More About Grand Coulee Dam
An incredible feat of ingenuity and hard labor, Grand Coulee Dam is a modern wonder. The US Bureau of Reclamation began to construct Grand Coulee Dam in 1933 during the Great Depression. The project took nine years to build the initial structure and canals for irrigation of the fertile soil of the Columbia Basin. Before President Franklin D. Roosevelt authorized the construction, a political battle raged between building the dam here or building a 134-mile canal from Lake Pend Oreille, Idaho, to the area.
Massive Grand Coulee Dam fills the channel.
Grand Coulee Dam stands 550 feet above bedrock which is about as high as the Washington Monument. The height above the water below the dam is 380 feet. The dam is 500 feet wide at the base and the total length of the dam is 5,223 feet, nearly a mile! The spillway measures 1650 feet wide bordered by the left and right powerplants.
As noted above this huge pile of sand dwarfs the town of Grand Coulee. The green area in lower center is a combination baseball diamond and football field. The sand is just a few blocks away and is part of the 38,574,503 cubic yards of material excavated during the construction. That amount of sand, clay, gravel and boulders that were removed could have built a highway 10,500 miles long. The material was taken by a mile-long conveyor belt system up 500 feet and was called the "river of dirt". Nearly 12 million cubic yards of concrete were used in building the dam. It is estimated that this is enough concrete to build a six-foot wide sidewalk clear around the Earth at the equator.
The photo at left shows the powerhouse which was added after the initial construction. The tiny white dots in the bottom left corner are parked cars. Started in 1967, this portion took eight years to build and 757,524 cubic yards of concrete. The total electric power generated by the dam is 6,809 megawatts.
In addition to electric power generation the dam provides a source for irrigation. Water is pumped up 280 feet from Lake Roosevelt into Banks Lake reservoir. Over 500,000 acres of farmland is irrigated, more than twice the size of the state of Delaware.
When an ice dam blocked the Columbia River at this same spot Glacial Lake Columbia was formed. When the ice dam holding Glacial Lake Missoula broke, floodwaters could not get past this ice dam and flowed south creating the Grand Coulee. Banks Lake reservoir partially fills the coulee. This USBR aerial view of the area shows where the ice age floodwaters traveled to create the Grand Coulee. The USGS aerial view shows more of the area.
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Here are some basic terms used in the tour. Find more geology terms in the Glossary.
- Volcanic rock caused by partial melting of the Earth's crust.
- Channeled Scabland
- Area in Washington state where huge floods made channels in a large, deep basalt flow. Named by J Harlan Bretz during the 1920's in various publications. See also Channeled Scabland and Glacial Lake Missoula.
- Long winding channel cut through lava formations. A term primarily used in the northwestern United States.
- Large rock or boulder carried by water or glaciers and left behind.
- Coarse-grained igneous rock usually without obvious bands or markings.
- Rounded rock fragments larger than sand.
- Ice Age
- A period in Earth's history when much of the continents are covered with ice sheets and glaciers.
- Pale yellow, glassy material that forms when hot steam and other gases contact water during a lava flow. Sand and clay is usually mixed in as well.
- Pillow Basalt
- Basalt formed underwater or as a basalt flow contacts a river or lake.
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