Dam Failure Case Study: Swift and Two Medicine Dams (Montana, 1964)

The second week of June 1964 brought one of the worst natural disasters in Montana’s recorded history. In all, the flooding caused 30 deaths, damages of over $500M (in 2020 dollars), and exceeded many of the peak flow records across the state. Precipitation during the 36-hour storm period, June 8-9, 1964, was recorded at upwards of 16 inches, and caused the most severe floods of record on both sides of the Continental Divide. The area affected by resultant flooding covered an area of nearly 30,000 square miles, or about 20% of the state of Montana. While much of the media coverage of this event focused on flooding in more populated areas like Great Falls and Kalispell, all of the fatalities from the flood occurred on the Blackfeet Indian Reservation, where the Swift and Two Medicine Dams failed. This case study discusses the many lessons to be learned from the tragic events surrounding the 1964 flood, and the consequent failures of these dams.