Assessment of channel morphological change in the Robit River, Awash Basin, Ethiopia

Over time, the movement of bed material and the banks of a channel lead to the shifting of a river. This study includes the morphological changes of the 23 km Robit River, which drains into the Awash Basin. The main objectives of this research to determine and investigate morphological changes over the past 30 years, classify streams based on Rosgen method and HEC-RAS 6.2 was used to assess the vertical bed changes. Primary data (river cross-section obtained using a total station and soil sample data taken from the river). Secondary data, including stream flow, sediment, rainfall, and climate, were collected from the Ministry of Water and Energy (MOWE), while meteorological data were obtained from the National Meteorological Agencies. These data were then used for preparation and analysis in ArcGIS, Civil 3D, and the HEC-RAS model. The total sinuosity index of the river channel has slightly increased from satellite images taken in 1992, 2002, 2012, and 2022. The increment is presented from 1.193 in 1992, 1.192 in 2002, 1.200 in 2012 and 1.194 in 2022. The data indicates that the river channel of Robit River is low sinuous types of river. Braiden’s index values were 1.265, 1.324, 1.267, and 1.268 for the years 1992, 2002, 2012, and 2022, respectively. The width-to-depth ratios were above 50 m/m, and the longitudinal slope ranged from 0.01 to 0.02. These planform results classify the reach as a D-stream type. Annually, the river channel has 3.2 ha of bank deposition and 8.2 ha of bank erosion. A 10-year simulation showed a maximum deposition of 2.27 m and maximum erosion of 2.05 m.