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Please use this identifier to cite or link to this item: http://hdl.handle.net/123456789/2844

Title: GROUNDWATER RESOURCE ASSESSMENT IN THE GIDABO RIVER CATCHMENT IN THE SOUTHERN MAIN ETHIOPIAN RIFT PROVINCE./YIRGALEM-WONAGO
Authors: Birhanu, Debisso
Advisors: Dr. Tenalem Ayenew
Keywords: GROUNDWATER RESOURCE
GIDABO RIVER CATCHMENT
Copyright: Oct-2009
Date Added: 9-May-2012
Publisher: AAU
Abstract: The Gidabo River Catchment area is found within southern Main Ethiopian rift, North-east of Lake Abaya; or more specifically lies in Sidama and Gedio Zones of Southern region and Borena Zone of Oromia region. The Catchment area coverage and the perimeter of the Gidabo River are 3342.37 square kilometers and 305.25 kilometers respectively. Assessment of groundwater resource potential of the catchment is studied based on conventional hydrogeological techniques, by gathering and interpreting geological, hydrometeorological, hydrogeological and hydrochemical data. The Gidabo River Catchment area is dominantly covered by pyroclastic fall (flow) deposits and Trap-Series basalts with Trachytic compositions; alluvial and lacustrine deposits also cover considerable area of the Catchment. Using analysis of the available meteorological data, potential evapotranspiration (PET) was calculated by two methods; (i.e. Thornthwaite (1948) and Penman). PET values obtained by Thornthwaite method for Highland, Escarpment and rift floor are estimated to be 689.85mm 786.8mm and 1307mm respectively. Modified Penman approach is used only for calculating PET of the rift floor and gave the value of 1301mm. Actual Evapotranspiration (AET) was calculated using Turc and Soil water balance method. The AET values obtained by Turc method for Highland, Escarpment and Rift floor is 665mm, 950mm, 1456mm respectively. AET values obtained by soil-water balance method for the Highland, the Escarpment and the Rift floor are estimated to be 688.9mm, 803.9mm, 1063.6mm respectively. Conventional water balance method has been used to compute the total groundwater recharge of the basin and recharge value of 353mm/year is obtained. Ground water potential of the Gidabo Rive Catchment is seen to be under the control of fractures (faults) and weathering. Higher hydraulic conductivity zones are mapped at or near fractured regions and their values are decreasing away from the fractures (faults). Graphical presentation (i.e. Piper (1944)) is used in order to facilitate the interpretation and analyses of the chemical data. The piper plot shows that most boreholes and spring water samples are Ca-Mg-HCO3 type in the discharge area and Na-HCO3 type towards the recharge areas. The surface and shallow groundwater systems are characterized by high iron concentrations. The source is believed to be the red soils that cover the study area. According to Kedir Yasin (2002), the concentration of iron in the water is greater in the wet season than the dry season due to leaching effect. High concentration of fluoride within the study area is noticed in the western part (discharge area) in geothermal borehole and hot springs.
URI: http://hdl.handle.net/123456789/2844
Appears in:Thesis - Earth Sciences

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