The Wajid Sandstones are made up of two permeable formations, the Upper and Lower Wajid Sandstones, which are separated by a less permeable shale formation. They are hydraulically connected over a long distance to constitute a regional aquifer system.
The Wajid Aquifer System extends across the border of Saudi Arabia and Yemen, from the Asir-Yemen Highlands to the Rub’ al Khali Depression. In the subsurface, the aquifer system extends from the Wadi Najran area to the eastern areas of the Rub’ al Khali and possibly to the Gulf coast. On the surface, the Upper Wajid is found mainly in the Sa’dah-Najran area while only the Lower Wajid is exposed in the Jibal al Wajid further north. The combined thickness of the Upper and Lower Wajid may be anywhere between 100 and 900 m in the areas where it is currently exploited.
The water level in the aquifer system has dropped at a rate of 3 m/yr for the past 20 to 30 years and as much as 6 m/yr in some areas around Wadi Dawasir-Sulayyil (Saudi Arabia) and Sa’dah (Yemen). Heavy abstraction for agricultural development in these areas has led to the exhaustion of the aquifer system in some areas, while other areas are threatened by exhaustion in the coming 10 to 15 years.
|Riparian Countries||Saudi Arabia, Yemen|
|Alternative Names||Bani Khatmah Formation|
|Renewability||Very low to low (0-20 mm/yr)|
|Hydraulic Linkage with Surface Water||Weak|
|Aquifer Type||West: Unconfined
|Age||Paleozoic (Permian and older)|
|Thickness||100-900 m (AVG: 300 m)|
|Average Annual Abstraction||Saudi Arabia: 2,260 MCM (2004)
Yemen: ~100 MCM (2002)
|Storage||Saudi Arabia: 30-225 BCM
Yemen: 4-6 BCM
|Water Quality||Fresh to slightly brackish
(700-1,000 mg/L TDS)
|Water Use||Predominantly agricultural; limited municipal and industrial|
|Sustainability||Water level decline and salinization due to overexploitation, resulting in partial exhaustion of the resource|