Projects & Programs
Computational Fluid Dynamics Modeling of the North Fork Dam Forebay, Clackamas River, Oregon
Portland General Electric (PGE) operates the Clackamas Hydroelectric Project consisting of the "Oak Grove" and the "North Fork" hydroelectric developments. Project operations result in storage of water in the reservoirs, diversions from the main stem of the river reaches, peaking mode power generation releases and spills at various locations in the river system. Consequently, the hydraulic regime is altered relative to the natural flow. It is expected that changes in travel times, velocities and water depths alter the temperature and water quality response of the Oak Grove Fork and Clackamas River relative to the pre-project conditions. PNNL staff developed a temperature and water quality model of the entire Clackamas River as part of the 401 water quality certificate process to assess and document the extent and significance of water quality impacts due to project existence and operations.
PNNL staff used the extensive hydraulic and water quality data collected by PGE during the period April 2000 through September 2001 to calibrate the CE-QUAL-W2 model of the system. For computational economy and efficiency, the system was divided into eight different reaches. The objective was to calibrate the individual reaches as stand-alone models so that they may be linked externally as required. Following calibration, the model was applied to the project and alternative analysis conducted to evaluate the impact of hydroelectric projects on temperature, water quality and nutrient cycles in the Clackamas River.
The results of the modeling study showed that overall water quality of the river was very good, characterized by low algal biomass, high dissolved oxygen and temperature very close to natural temperatures. The effect of project operations on dissolved oxygen and algal biomass were very small, and the only parameter significantly affected was temperature in selected reaches. PGE is currently evaluating operational modification alternatives that would allow sufficient water to remain in the affected reaches to assist fisheries' goals, which would also provide the added benefit of reduced temperatures relative to existing conditions.
Project Highlights:
- Developed a three-dimensional computational fluid dynamic model of the North Fork Dam forebay using the STAR-CD model
- Developed an ability to estimate hydrodynamic loads on the screens and net structures using a thin porous baffle in the model
- Used model results to optimize initial placement and design of net configuration and to support design of fish collection and attraction structures for downstream migration.