Origin of flash flood water of a Mediterranean river in karstic and urban environments by CTD monitoring (Las - Toulon - SE France)

International audienceThis study deals with flash flood generation in Mediterranean karstic and urban environments. Flash floods in streams are characterized by short response times to rainfall events, and high and rapid discharge variations (Nied et al. 2014, Merz and Böschl 2003, Gaume et al. 2009). They are usually generated by short, high-intensity rainfalls, mainly of convective origin that occur locally. In urban environments, impermeable areas and storm water conveyance systems significantly increase the flash floods caused by storm runoff (Miller et al. 2014). Moreover, in karstic environments, the karst groundwater baseflow supplying the stream can be highly variable. The karst groundwater discharge, mainly flowing at springs, is also disturbed by rainfall events that could quickly recharge the aquifer through permeable karst features (sinkholes, caves, shafts, karrens, open fractures…) in the catchment area and propagate through vadose and saturated zones. The resulting flood from the karst groundwater overflows into the stream. Simultaneous discharge of urban runoff origin and groundwater origin increase flash flood and hazard consequences