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| One estimate placed damage to Hibbard and Rexburg area, with a population of about 10,000, at 80 percent of existing structures. The Snake River flows through the industrial, commercial and residential districts of north Rexburg. A significant reason for the massive damage in the community was the location of a large commercial lumber yard directly upstream. When the flood waters hit, thousands of board feet of timber caught fire from leaking gas, and |
One estimate placed damage to Hibbard and Rexburg area, with a population of about 10,000, at 80 percent of existing structures. The Snake River flows through the industrial, commercial and residential districts of north Rexburg. A significant reason for the massive damage in the community was the location of a large commercial lumber yard directly upstream. When the flood waters hit, thousands of board feet of timber caught fire from leaking gas, and were swept downstream. The force of the logs and cut lumber, and the subsequent fires, practically destroyed the city. | ||
| The flood waters traveled west along the route of the south fork of the Snake, around the ], significantly damaging the community of ]. The city of ], even further down on the flood plain, had time to prepare. At the older ] downstream, engineers increased discharge by less than 5% before the flood arrived.<ref>{{cite web|title=Data From American Falls Dam|publisher=Zeb Palmer (data courtesy Bureau of Reclamation)|url=http://www.zebpalmer.com/oldblogarchive/teton-dam-failure-actual-data-for-american-falls/|accessdate=2008-12-20}} {{Dead link|date=September 2010|bot=H3llBot}}</ref> That dam held, and the flood was effectively over, but tens of thousands of acres of land near the river were stripped of fertile topsoil.<ref name="CD407"/> | The flood waters traveled west along the route of the south fork of the Snake, around the ], significantly damaging the community of ]. The city of ], even further down on the flood plain, had time to prepare. At the older ] downstream, engineers increased discharge by less than 5% before the flood arrived.<ref>{{cite web|title=Data From American Falls Dam|publisher=Zeb Palmer (data courtesy Bureau of Reclamation)|url=http://www.zebpalmer.com/oldblogarchive/teton-dam-failure-actual-data-for-american-falls/|accessdate=2008-12-20}} {{Dead link|date=September 2010|bot=H3llBot}}</ref> That dam held, and the flood was effectively over, but tens of thousands of acres of land near the river were stripped of fertile topsoil.<ref name="CD407"/> | ||
Revision as of 01:18, 4 September 2012
Dam| Teton Dam | |
|---|---|
 | |
| Construction cost | $48,825,000 |
The Teton Dam was a federally-built earthen dam in Idaho in the United States, put up by the Bureau of Reclamation, one of eight federal agencies authorized to construct dams. Located on the Teton River in the eastern part of the state between Fremont and Madison counties, it suffered a catastrophic failure on June 5, 1976, when it was being filled for the first time. The collapse of the dam resulted in the deaths of 11 people and 13,000 head of cattle. 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. The dam has not been rebuilt.
History and geology
There had been interest in building a dam in the eastern Snake River Plain 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 serious 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 310 feet high and 0.6 miles long which would create a reservoir 17 miles long. 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.
The primary contractor for the dam was Morrison-Knudsen Co. of Boise, assisted by Peter Kiewet Sons Co. of Omaha, Nebraska. The $39 million contract was awarded in December 1971 and work began in 1972.
The Snake River Plain is a broad tectonic depression on top of rhyolitic ash-flow tuff. The tuff, a late-Cenozoic volcanic rock dates to about 1.9 million years and sits on top of sedimentary rock. The area is very permeable, highly fissured and unstable. Test boreholes, drilled by engineers and geologists employed by the Bureau of Reclamation, showed that right side of the canyon was highly fissured, but the widest fissures were determined to be only 1.7 inches wide, and therefore could be remediated by the Bureau's favored method of "grouting" – injecting concrete into the substrates under high pressure.
In addition, an investigation of the area by geologist of the United States Geological Survey indicated that it was seismically active: there had been five earthquakes which occured within 30 miles 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 six-month re-drafting process before the USGS sent the final version of the memo to the BOR in July 1973.
In 1973, when the dam was only half-built, but almost $5 million had already been spent on the project, it was discovered that the right bank was much more significantly fissured than had been thought, with "caves" large enough for a person to walk through. This necessitated using twice as much grouting as had been originally anticipated – 118,000 linear feet was used in total. Later, the report of a committee of the House of Representatives which invesitgated the dam's collapse felt that the discovery of the "caves" should have been sufficient for the Bureau of Reclamation to doubt its ability to fill them in with grout, but this did not happen: the Bureau continued to insist, even after the dam had failed, that the grouting was appropriate.
Filling the dam
The dam was completed in November 1975, and filling the reservoir began at the standard rate of 1 foot (0.30 m) a day. However, snows were heavy that winter, and five months later the project's construction engineer requested permission to double the filling rate in order to deal with the additional spring run-off, while continuing to inspect for leaks and monitor the groundwater. A month later, even though monitoring showed that groundwater was flowing a thousand times faster than had been originally anticipated, the filling rate was doubled again, to 4 feet (1.2 m) a day.
On June 3 and 4, 1976 three small springs were discovered downstream of the dam, although the water running through the leaks was clear, and such leaks are not unexpected for an earthen dam. At the time, the reservoir was almost at capacity, with a maximum depth of 240 feet (73 m). The only structure that had been initially prepared for releasing water was the emergency outlet works, which could carry just 850 cubic feet per second (24 m/s). The main outlet works and spillway gates were not yet in service: the gates were cordoned off by steel walls while they were being painted.
The collapse and flood
On Saturday, June 5, 1976, at 7:30 a.m. Mountain Daylight Time (MDT), a muddy leak appeared, suggesting sediment was in the water, but engineers did not believe there was a problem. By 9:30 a.m. the downstream face of the dam had developed a wet spot which began to discharge water at 20 to 30 cubic feet per second (0.57 to 0.85 m/s) and the embankment material began to wash out. Crews with bulldozers were sent to plug the leak, but were unsuccessful. Local media appeared at the site, and at 11:15 officials told the county sheriff's office to evacuate downstream residents. Work crews were forced to flee on foot as the widening gap, now larger than a swimming pool, swallowed their equipment. The operators of two bulldozers caught in the eroding embankment were pulled to safety with ropes.
At 11:55 a.m. MDT (UTC-17:55), the crest of the dam sagged and collapsed into the reservoir; two minutes later the remainder of the right-bank third of the main dam wall disintegrated. Over 2,000,000 cubic feet per second (57,000 m/s) of sediment-filled water emptied through the breach into the remaining 6 miles (9.7 km) of the Teton River canyon, after which the flood spread out and shallowed on the Snake River Plain. By 8:00 p.m. that evening, the reservoir had completely emptied, although over two-thirds of the dam wall remained standing.
Cause of the collapse
Study of the dam's environment and structure placed blame for the collapse on the permeable loess soil used in the core and on fissured (cracked) rhyolite in the foundations of the dam that allowed water to seep under the dam. The permeable loess was found to be cracked. It is postulated that the combination of these flaws allowed water to seep through the dam and led to internal erosion, called piping, that eventually caused the dam's collapse.
An investigating panel had quickly identified piping as the most probable cause of the failure, then focused its efforts on determining how the piping started. Two mechanisms were possible. The first was the flow of water under highly erodible and unprotected fill, through joints in unsealed rock beneath the grout cap, and development of an erosion tunnel. The second was "cracking caused by differential strains or hydraulic fracturing of the core material." The panel was unable to determine whether one or the other mechanism occurred, or a combination:
The fundamental cause of failure may be regarded as a combination of geological factors and design decisions that, taken together, permitted the failure to develop.
A wide-ranging controversy ensued from the dam's collapse. According to the Bureau of Reclamation, BOR engineers assess all Reclamation dams under strict criteria established by the Safety of Dams program. Each structure is periodically reviewed for resistance to seismic stability, internal faults and physical deterioration.
Deaths, damage and property claims
Teton Canyon ends approximately six miles below the dam site, where the river flows onto the Snake River Plain. When the dam failed, the flood struck several communities immediately downstream, particularly Wilford at the terminus of the canyon, Sugar City, Salem, Hibbard and Rexburg. Thousands of homes and businesses were destroyed. The small agricultural communities of Wilford and Sugar City were wiped from the river bank. Five of the fourteen deaths attributed to the flood occurred in Wilford. The similar community of Teton City, on the south bank of the river, is sited on a modest elevation and was largely spared. One Teton resident was fishing on the river at the time of the dam failure and was drowned. An elderly woman living in Teton City died as a result of the evacuation.
One estimate placed damage to Hibbard and Rexburg area, with a population of about 10,000, at 80 percent of existing structures. The Snake River flows through the industrial, commercial and residential districts of north Rexburg. A significant reason for the massive damage in the community was the location of a large commercial lumber yard directly upstream. When the flood waters hit, thousands of board feet of timber caught fire from leaking gas, and were swept downstream. The force of the logs and cut lumber, and the subsequent fires, practically destroyed the city.
The flood waters traveled west along the route of the south fork of the Snake, around the Menan Buttes, significantly damaging the community of Roberts. The city of Idaho Falls, even further down on the flood plain, had time to prepare. At the older American Falls Dam downstream, engineers increased discharge by less than 5% before the flood arrived. That dam held, and the flood was effectively over, but tens of thousands of acres of land near the river were stripped of fertile topsoil.
The force of the Teton Dam failure destroyed the lower part of the Teton River, washing away riparian zones and reducing the canyon walls. This seriously damaged the stream's ecology, and the native cutthroat trout population has been endangered. The force of the water and excessive sediment also damaged stream habitat in the Snake River and some tributaries, at least as far downstream as Fort Hall, Idaho.
After the dam's collapse, debris clean-up began immediately and took the remainder of the summer. Rebuilding of damaged property continued for several years. Within a week after the disaster, President Gerald Ford requested a $200 million appropriation for initial payments for damages, without assigning responsibility for Teton Dam’s failure.
The Bureau of Reclamation set up claims offices in Rexburg, Idaho Falls, and Blackfoot. By January 4, 1977, disaster victims filed over 4,800 claims totalling $194 million. By that date, the federal government paid 3,813 of those claims, $93.5 million. Originally scheduled to end in July 1978, the claims program continued into the 1980s. At the end of the claims program in January 1987, the federal government had paid 7,563 claims for a total amount of $322 million.
No plans have been made for rebuilding the Teton Dam, but its reconstruction has been brought up on at least one occasion.
See also
References
Notes
- ^ Associated Press (December 17, 1971). "Crews due at planned dam site". Spokesman-Review. p. 7.
- ^ Perrow, Charles. Normal Accidents. New York: Basic Books, 1984. ISBN 0=465-05144-8 pp.233-238
- ^ "The Failure of Teton Dam". Bureau of Reclamation. 2011-04-18. Retrieved 2011-10-27, 2007-07-29.
{{cite web}}: Check date values in:|accessdate=(help) - ^ Reisner, Marc (1993). Cadillac Desert. p. 407. ISBN 0-14-017824-4. Cite error: The named reference "CD407" was defined multiple times with different content (see the help page).
- Smalley, Ian. "The Teton Dam: rhyolite foundation + loess core = disaster" Geology Today v.8, n.1 (January 1992), pp.19-22
- Johnson, Elaine. "Teton Dam Flood, June 5, 1976"
- "Data From American Falls Dam". Zeb Palmer (data courtesy Bureau of Reclamation). Retrieved 2008-12-20.
- Ford, Gerald."Remarks Upon Signing the Teton Dam Disaster Assistance Bill. September 7, 1976" on the American Presidency Project at the University of California Santa Barbara
- Laden, Elizabeth. "State considers another Teton dam". Henry's Fork Country. Retrieved 2011-06-15.
External links
- Bureau of Reclamation overview with photos, and link to final report
- The Teton Basin Project, Eric A. Stene, Bureau of Reclamation History Program, 1996
- "The Bureau That Changed the West" One That Got Away: Teton Dam (site critical of USBR)
- Teton Dam Flood Museum, Rexburg, Idaho
- Teton Dam Collection – Oral History reports and newspaper articles, includes more than 50 oral history interviews of those living in the area when the disaster occurred.
- Images showing progressive dam erosion damage, taken at the time by Mrs. Eunice Olson
- Data from American Falls Dam (downstream) from the Teton Dam Failure
- Teton Dam Failure Case Study, engineering case study, University of Alabama at Birmingham
- Life in the Tetons.com Teton Valley Magazine, Spring 2009, "The River be Dammed"
43°54′35″N 111°32′21″W / 43.90972°N 111.53917°W / 43.90972; -111.53917
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