Simulation as a tool for anticipating rapid floods in small watersheds in Seine-Maritime

This paper aims at simulating the probable flash floods at the outlets of numerous basins (148) of small size (< 20km(2)) combining GIS-data obtained at local scales within the cellular automaton RUICELLS. A violent onset, a rapid rising time and a surge rushing down the main thalwegs a few minutes after rains peaked characterized such floods but forecasting their location and occurrence remains delicate. Thus, a modeling approach by anticipation has been carried out and it allows defining possible peak-flow discharges, specific discharges and time-of-flowing out for 16 predefined rainfalls. The simulations confirm that the land use organization and intensities are of paramount importance by guiding the spatial relationships between runoff production and infiltration areas. The modeling results also show interestingly that the highest discharges and shortest times-of-flowing out are observed on basins having a compact form, a hierarchical drainage network and the highest-slope gradients in this region. Finally, this modeling assessment has been aligned with the location of previous events.