ASSESSMENT OF SEDIMENT YIELD AND MANAGEMENT STRATEGY FOR UPPER TAMAKOSHI HYDRO-ELECTRIC PROJECT (456MW)

Abstract

This research investigates soil erosion dynamics and sediment yield at its outlet in a watershed, focusing on the Upper Tamakoshi Hydropower reservoir (UTKHEP) in Nepal which is mainly influenced by construction activities in its upstream catchment area. Utilizing a combination of primary and secondary data sources, including governmental and non-governmental organizations' datasets, alongside field survey and visits, the study employs the Revised Universal Soil Loss Equation (RUSLE) and sediment delivery ratio (SDR) models within the ArcGIS 10.8 environment and HEC-HMS respectively. Findings reveal a mean annual soil loss of 44.137 t/ha/year and a mean of sediment delivery ratio 0.2528 for the entire watershed, with high sediment delivery areas concentrated in the northeast and central-west regions, posing challenges to the UTKHEP reservoir. The study estimates an annual silt deposition rate of approximately 10.91 tons/ha/year in the reservoir, necessitating mitigation measures. Utilizing a combination of field surveys, bathymetric analysis, and software simulations, the study evaluates the sediment load and its impact on reservoir capacity. Analysis reveals a significant reduction in reservoir volume up to 51.3%, attributed to sediment deposition, with implications for hydropower generation and sustainability. Traditional and innovative sediment mitigation strategies, including flushing, dredging, and check reservoir construction, are explored, considering their effectiveness, cost, and environmental impact. Proposed strategies include mechanical and manual excavation methods, dredging, and the construction of sediment check reservoirs with bypass tunnels. These findings underscore the importance of implementing soil and water conservation measures to sustain power production and minimize reservoir siltation.