Operation and benefits

The dam's primary goal, irrigation, was postponed as the wartime need for electricity increased. The dam's powerhouse began production around the time World War II began, and its electricity was vital to the war effort. The dam powered aluminum smelters in Longview and Vancouver, Washington, Boeing factories in Seattle and Vancouver, and Portland's shipyards. In 1943, its electricity was also used for plutonium production in Richland, Washington, at the Hanford Site, which was part of the top-secret Manhattan Project.^[73][74] The demand for power at that project was so great that in 1943, two generators originally intended for the Shasta Dam were installed at Grand Coulee in an effort to hurry the generator installation schedule.^[75]

Irrigation

Main article: Columbia Basin Project

Water is pumped via the Pump-Generating Plant's 12-foot (3.7 m) diameter pipes 280 ft (85 m) from Lake Roosevelt to a 1.6 mi (2.6 km) feeder canal. From the feeder canal, the water is transferred to Banks Lake which has an active storage of 715,000 acre·ft (882,000,000 m³). The plant's twelve 65,000–70,000 horsepower pumps can transfer up to 1,605 cu ft/s (45 m³/s) to the lake. Currently, the Columbia Basin Project irrigates 670,000 acres (2,700 km²) with a potential for 1.1 million.^[68] Over 60 different crops are grown within the project and distributed throughout the United States.^[58]

Power

Grand Coulee Dam supports four different power houses containing 33 hydroelectric generators. The original Left and Right Powerhouses contain 18 main generators and the Left has an additional three service generators for total installed capacity of 2,280 MW. The first generator was commissioned in 1941 and all 18 were operating by 1950. The Third Powerplant contains a total of six main generators with a 4,215 MW installed capacity. Generators G-19, G-20 and G-21 in the Third Powerplant have a 600 MW installed capacity but can operate at a maximum capacity of 690 MW which brings the overall maximum capacity of the dam's power facilities to 7,079 MW. The Pump-Generating Plant contains six pump-generators with an installed capacity of 314 MW. When pumping water into Banks Lake they consume 600 MW of electricity. Each generator is supplied with water by an individual penstock. The largest of these feed the Third Powerplant and are 40 ft (12 m) in diameter and can supply up to 35,000 cu ft/s (990 m³/s). The dam's power facilities originally had an installed capacity of 1,974 MW but expansions and upgrades have increased generation to 6,809 MW installed, 7,079 MW maximum. In 2014, 20.24 TWh of electricity was generated, resulting in a plant factor of 35%.^[2]

Hydroelectric generators at Grand Coulee Dam^[76]

Location	Type	Quantity	Capacity (MW)	Total capacity (MW)
Left Powerhouse	Francis turbine, service generator	3 (LS1-LS3)	10	30
	Francis turbine, main generator	9 (G1-G9)	125	1,125
Right Powerhouse	Francis turbine, main generator	9 (G10-G18)	125	1,125
Third Powerplant	Francis turbine, main generator	3 (G22-G24)	805	2,415
	Francis turbine, main generator	3 (G19-G21)	600 (Max: 690 MW)	1,800
Pump-Generating Plant	Pump-generator, peak generator	4 (PG9-PG12)	53.5	214
	Pump-generator, peak generator	2 (PG7-PG8)	50	100
Totals		33		6,809

Spillway

Pump-Generating Plant and Roosevelt Lake at bottom, feeder canal to Banks Lake at top

Grand Coulee Dam's spillway is 1,650 feet (500 m) long and is an overflow, drum-gate controlled type with a 1,000,000 cu ft/s (28,000 m³/s) maximum capacity.^[69] A record flood in May and June 1948 flooded lowland below the dam and highlighted its limited flood control capability at the time,^[77] as its spillway and turbines hit a record flow of 637,800-cubic-foot-per-second (18,060 m³/s).^[68] The flood damaged downstream riverbanks and deteriorated the face of the dam and its flip bucket at the base (toe) of the spillway.^[78] The flood spurred the Columbia River Treaty and its provisions for dams constructed upstream in Canada, which would regulate the Columbia's flow.^[79]

Cost benefits

The Bureau of Reclamation in 1932 estimated the cost of constructing Grand Coulee Dam (not including the Third Powerplant) to be $168 million; its actual cost was $163 million ($1.85 billion in 1998). Expenses to finish the power stations and repair design flaws with the dam throughout the 1940s and '50s added another $107 million, bringing the total cost to $270 million ($2.6 billion in 1998), about 33% over estimates.^[80] The Third Powerplant was estimated to cost $390 million in 1967, but higher construction costs and labor disputes drove the project's final cost in 1973 to $730 million ($2.93 billion in 1998), about 55% over estimates. Despite estimates being exceeded, the dam became an economic success, particularly with the Third Powerplant exhibiting a benefit-cost ratio of 2:1.^[63] Although Reclamation has only irrigated about half of the land predicted, the gross value of crop output (in constant dollars) had doubled from 1962 to 1992, largely due to different farming practices and crop choices.^[36] The Bureau expects the money earned from supplying power and irrigation water will pay off the cost of construction by 2044.^[81]