Sediment Management of Nathpa Dam from Heavy Silt in River Satluj (India)

Most of India's hydropower potential exists in the Himalayan and north eastern region, where, due to the fragile geology of the hills and steep slope of the valley, the rivers carry a lot of sediment during monsoon. Hence, the storage capacity of reservoirs in these regions is lost rapidly due to sediment deposition. Such projects are required to be designed on different criteria from the conventional reservoir projects. They are required to be designed for sediment management rather than water storage. Handling of sediments is a major challenge in the design and operation of hydropower plants. At medium and high-head hydropower plants on sediment-laden rivers, hydro abrasive erosion on hydraulic turbines is an important economic issue because it increases maintenance costs, and reduces turbine efficiency, electricity generation and hence revenues. Reservoir sedimentation may have the many negative effects such as loss of active storage volume, and thus reduced ability to compensate in-and outflows for hydropower, irrigation, drinking water and flood retention, increased turbine erosion because of higher suspended sediment concentration (SSC) and coarser particles in power waterways due to reduced trap efficiency of the reservoir. The sediment deposition in the reservoirs can be controlled by different methods such as reducing the sediment reaching the reservoir by catchment area treatment or diverting sediment concentrated flows, passing sediment-laden flows through the reservoir by sluicing and thereby reducing the settlement of sediment in the reservoir and removing the already deposited sediment hydraulically by drawdown flushing or mechanically by dredging. This paper presents the sedimentation problems and management methods being adopted to tackle the sediment of the reservoir of Nathpa Jhakri Hydro Project (1500 MW) in Himachal Pradesh, India.