Geoelectrical Investigation for the Assessment of Ground Water Distributions in Becho Plain, South West Showa

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Date

2008-10

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Addis Ababa Universty

Abstract

This thesis work deals with the regional interpretation of electrical resistivity sounding, survey, carried out in the Becho plain, Southwest Showa. The principal objective is to study the ground water conditions such as depth to the water table, thickness and lateral boundaries of aquifer and possible flow direction. Parametric Transient Electromagnetic, sounding were also conducted at test borehole sites for calibration and comparison purpose. The geophysical survey was part of an integrated geotechnical work conducted by Water Works Design and Supervision Enterprise. The focus of this thesis work is interpretation thirty-one Schlumberger soundings with a maximum current electrode spacing ranging from 1.5m to1000m, from Becho plain and the surrounding area, and one Transient electromagnetic sounding, at Asgorie test well site. Interpretation of these soundings indicates the presence of a likely alluvial aquifer of 240m maximum depth and other water-bearing volcanic rocks, at the SW boarder the Becho plain. These volcanic aquifers show variable thickness and formation resistivity depending on composition and degree of saturation. Possible fault line is indicated in the eastern central part of the survey area and intrusion of volcanic rocks is identified near to the boarder line of southern part, possibly it may be the weak zone. In general, four geoelectrical layers are identified in this thesis work. These are the top layer, alluvium, aquifer and bedrocks. The top layer consists of mostly clay and silt. The alluvial consists of unconsolidated sediment such as sand, gravel and silt. The aquifer consists of unconsolidated sediment such as gravel, silt and in some part the basalt. The bedrock is consists of mostly basalt, ryyolite, and ignimbrite and fracture basalt

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Becho Plain

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