Hydrogeological assessment of a deep-seated coastal landslide based on a multi-disciplinary approach

Abstract This study focuses on the understanding of the hydrogeological functioning of a complex landslide affecting the coastal municipality of Villerville (Normandy, France). We wish to provide a conceptual model of functioning using a multi-disciplinary approach. A set of geomorphological, geological and hydrological data, as well as in-situ observations, were first used to understand the main landslides processes. New acquisitions were then carried out to strengthen our hypotheses thanks to passive geophysics (SP) and the characterization of physicochemical parameters of surface waters. The joint analysis of former ERT surveys and SP results is of significant interest for correlating hydrokinetic information measured at the surface with resistivity tomograms which provide internal information. This study highlights (1) a division of the behaviour into three parts, from east to west; (2) variable internal dynamics highlighted by geology and electric fields; (3) a preferential discharge of the continental water table upstream of the central area of the landslide. This work tends to demonstrate that on the basis of initial in-situ knowledge available on many study areas, the understanding of the hydrogeological functioning can be substantially improved by implementing light and inexpensive surveys, also suitable for large and complex landslides.