Tuesday, June 5, 2018

Eleven Dead, Millions in Damages Due to Teton Dam Failure [otd 06/05]

On the morning of Saturday, June 5, 1976, observers noticed a major leak in the north abutment of the Teton Dam. This came after two days of increasing seepage. Within about three hours, a whirlpool in the reservoir behind the structure signaled that a substantial flow was undermining the dam.
Spillway of intact dam. U.S. Bureau of Reclamation.

Located on the Teton River 13-14 miles northeast of Rexburg, Idaho, the structure was the culmination of over forty years of speculation, and then planning. In 1932, during the heyday of Western dam building, the U.S. Geological Survey studied the Teton River for potential water storage sites. Not much came of that investigation.

The Bureau of Reclamation took another look in 1947, again with no subsequent action. Interest revived in 1961, and a report the following year recommended that a dam be built.

After almost a decade of site studies, construction began in February 1972. By June 1976, the reservoir had been filling for about eight months.

Even some supporters had raised doubts about the siting for the Teton Dam. Unfortunately, their qualms, and protests from outright opponents, had been brushed off or dismissed as unfounded. The claimed benefits from irrigation and flood control supposedly made the project worth the cost. The risks were considered minimal.

Although supervisors sent bulldozers out to plug the growing gaps, subsequent analysis suggests that nothing could have stopped the collapse at that point. The tunnels designed to empty the reservoir were not yet in service, and were probably too small anyway.

By noon, a wall of water was roaring down the canyon. At least two towns were virtually wiped out and Rexburg suffered major damage. Idaho Falls only avoided catastrophe by frantic efforts in sandbagging and digging relief trenches to reduce pressure on a major bridge.

Failure in progress. U.S. Bureau of Reclamation.
Your blogster well remembers this disaster. I was returning from a conference in Phoenix. The first news I heard came from two men sitting behind me on the plane. They were Federal emergency response people headed for Idaho Falls. The two had no idea of the full scope of the crisis, but they knew it was bad.

Authorities let our plane land, but then sent it south to the Pocatello airport. At that point, all the hotels along the river had been evacuated and the bridges were closed. Since the airport is on the west side and we lived on the other, I ended up staying with friends. We escaped damage at our place. However, a young lady who worked for me lived in a mobile home in the flood’s path. Floating timbers from a pole mill battered everything in the trailer park beyond recognition.

In the end, the flood caused the deaths of eleven people and an estimated 13 thousand cattle. Financial losses included the $100 million building cost as well as over $300 million paid out for damage claims. It is difficult to quantify the value of farmland scoured bare of topsoil, habitat obliterated, and other damage, but some estimates run as high as $2 billion.

An investigating committee concluded that no one factor caused the disaster. They wrote, “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.”
References: Stacey Solava, Norbert Delatte, "Lessons from the Failure of the Teton Dam," Forensic Engineering: Proceedings of the Third Congress, American Society of Civil Engineers, Reston, Virginia (October 19-21, 2003).
Committee on the Safety of Existing Dams, Safety of Existing Dams: Evaluation and Improvement, National Academies Press, Washington, D.C. (1983).
Dylan J. McDonald, The Teton Dam Disaster, Arcadia Publishing, Mount Pleasant, SC (2006).

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