Assessment on Interpretive Technique of Transmissivity and Storativity on Aquifers: Case of Legedadi Deep Wells.
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Date
2016-05
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Addis Ababa
Abstract
Urban part of our country has seen a very dramatic expansions and population growth in the past two decades. Addis Ababa is one of the major city that’s affected by this expansion and population growth. Due to this the water supply demand for the city has also increased dramatically. To meet this ever growing demand Addis Ababa Water Supply and Sewerage Authority has been developing groundwater around Addis Ababa area. One of these groundwater developments is in Legedadi well fields. The Legedadi well field’s yield capacity is estimated to be around 45,000m3/d. This potential will be harvested by development of 40 deep wells in the area of which 10 deep wells have been constructed and tested around Legedadi Legetafo Ayat areas. This ten wells have been drilled with average depth of 300m and are sparsely located over the Legedadi well filed. The currently drilled and developed ten well in the well fields do not have an observation well thus, they are considered as a single well tests. The drawdowns for each of the well is measured in the drilled well itself and the analysis is based on this drawdowns. The fact that effects of partial pentation and well head loss have not be counted in the analysis of the wells caused the transmissivity and storativity to vary greatly form the true aquifer nature in the Legedadi well fields.The two major emphasise that was given in this research when trying to determine the transmissivity and storativity using the Copper-Jacob method, Theis method and recovery method is the well efficiency and the effects of partial penetration of the wells. When the well efficiency was determined for the wells, for two wells there efficiency fail drastically below the accepted range of well efficiency and grater partial penetration effect was observed in two other wells. When this three methods are applied to this for the observed and drawdown data the result of the transmissivity and storativity greatly differ from the values that’s is determined when the head loss in the well is considered using the well efficiency or effect of partial penetration. Thus this indicates the well to be over pumped or underestimate in some case in this ten wells.
Key words: - Addis Ababa Water Supply, Legedadi Well Fields, Partial Penetration, Storativity, Transmissivity and Well Efficiency
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Keywords
Addis Ababa Water Supply, Legedadi Well Fields, Partial Penetration, Storativity, Transmissivity and Well Efficiency