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Title: Water Quality and Groundwater
Other Titles: Akaki River Interaction in the Sekelo Basin (Lower Akaki River Sub-Basin)
???metadata.dc.contributor.*???: Dr. Tenalem Ayenew
Prof. Paolo Billi
Ali, Aynalem
Issue Date: May-1999
Publisher: Addis Ababa University
Abstract: The thesis presents the results of geological, hydrogeological and hydrogeochemical studies in the Akaki subbasin (Sekelo). This study was to provide an overview of the water quality and the mixing of the groundwater and the surface water. In the study the geology and the hydrogeology of the area was investigated to provide basic information concerning the different lithologies and the local and sub-regional groundwater flow patterns. The chemistry and the stable isotopic composition of both the groundwater and the river water were considered in order to understand the nature and origin of the waters and to further explain groundwater and river water mixing patterns. Analysis of the relationship between rainfall and Akaki River shows that the highest flow and level in the river correspondences to the rainy season (June-September). Therefore, influent condition is anticipated during this rainy season. Preliminary water balance estimates using soil moisture budgeting method in the study area suggest 137 mm groundwater recharge annually. Geological and hydrogeological mapping of the Sekelo basin was conducted in the field and mainly from aerial photograph interpretation. a detailed study of the geology and the hydrogeology was carried out in the Akaki Well Field D. The rocks of the area are generally volcanic rocks with only minor fluvial sediments. The volcanic rocks are distinguished into lower basalt flows and young basaltic scoria and lava. Hydrogeological data were collected. These are information from 34 boreholes in the Akaki Well Field D abstracted from records and supplemented by data collected in the field. The types of data collected included lithological information, aquifer parameter data and borehole construction details. Analysis of these data has shown that on regional scale the groundwater flows from the water divide to the discharge area on the river valleys. The permeability‚Äôs of the volcanic rocks in this area are generally high. The important aquifer in the area is the lower basalt in which the aquifers are found in the fractured volcanic and are usually semi-confined. The young basaltic scoria is the main recharge area. Water samples for hydrochemical and stable isotopic analysis were taken from 9 sites both from the groundwater and river water. Chemical analysis data of 27 boreholes in the Akaki Well Field D was collected from Addis Ababa Water Supply and Sewage Authority (AAWSA) 1996-97. In addition, stable isotopic data of rainfall for Addis Ababa were collected from International Atomic Energy Agency (IAEA) Vienna. Correction was made on these data for altitude difference to get the local meteoric water line. Analyses and evaluation of these data enabled to obtain information on the nature of the water, in particular the mixing between the groundwater and the river water. The chemical analysis of the groundwater and the river water shows similar Ca-Mg bicarbonate water type. Based on U.S. Environmental Protection Agency's (USEPA) drinking water standard the groundwater proved to have good quality. However the river water which is remarkably influenced by human activities is highly polluted. The evaluation of the chemical composition and stable isotope techniques led to the conclusion that the groundwater can be explained in terms of mixing series between the rain water and the river water.
Description: A Thesis Submitted to the School of Graduate Studies Addis Ababa University in Partial Fulfillment of the Requirement for the Degree of Master of Science in Geology.
Appears in Collections:Thesis - Earth Sciences

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