Groundwater Potential Assessment of Welenchiti Area

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Addis Ababa Universty


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.



Welenchiti Area