Contribution of electrical prospecting to the structural study of the Oued Gueniche plain (Northern Tunisia): hydrogeological implications

The Oued Gueniche plain aquifer system in the Bizerte region is one of the most important groundwater reserves in the Northern Tunisia. However, the characteristics of this aquifer system, as well as its water potential, are still little known. Based on the combination of multidisciplinary data (geology, hydrogeology and geophysics via vertical electrical soundings (VES)), this study aims to (i) improve geological knowledge both stratigraphically and structurally, (ii) characterize the multilayer aquifer system and its hydrodynamics in the Oued Gueniche plain, and (iii) delineate the most favorable areas for the exploitation of high-quality underground water. The calibration of the VES on boreholes reveals that the aquifer system of the Oued Gueniche plain is multilayered, consisting of (1) a shallow aquifer, characterized by a resistant level (25–45 Ωm) and constituted by Quaternary deposits; (2) a deep freshwater aquifer characterized by a resistant level (> 50 Ωm) constituted by upper Pliocene fine sands; and (3) a deep saltwater aquifer (34 g/l) characterized by a highly conductive level (1–2 Ωm) and constituted by clayey sands of the Quaternary. The geo-electrical and electro-stratigraphic cross-sections, as well as the isobaths and isopachs maps established in this study, indicate the importance of the tectonics affecting the region and its influence on the aquifer system. Indeed, the Oued Gueniche plain is affected by NE-SW, E-W, and NW–SE faults, which have resulted in compartmentalizing the plain into high and low (horsts and grabens) areas, thus complicating the geometry and hydrodynamics of this aquifer system both laterally and vertically. These interesting results are crowned by the establishment of a synthetic map delineating areas favorable to the exploitation of water of good quality at various depths. This document will be an essential reference to optimize the hydrogeological models and plan a rational management of the water resources of this plain.