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| 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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