Comparison of three automated flood inundation mapping methods in a context of flash floods

Although flash floods observed in headwater catchments often cause catastrophic material and human damage, the knowledge of threatened areas and the prediction of potential impacts of these floods have still to be improved. Considering the large number of small watercourses possibly affected, the use of automated methods for flood inundation mapping at a regional scale should be of great help for this purpose. A comparison of three mapping methods based either on the Height Above Nearest Drainage concept (HAND/MS), or on 1D/2D shallow water equations(caRtino 1D and Floodos 2D), is presented herein. The common features of the three approaches are their high level of automation, their application based on a high-resolution (5m) DTM, and their reasonable computation times.<br />
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Observing strategy: <br />
The mapping methods are used to estimate the flooded areas of three major flash floods observed during the last ten years in South-Eastern France: the 15th of June 2010 flood on the Argens river and its tributaries (585 km of river reaches), the 3rd of October 2015 flood on small coastal rivers of the French Riviera (131 km of river reaches) and the 15th of October 2018 floods on the Aude river and its tributaries (561 km of river reaches). Hydraulic simulations are run in steady-state regime, based on peak discharges estimated using a rainfall-runoff model preliminary adjusted for each event. The simulation results are compared with the reported flood extent maps and the high water level marks.