p Cushman Dam No. 2 on the North Fork Skokmish River in Mason County
Tacoma Power provides customers with clean, renewable hydroelectric energy 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.
“We are fortunate that we can generate almost half of our customers’ energy needs ourselves,” said Generation manager Chris Mattson. “Having these resources provides us with generating flexibility, and that helps us keep costs low for our customers.” 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
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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.
