The Rock Island Project was the first dam to span the Columbia
River.
The hydro 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 Dam:
- Length of Powerhouse 1 - 870 ft
- Length of Power house 2 - 470 ft
- Total length of Dam - 3,800 ft
- Height of Powerhouse 1 - 110 ft
- Height of Powerhouse 2 - 135 ft
- 19 generators
- First powerhouse - 11 generators
- Second powerhouse - 8 horizontal shaft (bulb) generators
- Generator nameplate capacity is 629 megawatts
- Dam contains 31 spillway gates
- Original construction of first powerhouse completed in 1933
- Capacity expanded in 1952-1953 for Alcoa
- Second powerhouse was constructed in 1979
- Project license expires in the year 2028
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.
History
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.
Construction
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.
Project Description
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.
Generators
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.
Transmission
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.
Turbines
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.
Spillway Gates
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.