The hydrochemical characterization of the underground waters of the plain of Sidi Bel Abbès (northwestern Algeria).

Abstract

The population of the city of Sidi Bel Abbès has become over time reliant on the Wilayas of Tlemcen and Mascara to satisfy its growing needs for drinking water. The absence of big dams and the average and often irregular rainfall are superimposed to the poor understanding of the groundwater potential in the region. Notwithstanding this, the plio-quaternary alluvial aquifer of the Sidi Bel Abbès plain can be considered as an exception. This unconfined aquifer, which stretches over 800 km2 is drained by the Mekerra River and exploited by an impressive number of wells and boreholes, most of which are intended for irrigation. The strategic importance of this water resource for the city of Bel Abbès is immense. Thus, its characterization (by modeling) is a necessity. The present study aims to evaluate the groundwater potential in the plain of Sidi Bel Abbès, characterize the main parameters affecting both the quality and the quantity of said waters and propose practical solutions and recommendations, to protect them against deterioration and overexploitation. The results obtained at the end of this work permitted a better understanding of the morphological, climatic, geological and structural characteristics of the study area. The hydrochemical study emphasized the mechanisms and processes controlling the salinity of the plio-quaternary aquifer waters. The results obtained demonstrated the contamination of the aquifer waters by wastewaters. Therefore, they are in their majority, unfit for human consumption, unsuitable for irrigation from a salinity point of view and inappropriate due to their high concentrations in Cl, for most sensitive plants. The computer modeling of the plio-quaternary aquifer system performed using the program Visual Modflow, not only permitted the characterization of the aquifer boundary conditions, the approximation of its hydrodynamic proprieties, the estimation of its extension (lateral and vertical), its recharge and its destocking. Thus, the computer modeling of the plio-quaternary aquifer clearly demonstrates its overexploitation.