| Popis: |
The aim of this study is to present a framework giving new keys to characterize the spatio-temporal variability of lateral exchanges for flows and fluxes in a karst conduit network during flood events. An inverse model using an analytical solution of the diffusive wave model is applied on data from two successive gauging stations to simulate exchange dynamics after recharge. The study site is the karst conduit network of the Fourbanne aquifer in the French Jura Mountains, which includes two reaches of 5–10 km characterizing the network from sinkhole to cave stream, and to the spring. The model is applied after separation of the base and the flood components on discharge and total dissolved solids (TDS) in order to assess lateral flows and mass-fluxes and compare them to help identify water origin. Our results showed various lateral contributions in space – between the two reaches located in the unsaturated (R1), and in both unsaturated and saturated zone (R2) – as well as in time, according to hydrological conditions. Globally, the two reaches show a distinct response to flood routing, with important lateral inflows on R1 and large outflows on R2. By combining these results with mass flux exchanges and the analysis of flood routing parameters distribution, we showed that lateral inflows on R1 are the addition of diffuse infiltration (observed whatever the hydrological conditions) and localized infiltration in the secondary conduit network (tributaries) in the unsaturated zone, except in extreme dry periods. On R2, despite inflows on the base component, lateral outflows are observed during floods. This pattern was attributed to the concept of reversal flows of conduit/matrix exchanges, inducing a complex water mixing effect in the saturated zone. From our results we build the functional scheme of the karst system. It demonstrates the impact of the saturated zone on matrix/conduit exchanges in this shallow phreatic aquifer, and highlights the important role of the unsaturated zone on storage and transfer functions of the system. |
