Particular behaviour of Karst aquifer during high discharge period: Existence of double fracturation and/or deep circulation. Example from the Fontaine de Vaucluse

Lots of works demonstrate the complexity of functioning of the Fontaine de Vaucluse. A daily sampling during a flood period, using C-13 of the total d issolved inorganic carbon (TDIC), is compared to classical parameters. It e nables more accurate interpretation. With this experiment, we observed particular water outflows at the outlet d uring high flow periods. This water has a high magnesium content which reve als a long residence time; a TDIC C-13 enrichment, significant of a long re sidence time within the saturated zone, and a high temperature indicating a gain an origin within the saturated zone. This particular water flowing only during high discharge period can be assi gned to saturated zone with high pressure loss, which limits its participat ion to the flow in normal conditions. To explain this phenomenon, we propos e the double fracturing concept. An open one, mainly with a drain function and a second one which generally plays a storage role. This storage fractur ing could be made of joints or small fractures, but also of old drains with a bad connection to the present drainage system.