Flash Flood Forecast Hydrological Model

Abstract

Flash floods are characterized by their violence and the rapidity of their occurrence. Because they don ‘t occur frequently and are so unpredictable their anticipation is still subject to research : when flash floods occur, tools usually used by the Sercice d’Annonce des Crues (SAC : national flood forecast services of France) are not efficient to protect people form this kind of event. Our main goal here is to develop an operational and robust methodology for flash flood forecasting. This methodology should give relevant data about the flood evolution and should be applicable even if historical and observed data are sparse. The flash flood evolution model that we have developed consists in two steps : first, the flood runoff generation in the upstream part of the basin, then it’s propagation in the main river. Flash flood generation model (MARINE) is a rainfall - runoff model that only integrates data from space. Classical hydrology equations are resolved with enough hypothesis to allow real time exploitation. The minimum data required by the model are the Digital Elevation Model, used to calculate slopes that generate runoff, the rainfall data from meteorological radar and the soil properties viewed from space and that have hydrological influence (land cover map, main rivers). Flood propagation model resolves Saint Venant equations and simulates flood propagation in main rivers. In this paper, we will insist on the hypotheses we did to simplify hydraulic equations and their resolution in our model to do so we based our analysis on known past events defining how space data can replace observed data in hydrological simulation. This analysis has been tested in a 2D flood propagation model. Results for the Aude flood of November 1999 are very encouraging.