Sensitivity of 2D hydrodynamic modelling of urban floods to the forcing inputs: lessons from two field cases

This paper reports two urban floods in France: the September 2000 flood at the city of Marseille caused by heavy rainfall, and the November 2008 flood in Oullins induced by the Yzeron River overflow. A two-dimensional (2D) depth-averaged model was used to simulate flood hazard and to investigate the uncertainty associated to the forcing inputs. Using a rainfall simulator, several distributions of rainfall inputs over the whole domain were produced for the event of September 2000 in Marseille. Results showed these latter distributions changed the average peak water depth more than other input parameters. The Yzeron River water elevation was the main source of uncertainty in the case of Oullins, but the flow pattern in the floodplain was also influenced by the method representing the urban areas. For both cases, average uncertainty remains high (up to 20% for peak water depth or velocity) and local uncertainty is almost much higher.