Diachronic UAV study of coastal badlands supported by geophysical imaging in the context of accelerated erosion processes

• DOI: 10.1007/s10346-022-02006-2
• Publication Date: 2023-01-12T05:02:57Z
• Authors: Cyrille Fauchard; Vincent Guilbert; Raphael Antoine; Cyril Ledun; Bruno Beaucamp; Olivier Maquaire; Stéphane Costa; Mohand Medjkane; Thomas Roulland
• Keywords: Drone • Electrical resistivity imaging; 550; [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph]; [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces; environment; 01 natural sciences; 0105 earth and related environmental sciences

International audience ; This work presents a 4-year study carried out on the socalled Vaches Noires cliffs (VNCs), in Normandy, France, between April 2016 and January 2019. The VNCs are badlands facing the Channel sea, with Cretaceous to Jurassic formations. They are subject to strong erosion processes already described by former works. This study aims to gain greater insight into the erosion phenomena with the help of aerial surveys supported by geophysical imaging. For this purpose, Digital Elevation Models (DEMs) were established using photogrammetry applied to dozens of photos taken by an Unmanned Aerial Vehicle (UAV). Electrical Resistivity Imaging (ERI) was implemented according to profiles that were both transverse and parallel to the coastline, (i) from the top to bottom of the cliffs, (ii) as well as at the toe of the crests and on the beach. The main outcome is a global methodology to properly perform these methods and to combine all the results in a 3D environment using free software. This methodology was validated according to a 1-year experiment based on the comparison of two DEMs, then extended to a 4-year diachronic approach. Moreover, volumes of eroded and deposited materials were assessed in specific, morphodynamic areas of the cliffs. The ERI results were used to carry out thickness assessments of the layers involved in the erosion process, and served to clarify the local geology; however, their interpretation remains limited by the lack of a priori information, and underlines the need to carry out inversion processes via a 3D approach in a particularly complex topography. In conclusion, this work provides effective tools to anticipate the risks that threaten coastal habitats and infrastructures, and represents a solid basis for further study.