Résumé
The floods from Cevennes mountains are known for their suddenness and magnitude. These floods have been the subject of various studies, but the hydrological processes at the origin of these floods remain poorly understood. The objective of this presentation is to summarize the results and conclusions of an article recently published in Hydrological Processes, characterizing the vertical and lateral water flows in the critical zone (0-10m) during heavy rains. The study concerns a plot of 10 m2, monitored under natural rains and under artificial rains, located in the granite zone. Water transfers are monitored by various measurement sensors underlying the plot: water content probes, piezometers, tracers and electrical resistivities in the 0-1m zone, deep piezometer in the 0-10m zone. The results show that the rains are completely infiltrated at the surface, that the flows are essentially vertical in the 0-10m zone, and that lateral flows appear in depth, at the base of this zone. The relatively fast transfer speeds do not, however, explain the very short response times of the C ́evennes basins by a mass transfer, and suggest that the trigger of the C ́evennes floods is due to the propagation of a pressure wave along theslope.