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 thr