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Computational Ecology and Software, 2023, 13(2): 27-42
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Article

Geophysical investigation of Ankashasha dam site, Southern Ethiopia

Gebre Gidey Weldeabzgi1, Mulugeta Markos Tediso2
1Depatment of Natural Resource Management, Dambi Dollo University, Ethiopia
2Department of Physics, Dambi Dollo University, Ethiopia

Received 7 February 2023;Accepted 1 March 2023;Published online 10 March 2023;Published 1 June 2023
IAEES

Abstract
The study area, Ankashasha dam site is found in South Nations, Nationalities and Peoples Regional state of Ethiopia. The overall objective of geophysical investigations in the study area is to assist geological studies to determine the depth of bedrock and estimate the probable seepage that might encounter dam reservoir areas. Vertical Electrical Sounding (VES) and two-dimensional electrical resistivity imaging survey methods were used to assess the safety of the Ankashasha dam. The data were acquired from four VES points using Schlumberger cathode arrays with supreme half current electrode spacing, and two-dimensional electrical resistivity imaging three profile data points were analyzed qualitatively and quantitatively to understand the geology and identify aquifer bearing horizons. The qualitative analysis of VES data was accomplished by using curves, apparent resistivity, pseudo-depths, and the quantitative interpretations of the VES data were constructed by the VES data using IpI-res3, IPI2win and Surfer software and constructing geo-electric section sideways profiles using the result from VES point interpretations and lithological information from the Bedesa borehole. The VES results of the data revealed three geoelectric layers that differ in degree of fracturing, weathering and formation. The bedrock is closer to the surface on the delineated fracture boundaries on the geo-electric section of the NE flanks of the axis. The overburden materials consist of seepage flow paths that widen northeastwards parallel to clay, sandy clay and clayey sand. Seismic refraction work should be forwarded since the area is seismically active to map the structures and determine parameters such as densities of each layer, weak zones, depth to contacts and others.

Keywords electrical resistivity;lithology;geophysical;topography;resistivity imaging.


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