American Travel Journal: Gorge Powerhouse - Seattle City Light

The Skagit River Hydroelectric Project of Seattle City Light consists of Gorge Dam and Powerhouse, Diablo Dam, and Ross Dam. Together, these three facilities are capable of producing 847.9 megawatts of electricity. They generate about 40% of the power of the total power generated by Seattle City Light, but only about 20% of the power distributed by Seattle City Light.

Construction of the Gorge Dam and powerhouse began in 1919 with the first of two units beginning commercial operation on September 27, 1924. Diablo Dam went into service on October 30, 1936, and Ross Dam followed on December 30, 1952. The first Gorge Dam was a crib dam completed in 1923. It was replaced by a concrete diversion dam in 1950 and by the current Gorge High Dam in 1961. One additional turbine was added to the powerhouse with each new dam, increasing the capacity to 207.5 megawatts for the four turbines. Gorge Dam is located over two miles upstream of the powerhouse and is connected to the powerhouse by an 11,000-foot-long concrete-lined tunnel with a diameter of 21.5 feet. The tunnel descends 380 feet in its length. When added to the 140-foot depth of Gorge Lake, this produces a head of over 500 feet for the four turbines.

A gallery overlooking the turbine floor of the Gorge Powerhouse is open to the public. It contains a wall of historic photographs of the construction of each of the three generating stations as well as hands-on displays related to the generation of electricity. In addition, restroom facilities are also open to the public.

All of the dams, switchyards, transmission lines, and other facilities of the Skagit River Hydroelectric Project are located in the Ross Lake National Recreation Area (NRA) which bisects the North Cascades National Park. The recreation area, as well as the Lake Chelan NRA to the south, are managed in conjunction with the national park.