Management of Groundwater Resources in Eastern Saudi Arabia
Effective management of groundwater in arid countries, such as Saudi Arabia, is an important factor in sustainable development. A regional numerical simulation model of a multi-aquifer system including the Dammam and Umm Er Radhuma (UER) aquifers was developed to assess the behaviour of the aquifer system under long-term water stresses. The model was utilized to predict the responses of the aquifer system under three alternative pumping schemes over a planning horizon of 31 years (1995-2025). Model results postulate that dewatering of the Dammam aquifer will occur at low productivity sites and along the outcrop with the current trend towards increasing abstraction. The UER will exhibit significant cones of depression at large irrigation projects. Aquifer dewatering and drawdowns will be minimal with the conservation alternative. This management scheme should be adopted for the future development and protection of groundwater in the province.
Hydrogeological conditions in the Middle East
Summary The geology of Middle East is summarized under the subheadings: Precambrian basement, epicontinental sediments, geosynclinal and shelf deposits, Tertiary volcanics and Quaternary cover. The main tectonic episodes including epeirogenic movements, rifting and the Tertiary orogeny, are reviewed. The imposition of hydrometeorolocal and climatic conditions upon the regional geology provides the setting for the hydrogeological discussion. Five factors which influence infiltration to aquifers under conditions of low precipitation and high potential evaportranspiration are discussed. The predominance of fossil groundwater is the most striking hydrogeological phenomenon occurring on a regional scale in the Middle East. Its mode of formation during the pluvials is outlined and the isotopic evidence is reviewed. The main physical and chemical characteristics of fossil ground-waters are described. It is conservatively estimated that some 65 000 km3 of good- to medium-quality groundwater are stored in the great artesian basins of the Near East. These fossil ground-waters are a non-renewable natural resource. Current annual abstraction is, as yet, a small percentage of the total reserves but economic factors rather than the volume of reserves will determine the ultimate extent of their exploitation. The renewable groundwater resources of the Middle East tend, by comparison, to be of local rather than regional significance. Some originate outside the Middle East, coming in as surface flows in the Nile and Tigris-Euphrates and infiltrating into the sediments in and adjacent to the flood plains. Other renewable resources accumulate within the region where high precipitation and mountainous relief are associated. Such areas include the Djebel Akhdar of Cyrenacia, the Tertiary fold mountains from the Taurus through the Zagros to the Oman ranges, and the volcanic and basement highlands of Yemen, Asir and Ethiopa. Locally, in areas of lower precipitation, lenses of recent fresh groundwater float on regional more saline groundwater. In some areas subsurface flows towards and through wadi systems are also of importance.
Hydrogeology of the Kufra and Sirte basins, eastern Libya
Summary Two major sedimentary basins occur in eastern Libya. The uppermost horizons in each—post-Eocene in the Sirte and Cretaceous Nubian in the Kufra basin—constitute regional hydrogeological systems. The deposits of the Sirte basin include mainly fluviatile sands and clays in the S with marine carbonates and sandy carbonates with some evaporites progressively increasing to the north. In addition to a northwards thickening of the deposits there is an ‘inwards increase’ which attains a maximum thickness of about 1800 m along a broad N-S trending axial trough. The Nubian sandstone of the Kufra basin has a maximum thickness of 900 m and includes mainly cross-bedded sandstones, subordinate shales and conglomerates, which are fluvio-glacial and limnic in origin. The Cretaceous sandstone aquifer in the Kufra basin is essentially phreatic and groundwater flow is to the northeastwards discharging into the main Nubian artesian basin of Egypt. Present development of the aquifer occurs at only a few locations but at these the water quality is very fresh with dissolved solids typically less than 100 mg/1. The basin is bounded to W and S by highlands from which appreciable run-off can be assumed. Although not measured, assumptions of recharge from run-off of some 10–20% of annual rainfall over the elevated areas seems not unreasonable; this is approximately equivalent to the computed order of outflow from the basin of between 70–160 M m3/a based on transmissivity and piezometric gradient. Vertical recharge is unlikely to occur over the main basin where the rainfall is probably less than 3 mm/a. The age of the water at Kufra in the north of the basin is in excess of 30 000 years. The phreatic aquifer cannot therefore be in equilibrium with current recharge but it is believed that an approach to equilibrium may exist in marginal recharge areas. The groundwater in the S of the Sirte basin is fresh but in the N it becomes brackish to saline in the direction of flow. The known groundwater ages range from 30 000 to 5000 years BP and fall into three main groups. Water from recent recharge may also exist in the uppermost phreatic levels. Various evolutionary trends have been considered and modelling techniques are used to assist elucidation. The results demonstrate that present water levels may be fairly close to equilibrium, with recharge to the aquifer system occurring from several sources including lateral inflow from the Kufra basin, marginal recharge via run-off from the highlands to the W and SW, and direct recharge from precipitation in the N of the basin. Discharge occurs in the N into sabkhat areas between the Gulf of Sirte and Qattara.