INTEGRATED GEOPHYSICAL TECHNIQUES TO DELINEATE THE GROUNDWATER ACCUMULATION IN WADI HAFAFIT, EASTERN DESERT, EGYPT

The area under study extends in wadi Hafafit covering about 10km2. It occupies the southern portion of the Eastern Desert, and is characterized by arid climate most of the year. Geomorphologically, the area lies in the Red Sea mountainous belt (igneous and metamorphic rocks) dissected by wadi Hafafit which covered by wadi deposits. It characterized by high land surface that generally slopes southeastward.
The aim of this study is to delineate the groundwater accumulation and to find out suitable sites for drilling some water wells and testing the subsurface sequence to construct dams for supplying the study area with groundwater for development and to decrease the danger effect of the flooding. It is also aimed to determine the distribution of the main aquifers and the effect of the subsurface structures on these aquifers by using integrated geophysical techniques and aid of the drilled wells data.
For this study, ten Vertical Electrical Soundings (VES’es) of Schlumberger configuration, the 2D electrical resistivity imaging and the shallow refraction seismic profiles were carried out. The field data have been interpreted both qualitatively and quantitatively, in which geoelectrical profiles are constructed to evaluate the groundwater aquifers and to show the effect of the subsurface structures on the groundwater. The geoelectrical interpretation showed that the succession of the area consists of three geoelectrical layers (“A”, “B” and “C”). Layer “A” is adry wadi deposit and layer “B” represents the water bearing formation of wadi deposit, while layer “C” represents the basement rocks and is divided into two sub-layers, the upper one “C1” is water bearing layer of fractured basement, while the lower one”C2” is massive basement rocks having the highest resistivity value in the area.
The area is influenced by faults which resulted in uplifting or downlifting of the basement rocks at different levels reflecting the influence of the subsurface structures on the geologic succession and consequently, the groundwater occurrences. The integrated results obtained from the geoelectric (VES &2D) and geoseismic surveys shows that the potentiality of water bearing formation is good in the NW part of the study area due to presence of a graben structure forming the suitable thickness of wadi deposits and fractured basement rocks, while it is of limited potentiality in the SE part due to the uplift of the basement rocks. Generally, the groundwater potentiality decreases with depth due to presence of massive basement rocks at shallow depth, and the location of VES 7 is recommended suitable site for constructing the dam due to its shallow depth to basement rocks, acting as barrier. This dam will increase the recharge of the near surface aquifers and help in the increasing the quality of the groundwater in the study area.