Erosion and Deposition Volumes Estimation Using a Drone and Near Surface Geophysics Methods in Coastal Badlands Context.

International audienceA four-year diachronic study was carried out on coastal badlands cliffs ("les falaises des Vaches Noires", Normandy, France) to assess erosion and acretion volumes. Cretaceous to Jurassic facies at cliffs face are exposed to erosion activated by rainfalls on the tableland and tempests and high tidals at the bottom. Consequences have a direct impact both (i) on housing and civil engineering structures and (ii) on Le Havre harbor and the Seine river waterways. More than ten aerial drone surveys were carried out between 2016 and 2019. Recorded images by drone led to accurate Digital Elevation Model (DEM) models by means of photogrammetry. Each DEM georeferenced with differential global positionning system (DGPS) were then compared with each other. Near surface geophysical methods were also performed to understand materials and their properties involved in such processes . Cliff edge retreat can be assessed, while eroded and accumulated volumes are locally calculated. With help of geological study and mainly Electrical Resistivity Imagery, costline retreat and deposits evolution can be explained and evaluated. This study performed at hectometer scale finally allows a wider interpretation of erosion processes at the regional costline scale. The Vaches Noires cliffs are listed Natural zone of ecological interest, fauna and flora belongs to the 26 studied sites of the National Observation Service DYNALIT, labeled by INSU (National Institute of Sciences of the Universe). The presented outcomes stem from the Normandy regional project TéléDeTaC (Télédétection par Drone du Trait de Côte)