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Risks to the Glen Canyon Dam
Glen Canyon Dam, a concrete arch dam on the Colorado River in the U.S. state of Arizona, has been associated with a large amount of risk, most notably the risk of its siltation and failure. Because of high silt content carried in by the Colorado and San Juan rivers, Lake Powell is gradually filling with sediment, decreasing its capacity; eventually the sediment will build up against the dam and affect its safe operation.
The dam, anchored in unstable Navajo sandstone (sometimes said to be "solidified sand dunes"),〔(【引用サイトリンク】title=Glen Canyon Dam )〕 nearly failed in 1983 as the result of a flood on the upper Colorado River. Siltation, degradation of concrete and reinforcements, spillway operational problems, and unstable dam abutments are all key factors that affect the safe operation of the dam.〔(【引用サイトリンク】title=Glen Canyon Dam )〕 It is estimated that a breach of the dam would produce a floodwave that would overtop the Hoover Dam.〔 〔(【引用サイトリンク】title=Nuclear Green )〕 As the dam's useful lifespan is estimated by some to be no more than 85 to 100 years, the dam has been called "America's most regretted environmental mistake" by David Brower, then-head of the Sierra Club.〔(【引用サイトリンク】title=History of the River Restoration Movement )〕 Other estimates, by the Bureau of Reclamation and others suggest a lifespan of between 500–700 years.〔
==Overview==
(詳細はarch dam on the Colorado River in northern Arizona in the United States, just north of Page. The dam was built to provide hydroelectricity and flow regulation from the upper Colorado River Basin to the lower. Its reservoir is called Lake Powell, and is the second largest artificial lake in the country, extending upriver well into Utah. The dam is named for Glen Canyon, a colorful series of gorges, most of which now lies under the reservoir.
Construction of Glen Canyon Dam started in 1956 and was not finished until 1966. When the reservoir filled, the dam began to deliver a steady, regulated flow of water downstream and generate a cheap, plentiful supply of electricity. In 1983, major floods nearly led to the dam's collapse, but disaster was averted by a close margin. By taming floods and other factors that once characterized the Colorado, the dam has led to major physical and ecological changes in the lower river. Controversy continues over the effects both positive and negative of the dam, which has also been covered in many literary works.
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