Net offshore bar migration variability at a regional scale: Inter-site comparison (Languedoc-Roussillon, France)
Résumé
The Languedoc-Roussillon coastline is a large unit stretching out over 200 km of sandy low coast in a wave dominated environment. The nearshore is characterized by a quasi continuous system of double sandbar that displays a wide range of typology. The interannual sandbar dynamic was investigated using 2D bathymetric profiles and 3D LiDAR imagery. This study has allowed determining the sandbar systems affected by the Net Offshore Migration (NOM). At a regional scale, conditions necessary to NOM development depend on the sandbar morphologies (crescentic or straight), the wave energy and the associated coastal orientation (low or high energy, sheltered area), the coastal structures (harbour and coastal defences) and the nearshore sedimentary budget. The areas where the NOM occurs show cycle dynamic differences. This regional inter-site comparison highlights that nearshore morphology and bar parameters seem to influence the nearshore bar behaviour. Interaction between the nearshore slope, width of the bar zone and the migration rate control the NOM duration. The sandbar volume and the regional wave climate influence also the migration rate of the system. On the Languedoc-Roussillon coast, the sediment grain size does not appear to influence the seaward bar migration.