Water Resource Assessment and Management Options in Beles River Basin using HEC-HMS Model

Abstract

Ethiopia is commonly referred to as “the water tower of east Africa”, because of the huge amount of surface runoff from the Ethiopian highlands that make up over 86% of the flow of the Nile River but Ethiopia is constantly affected by shortage of water for rain-fed agriculture, mainly because of lack of proper water resources utilization and management practices. For efficient use of available surface water resources with balanced attention to maximize economic, social, and environmental benefits, it is necessary to have effective integrated water resources assessments and planning. Beles river basin is one of the most potential river basins in Ethiopia which is the main tributary for Blue Nile River Basin and accounting 14,200 km2. The objectives of this study was to assess the available surface water resources in the Beles River basin, using a HEC-HMS hydrological modeling system by estimating surface runoff and simulating hydrological processes due to distributed land use, soil, climatological and hydro- metrological condition in the entire river basin. The GIS layers that were used as input data for the flow simulation were prepared using Arc GIS 9.3 and used in the HEC-HMS 3.5 calibration of the Beles River sub basin using daily precipitation and flow data from 2003 and 2004 and validated by 2005 and tested statistically by relative error and the residual method. Then the validated surface runoff is used for water balance assessment. From the delineation of the entire basin and sub- basin; it has been obtained that drainage areas of 9078.20 km2, 3461.80 km2, and 747.11 km2 for the sub watershed Lower, Upper, and Gilgel Beles respectively. Result of mean monthly simulated runoff show that 76mm for Gilgel Beles, 55.7 mm for Upper Beles and 42.4 mm for Lower Beles. According to the result of water balance assessment; the highest water deficit was observed in 2004 (-463 mm/yr) & 2003 (-180 mm/yr) of Lower Beles but 2004 for Gilgel Beles (129 mm/yr) and Upper Beles (61.24 mm/yr) was observed to be a water surplus year were as 2003 showed the deficit year in the entire basin. However, there is no significant change in soil moisture storage in Beles River Basin in 2005. In the future, it would be advisable to consider immerging issues in water resource assessment like GIS modeling with Remote Sensing data for effective and efficient water resource management and planning when there is limited and lack of data.

Keywords: River Basin, HEC-HMS, Beles and DEM.