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Please use this identifier to cite or link to this item: http://hdl.handle.net/123456789/3473

Title: ASSESMENT ON THE HYDRAULIC PROPERTIES OF THE ETHIOPIAN ASHANGE FORMATIONS
Authors: SEID, GETAHUN
Advisors: Seifu Kebede(Dr.)
Dereje Ayalew(Dr)
Keywords: Ashange
Flood basalts
Aquifers
Pumping test
Theoretical relations
Transmissivity
Specific capacity
Copyright: Jun-2011
Date Added: 24-Jul-2012
Publisher: Addis Ababa University
Abstract: The Ethiopian Ashange formation is an extensive development of fissural and central type eruptions in Oligocene period (~ 30 mas) that produced a thick succession of the trap serious basalts that forms mainly the north western and southern Ethiopian plateau (see Fig.3). The Ashange basalt is thus considered to be the lower formation in the stratigraphy of Ethiopian volcanic plateau commonly injected by dolerite sills, acidic dykes and other intrusions. It covers an area and volume of about 85,000km2 and 66,300 m3 respectively contributing to 37 % of the overall volume of Ethiopian continental flood basalts. A total of 70 wells raw pumping test data are analyzed and used besides their respective lithological log to determine hydraulic property of Ashange formation. The dominant aquifer types recognized after analysis are consolidated, confined, double porosity and single plane vertical fractured aquifer systems. Ashange formation shows decreasing aquifer productivity with respect to increased drilled boreholes depth and age of formation. The established relationship between T and Sp.Ca data also shows R2 value 0.957 that shows Sp.Ca can be used as fair estimator of T in areas with only Sp.Ca data. A relatively less well loss coefficient is observed in the Ashange formation where the existing variation still indicates the existence of improper well site location, improper well design and construction factors and well yield deteriorations with time due to clogging, corrosion and incrustation activities of well screens. Comparison of transmissivity values of the Ethiopian Ashange formation with other continental flood basalts of the world shows a decreasing trend with respect to age which may be related to the gradual closing up of open spaces like fractures by secondary materials hindering free flow as well as storage of water .The productivity of Ashange formation can be generally categorized as moderate to high which is controlled by location and geomorphologic setup of the formation outcrop; hydrothermal processes and nature; extent, frequency and orientation of the associated structural features and nature and degree of weathering. This work can be considered as an effort to characterize the whole aquifer system of Ethiopia for a better understanding of the available ground water reserve and distribution for further use in developmental activities.
Description: A THESIS SUBMITTED TO THE SCHOOL OF GRADUATE STUDIES IN PARTIAL FULFILLMENTS OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN HYDROGEOLOGY
URI: http://hdl.handle.net/123456789/3473
Appears in:Thesis - Earth Sciences

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