Grand Coulee Dam is the largest concrete dam and the greatest single source of water power in North America. It stands across the Columbia River about 90 miles (140 kilometers) northwest of Spokane, Washington. The dam is near the head of the Grand Coulee, a steep-walled rock chasm where the Columbia River once flowed.
The dam is the chief engineering feature of the Columbia Basin Project. The United States Bureau of Reclamation designed and built the dam, which was completed in 1942. It took less than eight years to build. Since then, the dam has undergone additional construction. Grand Coulee Dam is 5,223 feet (1,592 meters) long, 500 feet (152 meters) thick at the base, and 550 feet (168 meters) high, or about as high as a 46-story building. It contains about 12 million cubic yards (9 million cubic meters) of concrete.
Grand Coulee Dam has three power plants. The first of these plants went into full operation in 1941, the second in 1951, and the third in 1980. The three plants house 24 main generators and 3 smaller generators.
Behind Grand Coulee Dam is Franklin D. Roosevelt Lake. This reservoir is 151 miles (243 kilometers) long and holds about 11.8 million acre-feet (6.4 billion cubic meters) of water. A pumping facility houses six pumps and six pump-generators. A pump-generator is a reversible unit capable of generating electric power and pumping water. The dam’s total generating capacity is about 7 million kilowatts.
The pumps raise water from the lake 280 feet (85 meters) to a canal that flows into a reservoir in the Grand Coulee. From the reservoir, which is 27 miles (43 kilometers) long, the water enters the Columbia Basin Project irrigation system. Large-scale irrigation began in 1952. Today, the system provides water for more than 660,000 acres (267,000 hectares) of land.
See also Columbia River (Hydroelectric power and irrigation) .
