Hydrodynamic modelling to develop design and operational options for sedimentation reduction in irrigation schemes, Ethiopia

Abstract

Study region: The Great Rift Valley Basin of Ethiopia, Arata-Chufa (100 ha) and Ketar (430 ha) irrigation schemes. Study focus: Sedimentation triggers malfunctioning in irrigated agriculture by decreasing canal discharge capacity and increasing operation and maintenance costs. The current study coupled a hydrodynamic sediment model with the output of an erosion model to analyse sedimentation problems, employing data on discharges, water levels, sediment load, and sediment concentration collected over two years (September 2017 to September 2018). The effects of design (canal lining, building a settling basin, and changing longitudinal bed slope) and operational (sediment flushing) modifications on sediment reduction were simulated with the Hydrologic Engineering Center's (HEC) River Analysis System (HEC-RAS) model. New hydrological insights for the region: The model simulation indicates that the most promising low-cost option to reduce sedimentation is flushing during the rainy season, reducing deposition by 82% (Arata-Chufa) and 57% (Ketar). The second option is lining the canal, particularly for a scheme mainly experiencing river sediment like Arata-Chufa, where deposition would be reduced by 28%. Construction of a new settling basin with a flushing option would reduce deposition by 63% (Arata-Chufa) and 42% (Ketar). Changing the bed slope of the severely silted canal section has little effect on sediment reduction. Therefore, operational changes are more promising low-cost options than design modification to reduce sediment deposition in SSI schemes.

Keywords

• Irrigation
• Sediment transport
• Design modification
• Operational changes
• Soil erosion