Geological modelling for hydrogeological purposes in Oum Zessar area (SE Tunisia)

To infer the hydro-geological features of an area wide about 1450 square km in the Saharan Platform we present a 3D hydro-geological model of the Lower Triassic succession in Medenine region (Jeffara plain, SE Tunisia), in order to design an aquifer artificial recharge system for drinking water and irrigation purposes. This region represent one of two study areas implemented in WADIS-MAR demonstration project (www.wadismar.eu) founded by European Commission through SWIM Programme (www.swim-sm.eu). A preliminary geological model was built based on previous geological, hydro-geological data (Yahyaoui, 2007) and remote sensing elaboration. Tectonic and geomorphologic features allow to divide this region into two domains: Jeffara plain and Dahar plateau. The Jeffara Plain represent the footwall of a pre-Cenozoic ENE-dipping fault system that tears apart the Jeffara basin. It consists of a wide sedimentary basin involved in several tectonic events (Gabtni et al., 2009) in which mainly crops out a clastic Cenozoic sequence overlaying a thick Early to Middle Trias succession that generally outcrops along the oued. In the hanging wall of the same fault system, the Dahar plateau occurs. It is a thick Jurassic to Cretaceous carbonate succession representing a fault-bounded structural high that surrounds the Jeffara basin from the South to the West where a Permian succession is well exposed. This geological framework largely influences the various aquifers and the groundwater circulation (Chihi et al., 2013). The lower Triassic succession hosted a strategic aquifer with good quality water for households living in villages and cities of such arid region, up to now overexploited. The results of the geological model determine the boundaries of the Lower Triassic succession allowing to understanding the hydro-geological conceptual model and to plan an efficacious aquifer artificial recharge system. Based on the collected data and the hydro-geological feasibility, an aquifer artificial recharge system is designed. It consists of dry wells with recharge chambers to catch and infiltrate flash flood waters from the ephemeral streams (ouadi) in 4 intervention sites. WADIS-MAR Project website www.wadismar.eu Chihi H., Bedir M. & Belayouni H. 2013. Variogram identification aided by a structural framework for improved geometric modeling of faulted reservoirs: Jeffara Basin, Southeastern Tunisia. Natural Resources Research, 22(2), 139- 161. doi 10.1007/s11053-013-9201-0. Gabtni H., Jallouli C., Mickus K.L., Zouari H. & Turki M.M. 2009. Deep structure and crustal configuration of the Jeffara basin (Southern Tunisia) based on regional gravity, seismic reflection and borehole data: how to explain a gravity maximum within a large sedimentary basin?. Journal of Geodynamics, 47, 142-152. Yahyaoui H. 2007. Nappes des Grès du Trias Sahel el Ababsa de Médenine, aspects hydrogéologiques et gestion rationnelle des ressources. Internal Report, CRDA Médenine, 27 pp.