Teton Dam Failure
Collapse of the Teton Dam
The Teton Dam was an earthen dam on the Teton River in southeastern Idaho, located in the eastern Snake River Plain. When filling for the first time, the dam suffered a catastrophic failure on June 5, 1976. 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 the dam failure. Some total damage estimates have ranged close to $2 billion.Public domain photo courtesy Wikipedia
Public domain photo courtesy USA.gov/forces.si.edu
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Collapse of the Dam
When the collapse occurred, spring rains had almost filled the new reservoir to its 240 foot capacity. Water began seeping from the dam on the Thursday before the collapse, something not unusual for an earthen dam. The only structure that had been initially prepared for releasing water were the emergency outlet works, which could carry just 850 cubic feet per second. Although the reservoir was still rising over 4 feet per day, the main outlet works and spillway gates were not yet operational. The spillway gates were closed off by steel walls while they were being painted.
On Saturday, June 5, 1976, at 7:30 a.m., a muddy leak appeared, 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 erupting water at 20 to 30 cubic feet per second, and 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 as the widening gap, now over the size of a swimming pool, swallowed their equipment. At 11:55 a.m., the crest of the dam 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 of initially muddy water emptied through the breach into the remaining 6 miles of the Teton River canyon, after which on the Snake River Plain, the flood spread out and shallowed. By 8:00 p.m. that evening, the reservoir had completely emptied, although over two-thirds of the dam wall still remained standing.
The flood waters severely damaged several communities immediately downstream, particularly Rexburg, Wilford, Sugar City, Salem, and Hibbard. Thousands of homes and businesses were destroyed. The small community of Sugar City was literally wiped from the river bank. Estimates placed damage to Rexburg, population 10,000, at 80 percent of existing structures. The reason for the massive damage was the location of a large commercial lumber mill directly upstream from Rexburg. When the flood hit, thousands of board feet of timber snapped from their moorings, 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. To the southwest, communities such as Roberts on a lower section of the Snake River also received significant damage. The town 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 5% before the flood arrived. That dam held, and the flood was effectively over. The Teton Dam has never been rebuilt.