No abstract

Wadi Yalamlam is one of the Arabian Shield Wadis, located 70 km south of Makkah Al-Mukarramah city. The main rock units consist of Precambrian crystalline, meta−volcanic and metasedimentary rocks, with local Tertiary and Quaternary basalt flows AEThe geographic setting of Wadi Yalamlam basin can be divided into three main zones: the Red Sea coastal plain (Tihamah), the hills, and the Scarp-Hijaz Mountains. The catchment area starts from the Hijaz Escarpment (Ashafa area) in the east to the Red Sea at the west AEMorphometric analysis of the basin shows that it drains a large catchment area of about 1600 km 2 , very elongated, high relief, and of a moderate drainage densityAE The mean annual and seasonal rainfalls of hydrological stations around the study area have been analyzed AESeasonal rainfall occurs in the mountains area, but varies from year to year. It often occurs as thunderstorms of high intensity during a local storm followed by dry periods. The average annual rainfall exceeds 200 mm in the mountains and decreases to 80 mm towards the Red Sea coast. In addition, Wadi Yalamlam has surface running water in the upstream most of the year. Runoff hydrographs of 0.5 hour duration were constructed, based on Snyder method, for three sub-basins of wadi Yalamlam.

ABSTRACT. R-mode Factor analysis was used to interpret collected data concerning the groundwater chemistry from the shallow coastal plain aquifer and relating them to specific factors that brought about changes in the water quality. Five factors, accounting for nearly 81% of the total variance, were identified. These factors reflect different chemical processes that control the groundwater chemistry. Factor 1 reflects the most important process; namely the intensive evaporation which resulted in the highly mineralized water. Other processes that could be associated with this factor include the chemical weathering of silicate minerals, ion exchange reactions and mixing processes. Factor 2 represents the precipitation and dissolution of carbonate minerals (calcite and dolomite). Factors 1 and 2 could be considered the major factors controlling the chemical composition of the groundwater since they account for 50% of the total variance and together, they produce a chemical population ranging from low to extremely high saline water, which is confirmed by the chemical analysis results. The other three factors, which dominate the chemical processes, include oxidation of pyrite, groundwater pollution and solubility of silica. They could, therefore, be considered as contributor factors to the groundwater chemistry in an overall scale. Distribution score maps of the first four factors were constructed to delineate their relative spatial impact.