NEARSHORE BARS AND SHORELINE DYNAMICS ASSOCIATED WITH THE IMPLEMENTATION OF A SUBMERGED BREAKWATER: TOPO-BATHYMETRIC ANALYSIS AND VIDEO ASSESSMENT AT THE LIDO OF SÈTE BEACH

Abstract : Accurate topo-bathymetric data and video imagery analysis are combined to investigate the impact of the implementation of a 1-km long submerged breakwater on sandbar and shoreline dynamics at the microtidal wavedominated beach of Sète, SE France. The topo-bathymetric analyses are used to quantify sand volume associated with morphological changes and the video imagery is used to address the high-frequency response of the sandbar-shoreline geometry. While the structure is found to reduce erosion and submersion hazards, our results also indicate that the structure had a profound impact on the coupled shoreline-sandbar system, particularly onshore of the breakwater. This impact cascades alongshore and deeply modified the nearshore system dynamics a few kilometers away from the structure. A progressive rotation and linearization of the sandbar was observed shoreward of the submerged breakwater. This resulted in the splitting of the sandbar adjacent to the structure during an episodic net offshore sandbar migration event. The typical formation of a salient or tombolo was not observed. Instead, shoreline coupled to the sandbar geometry, which resulted in a slight seaward migration of the shoreline in front of the structure.