142. Sediment Management at Marsyangdi Hydro Power Station, Nepal

The sediment transportation of rivers in Nepal is quite high. The specific sediment load is in the order of 1000 t/km²/yr in High Mountain to 8000 t/km²/yr in Siwalik. The huge amount of sediment coming every year during rainy season is causing serious problem in the operation of the plant, resulting in frequent flushing of the settling basin, wear and tear of the hydraulic structures and turbines. However, the sediment is being managed successfully by discharging through the gates and flushing operation. Its impact on the hydraulic structures and turbines has been managed through the proper maintenance using highly wearing resistant materials. Since, the run of river hydropower plants are being built in the sediment laden rivers, the desanding basin is normally provided to trap mostly sand size particles. However, the silt particles remain suspended in the flow with the concentration of 5000 ppm to 6000 ppm causing the wear and tear of the runner blades, wearing rings and other internal parts. The rate of erosion of runner blades and other internal parts is found high. The effect of the wear at the turbine was maintained by annual maintenance. Similarly, the bed load discharging through the gates during the rainy season is causing serious erosion in the concrete ogee surface and invert of the sluice channel. The monitoring of the erosion in the hydraulic turbines and hydraulic structures is done immediately after the monsoon season and then maintenance activity is started. The paper discusses about the silting problem, its remedial measures and sediment management at Marsyangdi Hydro Power Plant (69MW).