Application of electrical resistivity for groundwater exploration in Wadi Rahaba, Shalateen, Egypt

Shalateen area is located on the Red Sea coast at the southeastern part of the Eastern Desert. It is suffering from shortage in fresh water, where the main source of water is the rain water. Desalinated water is another source but it is more expensive. So, groundwater is the alternative solution to face the gap between the water demand and available water in this area. Vertical electrical sounding (VES) is considered as one of the most common methods in groundwater exploration. Twenty Schlumberger VES's with maximum current electrode spacing of 400 m were carried out in the coastal zone of Shalateen area at the alluvial fan of Wadi Rahaba. The obtained data were processed and interpreted qualitatively and quantitatively. The geoelectric layers that were detected in the study area are Quaternary dry alluvial sediments, Quaternary alluvial deposits and Miocene sandstone aquifer, clay lens, sill, fractured basement, non-fractured basement. The Quaternary alluvial deposits and Miocene sandstone represent the main shallow aquifer in the study area. The salt water appears at the eastern part while fresh water is concentrated at the western part. Resistivity values of the fresh to slightly brackish water ranges between 38.6 and 98.4 Ω·m with thickness varies from 1.18 to 24.4 m and depth range between 1.31 and 19 m. Clay lenses appear in the alluvial fan channel with resistivity values ranges between 1.3 and 9.1 Ω·m and thickness varies from 2.1 to 13.7 m. The fresh coastal aquifers are affected by set of faults. These faults appear in all profiles distributed orthogonally through the study area. In the study area, a fractured sill intrusion is intruding the groundwater aquifer. It is located near a granodiorite-tonalite exposure with resistivity values (230-315 Ω·m) at (5.6-16.4 m) depth. Basement is also detected at shallow depths especially in the western part of the study area.