Overview

Grand Coulee Dam is a large hydroelectric dam located on the Columbia river in Central Washington. Made from 12 million cubic yards of concrete, Grand Coulee Dam is the largest concrete structure in the United States and the third largest hydroelectric facility in the world. Sharing the river with 10 other U.S. dams, Grand Coulee is the first dam encountered on the Columbia after the river enters the U.S from Canada. Lake Roosevelt, the reservoir created by the dam, contains 9 million acre-feet of water and streches over 150 miles back to the border.

Grand Coulee Dam fills three primary rolls. First, with its 24 generators providing up to 6.5 million kilowatts of power, it is a major provider of electrical power to the Northwest. Secondly, water pumped from behind the dam provides irrigation for over half a million acres of the Columbia basin from Coulee City in the north to Pasco, WA in the south. Finally, by strictly regulating the Columbia's highly variable flow rate, the dam provides much needed flood control to the river basin.

History

Grand Coulee Dam and the Columbia Basin Project are managed by the U.S. Bureau of Reclamation, an agency of the Department of the Interior. The Bureau was established by congress in 1902 and was tasked with boosting development in the West by developing water storage and irrigation networks west of the 100th meridian. The Bureau took a tentative interest in providing Central Washington with irrigation water pumped from the Columbia as early as 1904. For one reason or another this idea was not followed up for several years.

The idea for damming the Columbia below the Grand Coulee was first proposed by Ephrata attorney William M. Clapp in the spring of 1917. The idea gained rapid support from the citizens of Ephrata and the surrounding area. Eventually the state government took an interest in the project as well.

Preliminary feasibility studies were carried out in the 1920s. Initially the primary purpose of the dam was to provide irrigation water. Although the dam idea had a great deal of local support there were other irrigation proposals in the works. In particular, a plan to build a long canal to carry water down from the Pend Oreille river in Northern Idaho was under serious consideration.

A final report favoring the construction of the dam was produced by the Corp of Engineers in late 1931 and presented to the 73d Congress of the United States as House Document #103. This was supplemented in January of 1932 by a report from the Bureau of Reclamation outlining the details of a dam-based irrigation project.

$377,000 was comitted to the project by the State of Washington in 1933. This was followed soon afterward by a promise from president Franklin D. Roosevelt to provide initial funds to the tune of 63 million dollars to begin work on the dam as a project under the Public Works Administration.

Not wanting to back up water into Canada, it was decided that the Canadian border would be the ultimate limiting factor as to how high the dam could be built. However, at the time there was a surplus of electric power in the Northwest and no major increase predicted for the foreseeable future. For this reason the original proposal called for a LOW dam. This dam would be 200 feet lower than the maximum height allowed by the Canadian border restriction. It would provide irrigation and flood control with the possibility of a reduced amount of power generation. However, it was decided to design the structure in such a way that it could be raised to its full height providing a corresponding increase in generation capacity if the need ever presented itself.

Initial excavation of the dam site began in December of 1933 with work toward improving the local infrastructure proceeding in parallel. On August 30, 1935 congress authorized the construction of the full high dam and no low dam version was ever completed. By 1941 the main dam was essentially finished with construction of the powerhouses and pumping plant underway.

Ironically, because of the Second World War and the importance of the Northwest's aluminum industry to that effort, the production of electricty became the overriding priority for the dam. Irrigation was deferred until later. During the war six Grand Coulee generators were brought on line as well as two generators borrowed from the yet to be completed Shasta dam.

After the war an emphasis was put back on irrigation. Construction was resumed on the pumping plant in 1946. By 1951 the plant and its six 65,000 horsepower pumps were ready for operation. The first water was delivered to the Banks Lake equalizing reservoir above the dam that same year. The first year only 66,000 acres were irrigated. Since then this figure has steadily increased as more canals, siphons, reservoirs and auxilary pumping plants have been added to the project.

In 1973 the pumping plant was extended to the south and two of six 67,500 horsepower pump-generator units were installed. Unlike the existing six pumps, these pump-generators can be reversed during periods of high power demands and operated as generators. In their generation mode each unit can produce 50,000 kW of electrical power. The remaining four pump/generator units were installed and operating by late 1983.