Simulation of Reservoir Drawdown using HEC-RAS

Abstract

Reservoir drawdown is an expensive and one of the most important operations for dams /reservoirs running, maintenance and operations. On Elwha river, Glinde Canyon and Elwha dams were suggested to be removed for the purpose of preserving the ecosystem and anadromous fisheries. To understand the effect of dam removal on water quality and sediment transport of the bed, an experiment was conducted by the U.S National Park Service, U.S Geological Survey, Bureau of Reclamation and Lower Elwha Klallam Tribe. This experiment was conducted in April 1994. The water level of the Elwha River has lowered 18ft in 14 days, and sediment transport in all the corresponding cross-sections was noted. Performing these experiments on actual structures is always time-consuming and uneconomical. For this purpose, many researchers have been using various tools like Dream 1, Flow 3D and HEC-RAS to simulate the phenomena and approach to the best results they can. In this research, we simulated this experiment on HEC-RAS using Ackers & White. Simulation performed in HEC-RAS is 1D, the cross-sectional comparison is showing that the trends of erosion and deposition using Ackers & White are similar. The main purpose of our research is to predict sediment erosion in this delta and compare Ackers & White with actual experiments. In the final part of this research, we simulated this experiment using two more formulas, Yang and Laursen. The formulas in HEC-RAS are selected according to the bed gradation of the river. Their comparison is showing that Ackers & White is giving us better results in this scenario.