2D modelling of freshwater-salt water interface in a hypersaline wetland: Pétrola Lake,SE Spain

The difficulties in the understanding and management of hydrogeological systems dominated by groundwater flow with variable density such as hypersaline lakes are further complicated. In these wetlands, the brine is located above. There, the relatively freshwater of the aquifer produces a gravitational instability that can generate convection cells. When the density differences between both fluids are sufficiently high, solute transport is the result not only of advection and diffusion dispersion, but also of mixed convective flows. Pétrola Lake is one of the most representative examples of hypersaline wetland in southern Europe. Its environmental importance is intimately associated with the hydrogeological functioning of the system. Regional groundwater flow is radial and centripetal from the boundaries of the basin to the lake. In Pétrola Lake, surface water density reached values up to 1.29 g cm-3. In contrast, most of groundwater samples showed density values of 1.00 cm-3. As a result of the difference in density between the lake and fresh groundwater, a density-driven flow (DDF) towards the underlying aquifer is produced in the lake-aquifer interface. The electrical resistivity tomography has clearly demonstrated the intrusion of saltwater wedges in the aquifer. This information is spatially guaranteed through the mathematical modeling of the groundwater flow (2D) under conditions of variable density. The results of the simulation have served to reinforce the conceptual model of the study area, improving our knowledge about the behavior and morphology of the freshwater-salt water interface. The convective flow driven by the density difference is affected to its see by the presence of clayey levels of low permeability present at about 15-20 meters below the saline lake.