Hydrological and Hydrogeological Study on the Kulfo River Basin
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Date
1996-06
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Addis Ababa University
Abstract
The study area, the Kulfo River basin, is located 500 km south of Addis
Ababa. It is bounded on the basis of the surface divide of the Kulfo River. The
area is composed of part of the rift floor and part of the western escarpment. More
than 85% of the area is underlain by Oligocene basalt and the lowland areas by
allu vium and Quaternary basalt.
Using three meteorological stations;-the weighted mean annual rainfall of
1232 mm was computed by using the Thiessen Polygon method. The
Thornthwaite method was applied to calculate the potential and actual
evapotranspiration of the area, which are 971 mm and 940 mm, respectively.
From the above data, the surplus water was obtained , which is 291 mm. The
mean annual runoff depth of the Kulfo river is 361 mm which is less than the
calculated surplus water. The reason might be that there is an inflow of
groundwater from an adjacent basin.
Concerning the aquifer characterstics of the different rock units, the
alluvium is more productive than the other rock units. One representative well from
AWTI was taken to calcualte the hydraulic parameters of this unit.
Using the discharge data from Arbaminch Springs, the general hydrological
conditions of the springs were computed. This includes the computation of the
recession constants and the recession cu rve for the spri ngs. The hydraulic volume
which feeds the springs in stant by instant were also computed. The study of the
chemistry of the springs was based on data from WSSA's Arbaminch water su pply
,
project. This study confirms that the quality of the water is suitable for drinking and
agricu ltura l purposes according to intern ational standards. However, the presence
of E. coli bacteria indicates that the water needs to be chlorinated on a regular
basis.
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Keywords
Kulfo River Basin, Hydrological and Hydrogeological