Hydrogeological and Hydrochemical Features of Wadi Adam,... 121 JKAU: Earth Sci., vol. 16, pp:121-139 (2005 A.D. / 1426 A.H.) 121 Hydrogeological and Hydrochemical Features of Wadi Adam, Makkah Al-Mukarramah Area ALI M. SUBYANI Faculty of Earth Sciences, King Abdulaziz University, Jeddah, Saudi Arabia Received: 14/9/2004 Revised: 19/3/2005 Accepted: 24/5/2005 ABSTRACT. The aim of this research is to assess the groundwater quan- tity and quality potentials of Wadi Adam as an additional strategic fu- ture water supply for Makkah Al-Mukarramah area. Wadi Adam is one of the undeveloped Arabian Shield Wadis, located 50 km south of Makkah Al-Mukarramah city. This Wadi drains a catchment area of about 380 km 2 and receives a moderate amount of rainfall of about 160 mm year 1 . Water table map was constructed for the existing un- confined alluvial aquifer. The hydraulic gradient is about 0.008. Aver- age transmissivity of 142 m 2 day 1 were calculated and the average storativity value is about 0.1, which indicated that the aquifer in this area is of moderate potential. The recharge rate to this basin, using chloride mass-balance method, is about 3 × 10 6 m 3 /year. The amount of the natural discharge into the Red Sea is about 0.9 million m 3 /year. The hydrochemical study indicated that the average total dissolved solids of the groundwater is 1500 mg/l. This means that this ground- water is suitable for irrigation and non-drinking purposes. Concentra- tions of trace elements are generally within the normal limits. Introduction The development of water resources programs in Saudi Arabia is the essential target of the government planning. Major wadis in Makkah Al-Mukarramah area, such as Fatimah, Naaman, and Khulais, have been developed and used for groundwater supply. The groundwater in these wadis is highly decreasing with time due to the scarcity of rain, extensive use for irrigation, domestic and in- dustries. The search for development of new water resources in this area is con- sidered among the top priorities as the consumption of water is rising with time, especially in Hajj and Omrah seasons. In the mean time most of water supply