Non-renewable groundwater resources: a ... - unesdoc - Unesco

NON-RENEWABLE GROUNDWATER RESOURCESThe Post Nubian Aquifer System (PNAS)The Post Nubian Aquifer System is bounded by no-flow boundaries in the south by the26th parallel, in the west by the 19 Meridian north of Tibesti, and in the east by the Red Seabasement mountains and the Suez Canal. In the north Post Nubian Aquifer System is boundedby the fixed head Mediterranean sea. Based on average formation bulk porosity of 10%, the totalvolume of groundwater in storage is in excess of 84,600 km 3 (refer to Table 2). If we limit thefreshwater occurrence to the north by the depression marked by several sabkhas along theparallel 30°N, the fresh ground water stored in the Post Nubian is 72,767.17 km 3 .Table 1. Storage capacity of the Post Nubian Aquifer SystemREGIONArea(km 2 )Saturatedthckness(m)Groundwatervolume in storage(km 3 )Stored volumeSouth of the 30°N(km 3 )Libya 426479.32 1143.00 48746.586 39427.5Egypt 494039.44 726.00 35867.263 32839.67Total 920518.76 84613.849 72767.17Determining exploitable volume of groundwaterExploitation of groundwater reserves in the Nubian Sandstone Aquifer System is currentlytaking place. As shown in Figure 2, this exploitation is increasing each year. In the past 40 yearsover 40 billion m 3 of water has been extracted from the system in Libya and Egypt. This has produceda maximum drawdown of about 60 m. All but 3% of the free flowing wells and springshave been replaced by deep wells. Most of the present water extracted is used for agriculture,Figure 2Growth of groundwater extraction from the Nubian Sandstone Aquifer Systems78