page_title: Auburn Dam
section_title: Failure risk
hierarchical_section_title: Auburn Dam / Stopping the project / Failure risk
caption_attribution_description: Map of the area that would be inundated by a failure of the proposed Auburn Dam, CA
context_page_description: Auburn Dam was a proposed concrete arch dam on the North Fork of the American River east of the town of Auburn, California in the United States, on the border of Placer and El Dorado Counties. Slated to be completed in the 1970s by the U.S. Bureau of Reclamation, it would have been the tallest concrete dam in California and one of the tallest in the United States, at a height of 680 feet and storing 2,300,000 acre feet of water. Straddling a gorge downstream of the confluence of the North and Middle Forks of the American River and upstream of Folsom Lake, it would have regulated water flow and provided flood control in the American River basin as part of Reclamation's immense Central Valley Project.
  The dam was first proposed in the 1950s; construction work commenced in 1968, involving the diversion of the North Fork American River through a tunnel and the construction of a massive earthen cofferdam. Following a nearby earthquake and the discovery of an unrelated seismic fault that underlay the dam site, work on the project was halted for fears that the dam's design would not allow it to survive a major quake on the same fault zone.
context_section_description: The Auburn Dam would also be at risk for failure from an earthquake, due to the risk of the reservoir inducing a quake on one of the many fault lines that crosses the area, known as the Bear Mountain fault zone. Surface displacement of the ground might range from a few inches/centimeters to 3 feet (0.91 m) in each direction, depending on the magnitude of the earthquake. Although a new concrete-gravity design by Reclamation was modeled to survive a magnitude 6.5 earthquake, it performed poorly under the 7.0 that the USGS had originally estimated.
  A Bureau of Reclamation study released in 1980 projected that a failure of Auburn Dam would result in a giant wave reaching Folsom Lake within five minutes; depending on reservoir levels, it would cause a cascading failure of Folsom and Nimbus Dams downstream within an hour, unleashing millions of acre-feet of water which would cause far greater damage downstream than any natural flood. Most of the greater Sacramento area would be inundated; Nimbus Dam would be overtopped by 70 feet (21 m) of water and the California State Capitol would be under 40 feet (12 m) of water. An earlier study in 1975 predicted that a failure of Folsom Dam alone would result in over 250,000 deaths. If Auburn were to fail at full capacity, the resulting flood would be over three times larger, and cause even greater damage, inundating land for miles on either side of the American and Sacramento rivers.
caption: Map of the area around the confluence of the Sacramento and American Rivers that would be inundated if Auburn Dam were to fail
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