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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Keywords
Hydrology