Morphometry of upper Gilgel Abay watershed in southern Tana Basin, Ethiopia, 2023: analysis and implication for land and water resource management

Abstract

Upper Gilgel Abay watershed (UGAW) has important physiographical and hydrological implications for the Blue Nile basin, but research on its morphometry and hydrology is limited. This study tried to delineate the UGAW and its sub-watersheds, compute basic morphometric parameters, and link each value with its drainage characteristics. Ranking and prioritization of the sub-watersheds were also done to suggest future interventions. GIS and remote sensing techniques were utilized to delineate the sub-watersheds and compute 32 selected basic morphometric parameters. A 12.5-m resolution ALOS PALSAR DEM was the input data used in GIS software to analyze and characterize the hydro-geo-morphometric features. The findings indicated that the watershed exhibits a dendritic pattern with six stream orders. A 1314.4 km total flow length for all orders is distributed within a 1657.5 km² catchment area. The infiltration number is high, causing greater surface runoff, while its low circularity ratio (0.27), elongation ratio (0.52), and bifurcation ratio (2.1) connote the basin’s nearly compact shape. Besides, it has high basin relief (1650 m), slope, and ruggedness number, implying high erosional potential in the area. Generally, the watershed experiences high runoff and minimal infiltration, making it highly prone to soil erosion and land degradation. UGAW was divided into six sub-watersheds (SW1–SW6), each characterized by distinct hydro-geo-morphometric features. The prioritization of these sub-watersheds was based on 20 purposely selected parameters. Consequently, the sub-watersheds were ranked from highest to lowest priority as follows: SW6, SW5, SW4, SW3, SW1, and SW2. This ranking indicates that SW6 and SW5 are more susceptible to various forms of degradation in land, water, and other natural resources, necessitating a high priority for the implementation of integrated land and water resource management strategies.