Daddi, Gaddissa Deyassa (2015) Aquifers Developed on Basement Rocks of Ethiopia: Their Genesis, Properties and Classification. PhD thesis, Addis Ababa University.
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Abstract
The basement rocks of Ethiopia were traditionally described as a system of regional aquiclude. This attribution ignores regional differences in aquifer properties, structure and functioning. In contrast, this work presents how the interactions of evolutionary and modern geological processes determine aquifer development and hydrogeological characteristics of the basement terrain of Ethiopia. It specifically addresses the role of geomorphic history (deep weathering and stripping) in affecting aquifer genesis and their control on vertical and spatial heterogeneity. In addition, the study provides field evidences for existing literature based weathering-stripping model previously developed for the country. Detailed examination of geological, hydrological and hydrogeological evidences enabled the understanding of the causes of regional variation in aquifer properties. The aquifers exhibit noticeable regional differences. Thus, conceptual hydrogeological model depicting three coherent categories of aquifers are developed: (a) in western basement terrain, aquifer is relatively extensive in the thick weathered mantle over fractured bedrocks of low to high-grade metamorphic rocks. High groundwater storage but low hydraulic conductivity characterizes this aquifer. (b) in the northern, groundwater occurs in fractures and discontinuities in bedrocks toward the surface and tectonically induced relatively deeper fracture zones. These aquifers have high hydraulic permeability but low storage capacity. (c) in the Borena lowlands of southern basement region, groundwater occurs in wadi beds, fractures, and preferentially weathered mantles. The orientations of wadi beds follow regional fractures, which control groundwater flow regime and enhance preferential weathering of bedrocks. Aquifers are of intermediate type with regard to hydraulic properties. The variations in low-flow indices and shapes of flow duration curves of streams manifest contrast in bulk storage capacity and hydraulic conductivity of catchments in the three basement regions. This contrast has been used as evidences for characterization of aquifers.The implication of these regional differences on groundwater exploration and exploitation has been the subject of this study.
| Item Type: | Thesis (PhD) |
|---|---|
| Subjects: | Q Science > Q Science (General) Q Science > QE Geology |
| Divisions: | Africana |
| Depositing User: | Selom Ghislain |
| Date Deposited: | 01 Nov 2018 09:58 |
| Last Modified: | 01 Nov 2018 09:58 |
| URI: | http://thesisbank.jhia.ac.ke/id/eprint/7257 |
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