The first goal of this work is to quantify, at event-driven and instantaneous scales, the swash effects on the evolution of a beach scarp formed in the high beach during stormy conditions. This study leads then to the determination of a formula to calculate and predict the eroded volume of the berm by the scarp retreat that depends on the hydrodynamic conditions. To correctly study this phenomenon, an artificial berm with a scarped face has been built on the beach of Luc-sur-Mer. The field area was instrumented during several tides in moderate to strong hydrodynamic conditions. In parallel, meteorological, topographical, hydrodynamical and video imaging were regularly acquired during the two experiments to survey the morphological changes of the scarp. These measurements have permitted to highlight the importance of dynamic and static water levels, as well as the wave angles on the cross-shore and longshore evolutions of the beach scarp. The similarity between the dune scarp and the beach scarp allowed us to develop a new formula to estimate the eroded volume from the beach scarp on the berm. The calibration of the different parameters of this formula has been done with the computation of the runup and a very accurate acquisition of the scarp topographic evolutions at high tide with a terrestrial laser scanner, coupled with a temporal video analysis of the impact of the swash on the scarp during a highly erosive tide.
Swash effect on the erosion of a foreshore beach scarp