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Why Dams Fail

This page includes information on the reasons that dams can fail, the dam failures that led to dam regulation and inspection, and a description of the Johnstown Flood, caused by the failure of the South Fork Dam.

Reasons Dams Fail

Dams can fail for one or a combination of the following reasons:

View from below Lake Delhi Dam breach that shows the force of the rushing water
View from below Lake Delhi Dam breach that shows the force of the rushing water
  • Overtopping caused by floods that exceed the capacity of the dam
  • Deliberate acts of sabotage
  • Structural failure of materials used in dam construction
  • Movement and/or failure of the foundation supporting the dam
  • Settlement and cracking of concrete or embankment dams
  • Piping and internal erosion of soil in embankment dams
  • Inadequate maintenance and upkeep

Dam Failures in the United States

A series of dam failures in the 1970s resulted in a national focus on inspecting and regulating dams.

  • On February 26, 1972, a tailings dam owned by the Buffalo Mining Company in Buffalo Creek, WV, failed. Within minutes, 125 people were killed, 1,100 people were injured, and over 3,000 were left homeless.
  • On June 5, 1976, Teton Dam, a 123-meter-high dam on the Teton River in Idaho, failed, causing $1 billion in damage and leaving 11 dead. Over 4,000 homes and over 4,000 farm buildings were destroyed as a result of the Teton Dam failure.
  • In November 1977, Kelly Barnes Dam in Georgia failed, killing 39 people, most of them college students.

For lessons learned from dam incidents and failures, visit

The Johnstown Flood

On May 31, 1889, at 4:07 p.m., the residents of Johnstown, PA, heard a low rumble that grew to a “roar like thunder.” After a night of heavy rains, the South Fork Dam failed, sending tons of water crashing down the narrow valley. Carrying huge chunks of debris, the wall of flood water grew to 60 feet high at times, tearing downhill at 40 miles per hour and leveling everything in its path.

Thousands desperately tried to escape the wave. Those caught by the wave found themselves swept up in a torrent of oily, muddy water, surrounded by tons of grinding debris, which crushed some, but provided rafts for others. Many became helplessly entangled in miles of barbed wire from a destroyed wire works.

The destruction of the crushing wave was over in 10 minutes, but for some, the worst was yet to come. Darkness fell, thousands were huddled in attics, and others were floating on debris. Many more had been swept downstream to the old Stone Bridge at the junction of the rivers. Piled up against the arches, much of the debris caught fire, entrapping 80 people who had survived the initial flood wave.

Last Updated: 
07/07/2020 - 11:02