Hydrogeological Characterization of the Multilayer Aquifer System in the Tunisian-Algerian Border Region Using Geological and Geophysical Techniques

Groundwater resources in the Tunisian-Algerian border region predominantly originate from karstified limestone formations of the Upper Cretaceous and Lower Eocene, contributing 13.5% of Tunisia’s shallow groundwater reserves. In the northwestern region of Tunisia, the Medjerda Middle Plain hosts a complex multilayered aquifer system, confined within Quaternary alluvial deposits and recharged by the Medjerda River and its tributaries. A multidisciplinary methodology was adopted, combining geological and geophysical approaches. Geological investigations, including fracture analysis and geological cross-sectioning, were integrated with geophysical techniques such as gravimetric surveys and two-dimensional seismic reflection to examine geological and hydrological variations, delineate the geometries of geological structures, and assess the hydrogeological potential of the area. These analyses revealed the significant role of fracture systems in controlling aquifer recharge dynamics. Gravimetric studies identified both positive and negative anomalies indicative of subsurface heterogeneity. Gravimetric processing techniques, including horizontal gradient analysis, upward continuation, and Euler deconvolution, were applied to trace geological contacts, fault systems, and spatial variations in the subsurface. Seismic profiles, processed using filtering and gain enhancement techniques, provided critical insights into geological interfaces, stratigraphic separations, and geological discontinuities. These profiles also revealed sediment deposition patterns and potential post-depositional processes, such as unconformities and lithostratigraphic gaps, which play a crucial role in the behavior and management of the aquifer system. This combination of methods has provided valuable insights into the hydrogeology of the Medjerda Plain, offering essential information to support decision-making for the sustainable management and development of water resources along the Algerian-Tunisian border.