On the role of the Chezy frictional term near the shoreline

The behavior of the Chezy frictional term near the shoreline has been studied in detail. An asymptotic analysis valid for water depths going to zero clearly shows that the use of such a term implies a non-receding motion of the shoreline. This phenomenon is induced by a thin layer of water which, because of frictional forces, remains on the beach and keeps it wet seaward of the largest run-up. However, the influence of such a frictional layer of water on the global wave motion is very weak and practically negligible for most of the swash zone flow dynamics. The existence of a non-receding shoreline has led to some clarifications on the role of some ad-hoc tools used in numerical models for the prediction of the wet/dry interface.