Challenges with Tailwater Analysis
Assessing the potential for tail-water scour downstream of a dam is a key issue in hydro projects. Dam failure due to poorly designed spillways and forebays can result in significant loss of life and property.
Furthermore, dams often withdraw water from the hypolimnion where dissolved oxygen levels are lower, impacting water quality in the tailwater. Tailwaters may also be found to contain potentially toxic substances.
Solutions Provided by EEMS
The EFDC model is commonly used to predict scour and deposition patterns in the forebay, main channel and floodplain downstream of a dam. EE allows the user to readily visualize the flow regime, shear stress, and sediment bed erosion patterns. Lagrangian particle tracks may also be implemented to better understand the 3D hydrodynamic system. EEMS is also frequently used to simulate low DO levels in the tailwater and assess possible impacts on the habitat.
Examples of Studies Done with EEMS
A study using the EFDC model was used to predict scour and deposition patterns for the main channel and floodplains downstream of the Pa Vinh Dam, Son La. The Hoa Binh Reservoir is located about 15 km below the Pa Vinh Dam. It was determined that there would be significant scour regions and deposition areas. Fortunately, however, the erosion would be significantly reduced due to a naturally armored reach of the river about 2.5 km below the dam. One of the purposes of this study was to help set the turbine elevations for this hydropower dam in north west Vietnam.