WHERE AND HOW DO WE FIND GROUNDWATER IN ARID LANDS? AN INTEGRATED APPROACH FROM EGYPT AND SAUDI ARABIA

Water shortages in the Middle East are affecting human welfare and economic activity. The strong and growing demand for water in the region justifies concentrated efforts for identification and assessment of hydrologic settings favorable for groundwater entrapment and utilization that could potentially reduce these water shortages. We report two such settings currently overlooked: (1) highly fractured basement aquifers within the Najd Shear System (NSS), the largest (length: 1600 km; width: 200 km) recognized pre-Mesozoic (530-550 Ma) transcurrent fault system (Egypt and Arabia), and (2) areas of regional natural discharge in the Eastern Desert (ED), Egypt and in the Empty Quarter (EQ), Saudi Arabia. Spatial analysis of remote sensing, geologic, hydrologic, and geochemical data sets revealed a causal association between locations of productive wells and distribution of NSS structural elements. Specifically at: (1) intersection of Najd shear zones and fault systems, (2) intersections of two or more fault systems, (3) intersections of Najd-related dykes with main valleys, and (4) within tectonic mélange. Locations with similar settings should be targeted for groundwater exploration. Using isotopic, geochemical, field, and remote sensing data we show: (1) aquifers cropping out at the foothills of the Red Sea mountains were recharged by precipitation over high-elevation mountainous areas, and/or by precipitation during moist climate intervals of the late Pleistocene, (2) regional groundwater flow (ED: E to W; EQ: W to E) discharges via deep-seated fault systems defining the River Nile and Gulf of Suez complex (Egypt) and in extensive inland sabkhas in SE Arabia. Using calibrated groundwater flow models for discharge areas (Wadi Asyuti) along the River Nile and assuming similar geologic settings and discharge rates around the River Nile and the Gulf of Suez, an estimated 70 x 10⁷m³/yr of groundwater may be available for sustainable development. Utilization of groundwater discharged in Arabian sabkhas is hindered by excessive salinization (TDS up to 92,000 mg/L) due to dissolution of salts from sabkhas and/or salt diapirs and concentrated by significant evaporation (δH values ranging from –34‰ to +19‰). Instead, efforts should concentrate on harvesting groundwater in areas west of the sabkhas/salt diapirs.