Wave-Current Impact on Shear Stress Patterns around 3D Shallow Bedforms

Abstract

Observations from wave basin experiments and wave-resolving numerical simulations demonstrate the effect of wave-current interaction on shear stress around a sandy mound. Observations from the wave basin show that the mound deformation rate and morphological patterns depend on the mixture of waves and currents in the incident flow conditions. A SWASH nonhydrostatic numerical model was used to expand the parameter space of wave-current conditions observed in the flume and characterize the response of the near-bed shear stress to the mound. The model was validated with observations from wave-alone, current-alone, and wave-current flume tests and then ran for a suite of numerical flow conditions which isolate the impact of the ratio of wave-current energy on the bed shear stress. Results show how the current-to-wave ratio impacts the spatial heterogeneity of shear stress across the mound, with the region of shear stress intensification around the mound and the location of the peak shear stress becoming asymmetric with more mixed wave-current flows. These results show the nonlinear response of shear stress patterns to combined wave-current flows and how these patterns may impact eventual sediment transport and mound evolution.