Sediment Yield Estimation of Cascading Hydropower Reservoirs Using Geospatial Techniques in the Western Himalayas, Himachal Pradesh

Sedimentation poses a huge threat to the river ecosystem around the world. Sediment deposition reduces the storage capacity of the reservoirs, though the effect diminishes in case of cascading reservoirs. Three hydroelectric projects on river Sutlej in Himachal Pradesh, India i.e., Karcham Wangtoo, Nathpa and Kol Dam were considered in the current study. The geospatial spatial technique was applied to estimate sediment yield in the reservoirs for a period of their commission 2015 (Wangtoo), 2011(Nathpa), and 2017(Kol Dam) to 2023. For Karcham Wangtoo, the average annual sediment yield was estimated at 423.62 tons, while the monthly average was 38.28 tons. The total estimated sediment input of Nathpa Jhakri over the 13-year period was 5,083.44 tons. An upward trend in sediment influx was observed in response to increased rainfall, although flash flood and extreme rainfall events were not considered in the analysis. An assessment on the Nathpa Jhakri reservoir downstream of Karcham Wangtoo (12370.42 tons) for the same duration resulted in comparable sediment yield (5083.43 Tons). For Kol Dam, where annual figures ranged from 141,458.62 tons in 2017 to 203,276.65 tons in 2020, contributing approximately 16.31% of the total estimated sedimentation of 1,245,832.88 tons. These findings establish a strong correlation between rainfall intensity and sedimentation rates. The cumulative sediment load of all three reservoirs was calculated to be approximately 14,956,108.84 tons, highlighting the urgent need for proactive sediment management in Himalayan hydropower projects.