Event-based hydrological processes and sediment yield at semi-arid catchments of Northern Ethiopia

Abstract

Study region Two adjacent small catchments located upstream of a reservoir-based irrigation system in the highlands of northern Ethiopia, characterized by semi-arid climate conditions. Soil erosion causes socioeconomic and ecological disturbances. Reservoir sedimentation is among the negative off-site effects of soil erosion. Study Focus The discharge-suspended sediment concentration hysteresis pattern was analyzed. An event-based hydrological model, OpenLISEM was also applied in small, paired catchments to evaluate the effectiveness of soil and water conservation measures in reducing sediment yield and reservoir sedimentation. Rainfall events were calibrated independently due to differences of model parameters between storm events. New hydrological insights for the region Initial soil moisture content was found to be the most sensitive parameter affecting simulated peak and total discharge. OpenLISEM performed satisfactorily for most of the calibrated events in capturing peak discharge and discharge hydrograph. Complex hysteresis patterns were observed during heavy rainfall events with multiple discharge peaks. The results indicate that implementing stone bunds on hillslopes together with check dams across gully channels reduces sediment yield at both catchment outlets by 36–74% relative to the calibrated baseline scenarios. The findings provide valuable insight for the potential of different soil and water conservation measures to reduce sediment yield and reservoir sedimentation, contributing to the long-term sustainability of reservoir-based irrigation schemes in the semi-arid highlands of northern Ethiopia.