Natural Hydrochemical Variations and Anthropogenic Influences on Surface Water and Ground Water Systems in the Selected Urban Centers in the Upper Awash Basin

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Date

2004-06

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Addis Ababa University

Abstract

The study areas are found in the upper Awash River basin situated in the central part of the country. The study areas (Debre Zeite, Mojo and Nazret) are the selected urban centres from the upper Awash River basin. The town of Debre Zeite is located at 8045'N latitude and 38058'E longitude; Mojo is located at 8036'N latitude and 39005'E longitude and Nazret is located at latitude 8032'Nand 39016'E longitude. Collection of water samples from surface (streams/ rivers, Lakes, and rainwater) and groundwater (boreholes, spring) was done in two field work periods in the year 2003/4. The physical parameters such as appearance, turbidity, colour and odour of the ground water are in good condition. But, surface waters are contaminated. The pH values of both groundwater and surface water in the areas range from 6.6 to 9.21. The conductivity and TDS values of all groundwaters in the study areas are lower than 1000mg/i. Le., groundwater is classified as fresh water. But, the conductivity and TDS values of certain surface water bodies are greater than 1000mg/i. The high values were recorded in crater lakes from Debre Zeite area and the polluted Mojo River from Mojo area. The ground and surface waters of the areas can be classified as dominantly as very hard water types. From the available water chemical analysis results of Debre Zeite area crater lakes are all sodium -bicarbonate type water and artificial lakes, boreholes and hand dug wells show calcium-magnesium- bicarbonate type water. On the basis of these major chemical constituents, it can be indicated that the chemical composition of the waters are continuously enriched by calcium and magnesium cations and bicarbonate anion due to the effect of the interaction between waters and the geological formations through which they reside and move. The waters from Mojo area show both calcium and sodium- bicarbonate type water. However, sodium- bicarbonate type water is the dominant water type in the area. The chemical analysis results of water from Nazret area also show the dominant waters are sodium- bicarbonate type water. The major ions constituent the waters from Mojo and Nazret areas are characterized by higher content of sodium and bicarbonate. The chemical and bacteriological analyses of surface and ground water samples confirmed the OCCUlTences of pollutants, which are organic and inorganic nutrients and micro-organisms in their origin. This is mainly attributed to the improper waste disposal from industrial and municipal sources. The major sources of water pollutant in the area include liquid and solid wastes generated from industries, municipal and agricultural activities. The extent of pollution is not unifOlUl through out the areas. It varies from highly polluted or affected to slightly affected areas. Highly affected areas are Mojo river at the vicinity of the town due to direct discharge of both industrial and municipal wastes, central palt of Nazret town due to municipal wastes, Awash river down the stream and Shimbira Meda seasonal stream due to agricultural wastes. The protective measures to be taken in order to protect surface and ground water are not to dump industrial and municipal wastes on surface water bodies prior to the necessary treatment.

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Hydrology

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