Hydrogeology of the Borkena River Basin Hollo – Ethiopia
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Date
1980-07
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Addis Ababa Universty
Abstract
The Borkena Hiver Basin is located in Wollo governorate general.
It is part of a major graben related to the Ethiopian Rift System,
which extends north to Korbeta graben around Maichew and south
upto Debre Berhan, and approximately stretches in a north-south
direction. There are significant contrasts of topography in the
basin where the structural control is very strong.
The hydrology of the area varies in different parts of the basin.
Consequently,the hydrogeology of the basin alse differs, such that
there is a great potential of groundwater in the flat low lying
alluvial sediments while a less signi fican t amount exists wi thin
the volcanic rocks forming the uplifted borders of the graben.
Several springs with discharges of less than 5 lilt/sec. occur in the
area issued from the volcanic rocks. There are eleven water
supplying drilled wells in the area, seven located in the alluvium
aquifers and the remaining four on basaltic aquifers; Pump tests
have been carried out in some of the wells which gave transmissibili
ty coe fficient of 91+ to 28.1 m3 per day per meter. However,
it was impossible to calculate the coefficient of storage, a
significant parameter which measures the volume of water, the
aquifer releases or takes into storage.
Proper chemical analysis of both the ground and surface waters
carried out in the area show low total dissolved solids. All of the samples in tho area have loss thun 1000 mg/l (1 mg/l = 1 ppm)
dissolved solids, except for the hot spring waters. Few of the
bacteriological tests of the waters in the area show low pathogenic
organism though most of the water samples, (particularly
the ground waters ) contain high ni tra te con ten t.
The water balance for the area has been determined. The total
annual rainfall calculated on the basis of the mean annual precipitation
for the basin is 1846.41 x 106 m3 • The groundwater
recharge for the area has been calculated based on the
evapotranspiration data at Cheffa, where the water loss is
maximum to approximate the minimum infiltration, and amounts to
185.11 x 10 6 m3 . This is 10.02% of the precipitation. The actual
evapotranspiration in the area amounts to 872, 834.8 and 836.1 mm.
for Cheffa, Dese and Kombolcha respectively. 218.5'5 x 106 m3 of
water leaves the basin at the BOrkena River outlet as runoff and
is equivalent to 11.83% of the precipitation •
Description
Keywords
Borkena River