This study investigates the local processes of surf-zone bed sediment destabilization, erosion and transport. It is based on a physical model in the LEGI wave flume using lightweight sediment to fulfill scaling laws. Optical, acoustical and pressure sensors measurements technics were developped. The sensors are used simultaneously to characterize the bottom boundary layer in terms of velocities and concentration. The bed response was also determined measuring erosion depth, sheet-flow thickness and pore-pressure pressure transmission. This work mainly focuses on non-linearities of the flow and their effect on transport, especially the acceleration skewness. It is shown that this asymmetry contributes to the sediment transport in two different ways. One mechanism is that the free-stream asymmetry of the flow results in a velocity skewness near the bed, it produces a net transport. The second one is that the free-stream acceleration is proportional to the horizontal pressure gradient. This pressure stress can destabilize the bed in a form of a plug-flow. Our results show that shear stress (characterized by the Shields number) and pressure gradients (characterized by the Sleath number) can in turn destabilize the bed.
