This model simulates the Great Falls Hydropower Plant Project, a series of five hydroelectric dams near Great Falls, Montana. The model incorporates many features present in customized hydroelectric power programs, such as tabulated functions of power, output as a function of turbine flow, and reservoir volume as a function of pool elevation. The model itself is based on an analysis done in support of an Environmental Impact Statement submitted as part of a license application for a change in operations at the dams. The application includes typical operational constraints of hydropower dams, such as the need for a constant pool (water surface) elevation in some reservoirs, the mandatory satisfaction of minimum downstream flow demands (for fish populations), and the desire to provide extra electrical power at peak times of the day. The model allows the user to experiment with a few operating strategies and evaluate the results in terms of power generation, downstream flows, and pool elevations.
The basic peaking flow operations incorporate three adjacent reservoirs: Cochrane is upstream, and fills during off-peak hours, saving the bulk of the water for running through its turbines during peak demand. In doing so, the pool elevation of Cochrane can vary by as much as 25 feet in a day. Ryan, the next reservoir down, receives this peaking flow and simply routes it through its turbines, maintaining a level pool. In effect, then, Ryan's generating capacity is synchronized exactly with that of Cochrane, and the two powerhouses run almost as one. Downstream of Ryan is Morony, which fills during peaking operations, receiving the substantial flows from Cochrane and Ryan. Morony, therefore, also experiences extremes in pool elevation. Being the last reservoir in the project, Morony is charged with meeting downstream water flow demands. These demands are generally not satisfied by the storage in Morony alone, so Rainbow Reservoir, above Cochrane, shares its storage capacity, routing flows through Cochrane and Ryan as necessary to meet downstream demand.