Hydrodynamics and Recharge of the Aioune Sandstone Aquifer in the Taoudenni Transboundary Basin in Mauritania

Abstract

In Mauritanian, 4/5 of the territory is subject to an arid climate, where groundwater resources are the main sources of drinking water for populations and livestock. The study area is located in south-eastern Mauritania and in the western part of the Taoudenni Transboundary Basin. A better knowledge of the hydrogeological system to ensure a sustainable and rational management is necessary for this vulnerable water resource. This pioneering study, based on the compilation of hydrogeological, geochemical and isotopic data, aims to characterize the hydrodynamics and recharge of this one layer aquifer system, composed of Aioune infracambrian sandstone. The piezometric surface exhibits relatively the same morphology of the soil topography, and computed effective velocity is 94 m/yr (Northeast area), and the direction of flow is generally from cliff to plains area. The chemical data show water types evolving between two poles namely the HCO 3 -Ca/Mg pole (low mineralized), and the Cl-Ca/Na pole; these waters are characterized by a high vulnerability to pollution, especially at shallow depth area (Douerare, Aioune). The dissolution of bicarbonate and evaporate minerals is likely the main source of mineralization. The isotopic tool used to support comprehension of the system functioning, evidences a local indirect recharge water localized at the cliff or Wadi zones. The age of the waters ranges from the present to 1060 year. The recharge rate calculated by 14 C and the chloride masse balance is respectively 0.4 to 5 mm/year. This recharge compared to the water pumping rate is lower and hence this imbalance is likely the cause of water shortages particularly during summer season period.