Cross-shore sediment transport measurements at the beach of Sète, Gulf of Lion

The observation of the cross-shore sediment displacement in the off-shore direction is one of the objectives of the repeated measurement campaigns that took place at the beach of Sète, Gulf of Lion (NW Mediterranean Sea). The site has been instrumented in 1999, 2000 and more recently in 2009 using wave recording current meters, pressure sensor arrays, ADVs and bottom mounted ADCPs in the depth range 2-6m. It is characterized by micro-tidal condition. The location of Sète is one of the experimental sites chosen to study the phenomenon of coastal erosion that largely affects the sandy coast of the Gulf of Lion. Waves generated by winds coming from the southwest-south-southeast directions have been identified as the main forcing for sediment displacement. Moreover, we observe that such process occurs during storm condition where the cross-shore velocity is >~30cm/sec. During good weather, the data of the cross-shore velocity cannot be trusted due to the very small values. In addition, sediment transport computation shows that the dominant direction for cross-shore sediment displacement is off-shore during storm conditions, and its magnitude largely exceeds the transport in the long-shore direction. Thus, we conclude that in the particular condition of a micro-tidal beach, the off-shore sediment transport due to wind-waves has a dominant role in costal erosion.