Geophysical Investigations for Groundwater in a Complex Subsurface Terrain, Wadi Fatima, KSA: A Case History

Geological contacts in a complex subsurface terrain have favorable potentiality for groundwater; particularly in semiarid/or arid areas. Magnetic and DC resistivity surveys were proposed and conducted at Wadi Fatima for the groundwater exploration in this geologically complex media. Magnetic survey was used to delineate the basement structures which control the groundwater flow. On the other hand, DC resistivity profiling and sounding techniques were used to investigate and ensure the potentiality of the groundwater occurrence in the structurally complex basement. Magnetic data were subjected to analytic signal analysis, where it showed clearly the complexity of the study area. Many magnetic contacts were delineated at the maximum amplitudes of the analytic signal curves. Two selected profiles along the Wadi have been quantitatively interpreted using analytic signal, spectral analysis, horizontal and vertical derivatives. These analyses delineate the geological structures that may accommodate the groundwater. DC resistivity profiling technique was used along one profile, to define the effect of the basement structures on the ground water distribution under this profile. On the other hand, Vertical Electrical Sounding (VES) was conducted at selected sites along the magnetic and DC profiles. Ground magnetic and DC resistivity techniques led to a better understanding of the study area. Thus, the integration of the obtained results from these two methods was successful to define new sites for drilling wells for the groundwater supply that would be at VES9 and VES7. It was recommended to conduct more detailed studies in the southwestern part of the study area.