Monitoring the Mean High Water Shoreline Along the Meso-Macrotidal Cap Ferret Sand Spit, SW France, Using the Satellite-Derived Wet/Dry Sand Line

Abstract Building long shoreline position databases is critical to improve knowledge on past coastal dynamics and predict future changes. Several satellites acquiring recurrent optical images over land and coastal areas have been commissioned since the 1980s. This has allowed the implementation of various satellite-imagery-based shoreline detection algorithms for sandy coasts, which rely on the waterline delineation. However, the detection accuracy decreases with increasing tidal range at sites exhibiting a non-uniform intertidal profile slope. This generally forces to exclude satellite images acquired near low tide at meso and macrotidal coasts. This communication explores the ability of the wet sand/dry sand line extracted from satellite images to reproduce the mean high water shoreline along the km-scale meso-macrotidal Cap Ferret sand spit, SW France. The results show that satellite-derived wet/dry line provides a consistent proxy of the mean high water shoreline, with almost no influence of low water levels at image acquisition time. However, the use of satellite-derived waterline to retrieve the MHW shoreline should still be preferred for images acquired at high water levels.