Impact de digues ISC sur la dynamique littorale : Etude de cas des plages de Saint-Hilaire de Riez en Vendée

Abstract

Le littoral vendeen est expose a des conditions de houle severes et a subi ces dernieres annees d’importants desordres hydrosedimentaires. Les plages du littoral de Saint-Hilaire de Riez sont constituees d’une succession discontinue d’ouvrages de protection contre la mer sur un lineaire naturel. Ces perres et digues en enrochements ou maconnes ont ete installes sans etude ciblee au prealable concernant leur impact sur leur environnement. Ces digues sont maintenant classees ISC (Interessant la Securite Civile) et font l’objet d’un suivi particulier. Les degradations importantes de ces ouvrages subies ces dernieres annees justifient la realisation d’une etude hydrosedimentaire pour verifier leur impact sur la dynamique littorale et proposer des solutions d’amenagement permettant de retablir un equilibre sur ce littoral. Une chaine de calcul de modelisation hydrosedimentaire, dont les logiciels sont entierement developpes par le CETMEF, a ete mise en place. Cette etude vise a valider numeriquement la strategie de recul des ouvrages preconisee pour retablir l’equilibre de la dynamique littorale de Saint-Hilaire de Riez. Translated version: Impact of dikes on the coastal dynamics: Study of the beaches of Saint-Hilaire de Riez (France) The French Atlantic coastline is submitted to severe wave conditions. These past few years, this area and especially the region called Vendee went through consequent sedimentary issues. There are a lot of coastal defence structures on the natural beaches of Saint-Hilaire de Riez. Those dikes or ripraps either made with rocks or with concrete material have often been built without any specific impact studies regarding their environment. Nowadays, in France, these dikes are classified "ISC" (Interesting Civil Security). A specific monitoring of these structures is performed. Huge damages happened on these coastal structures these past few years. It is essential to study their influence on the hydrodynamics of the area. It aims to elaborate management solution to restore a stable situation from the coastal dynamics point of view. Software developed by the CETMEF has been used to study those hydrodynamics and sedimentary issues. The present study aims to numerically ensure the coastline setback strategy recommended to restore the balance considering the coastal dynamics of de Saint-Hilaire de Riez. Keywords: Coastal structure; Coastal management; Coastal dynamics; Numerical modeling; Hydrodynamics; Sediment transport.