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The battering of bedrock by bedload collisions is the primary mechanism by which bedrock rivers erode and landscapes evolve. The energy imparted via impacts acts to detach bedrock via the growth and intersection of surface fractures. We present impact experiments designed to test the influence of particle impact energy on bedrock erosion rates. We found that erosional efficiency increased with increasing impact energy. Notably, these increases in efficiency are not captured by a widely‐used mechanistic bedrock erosion model. Observed increases in erosional efficiency were linked with enhanced elastic energy dissipation captured by differences in the coefficient of restitution. We suggest that this increase in energy dissipation is indicative of enhanced crack extension for high velocity impacts. Our experiments indicate a clear energy‐dependence for bedrock detachment processes that is not yet captured by bedrock incision models but may be integrated into long‐term erosion rates and landscape evolution. Plain Language Summary: Bouncing sediment grains batter the bedrock beds of rivers during floods. As these impacts collide with the bed, they slowly chip away at the riverbed bedrock. It's perhaps intuitive that a grain with more energy when it collides with the riverbed is able to chip away more bedrock. But, how much more destructive are these high energy impacts? We designed an experiment where we hit a bedrock sample with a steel ball at a range of impact energies, over and over again, up to 30,000 times, and measured how much material was chipped away. High energy impacts eroded more material, but this increased efficiency of erosion is not fully captured by impact‐based erosion models. We hypothesize that for higher energy impacts, a larger fraction of the incoming energy is used to crack the bedrock, more easily eroding material. We liken the relative influence of these high energy impacts to a battering ram, where only a few strikes can easily break down a door, whereas lower energy impacts, similar to a simple knock, are unlikely to achieve the same result. We suggest that this effect may be important in determining the influence of extreme events on bedrock erosion over long timescales. Key Points: Impact experiments demonstrate that bedrock erosional efficiency is enhanced with increasing impact energyExperimentally‐derived coefficients of restitution and rock resistance coefficients indicate enhanced elastic energy dissipation with increasing impact energyResults suggest that more energetic impacts enhance crack extension, increasing erosional efficiency [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering (17264073) is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Bedload transport in a river is a deeply analyzed problem, with many methodologies available in the literature. However, most of the existing methods were developed for reaches of rivers rather than for confluences and are suitable for a particular type of material, which makes them very inaccurate in cases where the sediments are comprised of a mix of different types of soil. This study considers the effect of two different bed sediment sizes, gravel and sand, in relation to bed load transport in a confluence. Five well-known and validated equations (namely Meyer-Peter and Müller, Parker + Engelund and Hansen, Ackers and White, and Yang) are applied to the case study of the Tagus–Alberche rivers confluence (in Talavera de la Reina, Spain), where main and tributary rivers transport different materials (sand and gravel). Field works in the area of the confluence were conducted, and a set of alluvial samples were collected and analyzed. The previously mentioned methods were employed to analyze the geomorphology in the confluence area and downstream of it under different flooding scenarios, concluding different trends in terms of deposition/erosion in the area under historic flooding scenarios. When the trends show erosion, all methods are very consistent in terms of numerical predictions. However, the results present high disparity in the estimated values when the predictions suggest deposition, with Parker + Engelund and Hansen yielding the highest volumes and Meyer-Peter and Müller the lowest (the latter being around 1% of the former). Yang and Ackers and White predict deposits in the same range in all cases (around 15% of Parker and Engelund Hansen). Yang's formula was found to be suitable for the confluences of rivers with different materials, allowing for the estimation of sediment transport for different grain sizes. The effect of different flow regimes has been analyzed with the application of Yang's formula to the Tagus-Alberche confluence. [ABSTRACT FROM AUTHOR]

Bedload sediment transport is an ubiquitous process in natural surface water flows (rivers, dams, coast, etc), but it also plays a key role in catastrophic events such as dyke erosion or dam breach collapse. The bedload transport mechanism can be under equilibrium state, where solid rate and flow carry capacity are balanced, or under non-equilibrium (non-capacity) conditions. Extremely transient surface flows, such as dam/dyke erosive collapses, are systems which always change in space and time, hence absolute equilibrium states in the coupled fluid/solid transport rarely exist. Intuitively, assuming non-equilibrium conditions in transient flows should allow to estimate correctly the bedload transport rates and the bed level evolution. To get insight into this topic, a 2D Finite Volume model for bedload transport based on the non-capacity approach is proposed in this work. This non-equilibrium model considers that the actual bedload sediment discharge can be delayed, spatial and temporally, from the instantaneous solid carry capacity of the flow. Furthermore, the actual solid rate and the adaptation length/time is governed by the temporal evolution of the bedload transport layer and the vertical exchange solid flux. The model is tested for the simulation of overtopping dyke erosion and dambreach opening cases. Numerical results seems to support that considering non-equilibrium conditions for the bedload transport improves the general agreement between the computed results and measured data in both benchmarking cases. [ABSTRACT FROM AUTHOR]

A two-dimensional, vertically integrated, non-linear numerical model was applied to investigate the Urias coastal lagoon's (URCOL) tide-driven currents, bed load sediment transport, and seabed morphodynamics. The coastal body of water, located on the eastern side of the Gulf of California, includes the Mazatlán harbour, the most important port on the Pacific Mexican coast due to the relevant activities like the heavy vessel traffic. URCOL also includes an extensive aquaculture infrastructure at the lagoon head. The tidal hydrodynamic modelling revealed the mixed character of tides predominantly semidiurnal in the lagoon. The numerical computation at the harbour entrance showed an ebb-dominant tidal distortion. The distribution patterns of the erosion and accretion rates are consistent with the convergent and divergent character of the vectors of sediment transport rates. The sediment accretion has been predicted mainly in the middle part of the channel, right where the channel starts curving, changing the alignment of the lagoon. The tidal hydrodynamics, sharp topographic gradient, and geometric features of the lagoon seem to determine the location of accretion and erosion areas. Article Highlights: A mixed character of predominantly semidiurnal tides and an ebb-dominant tidal distortion were predicted in the lagoon. The erosion and accretion areas are consistent with the sediment transport vectors predicted by the model. A non-linear numerical model study determined that tidal hydrodynamics and morphodynamics influence sediment transport in the lagoon. The sediment accretion-erosion areas mostly occur in the middle part of the lagoon. Sediment exchange took place occur between the lagoon and the Gulf of California; the predicted net bed load sediment transport was seaward. [ABSTRACT FROM AUTHOR]

Bedrock rivers carry large amounts of fine sediment in suspension. We developed a mechanistic model for erosion of bedrock channel banks by impacting bedload and suspended load particles that are advected laterally by turbulent eddies (advection‐abrasion model). The model predicts high lateral erosion rates near the bed, with rates decreasing up to the water surface. The model also predicts greater erosion within the suspended load layer than the bedload layer for many typical sediment supply and transport conditions explored. We compared the advection‐abrasion model with a previously derived model for lateral erosion of bedrock banks by bedload particles deflected by stationary bed alluvium (deflection‐abrasion model). Erosion rates predicted by the deflection‐abrasion model are lower, except within limited conditions where sediment is transported near the threshold of motion and the bed is near fully covered in sediment. Both processes occur in bedrock rivers at the same time, so we combined the advection‐abrasion and deflection‐abrasion models and found that the lateral erosion rate generally increases with increasing transport stage and relative sediment supply for a given grain size. Application of our combined‐abrasion model to a natural bedrock river with a wide distribution of discharge and supply events, and mixed grain sizes, indicates that finer sediment dominates the lateral erosion on channel banks in low sediment supply environments and can be as important as coarser sediment in high sediment supply environments. Plain Language Summary: The width of bedrock rivers is controlled by the competition between vertical and lateral erosion against a backdrop of vertical uplift. Both processes are governed by the quantity and size of sediment that is transported. Bedrock rivers transport small particles suspended in the water column and large particles along the bed. Compared with large particles, bedrock erosion by impacts of small particles transported in suspension is poorly understood. Here, we develop a model to explore whether the small particles can be responsible for eroding bedrock channel banks. The new model shows that particles transported in suspension cause higher erosion on channel banks than the particles transported along the bed, except where bedrock channels are especially steep. Compared with a model of large particles transported along the bed, the new model predicts higher bank erosion rates, except in bedrock rivers where sediment covers the whole bed and is transported near the threshold of motion. We find that small particles cause more lateral erosion than large particles when the river transports only small amounts of sediment. Small particles can be as important as large particles when the river transports large amounts of sediment. Key Points: A new model is developed for lateral bank erosion by bedload and suspended load particle impacts from advection by turbulence eddiesThe model predicts higher lateral erosion within the suspended load layer than the bedload layer for many sediment supply and transport conditionsCombining the model with a bedload‐deflection‐based abrasion model indicates that finer sediment is important for eroding bedrock banks [ABSTRACT FROM AUTHOR]

The slope effects on sediment trapping process in vegetative filter strips (VFS) are usually neglected in current modelling practices for VFS operation, which hamper the VFS design and performance evaluation, especially on steep slopes. To fill the knowledge gap, 12 laboratory experiments of sediment trapping in VFS were conducted with three different inflow discharge (80, 100, and 120 ml s−1) and four slope angles (5,10, 15, and 20°). The experimental results show that, on steep slopes (10, 15, and 20°), a part of trapped sediment particles in VFS can be eroded again and then dragged to the downstream as bed load, whilst they do not move on gentle slope (5°). To describe the complex processes, a simple and effective modelling framework was developed for sloped VFS by coupling the slope infiltration, runoff, and modified sediment transport model. The model was tested against the experimental results and good agreements between the modelled and observed results were found in both runoff and sediment transport processes for all cases. On steep slopes, the sediment trapping performance of VFS decreases significantly because the erosion of deposited sediment particles can account for more than 60% of the sediment load in the outflow. The slope effect on sediment trapping efficiency of VFS varies greatly with soil, VFS, and slope properties. The model was compared with previous sediment transport equation and found that both methods can satisfactorily predict the sediment trapping of VFS on gentle slopes, but previous sediment transport equation is likely to overestimate the sediment trapping efficiency in VFS on steep slopes. This model is expected to provide a more realistic and accurate method for predicting runoff and sediment reduction in VFS on sloping surfaces. [ABSTRACT FROM AUTHOR]

The study is to evaluate the total sediment transport (suspended and bed load) in a Mediterranean river (Bellah, Tipaza, Algeria). To understand this study, we based our analysis on hydrometric data related to the instantaneous discharge and to the concentration of suspended sediment, over a period of 33 years (from 1974/75 to 2006/07). The results show that a good correlation between the suspended sediments and water discharge. The exponent b of our model is equal to 1.38, a value close to those found by researchers who worked in semi-arid region. The suspended sediment transport is about 610 t km-2 year-1. This value is comparable to those found in other regions with similar hydrologic regimes. The bed load is about 170 t km-2 year-1 for τ0 = γ × I × Rh t km-2 year-1 and it is about 115 t km-2 year-1 for τ0 = 0.7×γ × I × Rh. The total sediment transport is estimated at 725 t km-2 year-1 if we take into account the corrective coefficient of roughness in the bed of the wadi and equal to 780 t km-2 year-1 in other direction. To better judge our results, we compared them with those obtained by the relationship Tixeront which remains the most used for estimating the specific degradation in the basins of the Maghreb. The value obtained by the relation of Tixeront is slightly below our own values, but it is permissible to say that the results are of the same order of magnitude. This slight difference can be explained by the introduction of the amount of sediments carried in the determination of the specific erosion of the watershed rates. [ABSTRACT FROM AUTHOR]

In natural rivers, sediment heterogeneity and flow variability control the diversity of transport modes that occur. Although these different modes contribute to the total sediment transport, a law extending from bed load to suspended load that is, relevant for a wide range of sediment mixtures and flow conditions is lacking. Besides, a transport‐limited assumption is often made in modeling of fluvial morphodynamics and thus potentially misses under‐/over‐capacity regimes associated with a particular range of grain sizes and hydraulic conditions. We present a Multi Grain‐Size Total Load model based on widely accepted concepts of sediment transport and developed within the transport length framework in combination with an erosion‐deposition formulation. The new transport length model captures the diversity of transport modes as a physical continuum. Transport capacities for single or bimodal grain sizes are reasonably predicted when compared to published data and scale with the bed shear stress through a continuously varying exponent linked to the characteristic transport height. Modeled transport lengths extend over several orders of magnitude at given flow conditions. Extremely long distances suggest that suspended transport is probably never at capacity. The model can be extended to populations of various grain sizes with a threshold of motion corrected from hiding‐exposure. However, further experimental constraints are needed to better describe entrainment and saltation in strongly heterogeneous bed load transport. The new theoretical formalism we introduce paves the way for a Multi Grain‐Size Total Load Sediment Transport model that includes the variety of transport modes in both non‐stationary and stationary regimes. Plain Language Summary: In natural rivers, flow variability and sediment heterogeneity affect how sediment grains are transported. Whether grains move close to the bed or higher in the water column, they all contribute to the total sediment transport as bed load and suspended load, respectively. However, a unique law that predicts the total amount of sediment that can be transported by a river for a wide range of sediment mixtures and flow conditions is lacking. Besides, in modeling of fluvial morphodynamics, the river is often assumed at capacity, meaning that it carries the maximum sediment load it can, and thus under‐/over‐capacity regimes are potentially missed. We present a Multi Grain‐Size Total Load model, built by bringing together widely accepted concepts of sediment transport, that includes the variety of transport modes in both capacity and under‐/over‐capacity regimes. The two main components of this model are: (a) the transport length defined as the distance over which sediments are transported and (b) the erosion‐deposition formulation that explicitly describes the transfer of sediment from the sediment bed to the above water column, and conversely. While the new transport length model captures the transport from bed load to suspension continuously, the erosion‐deposition model applies to several grain sizes. Key Points: Emergence of a continuous description of sediment transport using the transport length model and the erosion‐deposition frameworkUnified theory of sediment transport encompassing the diversity of transport modes such as bed load and suspended loadModel applicable to both non‐stationary and stationary regimes while showing that transport in suspension is likely never at capacity [ABSTRACT FROM AUTHOR]

Trapezoidal-shaped hydrographs are typical of anthropized rivers, as this form is generally associated with the release of water from hydropower dams. To investigate how such unnatural waves can affect bedload rate, preliminary flume experiments were performed in Krakow, Poland, looking at bedload transport rate, bed shear stress and bed morphology. In addition, close-range bed surface photogrammetry was used to investigate bed changes due to the passage of the flood wave. Three scenarios, having the same water volume but different wave magnitudes, were tested. The lowest wave showed almost no sediment transport and no visible changes in bed morphology, while higher waves changed the bed morphology, creating erosion and accumulation zones. The highest wave was characterized by an 8-shaped hysteresis of the bedload rate with a peak during the wave maximum. The lag time between the maximum bedload rate and the wave plateau was longer than expected due to zero-slope conditions. [ABSTRACT FROM AUTHOR]

This paper presents a numerical model study on the ice cover effect on bank stability in non-cohesive alluvial channels. The model consists of a coupled two-dimensional finite element unsteady hydrodynamic model with bank erosion and mass failure processes for open water and ice-covered conditions. The associated morphological change is modeled with non-equilibrium sediment transport, including the side slope effect on bed load transport. The model adopts two sets of repose angles for emerged and submerged bank materials in analyzing non-cohesive bank mass collapses and redistributions. The model is validated with published laboratory experiments on bank retreat caused by dam-break flow and equilibrium cross-section evolution and showed improvements over existing numerical models. Simulated results showed that the ice cover caused larger bank retreats and bed depositions and slower channel cross-sectional change due to the reduced bed shear stress and the increased flow depth. Article Highlights: A bank stability model is developed by coupling the unsteady hydrodynamics, non-equilibrium sediment transport, and bank erosion and mass failure processes. The model is validated with published laboratory experiments and other models. The ice-covered flow causes larger riverbank retreats and slower cross-sectional changes than that of the open channel flow. [ABSTRACT FROM AUTHOR]

The projected climate change for Norway through the 21st century predicts that the temperature will increase significantly. Events with heavy rainfall will be more intense and occur more frequently. Rain floods will increase in magnitude and also occur more frequently. Extreme flooding and heavy rain will significantly impact the sediment dynamics in rivers. In the mountain areas, floods are often associated with erosion, transport and deposition of coarse sediment along the streams. These processes are related to bed load transport and pose a hazard in addition to the elevated water discharge and have to be included in management plans for river basins. This article studies the bed load delivery from sources that contribute the most to the sediment budget in the Gudbrandsdalslågen river basin during the large magnitude floods in 2011 and 2013. More than 100 debris slides and debris flow were triggered in the tributary river Veikleåi by the heavy rain and snowmelt during these floods. The volume of the contribution from debris flows and erosion and deposition of the river bed was determined by subtracting digital elevation models acquired during repeated airborne LIDAR surveys. In the river Dørja the supply of sediment from a number of debris flows caused extensive aggradation and channel changes. In their new position, lateral erosion by these channels triggered slides on the adjacent slopes. The contributing volumes of debris flows, lateral erosion, and river bed erosion and deposition were determined from the LIDAR surveys. Relations obtained from studies of sediment transport in modern glacier rivers were used to obtain estimates of the ratio of bed load versus suspended load derived from the Pleistocene moraine deposits. Several monitoring stations using conventional methods for measuring bed load and suspended load recorded very large volumes of sediment delivery during both of the extreme floods. The results of the study may be used to identify necessary locations for check‐dams and erosion protection works in order to adapt to climate change. [ABSTRACT FROM AUTHOR]

To implement soil conservation approaches, it is necessary to estimate the amount of annual sediment production from a watershed. The purpose of this study was to determine the erosion intensity and sedimentation rate from a watershed by employing empirical models, including the modified Pacific Southwest Inter-Agency Committee (MPSIAC), the erosion potential method (EPM), and Fournier. Moreover, the accuracy of these empirical models was studied based on field measurements. Field measurements were conducted along two reaches of Babolroud River. Total sediment transport, including suspended load and bed load, was predicted. Bed load transport rate was measured using a Helly–Smith sampler, and suspended load discharge was calculated by a sediment rating curve. The results of this study indicate that the erosion intensity coefficient (Z) of the Babolroud watershed is 0.54, with a deposition rate of 166.469 m3/(km2.year). Due to the existence of unusable crops, the highest amount of erosion appeared in the northern region of the watershed. The results using the EPM and MPSIAC models were compared with field measurements and indicated that both models provided good accuracy, with differences of 22.42% and 20.5% from the field results, respectively. Additionally, it could be concluded that the Fournier method is not an efficient method since it is unable to consider the erosion potential. [ABSTRACT FROM AUTHOR]

• A new 2D meshless bedload sediment transport model is developed based on ESPH. • A formulation for calculating the time step size for an HLLC Riemann solver in a weakly coupled approach is proposed. • The simulated results based on the developed 2D ESPH-SW-BST model show good agreement with the measured results. • A particle configuration of eight interacting particles can yield more accurate predictions of erosion peaks in cases with significant lateral flow effects. A 2D Eulerian meshless bedload sediment transport model is developed using smoothed particle hydrodynamics (SPH) to simulate rapidly varied flows over mobile beds. In the developed model, we adopt a weakly coupled numerical approach to explicitly solve the governing equations, including 2D shallow water equations for fluid flow motion and the Exner equation for bed sediment movement at the same time step. A defined virtual bedload velocity in a weakly coupled approach is involved in the calculation of time step sizes. However, nonphysical virtual bedload velocities, which often occur in cases with nearly flat beds, require extremely small time step sizes. A formulation of the lower and upper bounds of information propagation speeds for an HLLC approximate Riemann solver is thus proposed to remedy the problem. Four case studies involving dam break flows in prismatic and erodible channels, knickpoint migration, dam erosion due to overtopping flow and dam-break flow in an erodible channel with an abrupt expansion are adopted to validate the developed model. In addition, to compare the performances of different particle interaction configurations under Cartesian uniform particle arrangements, four and eight interacting particles are obtained by changing the smoothing length. Against the measured results, the case of eight interacting particles shows more accurate predictions of erosion peaks along the measured cross-sections because the lateral flows are significant. The good agreement between the simulated and measured results shows that the developed 2D Eulerian SPH bedload sediment transport model with eight interacting particles is well suited for simulating complicated flow-induced bed erosion. [ABSTRACT FROM AUTHOR]

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The Labyrinth in the McMurdo Dry Valleys of Antarctica is characterized by large bedrock channels emerging from beneath the margin of Wright Upper Glacier. To study the morphodynamics of large subglacial channels cut into bedrock, we develop herein a numerical model based on the classical theory of subglacial channels and recent results on bedrock abrasion by saltating bed load. Model results show that bedrock abrasion in subglacial channels with pressurized flow reaches a maximum at an intermediate distance up-ice from the glacier snout for a wide range of sediment grain sizes and sediment loads. Close to the snout, the velocity is too low and the sediment particles cannot be mobilized. Far from the snout, the flow accelerates and sediment is transported in suspension, thus limiting particle impacts at the channel bottom and reducing abrasion. This non-monotonic relationship between subglacial flow and bedrock abrasion produces concave up bottom profiles in subglacial channels and potential cross-section constrictions after channel confluences. Both landforms are present in the bedrock channels of the Labyrinth. We therefore conclude that these geomorphic features are a possible signature of bedrock abrasion, rather than glacial scour, and reflect the complex interplay between transport rate, sediment load, and transport capacity in subglacial channels. [ABSTRACT FROM AUTHOR]

The width of bedrock rivers is set by the competition between vertical and lateral erosion in uplifting landscapes. Compared with vertical erosion rates, less is known about the lateral erosion rates that are thought to dominate when river beds are alluviated. Here, we derive an analytical model for lateral erosion by saltating bedload particle impacts that are deflected by alluvial cover. The analytical model is a simplification of the Li et al. (2020, https://doi.org/10.1029/2019jf005509) numerical model of the same process. The analytical model predicts a nonlinear dependence of lateral erosion rate on sediment supply, shear stress, and grain size, revealing the same behavior observed in the numerical model, but without tracking particle movements through time and space. The analytical model considers both uniformly distributed cover and patchy partial cover that are implemented with a fully alluviated patch along one bank and bare bedrock along the other. The model predicts that lateral erosion rate peaks when the bed is ∼70% covered for uniformly distributed alluvium, or when the bed is fully covered for patchy alluvium. Vertical erosion dominates over lateral erosion for ∼75% and >90% of sediment supply and transport stage conditions for uniformly distributed cover and patchy cover, respectively. We use the model to derive a phase diagram of channel responses (steepening, flattening, narrowing, and widening) for various combinations of transport stage and relative sediment supply. Application of our model to Boulder Creek, CA, captures the observed channel widening in response to increased sediment supply and steepening in response to larger grain size. Key Points: An analytical solution to the Li et al. (2020) numerical model is derived for lateral erosion for uniformly distributed and patchy coverMaximum lateral erosion rates occur at ∼70% coverage for uniformly distributed case and full coverage when patches grow to cover whole bedApplication of our model to Boulder Creek, CA, indicates that it gets wider from bank erosion and steeper to transport larger grain size [ABSTRACT FROM AUTHOR]

Fluvial bedrock incision is driven by the impact of moving bedload particles. Mechanistic, sediment‐flux‐dependent incision models have been proposed, but the stream power incision model (SPIM) is frequently used to model landscape evolution over large spatial and temporal scales. This disconnect between the mechanistic understanding of fluvial bedrock incision on the process scale, and the way it is modeled on long time scales presents one of the current challenges in quantitative geomorphology. Here, a mechanistic model of fluvial bedrock incision that is rooted in current process understanding is explicitly upscaled to long time scales by integrating over the distribution of discharge. The model predicts a channel long profile form equivalent to the one yielded by the SPIM, but explicitly resolves the effects of channel width, cross‐sectional shape, bedrock erodibility, and discharge variability. The channel long profile chiefly depends on the mechanics of bedload transport, rather than bedrock incision. In addition to the imposed boundary conditions specifying the upstream supply of water and sediment, and the incision rate, the model includes four free parameters, describing the at‐a‐station hydraulic geometry of channel width, the dependence of bedload transport capacity on channel width, the threshold discharge of bedload motion, and reach‐scale cover dynamics. For certain parameter combinations, no solutions exist. However, by adjusting the free parameters, one or several solutions can usually be found. The controls on and the feedbacks between the free parameters have so far been little studied, but may exert important controls on bedrock channel morphology and dynamics. Plain Language Summary: Bedrock erosion by rivers is driven by the impact of moving sediment particles, chipping away tiny pieces of rocks in their passage. Sediment transport occurs infrequently, during floods. Over thousands of years, this slow process shapes the river, sometimes leading to the creation of spectacular landforms such as gorges. Mechanistic models of fluvial bedrock erosion explicitly take into account the effects of moving sediment particles, while models used for long time scales do not. Here, the connection between mechanistic and long‐term models is made explicit by integrating a mechanistic model over the entire distribution of floods, yielding solutions for the long‐term erosion rate and the channel bed slope. Some of these solutions are similar to those used previously, but other solutions are also possible, showing the rich dynamic behavior that rivers can exhibit. The solutions make explicit the role of lithology, channel width, and discharge variability, which were previously hidden in a single lumped calibration parameter. Key Points: Analytical solution from explicit upscaling of a sediment‐flux‐dependent fluvial bedrock incision model to long time scalesThe model includes solutions similar to those obtained in the stream power paradigm, in addition to other possible solutionsThe model explicitly resolves forcing behavior and highlights potential dynamic feedbacks that have so far not been considered [ABSTRACT FROM AUTHOR]

Literature review reveals that many erosion models have limitations for application to constructed landforms. The new EroCA model aims to address this gap. The model uses established erosion and sediment transport models applied to multiple particle size classes at fine spatial and temporal resolutions, covering both suspended load and bedload. Using data from an experimental plot in Northern Australia, global sensitivity analysis was used to investigate the sources of uncertainty, limitations of the model, and priorities for data collection. Further analysis explored sensitivity to model grid size. The results showed that the Manning roughness, erodibility parameters and particle size are the most important parameters. Results also showed low parameter identifiability and hence the difficulty of calibration, even when using high quality experimental data. EroCA has the capacity to be a powerful landform modelling tool at appropriate scales of application; however ideally its data needs would be considered during monitoring design. • In-depth attempt to develop and assess a high spatial resolution process-based erosion model for a mined landform. • Improved understanding of the effects of various parameters on soil erosion process and modelling. • New insight into the limitations of experimental plot data sets for supporting high resolution erosion models. [ABSTRACT FROM AUTHOR]

Coastal zones are dynamic environments where sediment transport significantly influences erosion, deposition, and ecosystem stability. Accurate modelling of the complex interactions between hydrodynamics, sediment transport, and morphological changes in high-energy shoreface areas is crucial for sustainable coastal management. This study aims to assess sediment dynamics and understand the dominant physical drivers of sediment transport in the shoreface by coupling high-resolution numerical modelling with a shoreface sand tracer experiment. Results from the field experiment showed high diffusion and a net onshore and downdrift movement of the tracer in agreement with the observed hydrodynamic data. The numerical modelling strategy, validated with in situ hydrodynamic data and tracer results, demonstrated good performance and highlighted the dominant modes of shoreface sediment transport. While during low energetic wave conditions, the dominant transport mechanism involves the slow-rate bed load sediment movement toward the shore, under moderate energetic wave conditions, longshore wave-induced suspended transport becomes the prevailing mode of transport. The study provides valuable insights to increase the understanding of sediment transport in the shoreface and highlights the importance of coupling numerical modelling with sediment tracer experiments. • Field observations and numerical modelling are used to understand sediment transport in the shoreface • Conceptual sediment dynamic model combines Lagrangian and Eulerian approaches • Energetic wave conditions increase wave-induced currents and sediment transport rates, with waves breaking over the bar crest. • Streaming and wave nonlinearities are the main drivers of sediment transport in the shoreface • Alongshore suspended transport dominates in the surf zone, distributing sediments downdrift [ABSTRACT FROM AUTHOR]

This paper presents a numerical investigation of multiple identical swash events to study the swash–swash interaction processes and their impacts on beachface evolution. The numerical model, based on the Nonlinear Shallow Water Equations, is first calibrated/validated against two different single-event-based data-sets. Multiple swash events are generated by identical solitary waves separated by different time intervals, to achieve weak and strong wave-backwash interactions. After a small number of weak interaction events the main feature is erosion from lower and mid swash region and deposition seaward of the swash in a bed-step, created by a backwash bore, primarily due to bed-load. As the number of waves increases, the strength of this backwash bore reduces because of the reduced beach slope caused by the growing bed-step. This eventually leads to a net quasi-equilibrium between bed- and suspended-load per period in most of the swash and surf zones. For strong interaction, initial bed evolution per event is much slower, due to interactions, and is bed load dominated. A quasi-equilibrium is also established as the influence of suspended load grows. Overall bed change per period within the domain eventually converges in both cases. Final bed profiles (i.e. after the same elapsed time, but different numbers of waves) are fairly similar, both with an offshore swash bar. Both profiles continue to evolve on the offshore side of this bar. However, this evolution is driven by suspended load for the weak interactions and bed load for strong interactions. The implication is that similar swash morphological features can emerge from different swash processes, and also be maintained distinctly. • The roles of weak and strong swash interactions in beachface evolution are studied. • Final bed profiles for both cases are similar, but evolve distinctly. • Different sediment transport modes dominate the bed evolution in the two cases. • Both bed profiles reach an quasi-equilibrium in most of the region. • An offshore swash bar develops in both cases, and continues to evolve. [ABSTRACT FROM AUTHOR]

A total maximum daily load for the Chesapeake Bay requires reduction in pollutant load from sources within the Bay watersheds. The Conestoga River watershed has been identified as a major source of sediment load to the Bay. Upland loads of sediment from agriculture are a concern; however, a large proportion of the sediment load in the Conestoga River has been linked to scour of legacy sediment associated with historic millpond sites. Clarifying this distinction and identifying specific segments associated with upland vs. channel sources has important implications for future management. In order to address this important question, we combined the strengths of two widely accepted watershed management models — Soil and Water Assessment Tool (SWAT) for upland agricultural processes, and Hydrologic Simulation Program FORTRAN (HSPF) for instream fate and transport — to create a novel linked modeling system to predict sediment loading from critical sources in the watershed including upland and channel sources, and to aid in targeted implementation of management practices. The model indicates approximately 66% of the total sediment load is derived from instream sources, in agreement with other studies in the region and can be used to support identification of these channel source segments vs. upland source segments, further improving targeted management. The innovated linked SWAT‐HSPF model implemented in this study is useful for other watersheds where both upland agriculture and instream processes are important sources of sediment load. Research Impact Statement: Novel SWAT‐HSPF linkage to simulate sediment sources in legacy sediment‐impacted agricultural watersheds. [ABSTRACT FROM AUTHOR]

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In this study, we conducted multiple physical experiments to estimate the efficacy and spatial pattern of erosion by abrading sediment moving through a simple U‐shaped channel bend with erodible bed and banks. The experiments showed that in the bend, lateral abrasion followed a monotonically increasing linear relationship with sediment feed rate. However, vertical incision had a more complex relation with the sediment feed rate, with an initial increase in abrasion as the feed rate increased followed by a decrease in abrasion of the bed as cover effects became dominant at higher feed rates. Bank erosion was large in places where the width and the lateral slope of the point bar were relatively large. On the other hand, in places where the width of the point bar was smaller, the bedrock bed was eroded primarily along the boundary of the point bar, resulting in a bedrock bench near the outer bank. Key Points: A U‐shaped channel with soft mortar bed and banks is used to study the effect of sediment on vertical and lateral erosion in a bedrock bendLateral erosion increased linearly with increasing sediment supply, but vertical erosion showed a more complicated relationBanks situated downstream of the bend apex showed higher lateral erosion [ABSTRACT FROM AUTHOR]

Sediment transport is an important process for rivers and natural channels. The determination of sediment transport is a very complex process due to the high variability and changing nature of the factors that intervene. As a contribution to the description of this kind of phenomenon and to highlight the problems, the needs and potentials of the numerical approaches, OpenFOAM solver settlingFoam is used to simulate sediment transport in a rectangular channel. The model used constitutes a simplification of a complex procedure based on the application of a single parameter (alpha) to determine the fluid-sediment mixture features. High variability was found between the results from different alpha values. Nevertheless, there is a lack of information to determine the appropriate value of this parameter. However, even though the procedure applied and the results obtained have to be taken as a reference, this study provides valuable criteria for future research of this complex topic. [ABSTRACT FROM AUTHOR]

Relation among estuarine processes, mixing mechanisms and turbidity maximum zone (TMZ) formation was evaluated in a microtidal tropical estuary of high fluvial discharge (Magdalena River, northwestern South America). Particularly, assessing the effects of vertical stratification over mixing, estuarine circulation and suspended sediment transport processes. Measurements of salinity, temperature, density, currents and suspended sediment concentration (SSC) were performed at the Magdalena river mouth during high and low streamflows to distinguish among two contrasting seasonal conditions (flow conditions, wind patterns, wave energy). Salinity, temperature, density and location of the freshwater-saltwater interface (FSI) exhibited a sharp seasonal variability. The river mouth and delta front were stratified regardless of the hydrologic season, whereas the riverine section was stratified during the low streamflow season, reflecting the balance between fluvial advection and vertical stratification. Reduction of the vertical mixing led to a more clearly defined and extended stratification. Bottom friction is the main mixing mechanism, but as stratification is strengthened along the river mouth, the vertical mixing weakens, promoting the developing of TMZ (SSC >4500 mg l −1 ). Our results indicate that TMZ developing is caused by the convergence of stratified layers near the nodal point and the weakening of bottom turbulence by stratification. Although the TMZ exhibited a strong seasonal variation in its magnitude and extent, it usually formed in the convergence front demarcated by saltwater intrusion. Streamflow is the major influence on the TMZ formation since it allows the development of stratified conditions, which weaken turbulent mixing, and thus promotes particulate matter settling. The Magdalena River estuary can be classified as turbid (4000 mg l −1  < SSC max  < 10,000 mg l −1 ) and extremely turbid during low streamflow seasons (SSC max  > 10,000 mg l −1 ). These values are of the same order as the SSC reported for the Yangtze and Yellow estuaries, classified as having the largest SSC values of the world. [ABSTRACT FROM AUTHOR]

Dam removals with unmanaged sediment releases are good opportunities to learn about channel response to abruptly increased bed material supply. Understanding these events is important because they affect aquatic habitats and human uses of floodplains. A longstanding paradigm in geomorphology holds that response rates to landscape disturbance exponentially decay through time. However, a previous study of the Merrimack Village Dam (MVD) removal on the Souhegan River in New Hampshire, USA, showed that an exponential function poorly described the early geomorphic response. Erosion of impounded sediments there was two-phased. We had an opportunity to quantitatively test the two-phase response model proposed for MVD by extending the record there and comparing it with data from the Simkins Dam removal on the Patapsco River in Maryland, USA. The watershed sizes are the same order of magnitude (102 km2), and at both sites low-head dams were removed (~3-4 m) and ~65 000 m3 of sand-sized sediments were discharged to low-gradient reaches. Analyzing four years of repeat morphometry and sediment surveys at the Simkins site, as well as continuous discharge and turbidity data, we observed the two-phase erosion response described for MVD. In the early phase, approximately 50% of the impounded sediment at Simkins was eroded rapidly during modest flows. After incision to base level and widening, a second phase began when further erosion depended on floods large enough to go over bank and access impounded sediments more distant from the newly-formed channel. Fitting functional forms to the data for both sites, we found that two-phase exponential models with changing decay constants fit the erosion data better than single-phase models. Valley width influences the two-phase erosion responses upstream, but downstream responses appear more closely related to local gradient, sediment re-supply from the upstream impoundments, and base flows. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to introduce a novel coupled method for simulating the fluvial erosion, cantilever failure and bedload sediment transport to describe the overhanging properties of experimental banks and natural riverbanks. For fluvial erosion results, the previous relationships between the critical shear stress, and the erodibility coefficient indicated that they do not follow the values of the experimental works and the U-Tapao River, Thailand. Therefore, it is necessary to determine these relationships locally. The cantilever failure results revealed that the dominant failure mechanism of the experimental works is beam-type failure, while shear-type failure is the dominant failure in the U-Tapao River. Finally, a numerical model was developed based on a triple-grid approach to simulate the behaviour of a cantilever within the framework of fluvial erosion, cantilever failure, and bedload transportation. The simulated results showed good agreement with experimental results, and the U-Tapoa River in terms of the temporal variations of spatially averaged bank width, dominant failure mechanism, and overhanging block dimensions. [ABSTRACT FROM AUTHOR]

A long-lasting rainstorm event from 20 to 22 August 2005 affected a large part of the northern Alps and Prealps in Switzerland. It resulted in elevated discharges and flooding in many headwater catchments and mountain rivers. The associated geomorphic processes included shallow landslides, deep-seated slope instabilities, debris flows, and fluvial sediment transport. In many parts of the affected areas human activities are important, including many buildings, traffic lines and other infrastructure. In the steeper parts, geomorphic processes were mainly responsible for flow overtopping and sediment deposition both in and outside of the channel network. In the lower parts, lateral erosion and exceedance of the channel discharge capacity were the main reasons for morphologic channel modification and flooding. Sediment-related processes contributed a lot to the overall damage. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

For the appropriate management and restoration of rivers, isolated vegetation is often a practical means for improving stream habitat and ecology. The effect of a finite vegetation patch on flow and bed morphology in an open channel was investigated using laboratory experiments. The patch containing emergent and submerged vegetation was modeled using circular cylinders and located mid-channel along a side wall. Several configurations of the patch and submergence ratio (i.e. water depth to the height of vegetation), and two flow conditions (i.e. below and above the sediment motion threshold) were considered. For flows below the sediment motion threshold, erosion occurred primarily on the opposite side of the patch and near the leading edge of the patch. The degree of scouring depth observed in both these regions was affected by the submergence ratio and it increased with the non-dimensional flow blockage (i.e. the product of the patch density and width). In contrast, for flows above the sediment motion threshold, sediment accumulated within and around the patch due to a reduction in bed shear stress, which was strongly influenced by the flow blockage and the obstruction ratio (i.e. the ratio of patch width to channel width). The eroded area observed within the patch was consistent with the interior adjustment region where the deceleration and diversion of flow occurred through the patch. As the flow blockage increased or as the obstruction ratio decreased, the deposition rate within and behind the patch decreased. Furthermore, the deposition rate increased with an increase in the ratio of flow rate through the patch to total flow rate regardless of the submergence ratio. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Sediment transport processes in rivers continue to pose a challenge when designing movable-bed physical models, particularly for reproducing the grain sorting and bank erosion (fluvial erosion and mass failure). This paper presents and discusses scale effects of a specific scaling approach for multi-grain size mixtures that preserves similarity of initial motion for each grain size class and of the bank stability coefficient between the model and the prototype, but relaxes strict similarity of the Shields and particle Reynolds numbers. This approach is appropriate when bed load transport near incipient motion conditions is being studied, and allows for larger grain size scales than when full Shields parameter similarity is enforced. As part of an environmental project to rehabilitate sediment transport through bank erosion, this method has been applied to scale a Froude number criterion physical model of a reach of the Old Rhine (France). This has resulted in an undistorted scale of 40, and the use of sand as the model bank material. Each grain size has a different geometrical scale. The time scale for sediment motion is grain size and flow discharge dependent. An average time scale of 6 has therefore been used (four model hours = one prototype day). A strategy devised for the field case consists of two higher, larger island groynes that replace the three existing groynes, producing bank erosion for flow rates below the mean annual flow rate. Extrapolation of model behaviour to the prototype is not a major problem, but the volume of eroded bank material may be underestimated, mainly because of the relaxation of the Shields number similarity and the apparent cohesive properties of the model bank material. [Copyright &y& Elsevier]

ABSTRACT Depth profiles of particle streamwise velocity, concentration and bedload sediment transport rate were measured in a turbulent and supercritical water flow. One-size 6 mm diameter spherical glass beads were transported at equilibrium in a two-dimensional 10% steep channel with a mobile bed. Flows were filmed from the side by a high-speed camera. Particle tracking algorithms made it possible to determine the position, velocity and trajectory of a very large number of particles. Approximately half of the sediment transport rate was composed by rolling grains, and the other half by saltation. This revealed a complex structure, with several concentration and flux peaks due to rolling, and one peak due to saltation. With an increase of the sediment transport rate, the depth structure remained the same at the water/granular interface, with peak value increases but with no shift in elevations. The saltation region expanded towards higher elevations with an increase of the particle velocity commensurate to the water velocity. The proportion of the sediment transport rate in saltation did not vary significantly. The particle streamwise velocity profiles exhibited three segments: an exponential decay in the bed, a linear increase where rolling and saltation co-existed, and above this, a logarithmic-like shape due to saltating particles. These results are comparable to profiles measured and modelled in dry granular free surface flows and in more intense bedload such as sheet flows. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]