The Southern Desert represents a rolling and/ or undulating plain, which may be a flat or slightly rolling in some parts. The drainage system is internal, with most of the surface water percolating to underground through permeable strata, fractures, fissures and karst cavities. All valleys are intermittent draining either into marshes and sebkhas bordering the Euphrates River or are blind valleys.
The Southern Desert is built up of sedimentary rocks, mostly of carbonate sequences and friable clastics with very gentle dip northeastwards. The main recharge to the groundwater is from direct rain fall, as well as seepage losses from intermittent wadis.
There is a hydraulic connection between the main aquifers within the whole Southern Desert. Aquifers of Hartha, Tayarat, Umm Er Radhuma and Dammam formations represent a complex hydrogeological unit. Dammam aquifer is considered the most important one, on a regional scale due to its extent and content of large amount of water. Aquifers in Dibdibba formation and Quaternary sediments are also important in supplying water for irrigation purposes within the southeastern parts. While the aquifer within Ghar – Euphrates Formation is less important, due to high salinity of water and its local extent.
Generally, groundwater movement is from west and southwest to east and northeast, that is from the recharge areas towards the main discharge zone along Euphrates River, Hor Al-Hammar and Shatt Al-Arab. There are local deviations from the main direction of the movement due to geological, structural and topographical nature of the region. Groundwater level varies from tens of meters from ground surface, in recharge areas to near surface or artizian, in discharge areas. Water salinity increses in general, from recharge areas toward discharge areas. Fresh water of bicarbonate type may represent areas of direct recharge, while the discharge zone is characterized by water of higher salinity and of sulphtic or chloridic type. |