Teton Dam Flood – 1976

The Teton Dam in the northwestern US state of Idaho enjoys a dubious reputation as one of the most short-lived constructions in the history of dam building. The earth fill dam had just been completed – workmen and machinery were still on site – when in June 1976 it burst, sending an estimated 80 billion gallons of water down the valley to inundate a huge area of farmland. A project of the US Bureau of Reclamation, the dam had been sited in the canyon of the Teton River, part of the Snake River system and 71 km (44 mi) northeast of Idaho Falls. Standing to a height of 93 m (305 ft) and with a crest width of 975 m (3,200 ft), it was built for a variety of purposes, including, ironically, flood protection.

The 27 km (17 mi) long reservoir was almost full with spring melt water when the breach occurred. Some seepage had been noticed several hours beforehand but was considered to be within normal operating limits. When a hole appeared near the right bank, however, bulldozers attempted to plug it. When they failed and the hole got steadily larger, workers watched helplessly as the whole western side of the dam collapsed and an angry cascade of water surged forth. Collecting rocks and debris from the valley floor as it moved down the canyon, the flood water had turned a muddy brown by the time it swamped the towns of Wilford and Rexburg. Because there had been a few critical hours’ notice of impending disaster, warnings had been issued and local residents had evacuated their homes. As a result, although damage to land and property ran into the tens of millions of dollars, loss of life was mercifully low.

When: June 5 1976

Where: Teton River, near Idaho Falls, Idaho, USA

Death toll: 11

You should know: There was considerable disagreement over the cause of the dam’s failure, but it is now widely assumed to have been due to the permeable nature of the loess soil used in the core of the dam.