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Tacoma Power provides customers with clean, renewable hydroelectric energy
p Cushman Dam No. 2 on the North Fork Skokmish River in Mason County
At Tacoma Power, approximately 98% of our electricity comes from clean, renewable hydroelectric energy. We generate about half of that at our four hydro projects: the Cowlitz River Project in Lewis County, Cushman Hydro Project in Mason County, Wynoochee River Project in Grays Harbor County, and the Nisqually River Project in Pierce County.
The hydroelectric power setup and system vary by project. Cowlitz has two dams and two powerhouses. Mossyrock Dam, the tallest in Washington state at 606 feet (a foot taller than the Space Needle), forms Riffe Lake, and Mayfield Dam forms Mayfield Lake. At Cushman, there are two dams and three powerhouses on the North Fork Skokomish River. The dams form Lake Cushman and Lake Kokanee. At Wynoochee, there is one dam (owned by the City of Aberdeen) and one powerhouse (built and owned by Tacoma Power). The dam forms Wynoochee Lake. At Nisqually, there are two dams, one forms Alder Lake, and the other forms the LaGrande reservoir, and there are two powerhouses. “Each hydro project has a unique operating license that comes with its own requirements. To meet those requirements and provide our customers with clean, low cost, reliable, and environmentally responsible energy, it takes a collective effort from staff,” said Cowlitz River Project manager Chad Chalmers. A powerhouse is a structure that houses the generators and turbines that create the power. Hydroelectric power generates when water flows through a system of tunnels or pipes (penstocks). The water pushes against the blades in a turbine. The turbine converts the kinetic energy from the falling water into mechanical energy. The mechanical energy converts into electrical energy through a generator. It then goes through a step-up transformer to change voltage before being sent to the transmission lines to provide clean energy to our nearly 180,000 customers.
Water runoff from rain and snow is stored in the lakes until needed to make electricity. That storage is one of the benefits of hydropower - it is available 24/7, which means that when the sun goes down and the wind dies down, hydropower is still there to meet energy demands. “Hydro generators have a unique ability that many other types of generation do not; hydro generators can respond to grid disturbances very quickly,” said Chad. “A disturbance can be anything from clouds coming in and blocking out the sun, or the wind not blowing, or an unexpected outage at a large baseload fossil fuel plant.” Generating hydroelectric energy provides many other benefits, such as family-wage jobs, flood mitigation (at some locations), and increased tourism due to recreational opportunities. Visitors use the dams’ reservoirs for boating, fishing, and swimming. Additionally, Tacoma Power owns and operates four beautiful parks - three at Cowlitz and one at Nisqually. Tacoma Power has robust fisheries and wildlife programs to mitigate the impact of the dams. “We use Lake Cushman as part of our sockeye reintroduction program,” said Cushman Hydro Project manager Brad Ennis. “We release some of our smoltsize sockeye into the lake to grow until they are ready to migrate out to the ocean.” Chris says Tacoma Power focuses on public safety, safeguarding the environment, protecting natural resources, and supporting the local economy in the communities where we generate hydroelectric power.
q Wynoochee Dam on the Wynoochee River in Grays Harbor County. p Mossyrock Dam on the Cowlitz River in Lewis County q Alder Dam on the Nisqually River in Pierce County
