page_title: Risks to the Glen Canyon Dam
hierarchical_section_title: Risks to the Glen Canyon Dam
context_page_description: Glen Canyon Dam, a concrete arch dam on the Colorado River in the American state of Arizona, is viewed as carrying a large amount of risk, most notably due to siltation. The Colorado and San Juan rivers deposit large volumes of silt into Lake Powell, slowly decreasing its capacity. The sediment will eventually build up against the dam and could affect its safe operation and lead to its failure.
  The dam, anchored in unstable Navajo sandstone, nearly failed in 1983 as the result of a flood on the upper Colorado River that led to extended use of its tunnel spillways. The spillways, designed for short-term use, soon underwent cavitation and began to fail. Emergency installation of eight-foot flashboards and other efforts narrowly averted total failure.
  Siltation, concrete degradation, spillway operational problems, and unstable dam abutments are all key factors that affect the safe operation of the dam. It is estimated that a breach of the dam would produce a floodwave that would overtop the Hoover Dam.
context_section_description: Glen Canyon Dam, a concrete arch dam on the Colorado River in the American state of Arizona, is viewed as carrying a large amount of risk, most notably due to siltation. The Colorado and San Juan rivers deposit large volumes of silt into Lake Powell, slowly decreasing its capacity. The sediment will eventually build up against the dam and could affect its safe operation and lead to its failure.
  The dam, anchored in unstable Navajo sandstone (sometimes said to be "solidified sand dunes"), nearly failed in 1983 as the result of a flood on the upper Colorado River that led to extended use of its tunnel spillways. The spillways, designed for short-term use, soon underwent cavitation and began to fail. Emergency installation of eight-foot flashboards and other efforts narrowly averted total failure.
  Siltation,  concrete degradation, spillway operational problems, and unstable dam abutments are all key factors that affect the safe operation of the dam. It is estimated that a breach of the dam would produce a floodwave that would overtop the Hoover Dam. The dam's useful lifespan has been estimated by some to be no more than 85 to 100 years, and was described as "America's most regretted environmental mistake" by David Brower, then-head of the Sierra Club. Different estimates by the Bureau of Reclamation and others suggest a lifespan of between 500–700 years.
caption: Glen Canyon Dam viewed from inside lower Glen Canyon
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