Groundwater Potential Assessment of Welenchiti Area
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Date
2007-07
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Addis Ababa Universty
Abstract
The welenchiti area is an extensive flat plain in the north Main Ethiopian Rift
bounded by Western highland escarpment to the north and volcanic mountains
to the south. It is situated between 390 14’ 57” to390 33’ 16” East and 8o27’ 37”
to 80 48’ 18.85” North covering a total area of 780 km2. The average monthly
temperature and the mean annual precipitation in the area are 21.1 oc and 874
mm respectively. Potential evapotranspiration for the area was calculated using
Penman and Thornthwaite gives annual potential evapotranspiration value of
1481mm/year and 577 mm/year respectively. Actual evapotranspiration for the
area estimated, from Turc method gives value of 697mm.While weighted actual
evapotranspiration from soil water balance is 842mm which is almost close to
the annual precipitation. The annual surface water out flow, estimated using
runoff coefficient methods, resulted 129.5 Mm3. The overall water balance of
the study area was computed with an aim of estimating the amount of annual
recharge to the ground water. Accordingly; annual recharge to the ground water
of the study area is approximated to be 8.58 Mm3. The study area is
characterized by deep groundwater systems encountered at an average depth of
170m. Their hydraulic characteristics are spatially variable, which is the result
of the complex nature of the lacustrine sediments and the degree of fracturing
of the volcanic rocks. Fractured basalts, scoraceous basalts and fractured
ignimbrites are the main aquifer units in the area. These aquifers were found to
be good groundwater potential zones. The general trend for groundwater flow
observed from pieziometric heads is from northern highland toward the plain in
the direction of north west to south east of the study area. Groundwater type of
the area evolves from Ca-Na HCO3 water type in areas close to northern
escarpment into Na-HCO3 water type in the southern tip of the study area.
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Keywords
Welenchiti Area