Application of Integrated Geophysical Techniques to Map Groundwater Potential Zones and Geological Structures at Woldia University and Mechare Meda,North Wollo Zone,North Ethiopia
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2018-06-03
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Addis Ababa University
Abstract
Integrated geophysical investigation using Vertical Electrical Sounding (VES) and Magnetic (with GPS coordinates) methods were conducted to investigate groundwater potential zones and geological structures at Woldia University and Mechare Meda, North Wollo Zone, North Ethiopia. The main objective of this study was to assess and evaluate groundwater potential of Woldia University and Mechare Meda and determines the location of preferred borehole sites and the depth at which the aquifers are located. The data acquired from twenty (20) VES points using Schlumberger electrode arrays with maximum half current electrode spacing (AB/2=700m) and 220 magnetic data points (supported by the high precision height control from GPS method) were analyzed both qualitatively and quantitatively in order to know the local geology and determine aquifer bearing horizons. The qualitative analysis of VES data was accomplished by using pseudo depth sections and different geoelectric sections. Similarly, the qualitative interpretation of magnetic data was performed by using 2D magnetic profile plots. Finally, the overall qualitative interpretation was done by integrating all the above results together with the topographic and geologic map, and borehole information.
The quantitative interpretations of the VES data were conducted by modeling the VES data using WinResist and Resix-Ip modeling software and constructing geoelectric sections along selected survey lines, using the result from individual VES point interpretations and lithological information from a different borehole. The VES results of the data revealed four main geoelectric layers which differ in degree of fracturing, weathering, and composition. Moreover, the vertical electrical sounding survey helped to determine the depth to the aquifer and identify groundwater potential areas, whereas the magnetic survey helped to map the basement topography and identify places having high groundwater reservoir potential. Generally, the result of interpretation specifies the study area composed of two aquifers, the first is the Upper Basalt aquifer, which is slightly confined between alluvial deposits (upper), and moderately fractured Basalt and Trachytes (lower) and the second is Lower Basalt aquifer which is confined by the moderately fractured Basalt. The depth of the upper aquifer is ranging from 20 to 60m while the depth of the lower aquifer is greater than 180m. The geological fractures found in the study area have orientation of NW–SE, and NE–SW.
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Pseudo and Geo-electric section, VES, GPS, Magnetic, and electrical method