Hydrogeological and Hydrogeochemical Characteriation of Beles River Basin, Northwestern Ethiopia

Addisu, Girma (2010) Hydrogeological and Hydrogeochemical Characteriation of Beles River Basin, Northwestern Ethiopia. Masters thesis, Addis Ababa University.

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Abstract

Beles River Basin is part of northwestern lowlands and its adjacent highlands. It is found in the southwestern direction of Lake Tana, It has the total areal coverage of 14,200 sq. Km and elevation varies from 500 to 2,700masl. The Basin has all climatic zones, except alpine. The objective of the thesis work was characterizing the hydrgeology and hydrogeochemistry of the basin using integrated methodology and approaches. Secondary data has been collected from the respective institutes and organizations and primary data of water samples for water chemistry was analyzed in the laboratory. The rainfall pattern of the Basin is unimodal. It has an aerial depth of precipitation of 1352.9mm/yr that was computed using isohyetal cotour map method. The precipitation condition has high orographic effect. The hydrograph of the two main rivers reflects the unimodality of the rainfall. The variation of these rivers discharge is very high from dry to rainy season that shows the infiltration of the Basin is low. The Basin has geology of Precambrian basement complex, undifferentiated formations, tertiary and quaternary volcanic and quaternary sediments. It has lithological units of gneiss and associated high-grade metamorphic rocks, low-grade supra-crustal metamorphic rocks, syn- and post-tectonic intrusive of acidic to intermediate composition, Cenozoic volcanic rocks, and quaternary sediments. The most important tectonic settings are dominantly aligned N-S and NE-SW direction. Hydrogeological map of the Basin was produced based on previous reports and maps and field observations of geology, topography and water point inventory, weathering and fracturing condition of the formations. Accordingly the hydrogeological characterization of the area revealed; porous aquifers (alluvium, colluviums), fissured and karst aquifers (marble), fissured aquifers (sandstone and volcanic rock), fissured aquifers of low potential (some non-carbonate metamorphic and intrusive rocks) and aquitards (some non-carbonate metamorphic and intrusive rocks). Accordingly the aquifer of the basin was classified in to very low, low, intermediate, intermediate to high and high productive formations. The regional recharge zones are the highlands of the Basin Such as; Wombera, Balay, Dangur and Kar mountains and highlands areas of Dangila and Achefer. The discharge areas are intimately linked with groundwater flow lines and the regional groundwater flow direction is to the southwest following the topographic gradient. Hydrochemical data shows that evolution of major ions, water types, and direction of groundwater flow. It shows a general trends increasing total ion concentration along flow direction. Graphical presentations of the physical and chemical parameters of the water samples provide a good deal of information on the characteristics of ground water flow systems, recharge and discharge zones, and evolution of major ions in the basin. The general natural water type of the basin is Ca dominated cation and HCO3 dominated anion (Figure6.9) and has low (fresh water range) TDS values. The TDS can be relatively grouped in to three groups (figure 6.9) low medium and high. But there are a very few samples with Na dominated cations and Cl dominated anions. In general the dominancy of bicarbonate ions shows the groundwater of the area is shallow.

Item Type:	Thesis (Masters)
Subjects:	G Geography. Anthropology. Recreation > GE Environmental Sciences Q Science > QD Chemistry Q Science > QE Geology
Divisions:	Africana
Depositing User:	Selom Ghislain
Date Deposited:	24 May 2018 14:31
Last Modified:	24 May 2018 14:31
URI:	http://thesisbank.jhia.ac.ke/id/eprint/4106

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