The study area has a total surface area of 152km2 with a wide difference in altitude rangingrnfrom 2000 m.a.s.l to 3000 m.a.s.l (meters above sea level). The high altitude topographyrnmainly occupies the western scarp of the study area. The central and eastern parts in turn havernrugged topography with flat to gentle slopes.rnThe paleozoic-mesozoic sedimentary rocks cover larger part of the study area. The dominantrnlithological units in the area are the alluvial sediments unit, the tertiary basalt unit, the Adigratrnsandstone unit, the Edagaarbi glacial unit, the Enticho sandstone unit and the metamorphicrnrocks unit.The main structures of the area are sedimentary beds, cross bedding, fracture/jointrnsets and foliation.rnFrom long term mean monthly rainfall data, the area receives 694mm mean annual rainfall.rnThe potential evapotranspiration of the area calculated using the Penman combined method isrn1261mm.The actual evapotranspiration computed by the Thorthwaite-Mathes soil balancernmodel is 583mm. The mean annual surface run off that leaves the catchment is 62mm ofrnwater. The amount of groundwater recharge is 46.4mm.rnBased on pumping test data analysis results and additional qualitative field descriptions suchrnas degree of weathering, extent and frequency of fractures, the rocks in the study area arernclassified in to four hydrogeological units These are rocks with high permeabilityrn(K>1.45m/d), rocks with high to medium permeability (K=1.45m/d to 0.15m/d), rocks withrnmedium to low permeability (K= 0.15m/d to 0.09m/d) and rocks with very low permeabilityrn(K