Large Saharan artesian basin
LARGE SAHARAN ARTESIAN BASIN, Algerian-Tunisian artesian basin (RU: Большой Сахарский артезианский бассейн, Алжиро-Тунисский артезианский бассейн) is situated mostly on the territory of Algeria, covers also the southern half of Tunisia, and partly Libya. The area is approximately 600 thousand square kilometres. It is confined to the submergence of the Saharan tectonic plate with the pre-Cambrian basement. It is bounded at the north by the structures of the Saharan Atlas, at the west by the Ugart mountain chains, at the south by the Ahaggar massif, the eastern boundary of the basin has not been precisely identified.
The main aquifer complex, which is embedded within the foundation of the basin, and which is distributed throughout its entire area, is associated with the variegated Lower Cretaceous sand-clayish depositions, which are known under the name of the "Continental Intercolour" (at the east, there are the Nubian sandstones). The thickness of the complex, which has been explored, is 350 metres (Great Eastern Erg), the depth of the roof is 100-1300 metres. The yield of the drilled wells is up to 300 litres per second self-flowing, the average specific yield is 1-3 litres per second, the coefficient of the water conductivity is 150 square metres per day. The waters are often thermal (60 degrees Celsius or more), fresh or slightly saltish (0.3-1.5 grams per litre, less often 2.4 grams per litre), the composition is SO42- with Cl-, SO42- with HCO3, HCO3- with SO42-.
There play the secondary role 4 horizons, which are confined to the Upper Cretaceous and Lower Eocene limestones, Miocene and Pliocene sands with lacustrine limestones, and to the Quaternary sands with gravel. The yields of the drilled wells are mostly several litres per second, less often 100-150 litres per second (self-flow and pumping). The salinity is 1-3 grams per litre on average. The major regions for the feeding of all the complexes and horizons are situated on the slopes of the surrounding mountain structures or of the internal uplifts. There plays certain role the condensational moisture (for example, within the regions of the large sand massifs, namely, of the ergs). The discharge is performed mainly through numerous drilled wells, and partly (at the foothills) in the form of the low-yield water sources. The natural resources are roughly estimated at 23 cubic metres per second. They use the underground waters of the basin for the water supply of the industrial enterprises, for irrigation and watering of the Saharan oases and plantations.
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