Application of remote sensing video systems to coastal defence monitoring

Shoreline stability is an important issue along much of the Mediterranean’s Coasts. European project MEDDOOC INTERREG BEACHMED-e focused on the strategic management of beach protection for the sustainable development of the Mediterranean coastal zone. In the framework of this project, a video system has been installed in Valras (Gulf of Lions / France) to monitor coastal evolutions and recent protection works. Over the past 20 years, coastal video remote sensing techniques represent an efficient alternative tool to classical in situ surveying techniques. Coastal video monitoring is based on Time exposure images (Timex) acquisition and photogrammetry technique which allows transforming 2D image coordinates into the corresponding 2D real world coordinates. This paper presents the use of video monitoring technique to estimate the impact of engineering works. Important beach retreat has been observed for decades along the 3 km of Valras beaches and 12 breakwaters have been built until 2007. From January to May 2008, a new similar protection, a submerged breakwater and 95,000 m sand nourishment have been added. As Empirical Orthogonal Function (EOF) analysis has become an established method for investigating temporal beach fluctuation, EOF is performed using weekly video monitored shorelines over a 6 months period. The results show: (1) the natural erosion / accretion phases of the already protected shoreline, (2) the impact of beach nourishment and the trend toward the equilibrium position of the restored shoreline, (3) the efficiency of video monitoring for shoreline management.