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Abstract: The paper introduces a 2D shallow water model based on a two-phase formulation for the analysis of fast geomorphic transients occurring in the context of river morphodynamics. Mass and momentum conservation principles are separately imposed for both phases. The model naturally accounts for non-equilibrium solid transport, since neither instantaneous adaptation hypothesis nor any lag equation is employed to represent sediment dynamics. The hyperbolic character of the proposed model is shown to be preserved independently on the flow conditions. Results from numerical simulations of both 1D and 2D test-cases are compared with literature experimental data and with available numerical solutions. [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: 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: This paper illustrates the results of an experimental investigation (model-to-prototype length ratio equal to 12) carried out to reproduce the cross-shore evolution of nourished sandy beaches. New two-dimensional experiments were performed to study the short-term response of the cross-shore profile for both “soft” (unprotected) and “mixed” (protected by submerged breakwaters) beach fill projects. Due to the simplified reproduction of prototype conditions in a two-dimensional geometry, only cross-shore sediment transport is considered. The results are related to the immediate post-nourishment evolution and far from beach fill boundaries where long-shore gradients of long-shore sediment transport are likely to be negligible. Three different pseudo-random wave trains were generated in order to simulate both accretive and erosive conditions. A fourth wave train, characterised by time-varying incident wave spectrum was generated for the investigation of the beach response to simplified storm time evolution. Dimensionless experimental results are given in terms of wave parameters, key features of cross-shore profile evolution and sediment transport rates. Furthermore, being highly resolved in both time and space, experimental data are suitable for mathematical model validation. It was observed that submerged breakwater switches erosive conditions to slightly accretive, at least within the tested experimental range. [Copyright &y& Elsevier]

Abstract: The development and application of the physically-based and spatially-distributed mathematical model CTSS8-SED is presented. The model simulates hydrologic-hydraulic processes produced by storm events and related soil erosion and sediment transport processes at basin scale in lowland areas. The model simulates (i) storm runoff, (ii) soil detachment by raindrop impact and overland flow (gross sediment yield), (iii) sediment transport by overland flow and associated erosion-deposition processes and (iv) sediment transport by stream flow and riverbed erosion-deposition processes. A quasi two-dimensional representation of water flow and sediment transport routing is made by means of interconnected cells approach. The model is applied to simulate two flooding events in the Ludueña Creek basin (Santa Fe, Argentina) occurred in April 1994 and March 2007 due to extraordinary rainfalls. [Copyright &y& Elsevier]

Abstract: The objectives of this work are (1) to examine the mechanisms that influence tsunami erosion and deposition mechanisms in the littoral zone via physical simulations of breaking solitary waves over a fine sand beach, and (2) to provide experimental data for validation of numerical models to predict tsunami erosion and deposition processes. The experiments were carried out in a 48.8m×2.16m×2.1m wave flume. The flume was instrumented to observe free surface elevations, cross-shore velocities, suspended sediment concentrations, vertical and cross-shore pore-pressure gradients near the shoreline, and morphological changes. In addition, wave–sediment interactions were observed via underwater video cameras. The results are systematically analyzed to investigate the roles of wave breaking, bore runup, wave drawdown, and wave-induced pore-pressure variations on tsunami erosion and deposition processes. The studies showed that the wave plunging on a thin layer of water prior to reaching the shoreline did not cause much sediment suspension, while the waterjet impinging directly on the beach entrained substantial amounts of sand. The suspended sediments were subsequently pushed up the slope by fluid momentum as the broken wave transformed to a turbulent bore. A small net deposition region was observed near the maximum runup point where both the flow velocity and the water depth were near zero. A significant amount of the sediment transport occurred during the wave drawdown in the form of thick sheet flow, which resulted in net erosion of the shore face and the beach. A hydraulic jump formed near the wave breaking region toward the end of the drawdown, which caused most of the suspended sand to deposit in the wave breaking region. Consequently, breaking solitary waves over a sloping fine sand beach led to net erosion of the shore face and the beach, net deposition in a small region immediately seaward of the max excursion point, and net deposition in the wave breaking zone. [Copyright &y& Elsevier]

Abstract: This paper presents a three-dimensional (3-D) numerical model to simulate morphological changes in alluvial channels due to bank erosion. A method for the simulation of bank erosion is established. This is incorporated into a 3-D mathematical model for turbulent flow and non-uniform, non-equilibrium sediment transport. This model is applied to simulate morphological changes in the Shishou bend of the middle Yangtze River in China, where serious bank erosions occurred during the last two decades. The double-layer sediment structure of the riverbank on the middle Yangtze River is taken into account in the bank erosion module. Both cohesive and non-cohesive bank material in the different layers are considered. The bank erosion module also includes other factors affecting the rate of bank erosion, such as the longitudinal length of failed bank, the thickness of each layer in the double-layer structure, and the erosion-resisting effect of cohesive material from the top layer of failed bank. A locally-adaptive grid system is proposed to efficiently simulate the lateral migration of alluvial channel due to bank erosion. The predictive capability of the 3-D model is examined by laboratory data. Simulated processes of bank erosion agree with field observations in the Shishou bend during the period of October 1996–October 1998, and the bank erosion module plays a significant role in simulating morphological changes of the study reach. In addition, the equivalent channel-forming discharge, which is defined as a constant discharge that can create the same amount of bank erosion in an alluvial channel as that created by natural runoff processes during the same period of time, is proposed to improve calculation efficiency for feasibility studies. [Copyright &y& Elsevier]

Debris flows are massive sediment transports of poorly sorted material that occur in small steep mountain catchments. The paper addresses the problem of the propagation of cohesionless debris flows, in which the erosion and sedimentation processes are important and the fixed bed assumption is not acceptable. The depth-averaged motion equations are integrated numerically in a two-dimensional domain. The model is based on a two-phase description of the flow with immediate adaptation of the transport to local flow conditions and with rheological closure valid in the grain-inertia regime. The set of partial differential equations is simplified in order to end up with a hyperbolic system that is solved numerically by means of a second order Godunov-type, finite volume scheme that is accurate in space and time. The scheme uses an approximated Riemann solver of LHLL type, which takes into account the non-conservative terms, and an implicit discretization of the bed shear-stress source terms. The model parameters are determined by means of laboratory flume tests on the site material. Two real-case applications show the effectiveness of the code and how it can be used in predictive situations as in the case of defensive work assessment and verification or hazard mapping. [Copyright &y& Elsevier]

A coastal area morphodynamics model was developed which is capable of modelling both short-term and long-term bathymetric changes in coastal areas. The model is composed of three main modules: wave transformation module, hydrodynamic module and sediment transport and morphology module. The three main modules run simultaneously where the waves and coastal currents information are passed to the sediment transport module, which calculates the sediment transport fluxes and the corresponding bathymetric changes. The model''s output is linked through dynamic plotting libraries, which produces contour plots, vector plots and animation files for the waves, currents, sediment transport fluxes and bathymetry. The model''s output compares very well with other commercial models for the case of an offshore breakwater over a sloping beach. [Copyright &y& Elsevier]

• Ephemeral Gully (EG) Erosion is a major erosion concern and needs to be addressed. • Very few models simulate EG erosion. • A thorough review of processes behind EG simulation in existing models is discussed. • Future needs and directions to improve EG simulation processes in models are enumerated. Modeling of ephemeral gully (EG) erosion has lagged that of other soil erosion processes despite its major contribution to watershed sediment losses. Several process and semi-empirical based simulation models have been used to assess the occurrence and location of EGs, magnitude of soil losses from EGs, and degradation, aggradation, and transport of sediment through EGs, but no comprehensive EG model exists. This paper reviews these models and presents a thorough discussion of their background, general formulations, key equations, field assessments, assumptions and limitations. Most current EG models evolved from the original formulations used in CREAMS, with incremental improvements by EGEM, WEPP, AnnAGNPS-REGEM, RUSLER-EphGEE models. These models provide process-based estimation of EG processes and field-scale soil-erosion contributions, but all models, except EphGEE, require users to have a priori knowledge of EG locations and all have significant shortcomings. Several topographic index models are discussed that provide simplistic approaches to locate EGs on the landscape using only topographic features. Process-based threshold index models may provide a more robust simulation of EG location and length, though testing has been limited. EG modeling appears to still be in its infancy, with great opportunities for future research, as discussed herein, to improve the understanding and simulation of EG erosion and transport processes. [ABSTRACT FROM AUTHOR]

Runoff and sediment transport are distinctively three-dimensional (3D) processes and occur through overland, tillage layer and subsurface pathways. The objective was to quantify water balance and sediment concentrations in runoff waters and to assess sediment loads via surface runoff and drainflow in a clayey, subsurface drained field section using the FLUSH model. The model can simulate field scale two-dimensional overland flow and 3D unsaturated and saturated subsurface flow, including preferential flow in macropores. The erosive processes, comprised of hydraulic and raindrop splash erosion, occur in the overland domain while suspended sediment is conveyed from the field surface to subsurface drains via preferential transport in macropores in the subsurface domain. The study site, located in southern Finland, is a clayey, subsurface drained field section with an area of 12 ha and an average slope of 2.8%. The growing seasons and the following autumns of two years with distinctly different rainstorm characteristics were modelled. The simulated sediment loads via tillage layer runoff and drainflow were 85 and 117 kg ha-1, respectively in 1988, and 63 and 189 kg ha-1 in 1984. Despite the high precipitation in October 1984 (143 mm), erosion in the field area was low due to minimal surface runoff and consequently minimal hydraulic erosion. The suspended sediment at the site was generated by raindrop impacts and the eroded material was transported to the open ditch through tillage layer flow and subsurface drainflow. The model was able to reproduce the measured sediment concentrations in the main open ditch into which both tillage layer runoff and drainflow are discharged from the field. Spatially distributed erosion simulations facilitate the detection of net erosion and deposition locations in the field and could be used to design intensive measurement campaigns and guide erosion control practices in the future. [ABSTRACT FROM AUTHOR]