Investigating the Groundwater Occurrence in Wadi Rahjan and Its Potential Contribution to Ain Zubaida Using Magnetic and Electric Methods, Makkah Al-Mukarramah, KSA

Abstract

Ground magnetic and DC resistivity surveys are imple- mented to explore groundwater in the northern part of Wadi Rahjan, Makkah Al-Mukarramah, Saudi Arabia. This part includes the down- stream area of Wadi Rahjan which flows into Wadi Nu'man where Ain Zubida is located. A system of E-W dikes is shown on available geologic map, which is cutting across the surrounding metavolcanic rocks and Wadi Rahjan stream. This study aims to locating the exten- sions of these dikes/discontinuities that may control the groundwater flow and distribution along this important part of Wadi Rahjan. Ground magnetic survey is utilized along wadi Rahjan and the mag- netic data are presented as contour map. Selected nine profiles are quantitatively analyzed using analytic signal analysis and horizontal gradient techniques. The present study reveals four discontinuities representing most probably dikes crossing the wadi. These dikes have great impact on the groundwater flow from upstream side to down- stream side reaching wadi Nu'man where these dikes act as barriers for groundwater flow. Electrical resistivity sounding using Schlumberger array is used along the wadi to delineate the extent of saturation zones, depth to basement, and to clarify the possible occurrence of the groundwater accumulations. It can be used also to show the effect of dikes occurrence on the groundwater flow and its distribution along this part of the Wadi. The study was successful in locating the water saturated zone and in determining its extension along the downstream part at the south of a major dike that partially prevents the groundwater flow to wadi Nu'man.