Teton Dam

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The Teton Dam is a ground dam on the Teton River in Idaho, USA. Built by the Reclamation Bureau, one of eight federal agencies authorized to build dams. Located in the eastern part of the state, between Fremont and Madison County, it suffered catastrophic failure on June 5, 1976, as it filled in for the first time.

The collapse of the dam resulted in the deaths of 11 people and 13,000 livestock. The dam spent about $ 100 million to build and the federal government paid over $ 300 million in claims relating to its failure. Estimated total damage ranges up to $ 2 billion. The dam has not been rebuilt.

Video Teton Dam

History and geology

There has been an interest in building dams in the eastern Snake River Plain for many years to control runoff and provide a more constant supply of water in the summer. The area suffered a severe drought in 1961, followed by severe floods in 1962. The Reclamation Bureau (USBR) proposed the Teton Dam in 1963 and Congress passed without opposition an authorization bill the following year. The planned dam is a 310 feet (94 m) tall soil structure and 0.6 mil (1.0 km) high and creates a 17 mile (27 km) reservoir. The confiscated water will be used to generate hydroelectric power. An environmental impact statement was issued for the dam in 1971, but it did not increase the likelihood of collapse. Lack of funding and workplace preparation and questions surrounding the environmental impact statement required to stop the project. Nearly 14 pages, the statement quickly attracted the anger of the opponents of the project.

On September 27, 1971, several environmental and conservation groups filed suit at the Idaho District Court to stop construction. Dam protesters question the project's justification. They argue that damming wild and beautiful rivers and destroying trout fisheries and other wildlife habitats will "replace unique resources with vulgar ones." The lawsuit questioned the economic return on investment, the Bureau's compliance with the National Environmental Policy Act and the geological health of the dam location. Concerns over the seismic conditions of the dam site delayed the bidding process pending further review by the Department of the Interior. Pressure from the Idaho congress delegation stopped the review and regardless of the lawsuit, the offer was taken at Idaho Falls on October 29, 1971. The contract was awarded to Morrison-Knudsen Co. from Boise, aided by Peter Kiewit Sons Co. from Omaha, Nebraska. The $ 39 million contract was awarded in December 1971. Regardless of the lawsuit, work began in February 1972. After various movements, fixing complaints, seeking orders and appeals, the lawsuit was dismissed on December 23, 1974.

The East Snake River plain is almost entirely based on basalt erupting from a large shield volcano above the ash-flow tuffs and ignimbrites. Tuff, the late-Cenozoikum volcanic rock is 1.9 million years old. The dam site consists of basal and rhyolite, both considered unsuitable for dam construction due to their high permeability. This is confirmed by long-term pump testing at a rate of 165 to 460 US gallons (620 to 1,740 liters) per minute. The test core, drilled by engineers and geologists employed by the Reclamation Bureau, shows that the canyon rocks at the dam site are highly flaked and unstable, especially on the right side (when one is facing the flow). The widest gap is defined to be 1.7 inches (4.3 cm) wide. The Bureau plans to close this gap by injecting grout into the rock under high pressure to create curtain grout in stone.

In addition, regional investigations by geologists The US Geological Survey shows that it is seismically active: five earthquakes have occurred within 30 miles (50 km) of the dam site in the preceding five years, two of which have been significantly large. This information was given to the Reclamation Bureau in a memorandum, but geologists' concerns were greatly reduced in the six-month reordering process before the USGS sent the final version of the memo to USBR in July 1973.

In 1973, when the dam was only half built, but nearly $ 5 million had been spent on the project, a huge open crack was found during the excavation of a key trench near the right end of the dam, about 700 feet (210 m) from the canyon wall. The two largest, near-vertical grooves are generally east-west and extend over 100 feet (30 m) below the bottom of the key trench. Some gaps are lined with calcite, and debris fills the other. Some voids, 6 inches wide (15 cm) wide, encountered 60 to 85 feet (18-26 m) below ground level beyond the right end of the dam and curtain grout. The biggest gap is actually cave big enough to enter. One of them is eleven feet (3.4 m) wide and one hundred feet (30 m) in length. Another one is nine feet (2.7 m) wide in place and 190 feet (60 m) in length. It's not grouting because they are outside the key sidewalks and outside the area where the Bureau has decided grouting is needed. This requires using twice as much grouting as previously anticipated - 118,000 linear feet used in total.

Subsequently, the report of the House of Representatives committee investigating the collapse of the dam felt that the discovery of the cave should be enough for the Reclamation Bureau to doubt its ability to fill it with grout, but this did not happen; even after the dam had failed, the Bureau insisted that the installation was right.

In December 1972, concerned about the geological conditions of the Teton River Canyon, USGS geologist David Schleicher wrote of the Teton Dam, still under construction, "The last point is that floods in response to seismic or other dam failures - perhaps the most likely at the time of water the highest - will make the February 1962 flood look like a small potato Because such a flood can be anticipated, we might consider a series of motion picture cameras strategically placed to document the process.

Maps Teton Dam

Charging Edit

The dam was completed in November 1975 and filled the reservoir starting at the standard level of 1 foot (0.30 m) per day. However, the snow was very heavy in the winter and five months later the project's construction engineer requested permission to double the fill rate to handle additional spring runoff, while continuing to check for leaks and monitor ground water. A month later, although monitoring indicates that groundwater flows a thousand times faster than anticipated, the loading rate doubles again, to 4 feet (1.2 m) per day.

On 3 and 4 June 1976, three small springs were found downstream of the dam, although the water flowing through the leaks was clear and such leaks were unexpected for a dam. At that time, the reservoir almost reached capacity, with a maximum depth of 240 feet (73 m). The only structure that was originally prepared to release water was emergency outlet work, which could only carry 850 cubic feet per second (24 m ³ /s). The main outlet worked and the overflow gate had not been in service: the gate was covered with steel walls while they were being painted.

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Close and hide Edit

• Teton Dam Breach, June 5, 1976

On Saturday, June 5, 1976, at 7:30 am Mountain Day Time (MDT), a muddy leak appeared, indicating the sediment was in the water, but the engineers did not believe there was a problem. At 9:30 am, the downstream part of the dam has developed a wet point that starts draining water at 20 to 30 cubic feet per second (0.57 to 0.85 m ³ /s) and the embankment material starts wiped clean. Crews with bulldozers sent to clog leaks, but to no avail. Local media appeared on the site and at 11:15 pm officials told the county sheriff's office to evacuate the downstream population. The work crews were forced to flee on foot because of the widening gap, which is now larger than the pool, swallowing their equipment. Operators from two bulldozers trapped in an eroded dike are pulled to safety with ropes.

At 11:55 am MDT (UTC-17: 55), the top of the dam slumped and fell into the reservoir; two minutes later the remaining third of the right bank of the main dam wall was destroyed. More than 2,000,000 cubic feet per second (57,000 m ³ /s) of sediment filled water was emptied through a gap to the remaining 6 miles (10 km) from the Teton River canyon, after which floods spread out and shallow in the Plain of the Snake River. At 8:00 that night, the reservoir was completely empty, although more than two-thirds of the dam wall remained standing.

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Cause Edit

Environmental studies and dam structures place errors on the collapse of permeable loess soils used on the terraces and on cracked (cracked) rhyolites in the dam abutment that allow water to seep around and through earth fill dams. Loess permeable found cracked. It is postulated that the combination of these deficiencies allows water to seep through the dam and cause internal erosion, called piping, which eventually leads to the collapse of the dam.

An investigative panel quickly identifies piping as the most likely cause of failure, then focuses on determining how piping begins. Two mechanisms are possible. The first is the flow of water under a very eroded and unprotected contents, through a connection in the unclosed rock beneath the grout cover and the construction of an erosion tunnel. The second is "cracking caused by a differential strain or hydraulic fracture of the core material." The panel can not determine whether one or another mechanism occurs, or a combination:

The underlying cause of failure can be thought of as a combination of geological factors and design decisions taken simultaneously, allowing failure to flourish.

Extensive controversy occurred from the collapse of the dam. According to the Reclamation Bureau, Bureau engineers assess all reclamation dams based on strict criteria established by the Safety of Dams program. Each structure is periodically reviewed for resistance to seismic activity, for internal faults, and for physical damage. The dam security program identifies two other dangerous dams - Fontenelle, which nearly failed 11 years earlier, when filled, in a manner similar to the Teton Dam, and again in May 1985; and the Jackson Lake Dam that will fail during an earthquake near the Teton Fault.

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Death, damage and property claims Edit

The Teton Canyon ends about six miles beneath the dam site, where the river flows into the Snake River Plain. When the dam failed, floods struck several communities downstream, especially Wilford at the edge of the canyon, Sugar Town, Salem, Hibbard, and Rexburg. Thousands of homes and businesses were destroyed. The small farming communities of Wilford and the City of Sugar were removed from the riverbank. Five of the fourteen deaths attributed to the flood occurred in Wilford. The same Teton community, on the southern edge of the river, is on a simple bench and largely spared. One Teton resident fishing in the river at the time of the dam failure and drowning. An elderly woman living in the city of Teton died as a result of the evacuation.

One estimate puts damage to the Hibbard and Rexburg regions, with a population of about 10,000, at 80 percent of the existing structure. The Teton River flows through industrial, commercial and residential areas in northern Rexburg. A significant reason for major damage in the community is the location of the wooden yard directly upstream. When water floods, thousands of logs are washed into the city. Dozens of them crashed into a large gasoline storage tank a few hundred yards away. Gasoline is lit and sends glowing flakes that are adrift over the water of racing. The strength of wood and cut wood and the next fire practically destroy the city.

Flood waters move west along the Henry Fork route from the Snake River, around both sides of Menan Buttes, significantly damaging the Roberts community. The town of Idaho Falls, even further on the flood plains, had time to prepare. In the older American Falls Dam, the engineers increased the discharge by less than 5% before the floods arrived. The dam was resistant and the flood effectively ended, but tens of thousands of hectares of land near the river were stripped of fertile topsoil.

The power of failure destroys the bottom of the Teton River, washing away the riparian zone and reducing the canyon walls. This greatly damages the river ecology and affects the original Yellowstone native trout population. Excessive water and sedimentary strength also destroys river habitats in the Snake River and several tributaries, as far downstream as the base of Fort Hall.

After the dam collapse, clearance of the debris starts immediately and takes the rest of the summer. Redevelopment of damaged property continues for several years. In the week after the disaster, President Gerald Ford requested $ 200 million for early repayment, without assigning responsibility for the failure of Teton Dam.

The Reclamation Bureau set up claims offices in Rexburg, Idaho Falls, and Blackfoot. On January 4, 1977, disaster victims filed over 4,800 claims totaling $ 194 million. On 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. By the end of the claim program in January 1987, the federal government had paid 7,563 claims totaling $ 322 million.

No plans were made to rebuild the Teton Dam, but the reconstruction has been raised at least on one occasion.

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See also Edit

• Great Sheffield Flood

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References Edit

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External links Edit

• Reclamation Overview Bureau with photos and links to final report
• The Teton Basin Project, Eric A. Stene, Bureau of the History Reclamation Program, 1996
• "Bureau Who Changed West" Uncovered: Teton Dam
• Museum of the Teton Dam Dam, Rexburg, Idaho
• Teton Dam Collection - Oral History Report and newspaper articles, includes more than 50 oral history interviews from those living in the area when the disaster occurred.
• The image shows the damage of progressive dam erosion, taken at that time by Ny. Eunice Olson
• Teton Dam Failure Narrative
• Teton River Canyon, Teton Dam ID Collapse and Flooding, Jun 1976 at GenDisasters.com
• Johnson, Elaine, "Teton Dam Flood, June 5, 1976" is now at http://www.fremont.idgenweb.org/history-flood.html

Source of the article : Wikipedia