Ground Water Potential Assessment of Gumara River Catchment, North West Ethiopia

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Addis Ababa University


The development of balanced plan for water resource utilization requires assessment of the water resources in terms of quality, quantity, spatial distribution and the land use land cover condition of the entire catchment area. The Gumara River catchment is located in North West part of Ethiopia particularly in south Gonder zone and enclosed between Mount Guna from the east and Lake Tana in the west. The area is generally characterized by two pronounced topographic features. The high land which comprises of about 80% of the study area is covered by Tarmaber formation of Miocene age and the remaining low land area consists of Quaternary volcanics, alluvial and lacustrine deposits. Different approaches have been used to quantify the main hydrometeorological components and estimate the recharge amount of the catchment. The annual rainfalls of point data from different nearby stations of the catchment are analysed using arithmetic, Thiessen polygon and Isohyetal methods. All the three methods provide nearly closer value. The analysis result of Thiessen polygon method which is more or less the average value (1377 mm) of three methods is used as the annual average rain fall of the study area. The actual evapotranspiration of the catchment is calculated by evaluating the land use land cover type, soil texture and their areal proportion and is computed to be 764 mm per year. The annual recharge of the catchment is estimated using base flow separation and water balance methods of which the water balance method (267 mm) is preferred to be the annual recharge of the catchment. Weathered and fractured basalt are the major aquifers of the area. The ground water potential recharge-discharge condition and ground flow system of the area is generally controlled by the amount of rain fall, topographic feature and prevailing structure. The general ground water flow direction is from the eastern towards west with minor irregularities reflecting local topographic variation, existence of deep well and prevailing structure. Aquachem software has been employed to identify the different water types. From the analysis of hydrogeochemical data different water types are identified of which the Na-Hco3- Co3 and Na-Co3-Co3 are thermal springs in Guramba and Wanzaye area. The dominant water type of the area is Ca-Mg-Hco3 .Waters of the area generally evolves from Ca-Hco3 and Ca- Mg-Hco3 in the recharge area to Na-Ca-Hco3 discharge area. Such evolutionary trend is controlled by dissolution, precipitation, cation exchange and Hydrolysis of silicate minerals.