Suspension and transport of sediment under a plunging wave breaker

To understand the mechanism of suspension and transport of sediment under breaking water waves, we perform large-eddy simulations of a plunging breaker over seabed. The breaking water surface is captured by a coupled level-set and volume-of-fluid method. The mass exchange of sediment between the water region and the bottom is computed through the local upward erosion and downward deposition fluxes. The erosion flux is modeled based on the local shear stress at the bottom, and the deposition flux is estimated based on the sediment concentration near the bottom. We analyze in detail the instantaneous velocity and sediment concentration fields, the erosion and deposition fluxes near the bottom, as well as the bottom deformation under breaking waves. It is found that the sediment is mainly picked up from the bottom at the early stage of wave breaking, brought upwards, mixed by the turbulent motion, and then transported in the wave propagation direction by the current generated by the breaker. The wave breaking significantly enhances the horizontal transport of the sediment. It is also found that the air pocket entrained by the breaking wave plays an important role in the suspension, transport, and redistribution of sediment.