Eastern Saharan artesian basin
EASTERN SAHARAN ARTESIAN BASIN (RU: Восточно-Сахарский артезианский бассейн), the Libyan-Egyptian artesian basin, is situated within the north-eastern part of Africa. The basin includes the territory of Egypt, the northern part of Sudan, the eastern regions of Libya, and the north-eastern regions of Chad. The area is 3.49 million square kilometres. The basin is confined to the Saharan platform with the pre-Cambrian basement. At the west, the basin is bounded by the structures of the Jebel-Nefus, El-Hamra, Es-Soda, Ben-Ghuneim, at the south-west and south, by the Tibesti highland, by the Erdi, Ennedi, and Darfur plateaus, and at the east by the Red sea mountains; at the north, the basin is opening into the Mediterranean sea. The main aquifer system is associated with the Lower Cretaceous (the Nubian series) sandstones, sands, and conglomerates, which have the interlayers and lenses of the clays and mudstones. The thickness of the system is from the tens of metres (at the south) to 1200 metres and more (at the north). At the south, the system is embedded on the surface, while to the north, the depth of the roof reaches 1885 metres (the Qattara depression). The yields of the boreholes are tens of litres per second, the coefficient of the water transmissibility is 1500-5000 square metres per day. The temperature of the water is 25-39 degrees Celsius, the mineralization to the south of the 28 degrees north latitude is 0.5-0.6 grams per litre, the composition is HCO3--Cl--Na+, while to the north, there are well developed the saltish and saline waters with the composition of Cl--Na+. There also has the important significance the aquifer system of the quaternary alluvial depositions, namely, of the gravel-pebble sands with the interlayers and lenses of the clays and silts within the valley of the Nile river. The yield of the pressurized waters is from 20 to 150-160 litres per second, sometimes up to 200 litres per second, the specific yields are 18-50 litres per second. The waters are usually fresh (0.5-1 grams per litre), the composition is HCO3--Ca2+, while within the Nile delta, there are also well developed the saltish waters with the mineralization of up to 3-10 grams per litre, the composition is Cl--Na+.
The secondary aquifers, namely, Upper Cretaceous, Eocene, Oligocene, and Miocene (the total thickness is 1800 metres) are formed of the terrigenous and carbonate depositions. The yields of the boreholes are from the fractions of the litre to 20-30 litres per second, the mineralization is 3-7 grams per litre on average, and up to 10-20 grams per litre at the surface, the composition of the water is Cl--SO42--Na+.
The supply of the underground waters within the basin is performed on the account of the infiltration of the atmospheric precipitations, on the account of the absorption of the waters from the rivers and irregular flows within the wadis, and on the account of the condensation of the moisture from the air. There is characteristic for the basin the regular increase of the mineralization of the underground waters along the direction from the south to the north, that is from the major region of the supply of the basin towards the Mediterranean sea, which is representing the zone of its regional discharge.
The natural resources of the waters within the zone of the active water exchange are 36 cubic kilometres per year. The underground waters of the basin are widely used for the water supply of the populated locations, and of the industrial enterprises, and for the irrigation (for example, the approximate extraction within the Kharga and Dakhla oases is 3.3 million cubic metres per day).
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