Investigation of the Hydrogeology at a Chalk Cliff Site in Normandy Using Multiple Research Approaches

Thomas Junique (1, 2) , Cyrille Fauchard (1) , Raphaël Antoine (1) , Vincent Guilbert (1) , Bruno Beaucamp (1) , Cyril Ledun (1) , Stéphane Costa (3) , Olivier Maquaire (3) , Robert Davidson (3) , Nicolas Coppo (4)

1 ENDSUM - Evaluation non destructive des structures et des matériaux
2 GEGENAA - Groupe d'Étude sur les Géomatériaux et Environnements Naturels, Anthropiques et Archéologiques - EA 3795
3 UNICAEN - Université de Caen Normandie
4 BRGM - Bureau de Recherches Géologiques et Minières

This study uses a multidisciplinary approach combining optical and geophysical methods to analyze the stability and seawater intrusion in chalk cliff at Sainte-Marguerite-sur-Mer, Normandy (France). Techniques employed include photogrammetry, thermal infrared spectroscopy (TIR), electrical resistivity imaging (ERI) and the towed transient electromagnetic (tTEM) method. The study focused on a 20-40 meter high cliff with a rocky platform at its feet. A visible and thermal photogrammetric model were made in September 2022. A total of six ERI profiles were carried out. The tTEM survey provided a resistivity mapping of the plateau as well as at the foot of the cliff. ERI and tTEM methods identified the presence of a conductive body interpreted as a saturated saline to brackish aquifer beneath the cliff, with marine intrusion only in the southwestern part. The interface between the salt water and the aquifer shows instabilities with haline convection and upwelling of brackish water at different places on the rock platform to the northeast. TIR spectroscopy complements ERI by helping to identify areas vulnerable to collapse at the top of the cliff.

Domaines: Sciences de l'environnement

Thomas Junique, Cyrille Fauchard, Raphaël Antoine, Vincent Guilbert, Bruno Beaucamp, et al.. Investigation of the Hydrogeology at a Chalk Cliff Site in Normandy Using Multiple Research Approaches. NSG2023 2nd Conference on Hydrogeophysics, Sep 2023, Edinburgh, United Kingdom. pp.1-5, ⟨10.3997/2214-4609.202320027⟩. ⟨hal-04394304⟩