Problems of Nepalese hydropower projects due to suspended sediments

Abstract

Nepal has high potential for hydropower due to glaciers in the Himalayas, regular monsoon rain and local topography. Himalayan Rivers contain large quantities of sediment with hard abrasive particles, which is a hurdle for the economic exploitation of hydropower resources. Erosion of the earth's surface takes place because of influence of climatic, tectonic and human activities. Almost all the power plants in the Himalayan region are affected by excessive sediment in rivers that reduce the life of plants either by filling reservoirs or by erosion of turbine components. The design and operation of headwork components in hydropower plants can only manipulate sediment particle size and hence only sediment concentration in the water. The erosion of hydraulic machinery depends on eroding particles, that is, their size, shape and hardness; on substrates, their chemistry, elastic properties, surface hardness and surface morphology; and on operating conditions, velocity, impingement angle and concentration. The shape, size and mineral content of sediment vary at different locations of the same river system depending on distance traversed by particles, gradient of the river and the geological formation of the river course and catchment areas.

The Khimti hydropower project in Nepal represents a typical high head power plant in the Himalayan River that is affected by river sediment. Erosion tests of turbine material carried out at Kathmandu University revealed the dependence of erosion rate on mineral content. The erosion tests have shown trends relative to the quartz content present in samples from river basins in different parts of the country. There was some indication that the shape of particles had some effect. Sediments in the hydropower projects are normally considered as a burden, but there is scope for industrial use of these sediments.