Managed realignment to mitigate storm-induced flooding: A case study in La Faute-sur-mer, France

Storm-induced coastal flooding is among the most destructive natural disasters while climate change together with increased populations along the coast will enhance the associated risk. This study presents the comparison of conventional coastal defense schemes against managed realignment schemes in La Faute-sur-Mer, a small village located in the central part of the Bay of Biscay that was severely impacted during Xynthia in 2010. This comparison relies on a 2DH fully coupled modeling system for the North East Atlantic Ocean, with a resolution ranging from 30 km to 5 m locally around the studied site. The comparison with available data reveals that water levels and flooding associated with Xynthia are well reproduced, with root mean squared errors below 0.2 m, and a fit measurement of 0.84, respectively. Numerical results show that the dikes maintained and raised after Xynthia won't be sufficient to protect the city against a future extreme event comparable to Xynthia in 2100 due to sea level rise. On the opposite, managed realignment and the creation of buffer zones in surrounding pastures would decrease maximum water levels up to locally more than 1.0 m, and prevent from any flooding in La Faute-sur-Mer. The optimal design and the applicability of such measures for la Faute-sur-Mer but also any other estuarine environment are finally discussed.