Cushman No. 1 Hydroelectric Power Plant, Spillway, North Fork of Skokomish River, 5 miles West of Hood Canal, Hoodsport, Mason County, WA

Significance: The Cushman No. 1 Hydroelectric Power Plant is a significant example of medium head hydroelectric technology in the west from the 1920s. Located in steep, inaccessible terrain prone to flooding, the plant construction was a significant engineering feat and used a revolutionary design for the time, a constant angle concrete arch dam, for the steep, narrow gorge in which it is located. When completed in 1925, the dam formed a lake 9.6 miles long, covering 4,000 acres, which was the largest reservoir in the Pacific Northwest and the tenth largest in the United States. The spillway is unusual for its converging chute design. It also is notable for hydrologic patterns (standing waves) that develop during spills and which result from the converging design of the structure.
Survey number: HAER WA-26-A
Building/structure dates: 1929 Initial Construction
Building/structure dates: ca. 1930 Subsequent Work
Building/structure dates: 1981 Subsequent Work