Dataset on onshore groundwaters and offshore submarine spring of a Mediterranean karst aquifer during flow reversal and saltwater intrusion.

Groundwater from various shallow and deep reservoirs converges in interaction with marine waters into the limestone aquifer of the Balaruc peninsula (Thau lagoon, southern France). This aquifer faces temporary phenomena of marine water intrusion through the Vise submarine spring located at -29.5 m below the lagoon level. Since the 1960s, seven flow reversal phenomena have occurred, the last one occurring between 11/28/2020 and 03/14/2022. During these phenomena, which can last from a few weeks to several months, the salty water is absorbed from the lagoon to the conduit of the submarine spring, which leads to the salinization of the underlying karst aquifer. The monitoring of flow, water specific conductivity and water temperature data from the karst submarine spring is a key element of the research project to understand the hydrogeological functioning of the karst aquifer under normal conditions or during flow reversal periods. This monitoring allows the characterization of the (in- or out-) flows at the submarine spring, the evaluation of the volume or mass balances, the identification of the hydrogeological and physico-chemical responses (water temperature, specific conductivity) observed within the karstic aquifer. Here, we present the means implemented offshore to acquire data at the submarine spring over the 06/25/2019 - 12/31/2022 time period together with lagoon water's physico-chemical parameters and levels and onshore groundwater's physico-chemical parameters and levels acquired at springs and boreholes from the karst aquifer.