Sediment Influx and Its Drivers in Farmers’ Managed Irrigation Schemes in Ethiopia

Abstract

Excessive soil erosion hampers the functioning of many irrigation schemes throughout sub-Saharan Africa, increasing management difficulties and operation and maintenance costs. River water is often considered the main source of sedimentation, while overland sediment inflow is overlooked. From 2016 to 2018, participatory research was conducted to assess sediment influx in two irrigation schemes in Ethiopia. Sediment influx was simulated using the revised universal soil loss equation (RUSLE) and compared to the amount of sediment removed during desilting campaigns. The sediment deposition rate was 308 m3/km and 1087 m3/km, respectively, for the Arata-Chufa and Ketar schemes. Spatial soil losses amounts to up to 18 t/ha/yr for the Arata-Chufa scheme and 41 t/ha/yr for the Ketar scheme. Overland sediment inflow contribution was significantly high in the Ketar scheme accounting for 77% of the deposited sediment, while only 4% of the sedimentation at the Arata-Chufa scheme came from overland flow. Feeder canal length and the absence of canal banks increased the sedimentation rate, however, this was overlooked by the stakeholders. We conclude that overland sediment inflow is an often neglected component of canal sedimentation, and this is a major cause of excessive sedimentation and management problems in numerous irrigation schemes in sub-Saharan Africa.

Impacts of small-scale irrigation water use on environmental flow of ungauged rivers in Africa

“…3). Both catchment's land use and land cover consisted of more than 50% cultivated land and less than 1% woodland (AZILDO 2017; Gurmu et al 2021; Sime and Abebe 2022). Both catchments have similar drainage classes and fine to medium soil texture.…”

Soil Water Erosion

“…Gurmu et al [15] simulated sediment influx using the RUSLE model and compared it to the amount of sediment removed during desilting campaigns. They found the sediment deposition rate to be 308 m 3 /km and 1087 m 3 /km, respectively, for the Arata-Chufa and Ketar schemes.…”