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Title: APPLICATION OF INTEGRATED GEOPHYSICAL TECHNIQUES TO MAP GROUNDWATER POTENTIAL ZONES AND GEOLOGICAL STRUCTURES AT GELCHET AREA, BORENA ZONE, SOUTH ETHIOPIA
Authors: Mulugeta, Chanie
Advisors: Elias Lewi(Dr.)
Tigistu Haile(Dr.)
Keywords: geophysical techniques
Gelchet
Borena
Copyright: Feb-2011
Date Added: 24-Jul-2012
Publisher: Addis Ababa University
Abstract: Integrated geophysical survey using vertical electrical sounding (VES) and gravity (with differential GPS) methods were conducted to investigate groundwater potential zones and geological structures at Gelchet area, Borena zone, South Ethiopia. The main objectives of this study were to map groundwater potential zones and determine depth to the basement. Geologically, the area is located within the Cenozoic volcanic plain that followed by Precambrian crystalline basement rocks to the southeast of main Ethiopian rift. The data acquired from twenty eight (28) VES points using Schlumberger electrode array with maximum half current electrode spacing (AB/2=1000m) and 115 gravity points (supported by high accuracy height control from GPS method) were interpreted both qualitatively and quantitatively in order to understand the local 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 gravity profile plots and different gravity anomaly maps. Finally, the overall qualitative interpretation was done by integrating all the above results together with the geologic , topographic maps and borehole information. As a result of this, geologic structures and groundwater potential zones are identified and drilling sites are recommended. The quantitative interpretations of the VES data were conducted by modeling the VES data using Resix-Ip and WinResist modeling softwares and constructing geoelectric sections along selected survey lines, using the result from individual VES point interpretations. The depth and lithologic units from the boreholes were used to fix parameters during the modeling of VES data. The information from the VES data and the boreholes were used to constrain the depth information in the gravity modeling which were conducted on two survey lines. The VES results of the data revealed four main geoelectric layers which differ in degree of weathering, fracturing, composition and depth of burial. The geoelectric sections enabled to identify the overburden thickness and the depth to the aquifer along survey lines whereas the gravity model helped to identify basement undulation in places where there is no VES data. Moreover, the vertical electrical sounding survey helped to identify groundwater potential areas and determine the depth to the aquifer whereas the gravity survey helped to map the basement topography and identify places having high groundwater reservoir potential.
Description: A THESIS SUBMITTED TO THE SCHOOL OF GRADUATE STUDIES OF ADDIS ABABA UNIVERSITY IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN EXPLORATION GEOPHYSICS
URI: http://hdl.handle.net/123456789/3474
Appears in:Thesis - Earth Sciences

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