Water Resources Potential Evaluation of Beressa River Catchment, in North Showa, Amhara Region

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Addis Ababa Universty


Water resource potential evaluation is carried out on Beressa river catchment which is located about 130 km from Addis Ababa on the way to Dessie. The study area covers 336 km2 and having average elevation ranges from 2100m to 3675 m above mean sea level. The area has 13-16 0c average annual temperature, 1120 mm annual rainfall and temperate (weyna daga) to cool (kur) climate. It is located in the Ethiopian highland plateau adjoining the western escarpment of the rift valley and the area is within Jema river basin which is one of the main tributaries of Blue Nile River. By analyzing the available meteorological data, open water evaporation and potential evapotranspiration is calculated using penman combined method and the results are 1336mm and 1180mm respectively. The actual evapotranspiration of the catchment is calculated using Thornthwait and Mather soil water balance model and the annual AET is 731mm. From the computed water balance, the amount of water infiltrated to subsurface is 122.46 mm. The local geology of the study area is Tertiary volcanic rocks which are lower basalt, rhyolitic ignimbrite, upper basalt and residual silty clay soil patches along the river valleys. These rock units are weathered, fractured and jointed. Based on groundwater circulation and storage controlling factors of the area that is degree of weathering, fracturing, faulting of the geological formation, topographic nature, recharge and discharge condition of the area; the hydrogeological map is produced classifying thearea into 3 similar hydrostratigraphic units having high, medium and low-very groundwater potential zone. From available pumping test data the high groundwater potential zone has 5-15 l/sec yield, 10-332 m2/d transmissivity and 0.3-7.8 m/d hydraulic-conductivity and where as the medium groundwater potential zone has 1- 4 l/sec yield, 1.5-2..22 m2/d transmissivity and 0.04-0.045 m/d hydraulic-conductivity. Physical parameters measurements, chemical and bacteriological laboratory analysis of water samples were conducted to study the water quality and the pollution of water resources of the catchmrnt. Accordingly, almost all sampled water show fresh water (TDS =55-307 mg/l), soft to moderately hard, CaHCO3 and Ca-Na- HCO3 water types. But two boreholes and one spring water sampled from water schemes located in the town show hard water and Ca HCO3-Cl, Ca-Na-HCO3-Cl and Ca–Cl-HCO3 type water. These three water sources have 46- 55 mg/l nitrate and 46-63 mg/l chloride ions concentration. The source of these ions in these three water samples might be due to contamination from disposal of the town municipal solid and liquid wastes released to open land surface. From 10 water samples microbiological test, 6 water samples were polluted by coliform bacteria due to waste disposal and poor sanitary protection.



Beressa River Catchment