As part of a preliminary study on the devastation caused by storm Xynthia, researchers assessed recurring incidences of flooding on the Atlantic coastline of France from the mid 1980s onwards (Feuillet et al., 2012). By taking into account the convergence of high tidal coefficients, very strong gusts of wind, and instances of high water occurring more or less synchronously with these gusts, ten events likely to have caused considerable flooding were identified.
In this study, we cross-referenced those results with extreme sea levels (100-year return period) and effective measures published by SHOM (the French Navy’s hydrography and oceanography department), to consider these flooding incidents in relation to these sea levels.
A number of points become clear from the graphs:
1) only five episodes resulted in sea levels bordering on extreme: in November 1984, October 1987, March 2008, February 2010 and February 2014;
2) in Brittany, the most significant episode was storm Johanna;
3) on the coastline between and including Saint-Nazaire and Arcachon Bay, storm Xynthia stands out everywhere as the event that generated the highest water levels, exceeding the mark for extreme sea levels everywhere between the Loire and Gironde estuaries;
4) in La Rochelle, the difference between the extreme sea level mark and the level reached during storm Xynthia is the most significant, at 65 cm, making it a noteworthy exception on the entire Atlantic coast;
5) the extreme water levels of 1 February 2014 occurred in moderate tidal surge conditions at high water (+ 40 cm), but at a tidal coefficient of 113.