The Teton Dam was an earthen dam in the western United States, on the Teton River in eastern Idaho. It was built by the U.S. Bureau of Reclamation, one of eight federal agencies authorized to construct dams. Located between Fremont and Madison counties, it suffered a catastrophic failure on June 5, 1976, as it was filling for the first time.
The collapse of Teton Dam killed 11 people and 16,000 livestock. The dam cost about $100 million to build and the federal government paid over $300 million in claims related to its failure. Total damage estimates have ranged up to $2 billion, and the dam was not rebuilt.
History and geology
Interest in building a dam in the eastern Snake River Plain had arisen for many years to control spring runoff and provide a more constant water supply in the summer. The area had suffered a severe drought in 1961, followed by severe flooding in 1962. The Bureau of Reclamation proposed the Teton Dam in 1963 and Congress passed, without opposition, an authorizing bill the following year. The planned dam was to be an earthen structure high and long, creating a reservoir in length. The impounded water would be used to generate hydroelectric power. An environmental impact statement was issued for the dam in 1971, but it did not raise the possibility of a collapse. Lack of funding and site preparation work and questions surrounding the required environmental impact statement stalled the project. Barely 14 pages long, the statement quickly drew the ire of opponents of the project.
On September 27, 1971, several environmental and conservation groups filed a lawsuit in Idaho District Court to stop the construction. Opponents of the dam questioned the project's justifications. They argued that damming a wild and scenic river would result in the destruction of its trout fishery and other wildlife habitat and "replace a unique resource with a vulgar one." The suit questioned the economic return on the investment, the bureau's compliance with the National Environmental Policy Act, and the geologic soundness of the dam's location. Concerns over the seismic conditions of the dam site delayed the bid process pending further review by the Department of the Interior. Pressure from Idaho's congressional delegation stopped the review, and in spite of the lawsuit, bids were taken in Idaho Falls on October 29, 1971. The contract was awarded to Morrison-Knudsen Co. of Boise, assisted by Peter Kiewit Sons Co. of Omaha, Nebraska. The $39 million contract was awarded in December 1971. In spite of the lawsuit, work began in February 1972. After various motions, amended complaints, attempted injunctions, and appeals, the suit was dismissed on December 23, 1974.
The eastern Snake River Plain is almost entirely underlain by basalt erupted from large shield volcanos on top of rhyolitic ash-flow tuff and ignimbrites. The tuff, a late-Cenozoic volcanic rock, is 1.9 million years old. The dam site is composed of basalt and rhyolite, both of which are considered unsuitable for dam construction because of their high permeability. This was confirmed by long-term pump-in tests at rates of per minute. Test cores, drilled by engineers and geologists employed by the Bureau of Reclamation, showed that the canyon rock at the dam site is highly fissured and unstable, particularly on the right side (as one faces the direction of flow). The widest fissures were determined to be wide. The bureau planned to seal these fissures by injecting grout into the rock under high pressure to create a grout curtain in the rock.
In addition, an investigation of the area by geologists of the U.S. Geologic Survey indicated that it was seismically active; five earthquakes had occurred within of the dam site in the previous five years, two of which had been of significant magnitude. This information was provided to the Bureau of Reclamation in a memorandum, but the geologists' concerns were considerably watered down in the 6-month redrafting process before the USGS sent the final version of the memo to the USBR in July 1973.