Ground Water Resources Evaluation of Walga River Basin Central Ethioipia, South West Shoa
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2005-03
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Abstract
Hydrometreological, geological, hydrogeological, hydrochemical investigation, basin & lake
water balance calculation were made for groundwater resource potential evaluation of Walga
Basin.
Walga basin is part of the western central Ethiopian plateau.Geological investigations reveal
that Walga area is found in the east-west trending Yerer-Tullu Welel volcano –tectonic
structures and three litho-stratigraphic succession prevail in the area, which include
Precambrian basement, Mesozoic sedimentary rocks and Cenozoic volcanics.
Annual precipitation of the basin calculated from long term mean monthly rain fall data is
1259mm.The actual and potential evapotranpiration for the basin are 853mm and 1080mm
respectively. The amount of evaporation from open water body (lake) is 6.6 Mcm.Of the
total rain fall ,17.9% leaves the basin in the form of surface runoff and 13.8 % water
infililtrate with in the basin which is the annual recharge of the basin.
Most perennial streams emerge from the base of mountains in this area and drain the basin as
gaining streams throughout & showing structurally controlled frow path.This also indicates
that groundwater plays very crucial role in the hydrology of the basin.
Based on qualitative and quantitative analysis of aquifer characterstics,the basin is
categorized in to three aquifer sytemswhich are low,medium & high productivity
aquifers.The scoraceous basaltic aquifer around Woliso area is the best well field with high
well yield & permeability.
Hydrogeological and geological maps are prepared from areal photographs and Satellite
images & Field observations.Land sat –TM image is used also to identify lineament or
structures in the basin together with areal ophotographs.
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Walga