The Rock Island Project was the first dam to span the Columbia River. The Project is located near the geographical center of Washington State, on the Columbia River about 12 miles downstream from the city of Wenatchee. By river, the dam is 235 miles below the Canadian border and 453 miles above the mouth of the river at Astoria, Oregon.
Quick facts about the Rock Island Hydro Project:
Rock Island dam is constructed on Columbia River basalt similar to that which is exposed on the cliffs near the dam. The dam is a reinforced concrete structure which has its base anchored to this solid basaltic bedrock. Looking from the Douglas county side, a 590-foot-long gravity dam section rises above and in front of the left bank fishway. Attached to this wall is the 870-foot-long headwork which includes the First Powerhouse. The spillway is divided by the center fishway and has a total length of 1,424 feet. The east spillway contains a total of 14 gates while the west spillway has 17 gates. The second Powerhouse is 470 feet wide. The remaining length of the dam is taken up by the right bank fish facilities and assembly area.
In 1927, the Rock Island site came to the attention of the Stone and Webster Engineering Corporation, a Boston-based holding company that managed Puget Sound Power & Light Company. The site was recognized for its potential to provide power for the growing electrical load in the state. On Dec. 17, 1928 an application was filed with the Federal Power Commission for a preliminary permit to investigate the site. This was followed by an application for license submitted in January 1929 by the Washington Electric Company, a subsidiary construction corporation of Puget Sound Power & Light. The license was authorized on Oct. 16, 1929, and on Jan. 14, 1930, at the beginning of the Great Depression, construction started on the first dam to span the Columbia River.
The development of Rock Island Dam occurred over a period of some 50 years. There were three main construction periods, each taking place about 20 years apart as the need for affordable hydroelectric power was paramount in the region. Development began in January 1930, and the dam, powerhouse and first four operating units were turned over to Puget Sound Power & Light Company, during construction of the project, on June 30, 1931, and construction was completed in December 1932. Work on completion of the dam, powerhouse expansion and installation of six additional units by Chelan County PUD began in July 1951 and was completed on April 30, 1953. Construction of the Second Powerhouse, with its eight turbine generators located on the west bank of the river, began on Aug. 4, 1974. The Second Powerhouse was placed in commercial operation on Aug. 31, 1979.
The dam is a reinforced concrete structure. The base of the project is anchored to solid basaltic bedrock. Looking from the Douglas County side, a 590-foot-long gravity dam section rises above and in front of the left bank fishway. Attached to this wall is the 870-foot-long headworks which includes the First Powerhouse. The spillway is divided by the center fishway and has a total length of 1,424 feet. The east spillway contains a total of 14 gates. The west spillway has 17 gates. The Second Powerhouse is 470 feet wide. The remaining length of the dam is taken up by the right bank fish facilities and assembly area.
A steel shaft directly connects the turbine to the electricity-producing generator. In Powerhouse One, there is one house unit rated at 1,230 kilowatts and all four of the original generators have been rewound. One generator retains its original nameplate rating of 15,000 kilowatts. The other three were upgraded and each have a nameplate rating of 20,700 kilowatts. The six additional generators are each rated at 22,500 kilowatts.
The Second powerhouse contains eight horizontal bulb turbine generators. They were the first installed in the United States and were the largest in the world when installed between 1974-79. The generators are encased in watertight steel shells. Each submarine-like bulb is located within a draft tube (water passage). Each generator has a nameplate rating of 51,300 kilowatts, bringing the nameplate capacity of the eight units to 410,400 kilowatts. The total nameplate rating of both powerhouses is 623,725 kilowatts. The total project generates enough electrical power to serve a city the size of Vancouver, Washington plus the rest of Clark County.
Power from Rock Island Dam flows to major distribution points where it can be delivered to Chelan County customers. Power also flows to the BPA transmission grid, and to the Puget Sound area.
Although classified as hydraulic turbines, the prime movers are immense water wheels closely resembling a ship propeller. There are 11 of these vertical shaft impellers in the First Powerhouse. The water wheel blades are adjustable to maintain maximum capacity and efficiency at different heads caused by varying river flow conditions. The 11 units produce 334,100 horsepower, which is equal to the horsepower generated by 66 mainline diesel electric locomotives or 2,371 mid-sized automobiles.
There are eight horizontal shaft turbines in the Second powerhouse, each developing 71,600 horsepower. The turbine shaft drives the generator at a speed of 85.7 revolutions per minute. The eight units produce a total of 572,800 horsepower, which is equal to the horsepower generated by 115 mainline diesel electric locomotives or 4,114 mid-sized automobiles.
The crest of the reservoir can be regulated by spillway gates, which open individually and allow water to pass through. The gates pass water seasonally that is surplus to power generation requirements or as required for downstream fish passage. There are 31 crest gates.