Use of ASTER DEM data for Morphometric Analysis of Megech Dirma-Watersheds, Blue Nile Basin, Ethiopia: Implications for Soil and Water Conservation

Abstract

Quantitative morphometric analysis was carried out for Megech-Dirma, sub-basin of the Blue Nile, by estimating (1) linear, (2) aerial, and (3) relief aspects. An endeavor has been made to measure the Megech-Dirma watershed’s morphometric characteristics to implement conservation methods for soil and water properly. ASTER DEM has been used as input data for extracting morphometric parameters. Strahler’s classification scheme was used to classify the extracted drainage network in ArcGIS extension ArcMap 10.4. The watershed covers a total surface area of 1309.56 km2. The shape of the watersheds as calculated from elongation, circularity, and form factors reveals the elongated shape and the watersheds parade dendritic pattern. The sub-watersheds include third-order for Megech and sixth-order streams. Lower stream orders, in particular first-order streams, dominate the sub-watersheds. The length of overland flow has a higher value (1.06) for Megech indicates low relief, whereas the values of length of overland flow, which are relatively low (0.20) for Dirma, indicate high relief. The drainage density of the study watershed was morphometrically analyzed and obtained 0.47 km/km2 for the Megech sub-basin, which indicates the basin is highly permeable and result in better underground water storage capacity and 2.46 for the Dirma sub-basin indicating very coarse and coarse channel, respectively. The ruggedness number for Megech and Dirma sub-basins was 0.56 and 0.07, respectively, indicating moderate and long, rugged topography, which could be susceptible to flash flood and soil erosion. The dissection index values for Megech 0.40 and 0.36 for Dirma show river sub-basins are moderately dissected. The ruggedness number is 0.56 for Megech implies moderate soil erosion probability, whereas the high infiltration number (14.29) for Dirma river shows the high runoff potential in the sub-basin. The findings of this study include drainage morphometry data that can be used to better understand watershed characteristics and serve as a framework for better planning, management, and decision-making to ensure the long-term use of watershed resources of water and soil.