and bedforms), many of which contrast with more humid fluvial environments. Although features common to many dryland fluvial environments can be identified (extreme temporal and spatial variability of rainfall, runoff and sediment transport, poor integration between tributary and trunk channels, importance of large floods as a control on channel morphology, lack of equilibrium between process and form), the fluvial diversity that exists within drylands requires recognition of the limitations to these generalisations. In particular, research in central Australia illustrates the need to understand the rivers of this region using empirical relationships, terms, and concepts additional to those defined by earlier work in drylands. Key deficiencies in dryland fluvial research an identified, and relate to three main areas: Limited study of some aspects of modern dryland rivers (floodplain characteristics, influence of vegetation, downstream changes, importance of scale); limited understanding of dryland river behaviour over longer (Cenozoic) timescales; and lack of integration between the results from short-term, process-form studies and studies of the longer term histories of river behaviour. Linking knowledge of past hydrological and channel changes to present-day changes in dryland rivers is suggested as a key research priority. This will help develop a sound theoretical basis for the assessment of future developments in dryland river systems which will contribute to their improved scientific understanding and environmentally sensitive management. (C) 2000 Elsevier Science B.V. All rights reserved.
Tooth, S., Downstream changes in dryland river channels: the Northern Plains of arid central Australia, Geomorphology, 34 (1-2), 33-54, 2000.
Many dryland rivers undergo marked downstream changes owing to factors such as infrequent floods, flow transmission losses, and typically few tributary inflows beyond the headwaters. Along the Sandover, Bundey (Sandover-Bundey) and Woodforde Rivers on the Northern Plains of arid central Australia, downstream channel changes are broadly similar. In upland zones, small, rocky channels transporting sand and gravel gradually increase in size before entering piedmont zones, where channels and narrow floodplains are confined by bedrock. alluvial terraces, or acolian dunes. In lower gradient lowland zones, channels and floodplains remain confined and, in the absence of tributary inflows, channel cross-sectional areas and discharges decrease downstream. Confining landforms are not present in floodout zones, which results in splay formation, increased floodplain widths, and marked overall downstream decreases in cross-sectional areas. Eventually, channelised now and bedload transport terminate, although occasional large floods continue across extensive unchanneled alluvial surfaces termed "floodouts". These broad similarities apart, downstream changes along the three rivers differ in detail. The Sandover is largely a single-thread channel, whereas many reaches of the Sandover-Bundey and Woodforde are anabranched. On the small Woodforde River, downstream decreases in parameters such as cross-sectional area and width are roughly linear. On the larger Sandover and Sandover-Bundey, downstream changes are more irregular, particularly through the floodout zones where there are marked fluctuations in widths, depths and bed slopes. The irregular downstream changes typical of the lower reaches of these large rivers may be due to the reduced influence of vegetation on bankline stability and width adjustment relative to that of smaller rivers. On the Northern Plains, as in other drylands, complex interactions between discharge, sediment transport, slope, patterns of tributary drainage, bank sediment type and vegetation result in variable patterns of downstream channel change. (C) 2000 Elsevier Science B.V. All rights reserved.
Topping, D.J., D.M. Rubin, J.M. Nelson, P.J. Kinzel, and I.C. Corson, Colorado River sediment transport - 2. Systematic bed-elevation and grain-size effects of sand supply limitation, Water Resources Research, 36 (2), 543-570, 2000.
ToroEscobar, C.M., G. Parker, and C. Paola, Transfer function for the deposition of poorly sorted gravel in response to streambed aggradation, Journal of Hydraulic Research, 34 (1), 35-53, 1996.
Trapani, J., Hydrodynamic sorting of avian skeletal remains, Journal of Archaeological Science, 25 (5), 477-487, 1998.
Trayler, C.R., and E.E. Wohl, Seasonal changer in bed elevation in a step-pool channel, Rocky Mountains, Colorado, USA, Arctic Antarctic and Alpine Research, 32 (1), 95-103, 2000.
Scour and fill patterns at East St. Louis Creek, Colorado, were investigated via repeat, detailed surveys of the channel bed at 11 cross sections during the 1995 snowmelt season. Spatial variability was remarkably high, with significant differences in cross section scour and fill patterns over distances as shea as 0.5 m. Most sites had small net changes in bed elevation, both daily and over the entire runoff season. The data and observations indicate the presence of small pulses of fine material that are temporarily deposited on top of the channel pavement in wider areas of the channel and near woody debris complexes. Scour and fill are primarily limited to the finer material of such pulses. ANOVA analysis indicates that although discharge was important in predicting changes in bed elevation, the relationship between discharge and bed mobility is complicated by the effects of local channel morphology and a slight hysteresis. Regression analysis shows that variations in channel width determine where finer sediments are deposited, and therefore the locations of greater change in bed elevation. The proximity of morainal ridges and boulders to the channel edge locally influence the channel width and also the distribution of woody debris complexes. Results of this study suggest that the channel morphology and sediment transport along some reaches of small, high-gradient streams in watersheds with a glacial history may not respond as substantially to changes in discharge characteristic as do other types of alluvial channels.
Tribe, S., and M. Church, Simulations of cobble structure on a gravel streambed, Water Resources Research, 35 (1), 311-318, 1999.
We present a two-dimensional, time independent, kinematic simulation of a gravel streambed that models impacts between clasts as elastic collisions without momentum transfer between discrete, circular disks. The prototype bed forms that we seek to simulate are the "stone cells" observed in Harris Creek, south central British Columbia. The basic algorithm causes simulated stones to cluster into longitudinal structures that resemble such gravel bed forms as imbricate clusters and cluster bed forms. A modified algorithm incorporating programming rules such as stone rotation, entrainment probability inversely proportional to stone size, and the shielding effects of neighbors causes simulated stones to cluster into structures that resemble transverse ribs. Trials incorporating the rotation rule, with or without additional rules, produce a cobble structure most similar to the prototype. Of all the parameters in the simulation, the number of stones seems to have the most control on the development of an extended surface structure.
Trimble, S.W., and A.C. Mendel, The Cow As a Geomorphic Agent - a Critical-Review, Geomorphology, 13 (1-4), 233-253, 1995.
Trimble, S.W., Contribution of stream channel erosion to sediment yield from an urbanizing watershed, Science, 278 (5342), 1442-1444, 1997.
Trimble, S.W., Streambank fish-shelter structures help stabilize tributary streams in Wisconsin, Environmental Geology, 32 (3), 230-234, 1997.
Tsihrintzis, V.A., and E.E. Madiedo, Hydraulic resistance determination in marsh wetlands, Water Resources Management, 14 (4), 285-309, 2000.
Restoration of degraded and creation of constructed wetlands require proper hydraulic design. Of particular importance is the accurate determination of flow resistance factors and the proper use of resistance equations, something essential for computing basic hydraulic parameters, such as depth and velocity, and for modeling the hydrodynamics of the system. In this study, selected previous theoretical, laboratory and field studies on wetlands and vegetated-channel hydraulics are reviewed, and existing data from these studies are extracted and compiled in a common database. Resistance determining parameters are discussed, and results are summarized and presented, aiming at obtaining laws governing the flow, and deriving values for frictional factors under various flow scenarios. Graphs of Darcy-Weisbach f or Manning's n versus appropriate hydraulic parameters are presented. A modified n-VR graph is also presented, appropriate for marsh preliminary hydraulic analyses and design. These graphs also indicate missing information and can guide in future research.
Tubino, M., and G. Seminara, Free Forced Interactions in Developing Meanders and Suppression of Free Bars, Journal of Fluid Mechanics, 214, 131-159, 1990.
Tubino, M., Growth of Alternate Bars in Unsteady-Flow, Water Resources Research, 27 (1), 37-52, 1991.
A theoretical model is formulated to investigate the development of the amplitude of alternate bars in unsteady flows. The problem is tackled by means of a weakly nonlinear analysis developed in a neighborhood of the threshold conditions for bar formation. Bar response to unsteady flow is found to depend on a parameter U-triple-over-dot that is a measure of the ratio between the time scale of the basic flow and the time scale of bar growth. The present theory shows that if U-triple-over-dot is O(1), as often occurs in nature, flow unsteadiness affects the instantaneous growth rate and phase of bar perturbations and controls the final amplitude reached by the bed configuration. A procedure for determining the final amplitude for a given flood event is proposed. Flume experiments were performed to test the main theoretical results. The bed response to unsteady flow was measured for different values of the period of the flood. The observed temporal behavior of the bar amplitude proves to be strongly affected by the unsteady character of the flow for U-triple- over-dot of O(1), as predicted by the theory.
Tubino, M., R. Repetto, and G. Zolezzi, Free bars in rivers, Journal of Hydraulic Research, 37 (6), 759-775, 1999.
In the paper we review some recent work on the mechanics of formation and development of river bars. The emphasis is placed on the instability process which leads to the spontaneous development of bars in almost straight reaches of alluvial rivers. A three dimensional formulation of the problem is presented along with a discussion on the relevant closure relationships. Results of linear and non Linear theories for free bars under bedload dominated conditions are summarised. Furthermore, account is given on the effect bn bar instability induced by suspended load, grain sorting and width variations. Some as yet unpublished:results are also presented.
Tucker, G.E., and R.L. Bras, A stochastic approach to modeling the role of rainfall variability in drainage basin evolution, Water Resources Research, 36 (7), 1953-1964, 2000.
We develop a simple stochastic theory for erosion and sediment transport, based on the Poisson pulse rainfall model, in order to analyze how variability in rainfall and runoff influences drainage basin evolution. Two cases are considered: sediment transport by runoff in rills and channels and particle detachment from bedrock or cohesive soils. Analytical and numerical results show that under some circumstances, rainfall variability can have an impact equal to or greater than that of mean rainfall amount. The predicted sensitivity to rainfall variability is greatest when (1) thresholds for runoff generation and/or particle detachment are significant and/or (2) erosion and transport are strong nonlinear functions of discharge. In general, sediment transport capacity is predicted to increase with increasing rainfall variability. Depending on the degree of nonlinearity, particle detachment capacity may either increase or decrease with increasing rainfall variability. These findings underscore the critical importance of hydrogeomorphic thresholds and other sources of nonlinearity in process dynamics. The morphologic consequences of rainfall variability are illustrated by incorporating the pulse rainfall theory into a landscape simulation model. The simulation results imply that, all else being equal, catchments experiencing a shift toward greater climate variability will tend to have (1) higher erosion rates, (2) higher drainage density (because of increased runoff erosion efficiency), and ultimately (3) reduced relief. The stochastic approach provides a useful method for incorporating physically meaningful climate data within the current generation of landscape evolution models.
Tunnicliffe, J., A.S. Gottesfeld, and M. Mohamed, High resolution measurement of bedload transport, Hydrological Processes, 14 (15), 2631-2643, 2000.
A bedload movement detector of novel design was installed in a gravel-bed stream as a component of the ongoing research on sediment transport dynamics in the Stuart-Takla Experimental Watersheds in north-central British Columbia, Canada, The device is designed to collect information on the patterns and timing of bedload transport during a flood event. The device is based on a passive magnetic sensor that produces signals of 10(-2) to 10(-5) V as its magnetic held is disturbed by passing clasts. A series of 82 sensors is housed in an aluminum beam placed across the stream, inserted such that its surface is flush with the gravel bed. The device can be raised or lowered to compensate for bed aggradation and scour. A data acquisition system gathers voltage signals from the sensors at rates of 30 to 100 Hz. This device is sensitive enough to record the movement of most volcanic, metamorphic, granitic and ultramafic clasts larger than a few millimetres. O'Ne-ell Creek watershed is a 68 km(2) tributary basin of the Middle River drainage system in the northern headwaters of the Fraser River. Bedload transport generally occurs twice a year in the Stuart-Takla streams: once during spring floods and again during salmon spawning activity. Bedload moved only during two days in 1998, at the peak of the relatively small nival food in May. Nevertheless, the device detected at least 3 x 10(6) passing clasts. A continuous record of bedload transport was obtained, showing. a pulsating pattern of activity seemingly independent of stage, lateral movement of the transport zone, and a sudden onset of bed movement with a tapered cessation. We anticipate that more sophisticated calibration of the sensors and accelerated sampling rates will provide detailed information on the size and/or velocity and magnetic permeability of particles moving over the device, and will contribute to a better understanding of bedload transport. Copyright (C), 2000 John Wiley & Sons, Ltd.
Turner, B., Small-Scale Irrigation in Developing-Countries, Land Use Policy, 11 (4), 251-261, 1994.
Urban, D.L., Using model analysis to design monitoring programs for landscape management and impact assessment, Ecological Applications, 10 (6), 1820-1832, 2000.
While ecologists have long recognized the key role of monitoring programs in natural-resource management, we have only recently come to appreciate the logistical difficulties of designing powerful yet efficient schemes for monitoring large, heterogeneous landscapes. Such designs are especially challenging if the signal to be monitored is uncertain, such as in the case of ecosystem response to climate change. I illustrate an approach in which a simulation model is used to design a monitoring scheme that focuses on application-specific sensitivities or uncertainties. Formal model analysis defines these sensitivities in the model's parameter space. These parametric domains are then mapped into geographic space by regressing model sensitivity on terrain variables in a geographic information system. Specific sites for monitoring are then selected by sampling with a two-stage stratified- cluster design from these parametrically sensitive or uncertain locations, As an example, I use a forest simulation model to design a monitoring scheme as part of a climate-change research program in the southern Sierra Nevada of California (USA). I analyze the model to summarize its sensitivity to variation in temperature and precipitation, and then add a consideration of uncertainty due to the influence of topographic convergence on soil moisture-an influence not simulated by the model. Sensitive and uncertain sites are further constrained by logistical concerns about ease of access, resulting in a target sampling domain that represents less than 2% of the study area.
Urban, D.L., C. Miller, P.N. Halpin, and N.L. Stephenson, Forest gradient response in Sierran landscapes: the physical template, Landscape Ecology, 15 (7), 603-620, 2000.
Vegetation pattern on landscapes is the manifestation of physical gradients, biotic response to these gradients, and disturbances. Here we focus on the physical template as it governs the distribution of mixed-conifer forests in California's Sierra Nevada. We extended a forest simulation model to examine montane environmental gradients, emphasizing factors affecting the water balance in these summer-dry landscapes. The model simulates the soil moisture regime in terms of the interaction of water supply and demand: supply depends on precipitation and water storage, while evapotranspirational demand varies with solar radiation and temperature. The forest cover itself can affect the water balance via canopy interception and evapotranspiration. We simulated Sierran forests as slope facets, defined as gridded stands of homogeneous topographic exposure, and verified simulated gradient response against sample quadrats distributed across Sequoia National Park. We then performed a modified sensitivity analysis of abiotic factors governing the physical gradient. Importantly, the model's sensitivity to temperature, precipitation, and soil depth varies considerably over the physical template, particularly relative to elevation. The physical drivers of the water balance have characteristic spatial scales that differ by orders of magnitude. Across large spatial extents, temperature and precipitation as defined by elevation primarily govern the location of the mixed conifer zone. If the analysis is constrained to elevations within the mixed-conifer zone, local topography comes into play as it influences drainage. Soil depth varies considerably at all measured scales, and is especially dominant at fine (within- stand) scales. Physical site variables can influence soil moisture deficit either by affecting water supply or water demand; these effects have qualitatively different implications for forest response. These results have clear implications about purely inferential approaches to gradient analysis, and bear strongly on our ability to use correlative approaches in assessing the potential responses of montane forests to anthropogenic climatic change.
Valdez, R.A., T.L. Hoffnagle, C.C. McIvor, T. McKinney, and W.C. Leibfried, Effects of a test flood on fishes of the Colorado River in Grand Canyon, Arizona, Ecological Applications, 11 (3), 686-700, 2001.
A beach/habitat-building flow (i.e., test flood) of 1274 m(3)/s, released from Glen Canyon Dam down the Colorado River through Grand Canyon, had little effect on distribution, abundance, or movement of native fishes, and only short-term effects on densities of some nonnative species. Shoreline and backwater catch rates of native fishes, including juvenile humpback chub (Gila cypha), flannelmouth suckers (Catostomus latipinnis), and bluehead suckers (C. discobolus), and all ages of speckled dace (Rhinichthys osculus), were not significantly different before and after the flood. Annual spring spawning migrations of flannelmouth suckers into the Paria River and endangered humpback chub into the Little Colorado River (LCR) took place during and after the flood, indicating no impediment to fish migrations. Pre-spawning adults staged in large slack water pools formed at the mouths of these tributaries during the flood. Net movement and habitat used by nine radio-tagged adult humpback chub during the flood were not significantly different from prior observations. Diet composition of adult humpback chub varied, but total biomass did not differ significantly before, during, and after the flood, indicating opportunistic feeding for a larger array of available food items; displaced by the flood. Numbers of nonnative rainbow trout (Oncorhynchus mykiss) < 152 mm total length decreased by similar to8% in electrofishing samples from the dam tailwaters (0-25 km downstream of the dam) during the flood. Increased catch rates in the vicinity of the LCR (125 km downstream of the dam) and Hell's Hollow (314 km downstream of the dam) suggest that these young trout were displaced downstream by the flood, although displacement distance was unknown since some fish could have originated from local populations associated with intervening tributaries. Abundance, catch rate, body condition, and diet of adult rainbow trout in the dam tailwaters were not significantly affected by the flood, and the flood did not detrimentally affect spawning success; catch of young-of-year increased by 20% in summer following the flood. Post-flood catch rates of nonnative fathead minnows (Pimephales promelas) in shorelines and backwaters, and plains killifish (Fundulus zebrinus) in backwaters decreased in the vicinity of the LCR; and fathead minnows increased near Hell's Hollow, suggesting that the flood displaced this nonnative species. Densities of rainbow trout and fathead minnows recovered to pre-flood levels eight months after the flood by reinvasion from tributaries and reproduction in backwaters. We concluded that the flood was of insufficient magnitude to substantially reduce populations of nonnative fishes, but that similar managed floods can disadvantage alien predators and competitors and enhance survival of native fishes.
Valero-Garces, B.L., A. Navas, J. Machin, and D. Walling, Sediment sources and siltation in mountain reservoirs: a case study from the Central Spanish Pyrenees, Geomorphology, 28 (1-2), 23-41, 1999.
Valett, H.M., Surface-Hyporheic Interactions in a Sonoran Desert Stream - Hydrologic Exchange and Diel Periodicity, Hydrobiologia, 259 (3), 133-144, 1993.
Valett, H.M., S.G. Fisher, N.B. Grimm, and P. Camill, Vertical Hydrologic Exchange and Ecological Stability of a Desert Stream Ecosystem, Ecology, 75 (2), 548-560, 1994.
van Geen, A., and S.N. Luoma, The impact of human activities on sediments of San Francisco Bay, California: an overview, Marine Chemistry, 64 (1-2), 1-6, 1999.
This note introduces a set of eight papers devoted to a detailed study of two sediment cores from San Francisco Bay with an overview of the region and a chronology of human activities. Data used in this study to constrain the range of sediment ages at different depths include Th-234,Pb-210, Cs- 137, Pu-239,Pu-240 and Be-10 concentrations in the sediment and the C-14 age of shell fragments. In order of first detectable appearance in the record, the indicators of contamination that were analyzed include PAHs > Hg > Ag, Cu, Pb, Zn > DDT, PCB > foraminiferal Cd/Ca. This study also documents a large memory effect for estuarine contamination caused by sediment mixing and resuspension. Once an estuary such as San Francisco Bay has been contaminated, decades must pass before contaminant levels in surface sediment will return to background levels, even if external contaminant inputs have been entirely eliminated. (C) 1999 Elsevier Science B.V. All rights reserved.
Vandenberg, J.H., Prediction of Alluvial Channel Pattern of Perennial Rivers, Geomorphology, 12 (4), 259-279, 1995.
Vanniekerk, A., K.R. Vogel, R.L. Slingerland, and J.S. Bridge, Routing of Heterogeneous Sediments Over Movable Bed - Model Development, Journal of Hydraulic Engineering-Asce, 118 (2), 246-262, 1992.
Veneziano, D., and J.D. Niemann, Self-similarity and multifractality of fluvial erosion topography 1. Mathematical conditions and physical origin, Water Resources Research, 36 (7), 1923-1936, 2000.
It is suggested that the scaling laws satisfied by fluvial erosion topography and river networks reflect a basic self- similarity or multifractality property of the topographic surface within river basins. By analyzing the symmetries of fluvial topography, we conclude that this self-similarity or multifractality condition should be expressed in a particular way in terms of the topographic increments within subbasins. We then analyze whether selfsimilar or multifractal topographies can be stationary or transient solutions of dynamic evolution models of the type partial derivative h/partial derivative t = U - f{beta, tau}, where U is the uplift rate, f is the fluvial erosion rate, beta is a vector of erodibility parameters, and tau is hydraulic shear stress. The hydraulic stress on a channel bed is assumed to satisfy tau proportional to A(m)S(n), where A is contributing area, S is slope, and m and n are parameters. We allow U to vary randomly in time and beta to vary randomly in space and determine conditions on these random functions as well as the parameters m and n under which the topography may remain in a self-similar or multifractal state. Simulation shows that self-similar states are attractive also for non-self-similar boundary and initial conditions.
Verrecchia, E.P., P. Freytet, J. Julien, and F. Baltzer, The unusual hydrodynamical behaviour of freshwater oncolites, Sedimentary Geology, 113 (3-4), 225-243, 1997.
Verstraeten, G., and J. Poesen, Modelling the long-term sediment trap efficiency of small ponds, Hydrological Processes, 15 (14), 2797-2819, 2001.
Vigilar, G.G., and P. Diplas, Stable channels with mobile bed: Formulation and numerical solution, Journal of Hydraulic Engineering-Asce, 123 (3), 189-199, 1997.
Natural rivers and screams are observed to maintain stable banks while transporting sediment over a central bed region. The development of a numerical model that accounts for this essential feature of natural rivers and streams is discussed in this paper. The model considers the concept of momentum diffusion, and assumes a channel comprising a flat-bed region and two curving bank regions. The resulting boundary stress distribution is such that boundary particles in the flat-bed region are subjected to stresses great enough to put them in motion, while particles in the bank regions are only in a state of incipient motion. It is the combination of this channel geometry and the phenomenon of momentum diffusion that allows for the successful simulation of the ''stable bank, mobile bed'' condition experienced by rivers. While this paper emphasizes the theoretical and numerical aspects of the problem, a companion paper deals with the application and verification of the model. It presents design equations and graphs that can be directly used to obtain channel dimensions, and tests the model against field and laboratory data.
Vigilar, G.G., and P. Diplas, Stable channels with mobile bed: Model verification and graphical solution, Journal of Hydraulic Engineering-Asce, 124 (11), 1097-1108, 1998.
Vincent, S.J., The role of sediment supply in controlling alluvial architecture: an example from the Spanish Pyrenees, Journal of the Geological Society, 156, 749-759, 1999.
Vogel, K.R., A. Vanniekerk, R.L. Slingerland, and J.S. Bridge, Routing of Heterogeneous Sediments Over Movable Bed - Model Verification, Journal of Hydraulic Engineering-Asce, 118 (2), 263-279, 1992.
A one-dimensional numerical model of heterogeneous size-density sediment transport has been developed to simulate the movement of graded sediments in natural and laboratory flow reaches. Predicted temporal and spatial variations in bed and armor- layer grain size distributions, eroded grain size distribution, eroded thicknesses, and total bedload transport rates compare quite favorably to observed variations in flumes, the San Luis canal, Colorado, and the East Fork River, Wyoming, for a large variety of flow scales and flow conditions. The main advantages of this model over others is the high degree of accuracy of model results obtained using only bed and flow variables as input, the treatment of turbulent fluctuations of bed shear stress, the minimization of calibration factors, and the explicit treatment of multiple grain densities. In addition, only the active layer thickness must be calibrated.
Walder, J.S., and A. Fowler, Channelized Subglacial Drainage Over a Deformable Bed, Journal of Glaciology, 40 (134), 3-15, 1994.
Walder, J.S., and J.E. Oconnor, Methods for predicting peak discharge of floods caused by failure of natural and constructed earthen dams, Water Resources Research, 33 (10), 2337-2348, 1997.
Wallbridge, S., G. Voulgaris, B.N. Tomlinson, and M.B. Collins, Initial motion and pivoting characteristics of sand particles in uniform and heterogeneous beds: experiments and modelling, Sedimentology, 46 (1), 17-32, 1999.
Wallbrink, P.J., and A.S. Murray, Determining soil loss using the inventory ratio of excess lead- 210 to cesium-137, Soil Science Society of America Journal, 60 (4), 1201-1208, 1996.
The anthropogenic nuclide Cs-137 is widely used to measure soil movement. However, changes in Cs-137 areal concentrations may not result from soil redistribution alone. There can be considerable variabilty in Cs-137 fallout due to rain shadowing and small-scale runon-runoff processes at the time of deposition. Fallout Pb-210 is also affected by these processes and thus areal concentrations of the two should be correlated. The ratio of fallout (210)pb to (CS)-C-137 reduces variability by up to a factor of two in undisturbed control forest sites at St. Helens, Tasmania. In addition, these two nuclides penetrate to different depths, thereby producing a varying activity ratio with depth, and this gives rise to a new method for determining soil loss. The average inventory ratios of fallout Pb-210 to Cs-137 from plots adjacent to the controls were measured; these had undergone ''normal'' and ''minimal impact'' logging procedures. The average core inventory ratio at the control locations was 2.24 +/- 0.14 (n = 18), compared with means of 0.74 +/- 0.09 (n = 10) and 1.73 +/- 0.29 (n = 10) from the normal and minimal impact sites. The average depth of soil removed from the logged sites was then calculated by comparing these ratios with the inventory activity ratio curve from their respective control sites (40 +/- 6 mm, normal site; 17 +/- 5 mm, minimal site). We concluded that, compared with areal concentrations alone, ratios of fallout nuclides are likely to provide a less randomly variable (and thus more sensitive) method for investigating surface erosion in landscapes where vertical soil mixing is not sufficiently recent to be of concern.
Warburton, J., Observations of Bed-Load Transport and Channel Bed Changes in a Proglacial Mountain Stream, Arctic and Alpine Research, 24 (3), 195-203, 1992.
Warburton, J., and T. Davies, Variability of Bedload Transport and Channel Morphology in a Braided River Hydraulic Model, Earth Surface Processes and Landforms, 19 (5), 403-421, 1994.
This paper investigates variability in bedload transport and channel morphology for 11 replicate experimental runs in an approximately 1:50 braided river model. The experiments, each of 90 h duration, were carried out in a 20 x 3 m tilting flume. All the experiments started with the same initial conditions. Bedload transport was measured at 5 min intervals in a collection drum at the exit from the flume. The model showed reasonable hydraulic similarity when compared to prototype rivers. Results show that mean bedload transport rates for the 11 runs vary in the range 0.98 to 1.49 g s-1 (mean = 1.21, coefficient of variation 11 per cent). Within-run transport rates commonly vary from close to zero, to two and occasionally three or four times the mean rate. Within the bedload series, several irregular phases of transport intensity can be observed, but time series analysis of the data show little underlying serial structure (an AR(2) auto-regressive model is appropriate). Channel patterns are narrow/braided, are established quickly and remain relatively stable throughout the runs, although channel widths increase between 20 and 103 per cent over the 11 runs. Channel behaviour varies from aggradational to transitional between aggradation and degradation. Time-averaged bedload transport rate is weakly correlated with braiding intensity. In general, these results demonstrate that for a given set of controlling variables, bedload transport and channel morphology can be approximately replicated.
Ward, J.V., K. Tockner, P.J. Edwards, J. Kollmann, G. Bretschko, A.M. Gurnell, G.E. Petts, and B. Rossaro, A reference river system for the Alps: The 'Fiume Tagliamento', Regulated Rivers-Research & Management, 15 (1-3), 63-75, 1999.
A major deterrent to a full understanding of the ecological ramifications of river regulation at the catchment scale is a lack of fundamental knowledge of structural and functional attributes of morphologically intact river systems. For example, both the River Continuum and the Serial Discontinuity Concepts, in their original formulations, had the implicit assumption of a stable, single-thread channel from headwaters to the sea. The Flume Tagliamento traverses a course of 172 km from its headwaters in the Italian Alps to the Adriatic Sea. No high dams impede the river's passage as it flows through the characteristic sequence of constrained, braided, and meandering reaches. The Tagliamento, the only large morphologically intact Alpine river remaining in Europe, provides insight into the natural dynamics and complexity that must have characterized Alpine rivers in the pristine state. The Tagliamento has a flashy pluvio-nival regime (mean Q = 109 m(3) s(-1), with flood flows up to 4000 m(3) s(-1)). Thousands of newly-uprooted trees were strewn across the active bed and floodplain along the river's course following a major flood in the autumn of 1996. The active floodplain is up to 2 km wide and contains a riparian vegetation mosaic encompassing a range of successional stages. Up to II individual channels per cross section occur in the braided middle reaches. Islands are a prominent feature of the riverine landscape and island dynamics are postulated to play a key role in determining pattern and process across scales. Future studies will examine the roles of island dynamics and large woody debris in structuring biodiversity patterns of aquatic biota and successional trajectories of riparian vegetation. The high levels of spatiotemporal heterogeneity exhibited by the Flume Tagliamento provide a valuable perspective for regulated river ecologists and those engaged in conservation and restoration. Copyright (C) 1999 John Wiley & Sons, Ltd.
Warren, A., Changing Understandings of African Pastoralism and the Nature of Environmental Paradigms, Transactions of the Institute of British Geographers, 20 (2), 193-203, 1995.
Wathen, S.J., R.I. Ferguson, T.B. Hoey, and A. Werritty, Unequal Mobility of Gravel and Sand in Weakly Bimodal River Sediments, Water Resources Research, 31 (8), 2087-2096, 1995.
Wathen, S.J., T.B. Hoey, and A. Werritty, Quantitative determination of the activity of within-reach sediment storage in a small gravel-bed river using transit time and response time, Geomorphology, 20 (1-2), 113-134, 1997.
Reach-scale sediment storage is rarely quantified in sediment budget studies, yet it has a considerable effect on the sediment delivery ratio at the basin scale, and on the accuracy of morphological methods of bedload estimation at the reach scale. Deployment of magnetic tracer particles allows accurate characterisation of sediment fluxes in gravel-bed rivers and provides the opportunity to quantify storage activity using reservoir theory. Activity was quantified at reach and sub- reach scales in two reaches of a small gravel-bed river and the possibility of quantifying the activity of smaller-scale sediment stores is explored. Reach-scale transit time functions were derived from the cumulative output of sediment against age or time. The shape of the functions in both reaches was determined by flood incidence and magnitude (hydraulics), sediment (tracer) availability, grain size and local morphology. Accurate transit time functions were difficult to determine due to reliance upon tracer output and the associated problems of tracer exhaustion over time and imperfect tracer recovery rates. In addition, if tracers of different ages are allowed to mix (for example where upstream input is possible), then the resultant transit time distributions (age) are not comparable with the timing of the hydraulic processes responsible unless the hydraulic conditions are constant. These results suggest that transit time is difficult to determine from tracer studies in gravel-bed rivers. Consequently, a refinement of transit time, the response time, is introduced and is defined as the time, after the initial input of tracer sediment, when cumulative tracer output exceeds the amount of tracer sediment remaining in storage. Whilst still based upon tracer output, the calculation of response time also utilises storage data and is expressed relative to time since the start of the study rather than age (it is therefore directly comparable with the incidence of hydraulic conditions). This provides a more informative measure of activity which is readily available from tracer data in gravel-bed rivers and allows evaluation of the importance of flood incidence and magnitude, grain size, morphology and reach characteristics/stability. Like transit time, response time estimates are hindered by mixing of sediment of different ages at the sub-reach scale. However, it does account for errors from less than 100% recovery and tracer exhaustion more effectively than transit time. Quantification of absolute and relative size effects in transport is also possible from response time.
Wathen, S.J., and T.B. Hoey, Morphological controls on the downstream passage of a sediment wave in a gravel-bed stream, Earth Surface Processes and Landforms, 23 (8), 715-730, 1998.
Sediment waves in river systems have been widely reported, although few studies have examined the interaction between these waves and the morphology of the reaches through which they pass. This interaction determines how waves are modified as they propagate downstream. This study documents the origin and downstream passage of an avulsion-generated sediment wave through a 374 m study reach of the Allt Dubhaig, Scotland. A nested survey framework was adopted, with volumes calculated from cross-sections spaced between 10 and 40 m apart documenting the origin and downstream passage of the wave. The wave moved through an intensively (c. Im cross-section spacing) monitored 120 m stretch (Reach A) within the study reach, allowing assessment of sediment exchanges between the incoming wave and the local morphology. Successive surveys show the movement of the wave through and out of the reach, and also that areas where wave sediment was deposited did not always correspond with areas of subsequent erosion. Reach A was divided into three morphologically distinct sub-reaches (1A, 2A and 3A) within which sediment fluxes and the three-dimensional distribution of erosion/deposition were estimated. Sediment wave input into 1A and 2A (relatively stable sub-reaches) caused forced bar aggradation and erosion of sediment from elsewhere within the reach, which then became part of the wave. The downstream transfer of this sediment into unstable 3A caused aggradation and, in response, widespread erosion which increased the magnitude of the sediment wave as it exited reach A. Sediment exchange between the recipient reach and the wave depends upon local morphological stability and is a crucial process affecting wave magnitude and attenuation. The macroscale sediment wave interacted with, rather than overwhelmed, the recipient morphology. (C) 1998 John Wiley & Sons, Ltd.
Weir, G.J., One-Dimensional Bed Wave Movement in Lowland Rivers, Water Resources Research, 19 (3), 627-631, 1983.
Welford, M.R., A Field-Test of Tubinos (1991) Model of Alternate Bar Formation, Earth Surface Processes and Landforms, 19 (4), 287-297, 1994.
This study investigates the fluvial dynamics of straight natural stream channels. In particular, this experimental field study quantitatively assesses a physically based non-linear mathematical theory of alternate bar formation under unsteady natural flow conditions within a straight alluvial stream. The study site is an artificially straightened section of the Embarras River located approximately 16 km south of Champaign, Illinois. Data were collected on channel form, gradient, alternate bar dimensions, bed sediment size and flow stage over a 2 year study period. Both linear and non-linear steady flow hydrodynamic theories suggest that alternate bars are critical to the process of meander development. But these theories do not predict bar development for unsteady flow conditions, which typically occur in natural alluvial channels. Tubino (1991) suggests that bar evolution for a flood hydrograph can be divided into three parts: (1) a period of limited bar growth during the rising stage of the flood; (2) a stage of modest bar decay near the peak of the flood; and (3) a stage of non-linear bar growth during the prolonged falling stage of the flood. Bars developed during the falling limb of a hydrograph, and exhibited sequential development rather than the uniform growth along the reach predicted by Tubino's model. As flow stage decreased, short, low, fine-grained bars were superimposed on long, high and coarser-grained bars that developed under preceding high flow stages. These results suggest that the process of bar formation in artificially straightened natural streams with heterogeneous bed material may occur under different flow conditions and in a different manner than predicted by theoretical models. Further work should focus on attempting to isolate the physical mechanisms responsible for alternate bar formation in straight natural streams with heterogeneous bed material and flashy hydrologic flow regimes.
Wharton, G., Flood Estimation From Channel Size - Guidelines For Using the Channel-Geometry Method, Applied Geography, 12 (4), 339-359, 1992.
A fundamental requirement of hydrology is the estimation of flood discharges at ungauged river sites. Although a catchment- based approach has often been used, channel dimensions have been shown to be valid indicators of flood flow characteristics. The channel-geometry method of indirect flood estimation was first developed and applied in the US by the US Geological Survey, but success has also been reported for rivers in New Zealand, northwestern Italy, Britain, Java and Burundi. Channel-geometry equations are developed by relating flood discharges, measured at gauging stations, and channel dimensions, measured from natural river reaches in the vicinity of the gauge. Flood discharges can then be estimated at ungauged locations on natural streams from measurements of channel size. This paper gives guidelines for applying the channel-geometry method and describes the development of channel-geometry equations for British rivers.
Wharton, G., The Channel-Geometry Method - Guidelines and Applications, Earth Surface Processes and Landforms, 20 (7), 649-660, 1995.
All river engineering schemes require flood discharge estimates as part of the design and appraisal process. Unfortunately, continuous measurement of flood discharges is limited to those river sites with instrumented gauging stations, which constitute only a small proportion of channel reaches where information is required. Therefore, considerable research effort has been devoted to the development of reliable indirect techniques of flood discharge estimation. Research on the interrelationship of stream channel geometry and river discharge has provided the basis for an indirect method of hood estimation - the channel-geometry method - which employs river channel dimensions alone to estimate discharge characteristics at ungauged river sites. Channel-geometry equations are developed empirically by relating streamflow data from gauging stations and channel dimensions measured from natural river reaches in the vicinity of the gauge, and take the form of power function relations. Once regional channel-geometry equations have been defined, a channel width or channel capacity measurement is the only variable needed to estimate the flood flow characteristics at a specified river site. The method is useful as an alternative to traditional catchment- based approaches or as a rapid reconnaissance technique. In addition to the application for flood discharge prediction, channel-geometry equations could prove helpful in the management of river channels, first, by providing a basis for assessing local deviations in the channel form-discharge relation, deviations which could be employed as indicators of the sensitivity of particular stretches of river channel to change, and secondly, in the computation of natural channel dimensions for use in river channel design and river restoration.
Whipple, K.X., G. Parker, C. Paola, and D. Mohrig, Channel dynamics, sediment transport, and the slope of alluvial fans: Experimental study, Journal of Geology, 106 (6), 677-693, 1998.
Whipple, K.X., E. Kirby, and S.H. Brocklehurst, Geomorphic limits to climate-induced increases in topographic relief, Nature, 401 (6748), 39-43, 1999.
Recognition of the potential for strong dynamic coupling between atmospheric and tectonic processes has sparked intense cross-disciplinary investigation and debate on the question of whether tectonics have driven long-term climate change or vice versa. It has been proposed that climate change might have driven the uplift of mountain summits through an isostatic response to valley incision. Because isostasy acts to compensate mean elevations, the debate hinges on the question of whether climate change can significantly increase topographic relief or, more precisely, increase the volume of 'missing mass' between summits and ridges. Here we Shaw that, in tectonically active mountain ranges, geomorphic constraints allow only a relatively small increase in topographic relief in response to climate change. Thus, although climate change may cause significant increases in denudation rates, potentially establishing an important feedback between surficial and crustal processes, neither fluvial nor glacial erosion is likely to induce significant isostatic peak uplift.
White, K., Field Techniques For Estimating Downstream Changes in Discharge of Gravel-Bedded Ephemeral Streams - a Case-Study in Southern Tunisia, Journal of Arid Environments, 30 (3), 283-294, 1995.
Whiting, P.J., W.E. Dietrich, L.B. Leopold, T.G. Drake, and R.L. Shreve, Bedload Sheets in Heterogeneous Sediment, Geology, 16 (2), 105-108, 1988.
Whiting, P.J., and W.E. Dietrich, Boundary Shear-Stress and Roughness Over Mobile Alluvial Beds, Journal of Hydraulic Engineering-Asce, 116 (12), 1495-1511, 1990.
Whiting, P.J., and W.E. Dietrich, Convective Accelerations and Boundary Shear-Stress Over a Channel Bar, Water Resources Research, 27 (5), 783-796, 1991.
Alternate bars are important features in alluvial channels as they determine flow and transport patterns. They appear fundamental to selection of meander wavelengths and the geometry of bends. Bend flow has been studied extensively: far less study has been made of flow over alternate bars. Field results from Solfatara Creek, a 5.2-m-wide, 0.2-0.7-m- deep gravel bed channel where flow exits an upstream bend and shoals over a bar in a straight reach, are used to examine patterns of flow and the fluid forces determining the flow field. Large cross-sectional area changes, tied primarily to variation in depth, force large stream-wise accelerations and substantial cross-stream flow off the central bar. The topographically driven downstream and cross-stream accelerations are sufficiently large that their influence upon the balance of forces is of the same order as the pressure gradient and the boundary shear stress. The importance of convective accelerations in the downstream flow equation in this straight reach concurs with bend flow results, but the similar importance of convective accelerations in the cross- stream equation contrasts with results from bend flow. While part of the difference may be attributed to the lower stage conditions herein, in the absence of significant curvature change the cross-stream force balance depends upon the flow going over and around the bar. Local boundary shear stress estimated from the law-of-the-wall and a roughness algorithm decreases out of the upstream bend, increases over the bar top to values approaching the threshold for motion, and then decreases in deeper flow. Strong bed surface coarsening maintains the topography in a stress field that would otherwise lead to planation of the bar top and filling of the deeper regions.
Whiting, P.J., and J.B. Bradley, A Process-Based Classification-System For Headwater Streams, Earth Surface Processes and Landforms, 18 (7), 603-612, 1993.
In this paper we develop a classification system for small headwater streams predicated upon an understanding of the dominant physical processes acting in the channel and its basin, and the conditions under which these processes operate. The variables used to build the classification are hillslope gradient, valley width as compared to channel width, channel gradient, channel depth and sediment size. Using physical laws and morphologic relationships, we recognize domains in which various processes dominate. Channels within the same process domain can be expected to behave in a similar manner in transporting sediment and water and responding to and recovering from basin disturbance, therefore we use the domains to recognize distinct channel types. This classification system provides the foundation for building an approach for identifying basins and streams that are comparably sensitive to landuse.
Whiting, P.J., and W.E. Dietrich, Experimental Constraints On Bar Migration Through Bends - Implications For Meander Wavelength Selection, Water Resources Research, 29 (4), 1091-1102, 1993.
The bed of an initially straight channel often deforms into a series of migrating alternate bars that can cause bank erosion and the development of periodic planform curvature which is often expressed as a meandering channel trace. The planform curvature in turn leads to topography similar to alternate bars, but stationary with respect to the meander. The migration of alternate bars over this steady topography may lead to interactions influencing meander initiation and wavelength selection. We studied these interactions in flume channels with bends of various lengths and angles, and having various width- to-depth ratios. In channels whose wavelength was equal to the length of bars in straight channels (nearly eight channel widths), bars migrated through sine-generated channels with angles up to 10-degrees. The critical bend angle was smaller for channels of longer wavelength and smaller width-to-depth ratio. Migration was nonuniform, and bars temporarily stalled when in phase with the curvature-induced topography, leading to amplification of the topography. Flow against an opposing bank can lead to such a strong boundary shear stress divergence that migration of the bars is prevented because sediment that otherwise would have led to bar migration is scoured from the bar front. We propose that the amplification of bar-pool topography in bends where free alternate bars are stalled enhances scour of the bank which leads to selection of a meander wavelength equal to that of the alternate bars.
Whiting, P.J., J.F. Samm, D.B. Moog, and R.L. Orndorff, Sediment-transporting flows in headwater streams, Geological Society of America Bulletin, 111 (3), 450-466, 1999.
The equilibrium alluvial stream channel has a geometry that allows it to pass the water and sediment supplied from the watershed, At the same time, the equilibrium alluvial channel is built and maintained by the flows and sediment delivered to it. A prerequisite fur understanding the creation of the equilibrium channel is an understanding of the sediment conveyance and competence of the Rows the channel receives. This study describes the bed-load transport regime as it is linked to hydrology and geomorphology in 23 headwater gravel- bed streams in snowmelt-dominated parts of central and northern Idaho. At sites, drainage areas range from 1.29 to 381 km(2), stream gradients range from 0.0042 to 0.0747, and median bed surface particle sizes range from 4 to 207 mm, Stream architecture includes riffle-pool, planar, and step-pool beds. The bed load is much finer than the surface and subsurface material, suggesting selective transport of the finer sizes. Nonetheless, the majority of the load is sand at all now discharges. Progressively coarser sediment was collected as now discharge increased, and painted rock experiments documented the transport of coarser particles at higher discharges, The supply of sediment to the streams appears limited, as indicated by observed clockwise hysteresis in bed-load transport rates during each spring snowmelt and by the coarse surface armor observed at sites, Flows above bankfull discharge move 37% of the bed load, whereas Bows between mean annual discharge and bankfull move 57% of the bed load. The bed-load effective discharge has a recurrence interval that averages 1.4 yr and the magnitude of effective discharge averages 80% of bankfull discharge. The recurrence interval of bankfull discharge averages 2.0 yr, The ratio of effective discharge to bankfull discharge is independent of basin size, grain size, and gradient, although the ratio increases with the relative magnitude of large infrequent events.
Whiting, P.J., and D.B. Moog, The geometric, sedimentologic and hydrologic attributes of spring-dominated channels in volcanic areas, Geomorphology, 39 (3-4), 131-149, 2001.
In volcanic areas of Idaho, Oregon and Montana, a number of perennial streams emerge from single springs or zones of springs. Surface drainage areas to these springs can be very small, often much smaller than the recharge area of the springs. Channels downstream of springs are often straight, or if sinuous, without regularity to the pattern. Bars are absent or poorly defined, but islands or downed timber are common in the channel. Channel width-to-depth ratios are large relative to those of runoff-dominated channels. Downstream hydraulic geometry exponents are similar, but the exponents for width and velocity are greater in spring-dominated channels. Manning roughness values are relatively large. The bedsurface in gravel-bed spring-dominated streams is armored. Computations indicate that bed material is probably capable of moving at bankfull stage. The hydrograph of spring-dominated streams is damped as compared to runoff-dominated streams locally and elsewhere. Peak flows occur months after precipitation or snowmelt. Mean annual flow for spring-dominated streams averages 72% of the flood with a recurrence interval of 2 years; the mean annual flow for runoff-dominated channels averages 18% locally and 25% elsewhere. The 50-year flood averages 1.6 times the 2-year flood on the annual series while the corresponding value for runoff-dominated channels in the region is 2.5. The damped hydrograph of spring-dominated streams suggests that they are somewhat different from runoff- dominated channels in the relationship between water and sediment. In spring-dominated channels, 34% of sediment is transported by flows above the 2-year flood-less than is observed typically in runoff-dominated channels. The effective discharge is similar in magnitude to the 2-year flood. (C) 2001 Elsevier Science B.V. All rights reserved.
Whittaker, J.G., and M.N.R. Jaeggi, Origin of Step-Pool Systems in Mountain Streams, Journal of the Hydraulics Division-Asce, 108 (6), 758-773, 1982.
Wicks, J.M., and J.C. Bathurst, SHESED: A physically based, distributed erosion and sediment yield component for the SHE hydrological modelling system, Journal of Hydrology, 175 (1-4), 213-238, 1996.
SHESED is introduced as a physically based, spatially distributed erosion and sediment yield component for the existing SHE hydrological modelling system, for use at the catchment scale. For hillslopes (represented spatially by the SHE grid square network) SHESED simulates soil erosion by raindrop impact, leaf drip and sheet overland flow (without rilling), and the transport of the eroded material by overland flow. For channels the component simulates the erosion of bed material and the downstream transport of this material together with that supplied by overland flow, In the channel sediment routing procedure it is assumed that the flow can carry any available load of fine sediments (less than 0.062 mm in diameter) but for coarser sediments the load is; limited by the calculated capacity transport rate of the how. The channel component also allows for bed armouring. Application of SHESED to rainfall-induced sediment yield events at two agricultural catchments (areas 5.1 and 6.4 ha) in Iowa shows generally good reproduction of the observed temporal variations in sediment yield. Application to a 3.3 km reach of the East Fork River, Wyoming, for a 37 day period shows good reproduction of observed sediment discharge magnitudes but some discrepancy in the timing of the simulated sediment discharge peak.
Wijdenes, D.J.O., and R. Bryan, Gully-head erosion processes on a semi-arid valley floor in Kenya: A case study into temporal variation and sediment budgeting, Earth Surface Processes and Landforms, 26 (9), 911-933, 2001.
A three year monitoring programme of gully-head retreat was established to assess the significance of sediment production in a drainage network that expanded rapidly by gully-head erosion on the low-angled alluvio-lacustrine Njemps Flats in semi-arid Baringo District, Kenya. This paper discusses the factors controlling the large observed spatial and temporal variation in gully-head retreat rates, ranging from 0 to 15 m a(-1). The selected gullies differed in planform and in runoff- contributing catchment area but soil material and land use were similar. The data were analysed at event and annual timescales. The results show that at annual timescale rainfall amount appears to be a good indicator of gully-head retreat, while at storm-event timescale rainfall distribution has to be taken into account. A model is proposed, including only rainfall (P) and the number of dry days (DD) between storms: Retreat = 0.22(DD x P-0.5) + 2.9 which explains 56 per cent of the variation in retreat rate of the single-headed gully of Lam1. A detailed sediment budget has been established for Lam1 and its runoff-contributing area (RCA). By measuring sediment input from the RCA, the sediment output by channelized flow and linear retreat of the gully head for nine storms, it can be seen that erosion shifts between different components of the budget depending on the duration of the dry period (DD) between storms. Sediment input from the RCA was usually the largest component for the smaller storms. The erosion of the gully head occurred as a direct effect of runoff falling over the edge (GH(waterfall)) and of the indirect destabilization of the adjacent walls by the waterfall erosion and by saturation (GH(mass/storage)). The latter component (GH(mass/storage)) was usually much larger that the former (GH(waterfall)). The sediment output from the gully was strongly related to the runoff volume while the linear retreat, because of its complex behaviour, was not. Overall, the results show that the annual retreat is the optimal timescale to predict retreat patterns. More detailed knowledge about relevant processes and interactions is necessary if gully-head erosion is to be included in event-based soil erosion models. Copyright (C) 2001 John Wiley & Sons, Ltd.
Wilcock, P.R., Methods For Estimating the Critical Shear-Stress of Individual Fractions in Mixed-Size Sediment, Water Resources Research, 24 (7), 1127-1135, 1988.
Wilcock, P.R., and J.B. Southard, Experimental-Study of Incipient Motion in Mixed-Size Sediment, Water Resources Research, 24 (7), 1137-1151, 1988.
Wilcock, P.R., and J.B. Southard, Bed-Load Transport of Mixed Size Sediment - Fractional Transport Rates, Bed Forms, and the Development of a Coarse Bed Surface-Layer, Water Resources Research, 25 (7), 1629-1641, 1989.
Wilcock, P.R., Flow Competence - a Criticism of a Classic Concept, Earth Surface Processes and Landforms, 17 (3), 289-298, 1992.
Wilcock, P.R., and B.W. McArdell, Surface-Based Fractional Transport Rates - Mobilization Thresholds and Partial Transport of a Sand-Gravel Sediment, Water Resources Research, 29 (4), 1297-1312, 1993.
Wilcock, P.R., Critical Shear-Stress of Natural Sediments, Journal of Hydraulic Engineering-Asce, 119 (4), 491-505, 1993.
Wilcock, P.R., Estimating local bed shear stress from velocity observations, Water Resources Research, 32 (11), 3361-3366, 1996.
Wilcock, P.R., A.F. Barta, C.C. Shea, G.M. Kondolf, W.V.G. Matthews, and J. Pitlick, Observations of flow and sediment entrainment on a large gravel-bed river, Water Resources Research, 32 (9), 2897-2909, 1996.
Wilcock, P.R., G.M. Kondolf, W.V.G. Matthews, and A.F. Barta, Specification of sediment maintenance flows for a large gravel- bed river, Water Resources Research, 32 (9), 2911-2921, 1996.
Wilcock, P.R., Entrainment, displacement and transport of tracer gravels, Earth Surface Processes and Landforms, 22 (12), 1125-1138, 1997.
Wilcock, P.R., and B.W. McArdell, Partial transport of a sand/gravel sediment, Water Resources Research, 33 (1), 235-245, 1997.
Wilcock, P.R., The components of fractional transport rate, Water Resources Research, 33 (1), 247-258, 1997.
Wilcock, P.R., Two-fraction model of initial sediment motion in gravel-bed rivers, Science, 280 (5362), 410-412, 1998.
Wilcock, P.R., Comment on "Effects of hydraulic roughness on surface textures of gravel-bed rivers" and "Effects of sediment supply on surface textures of gravel-bed rivers" by John M. Buffington and David R. Montgomery, Water Resources Research, 37 (5), 1525-1526, 2001.
Wilcox, B.P., B.D. Newman, D. Brandes, D.W. Davenport, and K. Reid, Runoff from a semiarid ponderosa pine hillslope in New Mexico, Water Resources Research, 33 (10), 2301-2314, 1997.
Willetts, B., Aeolian and fluvial grain transport, Philosophical Transactions of the Royal Society of London Series a-Mathematical Physical and Engineering Sciences, 356 (1747), 2497-2513, 1998.
Willetts, B.B., G. Pender, and I.K. McEwan, Experiments on the transport of graded sediment, Proceedings of the Institution of Civil Engineers-Water Maritime and Energy, 130 (4), 217-225, 1998.
Four large-scale experiments are reported on the transport of graded sediments in a straight channel in the domain of partial sediment mobility (in which not all size fractions are fully mobile). Particular attention is paid to the influence of sediment introduced near the head of the experimental channel in inbank and overbank flows, respectively. In addition to sediment transport rate, the composition and texture of the bed and the composition of the bed load were measured at intervals. The differences in sediment behaviour between the inbank and overbank flows tested were unexpectedly small; however, the input of sediment near the head of the channel changed the sediment mobility profoundly. Transport rate was suppressed ahead of a wave of material that propagated through the channel. This suggests that the artificial introduction of sediment changed the near-bed flow structure for more than 15m downstream, impairing the transporting capacity of the stream. The observed changes of surface composition and texture imply that a complex grain structure is laid down during the recession of sediment-transporting flows in the field, and this structure is important for prediction of subsequent sediment behaviour. Better understanding of the near-bed processes and, particularly, the role of the bed condition will have to be assembled before significantly more reliable prediction methods can be made available. However, awareness of the factors that limit the accuracy of present methods is valuable in deploying those factors, and this paper contributes to such awareness.
Williams, G.P., River Meanders and Channel Size, Journal of Hydrology, 88 (1-2), 147-164, 1986.
Willis, R., B.A. Finney, M. McKee, and A. Militello, Stochastic-Analysis of Estuarine Hydraulics .1. One Dimensional Steady Flow, Stochastic Hydrology and Hydraulics, 3 (2), 71-84, 1989.
Wing, M.G., R.F. Keim, and A.E. Skaugset, Applying geostatistics to quantify distributions of large woody debris in streams, Computers & Geosciences, 25 (7), 801-807, 1999.
Large woody debris (LWD) strongly influences morphology and aquatic habitat in streams within forested watersheds. Previous studies have used data to describe spatial distributions of LWD in qualitative terms. We used high-resolution spatial data collected from a forested stream in western Oregon to conduct three geostatistical analyses. The data were collected at five time periods prior to and following the addition of LWD into the stream. Each analysis is examined for its potential and shortcomings in quantifying distributions. Our findings indicate that semi-variograms, when used with a raster spatial data structure, can be useful quantitative descriptions of LWD distributions. (C) 1999 Elsevier Science Ltd. All rights reserved.
Wishart, M.J., The terrestrial invertebrate fauna of a temporary stream in southern Africa, African Zoology, 35 (2), 193-200, 2000.
Wohl, E.E., Bedrock Benches and Boulder Bars - Floods in the Burdekin Gorge of Australia, Geological Society of America Bulletin, 104 (6), 770-778, 1992.
The Burdekin Gorge of northeastern Australia lies within the seasonal tropics and is characterized by high discharge variability. Slackwater sediments and paleostage indicators in the gorge record seven large floods that have occurred during the past 1,200 yrs. These floods range in magnitude from 11,000 to 30,000 m3s-1 and are characterized by large downstream variations in hydraulics. The floods generate high values of velocity, boundary shear stress, and stream power per unit area. Downstream fluctuations in these variables help to explain the location of boulder bars, high flood levees, small- scale erosional features in the bedrock, and the formation of inner channels. Boulder bars and flood levees form where shear stress and stream power decrease due to channel widening. Small-scale erosional features, such as potholes and troughs, are best developed at sites of channel constriction and associated increases in shear stress and stream power. The development of the inner channel appears to be controlled by complex interactions between bedrock lithology and structure, and by flow hydraulics. All of the channel features are related to the hydraulics of large floods, which therefore are the dominant controls on many aspects of channel morphology in this bedrock gorge.
Wohl, E.E., Gradient Irregularity in the Herbert Gorge of Northeastern Australia, Earth Surface Processes and Landforms, 17 (1), 69-84, 1992.
The seventy-kilometre-long Herbert Gorge of northeastern Australia preserves a record of past floods in slackwater deposits and palaeostage indicators. Step-backwater modelling of water-surface profiles indicates that discharges ranging from 11 000 to 17 000 m3s-1 have occurred six times in the gorge during the last 900 years. These flood reconstructions provide insight into the role of extreme flows in shaping bedrock channel morphology. In particular, the hydraulics of extreme flows can be related to boulder transport, and to the location of large boulder bars. Large boulder bars occur throughout the Herbert Gorge, being best developed at loci of stream power minima along the inside of bends, at tributary junctions, and at obstructions in the channel caused by bedrock highs. Only the flows exceeding approximately 8000 m3s-1 are competent to transport the boulders which constitute the bars. In the straight channel reaches, the boulder accumulations and bedrock highs have a fairly regular spacing which appears to be independent of lithologic or structural controls. The bars provide an efficient means of energy dissipation, and they are interpreted as a result of the inherent high turbulence of flow in a steep channel. The regular spacing of the bars, and their correspondence with the hydraulics of large flows, suggest that the bars and associated bedrock highs may represent a self- regulating mechanism akin to the pool-riffle sequence of alluvial channels. It may therefore be appropriate to view bedrock channels as deformable on the timescale of extreme discharges.
Wohl, E.E., Bedrock Channel Incision Along Piccaninny Creek, Australia, Journal of Geology, 101 (6), 749-761, 1993.
Wohl, E.E., D.J. Anthony, S.W. Madsen, and D.M. Thompson, A comparison of surface sampling methods for coarse fluvial sediments, Water Resources Research, 32 (10), 3219-3226, 1996.
In order to characterize variability associated with sampling coarse fluvial sediment, surface grain-size distributions were characterized at eight sample sites within gravel- to boulder- bed channels. Four methods were used: (1) a random walk, (2) a sampling grid spaced at an interval equal to the intermediate diameter of the largest clast in the sampling area, (3) a sampling grid spaced at one half the interval of method 2, and (4) a randomly chosen subsection within which a patch count of most clasts at least partially exposed at the surface was conducted. At each site, six replicates of each method were performed, with each replicate consisting of 100 clasts. Sampling was performed by a single operator at six of the sites and by multiple operators at two of the same sites and at two additional sites. The research objectives were to characterize variability among replicates of a method, among methods, and among operators. Sample sites were divided into relatively well sorted (inclusive graphic standard deviation <1.4) and poorly sorted (greater than or equal to 1.5). The first three methods produce statistically indistinguishable values of D-50 and D-84 for both well-sorted and poorly sorted sites when performed by a single operator. Multiple operators may produce statistically different population measures (D-50, D-84, sample distributions, and variance) using any of the four methods at either type of site. Because of operator-induced variability, we caution against direct comparisons of grain-size distributions between channels or within a single channel through time if more than one operator performs the sampling.
Wohl, E., S. Madsen, and L. MacDonald, Characteristics of log and clast bed-steps in step-pool streams of northwestern Montana, USA, Geomorphology, 20 (1-2), 1-10, 1997.
The role of log and clast steps was studied in 53 step-pool reaches in 32 streams in northwestern Montana. In each reach, 20 consecutive steps were sampled. Drainage areas ranged from 0.5 to 11.5 km(2). Mean step spacing was found to be proportional to channel gradient, width of the bankfull channel, and drainage area; mean step height was proportional to the width of the channel. No significant difference exists between clast and log steps with regard to step spacing and step height. This suggested either that (1) woody debris is mobile in even the smallest channels in the study area, or (2) channel flows arrange clast steps around immobile woody debris. Calculations of theoretical entrainment and transport of sediment suggest that the coarse clasts forming steps are capable of being entrained at bankfull discharge in most channels. The presence of immobile log steps (composed of living roots) in the upstream reaches, an increase in the percentage of log steps with gradient, and a decrease in this percentage with the width of the bankfull channel and drainage area, imply that woody debris is mobile primarily in the downstream reaches. Calculations of flow resistance suggest that most steps serve to maximize flow resistance. These results support the second hypothesis, that the height and spacing of clast steps are adjusted around immobile log steps to maintain consistent step characteristics.
Wohl, E.E., and H. Ikeda, The effect of roughness configuration on velocity profiles in an artificial channel, Earth Surface Processes and Landforms, 23 (2), 159-169, 1998.
In order to determine the effect of bed roughness on velocity distribution, we used seven different configurations of bed roughness, with 16 test runs of varying discharge and slope for each configuration. For each run, one-dimensional velocity profiles were measured at 1 cm vertical increments over the crest of the roughness element, and at intervals of 4.25 cm downstream. Results indicate that velocity profile shape remains fairly constant for a given slope and roughness configuration as discharge increases. As slope increases, the profiles become less linear, with a much larger near-bed velocity gradient and a more pronounced velocity peak close to 0.6 flow depth at the measurement point immediately downstream from the roughness element, The zone of large near-bed velocity gradients increases in both length and depth as roughness concentration decreases, up to a length/height ratio of about 9, at which point maximum flow resistance occurs. Longitudinal roughness elements do not create nearly as much flow resistance as do transverse elements. Rates of velocity increase suggest that roughness elements spaced at a length/height ratio of about 9 are most effective at creating flow resistance over a range of discharges in channels with steeper slopes. (C) 1998 John Wiley & Sons, Ltd.
Wohl, E.E., D.M. Thompson, and A.J. Miller, Canyons with undulating walls, Geological Society of America Bulletin, 111 (7), 949-959, 1999.
Channels incised into cohesive substrates commonly develop undulating walls characterized by regular repetitive variations in channel width. Canyons with undulating walls are found in a variety of lithologic, climatic, and tectonic regimes, and are most commonly present downstream from a knick zone of active incision. Flume experiments and natural channel morphologic patterns lead us to infer that wall undulations are the remnants of breached, offset potholes or of sinuous longitudinal grooves formed during incision of the knick zone. Substrate characteristics seem to have little influence on these undulations. Using measurements from eight channels incised into the Navajo Sandstone of southern Utah, me found that intact rock strength, rock-mass strength, joint orientation and spacing, bedding, and porosity did not differ significantly between channel reaches with straight walls, undulating walls, and meanders. The wavelength and amplitude of wall undulations also did not correlate with any substrate characteristic. These results lead us to conclude that the primary control on formation of undulating walls is hydraulic processes. Along the study channels, deep, narrow reaches with undulating walls alternate with wider straight or meandering reaches. Using flume simulations and one- and two-dimensional hydraulic modeling, we found that the wall undulations act to reduce interreach (spatial) variability in energy expenditure, and to minimize energy expenditure within a reach. We propose that the wall undulations and flow hydraulics create a feedback whereby the wall undulations are preserved following knickpoint incision. The wall undulations then act to regulate downstream energy expenditure in a manner analogous to bedforms. This implies that generalized principles of uniform energy expenditure developed for alluvial channels may also apply at the reach scale to bedrock channels with relatively homogeneous substrates.
Wohl, E.E., and D.M. Thompson, Velocity characteristics along a small step-pool channel, Earth Surface Processes and Landforms, 25 (4), 353-367, 2000.
This paper summarizes measurements of velocity along three reaches of a small mountain channel with step-pool bedforms. A one-dimensional electromagnetic current meter was used to record velocity fluctuations at 37 fixed measurement points during five measurement intervals spanning the peak of the annual snowmelt hydrograph. Measurement cross-sections were located upstream from a bed-step, at the step lip, downstream from the step, and in a uniform-gradient run. Data analyses focused on characteristics of velocity profiles, and on correlations between velocity characteristics and the potential control variables bedform type, reach gradient and flow depth. To test the hypothesis that velocity characteristics are related to channel bedform types, ANOVA and ANCOVA tests were performed for the average velocity and coefficient of variation of point velocity data. Results indicate that high frequency velocity variations correlate to some degree with both channel characteristics and discharge. Velocity became more variable as stage increased, particularly at low-gradient reaches with less variable bed roughness. Velocity profiles suggest that locations immediately downstream from bed-steps are dominated by wake turbulence from mid-profile shear layers. Locations immediately upstream from steps, at step lips, and in runs are dominated by bed-generated turbulence. Adverse pressure gradients upstream and downstream from steps may be enhancing turbulence generation, whereas favourable pressure gradients at steps are suppressing turbulence. The bed-generated turbulence and skin friction of runs appear to be less effective energy dissipators than the wake-generated turbulence and form drag of step-pool bedforms. Copyright (C) 2000 John Wiley & Sons, Ltd.
Wohl, E.E., Substrate influences on step-pool sequences in the Christopher Creek drainage, Arizona, Journal of Geology, 108 (1), 121-129, 2000.
Step-pool sequences formed in alluvial and bedrock channel segments of the Christopher Creek drainage in central Arizona suggest that bedform geometries may reflect subtle differences in relative substrate resistance and in the ratio of driving forces to resisting forces. Three alluvial channel segments and two bedrock channel segments along a 72-km(2) drainage and a 4- km(2) drainage facilitated comparison across different substrates and hydraulic environments. As substrate resistance increased or the ratio of hydraulic driving forces and boundary resisting forces decreased, channel gradient increased, the ratio of step height to length normalized by gradient decreased, and pool dimensions normalized by gradient decreased. These changes in bedform geometry suggest that as the ratio of driving to resisting forces increases, proportionally more flow energy is dissipated within the flow as turbulence and shearing (as in the alluvial reaches) rather than being applied to erosion of the channel boundaries (as in the bedrock reaches).
Wohl, E.E., and D.A. Cenderelli, Sediment deposition and transport patterns following a reservoir sediment release, Water Resources Research, 36 (1), 319-333, 2000.
A reservoir sediment release on the North Fork Poudre River supplied similar to 7000 m(3) of silt- to pebble-sized sediment to an originally boulder bed channel. Deposition along the 12 km of channel downstream from the reservoir occurred primarily in pools. During the subsequent snowmelt hydrograph, sediment was progressively scoured from the upstream and then the downstream pools. Initial sediment reworking in the pools created a deep, narrow thalweg scoured to the original pool bed, with additional sediment deposition in lateral eddies. Continued reworking reduced but did not completely remove these eddy deposits. The channel became supply-limited with respect to finer grain-sized fractions (clay to medium sand) first at upstream and then at downstream sites and eventually became supply-limited with respect to coarser grain-sized fractions (coarse sand to pebbles). Bedload transport rates at a site were strongly linked to the depletion of sediment stored in upstream pools. Magnitude, duration, and sequence of flows were all important controls on bedload transport and return of the channel to its prerelease state.
Wohl, E.E., and D.M. Merritt, Bedrock channel morphology, Geological Society of America Bulletin, 113 (9), 1205-1212, 2001.
Wolman, M.G., Play - the Handmaiden of Work, Earth Surface Processes and Landforms, 20 (7), 585-591, 1995.
Wondzell, S.M., and F.J. Swanson, Floods, channel change, and the hyporheic zone, Water Resources Research, 35 (2), 555-567, 1999.
We investigated the influence of flood-induced channel changes on the hyporheic zone of 4th- and 5th-order reaches of a mountain stream network. Preflood versus postflood comparisons were made in three study reaches from well networks established before and reestablished after a major flood. Flood effects were scale dependent and varied with channel constraint and the dominant channel forming process. Large changes were observed in unconstrained stream reaches where channel incision drove large changes in subsurface flow paths and the extent of the hyporheic zone. However, subreach scale differences were apparent. In the lower portion of the studied reach, channel incision lowered the water table, leading to abandonment of secondary channels, and decreased the extent of the hyporheic zone that previously extended more than 30 m into the floodplain. In contrast, the extent of the hyporheic zone increased at the head of the studied reach where channel incision steepened head gradients through a meander bend. In another unconstrained reach, lateral channel jumps dramatically altered exchange flow paths. However, the extensive hyporheic zone was maintained throughout the reach. Less change was observed in the constrained stream reach where both the depth and area of sediment available to be reworked by the flood were limited by bedrock constraining the width of the valley floor. This flood dramatically changed the hyporheic zone at the three study sites and these physical changes are expected to be biologically important, considering the role of the hyporheic zone in stream ecosystem processes.
WoodSmith, R.D., and J.M. Buffington, Multivariate geomorphic analysis of forest streams: Implications for assessment of land use impacts on channel condition, Earth Surface Processes and Landforms, 21 (4), 377-393, 1996.
Multivariate statistical analyses of geomorphic variables from 23 forest stream reaches in southeast Alaska result in successful discrimination between pristine streams and those disturbed by land management, specifically timber harvesting and associated road building. Results of discriminant function analysis indicate that a three-variable model discriminates 10 disturbed from 13 undisturbed reaches with 90 per cent and 92 per cent correct classification respectively. These variables are the total number of pools per reach, the ratio of mean residual pool depth to mean bankfull depth, and the ratio of critical shear stress of the median surface grain size to bankfull shear stress. The last variable can be dropped without a decrease in rate of correct classification; however, the resulting two-variable model may be less robust. Analysis of the distribution of channel units, including pool types, can also be used to discriminate disturbed from undisturbed reaches and is particularly useful for assessment of aquatic habitat condition. However, channel unit classification and inventory can be subject to considerable error and observer bias. Abundance of pool-related large woody debris is highly correlated with pool frequency and is an important factor determining channel morphology. Results of this study yield a much needed, objective, geomorphic discrimination of pristine and disturbed channel conditions, providing a reference standard for channel assessment and restoration efforts.
Worman, A., and R. Olafsdottir, Erosion in a Granular Medium Interface, Journal of Hydraulic Research, 30 (5), 639-655, 1992.
If stratified soil structures are not designed according to conventional filter criteria, a flow of ground water may erode and transport an underlying, finer material through the pore system of the coarser stratum above. A constitutive equation for interfacial transport rate is derived from physical principles and verified through laboratory experiments. The relationship is incorporated in a mathematical formulation for interfacial erosion processes analogous to the one commonly applied to alluvial streams. Both analysis and experiments indicate that interfacial erosion depends strongly on variation in the grain size ratio between the two strata and the porosity of the coarser stratum. A simulation example demonstrates a case in which the core in an earth-fill dam is subjected to overflow and the crest of the core is eroded.
Worman, A., Incipient Motion During Static Armoring, Journal of Hydraulic Engineering-Asce, 118 (3), 496-501, 1992.
Worman, A., and S.L. Xu, Stochastic analysis of internal erosion in soil structures - Implications for risk assessments, Journal of Hydraulic Engineering-Asce, 127 (5), 419-428, 2001.
Wright, A., W.A. Marcus, and R. Aspinall, Evaluation of multispectral, fine scale digital imagery as a tool for mapping stream morphology, Geomorphology, 33 (1-2), 107-120, 2000.
Multispectral digital imagery acquired from Soda Butte and Cache Creeks, Montana and Wyoming was used in conjunction with field data to classify and map hydrogeomorphic stream units on four stream reaches. The morphologic units that were field mapped were eddy drop zones, glides, low gradient riffles, high gradient riffles, lateral scour pools, attached bars, detached bars, and large woody debris. Unsupervised and supervised classifications of the imagery were used to develop a Maximum Joint Probability classification and an Alternative Joint Probability classification of the stream reaches. The Maximum Joint Probability classification allowed only one of the image classes to represent each hydrogeomorphic unit on the field map and resulted in relatively low overall accuracies for identification of these units of 10% to 50%. The Alternative Joint Probability classification allowed each image class to represent any geomorphic unit where the probability of a correct classification was greater than random. In this technique, two or three image classes were assigned to represent each hydrogeomorphic unit, resulting in higher overall accuracies of 28% to 80%. Accurate classification of hydrogeomorphic units was hampered by poor rectification of imagery with the field maps because of inadequate ground control points. In general, the largest hydrogeomorphic units were most accurately classified, whereas units that were small in area or spatially linear were least likely to be accurately classified. The results of this study demonstrated that multispectral digital imagery has the potential to be a useful tool for mapping hydrogeomorphic stream units at fine scales. Imagery to be an effective tool, however, careful measures such as accurate documentation of ground control points must be taken to ensure accurate rectification of the imagery with field maps. (C) 2000 Elsevier Science B.V. All rights reserved.
Wu, W.M., and S.S.Y. Wang, Movable bed roughness in alluvial rivers, Journal of Hydraulic Engineering-Asce, 125 (12), 1309-1312, 1999.
Wu, W.M., S.S.Y. Wang, and Y.F. Jia, Nonuniform sediment transport in alluvial rivers, Journal of Hydraulic Research, 38 (6), 427-434, 2000.
Wu, J.X., H.T. Shen, and C.Y. Xiao, Sediment classification and estimation of suspended sediment fluxes in the Changjiang Estuary, China, Water Resources Research, 37 (7), 1969-1979, 2001.
Wyzga, B., River Response to Channel Regulation - Case-Study of the Raba River, Carpathians, Poland, Earth Surface Processes and Landforms, 18 (6), 541-556, 1993.
Processes induced by the channelization of the Raba River in the present century are examined to illustrate the response of a gravel-bed stream following narrowing and straightening of its channel. Up to 3 m of incision has occurred. The change from a slow and relatively steady degradation in the lower reaches to separate degradation events in the higher reaches is attributed to the differential rate of headcut retreat and to the control exerted by mid-channel bars upon the rate of river- energy dissipation. Progressive outwashing of finer grains from bed material has followed the diminishing sediment yield of the basin and the increase in stream power. The ensuing growth in mean grain size and changes in sediment fabric have increased boundary resistance to flow and reduced particle susceptibility to entrainment. Downstream magnification of peak discharges has become increasingly pronounced with the advancing incision. The decrease in flood-plain storage and self-acceleration of flows passing the relatively deep and straight channel has caused flood waves to become progressively more flashy in nature. An increase in channel depth and reduction in gradient caused by downward and backward erosion, as well as bed material coarsening has promoted the re-establishment of an equilibrium. Conversely, flow velocity increases due to flow concentration in the deepened channel. Reduction in grain mobility allows the river to attain a new equilibrium at flow-velocity and stream- power levels higher than before the channelization. Numerous disadvantages of the applied regulation scheme and its failure to reduce flood hazard raise the question of its maintenance. To be successful, any regulation design must take into account changes in sediment supply and flood hydrographs resulting from the simultaneous alterations in basin management.
Wyzga, B., A geomorphologist's criticism of the engineering approach to channelization of gravel-bed rivers: Case study of the Raba River, Polish Carpathians, Environmental Management, 28 (3), 341-358, 2001.
River engineers use sediment transport formulas to design regulated channels in which the river's ability to transport bedload would remain in equilibrium with the delivery of materials from upstream. In gravel-bed rivers, a number of factors distort the simple relationship between particle size and hydraulic parameters at the threshold of sediment motion, inherent in the formulas. This may lead to significant errors in predicting the bedload transport rates in such streams and hence to instability of their regulated channels. The failure to recognize a nonstationary river regime may also result in unsuccessful channelization. Rapid channel incision has followed channelization of the main rivers of the Polish Carpathians in the 20th century. A case study of the Raba River shows that incision has resulted from the increase in stream power caused by channelization and the simultaneous reduction in sediment supply due to variations in basin management and a change in flood hydrographs. Calculations of bedload transport in the river by the Meyer-Peter and Muller formula are shown to have resulted in unrealistic estimates, perhaps because the different degree of bed armoring in particular cross-sections was neglected. It would have been possible to avoid improper channelization if the decreasing trend in sediment load of the Carpathian rivers had been recognized on the basis of geomorphological and sedimentological studies. Allowing the rivers to increase their sinuosity, wherever possible without an erosional threat to property and infrastructure, and preventing further instream gravel mining are postulated in order to arrest channel incision and reestablish the conditions for water and sediment storage on the floodplains.
Xu, J.X., Underlying gravel layers in a large sand bed river and their influence on downstream-dam channel adjustment, Geomorphology, 17 (4), 351-359, 1996.
Due to the changes in environmental factors during a river's historical development, underlying gravel layers are found in many large plain rivers. When the buried depth of this gravel layer is within the reach of down-cutting by clear water scour after reservoir construction, it may be exposed and exert a far-reaching influence on channel adjustment. In Hanjiang River, the longest tributary of the Yangtze River in China, down-cutting has been greatly reduced and even stopped, due to the total change of bed material composition. The exposure of a gravel layer results in a dramatic increase in the bed's hydraulic roughness, so the channel slope may increase after a decline during the period prior to the exposure of the gravel layer. Moreover, the exposed gravel layer increases the erosion resistance of bed material, making a lower relative erosion resistance of bank to bed material. Where the bank's erosional resistance is weak, this may lead to a tendency towards channel widening.
Xu, J.X., Study of sedimentation zones in a large sand-bed braided river: an example from the Hanjiang River of China, Geomorphology, 21 (2), 153-165, 1997.
The concept of sedimentation zone is applied to the study of spatial and temporal variations of mid-channel bars in the middle Hanjiang River, a large sand-bed braided river in China. The river channel can be divided into alternating sedimentation zones and transport zones, the formation of which is basically controlled by local channel boundary conditions such as natural and artificial bank controls (bedrock outcrops, local hill spurs, terraces, artificial dikes and influence of tributaries). A systematic comparison between sedimentation and transport zones is made in this study, including the flow shear stress, stream power, mid-channel bar features and channel stability. The results obtained indicate that different channel boundary conditions in sedimentation and transport zones control channel width and width-depth ratio, which in turn control the reach's hydraulic and sediment transport characteristics. The storage and removal of sediment in sedimentation zones correspond to the increase and decrease of the degree to which mid-channel bars develop. When the sediment input of the channel system is altered by reservoir construction, the bed-load sediment historically accumulated is released by clear water scour, thus a macroscopic bed-load 'wave' forms and moves gradually downstream. Associated with this is the complex response phenomenon of mid-channel bar evolution. (C) 1997 Elsevier Science B.V.
Yang, J.C., and E.L. Hsu, Time-Line Interpolation For the Solution of the Dispersion- Equation - Reply, Journal of Hydraulic Research, 29 (4), 571-572, 1991.
Yang, J.C., and K.P. Chiu, Use of Characteristics Method With Cubic Interpolation For Unsteady-Flow Computation, International Journal For Numerical Methods in Fluids, 16 (4), 329-345, 1993.
The specified-time-interval (STI) scheme has been used commonly in applying the method of characteristics (MOC) to unsteady open-channel flow problems. However, with the use of STI scheme, the numerical error for the simulation results can always be induced due to the interpolation used to approximate the characteristics trajectory. Hence, in order to remedy the numerical errors caused by the interpolation, one needs to seek some kind of interpolation technique with higher-order accuracy. Instead of the linear interpolation technique, which has been used very commonly and can induce serious numerical diffusion, the Holly-Preissmann two-point method, which is a cubic interpolation technique with fourth-order of accuracy, is proposed here to integrate with the method of characteristics for the computation of one-dimensional unsteady flow in open channel. The concept of reachback and reachout in space and time directions for the characteristics is also introduced to assure the model stability. The computed results from this new model are compared with those computed by using the Preissmann four-point scheme and the multimode method of characteristics with linear interpolation.
Yang, M.S., and K.T. Lee, Determination of probability distributions for Strahler stream lengths based on Poisson process and DEM, Hydrological Sciences Journal-Journal Des Sciences Hydrologiques, 46 (5), 813-824, 2001.
Yee, L.Y., and H.K. Miyamoto, Improvement of Flow in Final Settling Tanks - Discussion, Journal of Environmental Engineering-Asce, 120 (3), 713-715, 1994.
Yeh, K.C., S.J. Li, and W.L. Chen, Modeling Non-Uniform-Sediment Fluvial Process By Characteristics Method, Journal of Hydraulic Engineering-Asce, 121 (2), 159-170, 1995.
This paper presents a numerical model based on a multimode characteristics method for fully coupled simulation of water and sediment movement in mobile-bed alluvial channels with nonuniform bed materials. Along with the characteristics, the temporal evolutions of flow depth and velocity, bed elevation, and bed-material composition of a well-defined river reach with proper boundary conditions can be simultaneously determined. From the results of the test runs, the proposed model provides useful information about the interactions among disturbance waves of different orders of magnitude and their influence on the formation of flow field, bed topography, and bed-material composition. Such information cannot be easily obtained from finite-difference methods.
Yen, C.L., S.Y. Chang, and H.Y. Lee, Aggradation-Degradation Process in Alluvial Channels, Journal of Hydraulic Engineering-Asce, 118 (12), 1651-1669, 1992.
The effects of sediment size gradation sigma(i) and sediment loading ratio m on the aggradation-degradation process and related flow characteristics in an alluvial channel were investigated experimentally. Three different size gradations of sediment were used. For each gradation, experiments were carried out for four different sediment loading conditions, namely, initial equilibrium, overloading, underloading, and clear water. Hydraulic characteristics, sediment transport rates, and gradations were measured during experiments. A linear model of sediment transport under overloading and underloading conditions was developed. Experimental results show that with nonuniform sediment, the aggradation-degradation cycle is found to be irreversible. Under a given loading ratio, speeds of the aggradation wave and degradation wave increase with increasing sigma(i) and with decreasing m. The recovery ratios of bed elevation and bed slope decrease as sigma(i) increases. Regression relations have also been derived from the experimental data obtained.
Yetton, M.D., Progress in understanding the paleoseismicity of the central and northern Alpine Fault, Westland, New Zealand, New Zealand Journal of Geology and Geophysics, 41 (4), 475-483, 1998.
Radiocarbon dates from trenching of the Alpine Fault trace at Crane Creek, between the Haupiri and Ahaura Rivers, demonstrate the last earthquake rupture at this location occurred between AD 1480 and 1645, with associated local river aggradation and terrace formation. A second trench 6 km farther north at Ahaura gives the same radiocarbon age for the last event. An enlarged record of radiocarbon ages for aggradation terraces and landslides in central and north Westland has a group of dates which are a reasonable match to the date range from the trenching. While this is compatible with regional aggradation and landsliding associated with an Alpine Fault earthquake during this period, this type of data cannot be used to demonstrate the dates were synchronous or coseismic. However, historical earthquakes have shown that, in steep forested terrain, an earthquake causes extensive forest mortality, with a corresponding synchronous period of regeneration. Recent information of forest age in Westland indicates two such periods in the last 600 yr, and the most recent of these reflects the earthquake rupture recorded in the trenches. This implies the earthquake occurred at the young end of the trench date range at c. AD 1600-1650.
Young, K.A., Riparian zone management in the Pacific Northwest: Who's cutting what?, Environmental Management, 26 (2), 131-144, 2000.
In the Pacific Northwest (PNW) of North America, forestry practices during the last century have degraded the ecological linkages between riparian forests and streams. In an attempt to protect the integrity of lotic ecosystems and associated fisheries resources (primarily anadromous Pacific salmon, Oncorhynchus so.), regional governments now restrict timber harvest in riparian forests. I summarize and assess the riparian zone management guidelines of the states of California, Oregon, and Washington (USA) and the province of British Columbia (Canada). Only Oregon and British Columbia protect fish-bearing streams with "no-harvest" zones, and only the wider (20-50 m) no-harvest zones for larger fish-bearing streams in British Columbia are likely to maintain near-natural linkages between riparian and stream ecosystems. All four jurisdictions protect most streams with "management zones" of variable width, in which timber harvest activities are restricted. All the management zone guidelines permit the harvest of the largest conifers from riparian forests and will, if applied over a series of timber harvest rotations (60-80 years), result in the continued removal of potential sources of large woody debris from the region's watersheds. All four jurisdictions require additional protection for streams and watersheds that are severely degraded or (in the United States) contain threatened or endangered species. The governments of the PNW have taken a "manage until degraded, then protect" approach to riparian forest management that is unlikely to maintain or restore the full suite of riparian-stream linkages necessary for lotic ecosystems to function naturally at the stream, watershed, basin, or regional scale.
Yu, B., and M.G. Wolman, Some Dynamic Aspects of River Geometry, Water Resources Research, 23 (3), 501-509, 1987.
Yu, G., and D.W. Knight, Geometry of self-formed straight threshold channels in uniform material, Proceedings of the Institution of Civil Engineers-Water Maritime and Energy, 130 (1), 31-41, 1998.
Zaghloul, N.A., Hydraulic exponents M and N for gravity flow pipes, Advances in Water Resources, 21 (3), 185-191, 1998.
Mathematical expressions are derived for the hydraulic exponents M and N as functions of the gradually varied flow (GVF) depth using a circular channel section. The derived expressions of M(y/d(0)) and N(y/d(0)) for continuously varying depth are compared to exponents M and N proposed by Chow [Chow, V.T., Integrating the equation of gradually varied flow. ASCE, Proc. 81, Vol. 11, 1955] using constant averaged GVF depths. The exponent N shows a remarkable difference (an opposite trend). The computation of the GVF length is calculated using the exponents M and N for varying and constant averaged GVF depths. Numerical integration approach based on the Simpson's rule method is used to calculate the GVF length. The results of the calculated GVF profile length using the derived exponents M(y/d(0)) and N(y/d(0)) are found to be closer to the GVF length calculated from the exact formulation of the GVF dynamic equation. The percentage difference ranges from 0.017 to 6.9% for various bed slopes and GVF depth limits. Using the Chow [ibid.] constant exponents M and N, the calculated GVF length resulted in a wider values with a percentage difference ranges from 1.2 to 130%. Hence, a remarkable improvement of the computation of GVF profile length is achieved using the derived M(y/d(0)) and N(y/d(0)) exponents.
Zanre, D.D.L., and D.J. Needham, On the Hyperbolic Nature of the Equations of Alluvial River Hydraulics and the Equivalence of Stable and Energy Dissipating Shocks, Geophysical and Astrophysical Fluid Dynamics, 76 (1-4), 193-222, 1994.
The depth-averaged hydraulic equations augmented with a suitable bed-load sediment transport function form a closed system which governs the one-dimensional flow in an alluvial river or channel. In this paper, it is shown that this system is hyperbolic and yields three families of shock-wave solutions. These are determined to be temporally stable in restricted regions of the (H, F-0)-plane, via the Lax shock inequalities. Further, it is demonstrated that this criterion is equivalent to the energy dissipation criterion developed by Needham and Hey (1991).
Zanre, D.D.L., and D.J. Needham, On simple waves and weak shock theory for the equations of alluvial river hydraulics, Philosophical Transactions of the Royal Society of London Series a-Mathematical Physical and Engineering Sciences, 354 (1721), 2993-3054, 1996.
This paper considers the hydraulic equations governing alluvial river dynamics. The shock-wave classes for this system were described and fully analysed by Needham & Hey (1991). The complementary expansion wave classes are determined in this paper. In addition, more general simple waves are considered and a weak-shock theory is established. This is used to consider several practical examples, including the dynamics of dredged river sections, the propagation of sediment slugs and the effects of sediment blocking and extraction.
Zeff, M.L., Salt marsh tidal channel morphometry: Applications for wetland creation and restoration, Restoration Ecology, 7 (2), 205-211, 1999.
The morphometry of tidal channels in a back-barrier salt marsh in New Jersey was investigated. Characteristics of the tidal channel drainage network plan form (order, bifurcation ratio, length, sinuosity) and cross section channel form (width:depth ratio, hydraulic geometry) are compared with data from other studies. Drainage patterns follow Horton's Law of Stream Numbers and Law of Stream Lengths. Mitigation sites should be designed in accordance with these laws. The degree to which site-specific substrate, vegetation, and flow conditions constrain or facilitate the development of sinuous, meandering channel reaches should be estimated to provide information for the design of tidal channel geometries and dimensions that will accommodate predicted discharges. Drainage networks in created and restored wetlands should reflect the spatial distribution of width and depth properties (width:depth ratios, cross- sectional areas, longitudinal slopes, hydraulic geometry) found in similar natural systems. Reproducing these characteristics will lessen the practice of oversizing channels. Hydraulic geometry relationships can facilitate the sizing of channels at Atlantic coast salt marsh mitigation sites. Recommendations are given to promote the development of drainage networks that function like the coastal back-barrier Avalon/Stone Harbor marsh in New Jersey.
Zeng, W., and M.B. Beck, Development and evaluation of a mathematical model for the study of sediment-related water quality issues, Water Science and Technology, 43 (7), 47-54, 2001.
A mathematical model (Sediment-Transport-Associated Nutrient Dynamics - STAND) has been developed for the study of sediment- associated water quality issues. The model is intended to simulate changes of water composition associated with sediment behavior. It has a 3-level structure. The first level accounts for the hydraulics of open-channel flow. The second computes sediment transport potential and actual rates based on the information provided by the first level. A non-equilibrium approach is used. In the third level, changes of nutrient concentrations along a studied river are computed with the consideration of nutrient transport, adsorption/desorption, and release. In order to calibrate the model, field data were collected from the Oconee River, a major tributary of the Altamaha River in Georgia, USA. Two stations, approximately 17 km distant from each other, were established along the river for the purpose of data collection. Observations of the river's hydraulics, suspended sediment, and water quality (mainly orthophosphate, nitrate, temperature, specific conductivity, oxidation-reduction potential, dissolved oxygen, and pH) were collected at the two stations. Another data set collected along a major tributary of the Yellow River in China was also used for calibration of the model's hydraulics and sediment transport parts. Calibration and validation results are encouraging, which suggests STAND may be a useful tool for the thorough study and understanding of nutrient dynamics associated with sediment behaviour.
Zhang, H., and R. Kahawita, Nonlinear Hyperbolic System and Its Solutions For Aggraded Channels, Journal of Hydraulic Research, 26 (3), 323-342, 1988.
Zhang, H., and R. Kahawita, Linear Hyperbolic Model For Alluvial Channels, Journal of Hydraulic Engineering-Asce, 116 (4), 478-493, 1990.
Zhang, S.Y., I. Cordery, and A. Sharma, A volume law for specification of linear channel storage for estimation of large floods, Water Resources Research, 36 (6), 1535-1543, 2000.
Zhu, J.C., C.J. Gantzer, R.L. Peyton, E.E. Alberts, and S.H. Anderson, Simulated Small-Channel Bed Scour and Head Cut Erosion Rates Compared, Soil Science Society of America Journal, 59 (1), 211-218, 1995.
Concentrated-flow erosion is often a major part of cropland erosion. The concentrated-Bow processes of bed scour and head cut need improved characterization to better predict and prevent erosion. This study was conducted to compare the erosion rates due to simulated small-scale bed-scour (Db) and head-cut (Db) processes. A 6.4-m-long by 0.15-m-wide hydraulic flume was used to simulate concentrated-flaw erosion on five Midwestern soils: Barnes (fine-Loamy, mixed Udic Haploboroll), Forman (fine-loamy, mixed Udic Argiboroll), Mexico (fine, montmorillonitic, mesic Udollic Ochraqualf), Sharpsburg (fine, montmorillonitic, mesic Typic Argiudoll), and Sverdrup (sandy, mixed Udic Haploboroll). For slopes of 1.5, 3.5, and 5.0%, Bow rates of 3.78, 5.67, 7.65, 11.34, and 15.12 L min(-1) were used to provide a range from low (0.5 Pa) to moderate (2.5 Pa) shear stresses (tau). Soil detachment rates are functions of slope, flow rate, and shear stress. Slope, how, their squares, and the slope X flow interaction were highly significant predictors of Db. Only flow, its square, and its interaction with slope were significant predictors of Dh. Nonlinear power regressions using tau as an independent variable were better predictors of detachment than simple linear regressions. Erodibility for the soils from this study does not relate well with soil erodibility calculated using the Universal Soil Loss Equation. Differences in the slope and intercept of detachment vs. tau exist among soils. The value of D-h was at least four times greater than D-b for all soils at equal slope and flow rate, indicating that head cutting is the main process of detachment for the conditions tested.
Ziegler, A.D., R.A. Sutherland, and T.W. Giambelluca, Partitioning total erosion on unpaved roads into splash and hydraulic components: The roles of interstorm surface preparation and dynamic erodibility, Water Resources Research, 36 (9), 2787-2791, 2000.
Field rainfall simulation experiments at two sites are used to partition sediment transport on unpaved roads into splash and hydraulic erosion components. Rain splash processes contributed 38-45% of total sediment output, with instantaneous contributions being variable throughout 60-min high-energy events. For low- and medium-magnitude rainstorms, splash erosion on roads is initially controlled by the removal of easily erodible material, followed by a dramatic reduction in sediment output associated with limited detachment from the resistant, highly compacted road surface. A conceptual model explaining temporal variations in splash and hydraulic erosion as functions of prestorm surface preparation (via traffic, maintenance, and mass wasting processes) is presented. For situations where loose sediment is readily available, rain splash energy is less important to sediment detachment. If the loose layer is diminished (e.g., following an overland flow event) or protected by a surface crust, splash energy is needed to detach material from the road surface. Equations in most physically based erosion models do not predict temporal variations in road sediment transport that result from the removal of a loose surface layer of finite depth. A strategy that successfully treats this removal as changes in road erodibility is introduced.
Ziemer, R.R., J. Lewis, R.M. Rice, and T.E. Lisle, Modeling the Cumulative Watershed Effects of Forest Management Strategies, Journal of Environmental Quality, 20 (1), 36-42, 1991.
There is increasing concern over the possibility of adverse cumulative watershed effects from intensive forest management. It is impractical to address many aspects of the problem experimentally because to do so would require studying large watersheds for 100 yr or more. One such aspect is the long- term effect of forest management strategies on erosion and sedimentation and the resultant damage to fish habitat. Is dispersing activities in time and space an effective way to minimize cumulative sedimentation effects? To address this problem, Monte Carlo simulations were conducted on four hypothetical 10 000-ha fifth-order forested watersheds: one watershed was left undisturbed, one was completely clearcut and roaded in 10 yr, with cutting starting at the head of the watershed and progressing toward the mouth, another was cut at the rate of 1% each year beginning at the watershed's mouth and progressing upstream, and another was cut at a rate of 1% each year, with individual cut areas being widely dispersed throughout the watershed. These cutting patterns were repeated in succeeding centuries, rebuilding one-third of the road network every 100 yr. The parameters governing the simulations were based on recent data from coastal Oregon and northwestern California. Mass wasting, the most important source of sediment in that environment, was the only hillslope process modeled. The simulation results suggest that (i) the greatest differences between management strategies appeared in the first 100 yr and were related primarily to the rate of treatment. By the second 100 yr, when all watersheds had been treated, the principal difference between logging strategies was the timing of impacts. (ii) Dispersing harvest units did not significantly reduce cumulative effects. (iii) The frequency of bed elevation changes between 1 and 4 cm is dramatically increased by logging.
Zimmermann, A., and M. Church, Channel morphology, gradient profiles and bed stresses during flood in a step-pool channel, Geomorphology, 40 (3-4), 311-327, 2001.
The stability of a step-pool channel is investigated on the basis of measurements during a median annual flood. The study reaches range in gradient from 5% to 10% and the flow was 3 m(3) s(-1) in an 8-m wide channel. The estimated shear stress based on the channel gradient was > 10(2) Pa, which implies that the channel ought to move half-meter class boulders. Calculations of the shear stress using flow resistance equations yield values of about 30 Pa. These figures imply that the largest boulders in the channel could be moved. In fact, the channel is stable. The effective stress remains well below the threshold to move the large, structure-forming boulders. The steps are stable structures that result from interlocking of the larger stones. They are semi-randomly located, depending on the location of keystones that are deposited in the channel by debris flows or fall out of the banks. The high variation in step-pool wavelength, step height, residual pool depth, and pool length is indicative of the random nature of step location and structure along a reach. There is no convincing evidence that special conditions govern their formation. (C) 2001 Elsevier Science B.V. All rights reserved.
Zolezzi, G., and G. Seminara, Downstream and upstream influence in river meandering. Part 1. General theory and application to overdeepening, Journal of Fluid Mechanics, 438, 183-211, 2001.