Search

Abstract: Coastal dunes can act as a method of soft coastal protection against inundation and direct impact of waves during storms if they are substantially large enough in volume to withstand erosion without breaching. However, the time evolution of sand dunes under direct wave impact is not well understood and many available models require site specific calibration and have had limited verification at field scales. Here we test three models of varying complexity in their ability to predict both dry beach erosion volumes and dune to a retreat for an East Coast Low storm event that occurred on the Gold Coast, Australia. The process-based model, XBeach, which models the entire profile was able to reproduce both dune toe retreat and dry beach volume, however, was sensitive to calibration parameters. The two parametric models that only modeled erosion above the initial dune toe position were capable of accurately predicting dune toe retreat, however, under-estimated dry beach erosion volumes. With no calibration, the parametric model proposed by Palmsten and Holman (2012) produced the smallest errors of dune toe retreat with mean error in final dune position of 6.6m, or 18% of the total measured dune retreat. With minimal calibration estimated absolute error in average dune toe retreat was less than 13% of observed retreat for all three models. [Copyright &y& Elsevier]

Abstract: The Wadden Sea and its associated barrier island system exhibit highly dynamic behaviour. Of major concern is the movement of water and air and the transport, erosion and deposition of sand and mud. These processes result in an ever-changing morphology (topography/bathymetry) of the islands, tidal channels, inter-tidal shoals and tidal flats. This dynamic development of the shape and nature of the Wadden area forms together with the biotic systems, the present Wadden system. The morphodynamic development of the Wadden Sea is influenced by changing environmental conditions e.g. sea-level rise as well as by human interferences. For the management and protection of the Wadden system knowledge on the morphodynamic development is essential. However, our present knowledge is not sufficient to predict the effects of human interferences under different climate change scenarios in sufficient detail and accuracy. This paper identifies the existing knowledge gaps, based on a review of the state of the art on morphodynamics of the Wadden Sea that is confronted with major requirements from a coastal zone management point of view. The identified knowledge gaps have to inspire and stimulate research in the fields of the large-scale sediment budgets, morphodynamic changes at smaller scales, processes and mechanisms of sediment transport, erosion and deposition and modelling tools. [Copyright &y& Elsevier]

Abstract: Understanding the dynamics of sediment fluxes is a key issue to constrain modern erosion rates in mountain belts and determine the still debated level of control exerted by precipitation, topography and tectonics. The well defined monsoon seasonality in the Himalayas, together with active tectonics and strong relief provide an ideal environment to assess these possible interactions. For this purpose, we present a new compilation of daily suspended sediment data for 12 stations of the major rivers of the Nepal Himalayas. We analyze the relationships of sediment transport with daily river discharge and precipitation data as well as with morphometric parameters. We show that suspended sediment concentrations vary systematically through the seasons and asynchronously to river discharge displaying a hysteresis effect. This clockwise hysteresis effect disappears when suspended sediment fluxes are directly compared with direct storm discharge. Therefore we attribute the hysteresis effect to groundwater dilution rather than a sediment supply limitation. We infer a rating model to calculate erosion rates directly from long river discharge chronicles. We show that, when normalized by drainage area and mean sediment flux, all rivers exhibit the same trend. This similarity implies that all river basins have the same erosion behavior, independent of location, size and catchment characteristics. Erosion rates calculated from suspended sediment fluxes range between 0.1 and 2.8mm/yr. The erosion rates of the three main basins of Nepal are in the range 0.9–1.5mm/yr, Erosion rates in the Higher Himalayas are relatively low (<0.5mm/yr, except for Kali Gandaki), while in the Lesser Himalayas they range from 0.2 to 2mm/yr. We propose that material transport in the rivers depends on hillslope sediment supply, which is, in turn, controlled by those rainfalls producing direct runoff. In other words, the rivers in the Nepal Himalayas are supply-limited and the hillsopes as a contributing source are transport-limited. We also show that erosion processes are not as much controlled by infrequently occurring extreme precipitation events, than by moderate ones with a high recurrence interval. [Copyright &y& Elsevier]

Abstract: This contribution presents a model approach to simulate the erosion, entrainment, deposition, and burial of the surface fine-grained laminae (SFGL) in low-gradient streams. We hypothesized that SFGL transport acts as a geomorphic control of the erosion and transport of sediment sources in a bedrock-controlled, low-gradient stream with fluvial deposits located in central Kentucky, USA. Results indicate that the SFGL development and temporary storage on the streambed surface plays a key role in maintaining an equilibrium streambed. The SFGL provides an easily erodible sediment source that satisfies the transport capacity of the stream during low to moderate flow events and thus protects deeper streambed sediment and streambank sediments from erosion. Modeling results showed that the simulation period was characterized by low to moderate hydrologic events which flush the SFGL from the stream and high flow events which deposit fine sediments into the SFGL. During the former, transported sediments were dominated by sediments of SFGL origin, i.e., 89% of sediments. During the latter, 33% of sediment input to the stream is deposited to the SFGL, which shows its importance as a temporary sink. Our model results support a novel concept that the ephemeral SFGL layers can satisfy sediment transport capacity of flow at low to moderate flows and thus protect other sources from erosion. While perhaps the bedrock, low-gradient stream studied provides an end-member to SFGL control, future research might investigate the importance of SFGL control in other stream systems. [Copyright &y& Elsevier]

Abstract: Experimental program was conducted to analyze scour – caused by a horizontal jet downstream of a rigid bed – and the flow velocity and turbulence characteristics within the scour hole. The experimental program was motivated by the fact that the knowledge of flow field, including turbulent characteristics, is fundamental to correctly simulate the bed-load transport and the temporal evolution of the scour hole and, thus, to define protective measures of scouring. In this paper some results of experiments – carried out to understand the role of flow turbulence in the prediction of scouring process and sediment movement – are reported. The analysis is conducted on the basis of detailed measurements of flow velocity at various sections in the scour hole region. Both a 2D LDA anemometer and an acoustic velocimeter profiler (DOP2000) were used to conduct the velocity measurements. The results show that the flow is characterized by alternating high-low speed fluid regions which lead to the formation of vertical turbulent coherent structures. The turbulent intensity assumes significant values along longitudinal planes (i.e. parallel to the flow direction) in the near-bank zones. Maps documenting the correlations between the vertical and the longitudinal turbulent intensities are shown. With the aid of the experimental data, a relationship between the bed shear stress and the volume of sand eroded is defined. The quadrant analysis is applied for the qualitative description of the turbulent events. Analysis indicates that the major turbulent activity occurs in the deepest region of the scour hole. It seems that sweep and ejection events, which correspond to positive production of the turbulent energy, play an important role in erosion and transport of the sediment particles. [Copyright &y& Elsevier]

Abstract: A 2D depth-averaged model for hydrodynamic, sediment transport and river morphological adjustment is presented. The sediment transport submodel considers non-uniform sediment, bed surface armoring, impact of secondary flow on the direction of bed-load transport, and transverse slope of river bed. The bank erosion submodel incorporates a simple simulation method for updating bank geometry during either degradational or aggradational bed evolution. The model is applied to a 180° bend with a constant radius under unsteady flow conditions, and to Friedkin''s laboratory meander channels. The results are in acceptable agreement with measurements, confirming the two dimensional model''s potential in predicting the formation of river meandering and improving understanding of patterning processes. Future researches are needed to clarify some simplifications and limitations of the model. [Copyright &y& Elsevier]

Abstract: The development of meanders has been the focus of research for decades because the shifting of bank lines may potentially cause serious problems in river engineering. This study assesses the roles of secondary flows in meander evolution by testing two model parameters, A and A s , which represent the effects of momentum redistribution exerted by the topography-driven and curvature-driven secondary currents, respectively. The meander-evolution model couples an analytical solution of flow field in a sine-generated channel with the Bank Erosion and Retreat Model (BERM). The contributions of this study lie in two areas. First, the authors isolated and quantified the roles of curvature-driven and topography-driven secondary flows in meander evolution. Second, the shifting processes of primary flow by secondary flows were investigated in detail by evaluating various variations of the dimensionless scour factor A. [Copyright &y& Elsevier]

Abstract: Landslides play an important role in the evolution of mountain topography and are a major source of sediment in tectonically active mountain belts. For the active orogeny of Taiwan, erosion rates have been assessed by various methods. The discrepancies observed between erosion rates integrated over modern and Quaternary time scales may result from various effects related to surface processes. More process-oriented research on the spatio-temporal distribution of hillslope processes and coupling relationships with the fluvial system is needed to reconcile the temporally heterogeneous data in the future. This paper assesses and describes the processes of subsequent erosion on hillslopes via a time series of topographic surveys of hillslopes after the initial failure in order to better understand the temporal and spatial variability of landslide erosion, sediment fluxes, and storage of landslide sediment within channels. The results demonstrate that hillslope-channel coupling is controlled by the relative frequency of erosive flooding events and the magnitude of rainfall-driven hillslope processes. The latter is assumed to be disproportionately high on larger failures in periods with less rainfall. Mass wasting may only affect part of the total failure’s area. Volumes of eroded sediment from gullies on the landslide scar may be as high as the volume estimated for the initial failure. The geometry of the sliding masses eroded after the initial failure appears to be uniform, and their depths average 6.1 ± 2.2 m. [Copyright &y& Elsevier]

Abstract: The tropics of northern Australia have received relatively little attention with regard to the impact of soil erosion on the many large river systems that are an important part of Australia''s water resource, especially given the high potential for erosion when long dry seasons are followed by intense wet season rain. Here we use 137Cs concentrations to determine the erosion processes supplying sediment to two major northern Australian Rivers; the Daly River (Northern Territory), and the Mitchell River (Queensland). We also present data from five sediment samples collected from a 100km reach of the Cloncurry River, a major tributary of the Flinders River (Queensland). Concentrations of 137Cs in the surface soil and subsurface (channel banks and gully) samples were used to derive ‘best fit’ probability density functions describing their distributions. These modelled distributions are then used to estimate the relative contribution of these two components to the river sediments. Our results are consistent with channel and gully erosion being the dominant source of sediment, with more than 90% of sediment transported along the main stem of these rivers originating from subsoil. We summarize the findings of similar studies on tropical Australian rivers and conclude that the primary source of sediment delivered to these systems is gully and channel bank erosion. Previously, as a result of catchment scale modelling, sheet-wash and rill erosion was considered to be the major sediment source in these rivers. Identifying the relative importance of sediment sources, as shown in this paper, will provide valuable information for land management planning in the region. This study also reinforces the importance of testing model predictions before they are used to target investment in remedial action. [Copyright &y& Elsevier]

Abstract: The ability to predict the effects of dam removal in highly sediment-filled systems is increasingly important as the number of such dam removal cases continues to grow. The cost and potential impacts of dam removal are site-specific and can vary substantially depending on local conditions. Of specific concern in sediment-impacted removals is the volume and rate of reservoir deposit erosion. The complexity and potential accuracy of modeling methods used to forecast the effects of such dam removals vary substantially. Current methods range from predictions based on simple analysis of pre-dam channel geometry to sophisticated data-intensive, three-dimensional numerical models. In the work presented here, we utilize data collected from past dam removals to develop an additional tool for predicting the rate and volume of sediment deposit erosion. Through the analysis of sediment, discharge, deposit, removal timeline, channel, and watershed data, in conjunction with post-removal monitoring data from a wide range of dam removal projects, some significant trends in the evolution of reservoir deposits following dam removal can be seen. Results indicate that parameters such as median grain size, level of cohesion, spatial variability of the deposit, and removal timeline are among the most influential factors in determining the rate and volume of sediment erosion. By comparing local conditions of dams and reservoirs slated for removal with those of past removals, we hope that predictions of the rate and volume of sediment deposit erosion can be usefully constrained. [Copyright &y& Elsevier]

Abstract: Our goal is to develop a model capable to discern the response of a watershed to different erosion mechanisms. We propose a framework that integrates a geomorphic component into the physically-based and spatially distributed TIN-based Real-time Integrated Basin Simulator (tRIBS) model. The coupled model simulates main erosive processes of hillslopes (raindrop impact detachment, overland flow entrainment, and diffusive processes) and channel (erosion and deposition due to the action of water flow). In addition to the spatially distributed, dynamic hydrologic variables, the model computes the sediment transport discharge and changes in elevation, which feedback to hydrological dynamics through local changes of terrain slope, aspect, and drainage network configuration. The model was calibrated for the Lucky Hills basin, a semi-arid watershed nested in the Walnut Gulch Experimental Watershed (Arizona, USA). It is demonstrated to be capable of reproducing main runoff and sediment yield events and accumulated volumes over the long term. The model was also used to study the response of two first-order synthetic basins representative of landforms dominated by fluvial and diffusive erosion processes to a 100-year long stationary climate. The analysis of the resultant slope-contributing area relationships for the two synthetic basins illustrates that the model is consistent with assumed principles of behavior and capable of reproducing the main mechanisms of erosion. [Copyright &y& Elsevier]

Summary: After the Yangtze River was closed by the Three Gorges Project (TGP) in 2003, erosion occurred from the dam site to the river mouth, especially in the middle and lower reaches of the Yangtze River. However, in some local areas of Chenglingji reach which holds the key position for flood management, there is actually deposition in contrast to the expected erosion. In this paper, a one dimensional mathematical model of the river network with sediment transport is used as the tool to simulate flow and fluvial processes. The calculation domain is from Yichang, which is downstream of the dam, to Hankou, the controlling node of flood management, 694km long in total. The model is calibrated based on the field data of hydrology and sediment transport during the period from October 2003 to October 2008. Then the model is utilized to simulate the erosion and deposition of the middle and lower reaches of the Yangtze River in the next two decades, and produce the results of a new river channel after river bed deformation occurs. The typical flood processes of 1954 and 1998 in the Yangtze River basin are used to check the flood management scheme for the research area, and results show that water storage of Three Gorges Reservoir (TGR) and a flood diversion program downstream of the Yangtze River should be taken into consideration. [Copyright &y& Elsevier]

Abstract: Experiments and numerical simulations are carried out to study clear-water scour around three bridge piers with cylindrical, square, and diamond cross-sectional shape, respectively. To handle movable-bed channels with embedded hydraulic structures, the fluid–structure interaction curvilinear immersed boundary (FSI-CURVIB) method is employed. The hydrodynamic model solves the unsteady Reynolds-averaged Navier–Stokes (URANS) equations closed with the k-ω turbulence model using a second-order accurate fractional step method. Bed erosion is simulated by solving the sediment continuity equation in the bed-load layer using a second-order accurate unstructured, finite-volume formulation with a sand-slide, bed-slope-limiting algorithm. Grid sensitivity studies are carried out to investigate the effect of grid resolution on the predictive capability of the model. Comparisons of the simulations with the experimental data show that for all three cases the agreement is reasonable. A major finding of this work, however, is that the predictive capability of the URANS morphodynamic model improves dramatically for the diamond shape pier for which sediment transport is driven primarily by the shear layers shed from the pier sharp edges. For piers with blunt leading edge, on the other hand, as the circular and square shapes, the URANS model cannot resolve the energetic horseshoe vortex system at the pier/bed junction and thus significantly underpredicts both the scour depth at the nose of the pier and the rate of scour growth. It is also shown that ad hoc empirical corrections that modify the calculated critical bed shear stress to enhance scour rate in the pier leading edge need to be applied with caution as their predictive capabilities are not universal but rather depend on the pier shape and the region of the flow. [Copyright &y& Elsevier]

Abstract: A three-dimensional flow-sediment model of the Wuhan portion of the Yangtze River was developed using the EFDC (Environmental Fluid Dynamic Code) in order to study the changing riverbed. The model was also calibrated and validated by daily measuring of the water surface elevation and using suspended sediment concentration data secured from June 1 to September 30, 2004. Based on this model, the mobile sediment on the riverbed was simulated for the high water period of the Yangtze River. The results indicate that erosion is the main issue, with maximum erosion (0.27m) occurring at the banks of Tian Xingzhou. In addition, according to a suspended sediment concentration analysis for the Han Kou Hydrologic Station section of the river, the concentration there increased from left bank to right bank. [Copyright &y& Elsevier]

Abstract: On 10th March 2008, the high energy storm Johanna hit the French Atlantic coast, generating severe dune erosion on Vougot Beach (Brittany, France). In this paper, the recovery of the dune of Vougot Beach is analysed through a survey of morphological changes and hydrodynamic conditions. Data collection focused on the period immediately following storm Johanna until July 2010, i.e. over two and a half years. Results showed that the dune retreated by a maximum of almost 6m where storm surge and wave attack were the most energetic. Dune retreat led to the creation of accommodation space for the storage of sediment by widening and elevating space between the pre- and post-storm dune toe, and reducing impacts of the storm surge. Dune recovery started in the month following the storm event and is still ongoing. It is characterised by the construction of “secondary” embryo dunes, which recovered at an average rate of 4–4.5cm per month, although average monthly volume changes varied from −1 to 2m3.m−1. These embryo dunes accreted due to a large aeolian sand supply from the upper tidal beach to the existing foredune. These dune-construction processes were facilitated by growth of vegetation on low-profile embryo dunes promoting backshore accretion. After more than two years of survey, the sediment budget of the beach/dune system showed that more than 10,000m3 has been lost by the upper tidal beach. We suggest that seaward return currents generated during the storm of 10th March 2008 are responsible for offshore sediment transport. Reconstitution of the equilibrium beach profile following the storm event may therefore have generated cross-shore sediment redistribution inducing net erosion in the tidal zone. [Copyright &y& Elsevier]

Abstract: Sediment dynamics have an important influence on the morphological evolution of tidal wetlands, which consist of mudflats and salt marshes. To understand the nature of sediment behavior under combined current–wave action at an exposed tidal wetland, we measured the waves, currents, water depths, bed-level changes, and sediment properties at a mudflat–salt marsh transition on the Yangtze Delta, China, during five consecutive tides under onshore winds of ~8m/s, and calculated the bed shear stresses due to currents (τ c ), waves (τ w ), combined current–wave action (τ cw ), and the critical shear stress for erosion of the bottom sediment (τ ce ). The bed shear stresses under combined current–wave action (τ cw ) were approximately five times higher on the mudflat (up to 1.11N/m2; average 0.27N/m2) than on the salt marsh (up to 0.14N/m2; average, 0.06N/m2). On the mudflat, τ cw was larger than the critical erosion shear stress (τ ce =0.103N/m2) for 70% of the period of submergence, whereas τ cw was always lower than τ ce at the salt marsh site (τ ce =0.116N/m2). This result indicates that the sediment dynamics on the mudflat were dominated by erosion, whereas at the salt marsh they were governed by deposition, which is in agreement with the observed bed-level change during the study period (−3.3mm/tide on the mudflat and 3.0mm/tide on the salt marsh). A comparison of τ cw values calculated using the models for bed shear stresses under combined current–wave action indicates that both models are applicable to the present case and effectively predict the bottom shear stress under combined current–wave action. Overall, we conclude that τ cw in combination with τ ce is useful in assessing the hydrodynamic mechanisms that underlie the morphological evolution of exposed tidal wetlands. [Copyright &y& Elsevier]

Abstract: The aim of this study was to evaluate four metrics to define the spatially variable (regionalised) hillslope sediment delivery ratio (HSDR). A catchment model that accounted for gully and streambank erosion and floodplain deposition was used to isolate the effects of hillslope gross erosion and hillslope delivery from other landscape processes. The analysis was carried out at the subcatchment (~40km2) and the cell scale (400m2) in the Avon-Richardson catchment (3300km2), south-east Australia. The four landscape metrics selected for the study were based on sediment travel time, sediment transport capacity, flux connectivity, and residence time. Model configurations with spatially-constant or regionalised HSDR were calibrated against sediment yield measured at five gauging stations. The impact of using regionalised HSDR was evaluated in terms of improved model performance against measured sediment yields in a nested monitoring network, the complexity and data requirements of the metric, and the resulting spatial relationship between hillslope erosion and landscape factors in the catchment and along hillslope transects. The introduction of a regionalised HSDR generally improved model predictions of specific sediment yields at the subcatchment scale, increasing model efficiency from 0.48 to >0.6 in the best cases. However, the introduction of regionalised HSDR metrics at the cell scale did not improve model performance. The flux connectivity was the most promising metric because it showed the largest improvement in predicting specific sediment yields, was easy to implement, was scale-independent and its formulation was consistent with sedimentological connectivity concepts. These properties make the flux connectivity metric preferable for applications to catchments where climatic conditions can be considered homogeneous, i.e. in small-medium sized basins (up to approximately 3000km2 for Australian conditions, with the Avon-Richardson catchment being at the upper boundary). The residence time metric improved model assessment of sediment yields and enabled accounting for climatic variability on sediment delivery, but at the cost of greater complexity and data requirements; this metric might be more suitable for application in catchments with important climatic gradients, i.e. large basins and at the regional scale. The application of a regionalised HSDR metric did not increase data or computational requirements substantially, and is recommended to improve assessment of hillslope erosion in empirical, semi-lumped erosion modelling applications. However, more research is needed to assess the quality of spatial patterns of erosion depicted by the different landscape metrics. [Copyright &y& Elsevier]

Abstract: We quantified the sediment volume transported by a major debris flow event in the Halltal, Austrian Alps, using a combination of terrestrial (TLS) and airborne laser scanning (ALS) which has rarely been carried out before. A digital terrain model (DTM) derived from ALS data (pre-event surface) was combined with a DTM derived from TLS data (post-event surface). Both datasets were aligned and compared in a cut and fill analysis estimating differential volumes. The main focus lay on the evaluation and accuracy assessment of the applied method. Tie-point based registration of both datasets proved to be insufficient; additional alignment by Multi Station Adjustment was necessary to minimise the averaged height error between both datasets, amounting for a volumetric error of less than 10% which is comparable to pure ALS-campaigns. Larger errors were estimated for complex terrain with low scanning resolutions. A particular problem in data processing was the low and dense shrub vegetation in the study area which required a specifically adapted filter algorithm. An insufficient ground representation was observed for the ALS-data overestimating ground heights for averaged 70cm. Despite these limitations, the approach proved to be suitable for accurate extreme event quantification. The starting zones of the debris flows lie at the bedrock-debris interface where runoff is concentrated. Volumes of 5000 to 12,000m3 were assessed. Volume estimation worked better for the erosional than for the depositional features; this is because the erosional gullies are relatively deep and the calculation is not affected by pre-event vegetation. While erosion and sedimentation are balanced for one of the three catchments investigated, the deposited volumes are higher than the detected eroded volumes for the other two. The reasons are not fully understood. The magnitude of the flows was determined by catchment size, topographical characteristics and deforestation by a major wildfire in 1946. [Copyright &y& Elsevier]

Abstract: We examined runoff and sediment transport associated with large-scale construction projects in Fujian Province, China. Six experimental plots, comprised of four plot types, were designed to mimic typical conditions immediately following disturbance. It was found that natural vegetative cover reduces both runoff and erosion by approximately 36 and 7457 times over bare ground, and 16 and 1801 times over typically planted grasses, respectively. The increase in erosion associated with the replacement of native vegetation with bare ground or grasses due to large-scale infrastructure projects in Fujian from 1999 to 2004, amounted to an estimated loss of 1.76×107 tonnes of top soil and 3.04×108 m3 of surface runoff from the province during the bare soil construction phase, and an additional 4.25×106 tonnes of top soil and 1.35×108 m3 of surface runoff from the province associated with the first year of operation for each project. This has implications for frequency and occurrence of landslides and other geographic hazards, the transport of chemicals into waterways, the transport of goods through shipping passages, and the fertility of land in Fujian. [Copyright &y& Elsevier]

Abstract: The largest plain in the North Vietnam has formed by the redundant sediment of the Red River system. Sediment supply is not equally distributed, causing erosion in some places. The paper analyzes the evolvement and physical mechanism of the erosion. The overlay of five recent topographical maps (1930, 1965, 1985, 1995, and 2001) shows that sediment redundantly deposits at some big river mouths (Ba Lat, Lach, and Day), leading to rapid accretion (up to 100m/y). Typical mechanism of delta propagation is forming and connecting sand bars in front of the mouths. Erosion coasts are distributed either between the river mouths (Hai Hau) or nearby them (Giao Long, Giao Phong, and Nghia Phuc). The evolvement of erosion is caused by wave-induced longshore southwestward sediment transport. Meanwhile sediment from the river mouths is not directed to deposit nearshore. The development of sand bars can intensively reduce the erosion rate nearby river mouths. Erosion in Hai Hau is accelerated by sea level rise and upstream dams. Sea dike stability is seriously threatened by erosion-induced lowering of beach profiles, sea level rise, typhoon, and storm surge. [Copyright &y& Elsevier]

Abstract: Geological effects of the 2010 Chilean tsunami were quantified at five near-field sites along a 200km segment of coast located between the two zones of predominant fault slip. Field measurements, including topography, flow depths, flow directions, scour depths, and deposit thicknesses, provide insights into the processes and morphological changes associated with tsunami inundation and return flow. The superposition of downed trees recorded multiple strong onshore and alongshore flows that arrived at different times and from different directions. The most likely explanation for the diverse directions and timing of coastal inundation combines (1) variable fault rupture and asymmetrical slip displacement of the seafloor away from the epicenter with (2) resonant amplification of coastal edge waves. Other possible contributing factors include local interaction of incoming flow and return flow and delayed wave reflection by the southern coast of Peru. Coastal embayments amplified the maximum inundation distances at two sites (2.4 and 2.6km, respectively). Tsunami vertical erosion included scour and planation of the land surface, inundation scour around the bases of trees, and channel incision from return flow. Sheets and wedges of sand and gravel were deposited at all of the sites. Locally derived boulders up to 1m in diameter were transported as much as 400m inland and deposited as fields of dispersed clasts. The presence of lobate bedforms at one site indicates that at least some of the late-stage sediment transport was as bed load and not as suspended load. Most of the tsunami deposits were less than 25cm thick. Exceptions were thick deposits near open-ocean river mouths where sediment supply was abundant. Human alterations of the land surface at most of the sites provided opportunities to examine some tsunami effects that otherwise would not have been possible, including flow histories, boulder dispersion, and vegetation controls on deposit thickness. [Copyright &y& Elsevier]

Abstract: Analyzed the sediment-transport process in high sediment-laden river, the new concept and calculating method for sediment-transport water volume are proposed. Based on field data of sediment and water volume in the Lower Yellow River from 1950 to 2000, the sediment-transport water volume and unit sediment-transport water volume in LYR are calculated. Meanwhile, relations between them and influencing factors are confirmed to calculate efficient sediment-transport water volume after construction of the Xiaolangdi reservoir. Results gained from these functions are consistent well with the facts of real water-sediment regulation in LYR. [Copyright &y& Elsevier]

Abstract: Analyzed the sediment-transport process in high sediment-laden river, the new concept and calculating method for sediment-transport water volume are proposed. Based on field data of sediment and water volume in the Lower Yellow River from 1950 to 2000, the sediment-transport water volume and unit sediment-transport water volume in LYR are calculated. Meanwhile, relations between them and influencing factors are confirmed to calculate efficient sediment-transport water volume after construction of the Xiaolangdi reservoir. Results gained from these functions are consistent well with the facts of real water-sediment regulation in LYR. [Copyright &y& Elsevier]

Summary: This study evaluated the potential impacts of sub-bankfull flows produced by stormwater control measures (SCMs) on stream geomorphic stability. In part, design standards for SCMs include peak flow attenuation to maintain pre-development flow conditions to those of undeveloped watersheds or return urbanized, developed watersheds back to the pre-developed state. Most SCMs target lower frequency storms, usually the 2-and/or 10-year discharge events, but leave peak flows resulting from higher frequency storms uncontrolled. SCMs are possibly subjecting streams to longer and more frequent periods of erosion, increasing stream channel instability. The d 65 substrate size, pattern, profile, and dimension of 33 reference stream cross-sections in Piedmont North Carolina were modeled using the continuous simulations program, SWMM, to develop (1) a unit critical discharge metric in L/s/ha, Qc =0.0035(d 65)1.5048, (2) allowable annual erosional hour standard, Log(AAEH)=−1.26Log(d 65)+1.21, and (3) allowable volume of eroded bedload standard, Log(AV)=−0.64(Qc )−1.52, for watersheds containing SCMs discharging into surface waters. The unit critical discharge represents a threshold that, once exceeded, incipient motion of the d 65 particle can occur. These standards represented benchmarks of stable, naturally eroding reference streams. Ninety-four percent of the unit critical discharges were less than the 2-year 24-h event, indicating the necessity of controlling higher frequency sub-bankfull flows. The standards were applied to an urbanized watershed (one sub-catchment containing a structural SCM and two sub-catchments without) in Raleigh, North Carolina. The unit critical discharge metric appeared to adequately represent urbanized stream geomorphic processes for the sub-catchment undergoing urbanization (4.5% difference) but not for the mature urbanized sub-catchments (47.5% and 68.8% difference). Depending on the long-term management goal of the unstable stream, this metric is not applicable for all urbanized watersheds due to the discrepancy between the field and calculated unit critical discharges. Standards developed from urbanized reference streams could possibly better represent SCMs in urbanized watersheds. All three sub-catchments failed to meet the erosional standards demonstrating the ability of the standards to predict unstable geomorphic processes in streams. The addition of a detention SCM (wet pond), in the urbanized sub-catchment extended the duration of erosive flows from 37 to 87h/ha/yr, but reduced the estimated volume of eroded bedload from 1.81 to 0.99m3/m/ha/yr when compared to uncontrolled urbanization (no wet pond). Alterations to the design of the wet pond, increased volume size and change in orifice diameter, were explored to see if erosional standards could be better met. This study demonstrated the effect of current SCM design standards on stream stability and why geomorphic processes of stream channels should be incorporated in SCM design standards. [ABSTRACT FROM AUTHOR]

Abstract: Beach profile surveys, gale climate and atmospheric variations were utilized to assess medium timescale morphological change at South Sands, Tenby, West Wales. Due to beach aspect in relation to offshore islands, gale wave height decreased as wave direction rotated eastwards (r=0.83) and westwards (r=0.88). Similarly, wave heights were in attuned to variations in positive (r=0.68) and negative (r=−0.72) NAO Index, showing a wave height reduction occurred during weakly negative/positive or transitory phases; morphological change was attuned to atmospheric variation at a 2-year timelag. Shelter from offshore islands is given to waves from the predominant southwesterly direction and was confirmed by negligible correlation with South Sands morphology. However, outside the shelter of these offshore islands, correlation was found between south-eastward rotating wave directions (135°–180°) and morphological change, which resulted in southern and central beach erosion and accretion to the north. With a southwesterly rotation (243°–256°) the opposite was true. Beach rotation expressed by volume change within the sub-aerial zone had a negative phased relationship between beach extremities (r=−0.94) and a timelagged association within the intertidal zone (r=0.55). Analyses resulted in the development of two medium timescale rotation models based on incident wave direction and climatic variability. Results have global implications for headland bays in the lee of offshore islands, as well as macro-tidal beach areas; and consequently similar models could inform local, regional and national beach management strategies [Copyright &y& Elsevier]

Abstract: We present the most complete and new high-resolution multibeam bathymetry datasets from the shelf to the basin in the Ribbon Reef region, northern Great Barrier Reef (GBR). Analysis of these data, combined with existing side-scan sonar data provides a detailed morphologic framework of the submarine canyon system and other related features, their spatial distribution, controlling factors on their evolution, and evidence of recent sedimentary activity. Two morphologically different submarine canyon types are recognised: 1) shelf-incised canyons whose heads are indented into the shelf-break at shallow-water depths (about 60 to 80m). These canyons can be single-fed or multi-fed depending on the number of tributaries that merge into the main canyon valley. According to the degree of connection with the shelf, these canyons can be reef-blocked, partly reef-blocked or shelf-connected; 2) slope-confined canyons, which are located at deeper waters in the slope and show a different canyon head morphology. Canyon formation and development of the different canyon types is explained according to a four-phase model. In the first phase, localised slope failures and/or sediment gravity flows may lead to the formation of an initial canyon by retrogressive headward or downslope erosion respectively. These processes continue during the second transitional phase, leading to upslope canyon progression. Finally, canyons breach the shelf-break during a mature stage that represents the more active phase in the canyon evolution. The development of an extensive shelf-edge barrier reef (Ribbon Reefs) represents a fourth phase that conditioned the sedimentary dynamics of the canyons. The location and morphology of this reef barrier determine the type and amount of sediment supply by controlling the connection of the canyon head with the shelf drainage system. Recent canyon activity is evidenced by the presence of erosive and depositional features that include submarine landslides, gullies and rills on the canyon walls and slopes, sandwaves migrating along the canyons floors, and sediment gravity flows deposited on the lower canyons and adjacent basin floor. [Copyright &y& Elsevier]

Summary: This paper presents a comprehensive review of sediment transport in ice-affected rivers by documenting a range of unique ice and sediment transport processes. In cold regions during winter, high sediment transport rates can occur under specific ice conditions, even if the channel discharge is low. River ice directly displaces and carries sediment, and some ice processes can move boulder-sized sediment, contributing to the sculpting of river channels in ways water alone could not. Special attention is directed to the ice breakup period, during which most dynamic ice processes take place and when sediment supply to river channels is maximized. Also discussed are the time and space scales over which ice processes affect sediment transport. Moreover, a global framework that describes the interconnectivity of climate, river discharge, channel morphology, in-stream hydraulics, and sediment transport response is proposed. Within this framework, ice processes are given a central function, as they influence and are affected by sediment transport, hydrological conditions, and channel morphology. A segment of this work reviews and explores the interconnectivity between river ice processes and river discharge as well as between river ice processes and channel morphology. The proposed framework represents a practical tool for a wide range of cold region river scientists and engineers, particularly in light of climate change. [Copyright &y& Elsevier]

Summary: Empirical power law sediment rating curves of the form C = aQb (where C is the sediment concentration, Q is the discharge rate, and the coefficient a and exponent b are fitted parameters), or the alternative form given by log(Qs )=log(a)+(b +1)log(Q) (where Qs = CQ is the sediment delivery rate, and the natural logarithm is used) are widely used for characterising sediment transport across a broad range of spatial and temporal scales. Fire frequently has a large effect on erosion rates and sediment delivery. We investigate the temporal changes in the coefficient a and exponent b for 3years following a wildfire between February 2003 and April 2006, for two South Eastern Australian Eucalyptus forested catchments (136 and 244ha) with mean annual rainfall of 1900mm. Storm-event integrated sediment loads and discharges were calculated for each of 596 storm events using stage-discharge control structures and in situ turbidity measurements at 15min intervals. Measurements were converted to sediment concentrations using regression relationships developed from storm activated water auto-samplers. The analysis identified: (i) strong negative linear relationships between the rating coefficient log(a), and the rating exponent b, reflecting sediment rating curves that “pivot” around a common fulcrum point in log–log space, (ii) a systematic shift in this linear relationship between log(a) and b as a function of time since fire, (iii) maximum values of b of ca. 2.5 (i.e. maximum non-linearity in the relationship between discharge and sediment delivery, and therefore maximum sensitivity to high peak-discharge events) immediately following the fire, which decline rapidly and monotonically by a factor of 10 to ca. 0.25 in the first 8months, attributed to a dominance of hillslope erosion processes and declining rill and interill erodibility, (iv) irregular patterns in the value of b during the vegetation recovery period, probably reflecting a shift from hillslope dominated erosion processes to a greater contribution from channel processes (8–24months after the fire) and (v) annual cycles in the value of b in the recovered state (24–38months after the fire) ranging from a minimum of ca. 0.5 in the dry season to a maximum of ca. 1.5 in the wet season. The physical cause of these cycles could not be isolated in this study. The results provide a robust quantitative perspective on the magnitude and temporal variability of the sensitivity of catchments recovering from wildfire. [Copyright &y& Elsevier]

Abstract: In order to assess the extent of sediment connectivity between uplands and lowlands and to quantify the processes of in-channel deposition and remobilization, measurements of suspended sediment fluxes were conducted in a nested rural catchment of the Mexican Volcanic Belt. Data were collected over one year at three upland sites (3 to 12km2) and two downstream stations (390–630km2). Our results show that a structural discontinuity in the catchment (i.e. abrupt slope decrease at the junction between piedmonts and the alluvial plain from 2 to 10% to<0.1%) could be compensated by functional continuity during floods. Direct conveyance of fine sediment to the outlet occurred when a high stream transport capacity was reached. Erosion of the streambed was observed on various occasions and accounted for up to 50% of the flux leaving the catchment during one event. Conversely, temporary in-channel storage was apparent on other occasions, amounting to up to 52% of the flux recorded upstream during one storm. These two distinct behaviours were approximately equally distributed along the rainy season and strongly driven by the extent of coupling between surface and subsurface water. This work indeed highlights the role of baseflow spatial variations in determining the extent of lowland sediment conveyance. Riverbed erosional processes occurred when large differences in pre-event baseflow values (i.e. at least a twofold longitudinal increase) were observed between the 5-km distant lowland stations. Our findings outline the importance of systematically taking into consideration the baseflow parameter in research focusing on fine sediment transport across scales. [Copyright &y& Elsevier]

Abstract: Future shoreline changes on a sandy beach with a structure such as a jetty or groin can be estimated when wave time series is known (i.e. sequence of wave height, period, and direction). This paper presents an extension of an existing solution () for the linearized partial differential equation for shoreline change at an infinite jetty where waves are time varying and when the angle of the shoreline is small with respect to the waves breaking at the shoreline. The novel solution provided in this paper allows the previous constant wave condition solution to be extended to the case where wave properties (i.e. wave direction, wave height, and wave period) are time varying. Example usage of the method presented shows that shorelines may be of different final plan form shape for time varying wave conditions even though the sediment transport along adjacent beaches is not spatially varying (i.e. spatially constant) from time step to time step. Although this difference in shape may have been known previously using numerical models, it could not be proved analytically. Reversals of wave height, period, and direction time series are shown to provide different final shoreline shapes even though the time series consists of the same waves although in different ordered time. The solution provided will allow one line numerical shoreline models to be tested using an analytic solution. [Copyright &y& Elsevier]

Abstract: Variations in water level observed in Lakes Michigan and Huron during the last few decades have motivated a comprehensive study involving climatic, hydrologic and hydraulic factors organized by International Joint Commission of the Great Lakes. It has been submitted, among other possible causes, that changes in conveyance in the St. Clair River could be contributing to the lowering of the upper Great Lakes water level. Sediment transport processes, in particular bed scour and erosion, can affect significantly a river''s conveyance, thus creating the need to assess the erodibility properties of the river bed. To this end, laboratory tests were performed in order to obtain the value of the critical shear stress needed to erode the cohesive fraction of the bed sediment material, known as glacial till, from the St. Clair River. Different flows with increasing velocities were run up to the point where initial sediment erosion could be observed. Through detailed near-bed velocity measurements using a laser Doppler velocimetry (LDV) system, a value of 4.2N/m2 was obtained as the critical shear stress for the erosion of glacial till. A threshold for the critical shear stress for erosion of similar cohesive sediments was also found and expressed in dimensionless form. These results could be used in combination with mathematical models to estimate the risk of scour and erosion at locations where the glacial till is exposed to both strong currents and flow forces induced by the large navigation vessels commonly observed along the course of the St. Clair River. [Copyright &y& Elsevier]

Abstract: The coastline of Kannyakumari (8°4′N 77°33′E to 8°13′N 77°14′E), along the Arabian Sea is located near the southern tip of the Indian peninsula. This coast experiences heavy erosion particularly during the seasonal monsoons. This in turn results in considerable damage to properties, economic loss and leads to a number of socio economic problems. Protection measures in the form of groins have been implemented at selected locations along the coast. Prediction of shoreline oscillation due to the presence of such structures is extremely important prior to their construction. Although several formulae are available in the literature for the prediction of long shore sediment transport, studies regarding their application and validation with field problems along this coast are scanty. In the present work, seasonal measurements of shoreline oscillation adjacent to the shore connected structures were carried out during the year 2007 for which satellite data have also been adopted. These measurements are adopted to validate a finite difference based numerical model based on the formulation of for the prediction of shoreline evolution in the presence of shore connected structures. The offshore wave climate for the year 2007 is simulated from National Centre for Environmental Prediction (NCEP) wind data using Wave Analysis Model (WAM) model, whereas, the near shore wave climate was derived by adopting MIKE21 Parabolic Mild Slope (PMS) module The alongshore sediment transport is calculated using the approach of . The prediction revealed that the net average annual alongshore transport varies from about 0.008 to 0.040 million m3 and is towards the west. [Copyright &y& Elsevier]

Abstract: A thorough discussion of results from laboratory experiments with regular waves sheds light on the gap that lies between the sediment transport associated with ripple migration and the performance of a standard bedload transport formula in terms of bed shear concept. It is found that the extent of deviations of the bedload transport formula by Ribberink (1998) from the measured rate of sediment transport associated with ripple migration becomes systematically apparent under conditions of increasing settling time factor Ω s (= η/(w 0 T); η is the ripple height, w 0 the settling velocity and T the wave period). Re-examination of previous two field studies demonstrates a further reinforcement for phase-lag argument addressed in this paper. [Copyright &y& Elsevier]

Abstract: Our understanding about the regional variation of Sediment Yield (SY) in Europe and its scale dependency currently relies on a limited number of data for mainly larger river systems. SY is the integrated result of all erosion and sediment transporting processes operating in a catchment and is therefore of high value for environmental studies and monitoring purposes. Most global assessments of SY consider catchment area (A), climate and topography as the main explanatory variables. However, it is still unclear if these factors also control regional variations of SY within Europe. This paper aims at bridging this gap. Therefore, we i) present a large database of SY-values which was constructed through an extensive literature review; ii) describe the spatial patterns of SY across Europe; and iii) explore its relation with A, climate, and topography. In total, sediment yield data from 1794 different locations throughout Europe were collected (507 reservoirs and 1287 gauging stations), representing a minimum of 29,203 catchment-year data. Only SY-data measured at gauging stations or derived from reservoir siltation rates over a period of a minimum of one year were included in the database. This database comprises a large range of catchment areas (A): i.e from small upland catchments (≥0.01km²) to major European river basins (≤1,360,000km²). An overview of the collected SY-data is provided and sources of uncertainty on the available data are discussed. Despite potentially large uncertainties on several of the individual SY-values, analysis of this database indicates clear spatial patterns of SY in Europe. The temperate and relatively flat regions of Western, Northern and Central Europe generally have relatively low SY-values (with ca. 50% of the SY< 40tkm−2 yr−1 and ca. 80% of the data <200tkm−2 yr−1), while Mediterranean and Mountainous regions generally have higher SY-values (with around 85% of the SY-data >40tkm−2 yr−1 and more than 50% of the data >200tkm−2 yr−1). These differences are attributed to a combination of factors, such as differences in climate, topography, lithology and land use. Although larger differences in SY were found between the climatic regions than between topographic zones, it is currently difficult to identify the individual importance of the various controlling factors of SY. SY–A relationships were calculated for the entire dataset and for subgroups stratified according to the measurement method (gauging stations or reservoir surveys), range of the catchment area, climatic region, topographic zone of the river outlet, and major European river system. Although typically a negative relationship between SY and A is expected due to a decrease in topsoil erosion rates on more gentle slopes and an increase in sediment deposition with an increase in catchment size, this relationship was found to be generally very weak and subject to a lot of scatter. Furthermore, results illustrate important differences in scale dependency: whereas a weak but significant negative trend is generally observed for the temperate and relatively flat regions, no significant or even positive trends were observed in mountain regions and Mediterranean Europe. When only larger river catchments (i.e. >100km² and especially >10,000km²) are considered, catchment area exerted a larger control on SY. These findings confirm previous studies and indicate that the relationship between SY, spatial scale and other controlling factors is often complex and non-linear. [Copyright &y& Elsevier]

Abstract: Occupation of the coast has significantly increased in recent decades, mostly due to a greater demand for recreation and tourism. Today, erosion threatens many human-made structures and activities, requiring an integrated approach for the understanding of coastal dynamics and identification of alternatives to associated problems. This study investigates a 64km-long coastal physiographic unit in the northern microtidal littoral of Tuscany (Italy). Vertical aerial photographs and direct field surveys were used to retrieve changes in shoreline position over 1938–1997 and 1997–2005 time intervals. Significant beach accretion was observed during the first period updrift of Carrara (84m) and Viareggio (280m) harbours and at Marina di Pietrasanta (100m), whereas severe erosion occurred downcoast of Carrara harbour (−130m, at Marina dei Ronchi) and on the northern side of Arno river mouth (−400m). Similar trends were observed between 1997 and 2005; beach slope between the 1997 shoreline position and the closure depth correlated well with the distribution of erosion/accretion patterns from the 1938–1997 period (slopes were lower in eroded areas than at sites under accretion). Longshore distribution of erosion/accretion patterns was controlled by coastal compartmentalisation. Three of the main littoral cells were mostly formed by natural limits (i.e., Punta Bianca promontory, Marina di Pietrasanta, the Arno river mouth and the port of Livorno). Several sub-cells were created within these cells due to the introduction of human-made structures (such as Carrara and Viareggio harbours), which formed artificial fixed limits that allowed the transport of sediments (exclusively fines) in one direction only. Results will help improve the understanding of coastal processes and manage littoral sediment transport in a sustainable manner. This will reduce the need for structural interventions, such as breakwaters and groynes, which in the past decades prevented coastal retreat at local scale but shifted erosion downdrift, leading to degradation of the investigated area and requiring continuous maintenance. [Copyright &y& Elsevier]

Abstract: Appropriate descriptions of turbulence are important in predicting sediment transport and seabed evolution. We use here a three-dimensional model to investigate the impacts of sediment-induced stratification, erosion parameterization, and turbulence closures on sediment transport and morphological simulations. The model is implemented in the Proudman Oceanographic Laboratory Coastal Ocean Modelling System (POLCOMS), which couples a hydrodynamic model to the General Ocean Turbulence Model (GOTM) and to a sediment transport model. This sediment transport model calculates both suspended sediment concentrations and bed evolution. A large number of turbulence closures can be tested and we focus on the methods used to calculate the turbulent length scale and the stability functions. Different modelling scenarios are assessed against experimental data of velocity profiles, suspended sediment concentrations, and trench migration in a laboratory flume. Numerical results show that the processes investigated have little impact on the flow velocity profiles, in spite of some differences on the bed shear stress. The only exception is the one-equation turbulence closure, which cannot reproduce velocity profiles appropriately. Sediment-induced stratification, erosion parameterization, and turbulence closures can all have significant impacts on the suspended sediment concentration and the bed evolution. Model-data comparisons are found to be particularly sensitive to the method used to calculate the turbulent length scale. [Copyright &y& Elsevier]

Abstract: Runoff from agricultural watersheds can carry a number of agricultural pollutants and pathogens; often associated with the sediment fraction. Deposition of this sediment can impact water quality and the ecology of the river, and the re-suspension of such sediment can become sources of contamination for reaches downstream. In this paper a modelling framework to predict sediment and associated microbial erosion, transport and deposition is proposed for the South Nation River, Ontario, Canada. The modelling framework is based on empirical relationships (deposition and re-suspension fluxes), derived from laboratory experiments in a rotating circular flume using sediment collected from the river bed. The bed shear stress governing the deposition and re-suspension processes in the stream was predicted using a one dimensional mobile boundary flow model called MOBED. Counts of live bacteria associated with the suspended and bed sediments were used in conjunction with measured suspended sediment concentration at an upstream section to allow for the estimation of sediment associated microbial erosion, transport and deposition within the modelled river reach. Results suggest that the South Nation River is dominated by deposition periods with erosion only occurring at flows above approximately 250 m3 s−1 (above this threshold, all sediment (suspended and eroded) with associated bacteria are transported through the modelled reach). As microbes are often associated with sediments, and can survive for extended periods of time, the river bed is shown to be a possible source of pathogenic organisms for erosion and transport downstream during large storm events. It is clear that, shear levels, bacteria concentrations and suspended sediment are interrelated requiring that these parameters be studied together in order to understand aquatic microbial dynamics. It is important that any management strategies and operational assessments for the protection of human and aquatic health incorporate the sediment compartments (suspended and bed sediment) and the energy dynamics within the system in order to better predict the concentration of indicator organism. [Copyright &y& Elsevier]

Abstract: Benthic trawlers, through the scraping of the upper layers of the seabed sediment, are responsible for major alterations to the distribution of suspended matter in coastal areas. A major trawling site in Greece is that of the Gulf of Thermaikos, located in the NW Aegean Sea (Eastern Mediterranean). In an attempt to assess, for the first time, the quantities of the mobilized sedimentary masses and the properties of their motion in the aquatic domain of the Gulf of Thermaikos, a mathematical model has been formulated. The modeling approach includes the determination of the mechanical erosion rate, the production of turbulence due to the flow through the mesh of the net and the physical processes that control the propagation of the generated sedimentary plume in the marine environment. In the absence of information regarding the haul paths in the gulf, their determination was made stochastically, based on the existing legislative restrictions and trawlers'' fishing practices. The trawling-activated masses thereby defined for the duration of the trawling period in the gulf were very high, indeed several times greater than the related contribution from the major rivers of the area, emphasizing the significance of the activity to the sedimentary input of the local marine environment. The total annual erosion by trawls in the gulf was calculated at 3.38×106 t/yr. Τhe mean mechanical erosion rate per trawled surface (parameter free from the bias raised by the stochastic simulation of the trawl trajectories) was estimated at 430g/m2, values directly comparable to ones defined for similar coastal areas. Results from a simulation of the 2001–02 trawling period were well correlated with in-situ measurements for the same period, while the investigation of the matter''s suspension level and times revealed that the matter exhibits low residence times in the water column and at the same time moves in the vicinity of the bed, contributing to the formation and distribution of benthic nepheloid layers in the gulf. [Copyright &y& Elsevier]

Abstract: Large earthquakes deform the Earth''s surface and drive topographic growth in the frontal zones of mountain belts. They also induce widespread mass wasting, reducing relief. The sum of these two opposing effects is unknown. Using a time series of landslide maps and suspended sediment transport data, we show that the MW7.6 Chi-Chi earthquake in Taiwan was followed by a period of enhanced mass wasting and fluvial sediment evacuation, peaking at more than five times the background rate and returning progressively to pre-earthquake levels in about six years. Therefore it is now possible to calculate the mass balance and topographic effect of the earthquake. The Choshui River has removed sediment representing more than 30% of the added rock mass from the epicentral area. This has resulted in a reduction of surface uplift by up to 0.25m, or 35% of local elevation change, and a reduction of the area where the Chi-Chi earthquake has built topography. For other large earthquakes, erosion may evolve in similar, predictable ways, reducing the efficiency of mountain building in fold-and-thrust belts and the topographic expression of seismogenic faults, prolonging the risk of triggered processes, and impeding economic regeneration of epicentral areas. [Copyright &y& Elsevier]

Abstract: Cohesive sediment is an important component of aquatic environments, which must be monitored and managed for environmental, engineering, and human health reasons. While the hydrodynamic aspects of sediment erosion and transport are well understood, the erodibility of cohesive sediment has proved more difficult to address and predict. Erodibility is the propensity for the sediment to be eroded, and is represented typically as an erosion threshold or erosion rate. It is an attribute of the sediment itself, and is dependent on the sediment properties that dictate the resistive forces in the sediment, such as gravity, friction, cohesion, and adhesion. This paper reviews recent findings from a range of disciplines to create a comprehensive picture of the physical, geochemical and biological properties that influence the erodibility of cohesive sediment. By identifying these key sediment properties, we provide the background for a discussion on how changes in and interactions between the properties generate significant spatial and temporal variations in erodibility. We discuss the development of a predictive model of erodibility, and emphasize the need for more comparable field and laboratory data. [Copyright &y& Elsevier]

Abstract: The contributions and relationships of erosion by splash and overland flow over a steep slope in a Japanese beech forest in plots with different percentages of ground cover were examined. Three erosion plots (2m wide×5m long) with average understory coverage of 1%, 45%, and 94% were installed. Sediment transported by rain splash and by overland flow was sampled separately. For the plots with sparse, moderate, and high understory coverage, the average proportions of splash soil to total soil erosion during the monitoring period were 16%, 32%, and 18%, respectively. A significant correlation between the amount of splash soil and precipitation was found in the plots with 1% and 45% understory coverage, whereas no statistical relationship was identified for the plot with high understory coverage. At the sparse ground cover plot showing the largest sediment movement, the contribution of splash transport decreased with increasing precipitation. The amount of sheetwash erosion was significantly correlated with the amount of splash soil under the condition of sparse ground cover. This relationship was more pronounced during high precipitation events and the rainy season. Splash contribution to the sediment transport was in the range of 0.8%–76.7%, 2.8%–81% and 2.1%–60.8% for plot with high, moderate and low ground cover, respectively. The sparse ground cover showed the largest variation of splash and sheetwash contribution in soil erosion. This variability was due to variation in ground cover and soil surface wetness condition which led to a variation of detachment and non-linear relationship of sheetwash splash. [Copyright &y& Elsevier]

Abstract: In this study an Euler–Euler two-phase model was developed to investigate the tunnel erosion beneath a submarine pipeline exposed to unidirectional flow. Both of the fluid and sediment phases were described via the Navier–Stokes equations, i.e. the model was implemented using time-averaged continuity and momentum equations for the fluid and sediment phases and a modified turbulence closure for the fluid phase. The fluid and sediment phases were coupled by considering the drag and lift interaction forces. The model was employed to simulate the tunnel erosion around the pipeline laid on an erodible bed. Comparison between the numerical result and experimental measurement confirms that the numerical model successfully predicts the bed profile and velocity field during the tunnel erosion. It is evident that the sediments are transported as the sheet-flow mode in the tunnel erosion stage. Also the transport rate under the pipe increases rapidly at the early stage and then reduces gradually at the end of the tunnel erosion beneath pipelines. [Copyright &y& Elsevier]

Abstract: We demonstrate that alluvial channel response to regulation depends on the characteristic mode of sediment transport in a channel and, thus, for a channel in supply-transport equilibrium, on the caliber of sediment mantling the channel bed, as well as changes in characteristic water discharge and sediment load. We find that regulated, coarse gravel- and cobble-bed alluvial rivers dominated by bedload transport are predicted and observed to preserve the value of a dimensionless ratio of characteristic water discharge, channel slope, width, and size of sedimentary particles mantling the bed associated with the critical conditions required for the onset of significant sediment transport. The covariant geomorphic adjustment of such rivers to regulation is independent of the degree of sediment impoundment, although the nature and rate of changes in any specific characteristic appear to be sensitive to changes in sediment supply. In contrast, covariant geomorphic changes in sand- and fine gravel-bed alluvial rivers dominated by weak suspension transport are predicted and observed to be dependent on the degree of sediment impoundment and commensurate with the change in the sediment concentration of characteristic, formative flows. In both cases, specific geomorphic characteristics of alluvial rivers exhibit varied responses to regulation in different rivers, but across all rivers a systematic covariation in channel slope, width, and grain size is observed that, for a given mode of sediment transport, preserves a characteristic value of the Shields number. [ABSTRACT FROM AUTHOR]

Abstract: We present new major and trace element data, together with U–Pb ages for zircon sand grains from the major tributaries of the Indus River, as well as the adjacent Ghaggar and Yamuna Rivers and from bedrocks within the Sutlej Valley, in order to constrain the origin of the sediment reaching the Arabian Sea. Zircon grains from the upper Indus are generally younger than 200Ma and contrast with those from the eastern tributaries eroded from Himalayan sources. Grains younger than 15Ma, which typify the Nanga Parbat Massif, comprise no more than 1–2% of the total, even in the upper Indus, showing that this terrain is not a major sediment producer, in contrast with the Namche Barwe Massif in the eastern Himalayan syntaxis. The Sutlej and Yamuna Rivers in particular are very rich in Lesser Himalayan-derived 1500–2300Ma zircons, while the Chenab is dominated by 750–1250Ma zircons, mostly eroded from the Greater Himalaya. The upper Indus, Chenab and Ravi yield zircon populations broadly consistent with the outcrop areas, but the Jhelum and the Sutlej contain many more 1500–2300Ma zircons than would be predicted from the area of Lesser Himalayan rock within their drainages. A significant population of grains younger than 200Ma in the sands of the Thar Desert indicates preferential eolian, monsoon-related transport from the Indus lower reaches, rather than reworking from the local rivers. Modelling of observed zircon ages close to the delta contrasts with modern water discharge. The delta is rich in zircons dating 1500–2300Ma, while discharge from modern rivers carrying such grains is low. The modest size of the Sutlej, the richest source of these materials in the modern system, raises the possibility that the compositionally similar Yamuna used to flow westwards in the recent past. Our data indicate a non-steady state river with zircon transport times of 5–10k.y. inferred from earlier zircon dating of delta sands. The modern delta zircons image an earlier, likely Early-Mid Holocene, erosional state, in which the Lesser Himalaya were more important as sediment suppliers. Early-Mid Holocene sands show much less erosion from the Karakoram–Transhimalaya compared to those deposited at the Last Glacial Maximum, or calculated from the modern discharge. We favour variations in summer monsoon intensity as the primary cause of these temporal changes. [Copyright &y& Elsevier]

Abstract: The study is aimed at investigating the mean flow and turbulence characteristics in scour geometry developed near a circular cylinder of length 10cm placed over the sand bed transverse to the flow. The obstacle placed on a sand bed, on the way of a unidirectional flow, develops a crescent-shaped scour mark on the bed. The scour is caused by generation of vortex developed on the upstream side of the obstacle. Sand grains eroded by this vortex, are deposited on the downstream side of the obstacle as wakes. The turbulent flow field within the scour mark was measured in a laboratory flume using an Acoustic Doppler Velocimeter (ADV). The scour marks named as current crescents preserved in geological record are traditionally used as indicators of palaeocurrent direction. The distribution of mean velocity components, turbulent intensities and Reynolds stresses at different positions of the mark are presented. The experimental evidence also shows that the geometric characteristics of the scour mark (width) depend primarily on the cylinder aspect ratio, cylinder Reynolds number and sediment Froude number. [Copyright &y& Elsevier]

Abstract: The disruption of sediment supply from river to coast by dam development has been a topic of global concern. In Japan, among the top 30 dams in terms of height, 14 dams were constructed prior to 1970 and another 6 dams before 1980. However, the coastline erosion did not surface up as a grievous problem until the 1980s. According to the River Bureau of Japan, the overall erosion rate along the coastline of Japan was 0.72×106m2/yr prior to 1980, but sharply increased to 1.6×106m2/yr since 1980. Therefore, there was a time lag between the disruption of sediment supply by dam and beach erosion. This paper presents a case study on what may have delayed the response of beach to the effect of dam construction. [Copyright &y& Elsevier]

Abstract: Cosmogenic nuclide-based denudation rates and published erosion rates from recent river gauging in the Napo River basin (Peruvian Amazonia) are used to decipher erosion and sedimentation processes along a 600 km long transect from the headwaters to the lowlands. The sediment-producing headwaters to the Napo floodplain are the volcanically active Ecuadorian Andes, which discharge sediment at a cosmogenic nuclide-based denudation rate of 0.49 ± 0.12 mm/yr. This denudation rate was calculated from an average 10Be nuclide concentration of 2.2 ± 0.5 × 104 at/g(Qz) that was measured in bedload-derived quartz. Within the Napo lowlands, a significant drop in trunk stream 10Be nuclide concentrations relative to the Andean hinterland is recorded, with an average concentration of 1.2 ± 0.5 × 104 at/g(Qz). This nuclide concentration represents a mixture between the 10Be nuclide concentration of eroded floodplain deposits, and that of sediment eroded from the Andean hinterland that is now carried in the trunk stream. Evidence for addition of sediment from the floodplain to the trunk stream is provided by published decadal-scale sediment flux measurements from gauging stations operated in the Napo basin, from which an increase from 12 × 106 t/yr at the outflow of the Andes to ∼47 × 106 t/yr at the confluence with the Solimões (upper Amazon River) is recorded. Therefore, approximately 35 × 106 t of floodplain sediment are added annually to the active Napo trunk stream. Combined with our nuclide concentration measurements, we can estimate that the eroded floodplain deposits yield a nuclide concentration of ∼0.9 × 104 at/g(Qz) only. Under steady state surface erosion conditions, this nuclide concentration would translate to a denudation rate of the floodplain of ∼0.47 mm/yr. However, we have no geomorphologic explanation for this high denudation rate within the low relief floodplain and thus suggest that this low-nuclide concentrated sediment is Andean-derived and would have been deposited in the floodplain at a time when erosion rates of the Andes were elevated. Therefore, the recently eroded floodplain sediment provides an Andean “paleo denudation rate” of 1.2 mm/yr that was calculated for high Andean production rates. A likely period for elevated erosion rates is the LGM, where climate and vegetation cover of the Andes differed from that of the Holocene. A possible cause for the erosion of the floodplain is the tectonic uplift of the Eastern Andes, which progressively shifts the Napo River northwards. Hence, the river cuts into ancient lowland sediment, which is admixed to the Andean sediment carried in the main Napo River. [Copyright &y& Elsevier]

Abstract: The erosion characteristics and bed stability of wildfire-affected stream sediment were measured in an annular flume. Biofilms were grown in the flume on cohesive streambed sediments collected from a wildfire affected stream and a reference undisturbed stream in southern Alberta, Canada. Examined factors that influence sediment erosion, settling and bed stability included applied shear stress, geochemical and physical properties of the sediment, floc structural characteristics and consolidation period (2, 7, 14 days). Erosion characteristics and sediment properties were strongly influenced by wildfire, consolidation period and bed biostabilization. The fire-modified sediment was more resistant to erosion than the reference unburned sediment. Settling velocities were lower in the burned sediment due to higher organic content and porosity. The critical shear stresses for erosion were 1.6 and 1.8 times higher for the burn-associated sediment after 7 and 14 days of consolidation. The differences are related to the greater degree and spatial extent (depth) of biofilm attachment in the burned sediment. Erosion depths were 4–8 times higher in burned sediment as a result of wildfire-associated biostabilization. [ABSTRACT FROM AUTHOR]

Abstract: It is shown that the middle Cretaceous succession in the northern Cordilleran foreland basin consists of several-million-year tectonically-driven cycles comprising two components: strata deposited in an underfilled basin with a prominent forebulge zone and strata deposited in an overfilled basin lacking evidence of a forebulge. The episodic thrusting of the Cordilleran orogenic wedge and its rich sediment supply to the basin are two main controlling factors for the formation of these cycles. A qualitative model of several-million-year tectonically-driven underfilled–overfilled cycle for migration and stratigraphic fill in this basin is proposed. During the early underfilled period (orogenic loading period), due to orogenic loading of emplaced thrust sheets, flexural subsidence is created in the region proximal to the mountain belt and a prominent forebulge is developed. During the late underfilled period (early orogenic unloading period), as the cratonward migration of the subsidence center of sediment loading in the foredeep zone, forebulge zones and backbulge zones migrate cratonwards, forming a diachronic erosion surface in the central basin. During the overfilled period (late orogenic unloading period), a prominent erosion forms in the proximal basin and a peripheral sag develops above the forebulge area of the previous underfilled period. This model may provide a pattern to subdivide sedimentary successions in the Cordilleran foreland basin. Using this model, alternative interpretations are suggested for some important, but controversial stratigraphic phenomena in the Cretaceous Cordilleran foreland basin: traditionally defined eustatic highstands, wide sedimentation area of the basin, erosion surfaces and widespread subtle topographic uplifts in the central basin, high-frequency coarsening-up cycles, extensively distributed erosive-based sandstones and conglomerates enclosed in marine mudstones. [ABSTRACT FROM AUTHOR]

Abstract: Quantifying suspended sediment exports from catchments and understanding suspended sediment dynamics within river networks is important, especially in areas draining erodible material that contributes to the siltation of downstream reservoirs and to the degradation of water quality. A one-year continuous monitoring study of water and sediment fluxes was conducted in three upland subcatchments (3.0, 9.3, and 12.0km2) located within the Cointzio basin, in the central volcanic highlands of Mexico (Michoacán state). Two subcatchments generated high sediment exports (i.e., Huertitas, 900–1500tkm−2 y−1 and Potrerillos, 600–800tkm−2 y−1), whereas the third subcatchment was characterized by a much lower sediment yield (i.e., La Cortina, 30tkm−2 y−1). Such disparities in subcatchment behaviours were associated with the presence of severely gullied areas in Huertitas and Potrerillos rather than with rainfall erosivity indices. An adapted classification of hysteretic patterns between suspended sediment concentration (SSC) and discharge was proposed because 42% of flood events contributing to 70% of sediment export were not discriminated by the classical clockwise/anticlockwise typology. This new classification allowed the identification of relationships in the hydrosedimentary responses of successive floods. A stream transport capacity limit was also detected during hydrograph recession phases. Overall, hydrosedimentary processes proved to be seasonally dependent: sediment export was repeatedly limited by the stream transport capacity during the first part of the rainy season, whereas a channel minimum erosivity threshold was frequently reached at the end of the season. [Copyright &y& Elsevier]