Évaluation de l’évolution du trait de côte et du bilan sédimentaire littoral en baie de Wissant (nord de la France) par LiDAR aéroporté

Airborne topographic LiDAR surveys carried out between 2008 and 2014 over the coastal zone of the Bay of Wissant (northern France) were used for analyzing shoreline evolution and variations in sediment volumes in coastal dunes and across the beach. Successive storm events occurred at the end of 2013 and beginning of 2014 during which high water levels with return periods in excess of 10 years were responsible for significant coastal dune erosion. Although the shoreline retreat locally exceeded 20 m between 2008 and 2014, some areas were characterized by shoreline stability or even experienced a slight progradation due to the seaward progression of coastal dunes over the study period. The comparison of shoreline change with the initial sand volume on the upper beach in 2008 showed that the more significant retreat essentially took place where there was no upper beach at high tide. Our results also suggest that when a minimum sediment volume of 12 m(3) m(-1) is observed on the upper beach (i.e., above the mean high tide level), the shoreline is either stable or may prograde seaward, even when storms inducing high water levels with return periods > 10 years strike the coast. The identification of such a threshold in terms of sediment volume on the upper beach may represent a valuable contribution for improving the management of shoreline evolution in providing an estimate of minimum volumes of sand necessary to ensure shoreline stability.