STRUCTURAL IMPACT ON THE GROUNDWATER OCCURRENCE IN THE NUBIA SANDSTONE AQUIFER USING GEOMAGNETIC AND GEOELECTRICAL TECHNIQUES, NORTHWEST BIR TARFAWI, EAST EL OWEINAT AREA, WESTERN DESERT | ||||
| Journal of Egyptian Geophysical Society | ||||
| Volume 8, Issue 1, 2010, Page 47-63 PDF (1.77 MB) | ||||
| Document Type: Original Article | ||||
| DOI: 10.21608/jegs.2010.380902 | ||||
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| Authors | ||||
| A.M. M. Al Temamy; M.S.M. Barseem | ||||
| Geophysics Department, Desert Research Center, (1) Mathaf El Matariya St-B.O.P.11753, Matariya, Cairo, Egypt. | ||||
| Abstract | ||||
| Delineation of the geologic setting is a prerequisite for understanding the possibilities and limitations of exploiting groundwater. East El Oweinat area represents one of the most promising regions to become the source of food for Egypt in the near future. This area is characterized by available groundwater and soil resources. Nubian sandstone aquifer that overlies directly the basement rocks represents the main water-bearing formation in this area. The geophysical survey in the present study involved carrying out 7 land magnetic profiles and 15 Vertical Electrical Soundings with the object of determining the depth of the basement rocks, the lithologic variations in vertical and horizontal directions, the thickness of water-bearing layers and detecting subsurface geological structures and their impact on the groundwater occurrence. The interpretation results of the modeled land magnetic profiles were used in construction of depth to the basement surface and level of the basement contour maps. These maps revealed that the depth to basement ranges from a few tens of meters in the south and middle parts to more than four hundred meters in the western and northern parts. This variation is due to the effect of structural faults which leads to a formation of a group of horests and grabens. These faults have more or less E-W, NE-SW, NW-SE and N-S trends. The E-W trend is the most dominant one. The interpretation of the resistivity sounding led to the detection of three main geoelectrical units, Unit “A” (dry wadi deposits and part of the Nubian sandstone), Unit “B” (water-bearing Nubian sandstone) and Unit “C” (Basement rocks).The Inferred structural faults from the constructed geoelectrical cross-sections confirmed well with that detected from the magnetic maps. The thickness of the Nubian sandstone aquifer as detected from geoelectrical study ranges from 71- 238 m with general increase northward. On the other hand, the depth to the basement was not detected at some sounding stations because the basement depths at these sites have a high value as indicated from the detected grabens at these locations .The resistivities of the water-bearing Nubia sandstone showed some anomalies with high resistivity values (more than 200 Ohm.m). These high values appear as a result of hydrothermal solutions that cause the rock more to be more massive, and consequently decreases its permeability i.e. decreases its hydraulic conductivity. The recommended sounding station sites for drilling are 3, 5 and 14 with recommended drilling depth ranging between 250 m at the southern part and increases northward to reach more than 400 m. A detailed geoelectrical study is required at the detected grabens from land magnetic results to detect whether the hydrothermal solution has any effect in these locations or not | ||||
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