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A 3D numerical model is developed to investigate the flow motion and sediment transport around a spur dike. In this model, fluid motion is described by the Navier–Stokes equations, adopting large eddy simulation to capture turbulent transport and dissipation. The spur dike and sand bed are treated by the porous media method. The suspended load concentration and the bed load transport rate is calculated separately, and then the bed variation is updated using the mass-balance equation. A series of flume experiments are employed to validate the model's performance before being applied for the case of partially emergent spur dikes and submerged spur dikes, respectively. Detailed analyses on the spatial-temporal variation of flow intensity, sediment concentration and shapes of scour holes are made, based on which some innovative findings are discussed such as the scouring process patterns, as well as the influence of flow conditions on the maximum scour depth and location, and then useful engineering suggestions are provided to improve structural safety. [ABSTRACT FROM AUTHOR]

Urban flood flow characteristics are usually computed using two-dimensional numerical models. How such modelling can be implemented in dense urban areas with obstacles is investigated in this paper. A strategy for representing the effect of urban obstacles in various flow conditions is proposed. The comparison between the available laboratory measurements and the model results show that if the water depth is high enough and the flow remains subcritical, two-dimensional modelling with constant eddy viscosity represents the effect of the obstacles on the flow distribution accurately, even with a coarse mesh. In contrast, if the water depth is low and/or the flow becomes supercritical, the description of the flow is not sufficient and it generates errors in the flow distribution at the crossroads. [ABSTRACT FROM PUBLISHER]