Assessment of Sedimentation and Reservoir Capacity Loss at Challawa Gorge Dam, Kano State

Reservoir sedimentation represents one of the most critical long-term threats to dam infrastructure performance in Nigeria, progressively reducing storage capacity and increasing flood risk. This study assesses sedimentation rates and storage capacity loss at Challawa Gorge Dam in Kano State, North West Nigeria. Bathymetric surveys were conducted using an echo sounder mounted on a survey boat, with measurements taken at 50-metre grid intervals across the full reservoir extent during the 2023 dry season. Reservoir capacity curves were derived from the survey data using GIS-based volume calculations and compared with the original design capacity curve. Sediment samples from five core locations characterised deposited sediment texture and mineral composition. Trap efficiency was estimated using the Brune curve. Results indicate that current reservoir storage capacity has declined from 124 million cubic metres at commissioning to 89 million cubic metres, representing a 28.2 percent capacity loss over 42 years of operation. Mean annual sediment accumulation rate is estimated at 0.84 million cubic metres per year. Fine-grained deltaic sediments account for 68 percent of total deposition by volume. Trap efficiency is estimated at 87 percent, indicating very high sediment retention. The study concludes that capacity loss is approaching critical thresholds that will affect water supply reliability and recommends a comprehensive sediment management programme including catchment erosion control, sluicing operations, and periodic mechanical dredging.

Keywords: reservoir sedimentation, capacity loss, dam management, Challawa Gorge Dam, Kano State