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The scour induced by wall jets may cause serious bed erosion and thus damage to hydraulic structures. Previous studies are largely empirical, providing only correlations of experimental data. At present, it is not clear what difference exists in the physical mechanisms of two-dimensional (2D) and three-dimensional (3D) wall jet scour. This study first summarizes previous efforts for predicting wall jet scour depths. Then, a scaling analysis is presented for investigating scour depths by applying the phenomenological theory of turbulence. It is shown that for wall jet cases, the dimensionless equilibrium scour depth can generally be expressed as a power function of the densimetric Froude number and relative roughness height, with the power index depending on jet configurations. The predictions of scour depth using the resulting formulas agree well with published data. The present analysis provides new insights into the understanding of the underlying physical mechanisms of wall jet scour as well as the difference between 2D and 3D configurations. [ABSTRACT FROM AUTHOR]

This paper presents experimental and numerical studies of the evolution of dam-break driven wave on a horizontal smooth bed and its implication to sediment transport. Laboratory experiments are carried out using high-speed video images in order to obtain the spatio-temporal evolution of the free surface. Furthermore, a numerical model based on the two-dimensional-vertical Reynolds-averaged Navier–Stokes equations, with ak−ϵ turbulence closure and a volume of fluid method, is validated with the laboratory observations. The numerical model is shown to accurately predict the measured free-surface profiles, the wave-front velocities, as well as the impingement location of the first forward breaking jet. In order to bring more insight on dam-break wave induced erosion, the numerical model is extended for simulating suspended sediment transport. Model results suggest that the maximum bed-erosion occurs at the gate location and it moves farther downstream depending on the ratio between the downstream and the upstream water depth. [ABSTRACT FROM PUBLISHER]

New experiments under sheet flow conditions were conducted in an oscillating water tunnel to study the effects of flow acceleration on sand transport. The simulated hydrodynamic conditions considered flow patterns that drive cross-shore sediment transport in the nearshore zone: the wave nonlinearities associated with velocity and acceleration skewness and a negative mean current, the undertow. Net transport rates were evaluated from the sediment balance equation and show that (1) the acceleration skewness in an oscillatory flow produces a net sediment transport in the direction of the highest acceleration; (2) the net transport in the presence of an opposing current is negative, against the direction of the highest acceleration, and reduces with an increase in flow acceleration; and (3) velocity skewness increases the values of the net onshore transport rates. [ABSTRACT FROM AUTHOR]

The modelling of swash zone (SZ) sediment transport and the resulting morphodynamics have been areas of active research over the last decade. However, many details are still to be understood, whose knowledge will be greatly advanced by the collection of high-quality data under the controlled large-scale laboratory conditions. The research describes tests carried out in the large wave flume of the Maritime Engineering Laboratory at Catalonia University of Technology, to investigate the SZ under the storm conditions. Its main aim was to compare beach-profile responses for monochromatic waves, monochromatic waves plus free long waves, bi-chromatic waves and random waves. Both erosive and accretive conditions were considered. Results discussed here were derived from the analysis of only a part of the whole data set. [ABSTRACT FROM AUTHOR]

A detailed description of how recently-developed sediment dynamics formulations are incorporated into the United States Environmental Protection Agency's Environmental Fluid Dynamics Code is presented. The new approach is an extension of previous models and accounts for multiple sediment size classes, has a unified treatment of suspended load and bedload, and appropriately replicates bed armouring. The resulting flow, transport, and sediment dynamics model is an improvement to previous models because it may directly incorporate site-specific data, while maintaining a physically consistent, unified treatment of bedload and suspended load. Experimental data from a noncohesive sediment erosion experiment in a straight channel help validate the numerical model. In this simulation, unknown parameters representing the active layer thickness and the erosion rates of the two largest sediment size classes when they are newly deposited are identified from the available data. [ABSTRACT FROM AUTHOR]

Dike overtopping is an important issue in both scientific and practical aspects of sediment embankment erosion. This research is concerned with the validation of a one-dimensional numerical code applied to an unsteady two-phase flow over an initially trapezoidal-shaped sediment dike, including the transition from sub- to supercritical flows and the flow propagation over a steep slope. The approach is based on the shallow-water equations coupled with a sediment erosion code. The numerical results are compared with recent laboratory experiments, resulting in a reasonable prediction of the temporal free surface and bed evolution. The remaining model inaccuracies mainly originate from overflow initiation with extremely small flow depths, streamline curvature effects with the related underestimation of flow velocities close to the sediment surface, and the changing saturation in the dike body not accounted for in the model. Despite these deficiencies, the computational model will be helpful, particularly in flood risk assessment and management. [ABSTRACT FROM AUTHOR]

Wooden debris structures are commonly used in stream restoration to alter sediment transport and flow distributions to improve fish habitats in degraded streams. Various wooden structures were tested in a laboratory flume to determine their ability to change flow patterns, resulting in local scour. A parametric study was made to predict scour hole depth. The results indicate that the underminer structure should cover the full channel width and divert the whole flow below the structure. Maximum scour depth was obtained with a single structure perpendicular to the flow direction and overall scour depth was governed by structural height and sediment particle size distribution. With increasing structure angle with respect to flow, the area and volume of the scour hole increase, whereas the scouring depth decreases. Coarser sediment size reduces scour depth for both single and consecutive structures. The optimum underminer spacing ratio was found to be 2 to 3 times the channel width. [ABSTRACT FROM AUTHOR]