Résumé
In southern France, karst flash-floods may be the result of two, potentially cumulative, phenomena: - Floods from highly localized events that mostly occur during autumn and are locally known as Cevenol rain events ; - Floods exacerbated by recent rainfall events that contributed to saturation of the aquifer before the storm event, thereby increasing runoff. In any case, flash floods occurring in a karst landscape are directly linked to the structure and hydraulic properties of the karst aquifer. A methodology was developed for the city of Nîmes for forecasting these dangerous events, based on the study and modelling of karst-aquifer response to rain events. This work was composed of: (i) Definition of how the Nîmes system functions, leading to a conceptual model; (ii) Modelling of this conceptual model; (iii) Definition of a tool for hazard management, presented as an abacus and tested on particular strong rainfall event.