Investigation of groundwater occurrence using gravity and electrical resistivity methods: a case study from Wadi Sar, Hijaz Mountains, Saudi Arabia

An integrated approach of Gravity Recovery and Climate Experiment (GRACE) and vertical electrical resistivity sounding (VES) technique has been carried out to investigate regionally and locally the groundwater potentialities of Wadi Sar in the Hijaz Mountains. Our findings are (1) the terrestrial water storage variations (ΔTWS) are estimated at −2.06±0.34 mm/year; (2) the Global Land Data Assimilation System–derived soil moisture storage variations (ΔSMS) are estimated at −0.067±0.005 mm/year; (3) the groundwater storage variations (ΔGWS) show a negative trend estimated at −2.00±0.34 mm/year during the period April 2002–July 2017; and (4) the average annual precipitation (AAP) rate is estimated at 115 mm during the period 2002–2018. Three geoelectrical layers are identified from the inversion of the electrical resistivity data: (5) the surface layer of high resistivity values is consisted of dry unconsolidated Quaternary deposits; (6) the second layer represents the fractured groundwater aquifer of low resistivity values and variable thickness; (7) the third layer is composed of fractured basement rocks of higher resistivity values. The streams are draining the surface water toward the Najd Pedi plain aquifer; (8) the faults are acting as conduits for groundwater flow away from the Wadi. The current study indicates the occurrence of groundwater at the downstream zones of the Wadi Sar, but with a general decrease trend. The integrated approach provides a better understanding of the groundwater potentialities in the arid regions.