مجلة النيلين لعلوم الارض

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Subject: search.filters.subject.Red Sea Hills

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    Calibration of geo-electrical measurements using borehole data for groundwater investigation in basement rocks in Wadi Orshab watershed, Red Sea State, Sudan
    (Faculty of Petroleum and Minerals, 2019) Mohammed Noor M. H. Hassan, Abdalla E. M. El Sheikh; Khalid A. Elsayed Zeinelabdein
    Orshab is a well-known gold prospective area in the Red Sea Hills of NE Sudan. Mining industry is now rapidly growing in this part of Sudan. Orshab watershed represents a main source of safe water for the mining companies as well as for artisanal miners and local people. Despite this fact, the area suffers from acute shortage in fresh water supply, since the area is mostly covered by crystalline basement rocks. Therefore, the overall objective of the present study is to investigate the groundwater occurrence in terms of the depth and thickness of viable aquifer using geophysical methods supported by some borehole lithological data. This requires appropriate and efficient techniques suitable for finding groundwater in such challenging conditions. Traditionally, electrical resistivity methods are generally used in similar investigations. In fact, resistivity measurements cannot be related directly to the lithological type in the subsurface without sampling or support of other geophysical or lithological data. Moreover, depth to the water bearing formation is not accurately estimated through the resistivity methods. Accordingly, the need for calibration of the measured values is crucial in this case. To this end, two VESs were measured close to productive boreholes situated within the investigated area. The extracted information from the interpretation of the two VESs supported by borehole lithological data revealed that the depth of the geo-electric layer is equal to AB/2. Accordingly, this finding will be used in the interpretation of the all the VESs acquired within wadi Orshab. Twenty-five Vertical Electrical Sounding measurements were recorded. The interpretation of these data revealed the presence of different geo-electric layers in the sub-surface. The geo-electric layers are topsoil and alluvial deposits. The top layer was found to have resistivity varying from 1997ohm-m - 27 ohm-m. Its thickness was found to be around 5m. The second and third layers have thicknesses ranging from 2m to 10 m and from 20 m to 45 m, respectively overlying the basement. The present study showed that two types of water bearing formations are present within the watershed: alluvial deposits and weathered basement. The maximum depth of aquifer in the investigated area was found to be 65 m approximately. Therefore, this is the recommended depth for drilling any new boreholes for sustainable water supply in Wadi Orshab. The obtained results from the calibration of the acquired data enhanced the interpretation of the resistivity data and produced depth estimations that are very close to the actual depth. Consequently, this method should be used in area with similar geological setting.