Modeling of a tidal bottom boundary layer with suspended sediment

A one-dimensional model of the vertical exchange of suspended sediment in a tidal boundary layer is proposed. The model includes two linearized momentum equations for the horizontal velocity components and a series of advection-diffusion equations for concentrations of suspended sediment of specific size. Turbulence generated at the sea-bed is computed with the aid of a two-equation closure describing the time-space evolution of the turbulent kinetic energy, K, and of the turbulence macroscale, Lambda (K-Lambda model). Special attention is paid to the bottom boundary condition for the sediment concentration, which is of mixed type to take into account downward fluxes at times of decelerating flow and slack waters. The model is applied to conditions encountered in a shallow site located in the eastern part of the English Channel. The model is forced with pressure gradients computed with a two-dimensional vertically-integrated tidal model covering the eastern English Channel and the southern part of the North Sea. The tidal currents and the total suspended sediment load predicted by the model are compared with field data collected over the full water depth.