Reduction in storage capacity of the reservoir and inflow of sediment into the water conveyance systems are two of the main problems faced during development of hydropower projects in recent years. The flow velocities in river upstream of dam are reduced due to storage of water. As a result, the sediment transport capacity is reduced and sediment is deposited in the reservoirs. Prediction of sediment distribution in reservoirs is essential in feasibility studies and during planning stage for design of various components of new projects and for performance assessment of existing projects. Several methods including empirical and numerical simulation models developed for prediction of deposition pattern in reservoirs are reported in literature: The commony adopted approach of long-term simulation over 25 to 50 years is suitable for reservoirs having storage capacity much larger than the average annual sediment inflow. The criteria to be adopted for reservoirs witll smaller capacity and large sediment inflow rate as in case of run-of-river power generation projects should be simulation for short term periods. The common practice is to restore the storage capacity of reservoir by hydraulic flushing/sluicing. In such cases, prediction of flushing frequency is important for estimating loss of revenue due to shutdown for flushing of sediment. Case study for prediction of sedimentation profile and flushing frequency of a reservoir for Tapovan Vishnugad Hydro Electric Project across river Dhauliganga is presented.
