Recharge processes in karst at different time scales

English Abstract:

In karst, the heterogeneity of the transfer processes within the different compartments (soil, epikarst, unsaturated zone, saturated zone) control the recharge-discharge relationship. The MEDYCYSS observatory (www.medycyss.org), an observation site of the KARST (www.sokarst.org) and RBV (http://portailrbv.sedoo.fr/) multi-disciplinary research networks, has been set up to better understand these transfers in a Mediterranean climatic context. Within the Lez karst catchment (South of France), part of the MEDYCYSS observatory, a 333m deep borehole has been equipped with the PMPS Multi-level monitoring system (SolExperts). This borehole is located 100 m from an intermittent river and 500 m from the aquifer main outlet (Lez Spring) where intermittent pumping is performed. Continuous pressure and temperature monitoring is realized at 5 levels isolated by packers where discrete water sampling can also be achieved. The main objective of this karst monitoring, realized in the framework of the CRITEX project, is to assess the different mechanisms of the recharge at various time scales. The collected data will implement the existing spatial monitoring of the hydrodynamic and geochemical variations followed in bore-holes, karst features (cave and estavelles), perennial and temporal springs of the karst aquifer. In this study we aim at specifying the contribution of the different karst compartments, from the recharge zone towards the main outlets. The preliminary results obtained during a flash flood event show a contrasted hydrodynamic response for each compartment in agreement with the karst functioning assessed from the analysis of the chemical variations. These data are essential to better assess the recharge processes and specify the role of the vadose zone in the flow organization at short and long timescale.