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Abstract: We present a two-dimensional vertical (2DV) flow and morphological numerical model describing the behaviour of offshore sand waves. The model contains the 2DV shallow water equations, with a free water surface and a general bed load formula. The water movement is coupled to the sediment transport equation by a seabed evolution equation. Using this model, we investigate the evolution of sand waves in a marine environment. As a result, we find sand wave saturation for heights of 10–30% of the average water depth on a timescale of decades. The stabilization mechanism, causing sand waves to saturate, is found to be based on the balance between the shear stress at the seabed and the principle that sediment is transported more easily downhill than uphill. The migration rate of the sand waves decreases slightly during their evolution. For a unidirectional steady flow the sand waves become asymmetrical in the horizontal direction and for a unidirectional block current asymmetrical in the vertical. A sensitivity analysis showed the slope effect of the sediment transport plays an important role herein. Furthermore, the magnitude of the resistance at the seabed and the eddy viscosity influence both the timescale and height of sand waves. The order of magnitudes found of the time and spatial scales coincide with observations made in the southern bight of the North Sea, Japan and Spain. [Copyright &y& Elsevier]

Abstract: The Adriatic Sea general circulation model coupled to a third generation wave model SWAN and a sediment transport model was implemented in the Adriatic Sea to study the dynamics of the sediment transport and resuspension in the northern Adriatic Sea (NAS) during the Bora event in January 2001. The bottom boundary layer (BBL) was resolved by the coupled model with high vertical resolution, and the mechanism of the wave–current interaction in the BBL was also represented in the model. The study found that, during the Bora event of 13–17 January 2001, large waves with significant wave height 2m and period of 5s were generated by strong winds in the northwestern shelf of the Adriatic where the direction of wave propagation was orthogonal to the current. The combined motion of the wave and current in the BBL increased the bottom stress over the western Adriatic shelf, resulting in stronger sediment resuspension there. Combining stronger bottom resuspension and strong upward vertical flux of resuspended sediments due to turbulent mixing, the model predicted that sediment concentration near the Po River was much higher than that predicted by the model run without wave forcing. The study also shows that wave–current interaction in the BBL reduced the western Adriatic Coastal Currents (WACCs) in the shallower north. It is concluded that wave forcing significantly changed the sediment distributions and increased the total horizontal fluxes over the western shelf. These results signified wave effect on sediment flux and distribution in the NAS, and suggested that waves cannot be neglected in the study of dynamics of sediment transport and resuspension in the shallow coastal seas. By including the tidal forcing in the coupled model, we also examined the effect of tides on the sediment transport dynamics in the NAS. [Copyright &y& Elsevier]

Abstract: The coast between Ngason and Haiphong is largely formed by accretion of the Red River system. In the region, five main surface sediment types (sand, sandy silt, silt, mud and sand at shoals) could be defined, which differ from one another in their sedimentary characteristics. Sand dominates along the shoreline between 0 and 15m water depth. Down to a water depth of about 25–30m, the sediment is dominantly silt. Further offshore the surface sediments are mainly sandy silt and sand of older units (Early-Middle Holocene, Late Pleistocene). Net sediment transport directions are defined by grainsize analysis according to the method of Gao and Collins [Gao, S., Collins, M., 1992. Net sediment transport patterns inferred from grain-size trends, based upon definition of transport vectors. Sedimen. Geol. 80, 47–60, 1992]. At river mouths, directions of sediment transport are variable where the depths are shallower than 5m. From 5 to 10 m water depth, sediments are mainly transported southeastward at the Ba Lat, Lach and Day mouths, northeastward at the Tra Ly mouth and eastward at the Thai Binh mouth. Recently, the Hai Hau erosional shoreline is not supplied with sediment from the Ba Lat mouth and sediments are transported southwestward alongshore in the region shallower than 5m. The region of depths from 10 to 30m is specified by southward sediment transport. [Copyright &y& Elsevier]

Abstract: The coastline of the Red River Delta is characterized by alternating patterns of rapid accretion and severe erosion. The main branch of the Red River, the Ba Lat, is presently expanding seaward with a main depositional area several km downstream and offshore the Ba Lat River mouth. Sediment deposition rates are approximately 6m in the past 50 years. Field measurements were done to determine the processes that regulate marine dispersal and deposition of sediment supplied by the Ba Lat. These measurements reveal that the waters surrounding the Ba Lat delta are strongly stratified with a pronounced southward-flowing surface layer. This southward-flowing surface layer is a coastal current which is generated by river plumes that flow into the coastal zone north of the Ba Lat. However, outflow of turbid river water is not continuous and most sediment enters the coastal zone when the alongshore surface velocities are low. As a consequence, most sediment settles from suspension close to the river mouth. In addition to the southward surface flow, the southward near-bottom currents are also stronger than northward currents. Contrasting with the residual flow near-surface, this southward flow component near-bottom is caused by tidal asymmetry. Because most sediment is supplied by the Ba Lat when wave heights are low, sediment is able to consolidate and therefore the long-term deposition is southward of, but still close to, the Ba Lat mouth. [Copyright &y& Elsevier]

Abstract: The fishery harbor of Karaburun coastal village is located at the south west coast of the Black Sea. The significant waves coming from north eastern direction cause considerable rate of sediment transport along 4km sandy beach towards the fishery harbor in the region. The resulting sediment deposition near and inside the harbor entrance prevents the boat traffic and cause a vital problem for the harbor operations. In order to determine the level and reasons of the sediment transport, the long-term observations of shoreline changes, the long-term statistical analysis of wind and wave characteristics in the region, and sediment properties have been performed. The data obtained from observations, measurements and analysis were discussed. The long-term statistics of deep water significant wave heights for each direction was discussed by comparing the results obtained from different data sources and methods. For shoreline evolution, the numerical study using one-line model was applied to describe the shoreline changes with respect to probable wave conditions. Initial shoreline was obtained from the digitized image in 1996 since there was no previous shoreline measurement of the site. The results were compared using the techniques of remote sensing obtained from sequent images using IKONOS and IRS1C/D satellites. [Copyright &y& Elsevier]

Abstract: Recent years have seen a rapid expansion in the acquisition and use of information on diffusive transport in phases relevant to the solid Earth (crystals, melts and fluids). Although far from complete, the data base on diffusion coefficients is now sufficiently large that broad constraints can be placed upon the length- and time scales of many natural transport phenomena in which diffusion plays a role. Conversely, observations of diffusion progress in specific natural samples can be used to extract time–temperature information for a variety of geologic and geochemical processes, ranging from sediment burial and crustal erosion to fluid-mediated reactions and biosignature retention. Despite this undeniable progress, several major challenges remain that largely define the frontiers of research in solid-Earth diffusion. Perhaps foremost among these is the need to address and understand the multi-scale, multi-path aspects of diffusion in many systems—a complication that is not limited to polyphase materials (individual mineral grains can exhibit clear indications of multi-path behavior even when visible evidence of such paths is lacking). Many other diffusion frontiers are linked in one way or another to this multi-scale issue; they include: diffusion of molecular H2O and the effect of H species on diffusion in minerals and rocks; diffusive fractionation of multiple isotopes of a single element; diffusion at the extreme conditions of the deep Earth; reconciliation of observations from natural samples and laboratory studies; and development of theoretical approaches to ‘predict’ diffusion behavior in regions inaccessible to observation. [Copyright &y& Elsevier]

Abstract: This paper analyses the morphological response induced by low-crested structures on the adjacent seabed, with particular interest in the erosion patterns that frequently develop at gaps and roundheads. The mechanisms responsible for erosion processes are examined by means of morphodynamic simulations with the numerical suite MIKE 21 CAMS developed by DHI Water & Environment. The main purpose of the paper is to verify how and how far a commercial code can predict bed evolution, in vicinity of defence structures in a real case, in order to get information that may be very useful for structure design and possible maintenance of existing works. The code is applied to a long-term simulation on a study site that is characterized by a composite intervention and suffers from severe erosion, Lido di Dante (Italy). The simulation covers the period (one year and a half) between two available multi-beam surveys, in order to have a detailed real bathymetry as starting point and another one, as accurate as the first, to compare numerical with surveyed results. All the other input data for the model, as waves, tide, wind and sediment characteristics, are derived from measurements in the area; moreover, the code is calibrated using wave and current data acquired during a field campaign. The bed evolution derived from simulations shows a good agreement with the survey both in the locations and in the intensity of erosive and depositional areas. A sensitivity analysis of results to some selected modelling parameters is performed on a shorter simulation period (one month), showing that accounting for bed slope in sediment transport modelling has greater effects in bathymetry evolution than the use of a complex sediment bathymetry or the representation of wave diffraction. [Copyright &y& Elsevier]

Abstract: This study documents two different modes of berm development: (1) vertical growth at spring tides or following significant beach cut due to substantial swash overtopping, and (2) horizontal progradation at neap tides through the formation of a proto-berm located lower and further seaward of the principal berm. Concurrent high-frequency measurements of bed elevation and the associated wave runup distribution reveal the details of each of these berm growth modes. In mode 1 sediment is eroded from the inner surf and lower swash zone where swash interactions are prevalent. The net transport of this sediment is landward only, resulting in accretion onto the upper beach face and over the berm crest. The final outcome is a steepening of the beach face gradient, a change in the profile shape towards concave and rapid vertical and horizontal growth of the berm. In mode 2 sediment is eroded from the lower two-thirds of the active swash zone during the rising tide and is transported both landward and seaward. On the falling tide sediment is eroded from the inner surf and transported landward to backfill the zone eroded on the rising tide. The net result is relatively slow steepening of the beach face, a change of the profile shape towards convex, and horizontal progradation through the formation of a neap berm. The primary factor determining which mode of berm growth occurs is the presence or absence of swash overtopping at the time of sediment accumulation on the beach face. This depends on the current phase of the spring-neap tide cycle, the wave runup height (and indirectly offshore wave conditions) and the height of the pre-existing berm. A conceptual model for berm morphodynamics is presented, based on sediment transport shape functions measured during the two modes of berm growth. [Copyright &y& Elsevier]

Abstract: In forested, mountain landscapes where debris flows are common, their deposition commonly forms valley-spanning dams of wood, boulders, or complex mixtures of both in headwater valleys. Sediment impoundment behind these dams causes alluviation in what would otherwise be bedrock channels. In this paper, the effects of debris dams on the evolution of headwater valley profiles over geologic time are examined. In the Oregon Coast Range, USA, longitudinal profiles of three headwater channels (approximately 2 km2 maximum contributing area), two of which are nominally bedrock, and all debris dams were surveyed. Channel and valley widths were measured, and surface bed material measurements (pebble counts) were taken at several locations along one stream. Cumulative relief in debris dams is highly variable within and among streams, reaching a maximum of 58% of profile relief at one location. The surveyed dams comprise 9.8%, 19%, and 6.4% of total basin relief in the three corresponding drainage basins, respectively. A model of bedrock erosion and channel profile evolution is derived that accounts for (a) fractional coverage by the channel of total valley width at any given time and (b) shielding by sediment impounded behind debris dams. The equation for incision rate, assumed constant, is solved for valley gradient as a function of contributing area, and parameter values are estimated from or supplied by field data. Results are compared to stream-gradient–contributing-area relationships obtained for the field sites. These comparisons suggest a strong effect of network structure, which varies significantly among the sites, on profile shape and relief because of the different susceptibilities to debris-flow deposition and, therefore, debris-dam formation. Longitudinal profiles with and without the effects of debris dams are modeled for one forced-alluvial, i.e., nominally bedrock, channel. For these model profiles, which extend only as far as the surveyed profile at this site, 55% of the profile relief is due to debris dams and the concomitant shielding of the bed by impounded sediment. The results suggest that a significant fraction of the relief of such forested, mountain landscapes is due to the effects of relatively immobile wood and boulders deposited in the valleys by debris flows. [Copyright &y& Elsevier]

Abstract: The saltation–abrasion model is a mechanistic model for river incision into bedrock by saltating bedload, which we have previously derived and used experimental data to constrain all parameter values. Here we develop a method for applying the saltation–abrasion model at a landscape scale, and use the model as a reference for evaluating the behavior of a wide range of alternative incision models, in order to consider the implications of the saltation–abrasion model, as well as other models, for predicting topographic steady-state channel slope. To determine the single-valued discharge that best represents the effects of the full discharge distribution in transporting sediment and wearing bedrock, we assume all runoff can be partitioned between a low-flow and a high-flow discharge, in which all bedload sediment transport occurs during high flow. We then use the gauged discharge record and measurements of channel characteristics at a reference field site and find that the optimum discharge has a moderate magnitude and frequency, due to the constraints of the threshold of grain motion and bed alluviation by high relative sediment supply. Incision models can be classified according to which of the effects of sediment on bedrock incision are accounted for. Using the predictions of the saltation–abrasion model as a reference, we find that the threshold of motion is the most important effect that should be represented explicitly, followed in order of decreasing importance by the cover effect, the tools effect and the threshold of suspension effect. Models that lack the threshold of motion over-predict incision rate for low shear stresses and under-predict the steady-state channel slope for low to moderate rock uplift rates and rock strengths. Models that lack the cover effect over-predict incision rate for high sediment supply rates, and fail to represent the degree of freedom in slope adjustment provided by partial bed coverage. Models that lack the tools effect over-predict incision rate for low sediment supply rates, and do not allow for the possibility that incision rate can decline for increases in shear stress above a peak value. Overall, the saltation–abrasion model predicts that steady-state channel slope is most sensitive to changes in grain size, such that the effect of variations in rock uplift rate and rock strength may affect slope indirectly through their possible, but as yet poorly understood, influence on the size distribution of sediments delivered to channel networks by hillslopes. [Copyright &y& Elsevier]

Abstract: The south-western shoreline along the entrance channel inside the Port of Richards Bay has experienced continued erosion. Four groynes were constructed to stabilise the shoreline. Monitoring of shoreline evolution provided valuable data on the accretion adjacent to two of the groynes and on the sediment transport rates at these groynes. Tides, beach slopes, winds, wave climate, current regime, and sand grain sizes were documented. The one site is “moderately protected” from wave action while the other is “protected” according to the Wiegel [Wiegel, R. L. (1964). Oceanographical engineering. Prentice Hall, Inc., Englewood Cliffs, NJ.] classification. The shoreline accreted progressively at the two groynes at 0.065 m/day and 0.021 m/day respectively. The shorelines accreted right up to the most seaward extremity of the groynes. Equilibrium shorelines were reached within about 3.5 years to 4 years, which compare well with other sites around the world. The mean wave incidence angle is large and was found to be about 22°. The median sand grain sizes were 0.33 mm and 0.37 mm. The groynes acted as total traps, the beach surveys were extended to an adequate depth, and cross-shore sediment transport did not cause appreciable net sand losses into the entrance channel. The net longshore transport rate along the study area, which is north-westbound, is only slightly lower than the gross longshore transport. The actual net longshore transport rates are 18 000 m3/year and 4 600 m3/year respectively at the two groynes. A rocky area limits the availability of sand at one groyne. There is fair agreement between the predicted and measured longshore transport rates at the other groyne. [Copyright &y& Elsevier]

Abstract: The formation and spatial evolution of Chandeleur Island, Louisiana, has been investigated extensively during the past several decades. No significant evaluation of the longshore sediment system, which is instrumental in the island''s evolution and morphodynamic maintenance, has been completed. This paper provides the first quantitative description of the longshore transport system that operates along this transgressive, overwash-dominated barrier island system. The net longshore sediment transport system was investigated via the wave refraction model, WAVENRG, which provided estimates of the transport volumes and drift directions alongshore. Surficial samples were collected from the foredune, midtide and step environments in an effort to characterize the sediments along the island and determine if textural or compositional trends have developed in response to a predicted longshore sediment transport system. Data obtained during this research indicate that the longshore transport system along Chandeleur Island is characterized by a bi-directional drift system, with drift directed both north and south from a nodal point located in the south-central portion of the barrier island. Analysis of the predicted transport volumes indicates that the degree of wave refraction, and therefore the breaker angle, is more instrumental in controlling the alongshore volume rate of sediment transport than the breaker wave heights. Additionally, a larger magnitude of sediment transport is predicted in the southern portion of the barrier, which is in a greater state of deterioration than the north and central portion of the island. This apparent contradiction indicates that factors such as a variable subsidence rate along the island are contributing to the alongshore geomorphology. No significant textural or compositional trends were identified alongshore. This absence of granulometric trends is attributed to the lack of variability of the sediments that comprise the barrier and the frequency of overwash events which occur on this low-profile island. [Copyright &y& Elsevier]

Abstract: For the general purposes of morphodynamic computations in coastal zones, simple formula-based models are usually employed to evaluate sediment transport. Sediment transport rates are computed as a function of the bottom shear stress or the near bed flow velocity and it is generally assumed that the sediment particles react immediately to changes in flow conditions. It has been recognized, through recent laboratory experiments in both rippled and plane bed sheet flow conditions that sediment reacts to the flow in a complex manner, involving non-steady processes resulting from memory and settling/entrainment delay effects. These processes may be important in the cross-shore direction, where sediment transport is mainly caused by the oscillatory motions induced by surface short gravity waves. The aim of the present work is to develop a semi-unsteady, practical model, to predict the total (bed load and suspended load) sediment transport rates in wave or combined wave-current flow conditions that are characteristic of the coastal zone. The unsteady effects are reproduced indirectly by taking into account the delayed settling of sediment particles. The net sediment transport rates are computed from the total bottom shear stress and the model takes into account the velocity and acceleration asymmetries of the waves as they propagate towards the shore. A comparison has been carried out between the computed net sediment transport rates with a large data set of experimental results for different flow conditions (wave-current flows, purely oscillatory flow, skewed waves and steady currents) in different regimes (plane bed and rippled bed) with fine, medium and coarse uniform sand. The numerical results obtained are reasonably accurate within a factor of 2. Based on this analysis, the limits and validity of the present formulation are discussed. [Copyright &y& Elsevier]

Abstract: Sediment output (solid and dissolved load) from two small Alpine rivers (Partnach and Lahnenwiesgraben in the Bavarian Alps) was measured during three summer field seasons from 2001–2003. There is high spatial variability of sediment output between the catchments and a high temporal variability between observation periods. Sediment transport in the Partnach river (Reintal) is dominated by solute load, whereas the Lahnenwiesgraben river transports a much greater proportion of solid load. This difference can mainly be explained by the different lithologies of the systems. The Reintal catchment is dominated by massive Triassic limestone. In the Lahnenwiesgraben catchment, in addition to limestones, unconsolidated rocks, marls and mudstone layers are significant. Furthermore, large rockslide dams in the Partnach valley isolate large parts of the Reintal catchment from solid load output. The components of fluvial sediment transport were, where possible, calculated by using flow duration curves and rating curve techniques. In the Lahnenwiesgraben event specific rating curves were used to determine suspended load. On the broad database of 55 measured flood events in the Lahnenwiesgraben a good correlation (r Pearson =0.9) between event peak discharge and suspended load of the event was established. Effective discharge was calculated for the different types of sediment load (solid and dissolved) and total load. In the Reintal effective discharge for total load is found in low flow classes close to mean discharge, because sediment output is dominated by dissolved load, which has its maximum efficiency at low and moderate discharges. In the Lahnenwiesgraben most work is done by discharges much higher than mean discharge during extreme individual flood events. [Copyright &y& Elsevier]

Abstract: Intensity and spatio-temporal variability of fluvial sediment transfers and mechanical fluvial denudation were analyzed in the periglacial Latnjavagge catchment (9km2; 950–1440m a.s.l.; 68.20N, 18.30E) in Arctic-oceanic northernmost Swedish Lapland. The present-day rates of fluvial sediment transfer are low. The mean annual mechanical fluvial denudation rate at the inlet of lake Latnjajaure, as calculated after five years of process monitoring (2000–2004), and excluding a “rare rainfall event” which caused 3.2 times higher suspended sediment transport during one day as compared to the total mean annual suspended sediment transport, is 2.3t km−2 yr−1. In years without “rare rainfall events”, most of the total annual sediment load is transported in a few days during annual snowmelt runoff. In the calculation of longer-term sediment budgets, rare rainfall events like the July 20th–21st, 2004 event have to be considered as essential components. Reliable estimation of the recurrence intervals of such events is problematic. The pattern of ice patches and snow fields within the valley, the steepness of streams and channels and the location of areas showing slushflow activity are the major factors controlling spatial variability of mechanical fluvial denudation in the drainage basin. The five lakes in Latnjavagge, especially lake Latnjajaure, are significant sediment traps and ground below 1300m a.s.l. is protected by a very stable and closed vegetation cover and rhizosphere across the entire lower catchment. [Copyright &y& Elsevier]

The modern Penghu Submarine Canyon is a sea floor expression of the convergent boundary between the frontal Taiwan orogenic wedge and the Chinese cratonic margin. The canyon is about 180km long and trends N–S, parallel to the strike of the Taiwan mountain belt. It is ∼240m deep at the head increasing to ∼3200m deep at its mouth before merging gradually into the Manila Trench. The Penghu Canyon is considered a tectonically controlled canyon rather than a slope canyon dominated by down-slope processes. Tectonic controls prevail over sedimentary processes. Tectonics controls the orientation and location of the Penghu Canyon while sedimentary processes contribute to its excavation and enlargement. The axis of the deep-water, underfilled basin off SW Taiwan dips southward and parallels the strike of the Taiwan orogen with a characteristic longitudinal sediment transport route. Hence, the Penghu Canyon developed under the gravitational mass movement with its main course along the N–S basin axis, not in a SW or SE downslope direction of both margins. The initial Penghu Canyon began at the intersection of the upper slopes of the South China Sea and Kaoping Slopes. Sediment flows cut into the slope sediments following regional dip toward the south, and excavated along the deepest part of the sea floor, forming the present Penghu Canyon. Shifting of axes of Late Pliocene–Pleistocene canyons from onshore SW Taiwan to the present-day position of the Penghu Canyon reflects the evolving foreland basins with a longitudinal canyon transport system progressively migrating southwestward. The linkage of canyon migration and evolution of the foreland basin may have significant implications for the overall sedimentation and tectonics of the SW Taiwan region. [Copyright &y& Elsevier]

Abstract: High frequency measurements of water depth, current velocity and suspended sediment concentration were used to investigate sediment transport processes in the swash zones of a dissipative beach and a steeper (intermediate) beach. Infragravity frequency motions dominated velocity spectra of the dissipative beach swash, while incident wave frequencies dominated the velocity spectrum of the intermediate beach swash. Velocity variance, the ratio of local wave height to water depth, mean bed shear stress and the mean friction velocity were greater on the intermediate beach. Mean suspended sediment concentrations were an order of magnitude greater on the intermediate beach. Infragravity frequencies dominated the oscillatory component of sediment transport on the dissipative beach. Incident wave frequency sediment transport dominated the intermediate beach. A maximum in the net shoreward transport occurred in approximately the mid swash zone on both beaches, suggesting accretion in the shoreward half of the swash, and erosion in the seaward part of the swash. Net sediment transport rates were lower on the ebb tide than on the flood tide, despite similar incident wave conditions. [Copyright &y& Elsevier]

Abstract: Implementation of the EU Water Framework Directive (2000/60/EC) has forced regulatory authorities to take an integrated view of the link between water quality and catchment management. In Northern Ireland, concern over progressive habitat degradation of one of the Province''s prime salmon rivers (the River Bush) provided the stimulus for a sediment monitoring programme. The aims of this study were to quantify instream sediment loads and to identify sources of fine sediment feeding into the river channel. This information would then be used to justify changes in the way the catchment''s resources were managed. Sediment loads were assessed at four sampling stations on the River Bush system over a one-year period (between 18/07/02 and 24/07/03) using sediment collection tubes and pit-type traps. These ranged between 0.196 and 4.98 t yr−1 for bed load and 1.70 and 102 t yr−1 for suspended load. A combination of desktop studies (erosion potential mapping), monitoring (visual observations, bank erosion magnitude and yield) and analytical work (sediment fingerprinting) was then applied in order to elucidate links between catchment sediment erosion and downstream sediment delivery. Bank erosion was highest in regions of the catchment with the least cohesive bank materials during high flow conditions. Livestock poaching and peak flows caused damage to banks at a localised scale and led to selective patches of bare land being susceptible to further erosion, augmenting the sediment load (approximately 2% of the annual suspended sediment and 60% of the annual bed load). Drainage maintenance work (60% and 30%), forest clearfell (1% and 2%) and ploughed land (37% and 8%) also contributed to the annual suspended sediment and bed load, respectively. Nine key actions were suggested in order to improve habitat quality in relation to sediment supply in the River Bush. These included wetland restoration; prohibiting drainage maintenance work; strategies to control conifer plantation felling; reducing bare ground; livestock access restrictions; construction site management; macrophyte clearance; employment of a river warden and systematic dissemination of project recommendations to the general public to generate community involvement. It was essential that these actions were both cost effective and practical in order to maximise catchment stakeholder uptake. [Copyright &y& Elsevier]

Abstract: The hydrologic regime of the Tiber River basin in central Italy has been impacted considerably in the last decades by intensive anthropic activities, and hydraulic works in particular (e.g. hydropower reservoirs, land use modification). In the Tiber River the wash load, in particular, plays an important role in sediment transport, and the knowledge of this hydrological variable is very important for the evaluation of medium–long-term dynamic of shoreline, and the evaluation of reservoir landfill. The Ripetta flow gauge, located in downtown Rome, has been continuously monitoring the daily discharge for decades, while daily sediment load measurements are available only for short terms. In this research, the yearly sediment rate is simulated using a simple stochastic model based on the evaluation of sediment rating curves. The sediment rating curve, i.e. the average relation between discharge and suspended sediment concentration for a specific location, is estimated using a power law model. The fitting curve, obtained by regression analysis, lacks the physical characterization of the phenomenon, often represented by the empirical evidences of erosion severity and the erosional power of river. Model results provide useful insights on the impact of recent hydraulic works on the sediment transport regime. [Copyright &y& Elsevier]

Abstract: The 25-m onshore migration of a nearshore sandbar observed over a 5-day period near Duck, NC, is simulated with a simplified, computationally efficient, wave-resolving single-phase model. The modeled sediment transport is assumed to occur close to the seabed and to be in phase with the bottom stress. Neglected intergranular stresses and fluid–granular interactions, likely important in concentrated flow, are compensated for with an elevated (relative to that appropriate for a clear fluid) model roughness height that gives the best fit to the observed bar migration. Model results suggest that when mean-current-induced transport is small, wave-induced transport leads to the observed onshore bar migration. Based on the results from the simplified phase-resolving model, a wave-averaged, energetics-type model (e.g., only moments of the near-bottom velocity field are required) with different friction factors for oscillatory and mean flows is developed that also predicts the observed bar migration. Although the assumptions underlying the models differ, the similarity of model results precludes determination of the dominant mechanisms of sediment transport during onshore bar migration. [Copyright &y& Elsevier]

Abstract: Rivers from the upper Rio Madeira basin (Bolivia) have been studied with uranium-series isotopes in order to constrain the timescales of weathering and sediment transfer from the Andes through the Amazon tropical plain. Uranium (U), thorium (Th) and radium (Ra) isotopes (238U–234U–230Th–226Ra and 232Th) have been analyzed in the suspended load (>0.2 μm) of rivers. Increasing 230Th excesses relative to 238U in suspended particles from the Andes to the tropical plain is interpreted as an increasing duration of weathering during sediment transport and storage in the foreland basin. Model calculations for (230Th/238U) and (226Ra/230Th) activity ratios in suspended particles using a continuous weathering model indicates that: (i) the timescale for production, storage and transport of sediments in the Andean Cordillera is only a few kyr, (ii) the storage time of suspended sediments in the foreland basin is 5±1 kyr and (iii) the average transfer time of suspended sediments from the Andes to the confluence of Rio Madeira with the Amazon River is 17±3 kyr. An implication of these short timescales is that the bedrock eroded must have lost part of its uranium during one or several past erosion cycles. This demonstrates the recycling of sediments through several erosion cycles before transfer to the oceans. The calculation of long-term (>1 kyr), steady-state erosion rates indicates that they are much lower than present-day rates. This increase in denudation rates must be recent and could be explained by an increase in precipitation ∼4 ka ago, as suggested by palaeoclimatic evidences and the draining of transient sedimentary basins encountered on the Altiplano and easily eroded. This suggests that climatic variability rather than tectonics alone produces high erosion rates. [Copyright &y& Elsevier]

Abstract: Rates of sediment supply by landsliding to an alluvial channel in a small catchment in central Switzerland were estimated over an 11-month study period. Fluvial sediment transport in the channel is independently monitored at the upstream and downstream ends of the study reach, yielding a unique opportunity to quantitatively compare the volume of sediment supplied to the channel with the volume in fluvial transport. Landslide-derived sediment discharge to the channel was greatest during the winter and spring months, while most of the fluvial sediment transport occurred during short, intense summer storms. Approximately 98m3 of sediment was delivered directly to the study reach by landsliding, ∼80m3 was transported into the reach from upstream, and ∼70m3 was transported out of the reach. Thus, there was a net accumulation of ∼100m3 of sediment during the 11-month study. Decadal-scale channel aggradation was independently assessed by comparing channel longitudinal profiles in 1993 and 2004. During this 11-year period, a total of ∼1500m3 of sediment has accumulated in the study reach. Aggradation has occurred largely in two broad zones that correspond with both the locations of major landslide complexes and reaches of high channel slope, indicating that hillslope sediment input left an imprint on the morphology of the channel bed that appears to be stable over at least decadal time scales. [Copyright &y& Elsevier]

Abstract: Channel pattern effectively stratifies the dynamics of rivers and floodplains in forested mountain river systems of the Pacific Northwest, USA. Straight channels are least dynamic, with relatively slow floodplain turnover and floodplains dominated by old surfaces. Braided channels are most dynamic, with floodplain turnover as low as 25 years and predominantly young floodplain surfaces. Island-braided and meandering channels have intermediate dynamics, with moderately frequent disturbances (erosion of floodplain patches) maintaining a mix of old and young surfaces. Return intervals for the erosion of floodplains increase in the order of braided, island-braided, meandering, and straight (8, 33, 60, and 89 years, respectively). A threshold for the lateral migration of a channel occurs at a bankfull width of 15–20 m. The most likely mechanism underlying this threshold is that larger channels are deep enough to erode below the rooting zone of bank vegetation. Above this threshold, channels not confined between valley walls exhibit channel patterns distinguishable by slope and discharge, and slope–discharge domains can be used to predict channel patterns. Meandering and braided patterns are most consistently identified by the model, and prediction errors are largely associated with indistinct transitions among channel patterns that are adjacent in plots of slope against discharge. Locations of straight channels are difficult to identify accurately with the current model. The predicted spatial distribution of channel patterns reflects a downstream decline in channel slope, which is likely correlated with a declining ratio of bed load to suspended load. Ecological theory suggests that biological diversity should be highest where the intermediate disturbance regime of island-braided channels sustains high diversity of habitat and successional states through time. [Copyright &y& Elsevier]

Abstract: Quantitative stratigraphy predicts the geometry of geologic strata and their petrophysical properties based on mathematical models of geological processes and parameters which affect the formation and evolution of geologic strata. Such processes include erosion, sediment transport, and deposition. Quantitative stratigraphic inversion estimates the process parameters from a priori data by systematic modeling until the predictions are compatible with the observations. In the case of quantitative seismostratigraphic inversion, the a priori data are predominantly of the seismic kind. To evaluate feasibility, we designed a preliminary algorithm which we applied in a prograding delta environment. We found that by fixing the sediment influx rate, subaerial transport rate, and the initial topography, we were able to reproduce the basic features of the delta with only three to five parameters which included subaqueous transport rate and its depth-dependent decay rate, base level, and sediment source location and spatial extent. [Copyright &y& Elsevier]

Abstract: The present paper aims at studies of the suspended sediment transport in inner Ishikari Bay in snowmelt season using a numerical approach and field observation data. The sediment transport and bottom boundary layer models are coupled into the Princeton Ocean Model to compute suspended sediment concentration in the system. The following findings have been deduced: (1) The suspended sediment transport in the study area in snowmelt season is dominated by the sediment discharge from the Ishikari River. The effect of sediment resuspension due to wave current interaction is limited to a very shallow area along the coast. (2) A comparison between observed and computed suspended sediment concentrations shows that the model can reproduce reasonably well the general features of the dynamics of suspended sediment transport in Ishikari Bay in snowmelt season. (3) The suspended sediment matter (SSM) from the Ishikari River is mainly transported northward. The vertical structure of SSM concentration displays a slow sinking of sediment matter supplied to the water column from the surface i.e. high sediment concentration is seen in surface layers and it gradually deceases in the lower layers. (4) After two months of simulation, net erosion occurs in a narrow area nearshore. The average erosion depth in this area is 0.16 mm. Net deposition locates in a wider area north of the inner bay. The average deposition depth in this area is 0.04 mm. [Copyright &y& Elsevier]

Abstract: We have measured 238U–234U–230Th radioactive disequilibria in five size fractions of colloids and suspended sediments for four rivers from the Murray–Darling River basin (SE Australia). Continuous compositional trends of composition are observed for (234U/238U) and (230Th/238U) activity ratios over the range of size fractions studied. They are explained by the variable contribution of two components: detrital alumino-silicates and organic matter. Using relationships between activity ratios and the loss-on-ignition, it is possible to estimate the U-series isotopic composition of both detrital and organic end-members, which provide the best estimate for the composition of the true detrital phase (i.e. controlled only by the removal of elements through weathering) and the true dissolved phase (i.e. colloid-free), respectively. When performing a single filtration at 0.2 μm, it appears that size fractions > and <0.2 μm underestimate the disequilibrium in both the true detrital and dissolved phases, respectively. We show that erosion does not currently operate in steady state in the Murray–Darling basin and catchment soils are currently being degraded. This could be a consequence of the intensification of agriculture and deforestation over the past 100 yr. The residence time of sediments in the different sub-basins is calculated by computing the composition of the detrital phase with a continuous weathering model. It yields 11±2 kyr for the Darling River basin, only 2–3±1 kyr for the Murray River and 7±2 kyr for the Goulburn River. These values are correlated with the age of changes in river dynamics, in turn probably controlled by climate fluctuation, and indicate the age of the modern river system for each sub-basin. [Copyright &y& Elsevier]

Abstract: Submarine channels have long been considered analogous to meandering fluvial channels due to their similar planform geometry, and this has given rise to strong analogies in terms of the fluid dynamics of these channel types. However, there is a paucity of direct measurements detailing the structure of velocity or sediment concentration, and nothing is known about the structure of secondary flow, within submarine channels. Within fluvial channels, secondary circulation has been shown to be an important control of erosion, deposition, lateral sediment transport and overall bend stability. This paper presents a series of experiments in which saline gravity currents flowed through a submerged, fixed-form, sinuous channel model. Ultrasonic Doppler velocity profiling provided high-resolution, three-dimensional visualisation of flow fields, thereby allowing the first quantitative visualisation of velocity profiles and secondary flows of a saline gravity current within a sinuous submarine channel. The same model was also used to measure the structure of flow within a subaerial channel, thereby providing a detailed comparison between a submarine and fluvial channel. The data reveal that secondary flow cells in submarine channels are best developed at bend apexes and that the basal component of the flow cell moves from the inside to the outside of the bend, in a reversed direction to that expected from models of fluvial bend flow. These results are of prime importance when assessing the validity of comparisons between submarine and fluvial channels, and the role of secondary flow cells in the migration and evolution of meander bends. This work demonstrates that the fundamental flow processes controlling the evolution and migration of submarine and fluvial channels may be very different, and suggest that the form and evolution of submarine channels may also show different properties to their fluvial counterparts. [Copyright &y& Elsevier]

Abstract: Distributed erosion models are potentially good tools for locating soil sediment sources and guiding efficient Soil and Water Conservation (SWC) planning, but the uncertainty of model predictions may be high. In this study, the distribution of erosion within a catchment was predicted with a semi-empirical erosion model that combined a semi-distributed hydrological model with the Morgan, Morgan and Finney (MMF) empirical erosion model. The model was tested in a small catchment of the West Usambara Mountains (Kwalei catchment, Tanzania). Soil detachability rates measured in splash cups (0.48–1.16gJ−1) were close to model simulations (0.30–0.35gJ−1). Net erosion rates measured in Gerlach troughs (0.01–1.05kgm−2 per event) were used to calibrate the sediment transport capacity of overland flow. Uncertainties of model simulations due to parameterisation of overland flow sediment transport capacity were assessed with the Generalized Likelihood Uncertainty Estimation (GLUE) methodology. The quality of the spatial predictions was assessed by comparing the simulated erosion pattern with the field-observed erosion pattern, measuring the agreement with the weighted Kappa coefficient of the contingency table. Behavioural parameter sets (weighted Kappa >0.50) were those with short reinfiltration length (<1.5m) and ratio of overland flow power α to local topography power γ close to 0.5. In the dynamic Hortonian hydrologic regime and the dissected terrain of Kwalei catchment, topography controlled the distribution of erosion more than overland flow. Simulated erosion rates varied from −4 to +2kgm−2 per season. The model simulated correctly around 75% of erosion pattern. The uncertainty of model predictions due to sediment transport capacity was high; around 10% of the fields were attributed to either slight or severe erosion. The difficult characterisation of catchment-scale effective sediment transport capacity parameters poses a major limit to distributed erosion modelling predicting capabilities. [Copyright &y& Elsevier]

Abstract: The inception of the sheet flow regime as well as the effects of the phase lag when the sheet flow regime is established were investigated for oscillatory flows and combined steady and oscillatory flows. A new criterion for the inception of sheet flow is proposed based on around 300 oscillatory flow cases from experiments. This criterion was introduced in the Camenen and Larson [Camenen, B., Larson, M., 2005. A bedload sediment transport formula for the nearshore. Estuarine, Coastal and Shelf Science 63, 249–260.] bed load formula in order to take into account phase-lag effects in the sheet flow regime. The modification of the Camenen and Larson formula significantly improves the overall agreement with data and yields a correct behavior in relation to some of the main governing parameters, which are the median grain size d 50, the orbital wave velocity U w, and the wave period T w. The calibration of the new formula was based on more than 200 experimental data values on the net sediment transport rate for a full wave cycle. A conceptual model was also proposed to estimate the ratio between sediment transport rate with and without phase lag, (r pl = q s,net / q s,net,ϕ=0). This simple model provides accurate results and may be used together with any quasi-steady model for bed load transport. [Copyright &y& Elsevier]

Abstract: A volume-of-fluid Navier–Stokes solver (RIPPLE) was used to simulate inner surf and swash zone flow with a 3s wave period and wave height of 0.14m on a planar, 1:10 sloping beach (Iribarren number of 1.0). In addition to other hydrodynamic information, RIPPLE was used to provide high-resolution predictions of the pressure gradient and fluid velocity in the horizontal and vertical dimensions that served as forcing to a discrete particle model (DPM). Sediment transport processes in the inner surf and swash zones were simulated for a thin veneer of sediment particles over a 5m test section in the DPM. Coupling between RIPPLE and the DPM was one-way such that particle–particle and fluid–particle interactions in the DPM did not provide feedback to alter the flow predicted by RIPPLE. The numerical simulation showed strong sediment suspension localized under vortices that reach the bed. Interestingly, the bulk of the sediment located in the small-scale vortex originated from locations nearly 0.2m landward. These findings suggest that (1) sediment motion for a single swash event can be significant, (2) that sediment measured in suspension likely originates from locations other than the bed directly below the suspension plume suggesting the importance of sediment advection and (3) that sparse cross-shore measurements in the field will only sporadically capture localized suspension events. [Copyright &y& Elsevier]

Abstract: In the present work, the sediment transport rate in the swash zone is estimated using a Boussinesq model coupled with a porous flow model in order to incorporate the infiltration–exfiltration effects. The transport rate is estimated from a modified Meyer–Peter and Müller formula using different values the multiplier C for uprush and backwash to incorporate the observed higher transporting efficiency of the uprush due to the presence of pre-suspended sediment from the bore collapse. Alternatively, the depth-integrated transport equation for suspended sediment is solved. The comparison between model results and experimental data shows that both approaches are able to give satisfactory results. [Copyright &y& Elsevier]

Abstract: The amount of sediment, wood, and detritus (leaves and small branches) accumulations were examined in four headwater tributaries subjected to different treatments (unlogged, logged with riparian buffer, and logged with no buffer) 16 and 40 months after timber harvesting in the Bukit Tarek Experimental Watershed, Peninsular Malaysia. Sediment transport from hillslope logging roads and skid trails resulted in large sediment storage in the stream channels. Riparian reserves appear to mitigate logging impacts to streams; however, more sediment was found in a tributary channel with a 20-m buffer than an unlogged channel because some of the nearby roads and skid trails were connected to the stream. Sediment storage in channels declined within 40 months after logging in catchments with and without riparian buffers. Vegetation recovery on skid trails and logging roads reduced both sediment supply and delivery. The volume of large wood was 1.5 to 2-times greater in the stream without riparian reserves than the stream of an unlogged catchment or in a stream with a riparian buffer. No consistent change in detritus accumulations was found among streams in 2001 and 2003, although more detritus was present in 2003 in all streams. The effects of logging and the effectiveness of riparian buffers appear to depend on the hydrologic connections between hillslopes and headwater streams. [Copyright &y& Elsevier]

Abstract: Low crested structures for beach defence purposes are frequently configured in the form of cells. This paper investigates the hydrodynamic and morphological response of such defence schemes by means of laboratory experiments and numerical simulations. Experiments were carried out at the large mobile-bed basin of the “Laboratorio di Idraulica Costiera” of the “Politecnico di Bari”, IT. Tests peculiarity is the simultaneous simulation of three different types of lateral confinement: a channel, representative of an indefinitely long structure, and two areas with narrow and wide gaps, representative of a common scheme and of an almost isolated structure respectively. Submerged, zero freeboard and emerged conditions were tested. A typical storm of the Northern Adriatic sea was reproduced by 6 wave attacks. Water level and currents were measured in front and behind the structures, at gaps and roundheads. Results, focusing on rip current intensities and piling-up, are presented and discussed. An extensive plan view of wave intensities and flow patterns inside the basin is provided through numerical simulations with MIKE 21 numerical suite. The sand bed was surveyed along 30 profiles covering the narrow gap area and the isolated structure roundheads. For the submerged conditions tests, 15 of these profiles and the shoreline position were monitored after each step of the simulated storm. Average and maximum values of local erosion at the structure toe are presented. Time evolution of erosion at gaps is related to the main hydrodynamic variables through Bijker sediment transport formula. Evaluation of volume changes in the protected area shows that sand is in average trapped behind the barriers, being transported offshore from gaps and returning inshore over the crest. The observed and reconstructed transport mechanism is a combination of bed load and suspended transport, the latter being slightly more important. Bed level changes are well predicted by morphodynamic simulations performed with MIKE 21 CAMS. [Copyright &y& Elsevier]

Abstract: This study presents the results of a long-term monitoring program of bed level changes measured during 8 yr at an intertidal mudflat in a microtidal, temperate coastal lagoon. Additionally, bed level measurements obtained at a 10-min temporal resolution at the same tidal flat and at the bed of a nearby tidal channel are presented. Short-term changes in bed level are one or two orders of magnitude larger than the annual net-deposition rate, which shows that the environment is highly dynamic with respect to erosion, transport and deposition of fine-grained sediment. Some seasonality in the bed level changes was observed and there is a tendency for mudflat deposition in spring, summer and early autumn and erosion during the rest of the year, but interannual variations are large and different parts of the mudflat show different seasonal signals. A close coupling between sub- and intertidal deposition and erosion was observed. The time-series showed that some of the material eroded from the mudflat was not exported to the open sea, but instead temporarily deposited in a nearby shallow tidal channel and later returned to the mudflat during calmer weather conditions. These findings support previously published hypothesis and results of modelling studies. Based on the observed abundance of fine-grained sediment at the study sites and the high accretion rates generally found on fine-grained tidal flats in the Danish Wadden Sea area, it is argued that these fine-grained tidal flats are not seriously threatened by the expected sea level rise in the 21st century. [Copyright &y& Elsevier]

Abstract: Significant portions of the global soil organic carbon (SOC) pool must reside on sloping terrains where the spatial distribution of SOC reflects the combined effects of geomorphic processes and biological C cycling. Using a newly developed soil C mass balance model that explicitly includes soil production and sediment transport, we investigated the relative roles of sediment production/transport vs. biological C cycling in creating the observed spatial patterns of SOC storage within two grass-covered hillslopes in California. The study sites differed in bedrock geology, climate, and erosion rates. Measurements of SOC, soil texture, plant C inputs, and soil thickness were combined with topographic surveys and published soil erosion and production rates in the analysis. Soil thickness was found to be the key control on SOC storage, and soil thickness is balance between soil production and curvature-dependent erosional losses. Additionally, topographically varying rates of plant C inputs, decomposition rates, and SOC erosional losses or depositional inputs were found to only partially explain the observed SOC storage patterns. We used the measured relationships between SOC storage, soil thickness, and topographic curvature to create SOC storage maps of the two watersheds. At both sites, about 70% of the hillslope SOC is stored in depositional areas that are susceptible to episodic mass wasting. At the drier site, there was a larger SOC storage despite the lower soil C % because the clay-rich bedrock resulted in the development of relatively thick soils for a given slope curvature. We conclude that the geomorphic processes driving soil thickness provide fundamental mechanisms that control the spatial SOC patterns on vegetated hillslopes. [Copyright &y& Elsevier]

Abstract: Based on data from the middle Yellow River, a model of erosion and sediment yield is proposed to describe coupled eolian and fluvial processes in a transitional zone from arid to sub-humid climates, and to explain rapid erosion and a high sediment yield in the zone. In the study area, wind action predominates from March to June, which erodes weathered bedrock and transports eolian sand to gullies, river channels and floodplains. In the following summer, especially from July to September, rainstorm runoff in gullies and river channels transports large quantities of fine loessic material, in the form of hyperconcentrated flow. As a result, most of the previously stored eolian sand and material supplied by mass-wasting of loess can be transported to the major tributaries and the main stream of the Yellow River, resulting in the high specific sediment yield. There exists an optimal grain size composition which maximizes suspended sediment concentration in the study area, resulted from the combined wind–water processes. [Copyright &y& Elsevier]

Abstract: Biogeochemical data from four sequential sediment traps deployed for one full year (April 1987–March 1988) at the shelf edge (200m isobath) of the Canadian Beaufort Sea are presented. In addition, multi-traps and Kenney traps, which collect material suspended near the bottom, provided data from the inner shelf for short intervals in spring and summer. A novel aspect of this work is the discrimination of biogenic and terrigenous contributions to the total carbon using a relationship between terrigenous carbon and aluminum (Al). The vertical flux in the Beaufort Sea derives primarily from three sources: marine biological production, the Mackenzie River Plume, and coastal and seabed erosion. The material trapped at all shelf edge sites was predominantly biogenic and the seasonal fluxes of both biogenic and terrigenous matter varied with geographical location. In open-water conditions, deposition of terrigenous material can be attributed at various times and places to (1) transport by the Mackenzie Plume to the shelf edge during freshet; (2) resuspension of sediment during north-westerly gales; and (3) erosion of steep coastlines during south-easterly gales followed by northward transport. On the west side of the shelf, the biogenic and terrigenous fluxes were highest in summer and were primarily influenced by the Mackenzie River freshet, increased solar flux, available nutrients, sea ice break-up, and water column stability. On the east side of the shelf, biogenic and terrigenous fluxes were highest in the fall and the most important controlling factors were the extensive open water, intense resuspension events accompanying storms from the northwest, and the flow of the fresh, warm, turbid waters of Mackenzie River to the northeast. There was strong evidence of sediment transport in mid-water and bottom layers, but the mechanisms involved cannot be inferred from this study. Stable isotopes of carbon and nitrogen, C/N ratios, biogenic silica, and chlorophyll a measurements help to distinguish between marine autotrophic production and heterotrophic production, of which the latter appears to dominate in the fall and continue beneath the ice into the polar night. Al and iron correlate strongly and are primarily associated with the terrigenous fraction whereas calcium and phosphorus have both terrestrial and biogenic associations. [Copyright &y& Elsevier]

Abstract: This study reviews the existing erosion and sediment transport models developed at hillslope and watershed scales. The method followed in this review is to summarize the models with a focus on the physically based modeling technique as well as with a brief discussion about empirical and conceptual models. Approaches for determining the sediment transport capacity of flow are explained. The extension of a sediment transport model to a nutrient transport model is then discussed. Finally, the future of erosion and sediment transport models are projected to include the probabilistic description of hydrology, the physical characteristics of the watershed, and the stochastic structure of soil properties. The review is expected to be of interest to researchers, watershed managers and decision-makers while searching for models to study erosion and sediment transport phenomena and related processes such as pollutant and nutrient transport. [Copyright &y& Elsevier]

Abstract: The erosion behaviour of various fine-grained sediment deposits has been investigated in laboratory experiments. This work mainly focused on tests using sewer sediment in which strong biochemical reactions were observed during the deposit formation period. A small number of initial tests were conducted in which the deposits were made from mixtures of “clean” mineral and organic sediments. The erosion behaviour observed in these tests was compared with the erosion characteristics for sediments taken from deposits in a sewer. The impact of the biological processes on physical properties such as bulk density, water content, deposit structure and the erosive behaviour as a function of bed shear stress are quantified and discussed. Based on these observations it is believed that bio-processes weaken the strength of the in-pipe sediment deposits. A significantly weaker sediment surface layer was observed during deposition under quiescent oxygen-rich conditions. This resulted in a deposit with low shear strength which may be a cause of a first foul flush of suspended sediment when flow rates were increased. Comparison between tests with sewer sediments and the artificial representative surrogates suggested that the deposits of the later did not correctly simulate the depositional development and the resultant erosion patterns observed with the more bio-active sewer sediment. [Copyright &y& Elsevier]

Abstract: The scarcity of grain-size data from gravel-bed rivers has traditionally hindered hydraulic, sediment transport and river habitat studies. A new remote sensing methodology to estimate grain-size distribution is presented. It combines textural digital images of the riverbed at 1:1000 and 1:40 scales with grain-size sampling. It was applied to a 12-km reach of the Isábena River (Central Pyrenees NE Spain). First, textural patterns for each grain-size range were obtained, selecting the most closely related texture variables, including the use of semivariograms. Second, multiple linear regression equations were derived from the textural variables to estimate each value of the grain-size distribution. The highest correlation values (r 2) were obtained from the central part of the distribution (D 50 with a RMS error of 12.7%). Finally, new multiple linear regression equations to estimate the D 50 and D 84 were obtained from 1:1000 images and four textural variables. These were used to derive D 50 and D 84 maps of the riverbed, re-sampled at a resolution of 1.5 m pixels, with RMS estimation errors of 26% and 32%, respectively. Downstream change in grain-size is also well reproduced by the method. The mean D 50 of 72 and 32 mm were estimated in the upper and the lower reaches of the river, respectively. The methodology shows great potential for application, the relation between the spatial resolution of the images and the mean grain-size of the riverbed sediment being the main issue for future development. [Copyright &y& Elsevier]

Abstract: An extensive barrier-spit system 20 to 30 km long developed on the delta front platform of the Ba lat Delta within a relatively short period (10–20 years). However, it was not evident whether the formation was related to river floods, typhoons or calm weather conditions, or to cross-shore or alongshore sediment transport mechanisms. Therefore a process-based numerical model that simulates sediment transport and morphologic changes by waves, tides, wind, and river flow, is used to analyze the processes that govern this barrier formation. The mechanism that initiates the barrier formation is concluded to be onshore transport by wave asymmetry of sediment previously transported seaward in the buoyant river plume. The main mechanism that counteracts the barrier formation is probably destruction of the barrier by river flow. During the subsequent transformation from a subaqueous barrier into a sub-aerial barrier-spit system, overwashes and alongshore sediment transport become increasingly important. This spit system therefore appears to be dominated by alongshore processes, even though its initial formation is more strongly regulated by cross-shore processes. The importance of cross-shore processes results in a minor contribution of typhoons to the initial formation of these barriers. Typhoons are not very important to destruction of barriers as well, because wave energy is gradually dissipated over the gentle offshore profile, which in turn results from river plume sedimentation. [Copyright &y& Elsevier]

Abstract: This paper focuses on the analysis of the morphological response induced by low-crested structures on the adjacent seabed, with emphasis on the far-field erosion that is frequently observed close to roundheads and at the gaps between structures. The analysis is based on observations of far-field erosion, both at prototype scale and in laboratory experiments. Mechanisms responsible for the observed erosion are highlighted using coastal area numerical modelling tools to simulate the flow patterns induced by schemes involving low-crested structures. Finally, an example of the use of a coastal area morphological modelling system to investigate the dependence of the far-field erosion processes on the freeboard of the coastal protection structures is presented and discussed. [Copyright &y& Elsevier]

Abstract: We study the effects of incorporating surface mass transport and the gravitational potential energy of both crust and lithospheric mantle to the viscous thin sheet approach. Recent 2D (cross-section) numerical models show that surface erosion and sediment transport can play a major role in shaping the large-scale deformation of the crust. In order to study these effects in 3D (planform view), we develop a numerical model in which both the dynamics of lithospheric deformation and surface processes are fully coupled. Deformation is calculated as a thin viscous layer with a vertically-averaged rheology and subjected to plane stresses. The coupled system of equations for momentum and energy conservation is solved numerically. This model accounts for the isostatic and potential-energy effects due to crustal and lithospheric thickness variations. The results show that the variations of gravitational potential energy due to the lateral changes of the lithosphere–asthenosphere boundary can modify the mode of deformation of the lithosphere. Surface processes, incorporated to the model via a diffusive transport equation, rather than just passively reacting to changes in topography, play an active role in controlling the lateral variations of the effective viscosity and hence of the deformation of the lithosphere. [Copyright &y& Elsevier]

Abstract: Rippled scour depressions (RSDs) are distinct morphologic and textural features that have been observed in numerous nearshore environments as depressions containing coarse rippled sediments. The nature and significance of these features can be better understood with the use of multibeam sonar systems that acquire high-resolution bathymetry and co-registered backscatter intensity data and reveal both the small-scale characteristics of RSDs and larger-scale seabed patterns associated with them. In this paper, we compare RSDs identified in high-frequency (300kHz) multibeam sonar surveys on the inner shelves of southwest Washington, northern California and Long Island, New York. RSDs at these sites are evident as distinct features that are generally up to 1m deeper than the adjacent seabed and exhibit high acoustic backscatter intensity due to the presence of coarse sediments, typically gravel. Shore parallel oscillatory ripples (typically 1m wavelength) exist within the coarse material associated with RSDs and are attributed to wave-orbital motion. We propose a classification of RSDs based on their morphology and textural characteristics as well as the larger-scale seabed patterns associated with them, which together provide insight about the processes that affect their development and evolution. The RSDs described here are apparently the result of localized flow that can redistribute significant volumes of sediment in the nearshore zone under a range of energetic regimes over relatively short time scales. One type of linear shore-normal RSD always corresponds to larger-scale low-amplitude transverse bedforms that appear to be related to longshore currents. Some of these low-amplitude bedforms migrated as much as 50–150m over 2 years. Another type of elongate RSD, appears to be relatively stable over time, is characterized by bathymetric and textural asymmetry with one distinct upcurrent edge and one diffuse downcurrent edge, and is apparently a result of transverse flow. Other irregularly shaped nearshore RSDs that can be created and destroyed on time scales of less than 1 year, are the result of localized erosion and accretion of up to 1m, and are distributed rhythmically along-shore in water depths of 8–16m suggesting that they are related to hydrodynamics associated with the breaker zone. The characteristics of RSDs elucidated by high-frequency multibeam sonar data provide evidence of a variety of physical processes associated with RSDs and emphasize the importance of these features with respect to sediment transport on the inner shelf. [Copyright &y& Elsevier]

Abstract: In the Sahelian zone of West-Africa, erosion by both wind and water causes a serious decline in fertility of the already low fertile soils. Despite the fact that the flow of nutrients has been intensively investigated by the use of nutrient balances, little attention has been paid to the contribution of the soil erosion to the nutrient balance. Two physically based models (WEPS and EUROSEM, both written in PCRaster) were extended with nutrient modules to investigate the role of wind and water erosion in the loss and gain of nutrients at the scale of a Sahelian field. The models are applied at three geomorphic units in the Katchari catchment in northern Burkina Faso. WEPS can predict spatial patterns of erosion and deposition due to wind-blown particle transport. Depending on wind direction, crusting and vegetation cover net erosion or deposition can occur. When erosion occurs considerable amounts of nutrients are lost, but when deposition occurs, most of these nutrients may be regained. Soil loss by water erosion is closely related to the crust type present, which regulates infiltration and thus runoff. Nutrient losses by water erosion are small compared with those by wind erosion, but are forever lost for the area. Sediment transport by wind in saltation mode results in the largest soil and nutrient loss at the time scale of an event. [Copyright &y& Elsevier]

Abstract: Using the average directions of the principal wavefronts that approach the northeastern Brazilian coast, which are coincident with the directions of the prevailing winds, a wave climate model was defined, for approximately 3000 km of coast by construction wave refraction diagrams. A resulting sediment transport model that was obtained by numerical modeling starting with refraction diagrams, taking into account the wave approach angles and their heights permitted the reproduction, on a regional scale, of the sediment dispersion pattern. Several drift cells were identified, the limits of which were based on alterations in the direction or intensity of potential net longshore drift. Although also dependent on other factors such as the supply of fluvial sediments to the coastal zone and to wind activity, the coastal sections that present progradation, erosion or non-deposition, can be reasonably explained, in a first order approximation, by these variations. As a generalization, geomorphic drift indicator match patterns of regional scale sediment dispersal. [Copyright &y& Elsevier]

Abstract: The physical basis of Bagnold''s equation for critical stream power is examined. Although the general approach is well founded, the original equation can be criticised for (1) failing to distinguish between the grain size in transport and the grain size that represents bed roughness; (2) requiring a knowledge of critical flow depth in addition to gross channel properties; (3) failing to allow for hiding and protrusion effects on the mobility of mixed-size stream beds. More general equations are presented which overcome these limitations. They require a knowledge of channel slope, but not depth. The analysis suggests that the presence of form resistance in addition to grain roughness does not affect the calculation of critical power. Critical power is expected to depend more sensitively on grain size between reaches than within reaches. [Copyright &y& Elsevier]

Abstract: This review paper aims to present a practical, integrated procedure for the prediction of sediment transport rates in both the continental and marine environment, based on the settling velocity of particles. Such studies have important applications in diverse fields such as civil and coastal engineering, sedimentology and environmental geology, where they can assist in flood control and the prevention of contaminant dispersal by wind and water, as well as the siltation of dams and harbours. The formation of placer deposits including gold, diamonds and other heavy minerals is also controlled by sediment transport processes, so that these studies can form the basis for more efficient exploration programs. The first part of the paper discusses some basic principles important in sediment transport, followed by an overview of published methods to determine the settling velocity of differently shaped particles, including natural grains. The application of settling velocity to predict the entrainment threshold of sediments on plane, horizontal and inclined beds by unidirectional currents and oscillatory waves is then discussed, which finally leads to the determination of sediment transport rates over plane and rippled beds. The validity of this approach to natural conditions is tested against published field data where possible. Other, widely used methods are also critically discussed, pointing out severe problems in current sampling technology and the calculation of bedload transport in natural environments. [Copyright &y& Elsevier]

Abstract: A calibrated morphodynamic model of the barrier island of Terschelling, The Netherlands [Grunnet, N.M., Walstra, D.J.R., Ruessink, B.G., 2004. Process-based modelling of a shoreface nourishment. Coastal Eng. 51/7, 581–607], comprising the island and its two adjacent tidal inlet systems, is applied to identify the relative contribution of tides, wind and waves to the cross-shore and alongshore redistribution of a 2 Mm3 nourishment supplied to the nearshore zone along the island. Several model simulations with varying combinations of horizontal and vertical tide, wind and wave forcing were designed to investigate the effect of each individual forcing on a large spatio-temporal scale (order of kilometres and months, respectively). As expected, stirring and transport by waves and wave-induced currents are predicted to be by far the dominant contributor to the net sediment transport along the coast of Terschelling. Because of the strong obliquity of the winds and the relatively small tidal currents in front of the island (≈0.5 m/s), alongshore wind-driven currents increase sediment transport rates and horizontal tides virtually have no net transport capacity. This motivated a local model of the study area along the closed coast of Terschelling, not including tidal inlets and further simplifying tidal boundary definitions by omitting the horizontal tides: morphodynamic simulations of the local model show virtually identical results as the larger model predictions. The reduction in complexity in setting up a local model instead of a regional model coupled with the corresponding significant reduction in computational time points to an increasing applicability of complex process-based models. [Copyright &y& Elsevier]

Abstract: The latest Holocene sedimentary record of a cohesive channel and subtidal shoal in the lower Hudson River Estuary was examined to elucidate natural (sea-level rise, sediment transport) and anthropogenic (bulkheading, dredging) influences on the recent morphodynamic evolution of the system. To characterize the seafloor and shallow subbottom, ∼100 km of high-resolution seismic reflection profiles (chirp) were collected within a 20-km reach of the estuary and correlated with sediment lithologies provided by eight vibracores recovered along seismic lines. Sediment geochronology with 137Cs and 14C was used to estimate intermediate and long-term sedimentation rates, respectively, and historical bathymetric data were analyzed to identify regional patterns of accretion and erosion, and to quantify changes in channel geometry and sediment volume. The shoal lithosome originated around 4 ka presumably with decelerating eustatic sea level rise during the latest Holocene. Long-term sedimentation rates on the shoal (2.3–2.6 mm/yr) are higher than in the channel (2 mm/yr) owing to hydrodynamic conditions that preferentially sequester suspended sediment on the western side of the estuary. As a result, the shoal accretes oblique to the principal axis of tidal transport, and more rapidly than the channel to produce an asymmetric cross-section. Shoal deposits consist of tidally bedded muds and are stratified by minor erosion surfaces that seismic profiles reveal to extend for 10s of meters to kilometers. The frequency and continuity of these surfaces suggest that the surficial shoal is catastrophically stripped on decadal-centennial time scales by elevated tidal flows; tidal erosion maintains the shoal at a uniform depth below sea level and prevents it from transitioning to an intertidal environment. Consequently, the long-term sedimentation rate approximates the rate of sea-level rise in the lower estuary (1–3 mm/yr). After the mid 1800s, the natural geometry of the lower Hudson River Estuary changed rapidly in response to engineering works that forced the channel to self-deepen. Analysis of historical bathymetric data indicates that the channel lost an estimated 3×106 tons of sediment between ca. 1939 and 2002 (50,000 tons/yr average) by subaqueous erosion, increasing in depth by as much as 4 m in places. Erosion appears to have been concurrent with systematic bulkheading of the shoreline after ca. 1865, which decreased the estuary surface area by ∼19% overall. Evidently, self-deepening of the channel is a morphodynamic adjustment to reestablish equilibrium cross-sectional area, yet the state of this change locally and elsewhere in the estuary is unknown. Subaqueous erosion documented in this study is a significant source of sediment with implications to the sediment budget and environmental quality of the Hudson River Estuary. [Copyright &y& Elsevier]