Projects & Programs
Temperature and Water Quality Modeling of Lake Billy Chinook, Oregon
The construction of Round Butte Dam and creation of Lake Billy Chinook on the Deschutes River in Central Oregon affected the downstream migratory fish passage of juvenile salmonids. Fish passage was discontinued in the late 1960s due to ineffective downstream passage. As part of the current re-licensing process, Portland General Electric is attempting to re-establish fish passage at Round Butte Dam.
PNNL staff set up and calibrated the two-dimensional Box Exchange Transport Temperature Ecology Reservoir (BETTER) model developed by the Tennessee Valley Authority to simulate water quality and the development of temperature stratification and mixing among three branches of the Lake Billy Chinook reservoir. Application of the calibrated temperature model and coupling the model to a three-dimensional hydrodynamic model allowed the evaluation of various proposed flow modification structures on reservoir stratification and circulation. The immediate goal of the project was to identify the modification(s) most favorable to the downstream passage of juvenile salmon through the project. The ultimate goal is the restoration of anadromous fish runs to the upper tributary reaches of the Deschutes River above the project.
The calibrated temperature model successfully simulated the development of stratification and mixing patterns observed during water quality studies conducted in 1995. Simulation of four reservoir flow modification alternatives using the calibrated model and 1995 conditions indicated that the hydrothermal behavior of the reservoir could be significantly modified. Three of the simulated alternatives (surface withdrawal and two curtain alternatives) resulted in conditions that would likely be more favorable to downstream fish passage. A fourth alternative (permanent drawdown) produced stratification patterns that were very similar to the existing reservoir condition. The model also successfully simulated the water quality parameters such as dissolved oxygen (DO), pH, nutrients and algal concentrations. The model was used to demonstrate that modification of hydrothermal behavior using selective withdrawal would not adversely impact in-lake or discharge water quality. The lake would hold an increased volume of cooler water with higher DO concentrations, thereby improving the health of the system.
Project Highlights:
- The calibrated water quality model successfully simulated de-stratification and formation of epilimnion in the summer
- The water quality model successfully reproduced annual cycles of DO, pH and algal growth
- The model was used to design an alternative "selective withdrawal" that would allow compliance with temperature and water quality (DO, pH) criteria
- The model was used to demonstrate the effectiveness of selective withdrawal in improving in-lake DO and lower temperatures in the summer.