Adams, C.E., L. Xu, N.D. Walker, and S.P. Murray, Flow and sediment transport in a shallow bar-built estuary, northern Gulf of Mexico, Journal of Coastal Research, 13 (1), 164-180, 1997.

A field experiment was undertaken in Lake Barre, a shallow estuary within the Louisiana coastal zone, in November 1991 with the primary goal of acquiring a better understanding of time-mean flow and sediment transport in a shallow Louisiana bay on the periphery of a deteriorating marsh. A network of four monitoring stations recorded current velocity and water turbidity at various levels within the water column while water level, wave, salinity, and wind speed and direction data were acquired at a single station. Results show a response of the water column and the seabed to winds, waves, and tides during the period of study. Variations in velocity profiles, roughness lengths, and to a lesser extent, friction velocities suggest the existence of at least two distinct flow regimes during the periods of study that encompassed four cold fronts. One, characterized by small roughness and weak vertical velocity shear, occurred near the time of cold front passages when winds were northerly. The other, identified by large and frequently variable roughness and vertical velocity shear distributed uniformly through the water column, was predominately associated with tidal flows. The former was attributed to current ripples while the latter appeared to be related to the activity of benthic organisms. A large positive vertical sediment gradient that appeared during the first cold front was attributed to advection of sediment from an area of rapid degradation upstream. Sediment transport calculations reveal fluxes of sediment from the marsh into the study area during cold front passages, the largest magnitudes associated with the earliest cold fronts. Flux magnitude generally decreased with each succeeding cold front. Quantities of fine-grained sediment moving landward during strong prefrontal events are available for nourishing the marsh and contributes material for upward building of a bayou mouth bar. However, long-term subsidence rates are sufficient to mask the effects of deposition. Because much of the sedimentary material within Lake Barre is of sandsize, the bar is armored against the effects of subsequent storms from either direction.

Amos, C.L., A.J. Bowen, D.A. Huntley, J.T. Judge, and M.Z. Li, Ripple migration and sand transport under quasi-orthogonal combined flows on the scotian shelf, Journal of Coastal Research, 15 (1), 1-14, 1999.

Bed state, ripple migration and bedform transport of fine sand (D-50 = 0.23 mm) were recorded with time-lapse photography for 12 days in 22 m of water on Sable Island Bank, the Scotian Shelf, Canada. Near-bed wave and steady flows were recorded and correlated with observed bed state and ripple migration. A well-defined threshold for the traction of fine sand under largely orthogonal combined flows is apparent in our data. It is defined by the expression Theta(cb)' = [Theta(w)' + Theta(c)'] = 0.04. The value is 20% less than the threshold criterion defined by GRANT and MADSEN (1979) for wave-dominant flows and extends it to the current dominant flow conditions when flows are orthogonal to each other. In addition, a threshold for saltation/suspension under combined flows is defined by the expression Theta(cb)' = [Theta(w)' + 1.5 Theta(c)] = 0.17. This threshold marks the onset of saltation and grain bypassing of ripple lee faces and approximates closely the breakoff Shields parameter (Theta(br)' = 0.16) of GRANT and MADSEN (1982). Bedform transport measurements are applicable only below this point; termed the equilibrium range by GRANT and MADSEN (1982). The sediment transport model SEDTRANS matched the duration and magnitude of sand transport over a wide range of conditions of combined flow. This was achieved by using the method of GRANT and MADSEN (1979), but minimizing the friction factor (f(cw)') to 0.006. This value equals the pure unidirectional flow drag coefficient of SOULSBY (1983).

Anastas, A.S., R.W. Dalrymple, N.P. James, and C.S. Nelson, Cross-stratified calcarenites from New Zealand: subaqueous dunes in a cool-water, Oligo-Miocene seaway, Sedimentology, 44 (5), 869-891, 1997.

Cross-bedded, cool-water, bioclastic limestones of the Te Kuiti Group on the North Island of New Zealand are composed primarily of bryozoans, echinoderms, and benthic foraminifers. Their prominent, large-scale, unidirectional cross-stratification is interpreted as produced by migrating subaqueous dunes on the floor of a 50-100 km wide, north-east-trending seaway in water depths of 40-60 m. These dunes are thought to have developed in response to strong, seaway-parallel, tidal currents combined with a north-east-directed, set-up or oceanic current. Cross- stratification is organized into four hierarchical levels: (1) cross-lamination; (2) first-order sets; (3) second-order sets; and (4) cross-stratified successions. The levels are based on increasing degrees of internal complexity. Distinct attributes such as internal organization, cross-set thickness, foreset shape, and lower bounding-surface shape are used to describe and interpret the cross-stratification. All these attributes are here integrated in a. new and expanded classification of unidirectional cross-stratification that emphasizes flow and bedform dynamics rather than overall set shape. Individual cross-stratified successions are interpreted to have formed by dunes with varying sinuosity, superposition, and flow history, under conditions of different current strength but constant sediment production. Horizontally bedded successions are the result of robust, active dune fields that grew during times of vigorous sediment transport. Formset successions were produced from large compound dunes and are the expression of languid and decaying dune fields that developed during times of decreasing sediment transport. These decaying dunes were gradually smothered by continuously and locally produced bioclastic sediment. Formset cross-stratified successions are most likely to develop in carbonates, where the sediment is produced in place, than in terrigenous clastics where the sediment is imported.

Andersen, K.H., A particle model of rolling grain ripples under waves, Physics of Fluids, 13 (1), 58-64, 2001.

A simple model for the formation of rolling grain ripples on a flat sand bed by the oscillatory flow generated by a surface wave is presented. An equation of motion is derived for the individual ripples, seen as "particles," on the otherwise flat bed. The model accounts for the initial appearance of the ripples, the subsequent coarsening of the ripples, and the final equilibrium state. The model is related to the physical parameters of the problem, and an analytical approximation for the equilibrium spacing of the ripples is developed. It is found that the spacing between the ripples scales with the square-root of the nondimensional shear stress (the Shields parameter) on a flat bed. The results of the model are compared with measurements, and reasonable agreement between the model and the measurements is demonstrated. (C) 2001 American Institute of Physics.

Anderson, R.S., Eolian Ripples As Examples of Self-Organization in Geomorphological Systems, Earth-Science Reviews, 29 (1-4), 77-96, 1990.


Bennett, S.J., and J.L. Best, Mean Flow and Turbulence Structure Over Fixed, 2-Dimensional Dunes - Implications For Sediment Transport and Bedform Stability (Vol 42, Pg 491, 1995), Sedimentology, 42 (5), 830-830, 1995.


Bennett, S.J., and J.L. Best, Mean Flow and Turbulence Structure Over Fixed, 2-Dimensional Dunes - Implications For Sediment Transport and Bedform Stability, Sedimentology, 42 (3), 491-513, 1995.

Detailed measurements of flow velocity and its turbulent fluctuation were obtained over fixed, two-dimensional dunes in a laboratory channel. Laser Doppler anemometry was used to measure the downstream and vertical components of velocity at more than 1800 points over one dune wavelength. The density of the sampling grid allowed construction of a unique set of contour maps for all mean flow and turbulence parameters, which are assessed using higher moment measures and quadrant analysis. These flow held maps illustrate that: (1) the time- averaged downstream and vertical velocities agree well with previous studies of quasi-equilibrium flow over fixed and mobile bedforms and show a remarkable symmetry from crest to crest; (2) the maximum root-mean-square (RMS) of the downstream velocity values occur at and just downstream of flow reattachment and within the flow separation cell; (3) the maximum vertical RMS values occur within and above the zone of flow separation along the shear layer and this zone advects and diffuses downstream, extending almost to the next crest; (4) positive downstream skewness values occur within the separation cell, whereas positive vertical skewness values are restricted to the shear layer; (5) the highest Reynolds stresses are located within the zone of flow separation and along the shear layer; (6) high-magnitude, high-frequency quadrant-2 events ('ejections') are concentrated along the shear layer (Kelvin- Helmholtz instabilities) and dominate the contribution to the local Reynolds stress; and (7) high-magnitude, high-frequency quadrant-4 events occur bounding the separation zone, near reattachment and close to the dune crest, and are significant contributors to the local Reynolds stress at each location. These data demonstrate that the turbulence structure associated with dunes is controlled intrinsically by the formation, magnitude and downstream extent of the flow separation zone and resultant shear layer. Furthermore, the origin of dune-related macroturbulence lies in the dynamics of the shear layer rather than classical turbulent boundary layer bursting. The fluid dynamic distinction between dunes and ripples is reasoned to be linked to the velocity differential across the shear layer and hence the magnitude of the Kelvin-Helmholtz instabilities, which are both greater for dunes than ripples. These instabilities control the local now and turbulence structure and dictate the modes of sediment entrainment and their transport rates.

Bennett, J.P., Algorithm For Resistance to Flow and Transport in Sand-Bed Channels, Journal of Hydraulic Engineering-Asce, 121 (8), 578-590, 1995.

An algorithm is developed that relates depth to discharge and determines bed- and suspended-load transport for the entire range of bed forms found in sand-bed channels; equilibrium- state geometry of lower flow regime bedforms is also predicted. Grain shear stress and form resistance are differentiated using a drag coefficient closure and a two-segment logarithmic velocity profile. A Meyer-Peter-type formulation is used to compute sand transport in the bed-load layer and for computing suspended sand transport, McLean's procedure of 1991 and 1992 is adopted. A bed-form classification scheme is developed that uses a particle size parameter and the transport strength to predict bed-form type; it correctly identifies 73% of the 1,192 mostly flume-scale calibration data sets. For 194 sets of dune- transition bed-form calibration data, a modified version of van Rijn's 1984 bed-form geometry predictor yields a geometric average predicted to observed height ratio of 1.00. After calibration, the algorithm produces overall geometric averages of predicted to observed depth and predicted to observed transport of 1.00. For a verification data set of 855 observations, mostly from rivers and canals, the overall geometric averages of predicted to observed depth and transport are 0.87 and 1.14.

Betat, A., V. Frette, and I. Rehberg, Sand ripples induced by water shear flow in an annular channel, Physical Review Letters, 83 (1), 88-91, 1999.

We have studied experimentally the formation and evolution of sand ripples under water shear flow in a narrow annular channel. The amplitude of the sediment ripples vanishes at a critical value of the shear rate. Near this onset, a band of Fourier modes an be described by exponential growth functions. The growth rates vary linearly with the shear rate. On longer times the sand ripples display complex dynamics.

Billi, P., A Note On Cluster Bedform Behavior in a Gravel-Bed River, Catena, 15 (5), 473-481, 1988.


Black, K.P., and J.W. Oldman, Wave mechanisms responsible for grain sorting and non-uniform ripple distribution across two moderate-energy, sandy continental shelves, Marine Geology, 162 (1), 121-132, 1999.

Mechanisms responsible for observed ripple geometry and grain size trends at two open coast sites are considered. The field sites an two moderate-energy sandy shelves on the inner continental shelf out to 50 m depth at East Gippsland in southeastern Australia and at Pakiri in northeast New Zealand. Both are characterised by bands of medium sediments inshore and offshore, separated at 20-45 m depth by a zone with significantly coarser grain size (0.9 mm cf. 0.3 mm). Video observations of the seabed at 126 sites on the East Gippsland shelf revealed that the band was also characterised by larger wavelength ripples (1.0 m cf. 0.3 m). The size of the band stretching over an average of 20 km from 20-45 m depth and its presence at both field sites suggests that the observed characteristics are a long-term response to physical forcing, possibly in near-equilibrium with modem processes. Numerical modelling demonstrated that grain sorting on the shelf is initiated by the presence of maxima in predicted ripple activity and seabed roughness around 35 m depth. The local grain size evidently increases due to winnowing of the fines. Positive feedback, through dependence of ripple size on grain size, causes further lengthening of ripple wavelength, until the pattern has evolved to become highly pronounced on the shelf and self-sustaining, but limited by reducing sediment mobility as grain size increases. (C) 1999 Elsevier Science B.V. All rights reserved.

Bose, P.K., A.K. Chaudhuri, and A. Seth, Facies, Flow and Bedform Patterns Across a Strom-Dominated Inner Continental-Shelf - Proterozoic Kaimur Formation, Rajasthan, India, Sedimentary Geology, 59 (3-4), 275-293, 1988.


Bose, P.K., S. Chakrabarty, and S. Sarkar, Recognition of ancient eolian longitudinal dunes: A case study in Upper Bhander Sandstone, Son Valley, India, Journal of Sedimentary Research, 69 (1), 74-83, 1999.

Straight-crested and internally bipolar cross-stratified eolian dunes are common in the upper part of progradational cycles within the late Proterozoic Upper Bhander Sandstone, Son Valley, India. The Sandstone formed in a coastal setting, and it encompasses supralittoral storm, eolian sand sheet, draa, pond, and ephemeral stream deposits. Ripples of three different size and vector populations typically occur within the dune deposits. The smallest population shows migration parallel to the dune crests, and other two show migration obliquely towards the dune crests. Simple interpolation reveals only 9 degrees deviation of the dune trend from the long-term resultant wind direction. In addition to the two primary wind vectors that control the duneforms, the sand transport ratio less than 1.2 suggests that these are longitudinal dunes. Forward computer modeling and calculation of the maximum gross bedform-normal transport direction further corroborate that the dunes were longitudinal, The dunes are smaller and architecturally simpler than most other longitudinal dunes described in the literature. The methodology adopted here is a useful approach to evaluate longitudinal dunes in the rock record.

Brew, D.S., Late Weichselian to early Holocene subaqueous dune formation and burial off the North Sea Northumberland coast, Marine Geology, 134 (3-4), 203-211, 1996.

High resolution seismic profiles from the North Sea, 20 km off Northumberland, have shown the presence of a 25 km(2) subaqueous dune held buried beneath Holocene marine mud. The dunes are composed of fine to medium sand with occasional pebbles and have heights ranging from 0.5 m to 5.5 m and spacings from 100 m to 600 m. Most larger dunes (>2 m high) have their steeper slopes facing to the south and internal reflectors representing foreset bedding that dips to the south, suggesting dominant southward sand transport. The dunes are inferred to have been produced by tidal currents of between 1.00 and 1.50 m/s in a shallow water tidal embayment or large estuary during the initial stages of the post-glacial marine transgression in the area, sometime between about 10,700 and 9700 yr B.P. Burial of the dunes occurred when the dimensions of the tidal embayment were increased, tidal current velocities reduced beneath the threshold for dune formation and finer- grained sediment was deposited. The tops of the dunes were eroded and a deflation surface formed before burial.

Bridge, J.S., and J.L. Best, Flow, Sediment Transport and Bedform Dynamics Over the Transition From Dunes to Upper-Stage Plane Beds - Implications For the Formation of Planar Laminae, Sedimentology, 35 (5), 753-763, 1988.


Bridge, J.S., and J.L. Best, Flow, Sediment Transport and Bedform Dynamics Over the Transition From Dunes to Upper-Stage Plane Beds - Implications For the Formation of Laminae - Reply, Sedimentology, 37 (3), 551-553, 1990.


Briggs, S.R., and A.J. Williams, Bedform Roughness in a Tidal Flow, Transactions-American Geophysical Union, 59 (4), 290-290, 1978.


Brunone, B., The Albert Shields story - Discussion, Journal of Hydraulic Engineering-Asce, 123 (7), 663-665, 1997.


Bullard, J.E., and D.J. Nash, Linear dune pattern variability in the vicinity of dry valleys in the southwest Kalahari, Geomorphology, 23 (1), 35-54, 1998.

Linear sand dunes in the southwest Kalahari dunefield have been widely observed to change pattern, size and orientation in the vicinity of river valleys, yet few explanations for this change have been put forward. This paper identifies and describes four main associations between dunes and valleys which occur in the southwest Kalahari: (i) dunes which adjoin the valley on both sides with no discernible change in pattern or orientation; (ii) dunes which adjoin the valley and change pattern; (iii) dunes which adjoin the upwind valley flank but not the downwind side; (iv) dune-free zones on both sides of the valley. The two main factors which influence the evolution of these associations are identified as the effect of the valley upon sediment supply and the effect of the valley upon wind regime. Our current state of knowledge about the potential geomorphological effects of these two variables is evaluated with reference to each association described. (C) 1998 Elsevier Science B.V.

Cacchione, D.A., P.L. Wiberg, J. Lynch, J. Irish, and P. Traykovski, Estimates of suspended-sediment flux and bedform activity on the inner portion of the Eel continental shelf, Marine Geology, 154 (1-4), 83-97, 1999.

Energetic waves, strong bottom currents, and relatively high rates of sediment discharge from the Eel River combined to produce large amounts of suspended-sediment transport on the inner continental shelf near the Eel River during the winter of 1995-1996. Bottom-boundary-layer (BBL) measurements at a depth of similar to 50 m using the GEOPROBE tripod showed that the strongest near-bottom flows (combined wave and current speeds of over 1 m/s) and highest sediment concentrations (exceeding 2 g/l at similar to 1.2 m above the bed) occurred during two storms, one in December 1995 and the other in February 1996. Discharge from the Eel River during these storms was estimated at between 2 and 4 x 10(3) m(3)/s. Suspended-sediment flux (SSF) was measured 1.2 m above the bed and calculated throughout the BBL, by applying the tripod data to a shelf sediment-transport model. These results showed initially northward along-shelf SSF during the storms, followed by abrupt and persistent southward reversals. Along-shelf flux was more pronounced during and after the December storm than in February. Across-shelf SSF over the entire measurement period was decidedly seaward. This seaward transport could be responsible for surficial deposits of recent sediment on the outer shelf and upper continental slope in this region. Sediment ripples and larger bedforms were observed in the very fine to fine sand at 50-m depth using a sector-scanning sonar mounted on the tripod. Ripple wavelengths estimated from the sonar images were about 9 cm, which compared favorably with photographs of the bottom taken with a camera mounted on the tripod. The ripple patterns were stable during periods of low combined wave-current bottom stresses, but changed significantly during high-stress events, such as the February storm. Two different sonic altimeters recorded changes in bed elevation of 10 to 20 cm during the periods of measurement. These changes an thought to have been caused principally by the migration of low-amplitude, long-wavelength sand waves into the measurement area. (C) 1999 Elsevier Science B.V. All rights reserved.

Carlson, P.R., J.L. Chin, and F.L. Wong, Bedrock knobs, San Francisco Bay: Do navigation hazards outweigh other environmental problems?, Environmental & Engineering Geoscience, 6 (1), 41-55, 1999.

Three bedrock knobs (Arch, Harding, and Shag rocks) rise above the unconsolidated sediment of central San Francisco Bay to a water depth of less than -12 m (< -39.4 ft MLLW), These rocks are within the westbound vessel traffic area, and the northernmost, Harding Rock, is similar to 300 m (984 ft) from the two-way deep water traffic lane. The rocks pose a hazard to deep-draft vessels. Large ships with drafts deeper than -17 m (-55.8 ft) cross central San Francisco Bay bound for and returning from major port cities of the Bay estuary. Acoustic profiling data show that bedrock extends at a gentle to moderate slope away from the knobs. These data also show that two of the knobs, Harding and Shag, may be part of a bedrock ridge that extends to Alcatraz Island and perhaps southeast to Blossom Rock. The tops of these rocks should be lowered to a depth of -17 m (-55.8 ft), with a total volume of as much as 245,000 m(3) (320,460 yd(3)), at an estimated cost of nearly 27 million dollars, to eliminate the possibility that a tanker would strike one and rupture. A resulting large oil spill would likely cost many times more than the 10 million dollars needed to clean up a small 1996 spill. If the rocks were removed, local habitat for striped bass and other game fish would be altered, with potential negative impact on sport fishing. Currently, public officials are studying the benefits to the Bay environment of lowering the rock knobs.

Chauhan, P.P.S., Bedform association on a ridge and runnel foreshore: Implications for the hydrography of a macrotidal estuarine beach, Journal of Coastal Research, 16 (4), 1011-1021, 2000.

The association of bedforms occurring on a macrotidal 'ridge and runnel' foreshore (Silloth beach, NW England) is investigated. The ripple forms and their orientations point to distinctive stages of wave-current interaction as the topography is submerged and subaerially exposed in a tidal cycle. The estuarine tendency of the coast creates additional flows corresponding to the incursion and excursion of tides. The widespread presence of bedforms which are not related to the wave-generated flows points to an integral role of tidal currents in the hydro-sedimentary dynamics of strongly tidal beaches. Remarkable changes occur in the bedform configurations under extremely windy conditions, mainly expressed by the development of dunes in the zones which are normally rippled. Such changes, though occasional, bring sedimentologically significant alterations in the beach dynamics. The study shows that important inferences can be drawn from bedform association of barred foreshores about the intertidal hydrography and possible sediment movement trends.

Cheel, R.J., Flow, Sediment Transport and Bedform Dynamics Over the Transition From Dunes to Upper-Stage Plane Beds - Implications For the Formation of Planar Laminae, Sedimentology, 37 (3), 549-551, 1990.


Cheong, H.F., and H. Xue, Turbulence model for water flow over two-dimensional bed forms, Journal of Hydraulic Engineering-Asce, 123 (5), 402-409, 1997.

A boundary-fitted numerical model adopting the general conservation of mass and momentum equation is applied to free surface water flow over a two-dimensional topography. A three- layer near-wall k-epsilon turbulence model is used to partly account for the effect of the separated-reattaching region in front of each sand wave. A modification of the streamline curvature is introduced to achieve a proper response to the degree of anisotropy between the normal stresses. The geometric shape of the train of sand waves is simulated by introducing a general curvilinear coordinate system. The numerical results were compared with the available experimental data reported by Raudkivi in 1963 and 1966, and more recently by Van Mierlo and De Ruiter, in 1988, and overall agreement has been satisfactory. Detailed calculations indicate that the two- equation k-epsilon model with careful modifications can yield good predictions for the sand-wave problem. The present model provides a basis for the extended study of bed-load transport: and resistance to flow arising from the movement of sediment bedforms.

Chopard, B., and A. Masselot, Cellular automata and lattice Boltzmann methods: a new approach to computational fluid dynamics and particle transport, Future Generation Computer Systems, 16 (2-3), 249-257, 1999.

Cellular automata (CA) and lattice Boltzmann (LB) approaches are computational methods that offer flexibility, efficiency and outstanding amenability to parallelism when modeling complex. phenomena. In this paper, the CA and LB approach are combined in the same model, in order to describe a system where point-particles are transported in a fluid how This model is used to simulate the snow transport, erosion and deposition by the wind. (C) 1999 Elsevier Science B.V. All rights reserved.

Chopard, B., A. Masselot, and A. Dupuis, A lattice gas model for erosion and particles transport in a fluid, Computer Physics Communications, 129 (1-3), 167-176, 2000.

We consider a simple lattice gas model to simulate erosion, deposition and particle transport in a streaming fluid. In our approach, the fluid is described by a standard lattice Boltzmann model and the granular suspension by a multiparticle cellular automata. A good agreement is obtained between the predictions of the model and field measurements, as observed by analyzing the deposition patterns resulting from various snow and sand transport phenomena. In particular we study the case of ripples formation and simulate the scour appearing around a submarine pipe. (C) 2000 Elsevier Science B.V. All rights reserved.

Clark, C.D., Glaciodynamic context of subglacial bedform generation and preservation, in Annals of Glaciology, pp. 23-32, 1999.

Subglacially-produced drift lineations provide spatially extensive evidence of ice flow that can be used to aid reconstructions of the evolution of former ice sheets. Such reconstructions, however, are highly sensitive to assumptions made about the glaciodynamic context of lineament generation; when during the glacial cycle and where within the ice sheet were they produced. A range of glaciodynamic contexts are explored which include: sheet-flow submarginally restricted; sheet-flow pervasive; sheet-flow patch; ice stream; and surge or re-advance. Examples of each are provided. The crux of deciphering the appropriate context is whether lineations were laid down time-transgressively or isochronously. It is proposed that spatial and morphometric characteristics of lineations, and their association with other landforms, can be used as objective criteria to help distinguish between these cases. A logically complete ice-sheet reconstruction must also account for the observed patches of older lineations and other relict surfaces and deposits that have survived erasure by subsequent ice flow. A range of potential preservation mechanisms are explored, including: cold-based ice; low basal-shear stresses; shallowing of the deforming layer; and basal uncoupling.


Coco, G., D.A. Huntley, and T.J. O'Hare, Investigation of a self-organization model for beach cusp formation and development, Journal of Geophysical Research-Oceans, 105 (C9), 21991-22002, 2000.

A recent numerical investigation of "self-organization'' [Werner and Fink, 1993] suggests that the feedback process between currents and sediment response can result in "self- organized" patterns and can be used to predict beach cusp formation and spacing. A similar model based on self- organization is tested here in order to understand the processes occurring during beach cusp formation and development, to evaluate the sensitivity toward the parameters used, and to examine how the model might relate to field observations. Results obtained confirm the validity of the self-organization approach and its capacity to predict beach cusp spacing, with values in fair agreement with the available field measurements, with most of the input parameters primarily affecting the rate of the process rather than the final spacing. However, changes in the random seed and runs for large numbers of swash cycles reveal a dynamical system with significant unpredictable behavior. Cusp spacing tends to change with time, and cusp regularity shows large long-term variations. Cusps are found to be accretionary in the swash zone, and in agreement with most observations, mean flows are horn divergent over developed topography. Simulations over nonplanar slopes characterized by the presence of preexisting nonrhythmic or cuspate features have been performed. Results indicate that preexisting large-amplitude cusps are destroyed if their spacing is substantially different from that expected under self-organization and that the final spacing is consistent with that predicted by the model for an equivalent plane beach. These findings support the hypothesis that self- organization is a robust mechanism for beach cusp formation.

Cook, D.O., Nearshore Bedform Patterns Along Rhode-Island From Side-Scan Sonar Surveys - Discussion, Journal of Sedimentary Petrology, 52 (2), 677-679, 1982.


Csahok, Z., C. Misbah, and A. Valance, A class of nonlinear front evolution equations derived from geometry and conservation, Physica D, 128 (1), 87-100, 1999.

Based on geometry, conservation, and scaling arguments we derive a class of nonlinear front evolution equations that govern various physical systems. We exemplify the analysis on some specific systems ranging from crystal growth to sand ripples. We also show numerical results of strongly curved fronts exhibiting new patterns. (C)1999 Elsevier Science B.V. All rights reserved.

Csahok, Z., C. Misbah, F. Rioual, and A. Valance, Dynamics of aeolian sand ripples, European Physical Journal E, 3 (1), 71-86, 2000.

We analyze theoretically the dynamics of aeolian sand ripples. In order to put the study in the context, we first review existing models. This paper is a continuation of two previous papers (Z. Csahok et al., Physica D 128, 87 (1999); A. Valance et al., fur. Phys. J. B 10; 543 (1999)), the first one is based on symmetries and the second on a hydrodynamical model. We show how the hydrodynamical model may be modified to recover the missing terms that are dictated by symmetries. The symmetry and conservation arguments are powerful in that the form of the equation is model-independent. We then present an extensive numerical and analytical analysis of the generic sand ripple equation. We find that at the initial stage the wavelength of the ripple is that corresponding to the linearly most dangerous mode. At later stages the profile undergoes a coarsening process leading to a significant increase of the wavelength. We iind that including the next higher-order nonlinear term in the equation leads naturally to a saturation of the local slope. We analyze both analytically and numerically the coarsening stage, in terms of a dynamical exponent for the mean wavelength increase. We discuss some future lines of investigations.

Davies, T.R.H., Bedform Spacing and Flow Resistance, Journal of the Hydraulics Division-Asce, 106 (3), 423-433, 1980.


Deboer, P.L., Mechanical Effects of Microorganisms On Inter-Tidal Bedform Migration, Sedimentology, 28 (1), 129-132, 1981.


Dejong, C., A Reappraisal of the Significance of Obstacle Clasts in Cluster Bedform Dispersal, Earth Surface Processes and Landforms, 16 (8), 737-744, 1991.

The dispersal of cluster bedforms is examined in a short, partially braided reach of the River Quoich, northeast Scotland, after minor flood events in 1989 and 1990. In all cases, the eventual dispersal of clusters occurred without prior removal of the obstacle clast. Since none of the obstacle clasts was dispersed in 1989 and only two-thirds by 1990, obstacle clasts probably form a less significant delay to sediment entrainment than previously assumed and represent a relatively immobile component of bed sediment.

Dinehart, R.L., Gravel-Bed Deposition and Erosion By Bedform Migration Observed Ultrasonically During Storm Flow, North Fork Toutle River, Washington, Journal of Hydrology, 136 (1-4), 51-71, 1992.

Ultrasonic depth sounding provides useful and unexpected information about peak discharge and sediment transport when applied during storm flow in channels with erodible beds. Streambed elevation was measured with dual ultrasonic depth sounders during the rise, crest, and recession of a storm flow in the North Fork Toutle River, Washington, on 3 December 1987. The sounder transducers were held in the flow on a rigid pipe which was suspended from a boom over the channel thalweg. The 12 h episode of depth sounding detected the superposition of fine-gravel dunes on large bed waves, the depth-limited growth of mean dune heights from 13 to 25 cm, and bedform-related deposition and erosion in the channel thalweg. The streambed elevation rose 0.3 m in 2 h with increasing stream discharge. Dune heights diminished for about an hour before the peak river stage was attained. Scour of the streambed continued through the peak stage and recession, with 0.7 m of scour over 10 h. Rapid scour of the streambed produced a falling stage while discharge was still rising. Dune heights grew as flow depth increased after peak stage. Streambed elevation was lowered as large bed waves of fine gravel migrated along the thalweg with successively lower troughs leading each bed wave. Bed elevation records from the dual depth sounders were used to calculate dune celerities of 3-6 cm s-1 and bedform wavelengths of 2-11 m. The large bed waves were subtle, dune-like gravel bedforms with wavelengths of 25-30 m. The celerities and bedform dimensions yielded bedform transport weight rates between 3 and 20 kg s-1 m-1 and grain shear stresses between 40 and 100 N m-2 for the depth-sounding episode.

Dong, Z.B., X.M. Wang, and G.T. Chen, Monitoring sand dune advance in the Taklimakan Desert, Geomorphology, 35 (3-4), 219-231, 2000.

The migration rate of sand dunes is important for the design of the sand-control system in the Taklimakan Desert. Sand dune movement was monitored in a sample plot along the desert- crossing highway by means of a topographical survey in late 1991, 1992 and 1993. The results reveal that most of the morphometric parameters of the dunes are not as well correlated as they are generally supposed to be. The mean advance rate of the dunes was 7.29 and 5.56 m year(-1) in 1992 and 1993, respectively. The advance direction is towards the SW, approximately in accordance with the local resultant wind direction. The advance rate of the dunes was controlled by the local wind regime and dune morphometry. However, the relationships between advance rate and the morphometric parameters of the dunes are Variable for the immature dunes. The small scale and immaturity of the dunes, insufficient sand supply, and complex wind modes are responsible for the complex dune parameter relationship, involving frequent changes of dune morphology, as well as changes of dune advance rate. (C) 2000 Elsevier Science B.V. All rights reserved.

Doucette, J.S., The distribution of nearshore bedforms and effects on sand suspension on low-energy, micro-tidal beaches in Southwestern Australia, Marine Geology, 165 (1-4), 41-61, 2000.

Field measurements of bed morphologies, hydrodynamics and sediment suspension were made on 15 low energy (H-sig < 0.50 m) micro-tidal sheltered sandy beaches in Southwestern Australia. The aim of the study was to differentiate bedform types and cross-shore sequences on low-energy beaches. At each beach, a portable instrument pod capable of measuring steady currents, waves and suspended sediment concentrations, with minimal disturbance of the sandy bed, was deployed at 3-5 cross-shore locations. Cross-shore deployment locations were determined by differences in bedform morphologies and were restricted to the nearshore zone of active sediment suspension. Free divers concurrently measured the bedform wavelengths and heights while noting overall planform pattern at each location. Two general trends in cross-shore bedform patterns were identified among the low-energy beaches. The first trend, found on beaches of finer sand (median grain diameter of 0.24 mm), consisted of a cross-shore sequence from irregular ripples to cross ripples to parallel ephemeral ripples to plane bed in the direction of increasing bottom shear stress. The second sequence, found on beaches of medium sand (median grain diameter 0.39 mm), consisted mainly of parallel ripples with bifurcations that became increasingly organised into parallel ripples as water depth shallowed. The wavelength of the cross ripples was found to increase linearly with increasing near-bed orbital diameter while the wavelength of the ephemeral ripples was found to decrease slightly with increasing near-bed orbital diameter. Suspended sediment concentrations were found to be greater over cross ripples and parallel ripples than over plane bed and ephemeral ripples, even though bottom shear stresses were greater over ephemeral ripples. Co-spectra of suspended sediment and cross-shore currents revealed transport directions to be different over each of the ripple patterns. (C) 2000 Elsevier Science B.V. All rights reserved.

Eriksson, K.A., and E.L. Simpson, Controls on spatial and temporal distribution of Precambrian eolianites, Sedimentary Geology, 120 (1-4), 275-294, 1998.

Inversely graded stratification, generated by the migration of wind ripples, and adhesion structures permit unequivocal identification of Precambrian eolianites. These criteria, in combination with scale of cross-beds, angle of inclination of foresets, geometry of depositional units, and associated non- eolian facies, are used to discriminate between Precambrian dune/draa, dune-plinth, sand-sheet, and interdune deposits that formed in inland and coastal settings. Based on an analysis of published literature, fundamental conclusions can be drawn on the spatial and temporal distribution of Precambrian eolianites. The oldest reported eolianites are from the ca. 2.1 Ga Deweras Group in Zimbabwe and Hurwitz Group in Canada and numerous examples of eolianites are reported from the 1.8 Ga and younger rock record. Lack of Archean and early Paleoproterozoic eolianites and their widespread development after 1.8 Ga are examined with respect to: absence of vegetation, crustal growth and tectonic setting, relative sea- level fluctuations, unfavorable atmospheric and/or climatic change, and non-recognition. The lack of pre-2.2 Ga eolianites may be related to reworking by braided rivers combing across non-vegetated floodplains, reworking of coastal eolianites during transgression or their non-recognition in the Early Precambrian record. The temporal concentration of eolianites at 1.8 Ga may best be related to the early stages of breakup and the assembly phases of supercontinents. (C) 1998 Elsevier Science B.V. All rights reserved.

Flemming, B.W., Sand Transport and Bedform Patterns On the Continental-Shelf Between Durban and Port Elizabeth (Southeast African Continental-Margin), Sedimentary Geology, 26 (1-3), 179-205, 1980.


Folk, R.L., Folks Bedform Theory - Reply, Sedimentology, 24 (6), 864-874, 1977.


Frank, A.J., and G. Kocurek, Airflow up the stoss slope of sand dunes: Limitations of current understanding, Geomorphology, 17 (1-3), 47-54, 1996.

The windward (stoss) side of a sand dune acts as a streamlined obstacle in the path of the wind. Continuity principles necessitate compression of the flow field up the stoss slope of a dune, and shear stress must progressively increase as the flow accelerates. Measurements in transverse flow over thirteen dunes at Padre Island, Texas, the Algodones, California, and White Sands, New Mexico, confirm that velocity profiles on the stoss slope are not log-linear, and that flow acceleration occurs very close to the surface within an internal boundary layer. As a consequence, in the overlying flow where measurements have historically been made, an overall decrease in shear stress occurs up the slope. The actual shape of the velocity profiles, and the identification of the appropriate segment of the profile from which to derive the shear stress that drives saltation represent major problems not approachable by traditional means.

Frank, A., and G. Kocurek, Toward a model for airflow on the lee side of aeolian dunes, Sedimentology, 43 (3), 451-458, 1996.

The interaction between dunes and the primary wind results in a complex pattern of secondary airflow on the lee side of dunes. From 15 dunes studied during transverse flow conditions at Padre Island in Texas, White Sands in New Mexico, and the Algodones in California, distinct now regions can generally be recognized, with the overall flow structure comparing favourably to that proposed for subaqueous bedforms. Downwind of dunes with now separation is a back-now eddy that extends about four dune-brink heights downwind from the brink of the dune. Beyond the separation cell, the velocity profiles can be divided into regions based upon segments separated by 'kinks' in the velocity pro files. The interior is an area above the dunes of relative high. wind speed but low velocity gradient. Beneath the interior is the wake, which consists of two layers. The upper wake exhibits an uppermost portion where the flow decelerates while the remainder exhibits accelerating flow, so that the overall velocity gradient decreases downwind. The lower wake exhibits low velocity gradients and wind speeds that accelerate downwind at all heights, but primarily near the top of the layer, thereby causing the velocity gradient to increase downwind. At about eight dune heights downwind, the upper and lower wakes equilibrate to a single pro file with the kink between them no longer apparent. The lowest recognizable region is the internal boundary layer. It is recognized by a relatively steep velocity gradient below the wake, and never exceeds a few tens of centimetres in height for our data set. Because of acceleration and increasing shear stress within this layer, interdune flats are at least potentially erosional. Overall, the wake and internal boundary layer show a downward transfer of momentum from upper regions so that the flow recovers. Where flow separation does not occur, simple flow expansion down the lee-face causes flow deceleration.

Gallagher, E.L., S. Elgar, and E.B. Thornton, Megaripple migration in a natural surf zone, Nature, 394 (6689), 165-168, 1998.

Migrating megaripples are bedforms that appear in the surf zone of sandy coasts(1). With heights of 0.1 -0.5 m and wavelengths of 1-5m, they are similar in size and shape to small dunes, large ripples, or sand waves. Such sedimentary bedforms have been studied in subaerial(2), steady-flow(3) and intertidal(4) environments, as well as in laboratory flume experiments(5). They affect overlying currents by introducing hydraulic roughness(4,6), and may provide a mechanism for sediment transport(7,8) as well as forming sedimentary structures in preserved facies(9,10). The formation, orientation and migration of such bedforms is not understood well(11,12). Dunes, for example, can be aligned with their crests perpendicular to steady unidirectional winds(13), but in more complex wind fields their orientation becomes difficult to predict(14-17). Similarly, it is not known how sea-floor megaripples become aligned and migrate in the complex flows of the surf zone. Here we present observations in the surf zone of a natural beach which indicate that megaripples do not migrate in the direction of the vector sum of the currents, but are aligned so that the sediment transport normal to the bedform crest is maximized(17). This may need to be taken into account in modelling morphology change and interpreting existing and fossil morphologic patterns.

Gentile, R., L.R. Lando, and G. Scarsi, The threshold of sand motion under wave groups, International Journal of Offshore and Polar Engineering, 10 (2), 107-111, 2000.

The critical condition for general motion of a sand bottom under sea states of random waves is analysed through an experimental investigation carried out in a wave tank by adopting both proper wave groups able to describe the sea states in a synthetic form and the spectral waves associated with these groups. The analysis of the results obtained shows an analogous behaviour as regards the general motion, thus the mathematical models available for regular waves may be used to characterize the critical condition under sea states. Further experiments already scheduled, will help to confirm the present results.

GimenezCurto, L.A., and M.A.C. Lera, Oscillating turbulent flow over very rough surfaces, Journal of Geophysical Research-Oceans, 101 (C9), 20745-20758, 1996.

The forces on the seabed in shallow water under waves influence near-shore transport processes. However, the actual nature of these forces is not yet fully understood. Sleath [1987] simultaneously measured horizontal shear force per unit area and Reynolds stress in oscillating turbulent flow over granular beds with the striking result that maximum Reynolds stress was significantly less than total shear force per unit area of bed. Trying to explain these measurements, we use a formulation which considers two kinds of flow perturbations, namely turbulent fluctuations and some disturbances due to boundary irregularities. The resulting spatially averaged Reynolds equations contain in particular two terms which do not appear in the smooth bed case: the force due to the mean momentum flux for boundary disturbances, here called ''form-induced stress,'' which owes its existence to the vorticity of the disturbed motion, and the force exerted by the roughness elements on the fluid. The ''jet regime'' as introduced by Gimenez-Curto and Corniero [1993] for steady flow is extended to oscillatory flow. In this regime, pressure drag on roughness elements is the fundamental force acting on the boundary, and form-induced stress due to vorticity generated by flow separation from bed irregularities becomes the leading stress, thus providing an explanation for Sleath's measurements by means of a physical mechanism which was already envisaged by Longuet-Higgins [1981] for two-dimensional rippled beds. A simple expression is derived for the friction coefficient which is subsequently compared with extensive series of measurements in the laboratory for granular beds as well as for rippled surfaces, showing an excellent agreement.

Gonzalez, R., and A. Wetzel, Stratigraphy and paleogeography of the Hauptrogenstein and Klingnau Formations (middle Bajocian to late Bathonian), northern Switzerland, Eclogae Geologicae Helvetiae, 89 (2), 695-720, 1996.

The middle Bajocian to middle Bathonian epicontinental sediments of northern Switzerland consist of shallow-marine oolitic carbonates (Hauptrogenstein Formation, Celtic realm) and marly basinal deposits (Klingnau Formation, Swabian realm). Detailed biostratigraphic data based on ammonites and dinoflagellates provide a time frame for a sedimentologic analysis. The carbonate series of the Celtic realm is composed of three shallowing-upward successions, each capped by a hardground. In the basinal domain east of the Aare River, marls persist in a monotonous facies throughout the same lime period. The first shallowing-upward succession within the Hauptogenstein Formation, started during the Blagdeni Subzone with marry beds and intercalated tempestites (Rothenfluh Beds), covered in the western Jura by fine-grained, bioclastic tempestites (Grenchenberg Beds). Simultaneously, the Gislifluh Reef developed in the southeastern Jura, probably on a morphologic high. Oolitic sedimentation started in the central Jura during the Niortense/Subfurcatum Zone (Lower Oolitic Series). The units of 0.5-2 m thick, cross-bedded oolites are attributed to a tidal, shallow-marine, high-energy setting. At the same time, the oolitic beds in the eastern Jura contain up to 35% of mud, and a low-energy setting is inferred (Lower Acuminata Beds). During the Garantiana Zone oolite-belts prograded eastwards reaching the area of the Aare River. An up to 70 m thick oolitic succession was deposited during a period of moderate sea-level rise and a steady subsidence. The second shallowing-upward succession started in the early Parkinsoni Zone. The production of ooids ceased during a sea-level highstand and marls and bioclastic limestones accumulated in northern Switzerland: the Homomya Marls in the western and the Upper Acuminata Beds in the central and eastern Jura. Later, a drop in relative sea-level during the late Parkinsoni Zone re- established ooid production (Upper Oolitic Series). The third shallowing-upward succession started during the latest Bajocian and earliest Bathonian (Zigzag Zone). Marry sediments rich in coarse bioclasts (Movelier Beds) are again interpreted as formed during a relative sea-level highstand. They are overlain by micritic oncolites in the western Jura; to the east, sparry bioclastic, locally cross-bedded limestones occur (''Spatkalk''), probably deposited by storms and tides. The deposition of the ''Spatkalk'' lasted until early Middle Bathonian, prograding eastward and covering the top of the basinal KLingnau Formation. The facies belts within the Hauptrogenstein and Klingnau Formations suggest the evolution of a middle Jurassic, north-south trending oolitic barrier dominated by tides. Backbarrier facies belts formed to the west and off-barrier assemblages to the east of this barrier. A decrease in the production of sediments, as evidenced by platformwide facies changes and in the thickness of shallowing- upward successions, was probably caused by changes in water circulation and local climate. On the other hand, more or less abrupt lateral changes in thickness and facies within the successions suggest local and regional patterns of differential subsidence.

Gonzalez, R., Response of shallow-marine carbonate facies to third-order and high-frequency sea-level fluctuations: Hauptrogenstein formation, northern Switzerland, Sedimentary Geology, 102 (1-2), 111-130, 1996.

Facies patterns in shallow-marine carbonates of the Hauptrogenstein Formation of northern Switzerland (middle Bajocian to early Bathonian) reflect small changes in sea level. Third-order sea-level fluctuations, calculated from large-scale facies patterns (alternations of marl- and carbonate-dominated sedimentary units on the level of members) and subsidence, show two phases of sea-level rise and fall in the late Bajocian and a relative sea-level rise in the early Bathonian. Most of the sedimentary rocks were produced during phases of relative rise and highstand of sea level. No periods of emergence during lowstands are preserved. Sea-level changes of a higher order have been analyzed by facies changes at the outcrop scale. Thin shallowing-up parasequences (0.5-6 m thick) have been correlated across platform, ramp and offshore sedimentary environments. In each of these environments carbonates react differently to sea-level fluctuations. Relative rises in sea level are represented by non-deposition and biogenic sediments, periods of stable or slightly falling sea level are dominated by oolitic sediments: (1) in the offshoal environment, marl layers at the base of thin shallowing-up units are covered by increasingly proximal tempestites; (2) in the ramp environment, oblique-stratified, oolitic and bioclastic grainstones are bounded by marine flooding surfaces; (3) on the platform, marine flooding surfaces are overlain by beds deposited under moderate-energy conditions (coral beds, oncoid beds, platform tempestites) which are in turn covered by high-energy, oblique-stratified oolitic grainstones. Such parasequences, deposited in response to small-scale, high-frequency sea-level changes can be correlated over distances of more than 100 km. A model for evolution and response of carbonate facies to sea-level changes is presented.

Gonzalez, R., and G.P. Eberli, Sediment transport and bedforms in a carbonate tidal inlet; Lee Stocking Island, Exumas, Bahamas, Sedimentology, 44 (6), 1015-1030, 1997.

An active oolitic sand wave was monitored for a period of 37 days in order to address the relationship between the direction and strength of tidal currents and the resultant geometry, and amount and direction of migration of bedforms in carbonate sands. The study area is situated in a tidal channel near Lee Stocking Island (Exumas, Bahamas) containing an estimated 5.5 to 6 x 10(5) m(3) of mobile oolitic sand. Tidal ranges within the inlet are microtidal and the maximum current velocity at the studied site is 0.6 m s(-1). At least 300-400 m(3) of mostly oolitic sand are formed within, or brought into, the channel area every year. The tidal inlet is subdivided into an ocean-orientated segment, in which sand waves are shaped by both flood and ebb tides, and a platform-orientated segment, where sand waves are mainly shaped by flood tides. The studied sand wave lies on the platformward flood-tide dominated segment in a water depth of 3.5-4.5 m. During the 37 days of observation, the oolitic and bioclastic sand wave migrated 4 m in the direction of the dominant flood current. The increments of migration were directly related to the strength of the tide. During each tidal cycle, bedforms formed depending on the strength of the tidal current, tidal range and their location on the sand wave. During flood tides, a steep lee and a gentle stoss side formed and current ripples and small dunes developed on the crest of the sand wave, while the trough developed only ripples. The average lee slope of the sand wave is 24.2 degrees, and therefore steeper than typical siliciclastic sand waves. During ebb tides, portions of the crest are eroded creating a convex upward ebb stoss side, covered with climbing cuspate and linguoid ripples and composite dunes. The area between the ebb-lee side and the trough is covered with fan systems, sinuous ripples and dunes. The migration of all bedforms deviated to a variable degree from the main current direction, reflecting complex flow patterns in the tidal inlet. Small bedforms displayed the largest deviation, migrating at an angle of up to 90 degrees and more to the dominant current direction during spring tides.

Green, M.O., Test of sediment initial-motion theories using irregular-wave field data, Sedimentology, 46 (3), 427-441, 1999.

Sediment initial-motion theories predict the flow conditions that coincide with onset of sediment motion, but usually the most that can be determined from burst-sampled field data is whether or not sediment was in motion. Furthermore, initial- motion theories are usually based on regular-wave laboratory data, with little or no guidance given on how such theories are to be transferred to the real world of irregular waves. A field dataset obtained from the zone of wave shoaling beyond the surfzone is used to compare the performance of three initial- motion theories in a way that takes explicit account of wave irregularity and the limitations of burst sampling. The dataset comprises video images of the seabed and measurements of waves, currents and suspended sediment. The initial-motion theories tested were Komar & Miller's (1975, J. Sedim. Petrol., 45, 362- 367) 'wave-orbital-speed' theory, a 'wave-stress' theory, and a 'wave-plus-current-stress' theory. Fourteen transitions from no sediment motion to sediment motion were observed, but not all of those represented a challenging test of theory. Using the criterion that the best theory is the one that minimizes errors in classifying bursts as 'no sediment motion' or 'sediment in motion', Komar & Miller's (1975) theory was found to perform the best when waves were characterized by significant wave height and mean spectral period, both of which can be estimated directly from pressure data alone. Komar and Miller's theory was better at predicting the onset of extended transport events, which occurred during confused seas, rather than the transition back to moribund seabed under clean swell at the end of such events. The conclusion regarding best theory is dependent on the choice of scales used to characterize wave motion. The way forward therefore is to standardize and define terms precisely.

Guo, M.S., and J.H. Li, The multi-scale attribute of transport and reaction systems, Progress in Natural Science, 11 (2), 81-86, 2001.

This paper traces the development of chemical engineering, its expanding from original scope of the chemical industries to the present scope of practically all industries involving the physical and chemical processing of materials. It points out, with an example, the promising future of the multi-scale approach in dealing with the complex systems in chemical engineering, concluding with the hope of establishing a generic methodology of this approach.

Haque, M.I., and K. Mahmood, Sediment Convection-Diffusion and Bedform Length, Journal of Hydraulic Engineering-Asce, 113 (11), 1381-1401, 1987.


Harbor, D.J., Dynamics of bedforms in the lower Mississippi River, Journal of Sedimentary Research, 68 (5), 750-762, 1998.

The size and roughness characteristics of dunes in the Mississippi River are not predicted well by experimental and theoretical relations, even though intensive how measurements were made in the study area. Although dunes increase in scale with increasing discharge of water and sediment, the development of multiple dune sizes and nonuniform how obscure the relationship of dune geometry to synoptic hydraulic variables. Some nonuniformity is caused by the development of large bed undulations from kinematic waves that can deform into compound dunes, but most of it is related to how convergence and divergence in pools and riffles, varying flow geometry with increasing stage, and reach-controlled relations between flow and energy loss. Even though changes of bedform size are not found to lag the flow changes because sand transport is large, a considerable volume of sediment is required to initiate and propagate the largest compound dunes. This means that they might be profiled in different stages of growth and have a varying effect on the flow during their evolution spatially and temporally.

Harris, P.T., and M.B. Collins, Bedform Distributions and Sediment Transport Paths in the Bristol Channel and Severn Estuary, Uk, Marine Geology, 62 (1-2), 153-166, 1984.


Harris, P.T., and M.R. Jones, Bedform Movement in a Marine Tidal-Delta - Air Photo Interpretations, Geological Magazine, 125 (1), 31-49, 1988.


Hay, A.E., and D.J. Wilson, Rotary Sidescan Images of Nearshore Bedform Evolution During a Storm, Marine Geology, 119 (1-2), 57-65, 1994.

High resolution acoustic images are presented of bedform development on the crest of a nearshore bar during a storm. The images were obtained using a 2.25 MHz rotating sidescan sonar. The sonar system provides a continuous record of the evolution of the bedform field through time, within a 10-m diameter field of view. The images document the occurrence of ripples, cross ripples, and megaripples. During the waning stages of the storm, transitions among ripple types occurred on time scales of 1-3 h, beginning with flat bed and culminating in highly 3-D short-crested ripples.

Hesp, P.A., and S.M. Arens, Crescentic dunes at Schiermonnikoog, the Netherlands, Earth Surface Processes and Landforms, 22 (8), 785-788, 1997.

This paper describes the appearance and maintenance of crescentic dunes in high wind speed conditions on a frozen beach at Schiermonnikoog, The Netherlands. The dunes were crescentic forms with horns. They were barchanoidal in plan view, but had reverse morphologies to typical barchans: the highest and steepest slopes were upwind and led to long low slopes downwind. Slipfaces were absent. It is hypothesized that such crescentic dunes may be a stable aerodynamic form under high to very high (c.15-20ms(-1)) flow conditions. (C) 1997 by John Wiley & Sons, Ltd.

Hoyle, R.B., and A.W. Woods, Analytical model of propagating sand ripples, Physical Review E, 56 (6), 6861-6868, 1997.

We formulate a simple phenomenological model of aeolian sand ripple migration based upon a balance between grain hopping driven by saltation and grain rolling or avalanching under gravity. We develop a set of model equations governing the evolution of the ripple slope. The model has solutions describing steadily Propagating isolated ripples, produced by a horizontal saltation flux, and periodic trains of ripples, which develop when the saltation flux is inclined to the horizontal. In the case of an inclined saltation flux, the ripple wavelength is controlled by the length of the shadow zone, as suggested by R. P. Sharp [J. Geol. 71, 617 (1963)]. Although very simple, our model predicts some of the qualitative features shown by sand ripples in experimental or field studies [R. A. Bagnold, The Physics of Blown Sand and Desert Dunes (Methuen and Co., London, 1941); R. P. Sharp, J. Geol. 71, 617 (1963)]. We find that ripples only develop above a certain threshold value of the saltation flux intensity. Furthermore, at relatively low saltation fluxes, the lee slope of the ripple is a smooth curve, whereas above a critical value of the saltation flux, a slip face develops near the crest. The model predicts a decrease in the speed of propagation as the ripple becomes larger, consistent with observations that smaller ripples are eliminated by ripple merger [IR. P. Sharp, J. Geol. 71, 617 (1963)], and also with numerical simulations [R. S. Anderson, Earth-Sci. Rev. 29, 77 (1990); S. B. Forrest and P. K. Haff, Science 255, 1240 (1992); W. Landry and B. T. Werner, Physica D 77, 238 (1994)].

Hoyle, R.B., and A. Mehta, Two-species continuum model for aeolian sand ripples, Physical Review Letters, 83 (24), 5170-5173, 1999.

We formulate a continuum model for aeolian sand ripples consisting of two species of grains: a lower layer of relatively immobile clusters, with an upper layer of highly mobile grains moving on top. We predict analytically the ripple wavelength, initial ripple growth rate, and threshold saltation flux for ripple formation. Numerical simulations show the evolution of realistic ripple profiles from initial surface roughness via ripple growth and merger.

Ikehara, K., Sequence stratigraphy of tidal sand bodies in the Bungo Channel, southwest Japan, Sedimentary Geology, 122 (1-4), 233-244, 1998.

Tidally controlled scour holes, sand bodies and related bedforms occur in the Bungo Channel, located between Kyushu and Shikoku, southwest Japan. Submarine topography and bedforms change from erosional to depositional in a down-current direction, in accordance with the diminishing energy of tidal currents. The currents are strongly influenced by coastal and submarine topography, and consequently the sea bed has been eroded at the narrowest part of the Bungo Channel, and around promontories or islands, because of local acceleration of the tidal currents. Sand banks occur on the downstream side of scour holes, in response to decreasing current velocity. Large subaqueous dunes are distributed on the sand banks over the central part and the southern exit of the channel. Repeated observations of large dunes indicate that they are mainly inactive. The post-glacial depositional history of the Bungo Channel can be divided into three phases. An erosional surface (sequence boundary) is overlain by dune-covered sand banks which formed during Phase I, the lowest sea-level stage. As sea-level rose, and marine waters flowed into the Suo-nada Sea, the strong tidal energy eroded the sea bottom (formation of scour holes) and created the tidal sand banks near the scour holes and just above the ravinement surface (Phase II). Towards the sea-level highstand, tidal energy decreased because of increasing water depth. The decreasing tidal influence permitted the inflow of Kuroshio water to the southern Bungo Channel, and caused an ocean current influence on sediment transport and bedform formation in this area. Thus, this modification of transgressive tidal sediments by the Kuroshio Current defines the location of maximum flooding surface. (C) 1998 Elsevier Science B.V. All rights reserved.

Jackson, N.L., and K.F. Nordstrom, Aeolian transport of sediment on a beach during and after rainfall, Wildwood, NJ, USA, Geomorphology, 22 (2), 151-157, 1998.

A field investigation was conducted 9 March 1994 on a dissipative beach to compare wind characteristics and aeolian transport during and after a light rain. Winds blew alongshore during the monitoring period. Moisture content of surface sediment on the backbeach was above 7% during rain and 4% four hours after rainfall ceased. Trapping rates, measured using a cylindrical vertical trap, were 14.1 kg m(-1) h(-1) during rainfall and 140.2 kg m(-1) h(-1) for a period beginning 3 h 33 min after rainfall ceased. Results indicate that light rain, resulting in bulk surface moisture values over 7%, is not sufficient to eliminate transport, but the rate of transport is lower than can occur on the beach three to four hours following rain. The amount of sand trapped at Wildwood during rainfall is relatively high when compared to many previous studies on beaches in the absence of rain. The great length of the beach as a source area, combined with parallel or oblique winds are significant in increasing rates of sediment transport. (C) 1998 Elsevier Science B.V.

Jackson, D.W.T., and J.A.G. Cooper, Formation of ephemeral bedform turrets in coastal foredunes, Journal of Geology, 107 (5), 633-639, 1999.

Rare, erosional turret bedforms are described in a coastal foredune environment. These ephemeral structures are formed as a result of moist columns of sand being sculpted by aeolian action of saltating particles. Mature formation of these features appears to be facilitated by the action of an advancing foredune ridge, first preserving and then isolating the turrets for further enhanced erosion within a dune environment. It is envisaged that these structures may be preserved in dune stratigraphy.

Jan, C.D., and M.C. Lin, Bed forms generated on sandy bottom by oblique standing waves, Journal of Waterway Port Coastal and Ocean Engineering-Asce, 124 (6), 295-302, 1998.

This paper presents the results of a study of bed forms generated on a sandy bottom by an oblique standing wave resulting from obliquely incident long-crested waves on a fully reflecting vertical wall. Under antinodes of the oblique standing wave, the sand ripples have crests aligned perpendicular to the wall (type A); under nodes, the ripple crests are aligned with the wall and ride on the top of larger scale sandbars (type C), whereas "island" ripples of a honeycombed structure (type B) appear between nodes and antinodes of the oblique standing wave system. The type A and C ripples could be compared to those generated by long-crested progressive waves, whereas the sandbars at nodes, with ripples riding on them, were compared to those generated by two- dimensional standing waves. Results for the bed-form geometry of type A ripples, type C ripples, and sandbars, as well as type B "bottom islands," are presented as a function of water particle semiexcursion, mobility number, and Shields parameter.

Johns, B., and J.X. Xing, 3-Dimensional Modeling of the Free-Surface Turbulent-Flow of Water Over a Bedform, Continental Shelf Research, 13 (7), 705-721, 1993.

A knowledge of the structure of the turbulent flow of water over bedforms in the coastal, shelf and estuary environment is required in order to assess bedload and suspended load transport mechanisms. In an estuary environment, such as that of the River Taw, Devon, U.K., currently available observational measurements have been made during the peak tidal flow near the mid-point of bedforms having a characteristic downstream wavelength of order 10-20 m and a lateral extent of about two-three wavelengths. Accordingly, it is expected that three-dimensional effects associated with flow around the ends of a bedform structure will be of minimal significance. Nevertheless, there is no quantitative evidence available to determine how long a bedform should be to achieve consistency with this expectation. Of related relevance is the application of two-dimensional numerical models (in which the bedform has an assumed infinite lateral extent) to determine the kinematical bottom shear stress. Again, it is unclear as to what the lateral scale of the bedform should be in order to be consistent with the two-dimensional hypothesis. Using a three- dimensional non-hydrostatic model for the turbulent flow of water over a bedform with scale dimensions corresponding to those found in the Taw Estuary, Devon, U.K., experiments have been performed to determine the deviation of the flow field from its strictly two-dimensional counterpart. In particular, emphasis has been placed on the evaluation of physically relevant flow parameters in a downstream-directed vertical cross-sectional plane passing through the mid-point of the bedform and the comparison of these with the corresponding results obtained from a strictly two-dimensional model.

Klein, G.D., and M.L. Whaley, Hydraulic Parameters Controlling Bedform Migration On an Intertidal Sand Body, Geological Society of America Bulletin, 83 (11), 3465-&, 1972.


Kocurek, G., N. Lancaster, M. Carr, and A. Frank, Tertiary Tsondab Sandstone Formation: preliminary bedform reconstruction and comparison to modern Namib Sand Sea dunes, Journal of African Earth Sciences, 29 (4), 629-642, 1999.

The Tertiary Tsondab Sandstone Formation, which underlies much of the present Namib Sand Sea, is a key element in understanding the Cenozoic evolution of the Namib Desert. Outcrops of the aeolian facies of the Tsondab Sandstone at Elim and Diep Rivier consist of two sequences of bioturbated cross- strata separated by likely formation-scale surfaces of stabilisation. Cross-strata consist of scalloped sets about 200 m in width and separated by southeast dipping bounding surfaces. Internally, sets contain reactivation surfaces of probable seasonal origin. The north to south-southeast dipping foresets define crescent shapes with a trough axis trending northeast. Although additional data are needed to define the Tsondab bedform, the outcrop data is best satisfied in computer simulations by north trending, east migrating main bedforms, which had relatively large and slow-moving dunes superimposed upon their eastern flanks and migrated to the north. Foresets dipping to the south to south-southwest at Elim suggest that superimposed dunes also occurred on the western flanks of the main bedform and migrated to the south, but that their record was largely lost with net eastward migration of the main bedform. This preliminary Tsondab model shares attributes such as trend, scale of cross-strata, and presence of scalloped sets with reactivation surfaces with computer models of the modern linear dunes in which large-scale sinuosity migrates alongcrest to the north. Differences emerge in the overall set architecture and the orientation of cross-strata and bounding surfaces, as well as the degree of vegetation that must have characterised Tsondab dunes. (C) 2000 Elsevier Science Limited. All rights reserved.

Kocurek, G., and N. Lancaster, Aeolian system sediment state: theory and Mojave Desert Kelso dune field example, Sedimentology, 46 (3), 505-515, 1999.

The sediment state of aeolian dune fields and sand seas at a basinal scale is defined by the separate components of sediment supply, sediment availability and the transport capacity of the wind. The sediment supply for aeolian systems is the sediment that contemporaneously or at some later point serves as the source material for the aeolian system. Numerous factors impact the susceptibility of grains on a surface to transport, but these are cumulatively manifested by the actual transport rate, which serves as a proxy for sediment availability. Transport capacity is the potential sediment transport rate of the wind. Because the three aspects of sediment state can be given as a volumetric rate, they are directly comparable. Plotted simultaneously against time, the generated curves define nine possible classes of sediment state. Sediment supply that is stored occurs because it is transport or availability limited, or generated at a rate greater than the potential or actual transport rates respectively. Contemporaneous or lagged influx to an aeolian system may be limited by sediment availability, but cannot exceed the transport capacity of the wind. For the Kelso dune field in the Mojave Desert of California, a variety of stratigraphic and geomorphic evidence is used to approximate the sediment state of the system. The sediment supply was generated during the latest Pleistocene and earliest Holocene during humid periods of enhanced discharge by the Mojave River to form the Lake Mojave fan delta or terminal fan, and has been calculated over time from the sedimentation rate and the frequency of floods. Estimation of transport capacity over time was based upon modern wind data, with an allowance for greater winds during the Pleistocene based upon climatic models. Sediment availability was approximated by calculation of a modern dune mobility index, with variation over time based upon climatic inferences. While quantifying the Kelso or any natural system is subject to numerous uncertainties, the sediment state approach reflects the temporal and spatial disjointed nature of accumulations at Kelso, as well as illuminating questions for future research.

Komarova, N.L., and A.C. Newell, Nonlinear dynamics of sand banks and sand waves, Journal of Fluid Mechanics, 415, 285-321, 2000.

Sand banks and sand waves are two types of sand structures that are commonly observed on an off-shore sea bed. We describe the formation of these features using the equations of the fluid motion coupled with the mass conservation law for the sediment transport. The bottom features are a result of an instability due to tide-bottom interactions. There are at least two mechanisms responsible for the growth of sand banks and sand waves. One is linear instability, and the other is nonlinear coupling between long sand banks and short sand waves. One novel feature of this work is the suggestion that the latter is more important for the generation of sand banks. We derive nonlinear amplitude equations governing the coupled dynamics of sand waves and sand banks. Based on these equations, we estimate characteristic features for sand banks and find that the estimates are consistent with measurements.

Kurtze, D.A., J.A. Both, and D.C. Hong, Surface instability in windblown sand, Physical Review E, 61 (6), 6750-6758, 2000.

We investigate the formation of ripples on the surface of windblown sand based on the one-dimensional model of Nishimori and Ouchi [Phys. Rev. Lett. 71, 197 (1993)], which contains the processes of saltation and grain relaxation. We carry out a nonlinear analysis to determine the propagation speed of the restabilized ripple patterns, and the amplitudes and phases of their first, second, and third harmonics. The agreement between the theory and our numerical simulations is excellent near the onset of the instability. We also determine the Eckhaus boundary, outside which the steady ripple patterns are unstable.

Lancaster, N., The role of field experiments in studies of dune dynamics and morphology, Annals of Arid Zone, 35 (3), 171-186, 1996.

Field measurement of aeolian process-form interactions in the desert have provided in recent years many new informations on the characteristics of the dune-building winds and their patterns of interaction with the dune forms. It is now confirmed that flow acceleration along the dune slope leads to increased sediment flux towards the crest as well as net erosion. Dune shape and the wind direction in relation to the dune determine the pattern of lee side airflow and sand flow pattern there. Information on these and many other relationships have helped to understand how the different dune types interact with the wind regimes and evolve over space and time.

Lancaster, N., Field studies of sand patch initiation processes on the northern margin of the Namib Sand Sea, Earth Surface Processes and Landforms, 21 (10), 947-954, 1996.

Field studies of protodunes (sand patches) on the northern margin of the Namib Sand Sea suggest that they are initiated in a zone of spatially and temporally fluctuating winds on the distal plinth of one of the south-north linear dunes and migrate northward across granule to gravel substrates. The sand patches disperse as surface roughness increases in the net migration distance. Dispersal of the sand patches is also constrained by sand supply. These studies suggest the importance of interactions between surface and aerodynamic roughness, transport thresholds, and sand supply in the initiation of dunes.

Lancaster, N., Arid geomorphology, Progress in Physical Geography, 22 (4), 551-557, 1998.


Landry, W., and B.T. Werner, Computer-Simulations of Self-Organized Wind Ripple Patterns, Physica D, 77 (1-3), 238-260, 1994.

A variety of surficial patterns including beach cusps, sand dunes, wind ripples, stone stripes and sorted circles have been reproduced successfully with computer simulations in which the patterns develop via self-organization and both transporting agents and transported material are discretized. As an example, three-dimensional, grain-level computer simulations of wind ripple formation are described. The results of these simulations demonstrate that a model that includes only incremental transport of surface grains by impacts from wind- propelled hopping (saltating) grains is sufficient to produce self-organized wind ripples whose size, cross-sectional shape, plan-view geometry and time evolution from an original hat surface fall within observed ranges for natural ripples. Simulated wind ripples are initiated from a flat sand bed because of an instability deriving from a dependence of transport rate on slope. A characteristic ripple spacing that is proportional to the grain diameter and increases slowly with time develops as a result of interactions and mergers between ripples. Imperfections to the ripple pattern play a significant role in the determination and evolution of the spacing of simulated ripples.

Le Couturier, M.N., N.T. Grochowski, A. Heathershaw, E. Oikonomou, and M.B. Collins, Turbulent and macro-turbulent structures developed in the benthic boundary layer downstream of topographic features, Estuarine Coastal and Shelf Science, 50 (6), 817-833, 2000.

The characteristics and effects of large-scale flow structures developed in the benthic boundary layer downstream from large topographic features were analysed throughout a tidal cycle. The observed signature of the macro-turbulent features consisted of streamwise modules of low horizontal velocity and high suspended sediment concentration (SSC), alternating with modules of high horizontal velocity and low SSC. These modules extended 10 to 20 m streamwise and exceeded 1 m vertically, and are believed to be related to flow separation effects over large bedforms upstream of the deployment site. The macroscale flow modules intensified the 'burst-like' turbulent events and favoured sediment transport. ' Ejection-like ' events were magnified during modules of decreasing horizontal velocity and increasing turbidity, whereas ' sweep-like ' events were magnified during modules of increasing horizontal velocity and decreasing SSC. The enhanced turbidity of the macroscale modules may be the result of enhanced upward diffusion of sediment by ejection events, whereas the low-turbidity modules may be induced by increased downward transport of suspended sediment by sweep events. These hypotheses were supported by cross-spectral analysis performed on velocity and suspended sediment concentration time-series recorded at the site. An enhanced (negative) contribution of outward and inward interaction events to the Reynolds stress, compared to those reported in uniform BBLs, resulted in 'abnormally' low stress values. (C) 2000 Academic Press.

Leeder, M.R., Folks Bedform Theory, Sedimentology, 24 (6), 863-874, 1977.


Leeder, M.R., Bedload Stresses and Bagnolds Bedform Theory For Water Flows, Earth Surface Processes and Landforms, 2 (1), 3-12, 1977.


Li, B.L., Why is the holistic approach becoming so important in landscape ecology?, Landscape and Urban Planning, 50 (1-3), 27-41, 2000.

Landscape ecology is a way of thinking about the evolution and dynamics of heterogeneous landscapes. It is also viewed as the body of knowledge or facts about ecological space, spatial heterogeneity, and scaling. Studies in this field have been dominated by taking things apart and characterizing various attributes of spatial patterns. These studies generally do not address the intrinsic causality and underlying dynamics of the pattern. Therefore, they cannot explain why patterns change with biotic and abiotic conditions. The time is ripe for change; a holistic approach is needed. In this paper, I begin with mathematical formulation of the part-whole relation in ecological systems and show analytically why the ecological system cannot be understood by reducing it to its parts, which is the central theme for all holistic approaches. Using Prigogine's self-organization theory and Haken's synergetics, I further illustrate sufficiency and necessity of such a holistic approach to study how the cooperation of these subsystems of landscape brings about spatial, temporal and functional structures on macroscopic scales. Four fundamental principles that may govern these processes of self-organization of landscape are proposed. Several examples of applying this approach to theoretical and practical landscape problems are also given. (C) 2000 Elsevier Science B.V. All rights reserved.

Lobo, F.J., F.J. Hernandez-Molina, L. Somoza, J. Rodero, A. Maldonado, and A. Barnolas, Patterns of bottom current flow deduced from dune asymmetries over the Gulf of Cadiz shelf (southwest Spain), Marine Geology, 164 (3-4), 91-117, 2000.

The analysis of dune-like morphologies on the Gulf of Cadiz continental shelf, using high-resolution seismic reflection profiles and sediment samples, reveals a well-defined distribution pattern controlled by the area's hydrodynamics. These bedforms are considered to be modern features from the Holocene, and therefore they provide information about the bottom circulatory patterns established over the continental shelf. Most of the submarine dunes have been identified over a shallow physiographic feature named the Barbate High. The current flows that generate the bedform fields can be attributed to a complex interaction of several hydrodynamic agents, in which the process of current direction reversal related to the tidal cycle in the Straits of Gibraltar seems to be involved. Eastward-oriented submarine dunes located on the onshore zones of the inner shelf are generated by the Atlantic inflow, which over these shallow zones is mainly orientated towards the east during high-tide conditions in the Straits of Gibraltar. Bedforms oriented westwards and west-northwestwards in the offshore zones indicate that a previously undescribed flow occurs on the Gulf of Cadiz continental shelf. This flow is attributed to the influence of ebb tidal currents, which move preferentially towards the west over these zones. As a result of this complex bottom flow pattern, a clockwise sand transport pattern over the Barbate High is established. (C) 2000 Elsevier Science B.V. All rights reserved.

Love, D.W., T.M. Whitworth, J.M. Davis, and W.R. Seager, Free-phase NAPL-trapping features in intermontane basins, Environmental & Engineering Geoscience, 5 (1), 87-102, 1999.

Just as free-phase oil and gas are trapped in the subsurface, spilled nonaqueous phase liquids (NAPLs) can be trapped or pooled by decimeter- to hectometer-scale features at contaminated sites. Free-phase NAPL is that which is sufficiently saturated to flow as a body in the subsurface. In order to trap free-phase NAPLs, the height of the trapping feature (trap-closure height) must be greater than the capillary intrusion of water into the NAPL phase, and the trap boundary must be sufficiently fine-grained to prevent the NAPL from entering its pores. Capillary intrusion of water into a free-phase: NAPL body is a function of the physical properties of the liquid phases as well as the grain size within the trap, and it can be estimated using Hobson's formula. Calculations suggest that necessary trap-closure heights are on the order of one to several centimeters for coarse-grained material and range from one to more than five meters for fine-grained sands, Features in intermontane basins with centimeter- to meter-scale positive or negative topographic relief may form environmentally significant free-phase NAPL traps. These include alluvial-fan, fluvial, lacustrine, eolian, and spring- related (krenegenic) deposits and the contacts between them as well as biogenic, pedogenic, volcanic, and tectonic features. Examples of possible free-phase light nonaqueous phase liquid (LNAPL) traps include buried channels, natural levees, gravel bars; gilgai (swelling clay hummocks), spring mounds, eolian and base-surge dunes, and eolian wedges adjacent to fault scarps. Examples of possible free-phase dense nonaqueous phase liquid (DNAPL) traps include scoured channel bases, incised and backfilled arroyos, deformed soft sediments, larger root traces and animal burrows, buried interdune areas, volcanic collapse features, and rotated wedges of sediments adjacent to faults. High-resolution noninvasive geophysical techniques promise to delineate subsurface strata at adequate scales to show features capable of trapping free-phase NAPE at contaminated sites. However, knowledge of geosystem permeability, migration pathways, and free-phase NAPL trapping processes may be needed to guide remediation efforts.

Luthi, S.M., J.R. Banavar, and U. Bayer, Models to Interpret Bedform Geometries From Cross-Bed Data, Journal of Geology, 98 (2), 171-187, 1990.


Mahmood, K., and M.I. Haque, Bedform Length and Velocity Pulsations in Alluvial Channels, Journal of Waterway Port Coastal and Ocean Engineering-Asce, 114 (3), 315-330, 1988.


Makse, H.A., Grain segregation mechanism in aeolian sand ripples, European Physical Journal E, 1 (2-3), 127-135, 2000.

Many sedimentary rocks are formed by migration of sand ripples. Thin layers of coarse and fine sand are present in these rocks, and understanding how layers in sandstone are created has been a longstanding question. Here, we propose a mechanism for the origin of the most common layered sedimentary structures such as inverse graded climbing ripple lamination and cross- stratification patterns. The mechanism involves a competition between three segregation processes: (i) size-segregation and (ii) shape-segregation during transport and rolling, and (iii) size segregation due to different hopping lengths of the small anti large grains. We develop a discrete model of grain dynamics which incorporates the coupling between moving grains and the static sand surface, as well as the different properties of grains, such as size and roughness, in order to test the plausibility of this physical mechanism.

Malarkey, J., and A.G. Davies, Modelling wave-current interactions in rough turbulent bottom boundary layers, Ocean Engineering, 25 (2-3), 119-141, 1997.

The aim of the present paper is to explain some of the differences between previously published analytical and numerical models of combined wave and current bottom boundary layer flow. To this end, the Grant and Madsen (1979) model for wave-current, rough turbulent Bow is modified to include both first and second harmonic time variations in the eddy viscosity (K). The functional form of the coefficients controlling the amount of time variation is established by analysing the numerical model results of Davies (1990). The addition of time variation in K reduces the strong non-linearity exhibited by the mean stress in the original Grant and Madsen model for current dominated cases, and reproduces the veering of the current predicted by numerical turbulence closure models. (C) 1997 Elsevier Science Ltd.

Marin, F., Velocity and turbulence distributions in combined wave-current flows over a rippled bed, Journal of Hydraulic Research, 37 (4), 501-518, 1999.

This paper describes an experimental programme carried out in a laboratory channel, to investigate the velocity distributions over a rippled bed in combined wave-current flows. In this study, waves propagate against a turbulent current. Velocity measurements were made with a laser-Doppler anemometer. The Nikuradse roughness length k(s) of the bed has been estimated from the traditional logarithmic velocity profile for current alone. The most significant effect of the superposition of waves on a current is the increase of the apparent roughness of the bed with increasing wave height. This effect is well described by Sleath's [49] model. As for rough flat beds, the turbulence intensity over ripples varies inversely with height at sufficiently large distance from the bed for wave-dominated flows.

Marsh, S.W., C.E. Vincent, and P.D. Osborne, Bedforms in a laboratory wave flume: An evaluation of predictive models for bedform wavelengths, Journal of Coastal Research, 15 (3), 624-634, 1999.

Recent bedform dimensions measured in shallow waters in the nearshore zone (VINCENT and OSBORNE, 1993; OSBORNE and VINCENT, 1993; MARSH, 1996) compare poorly with published predictive models for bedform dimensions. A series of experiments were conducted in a large flume with a computer-controlled wave generator and a sand bed, using waves of various amplitudes and characteristics including waves from a field site and monochromatic waves. The ripple wavelengths were then compared to the wavelengths predicted by the models of NIELSEN (1981), GRANT and MADSEN (1982), MOGRIDGE et al. (1994) and WIBERG and HARRIS (1994), and to the semi-quantitative model of CLIFTON (1976), Under spectral waves from the field site the mean ripple wavelengths are anorbital remaining constant (within the scatter of the measurements) and showing none of the trends predicted by the models but falling between the dimensions predicted by NIELSEN (1981) for 'laboratory' and 'field' waves. Under monochromatic waves the ripples scaled with the wave orbital amplitude (lambda approximate to 0.4A(0)) and were much closer to the model predictions. It is suggested that it is rather difficult to change the wavelength of ripples once they have formed. Field waves generally have a broad spectrum of frequencies (and hence of orbital excursions) so there is no length scale of sufficient dominance to force the bed to reform. With regular waves every orbital excursion is the same and the bed rapidly scales to this length. Our data suggest that bed form dimensions in an event may therefore be determined by the first waves capable of imposing their length scale on the bed, or by bed forms from an earlier.

Martinez, H., M. Naaim, and F. NaaimBouvet, Experimental determination of wind erosion flux, Houille Blanche-Revue Internationale De L Eau, 51 (5), 49-52, 1996.


Masselink, G., and C. Pattiaratchi, Tidal asymmetry in sediment resuspension on a macrotidal beach in northwestern Australia, Marine Geology, 163 (1-4), 257-274, 2000.

A field experiment was conducted on a macrotidal beach in northwestern Australia to investigate the relation between sediment resuspension and sea bed morphology. Continuous measurements of waves, currents and suspended sediment concentrations were carried out over a period of several hours around high tide, concurrent with half-hourly visual observations of the sea bed morphology. The incident waves had a significant, wave height of 0.35 m and period 11 s. Most of the data were collected outside the surf zone where sediment resuspension was mainly by wave groups, and suspended sediment transport was primarily accomplished by mean longshore and cross-shore currents. The sediment resuspension process was further characterised by a pronounced tidal asymmetry with suspended sediment concentrations and transport rates during the falling tide significantly larger than during the rising tide. The asymmetry is attributed to the combined effects of a larger bed roughness and stronger mean nearshore flows during the falling tide. The increase in bed roughness occurred during the rising tide under the influence of decreasing bed shear stresses when post-vortex ripple morphology developed on a previously plane bed. Around high tide, the ripples were fully developed and had attained a ripple height of approximately 0.005 m and a ripple length of 0.06-0.08 m. Application of the Van Rijn [Van Rijn, L.C., 1989. Handbook Sediment Transport by Currents and Waves. Delft Hydraulics, Report H461] sediment transport model further confirmed that enhanced sediment resuspension during the falling tide was primarily the result of the development of ripple morphology, with increased mean current strengths playing a secondary role. The results have major implications for modelling suspended sediment transport on macrotidal beaches. (C) 2000 Elsevier Science B.V. All rights reserved.

Masselot, A., and B. Chopard, A lattice Boltzmann model for particle transport and deposition, Europhysics Letters, 42 (3), 259-264, 1998.

Solid particles (such as snow or sand) can get eroded and transported by the wind, and little understanding has been achieved in this domain. We propose a description of the phenomenon in terms of a cellular automata and lattice Boltzmann model. Numerical simulations show that plausible mechanisms are sufficient to explain a wide range of deposition patterns occurring at different space scales. In particular, we reproduce the so-called ripples, that is oscillations of the deposition surface for which no formation mechanism is clearly established.

May, J.P., and F.W. Stapor, Beach erosion and sand transport at Hunting Island, South Carolina, USA, Journal of Coastal Research, 12 (3), 714-725, 1996.

Hunting Island has experienced major shoreline erosion over the past 140 years. The beach has lost sand at the rate of approximately 130,000 m(3)/year. Over the period 1920-1971, the shoreline retreated 5-7 m/year. Beach renourishment has essentially stabilized the shoreline since 1968. Extensive shoals of the St. Helena Sound ebb tidal delta shield the island from northeast waves. Farther south, the Hunting Island Platform impedes waves approaching from east through southeast. Sediments occurring on the platform and beach are dominantly medium-to-fine sand. Computer simulation of longshore sand transport using the WAVENRG model predicts a gross longshore drift of about 100,000 m(3)/year and a net longshore drift to the north along Hunting Island of about 12,000 m(3)/year. Flood tidal currents dominate along the Hunting Island nearshore. These currents flow westward toward the coast, then northward into St. Helena Sound. It is concluded that sand is being suspended in the nearshore zone by waves, causing beach erosion, and transported northward into St. Helena Sound by longshore and flood tidal currents. Most of this sand is then swept seaward through ebb-dominated tidal channels to be deposited on the outer Hunting Island Platform. Shoaling waves transport the sand landward to a depocenter along the inner margin of the outer platform. Sand that is able to bypass this depocenter is delivered to the funnel-shaped inner platform. As the inner platform is largely flood-dominated, the sand entrained by waves is transported by flood tidal currents northward to St. Helena Sound. The Hunting Island beach is effectively isolated from any offshore source of replenishing sand. Similar sand transport systems can be expected to exist in regions characterized by similar morphodynamic attributes.

Mazumder, R., Turbulence-particle interactions and their implications for sediment transport and bedform mechanics under unidirectional current: some recent developments, Earth-Science Reviews, 50 (1-2), 113-124, 2000.

In spite of significant developments made in turbulent boundary layer research over the years, our understanding of particle interactions with organized flow configurations (coherent structures) and their implications for mechanics of bedform development is far from completion. Researchers have made sincere efforts to obtain fundamental understanding of bedform mechanics through theoretical and experimental studies supplemented by field observations. A brief outline emphasising the nature of recent advancements and their consequences in sediment transport and bedform mechanics in aqueous environment under unidirectional current is given in this paper. (C) 2000 Elsevier Science B.V. All rights reserved.

McLean, S.R., S.R. Wolfe, and J.M. Nelson, Spatially averaged flow over a wavy boundary revisited, Journal of Geophysical Research-Oceans, 104 (C7), 15743-15753, 1999.

Vertical profiles of streamwise velocity measured over bed forms are commonly used to deduce boundary shear stress for the purpose of estimating sediment transport. These profiles may be derived locally or from dome Sort of spatial average. Arguments for using the latter procedure are based on the assumption that spatial averaging of the momentum equation effectively removes local accelerations from the problem. Using analogies based on steady, uniform flows, it has been argued that the spatially averaged velocity profiles are approximately logarithmic and can be used to infer values of boundary shear stress. This technique of using logarithmic profiles is investigated using detailed laboratory measurements of flow structure and boundary shear stress aver fixed two-dimensional bed forms. Spatial averages over the length of the bed form of mean velocity measurements at constant distances from the mean bed elevation yield vertical profiles that are highly logarithmic even though the effect of the bottom topography is observed throughout the water column. However, logarithmic fits of these averaged profiles do not yield accurate estimates of the measured total boundary shear Stress.

McLean, S.R., S.R. Wolfe, and J.M. Nelson, Predicting boundary shear stress and sediment transport over bed forms, Journal of Hydraulic Engineering-Asce, 125 (7), 725-736, 1999.

To estimate bed-load sediment transport rates in flows over bed forms such as ripples and dunes, spatially averaged velocity profiles are frequently used to predict mean boundary shear stress. However, such averaging obscures the complex, nonlinear interaction of wake decay, boundary-layer development, and topographically induced acceleration downstream of flow separation and often leads to inaccurate estimates of boundary stress, particularly skin friction, which is critically important in predicting bed-load transport rates. This paper presents an alternative methodology for predicting skin friction over 2D bed forms. The approach is based on combining the equations describing the mechanics of the internal boundary layer with semiempirical structure functions to predict the velocity at the crest of a bedform, where the flow is most similar to a uniform boundary layer. Significantly, the methodology is directed toward making specific predictions only at the bed-form crest, and as a result it avoids the difficulty and questionable validity of spatial averaging. The model provides an accurate estimate of the skin friction at the crest where transport rates are highest. Simple geometric constraints can be used to derive the mean transport rates as long as bed load is dominant.

Mei, C.C., and J. Yu, The instability of sand ripples under partially standing surface waves, Physics of Fluids, 9 (6), 1606-1620, 1997.

We extend recent works on oscillatory flows over rigid ripples and the instability of sand ripples under such flows, by considering the instability of sand ripples under partially standing surface waves over a finite water depth. The variation of unstable ripples within a wavelength of the standing waves and inferences on the ripple distribution over a sand bar are examined. The steady circulation due to the combined effects of waves and ripples are also discussed. (C) 1997 American Institute of Physics.

Moll, J.R., T. Schilperoort, and A.J. Deleeuw, Stochastic-Analysis of Bedform Dimensions, Journal of Hydraulic Research, 25 (4), 465-479, 1987.


Momiji, H., R. Carretero-Gonzalez, S.R. Bishop, and A. Warren, Simulation of the effect of wind speedup in the formation of transverse dune fields, Earth Surface Processes and Landforms, 25 (8), 905-918, 2000.

A computer simulation model for transverse-dune-field dynamics, corresponding to a uni-directional wind regime, is developed. In a previous formulation, two distinct problems were found regarding the cross-sectional dune shape, namely the erosion in the lee of dunes and the steepness of the windward slopes. The first problem is solved by introducing no erosion in shadow zones. The second issue is overcome by introducing a wind speedup (shear velocity increase) factor, which can be accounted for by adding a term to the original transport length, which is proportional to the surface height. By incorporating these features we are able to model dunes whose individual shape and collective patterns are similar to those observed in nature. Moreover we show how the introduction of a non-linear shear-velocity-increase term leads to the reduction of dune height, and this may result in an equilibrium dune field configuration. This is thought to be because the non- linear increase of the transport length makes the sand trapping efficiency lower than unity, even for higher dunes, so that the incoming and the outgoing sand flux are in balance. To fully describe the inter-dune morphology more precise dynamics in the lee of the dune must be incorporated. Copyright (C) 2000 John Wiley & Sons, Ltd.

Morang, A., and R.L. McMaster, Nearshore Bedform Patterns Along Rhode-Island From Side-Scan Sonar Surveys, Journal of Sedimentary Petrology, 50 (3), 831-840, 1980.


Morang, A., and R.L. McMaster, Nearshore Bedform Patterns Along Rhode-Island From Side-Scan Sonar Surveys - Reply, Journal of Sedimentary Petrology, 52 (2), 679-680, 1982.


Mountney, N., and A. Howell, Aeolian architecture, bedform climbing and preservation space in the Cretaceous Etjo Formation, NW Namibia, Sedimentology, 47 (4), 825-849, 2000.

Sets of aeolian cross-strata within the Cretaceous Etjo Formation of NW Namibia are bounded by a hierarchy of surfaces, the origin of which are ascribed to one of four processes related to aeolian bedform and erg behaviour. The base of the main aeolian succession is characterized by a basin-wide erosional supersurface that formed in response to a period of aeolian deflation before the onset of the main phase of erg building. Interdune migration surfaces formed by draa migration are planar in sections parallel to the palaeowind and are inclined at up to 50 in an upwind direction (SW). Perpendicular to the palaeowind, interdune surfaces form 500-m-wide troughs, signifying crestline sinuosity within the original bedforms. Superimposition surfaces are inclined at 5-100 in a downwind direction and indicate the migration of crescentic oblique dunes over larger, slipfaceless transverse draa. Reactivation surfaces associated with minor changes in dune slipface orientation are distinct from other bounding surface types because overlying cross-strata lie parallel to them, rather than downlap onto them. Analysis of the geometry of these bounding surfaces, together with the orientation of the cross- strata within the sets that they bound, has enabled the detailed morphology of the original bedforms to be reconstructed. The maximum preserved thickness of individual aeolian sets varies systematically across the basin, from 52 m in the basin depocentre to only 8 m at the basin margin. The set architecture indicates that this spatial variation is primarily the result of decreased angles of bedform climb at the basin margin, rather than the presence of smaller bedforms. Similarly, a temporal reduction in the angle-of-climb, rather than a reduction in bedform size, is considered to be responsible for an upward decrease in preserved set thickness. Reductions in bedform climb angle reflect progressive loss of accommodation space as the accumulating erg filled the basin.

Murray, A.B., and C. Paola, A new quantitative test of geomorphic models, applied to a model of braided streams, Water Resources Research, 32 (8), 2579-2587, 1996.

Recent simple cellular models of self-organized geomorphic patterns embody a new understanding of complex, spatially extended systems. Such models can be difficult to test quantitatively because the statistics traditionally used can be insensitive even to visually obvious variations in a complex pattern. Here we develop a new approach to evaluating such models. We begin by applying to spatial patterns the state- space reconstruction techniques developed for dynamical systems, producing plots that summarize the patterns in a way that preserves more information than do the statistics usually used in geomorphology. Methods exist for characterizing some aspects of such plots. Here we develop a complementary method for quantitatively comparing state-space plots in a way that more directly evaluates the similarity between the typical features of spatial patterns. An application of this method to the patterns produced by a cellular braided-stream model and real braided streams indicates that this approach provides a relatively sensitive way of comparing model-generated and real spatial patterns.

Needham, D.J., The Development of a Bedform Disturbance in an Alluvial River or Channel, Zeitschrift Fur Angewandte Mathematik Und Physik, 39 (1), 28-49, 1988.


Neuman, C.M., N. Lancaster, and W.G. Nickling, The effect of unsteady winds on sediment transport on the stoss slope of a transverse dune, Silver Peak, NV, USA, Sedimentology, 47 (1), 211-226, 2000.

Rapid (10 s) measurements of sediment transport and wind speed on the stoss slope of a transverse dune indicate that the majority of sand transported is associated with fluctuations in wind speed with a periodicity of 5-20 min duration. Increases in the sediment transport rate towards the dune crest are associated with a small degree of flow acceleration. The increase in wind speed is sufficient, however, to greatly increase values of the intermittency index (gamma), so that the duration of saltation is extended in crestal regions of the dune. The pattern of sediment transport on the stoss slope and, therefore, the locus of areas of erosion and deposition change with the regional wind speed. Erosion of the crest occurs during wind speed events just above transport threshold, whereas periods of higher magnitude winds result in deposition of sand upwind of the crest, thereby increasing dune height. Although short-term temporal and spatial relations between sand transport and wind speed on the stoss slope are well understood, it is not clear how these relations affect dune morphology over longer periods of time.

Nino, Y., and A. Atala, Discrete computer simulation of bedforms, Mechanics Research Communications, 26 (1), 91-98, 1999.


Nishimori, H., M. Yamasaki, and K.H. Andersen, A simple model for the various pattern dynamics of dunes, International Journal of Modern Physics B, 12 (3), 257-272, 1998.

A simple computational model is proposed that reproduces various aspects of the complex dynamics of dunes such as the barchan dunes formation process, the evolution process from a barchan dune to a self dune, the network-dunes formation under time dependent directional winds, etc. Although this model may be oversimplified in several respects, there is a hope that it helps us to sift relevant factors out the vast sea of numerous factors influencing the rich dynamics of desert dunes.

O'Connor, P.W., and D.S.G. Thomas, The timing and environmental significance of late quaternary linear dune development in western Zambia, Quaternary Research, 52 (1), 44-55, 1999.

Optical luminescence dates for 19 samples from the degraded linear dune field of western Zambia indicate multiple periods of regional dune building for the late Quaternary, 32,000- 27,000, 16,000-13,000, 10,000-8000, and 5000-4000 yr ago. These dates show that the last glacial maximum was not the only time when dune construction, commonly linked to marked aridity, occurred in central-southern Africa during the late Quaternary. Whereas rainfall significantly less than today's ca. 1400 mm yr(-1) is a prerequisite for dune construction in the area, adequate sediment supply also determines dune construction and preservation, so that dune building cannot be simply and singularly linked to marked aridity. The Zambezi River system is proposed as an important source of dune sediments, with the nature of linear dune activity explaining why stacked sediments preserve several phases of dune formation. Chronologies of dune construction in western Zimbabwe and the southwest Kalahari are in broad agreement with our Zambian chronology and support a model of rainfall shifts along a SW-NE gradient, with some notable disparities. These are probably a function of interregional sediment supply differences, the number of samples used to delimit constructional periods, and the multicausal nature of forcing mechanisms. (C) 1999 University of Washington.

Paola, C., Quantitative models of sedimentary basin filling, Sedimentology, 47, 121-178, 2000.

Quantitative modelling of the filling of sedimentary basins was begun in earnest in the 1960s. Dozens of themes and variations have been proposed since then, and have yielded an abundance of idealized stratigraphic patterns as functions of both imposed changes and basin properties. Post-plate-tectonic modelling began with 'rigid-lid' models, which show the stratigraphic signature of subsidence variation. This work introduced the connection between stratigraphy and the rheology of the lithosphere. Rigid-lid models are the simplest type of geometric model, in which the sediment surface is assigned prescribed geometries, usually corresponding to different depositional environments. These can reproduce many aspects of overall stratal geometry but are formally restricted to relatively long timescales, for which quasi-steady surface topography can be assumed. So-called dynamic models attempt to represent the morphodynamics of the sediment surface by abstracting and averaging short-term transport processes. Most of the dynamic models proposed to date can be seen as special cases of a single general morphodynamic equation. The most important result of the first wave of quantitative basin- filling models is that even relatively simple models can produce reasonable stratal patterns. We now have a wide array of tools for exploring scenarios, searching for general behaviours and effects, and making initial quantitative predictions. We have also learned that basin response to external forcing as recorded in stratigraphy can be as sensitive to the characteristics of the basin as to the forcing. The main brake on the development of basin modelling is not computing power but lack of methods and data for testing the models we have already developed. Physical experiments, which are only just beginning, are one means of doing this. Experimental stratigraphy is a bridge to quantitative field tests, which will require collaboration among academic researchers from a wide range of areas, and between academia and industry, on projects of greater scale and degree of integration than we have seen so far. The advancement of quantitative sedimentary geology will also require significant changes in the way the subject is taught, at all levels.

Petersen, A.C., Philosophy of climate science, Bulletin of the American Meteorological Society, 81 (2), 265-271, 2000.

The use of climate simulations in scientific assessments of climate change and in the formulation of climate change scenarios has been contested for, among others, methodological reasons. The "philosophy of climate science" encompasses discussions about the methodology of climate science. Three issues with respect to climate simulation are discussed: (i) model hierarchy and complexity, (ii) tuning and falsifiability, and (iii) uncertainty. In this discussion paper it is argued that high-resolution and low-resolution climate models have complementary roles to play in the science of climate change. The role of computer simulations in climate science deserves further philosophical study in order to better assess their quality for informing climate policy making.

Phillips, J.D., Divergence, convergence, and self-organization in landscapes, Annals of the Association of American Geographers, 89 (3), 466-488, 1999.

sMany theories, old and new, of landscape and earth-surface system development involve concepts of self-organization. There are at least eleven distinct definitions of self-organization in the literature that are relevant to landscapes. Some have profoundly different implications with respect to the nature and trajectories of landscape evolution and earth-surface system behavior, including whether evolution is convergent or divergent, whether entropy or energy dissipation is maximized or minimized, the role of chaos, and the mechanisms by which self-organized patterns are generated. Despite these differences, most self-organization concepts can be broadly aggregated into two categories: those concerned with the evolution of order and regularity in the aggregate or ensemble properties of the landscape, and those concerned with the differentiation of landscapes into more diverse spatial units. This paper presents a theory of spatially divergent self- organization related to the latter, showing that autogenic differentiation is directly linked to dynamical instability and chaos. The determination of the self-organization properties of a landscape should be a starting point rather than a goal of geographic explanation. The extent to which field-testable hypotheses are generated, or explanations provided based on process mechanics or landscape history, will ultimately determine the utility of self-organization concepts and methods in physical geography.

Pietersma, D., L.D. Stetler, and K.E. Saxton, Design and aerodynamics of a portable wind tunnel for soil erosion and fugitive dust research, Transactions of the Asae, 39 (6), 2075-2083, 1996.

A portable wind tunnel was designed and built to research wind erosion of soil and simultaneous emissions of fine dust from agricultural fields. This approach allowed for time efficient in situ measurements of erosion processes under controlled wind conditions. The tunnel had an overall length of 13 m with a working section 7.3 m long, 1.0 m wide, and 1.2 m high. Power was supplied using a 33-kW gasoline engine driving a 1.4-m industrial fan. Tunnel aerodynamic design provided for development of a velocity profile comparable to that in an atmospheric boundary layer to a height of 1.0 m over a clean- tilled field. :This was accomplished using (1) extensive flow conditioning (perforated plates, honeycomb and screen) to eliminate flow instability, and (2) a non-uniform shear-grid positioned at the upstream edge of the working section. Experimental results indicate that the flow conditioning produced the desired velocity and turbulence profiles which were both maintained beyond a downstream distance of three times the tunnel height, 3H. In addition, the grid established lateral uniformity in both velocity and turbulence as a function of height. A tunnel Froude number of 12.3 indicated that the flow was free of constraint and shear velocity was relatively unchanged after a distance of less than 3H. These aerodynamic characteristics provided a measuring window in the working section that was 80 cm widex1.0 m high, a flow area of 0.8 m(2).

Prigozhin, L., Nonlinear dynamics of Aeolian sand ripples, Physical Review E, 60 (1), 729-733, 1999.

We study the initial instability of flat sand surface and further nonlinear dynamics of wind ripples. The proposed continuous model of ripple formation allowed us to simulate the development of a typical asymmetric ripple shape and the evolution of a sand ripple pattern. We suggest that this evolution occurs via ripple merger preceded by several solitonlike interaction of ripples. [S1063-651X(99)04507-9].

Rankin, K.L., and R.I. Hires, Laboratory measurement of bottom shear stress on a movable bed, Journal of Geophysical Research-Oceans, 105 (C7), 17011-17019, 2000.

A shear plate was developed to obtain direct measurements of bottom shear stress under nonbreaking surface gravity waves on a movable sand bed. The experiments were conducted under regular wave conditions in a large wave tank where time histories of bottom sheer stress and surface elevation were obtained from a shear plate and wave gauges. Measurements were made at scales approaching those encountered in the field. These data were obtained under steep, vortex ripples where form drag dominated over skin friction for all data presented. Wave friction factors were calculated from measurements and were compared with existing theories as well as with previous laboratory studies. Values of the wave friction factor obtained using the shear plate exhibited reasonable agreement with existing theory. Close agreement between values of the wave friction factor obtained from the shear plate and those measured by previous studies demonstrates that use of a shear plate is a reliable additional method for the measurement of bottom shear stress over a movable bed in the laboratory.

Rasmussen, K.R., and H.E. Mikkelsen, On the efficiency of vertical array aeolian field traps, Sedimentology, 45 (4), 789-800, 1998.

The efficiency of three vertical array field traps for measuring the distribution of aeolian mass transport with height was compared with measurements with an isokinetic trap. The vertical traps seem to work adequately (efficiency > 80%) at heights greater than approximate to 15 mm above the bed. Closer to the bed, however, the open array trap catches about 70%, the two continuous arrays only about 50%. Because most of the transport takes place close to the surface, the overall efficiency of the field traps ranges from 50 to 70%. Based on these wind tunnel tests, we have developed a low single- compartment wedge-shaped trap, its shape, in combination with flow straighteners at the entrance, minimizes stagnation effects, so that the efficiency is approximate to 80%. Our data indicate that with the wedge trap used in combination with the vertical array Aberdeen trap, we can sample mass transport in the held during periods with unidirectional winds with an overall efficiency of the order of 80%.

Rubin, D.M., D.S. McCulloch, and H.R. Hill, Bedform Observations With a Bottom-Mounted Rotating Side-Scan Soar in San-Francisco Bay, California, Transactions-American Geophysical Union, 58 (12), 1162-1162, 1977.


Rubin, D.M., and R.E. Hunter, Bedform Climbing in Theory and Nature, Sedimentology, 29 (1), 121-138, 1982.


Rubin, D.M., and R.E. Hunter, Bedform Alignment in Directionally Varying Flows, Science, 237 (4812), 276-278, 1987.


Rubin, D.M., J.M. Nelson, and D.J. Topping, Relation of inversely graded deposits to suspended-sediment grain-size evolution during the 1996 flood experiment in Grand Canyon, Geology, 26 (2), 99-102, 1998.

Before Glen Canyon Dam was completed upstream from Grand Canyon, floods scoured sand from the channel bed and deposited sand on bars within recirculating eddies, After completion of Glen Canyon Dam in 1963, peak discharge of the mean annual floods dropped from about 2600 to 900 m(3)/s, and 85% of the sediment supply was eliminated, Under the postdam flow regime, sand bars in eddies have degraded, In an experiment to study, in part, the effects of floods in rebuilding these bars, a controlled flood was released from Glen Canyon Dam in late March and early April 1996, Although fluvial sequences characteristically fine upward, the deposits of the experimental flood systematically coarsen upward, Measurements of suspended-sediment concentration and grain size and of bed- material grain size suggest that the upward coarsening results from the channel becoming relatively depleted of fine-grained sediment during the seven days of the high-flow experiment, Predam flood beds of the Colorado River also coarsen upward, indicating that supply-limitation and grain-size evolution are natural processes that do not require the presence of a dam.

Rutherford, J.C., G.J. Latimer, and R.K. Smith, Bedform Mobility and Benthic Oxygen-Uptake, Water Research, 27 (10), 1545-1558, 1993.

A non-consumptive probe was used to measure DO concentrations in mobile sand dunes of the Tarawera River, New Zealand, which receives pulp-mill effluent. Net oxygen depletion rates were low in the top 5-10 cm (occasionally 10-20 cm) of the sediments which indicates that turbulent dispersion transports oxygen to these depths. Below 10-20 cm the net depletion rate was independent of depth which implies that the oxygen resupply rate was negligible. Minimum DO concentrations were invariably found at the upstream (scouring) face of the dunes indicating that advection through the sediments was negligible. A simple analytical model showed that dune turnover explained 30% of the observed river deoxygenation rate. Benthic uptake arising from dune turnover was uniform down the river because an increase in dune height along the river was offset by a decrease in river DO. This helps explain why the river deoxygenation rate is uniform. A fragile layer of fluidized sediment covered the crests of each dune. It was inferred that oxygen uptake in this layer explained 60% of the river deoxygenation rate but an improved understanding of oxygen dynamics within the fluidized layer is required. In other mobile-bed rivers it is likely that dune turnover will be important in determining the benthic mass transfer rate.

Sauermann, G., P. Rognon, A. Poliakov, and H.J. Herrmann, The shape of the barchan dunes of Southern Morocco, Geomorphology, 36 (1-2), 47-62, 2000.

We present detailed shape measurements of several barchan dunes in southern Morocco, near Laayoune. Using these data. we disprove the concept of shape invariance of barchan dunes of different sizes. Nevertheless, some parts of the barchan dune scale and we try to distinguish these from non-scaling ones. Furthermore, we point out the importance of the exact position of the brink for the overall dune shape. Finally, we propose a simple model for dune shape, using our data to determine the model parameters. Despite its simplicity, this model is able to explain the difference between barchans where the crest and the brink coincide and those where they are separated. Typical side slopes can be obtained and the basic properties of the evolution of a barchan dune can be described. (C) 2000 Elsevier Science B.V. All rights reserved.

Schwartz, R.K., Bedform and Stratification Characteristics of Some Modern Small-Scale Washover Sand Bodies, Sedimentology, 29 (6), 835-849, 1982.


Seminara, G., Stability and morphodynamics, Meccanica, 33 (1), 59-99, 1998.

Linear and nonlinear aspects of the development of morphodynamical features of fluvial and coastal environments are reviewed. It is emphasized that, in spite of the as yet incomplete understanding of the mechanics of sediment transport, some essential mechanisms operating in morphodynamics have been recently clarified by employing classical tools of linear and weakly nonlinear stability theory.

Sen, D.P., Bedform, Facies and Basin Model of Ancient Glacial Deposit - a Study Based On Talchir (Upper Carboniferous) Rocks of Taratanr, Bihar, India, Palaeogeography Palaeoclimatology Palaeoecology, 32 (1-2), 45-67, 1980.


Southard, J.B., and J.C. Harms, Sequence of Bedform and Stratification in Silts, Based On Flume Experiments, American Association of Petroleum Geologists Bulletin, 56 (3), 654-&, 1972.


Southard, J.B., Experimental-Determination of Bed-Form Stability, Annual Review of Earth and Planetary Sciences, 19, 423-455, 1991.


Stam, J.M.T., Migration and growth of aeolian bedforms, Mathematical Geology, 28 (5), 519-536, 1996.

A two-dimensional analytical model is developed for the morphodynamics of aeolian dunes. The basis of the model is the sediment continuity equation, which is solved using a linearized sediment transport formula. The airflow over the topography is calculated with a steady-state boundary-layer model. This results in a series of analytical expressions for the shear stress, sediment transport, topography through time, and growth and migration of a sine-shaped dune. These expressions give quantitative relationships between bedform behavior (i.e., growth and migration) and factors such as wind velocity and surface roughness. In this way it can be seen that growth and migration rates increase for higher wind velocity, higher surface roughness and higher wave numbers (i.e., shorter wave lengths).

Stam, J.M.T., On the modelling of two-dimensional aeolian dunes, Sedimentology, 44 (1), 127-141, 1997.

In this study the modelling of aeolian dunes is treated from the background of the physical processes that form them. The paper concentrates on two-dimensional modelling, which can be applied to transverse and barchan dunes. The basic assumptions and equations are discussed and three models are presented: (a) a kinematic model which is based on a linear variation of the sediment transport with the topographic height; (b) an analytical model based on a boundary-layer model of the wind velocity and Bagnold's linearized sediment transport formula; (c) a generalization of this analytical model in a computer program which includes a simple routine for simulating the redistribution of sediment through avalanching. The relative importance of the simplifications is considered and indications are given for the practical applications of these three models in field studies.

Stear, W.M., Comparison of the Bedform Distribution and Dynamics of Modern and Ancient Sandy Ephemeral Flood Deposits in the Southwestern Karoo Region, South-Africa, Sedimentary Geology, 45 (3-4), 209-230, 1985.


Stegner, A., and J.E. Wesfreid, Dynamical evolution of sand ripples under water, Physical Review E, 60 (4), R3487-R3490, 1999.

We have performed an experimental study on the evolution of sand ripples formed under the action of an oscillatory flow. An annular sand-water cell was used in order to investigate a wide range of parameters. The sand ripples follow an irreversible condensation mechanism from small to large wavelength until a final state is reached. The wavelength and the shape of these stable sand patterns are mainly governed by the fluid displacement and the static angle of the granular media. A strong hysteresis affects the evolution of steep ripples. When the acceleration of the sand bed reaches a critical value, the final pattern is modified by the superficial fluidization of the sand layer. [S1063-651X(99)50110-4].

Sukhodolov, A., M. Thiele, and H. Bungartz, Turbulence structure in a river reach with sand bed, Water Resources Research, 34 (5), 1317-1334, 1998.

Measurements and analysis of the three-dimensional turbulence structure in a straight lowland river reach are presented. Accurate measurements of velocity profiles were taken with an acoustic Doppler velocimeter (ADV) and a multichannel micropropeller-based system. It is shown that analytical expressions derived from investigations of laboratory open- channel flows agree well with the measured data only in the central part of the river where flow can be considered weakly three-dimensional. At the same time, clear differences of empirical parameters between river and laboratory flows are detected. It was established that river turbulence is isotropic for spatial scales smaller than the river depth. The data also allowed the detection and analysis of the turbulence anisotropy impact on the formation of secondary currents. Special attention is paid to the investigation of coherent structures. Their spatial scales were evaluated applying the conditional- average procedure based on uw quadrant analysis. On average the scales of ejection and sweep events are as large as 1.5 times the flow depth.

Tengberg, A., and D.L. Chen, A comparative analysis of nebkhas in central Tunisia and northern Burkina Faso, Geomorphology, 22 (2), 181-192, 1998.

This paper reports a comparative analysis of nebkha morphology in central Tunisia and northern Burkina Faso based on a total of 473 measured nebkhas. Nebkhas are mounds composed of wind- borne sediment that accumulated around shrubs. The size of the mounds was measured by height (H) and a horizontal component (L), the latter being the mean of the length and width of the mound. In the Tunisian data set, three trends of development of the mounds were distinguished for Ziziphus lotus nebkhas. Initially, the height increases linearly with the increase in the horizontal component until it reaches about 17 m. When the horizontal component exceeds 17 m, the height stabilizes before a decreasing trend of the height occurs. These results provided the basis for mathematical modelling of nebkha development. A ion-linear and a linear fit were compared and a second-order polynomial function was found to best fit the data on nebkha size from Tunisia. The results indicate that nebkhas have three stages of development: a growing, a stabilizing, and a degrading stage. The model was applied to data on Acacia sp. nebkhas and Balanites aegyptiaca nebkhas from Burkina Faso with good results. The non-linear fit was slightly better than the linear fit. Nebkhas exist at all three stages of development in Tunisia, whereas Burkina Faso has nebkhas that are mainly at the growing stage. These differences are a function of time lag in land degradation between the two study areas, because the wind transport of sediment and the sediment supply are highly related to the density of the vegetation cover in semiarid areas. This conclusion is further supported by dating of nebkhas and of historical and recent vegetation changes in the study areas reported in the literature. The results show that differences in plant ecologies, however, are also very important for the rate of development of nebkhas, which is demonstrated by the much faster growth of Balanites nebkhas as compared to Acacia nebkhas, even though they occur in the same type of environment. (C) 1998 Elsevier Science B.V.

Terzidis, O., P. Claudin, and J.P. Bouchaud, A model for ripple instabilities in granular media, European Physical Journal B, 5 (2), 245-249, 1998.

We extend the model of surface granular flow proposed in [1] to account for the effect of an external 'wind', which acts as to dislodge particles from the static bed, such that a stationary state of flowing grains is reached. We discuss in detail how this mechanism can be described in a phenomenological way, and show that a flat bed is linearly unstable against ripple formation in a certain region of parameter space. We focus in particular on the (realistic) case where the migration velocity of the instability is much smaller than the grains' velocity. In this limit, the full dispersion relation can be established. We relate the critical wave vector to the mean hopping length and to the ratio of the flight time to the 'stick' time. We provide an intuitive interpretation of the instability.

Thais, L., G. Chapalain, and H. Smaoui, Reynolds number variation in oscillatory boundary layers Part I. Purely oscillatory motion, Coastal Engineering, 36 (2), 111-146, 1999.

A numerical model based upon a low Reynolds number turbulence closure is proposed to study Reynolds number variation in reciprocating oscillatory boundary layers, The model is used to compute the boundary layer for flow regimes ranging from smooth laminar to rough turbulent. Criteria for fully developed turbulence are derived for walls of the smooth and rough types. In particular, a new criterion to identify the rough turbulent regime is determined based on the time-averaged turbulence intensity. The reliability of the present model is assessed through comparisons with detailed experimental data collected by other investigators, The model globally improves upon standard high Reynolds number closures. Variation through the wave cycle of the main flow variables (ensemble-averaged velocity, shear stress, turbulent kinetic energy) is remarkably well-predicted for smooth walls. Predictions are satisfactory for rough walls as well. Yet, the turbulence level in the rough turbulent regime is overpredicted in the vicinity of the bed, (C) 1999 Elsevier Science B.V. All rights reserved.

Thibodeaux, L.J., and J.D. Boyle, Bedform-Generated Convective-Transport in Bottom Sediment, Nature, 325 (6102), 341-343, 1987.


Thieler, E.R., O.H. Pilkey, R.S. Young, D.M. Bush, and F. Chai, The use of mathematical models to predict beach behavior for US coastal engineering: A critical review, Journal of Coastal Research, 16 (1), 48-70, 2000.

A number of assumed empirical relationships (e.g., the Bruun Rule, the equilibrium shoreface profile, longshore transport rate equation, beach length:durability relationship, and the renourishment factor) and deterministic numerical models leg., GENESIS, SBEACH) have become important tools for investigating coastal processes and for coastal engineering design in the U.S. They are also used as the basis for making public policy decisions, such as the feasibility of nourishing recreational beaches. A review of the foundations of these relationships and models, however, suggests that they are inadequate for the tasks for which they are used. Many of the assumptions used in analytical and numerical models are not valid in the context of modern oceanographic and geologic principles. We believe the models are oversimplifications of complex systems that are poorly understood. There are several reasons for this, including: (1) poor assumptions and important omissions in model formulation; (2) the use of relationships of questionable validity to predict the morphologic response to physical forcing; (3) the lack of hindsighting and objective evaluation of beach behavior predictions for engineering projects; (4) the incorrect use of model calibration and verification as assertions of model veracity; and (5) the fundamental inability to predict coastal evolution quantitatively at the engineering and planning time and space scales our society assumes and demands. It is essential that coastal geologists, beach designers and coastal modelers understand these model limitations. Each important model assumption must be examined in isolation; incorporating them into a model does not improve their validity. It is our belief that the models reviewed here should not be relied on as a design tool until they have been substantially modified and proven in real-world situations. The "solution," however, is not to increase the complexity of a model by increasing the number of variables. What is needed is a thoughtful review of what beach behavior questions should or could be answered by modeling. Viable alternatives to the use of models do exist to predict the behavior of beaches. Three such alternatives to models are discussed far nourished beach design.

Tirsgaard, H., and I.E.I. Oxnevad, Preservation of pre-vegetational mixed fluvio-aeolian deposits in a humid climatic setting: an example from the Middle Proterozoic Eriksfjord Formation, Southwest Greenland, Sedimentary Geology, 120 (1-4), 295-+, 1998.

Sedimentological studies of a 30 m thick coastal cliff section within the Middle Proterozoic Eriksfjord Formation in western South Greenland reveals three distinct types of fluvial sand sheet deposits that reflect perennial streams (Type I), semi- perennial streams (Type II), and ephemeral flash floods (Type m). Perennial river sand sheets are characterised by co-sets of medium-scale trough cross-beds, interbedded with isolated medium- and large-scale, high-angle, tabular cross-beds. Indications of desiccation or subaerial exposure are absent. Semi-perennial fluvial sand sheets consist predominantly of low-angle cross-beds, interbedded with isolated sets of high- angle tabular cross-beds with common reactivation surfaces. Horizontal lamination and climbing ripple lamination form subordinate structures. Associated with the sand sheets are adhesion structures and 0.05-0.4 m thick sets of wind ripple- lamination indicating periods of subaerial exposure and aeolian reworking. High-energy ephemeral flash flood sand sheets consist almost exclusively of planar-parallel lamination and climbing ripple lamination with some isolated sets of low-angle cross-bedding. Scouring and internal truncation surfaces are common. The three types of sand sheets are considered to reflect deposition under changing climatic conditions, varying from humid to arid or semi-arid. Aeolian deposits are preserved within the sand sheets showing characteristics of dominantly perennial flow punctuated by shorter periods of desiccation (Type II), while sand sheets showing features typical of arid and or semi-arid flow conditions (Type m) contain no preserved aeolian deposits. This selective preservation is interpreted to be a result of the combined effect of groundwater table level and fluvial style which in turn are inferred to have been controlled by the climatic regime. The deposits show that during pre-vegetational times the preservation of aeolian deposits, under certain conditions, may be more optimal in fluvial systems formed in a humid climate than in fluvial systems formed under semi-arid or arid circumstances. The occurrence of aeolian deposits within a Precambrian succession of fluvial deposits therefore, need not be an indication of the most arid environmental conditions. (C) 1998 Elsevier Science B.V, All rights reserved.

Toimil, L.J., and E. Reimnitz, Herringbone Bedform Pattern of Possible Taylor-Gortler Type Flow Origin Seen in Sonographs, Sedimentary Geology, 22 (3-4), 219-228, 1979.


Traykovski, P., A.E. Hay, J.D. Irish, and J.F. Lynch, Geometry, migration, and evolution of wave orbital ripples at LEO-15, Journal of Geophysical Research-Oceans, 104 (C1), 1505-1524, 1999.

Observations of the temporal evolution of the geometric properties and migration of wave- formed ripples are analyzed in terms of measured suspended sand profiles and water velocity measurements. Six weeks of bedform observations were taken at the sandy (medium to coarse sized sand) LEO-15 site located on Beach Haven ridge during the late summer of 1995 with an autonomous rotary sidescan sonar. During this period, six tropical storms, several of hurricane strength, passed to the east of the study site. Ripples with wavelengths of up to 100 cm and with 15 cm amplitudes were observed. The predominant ripples were found to be wave orbital scale ripples with ripple wavelengths equal to 3/4 of the wave orbital diameter. Although orbital diameters become larger than 130 cm during the maximum wave event, it is unclear if a transition to non-orbital scaling is occurring. Ripple migration is found to be directed primarily onshore at rates of up to 80 cm/day. Suspended transport due to wave motions, calculated by multiplying acoustic backscatter measurements of suspended sand concentrations by flow velocity measurements, are unable to account for a sufficient amount of sand transport to force ripple migration and are in the opposite direction to ripple migration. Thus it is hypothesized that the onshore ripple migration is due to unobserved bedload transport or near-bottom suspended transport. Bedload model calculations forced with measured wave velocities are able to predict the magnitude and direction of transport consistent with observed ripple migration rates. Sequences of ripple pattern temporal evolution are examined showing mechanisms for ripple directional change in response to changing wave direction, as well as ripple wavelength adjustment and erosion due to changing wave orbital diameter and relative wave-to-current velocities.

Twichell, D.C., Bedform Distribution and Inferred Sand Transport On Georges Bank, United-States Atlantic Continental-Shelf, Sedimentology, 30 (5), 695-710, 1983.


Vajo, J.J., R.E. Doty, and E.H. Cirlin, Influence of O-2(+) energy, flux, and fluence on the formation and growth of sputtering-induced ripple topography on silicon, Journal of Vacuum Science & Technology a-Vacuum Surfaces and Films, 14 (5), 2709-2720, 1996.

The formation of ripples on Si(100) by O-2(+) sputtering at an angle of incidence of 40 degrees and energies from 1 to 9 keV has been studied using secondary ion mass spectrometry and scanning electron microscopy. At 1 keV no ripples are observed. Between 1.5 and 9 keV ripples are observed oriented perpendicular to the ion direction with average wavelengths that increase, from similar to 100 to 400 nm, approximately linearly with O-2(+) energy. Two-dimensional fast Fourier transforms of secondary electron images are used to investigate the frequency distribution of the ripples. For the conditions studied, the distributions of frequencies appear approximately Gaussian. At 1.5 keV, the wavelength and growth rate with sputtered depth are independent of flux for fluxes from 15 to 150 mu A/cm(2). Accompanying ripple formation are changes in secondary ion yields. The changes occur abruptly at depths that increase, from similar to 0.2 to 5.6 mu m, with O-2(+) energy. In contrast, sputtering with Ar+ at 1.5 and 7 keV to depths 5- 10 times those that produce ripples with O-2(+) produce no observable topography. These results are discussed using several existing theories for ripple formation and growth. Ripple growth and the variations in secondary ion yield are modeled by accounting for the change in local angles of incidence as the ripples grow. This model describes well the variation in secondary ion yield assuming an exponential growth rate. Ripple formation is discussed in terms of a balance between roughening (by sputtering-induced surface stress and by the dependence of the sputtering yield on surface curvature) and smoothing (by both diffusion and ion mixing). Variation in ripple wavelength with energy is not simply explained by these theories. Surface smoothing by cascade ion mixing can, however, make the wavelength, as observed, independent of ion flux. Finally, the possibility of formation of ripples by phase separation within the SiOx surface layer is discussed. (C) 1996 American Vacuum Society.

Valance, A., and F. Rioual, A nonlinear model for aeolian sand ripples, European Physical Journal B, 10 (3), 543-548, 1999.

Starting from the phenomenological model for sand ripple formation developed in [1], we proposed a new interpretation in the light of recent experiments. Furthermore, we derive, close to the threshold of ripple instability, a nonlinear equation for the spatio-temporal evolution of the sand bed profile, which to leading order has a quadratic nonlinearity. This equation is identical to that derived recently on the basis of geometry and conservation aw [2]. Our derivation connects the coefficients of the nonlinear equation to the underlying physical mechanisms (reptation length...). This equation reveals ripple structures which then undergo a coarsening process, as observed in wind tunnel experiment. Small, fast moving ripples are absorbed by larger, slower forms resulting in a growth of the mean wavelength.

Vandenberg, J.H., Bedform Migration and Bed-Load Transport in Some Rivers and Tidal Environments, Sedimentology, 34 (4), 681-698, 1987.


Vandewalle, N., and S. Galam, Ripples versus giant dunes in a saltation-avalanche model, International Journal of Modern Physics C, 10 (6), 1071-1076, 1999.

A simple stochastic cellular automaton model is proposed for ripples and dunes formation. Saltation and avalanches are the unique ingredients of the model. The dynamics of ripple formation is found to be logarithmic in time while the ripple merging as well as the dune growth is faster and occurs by bursts. The ripple state turns out to be metastable.

Vanwesenbeeck, V., and J. Lanckneus, Residual sediment transport paths on a tidal sand bank: A comparison between the modified McLaren model and bedform analysis, Journal of Sedimentary Research, 70 (3), 470-477, 2000.

In order to evaluate the validity of the modified McLaren model for sand transport on a tidal sand bank, 42 grab samples taken from the northern part of the Kwintebank were decalcified, sieved, and analyzed for statistical parameters. The areal distribution of mean grain size, standard deviation, and skewness were defined and used to determine the residual transport directions. The grain-size trends taken into consideration were that the sediment becomes finer, better sorted, and more negatively skewed along the transport pathways (F,B,-) and the sediment becomes coarser, better sorted, and more positively skewed along the transport pathways (C,B,+). These were compared with the transport paths inferred from bedform asymmetries obtained by side-scan sonar records. There were major differences between the sediment transport paths resulting from the two techniques. When the F,B,- trend and small dune asymmetries are compared, only 5 out of 24 cases showed agreement (+/-30 degrees), whereas in 9 cases, the trends were 180 degrees +/- 30 degrees different. There was even less agreement between the (C,B,+) trend and the asymmetry of the small dunes: only 1 out of 24 cases agreed +/-30 degrees, and almost half of the cases mere 90 degrees +/- 30 degrees different. The sediment transport directions deduced from the morphological analysis of the large danes all paint in the direction of the peak flood current. The large dunes seem to be more suitable indicators of the sediment transport paths than the small ones. However, they conflict with the vectors resulting from the (F,B,-) trend Only one out of 20 cases agrees +/-30 degrees, while in 13 cases the vectors are 180 degrees +/- 30 degrees different, and in three cases 90 degrees +/- 30 degrees. Neither do the transport directions from the (C,B,+) trend agree with those deduced from the large dunes. Only one case agrees +/-30 degrees, while in four out of 20 cases the vectors point in opposite directions. In four cases the vectors are 90 degrees +/- 30 degrees different. The asymmetric cross section of the sand bank suggests sediment transport in a northwest direction. It does not seem probable, however, that sediment transport occurs by migration of the whole sand bank. The transport directions inferred from the bank morphology are quite different from the (F,B,-) trend. In 12 out of 42 cases, the vectors agree +/- 30 degrees, in four cases the vectors paint in opposite directions, and in 15 eases they are 90 degrees +/- 30 degrees different. There is slightly more agreement between the (C,B,+) trend and the transport directions deduced from the sand bank. 16 out of 42 cases agree +/- 30 degrees, in nine cases the vectors point in opposite directions, and three cases are 90 degrees +/- 30 degrees different. From this study it seems that the residual sediment transport directions can best be deduced from the morphological characteristics of the large dunes. The departures between the results of the sediment trend analysis according to the modified McLaren model and the morphology of the subaqueous bedforms are partly explained by the location of the study area near the edge of the sand bank. probably better results of the sediment trend analysis would be obtained if samples over the whole length of the sand bank were analyzed and compared. Perhaps a smaller spacing between the samples would improve the results as well, and maybe the samples should not have been decalcified. Possibly the different transport patterns are attributed to different sediment transport processes, which makes a comparison virtually impossible.

Vincent, C.E., and P.D. Osborne, Bedform Dimensions and Migration Rates Under Shoaling and Breaking Waves, Continental Shelf Research, 13 (11), 1267-1280, 1993.

Ripple wave lengths, heights and migration rates have been measured during mainly swell wave conditions on a macrotidal beach in the U.K. Three high frequency acoustic backscatter sensors were used to follow the changes of the bed position at three locations while a fourth was used in a side-scan mode to examine the wave lengths and movements of the bedforms over a 1 m shore-normal section. Two scales of bedforms are clearly visible; low amplitude (approximately 0.5-2 cm) ripples with wavelengths of 7-20 cm and larger bedforms, usually correlating with lunate megaripples (LMR) observed by divers and discussed by OSBORNE and VINCENT, 1992, Proceedings of the 23rd Conference on Coastal Engineering ASCE, pp. 2321-2331, which are 3-8 cm in height and 0.3-0.8 m wavelength. Both forms coexist outside the breakpoint under shoaling waves but in the surf zone the smaller ripples can be destroyed by plunging breakers and high orbital current speeds. The larger bedforms occurred in the surf zone during all the tidal cycles for which measurements were made and appear to be significant surf zone features. No significant correlation was observed between the wave lengths of the small ripples and the orbital excursion A0 nor with the wave Reynolds number, Shields number or Mobility number, but the migration rate was significantly correlated (at 99%) with all these parameters. Conversely, for the larger bedforms, significant correlation was found for the wave lengths but not the migration rates, We conclude that deployment of high frequency ABS in a side-scan mode is a simple and relative effective method for obtaining bedform measurements in the surf zone.

Visser, M.J., Neap-Spring Cycles Reflected in Holocene Subtidal Large-Scale Bedform Deposits - a Preliminary Note, Geology, 8 (11), 543-546, 1980.


Walker, I.J., Secondary airflow and sediment transport in the lee of a reversing dune, Earth Surface Processes and Landforms, 24 (5), 437-448, 1999.

Lee-side windspeed and sediment transport were measured over a small (1.2 m) transverse ridge in the Silver Peak dunefield, west-central Nevada, USA, using an intensive array of 25 cup anemometers and seven total flux traps. During crest-transverse and transporting flow conditions (u(0.3crest) approximate to 8.4 m s(-1)), windspeed near the surface of the lee slope averaged half (48 per cent) that of crest speeds. Dimensionless speeds in the separation zone ranged from 0.2 to 0.8 that of the outer flow (u(12)). Along the boundary of the separation cell, windspeed increased by 10 per cent of the crest speed before separation. Equilibrium of upper and lower wake regions was not observed by the documented eight dune heights, suggesting that wake recovery may not occur over closely spaced dunes. Sediment transport measured directly on both the lee slope and interdune surfaces averaged approximately 15 per cent of crest inputs. This suggests that a significant amount (c. 70-95 per cent) of sediment transported over the crest moved as fallout. For this data set, flux was approximately proportional to the cube of the near-surface windspeed (u(0.3)) and in general there was an order of magnitude difference between flux measured at the crest and that measured within the separation zone. Transport direction in the separation zone was acutely oblique to the incident direction owing to secondary flow deflection. Beyond the interdune, transport direction progressed from oblique to crest-transverse. This indicates that an appreciable amount of sediment may move laterally along the lee slope and interdune corridor under crest-transverse flows. Regarding the grain size and sorting properties of transported sediment, there was no significant difference in mean grain size over the dune, although in general particles were finer and more poorly sorted in the lee. Copyright (C) 1999 John Wiley & Sons, Ltd.

Werner, F., Nearshore Bedform Patterns Along Rhode-Island From Side-Scan Sonar Surveys - Discussion, Journal of Sedimentary Petrology, 52 (2), 674-677, 1982.


Werner, B.T., and D.T. Gillespie, Fundamentally Discrete Stochastic-Model For Wind Ripple Dynamics, Physical Review Letters, 71 (19), 3230-3233, 1993.

We present a discrete, stochastic model for wind formed ripples in sand, which are observed to increase in size through mergers and seemingly approach an asymptotic spatial scale. The model is shown to predict (1) a logarithmic increase in pattern scale with time, (2) a proportionality between the microscopic discrete scale (sand grain diameter) and the macroscopic pattern scale (ripple height), and (3) a lack of scale separation. The implications are that growth and apparent stabilization of scale both can be explained by a single mechanism, and that the evolution of wind ripples and other physical systems of this type cannot be modeled by either deterministic methods or spatial continuum methods.

Werner, B.T., Eolian Dunes - Computer-Simulations and Attractor Interpretation, Geology, 23 (12), 1107-1110, 1995.

A simple computer-simulation algorithm for the transport of sand by wind produces forms resembling barchan, crescentic ridge, linear, and star natural dune classes. Sand is moved as slabs composed of many grains that are picked up at random, transported in a specified direction, and deposited (1) with a probability that depends on the local presence or absence of sand or (2) in shadow zones in the lee of dunes. The simulated dune fields are interpreted as complex systems, with sand-dune classes being dynamical attractors of these systems. The evolution of dunes once formed becomes decoupled from the details of eolian sand transport.

Werner, B.T., and G. Kocurek, Bed-form dynamics: Does the tail wag the dog?, Geology, 25 (9), 771-774, 1997.

Bed-form patterns reflect the dynamics of the defects in the pattern. From this new hypothesis, the differential migration of defects within a field of bed forms determines how crest- line orientation responds to changing transport conditions. Predictions from a model for defect dynamics compare well to field measurements and computer simulations of bed-form orientation. This model permits quantification of the time for bed-form reorientation across a broad range of scales, from hours in the rapidly changing nearshore environment to thousands of years for linear dune fields.

Werner, B.T., Bed-form dynamics: Does the tail wag the dog? (vol 25, pg 771, 1997), Geology, 26 (3), 286-286, 1998.


Werner, B.T., and G. Kocurek, Bedform spacing from defect dynamics, Geology, 27 (8), 727-730, 1999.

Spacing is a time-varying characteristic of bedform fields deriving from the behavior of defects (ends of crest lines) in the bedform pattern. In a model based on this hypothesis, crest line length is lost and spacing increases because bedform defects, which are smaller in height and faster migrating than surrounding bedform crest lines, merge with larger bedforms as defects migrate through bedform fields. Spacing in large bedform fields asymptotically increases with the logarithm of time as pairs of oppositely facing defects meet and annihilate. Spacing in small bedform fields, such as flumes, exponentially approaches a fixed value as defects are eliminated at the boundaries of the field. Model predictions are compatible with observed spacing of transverse bedforms, ripples formed under waves and linear dunes, calling into question the widespread assumption that bedform spacing approaches a steady-state value characteristic of fluid flow and sediment transport over two- dimensional bedforms.

Werner, B.T., Complexity in natural landform patterns, Science, 284 (5411), 102-104, 1999.

Patterns in nature, such as meandering rivers and sand dunes, display complex behavior seemingly at odds with their simplicity of form. Existing approaches to modeling natural Landform patterns, reductionism and universality, are incompatible with the nonlinear, open nature of natural systems. An alternative modeling methodology based on the tendency of natural systems to self-organize in temporal hierarchies is described.

You, Z.J., Laboratory investigations into wave period effects on sand bed erodibility under the combined action of waves and currents, by G. Voulgaris et al: Comments, Coastal Engineering, 30 (1-2), 157-160, 1997.


You, Z.J., Initial motion of sediment in oscillatory flow, Journal of Waterway Port Coastal and Ocean Engineering-Asce, 124 (2), 68-72, 1998.

A new model is developed to study the initial motion of sediment in oscillatory flow over a flat bottom on the basis of available experimental data. It is found that the initial motion of sediment in oscillatory flow is uniquely defined by the simple model of A/d = KA(2) omega/v + B, where A = semiexcursion of wave orbital motion near the bed; omega = angular frequency; d = grain diameter; v = kinematic viscosity; and K and B = dimensionless coefficients determined by the immersed sediment weight. For a given sediment, the onset velocity derived from the model is found to initially increase with the wave period T and then approach a constant. A practical formula is also presented to calculate the onset velocity of sediment in the coastal zone.

You, Z.J., A simple model of sediment initiation under waves, Coastal Engineering, 41 (4), 399-412, 2000.

A simple model is developed to study the initial motion of sediment on a horizontal bed under non-breaking waves. The model is derived to be A = C(T- T-0) based on a wide range of experimental data collected in different flow regimes, where A is the nearbed semi-excursion of wave motion, T is the wave period, and C and T, are the coefficients dependent on sediment properties only. For a given sediment, the onset velocity of sediment motion derived from the model is shown to initially increase sharply with wave period T and then approach a constant. The flow Reynolds number Re corresponding to an initiated sediment is also calculated from the simple model and found to be a function of sediment properties and wave period. For the completeness of this study, the initial motion of light sediment under very short waves is also investigated. The present model agrees well with the available laboratory and field data. (C) 2000 Elsevier Science B.V. All rights reserved.