| Abstract |
The North Sahara Aquifer System (NSAS), shared by Algeria, Libya and Tunisia, contains very large reserves of non-renewable water. It covers an area in excess of 1,000,000km2 of which 700,000km2 are in Algeria, 80,000km2 are in Tunisia and 250,000km2 are in Libya. It is composed of sedimentary rocks that include the Continental Intercalaire aquifer, which is made of lower Cretaceous (Neocomian, Barremian, Albien) interbeded sandstones within calcareous rocks. It consists of several horizons with different hydrodynamic characteristics. The geothermal gradient ranges from 2.9 to 3.5°C/100m, the temperature ranges from 46 to 81°C, pressure from 14 to 20bars, and TDS of 2.2-4.5g/l are of a sulphate-chloride type. Using isotopic indicators (18-O, Deuterium, 14C), radiocarbon ages, except near outcrop, are at or near detection limits and the δ18O and δ2H values indicate (?). The age of geothermal water is about 25-50 thousand years old (BP). At present, estimates of annual water extraction from this basin amount to 540 hm3 in Tunisia, 1,100 hm3 in Algeria and 250 hm3 in Libya. Tunisia holds an even bigger reserve of exploitable non-renewable groundwater than its neighbors Algeria and Libya, with estimates in the order of 1,700 km3 (OSS 2004). The total annual extraction from the NSAS ranges currently from 2.2 to 2.5 billion m3 and this rate has been increasing. Many problems occur in the deep wells (2800m depth) such as scaling, corrosion, etc. The result of this improved knowledge of the basin’s hydrogeology is the refined characterization of the aquifers, which are required for mathematical modeling. |