HYDROGEOLOGICAL CHARACTERIZATION OF A FRACTURED BEDROCK AQUIFER IN THE OUGARTA CHAIN SOUTHWESTERN ALGERIA

T. MERZOUGUI, A. MEKKAOUI, C. REZZOUG, B. REMINI

Abstract


The Ougarta Mountains, located in southwestern Algeria, correspond to an imposing geological entity that corresponds to the center of interest in the geology of the Saharan platform. It is a vast area of elongated NW–SE reliefs, covering an area of 400 x 200 km². The Cambro-Ordovician represents the largest aquifer in the Ougarta region. The cracked type is still poorly known; it is located on a cracked base, and is composed of quartzite sandstone and shale forming a multilayer system, the details of which still remain to be sought and constitute a perennial aquifer for the supply of drinking water for the population.

The present study is an attempt to better comprehend the structure and functioning of these basement aquifers. It mainly focuses on the description of soil profiles, structural investigations, and hydrogeological characterization improving knowledge on the hydrodynamic functioning of fractured base reservoirs (geometry of aquifers, hydrodynamic parameters, recharge, resource availability) with a view to the installation of catchment works to optimize, secure and sustain its exploitation in view of its strategic importance for the water supply of this region of Beni Abbes. This contribution is based on field observations and the use of several methods. Various joint approaches have been implemented to locate and characterize aquifers, zones favorable to hydraulic catchments. These are geology, hydrodynamics, piezometry and hydrochemistry.

The «Ougarta sandstone» layer of the Cambro-Ordovician is free at the edge, captive toward the center of the basin, and is characterized by a transmissivity varying from 10-3 to 4.10-4 m²/s. Its piezometry shows a northeasterly southwesterly direction of flow in the direction of the general slope, under a hydraulic gradient of 0.04 to 0.005. The water table flows toward the southeast. The static level of the Paleozoic aquifer oscillates between 06 and 31 m relative to the soil elevation.

Over 30 years, this system has remained stationary, however, the structures installed in the north show a drawdown of 0.1m east indicating large flows (plus 3000 m3/day), with high hydraulic productivity of the catchment works is related to heterogeneity factors.

From a hydrochemical point of view, the groundwater of the volcano-sedimentary base is, in general, poorly mineralized and predominantly chlorinated; it is rapidly charged with sulfates on the limits of the free surface area.


Keywords


Aquifer, hydrogeology, structure, Ougarta, cracked Socle, Paleozoic, Saoura, southwestern Algeria.

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References


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