Effect of streamflow and surface erosion/sediment transport from upland area to riverine floodplain on water management at Gilgel-Gibe Catchment Scale, Ethiopia

Surface erosion sediment transport from upland areas (UA) to riverine floodplain (RF) at Gilgel-Gibe catchment scale (GGCs), Ethiopia was affecting future water-food security. This study aimed to simulate the effect of streamflow surface erosion/sediment transport from UA to RF on water management at GGCs, Ethiopia using SWAT+ integration with RUSLE. The integration of RUSLE with GIS RS was used to simulate surface erosion from UA to RF, while QSWAT+ has been used to simulate the effect of streamflow sediment transport to help identify the priority area for water conservation planning. Sensitivity analysis, calibration, validation were performed using SWAT+Toolbox hydrological model performance was measured by R2 NSE, PBIAS. Mean annual surface erosion of the catchment was 68.2 t/ha/yr (varies from 0-156.08 t/ha/yr) sediment transport from UA (0-1.4 Mt/y) to RF (0-1.2 Mt/y) which is above tolerable limit. UA falls under severe erosion classes which need immediate conservation measures. Low erosion at RF is due to more resistance to erosion (good coverage of the riverine wetland). Both NSE R2 results were greater than 0.75 show a good statistical model performance. Compared to UA, RF streamflow increased (1982-2010) good condition but decreased (20210-2016). Compered to UA, sediment transport at RF shows a decrease, due to RF having good trapping of sediment in the riverine wetland channel before entering the river basin. This study provides useful information on how to adopt management strategies for water sediment at the catchment scale.