Axel Creach

The impact of storm Xynthia in 2010 on coastal flood prevention policy in France

Storm Xynthia occurred on 28 February 2010. It was one of the most destructive climatic events to hit metropolitan France for several decades, causing 47 victims in France, among whom more than half died in the department of Vendée. The occurence of various natural phenomena (atmospheric pressure, strength and orientation of the wind, tidal range) at the same time caused a major coastal flood in several urban areas from Vendée and Charente-Maritime (central Atlantic region of France). The evaluation of the disaster highlighted a number of problems, especially delays in approving the PPR-L (Plan de Prévention des Risques Littoraux) that allowed urbanization in the coastal flood plain that exposed population to major natural risks, such as sea level rise and floods. Since 28th February, 2010, the French government has focused on these issues and tried to define in a more accurate way the criteria used for the flood zonings of the PPR-L. A number of circulars and recommendations have been produced and they all specified rules of protection for properties against the risk of flood and the necessary measures for adapting or building current or future houses (e.g. height of the upper floor, presence of an upper floor refuge) in accordance with the level of risk. The objective of this paper is twofold: we wish to highlight the impact of the disaster Xynthia on the production of PPR-L in the short and medium terms while focusing on the example of the town of La-Faute-sur-Mer. We will also analyze the evolution of the regulations since 28 February 2010, with special attention paid to the proposed criteria to define the hazard.

The use of a micro-scale index to identify potential death risk areas due to coastal flood surges: lessons from Storm Xynthia on the French Atlantic coast

Storm Xynthia (February 2010) was responsible for a large sea surge along the French Atlantic coast. It resulted in the flooding of low-lying coastal areas during the night. Urbanized areas were impacted and 41 people died by drowning in their homes. The location and type of construction of the houses in the affected area contributed to the death toll. The fact that the inadequacy of construction with regard to coastal flood hazard could lead to death was one of the most important lessons of the storm. The French government decided to buy back and scrap the most dangerous buildings hit by Xynthia. In order to prevent future deaths by drowning, we have developed a tool (the V.I.E. index) to identify houses where a risk of death due to a coastal flood cannot be excluded. The goal is to propose individual-based solutions for risk mitigation of residential houses. This tool uses a micro-scale-level analysis along with four criteria: (1) the potential water depth per house, (2) the distance between the dike and the house, (3) the architectural typology and (4) the closeness to rescue point. The methodological background and the first results for three towns are presented in this paper. Limitations and further developments are also discussed.

Vulnerability to coastal flood hazard of residential buildings on Noirmoutier Island (France)

Storm Xynthia was responsible for the death of 41 people by drowning after the flooding by the sea of low-lying areas along French Atlantic coast in February 2010. This toll was partly explained by inadequacy of houses to flood hazard: 78% of the deaths occur in single-storey constructions. In this paper, we propose a map linking architectural typology of constructions with potential water depth in case of coastal flood event. The goal is to identify residential houses which present a high level of vulnerability for people to a potential coastal flood event. This work is presented on Noirmoutier Island which was few impacted by Storm Xynthia. However, it presents some common points with the most hit territories during the storm: 70% of the territory is under Xynthia level; 65% of the houses located in this low-lying area are single-storey constructions This map shows us different vulnerability between the four towns of the island.