Morphodynamic evolution of nearshore bars in response to winter storms (Lido de Sète, NW Mediterranean)

Abstract : This work aims to investigate the processes responsible for the morphodynamics of barred beach during storm events. The contribution compares the response of 2 nearshore bars during storm events at a microtidal double barred beach of the Gulf of Lions, NW Mediterranean Sea (France). Storm-specific experiments were undertaken to assess the morphological evolution of the shoreface. The initial and resulting morphologies are analysed together with wave parameters offshore and water level measurements. Current circulation on the bar system is simulated with MARS-SWAN numerical model. Both storm events presented almost similar hydrodynamic characteristics, and a pre-storm morphology characterised by crescentic bar patterns. However, the resulting morphological evolution was very contrasted. In first case, the bay of the well formed, small-size, crescentic bar was disrupted. In second case the longer crescentic pattern evolve to a more ample and skewed bar morphology. Model simulations indicate that the small size rhythmic crescentic bar patterns would be more able to generate rip circulation cells than the larger crescents patterns, even if a slight change in wave incidence is observed during one of the events. On this specific dataset, our analysis indicates that the nearshore hydrodynamics at the peak of the storm is driven mostly by the pre-storm morphology that is then responsible of the morphological response during the storm.