Assessing freshwater resources in coastal karstic aquifer using a lumped model: the Port-Miou brackish spring (SE France)

Abstract : Freshwater resources in coastal aquifers are restricted by seawater intrusion. Studying brackish spring can be an appropriate approach to assess this saline intrusion and to elaborate a conceptual model of the karst aquifer. The aim of this study is to model the hydrogeological flows and the salinity of a brackish spring using a lumped numerical model (Rainfall-Discharge-Salinity), and to quantify the freshwater discharge available. The model is based on a classical karst model composed of connected reservoirs representing the main storage elements of the karst aquifer, which can be deduced from the analysis of discharge and salinity recorded time series. The model was successfully applied on the Port-Miou spring (400 km²), in SE France, which is one of the main submarine springs around the Mediterranean Sea. Four reservoirs were used to model spring discharge and salinity: a SOIL reservoir feeding a DEEP brackish reservoir impacted by seawater intrusion, and two FAST and SLOW reservoirs representing the shallower freshwater resource. We showed that the spring water is always brackish more or less diluted by freshwater during flood events. These results improved the conceptual hydrogeological model of the Port-Miou spring and showed the effectiveness of lumped models to simulate discharge and salinity in coastal karst aquifers.