Oblique Flow over Dredged Channels. II: Sediment Transport and Morphology

A 3D investigation of sediment transport processes across long, straight channels exposed to an oblique incoming current is presented. For this purpose a detailed mathematical flow and sediment transport model is applied. The governing flow and sediment transport equations are solved in a curvilinear coordinate system. The sediment transport model is composed of bed and suspended load, applying a convection-diffusion equation for the latter. As the flow crosses a channel obliquely, it is refracted toward the channel alignment. The effect of the current refraction on the sediment transport is studied using both 2D (depth-averaged) and 3D models. Shortcomings of models based on depth-averaged descriptions are underlined through comparison with the 3D model. A reliable description of the backfilling process requires a flow and sediment transport model capable of capturing the following aspects: (1) The direction and magnitude of the bed-shear stress; and (2) the adaptation of suspended sediment to local sediment transport capacities. Calculations of the morphological development of small-scale excavations (e.g., pipeline trenches) exposed to an oblique incoming current are presented.