Flume experiments on wave non-linear interactions effects on beach morphodynamics
Résumé
Waves in the coastal zone are organized in groups. The breaking of those groups generates long waves. The effects of these long waves on the beach morphology are quite misunderstood. Experiments in similitude with nature were conducted in the LEGI wave flume in order to better understand non-linear interactions structures and to assess their influence on morphodynamics. Bichromatic waves were generated in order to develop different structures of standing waves. All conditions were tested on similar profiles characterized by a surf zone confined on the upper beach. On the lower beach including the shoaling zone, the morphological evolutions are found to be only induced by wave non-linearities and not influenced by breaking related effects such as undertow or turbulence. Morphological evolutions are very different from a wave condition to the others: bar formation, bar washing, bar displacement. Modulations of skewness and asymmetry were observed, related to both recurrence phenomena and long wave modulation. They explain the morphological evolution. Although a role of infragravity waves has been observed, bar formation is not consistently located under nodes or anti-nodes of the standing waves.