Hydro-geophysical interpretation of fractured and karstified limestones reservoirs: A case study from Amdoun region (NW Tunisia) using electrical resistivity tomography, digital elevation model (DEM) and hydro-geochemical approaches

Abstract

Groundwater from fractures and karst in limestone rocks is an important source of drinking water in the semi-arid climatic environment of North-Western Tunisia where cool and rainy seasons alternate with hot dry seasons. Due to varying climatic conditions and anthropogenic interventions the fractured limestone aquifer systems (Abiod and Boudabbous/El Gueria Formations) tend to be complex.The lack of data on the fractured and karstified aquifers in Amdoun region (NW Tunisia) to establish the hydrogeological potential between different rock formations of Upper Cretaceous and Lower Eocene has often discouraged researchers from attempting to model such aquifers. On the SE flank of the Jebel Sabbah anticline, Electrical Resistivity Tomography Data were collected along three different lines of 315 m of length each. The expected vertical penetration depth was 60 m.This hydro-geophysical investigation consisting of geological, structural, and geo-morphological studies, has demonstrated that groundwater in the carbonate rocks, in Amdoun area, occur in fracture zones and weathered parts of the rocks in the karst aquifers.The hydrochemical data (major ion geochemistry) indicate that these groundwaters are characterized by the dominance a Ca–Mg–HCO3 water type. Geochemical pattern is mainly controlled by the dissolution of carbonate minerals. Generally, TDS increases from the Amdoun Monts towards the discharge area (53 < TDS<332 mg l−1). These results are assessed using numerous geophysical data such as ERT imaging and geological knowledge. Finally, we show how these results could be used to improve the management of karst groundwater resources in Amdoun (NW Tunisia) complex terrain.