Processus de mobilisation des sédiments en zone de déferlement : expériences de laboratoire en similitude

In the surf zone, most of the sediment transport occurs close to the bed as sheet ow. Laboratory experiments were designed to reproduce natural beach dynamics with a beach of lightweight sediment. The wave climate for this experiment involved a succession of two groups of waves of period 2.5 and 3 s. The resulting equilibrium pro le is a barred beach with a long surf zone. Near bed sediment concentration, pressure and velocity measurements were performed. The sediment ux was computed as the product of the instantaneous velocity and concentration. It is larger under the wave crests than the wave troughs. This results from the strong acceleration at the wave front related to a large wave asymmetry typical of surf zone waves. The vertically integrated net sediment ux over the whole sequence is very weak, which is consistent for a nearly equilibrium beach pro le. Mots clefs : sheetow, transport sedimentaire, asymetrie