Valley in Douglas County, NE Washington, USA; the Grand Coulee Dam is a major gravity dam on the Columbia R, impounding L Franklin D Roosevelt; built 193342; height 168 m/550 ft; length 1272 m/4173 ft; can generate 6180 megawatts of hydroelectricity.
The Grand Coulee is an ancient river bed in the U.S. state of Washington.
Geological history
The Grand Coulee is part of the Columbia River Plateau.
About 10 to 15 million years ago volcanic eruptions from the Cascade Mountains began to fill the inland sea with lava.
Two million years ago the Pleistocene epoch began and Ice age glaciers invaded the area. In some areas north of the Grand Coulee they were as much as 3 km (10000 feet) thick. Grooves in the exposed granite bedrock are still visible in the area from the movement of glaciers and numerous glacial erratics in the elevated to the Northwest of the coulee.
Although early theories suggested that glaciers diverted the Columbia River into what became the Grand Coulee and that normal flows caused the errosion observed, geologists now agree that it was created by glacial diversion combined wtih massive glacial floods from Lake Missoula. The river bed is about 600 feet (200 m) below the Grand Coulee.
Modern Uses
The area surrounding the Grand Coulee is a shrub-steppe with an average annual rainfall less than ten inches.
The Columbia Basin Project changed this in 1952, using the ancient river bed as an irrigation distribution network. The lake is filled by pumps from the Grand Coulee Dam and forms the first leg of a hundred mile (160 km) system. Canals, siphons and more dams are used throughout the coulee and surrounding area, supplying over 600,000 acres (2,400 km²) of farm land.
Water has turned the area into a haven for wildlife, including Bald Eagles.
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