Use of high water marks and eyewitness accounts to delineate flooded coastal areas: The case of Storm Johanna (10 March 2008) in Brittany, France

Mapping flooded coastal areas can be carried out using different methods and can promote a better understanding and management of coastal flood risks. The delineation of the coastal areas in western Brittany inundated during a storm that came through on 10 March 2008 was determined based on eyewitness accounts and physical marks noted in situ. Using this methodology, 25 sites were mapped, representing an overall flooded area of more than 30 ha. The delineation of the flooded areas was compared with the official French (PPR-SM) flood zones, revealing some discrepancies. Finally, two case studies illustrate how coastal flood mapping can be useful for validating hydrodynamic models.