Sandbar formation under surface waves: Theory and experiments

We report a combined theoretical and experimental study of sandbar formation under simple-harmonic surface waves. For coarse grains and weak waves, an established empirical rule of bed load transport is used with an asymptotic theory for the fluid flow. The surface waves are governed by potential theory and a depth-linear eddy viscosity is employed in the turbulent boundary layer at the seabed. The derived bed stress is used to predict the sand-bed evolution. Laboratory experiments and corresponding numerical simulations for both high and low beach reflection are discussed. For weak reflection, the shear stress associated with the return current is found to be important. Partial simulation of a field record in Cape Cod Bay is also described.