Evaluation of Hydraulic Parameters in Old Akaki Well Fields
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Date
2018-03
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AAU
Abstract
The primary objective of this study is analysis and evaluation of pumping test data to
determine the aquifer hydraulic property of the Old Akaki bore holes by using Thies curve
matching method; Cooper Jacob and Thies recovery method on excel sheet and aquifer test
software. The proposed ground-water sources are from two main well-fields, Old Akaki and
North Fanta, located at the suburb of Addis Ababa city. Old Akaki well field is located at
about 22km South of Addis Ababa and East of Akaki Town. The abstracted water from Old
Akaki well-field is able to serve various condominium sites in Kilinto & Koye Feche. In
addition_ it serves other areas along the way & nearby the condominium sites in Akaki Sub
City with additional supplies from North Fanta Well field.
The transmissivity values obtained in this research has great variation from the study of
WWDSE which accounts for 97 to 2000%. Among the eight wells analysed four wells have
overestimated transmissivity, two wells underestimated and for two wells final result has not
been obtained because of poor fitting of the Thies curve. The overestimated Transmissivity
envisions good aquifer with better yield than the capacity of the aquifer. The underestimated
Transmissivity values found to have lower yield than their discharging capacity.
The well efficiencies were also computed for the expected yield (as suggested in the well
completion report). The results clearly show that majority of the wells (five wells out of the
eight tested wells) were found to work below the recommended operational efficiency. A
well is considered acceptable if it works above 65% efficiency. Within tested wells only one
well works in recommended efficiency range. Such a result clearly shows that the seven wells
have already failed during design phase as they are expected to yield the values
recommended in their well completion report. Such huge yield expectation from the wells
will create a larger draw down in the well that the pump inside the well will no longer be
sustainable. Therefore, in this evaluation it is recommended to conduct multiple well tests to
determine the actual hydraulic parameters of the aquifer in order to obtain the safe yield of
the wells which is intended to prolong the productivity of the aquifer and to delay excessive
loss of saturated thickness.
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Keywords
Hydraulic Parameter, Akaki Well Fields