Assessment of Sediment Accumulation and Its Impacts on the Hydraulic Capacity of Irrigation Canals in Kebbi State

This study assesses sediment accumulation rates and the resulting loss of hydraulic capacity in the irrigation canals of the Kainji Lake Irrigation Scheme in Kebbi State, North West Nigeria. Irrigation schemes in the Sahel region of Nigeria are critical for dry-season crop production, but sedimentation in distribution canals progressively reduces their conveyance capacity, leading to inadequate water delivery to tail-end farms and increased pumping costs. Cross-sectional surveys were conducted at forty stations along primary, secondary, and tertiary canals using standard surveying equipment and compared against original design dimensions from scheme engineering records. Sediment deposition depths were measured, and sediment samples were collected for particle size analysis. Hydraulic capacity reduction was computed using Manning's equation with measured channel geometry. Farmer interviews provided data on water delivery adequacy and observed deterioration. Results show that primary canals have lost an average of 18 percent of their original design hydraulic capacity due to sedimentation, while secondary and tertiary canals show losses of 31 and 47 percent respectively. Sediment particle size analysis indicates the dominant material is fine sand and silt consistent with aeolian deposition from dry season wind events and suspended sediment from irrigation return flows. Tail-end farmers in tertiary command areas report insufficient water delivery for a full crop cycle in the current state. Canal desilting has not been carried out for at least four years in most sections. Recommendations include annual desilting of tertiary canals and wind erosion control on the scheme perimeter. Keywords: sedimentation, irrigation canal, hydraulic capacity, Kebbi State, scheme maintenance.