Assessment of Groundwater Salinity Mechanisms in the Coastal Aquifer of El Haouaria, Northern Tunisia

In the El Haouaria region (N.E. Tunisia), our hydrodynamic survey revealed a decrease in unconfined groundwater reserves of approximately 11% over the last 30 years due to the abstraction of water. Over that same time period, the groundwater table displayed a natural decrease of about 10 m in depth over an area of 230 km2. Hydrogeological investigations have shown that two aquifers which vertically integrate all of the permeable zones in the region can be distinguished: a shallow aquifer formed by filling the Quaternary and another deeper one in the Pliocene. These two aquifers are separated by a semi-permeable layer through which vertical exchange by seepage is possible. Different methods using geochemistry (Na+, Cl-, Br−) and stable isotopes (18O, 2H) are compared with the hydrodynamic information for identifying the main processes involved in the salinization and recharge. Forty groundwater wells were sampled to obtain additional information on the hydrochemical and isotopic characteristics of the groundwater defined in previous studies.