Reservoir Sedimentation and Sustainable Development: Sediment Management Practice in Reservoirs of Two Power Stations Located on Himalayan Rivers of India

NHPC Limited, a Govt. of India Enterprise, is operating 19 hydropower stations with an installed capacity of 5121 MW along with two 1520 MW hydropower stations through joint venture. Most of the power stations of NHPC are located in high sediment prone Himalayas having small and medium size of reservoirs. Himalayan rivers carry much more sediment load than the capacities available in the reservoirs of power stations located in this region. Efficient sediment management techniques are needed in monsoon season to protect the economic and useful life of the reservoirs and turbines. NHPC ltd. has been successful in maintaining gross/live capacity of reservoirs of these power stations satisfactorily and is able to meet generation targets as per statutory requirement by practicing customized sediment management techniques for different projects having unique design features. This paper aims at sharing the experience of sediment management, being practiced in two reservoirs of NHPC's power stations, namely Chamera-I and Teesta-V power stations. Chamera Stage-I has relatively large reservoir capacity (391 MCM initially). The sediment management of this project is mainly done by following reservoir operation rules (at lower operating levels during monsoon season) and sluicing through low level sluice outlets. This method appears to be quite effective, resulting only 13.8% loss in the live capacity in 22 years meaning a, loss of around only 0.5% in live capacity per year, which is reducing with each passing year, as sedimentation profile reaches a stable regime. On the other hand, the reservoir of Teesta-V power station, which is a small reservoir having initial gross capacity of 13.5 MCM, has been maintained through sluicing combined with flushing. After 8 years of commissioning, the live capacity is maintained at 5–6 MCM as compared to initial capacity of 6.28 MCM. Loss in the live capacity is computed as only 3.8% in last 7 years meaning, 0.5% in live capacity per year (excluding 1st year).