The studied case is a disastrous hydrometeorological event that occured on Septembre 8-9, 2002 in the Cévènnes-Vivarais region of the Southern France. The hydrological instrumentation monitoring network of the Cévènnes-Vivarais region covers the three main river basins: the Gardon basin at Ners (1,090km²), the Cèze basin at Bagnols sur Cèze (1,110km²) and the Ardèche basin at Sauze Saint-Martin (2,240km²). Throughout the duration of this episode, the Gardons as a whole received an accumulation of 300mm of precipitation, with 200mm for the Cèze and around 100mm for the Ardèche.