Abstract

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 the 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 upper Blue Nile River Basin and accounting 14,200 km². In order to supplement planning and development of this area, a detailed characterization of the basin is important. The main objective of this study is to process and determine different terrain processing parameters and morphology by using Arc-Hydro tools in Arc-GIS for generating different data for the basin. Therefore, it has been observed from this study that the drainage density is higher in relatively elevated areas especially when the weathered section is thick or when the pattern of structures crossing the rocks is higher. Direction of flow of these rivers is controlled by the topography. The highlands (maximum 2729 m above sea level) from where the streams flow are general humid and rugged and the surrounding lowlands (minimum 458 m above sea level) in which the streams flow, are mostly arid and relatively flat. These topographic differences induce rapid run off, low retention in soil layers and soil erosion on the highlands. Considering a 30 × 30 m drainage area, 62 catchments, eight flow directions with 128 flow grids have been identified in the basin. The delineated watersheds were Gilgel Beles with 617.56 km², Upper Main Beles with 2866.05 km² and Lower Main Beles with 6613.84 km². Therefore, the watershed external boundary is determined to be 10,097.45 km². Important basin information, like slope and contour lines has been determined through spatial analysis and the result indicated that about 52.8 % of slope was found to be relatively suitable for agricultural soil and water management options in Beles River Basin. In the future, it would be advisable to consider emerging issues in water resource measures like GIS modeling with Remote Sensing data for effective and efficient water resource management when there is limited and lack of data.

Key words: River basin, Arc-Hydro, Arc-GIS, Degital Elevation Model (DEM).