Assessment of extreme flood hazard in the Wateringues plain

DREAL Nord Pas de Calais started a study in 2009 in order to get a better understanding of flood hazard in the Wateringues area induced by combined hydro meteorological, climatic and technological factors such as: floods from hill watershed, AA and Hem rivers, soil saturation from long rainy events in the plain area, tide and surge, wind effects during storms, mean water level elevation under climatic change, disruption of pumping stations. A method has been developed to assess inundation risk in this area: it is based on principles developed in the study of extreme water levels along the Loire estuary [Lepelletier 2010] which combine: hydro climatic analysis of the various factors involved in the inundation process, numerical simulation of reference events, and statistical combination of simulation outputs to get correct risk evaluation for large return periods events. This method is adapted to the particular Wateringues area using a more general approach involving complex hydrological systems which are influenced by a number of heterogeneous physical factors. Correct application of the method requires adequate statistical analysis of each factor and their joint probability and detailed hydrological and hydraulic modeling of the system.