Gravity and Electrical Methods for Groundwater Resoures Potential Assesement and Mapping of Aqufiers, Wobok-Dilo Area, Borena, South Ethiopia

Abdisa, Kawo Koji (2011) Gravity and Electrical Methods for Groundwater Resoures Potential Assesement and Mapping of Aqufiers, Wobok-Dilo Area, Borena, South Ethiopia. Masters thesis, Addis Ababa University.

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Abstract

A combined geophysical survey using vertical electrical sounding (VES) and gravity methods was conducted to investigate groundwater potential zones and geological structures at WobokDilo area, Borena zone, in South Ethiopia. The area being dominantly of basement rock lithology with interspersed volcanics and with scarcely known groundwater potential, the main objectives of this study were to map groundwater potential zones and determine depth to the basement. Geologically, the Wobok-Dilo area lies on dominantly volcanic terrain. The exposed basaltic formations over the area are highly vesicular and scoracious basalts. The geophysical surveys included twenty one (21) VES points, using Schlumberger electrode array ,with maximum half current electrode spacing AB/2=1000m and 103 gravity measuring points. These were interpreted both qualitatively and quantitatively in order to infer the subsurface geology and identify aquifer bearing horizons. The qualitative analysis of VES data were performed by using pseudodepth sections and different apparent resistivity maps. Similarly, the qualitative interpretations of gravity data were performed by using different gravity anomaly maps. The quantitative interpretations of the VES data were conducted by modeling the VES data using ResixIP and WinResist modeling software and constructing geoelectric sections along selected survey lines, using the result from individual VES point interpretations. The depth and lithologic units from the borehole was used to constrain the parameters during the modeling of VES data. The information from the VES data and the borehole were also used to constrain the depth information in the gravity modeling which were conducted on one survey line. The VES results revealed six to seven main geoelectric layers which differ in degree of weathering, fracturing, composition and depth of burial. The geoelectric sections enabled to identify the depth to the aquifer along survey lines whereas the gravity model helped to identify basement undulation and map structures. Finally, the overall interpretation was done by integrating all the above results together with the topographic maps and borehole information. As a result of these, geologic structures and groundwater potential zones are identified and drilling sites for potentially productive boreholes are recommended.

Item Type:	Thesis (Masters)
Subjects:	Q Science > QE Geology T Technology > T Technology (General)
Divisions:	Africana
Depositing User:	Selom Ghislain
Date Deposited:	13 Jun 2018 09:17
Last Modified:	13 Jun 2018 09:17
URI:	http://thesisbank.jhia.ac.ke/id/eprint/4203

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