Impact of Sedimentation on Storage Capacity of Mindu Dam, in Morogoro Municipal, Tanzania

Abstract

Sedimentation remains a major threat to reservoir sustainability because it progressively reduces dam storage capacity, shortens operational lifespan and weakens water-supply reliability. This study assessed the impact of sedimentation on the storage capacity of Mindu Dam in Morogoro Municipal, Tanzania. The assessment was conducted using the Soil and Water Assessment Tool and Bathymetric Survey to identify sediment hotspot areas and estimate the current reservoir storage capacity. The watershed was delineated into 62 sub-basins and 393 Hydrologic Response Units. Observed streamflow data for 2005–2013 and 2014–2025 were used for model calibration and validation, respectively, while model performance was evaluated using Nash–Sutcliffe Efficiency, coefficient of determination, percent bias and root mean square error. The model showed satisfactory performance, with Nash–Sutcliffe Efficiency and coefficient of determination values of 0.71 and 0.79 during calibration, and 0.78 and 0.85 during validation, respectively. Sediment hotspot analysis showed that the lower part of the catchment contributed the highest sediment yield, ranging from 40 to above 60 tonnes/ha/year. Bathymetric results showed that dam storage capacity declined by 14.8%, from 12,623,000.00 m³ to 10,772,879.56 m³ over 40 years, with an average sediment deposition rate of 46,250 m³/year and annual capacity loss of 0.37%. The estimated remaining life expectancy of the dam was 32 years. The study demonstrates that sedimentation is significantly reducing Mindu Dam storage capacity and recommends integrated structural and non-structural catchment-management interventions in the identified sediment hotspot areas.