Assessment of flooding hazards at an engineered beach during extreme events: Biarritz, SW France

This study focuses on flooding hazards along the Grande Plage of Biarritz. This pocket engineered beach, located in the south west of France, was highly battered by a series of storms during the winter 2013-2014 and experienced great damages to buildings and infrastructures. The vulnerability of this type of beaches to storm impact is assessed using the XBeach surf beat model. For validation purpose, a dedicated spectral wave model is also used on the coastal area to force XBeach at 15 m depth. This coastal wave model is first validated against nearshore wave measurements provided by two sensors deployed during the winter 2017. Then the total water level elevations measured at the shore with a video monitoring system are used to assess XBeach results. The model is then used to run a series of extreme storm scenarios with different return periods (1, 10 and 50 years). Results show how the occurrence of flooding events increases with storm intensity. The response of the beach is alongshore non-uniform for all the storm scenarios. The section, where the dry beach width is smaller, is more exposed to flooding whereas vulnerability is reduced by wider dry beach areas. This study constitutes a milestone and outlines next steps toward the development of an operational warning system for the GPB.