thumb|The Columbia Basin Irrigation Project
The Columbia Basin Project (or CBP) in Central Washington, United States, is the irrigation network that the Grand Coulee Dam makes possible. It is the largest water reclamation project in the United States, supplying irrigation water to over of the large project area, all of which was originally intended to be supplied and is still classified irrigable and open for the possible enlargement of the system. Water pumped from the Columbia River is carried over of main canals, stored in a number of reservoirs, then fed into of lateral irrigation canals, and out into of drains and wasteways. The Grand Coulee Dam, powerplant, and various other parts of the CBP are operated by the Bureau of Reclamation. There are three irrigation districts (the Quincy-Columbia Basin Irrigation District, the East Columbia Basin Irrigation District, and the South Columbia Basin Irrigation District) in the project area, which operate additional local facilities.
History
The U.S. Bureau of Reclamation was created in 1902 to aid development of dry western states. Central Washington's Columbia Plateau was a prime candidate—a desert with fertile loess soil and the Columbia River passing through.
Competing groups lobbied for different irrigation projects; a Spokane group wanted a gravity flow canal from Lake Pend Oreille while a Wenatchee group (further south) wanted a large dam on the Columbia River, which would pump water up to fill the nearby Grand Coulee, a formerly-dry canyon-like coulee.
After thirteen years of debate, President Franklin D. Roosevelt authorized the dam project with National Industrial Recovery Act money. (It was later specifically authorized by the Rivers and Harbors Act of 1935, and then reauthorized by the Columbia Basin Project Act of 1943 which put it under the Reclamation Project Act of 1939.) These flood basalts are exposed in some places, while in others they are covered with thick layers of loess.
During the last ice age, glaciers shaped the landscape of the Columbia River Plateau. Ice blocked the Columbia River near the north end of Grand Coulee, creating glacial lakes Columbia and Spokane. Ice age glaciers also created Glacial Lake Missoula, in what is now Montana. Erosion allowed glacial Lake Columbia to begin to drain into what became Grand Coulee, which was fully created when glacial Lake Missoula along with glacial Lake Columbia catastrophically emptied. This flood event was one of several known as the Missoula Floods. Unique erosion features, called channeled scablands, are attributed to these floods.
Component units of the project
Grand Coulee Dam Complex and Lake Roosevelt
- Grand Coulee Dam (1950)
- Right (north) Powerhouse
- Left (south) Powerhouse
- Third Powerhouse (1974) was added as a north wing of the dam from the original Right powerhouse. This addition expanded power generation by 300%.
- Lake Roosevelt
- Grand Coulee Pumping-Generating Plant (1953) consist of twelve pump units with combined power of , of which six are reversible pump-generator turbine units with a combined generating capacity of . The pumps are used to move water from Lake Roosevelt into Banks Lake, from which it can be either sent south into the Columbia Basin Irrigation system or returned to Lake Roosevelt by the reversible generating pump-turbines to create additional electricity for the grid. This amount is larger than the combined annual flows of the nearby Yakima, Wenatchee, and Okanogan rivers. There were plans to double the area of irrigated land, according to tour guides at the dam, over the next several decades. However, the Bureau of Reclamation website states that no further development is anticipated, with irrigated out of the original planned.
Interest in completing the Columbia Basin Project's has grown in the late 20th and early 21st centuries. One reason for the renewed interest is the substantial depletion of the Odessa aquifer. Agricultural operations within the CBP's boundaries but outside the developed portion have for decades used groundwater pumped from the Odessa aquifer to irrigate crops. of several types of salmon.
There are a number of issues regarding the runoff of irrigation water. The project region receives about 6 to of annual rainfall, while the application of irrigation water amounts to an equivalent 40 to . The original plans did not sufficiently address the inevitable seepage and runoff. The project itself involves costs that are difficult to determine. The farms that receive irrigation water must pay for it, but due to insufficient data from the Bureau of Reclamation, it is not possible to compare the total cost paid by the Bureau to the payments received. Nevertheless, the farm payments account for only a small fraction of the total cost to the government, resulting in the project's agricultural corporations receiving a large water subsidy from the government.