A Look at the Failure of Teton Dam 40 Years Later

Teton Dam was a 300-foot-high zoned earthfill dam in eastern Idaho that failed catastrophically on June 5, 1976, during initial filling of the reservoir. It took only five hours from the first sign of turbid seepage until failure. Eleven people were killed when the dam breach released 250,000 acre-feet of reservoir water. The town of Wilford, Idaho, was destroyed. The town of Sugar City, Idaho, was devastated by a wall of water 15 feet high and moving 10 to 15 miles an hour. Eventually, the flood spread out eight miles wide as it approached and flooded Rexburg, Idaho. Approximately 25,000 people were left homeless; 20,000 head of livestock were killed; and estimated economic damages ranged from hundreds of millions up to 2 billion dollars. The Teton Dam failure served as a turning point for the dam safety profession in the United States. It was a catalyst for national dam safety legislation and the creation of federal dam safety programs.

This article will address first filling, the initial signs of seepage, the failure timeline, and potential causes of the failure. It will also include background details such as site geology, embankment design and materials, the test grout pilot program, the abutment cutoff trench design, foundation design and construction, and embankment construction. As for the failure timeline, it will include a description of each step with sketches and a detailed interpretation of the failure mechanism. Much of the information in the article comes from the December 1976 “Failure of Teton Dam” report authored by the Independent Panel, which consists of subject matter experts including Ralph Peck, Arthur Casagrande, and H. Bolton Seed.