CONTRIBUTION OF THE GEOLOGIC SETTING TO THE OCCURRENCE OF GROUNDWATER IN WADI MORRA, SOUTH SINAI, EGYPT, USING GEOELECTRICAL TECHNIQUES

Wadi morra represents a morphotectonic depression in which Exploration for the groundwater is a vital element. As this area is important for touristic and development projects. Geoelectrical techniques are conducted to detect the water-bearing formation and to delineate the effect of geologic setting on the groundwater occurrence. The interpretation results of 12 Vertical Electrical Soundings (VES) in the form of three geoelectrical cross sections lead to the detection of three main geoelectrical units (A, B and C) which equivalent to Quaternary deposits, Cambrian sand of Araba Formation and Pre-Cambrian basement rocks, respectively. Three connected water-bearing layers belongs to unit B were detected. Therefore these connected layers represent a good aquifer which exists under confined to semi confined condition. The variation of the lithology and thickness laterally and vertically along these layers has an impact on the groundwater occurrence in the investigated area.
In order to augment the feasibility of the geophysical results and to make them more illustrative and useful for decision maker, priority map for the groundwater exploitation have been constructed. Although the priority is restricted to the certain sites, the study area has generally, high groundwater potential where the lowest compiled thickness of the three water-bearing layers attains 83 m.
Seven normal faults were also detected from the constructed geoelectrical cross sections and the level to the top of the basement map. These faults have an impact on the occurrence of the groundwater in the concerned area, where they form consecutive alternation of grabens and horests which affect on the thickness of the water-bearing layers.
The two-dimensional imaging profiles were carried out at three consecutive selected sites with the purpose of verifying the detected structural faults. The interpretation results of these profiles are compatible with that of VES stations.
Key words: Morphotectonic, depression, Groundwater, Geoelectric, Water-bearing, Vertical Electrical Soundings (VES), Faults, Two-Dimensional Electrical Imaging (2-D)