Reservoir Sedimentation and Flushing using Run-of-River Project

Abstract

Annually sedimentation causes 1 % of storage capacity of the reservoir all over the world. Blockage of intakes in the reservoirs and damage to tunnels/turbines can be also caused due to sediment inflow from the rivers in the catchment area. Due to the problems caused by sediments scouring of sediment from reservoir known as flushing is been done and this technique for removal of sediment is the most effective one. The process of flushing is done by lowering the water level necessarily to erode deposited sediment and also to flush them from/through the intakes and river catchment. The sediment size and other parameters such as the sediment characteristics within the catchment area of reservoir and technique used during the flushing process through the reservoir and also along the geometry of channel can be related to outflow sediment discharge. Run-of-the-river projects contribute a major part of power generation in India, but this type of projects face a very common problem of sediment accumulation in the reservoirs due to high amount of sediments coming from mountainous region. These sediments decrease the storage capacity of reservoir and also the life of turbine blades by choking and reacting with it. North and North-East India is facing severe problem of storage depletion in their reservoirs for the power generation. Hence, it is essential to keep proper sediment management plans in reservoirs of these types of projects during planning and design stage. This paper describes the prediction of sedimentation and flushing pattern in the reservoir of usual run of river project in Himalayan region, the paper describes the use of mathematical model simulations. The one dimensional HEC-RAS 5.0.3 was used as numerical modeling for the project and the results of flushing model was also. In this study, monsoon data was used to predict the year wise sedimentation pattern. Eight sets of transport equations (Ackers-White, Meyer Peter Muller, Engelund-Hansen, Laursen, Wilcock-Crowe, Yang, Toffaleti, MPM-Toffaleti.) were used with different sets of time interval to perform the study. The analysis of results and comparison with annual observed sediment volume indicated that simulations using HEC-RAS 5.0.3 with Ackers-White transport equation predicted the sediment load more accurately when the reservoir was operated at FRL. Hence, further studies for reservoir operating at FRL were carried out using the Ackers-White transport equation. Further, the worst condition of sediment accumulation was taken into flushing model to perform flushing analysis. Here, two different combinations of run were performed of 300 cumecs & 400 cumecs discharge for of 3, 6, 9, 12, 15, 18, 24, and 27 hours respectively. By analyzing the results coming from flushing runs, it was concluded that the run performed at FRL for 300 cumec discharge for 24 hours and 400 cumecs discharge for 15 & 18 hours were effective.