The Water Balance of May Nugus Catchment, Tigray, Northern Ethiopia

The paper presents results related to water balance of the May Nugus catchment, Tigray, Northern Ethiopia. The catchment covering an area of 14.73 km 2 includes a small dam called May Nugus having an effective watershed area of 13.05km 2 with reservoir capacity of 23.82 x 10 6 m 3 and command area of about 1.24 sq. km. Hydrology of the area was characterized on the basis of land use, soil, slope, rainfall, temperature, evaporation, evapotranspiration, and runoff using meteorological data. Different methods like rainfall coefficient method is used to determine monthly distribution of rainfall including rainy and dry months; Penman method to calculate evaporation from the reservoir; Thornthwaite method and Thornthwaite water balance model to determine potential and actual evapotranspiration; and runoff coefficient method to estimate runoff. The catchment is characterized by one rainy season and two dry seasons during the year. The rainy season has five months duration and dry season seven months. The mean annual rainfall of the catchment is 737.57 mm, out of which rainy season accounts for 81.24 % and the dry season for 18.76 %. The total annual water loss by evaporation from the reservoir is 1404.4 mm. The mean annual actual evapotranspiration of the upper catchment and the command area is 613.33 mm and 569.84 mm, respectively. The mean annual runoff generated from the upper catchment and the command area is estimated to be 1.54 million m 3 and 0.146 million m 3 respectively. The amount of water that percolates into the ground in the upper catchment and command area as groundwater is estimated to be about 0.06 million m 3 and 0.22 million m 3 respectively, and the same at the reservoir site is 1.24 million m 3 . The total amount of water which is actually available to recharge the groundwater within the catchment is 1.52 million m 3 . In general, the command area of May Negus catchment has very good groundwater potential. If developed and utilized properly, it can be used conjunctively with dam water for multi purposes.