On This Day in 1972: The Black Hills Flood

51 years ago today, very heavy rains over the eastern Black Hills of South Dakota produced record breaking floods, which devastated Rapid City.

On the afternoon of June 9, a nearly stationary round of thunderstorms developed over the eastern Black Hills, bringing heavy rain to the area. Rain had already fallen throughout the Black Hills area several days before, so soils were saturated. Additional rounds of repeating thunderstorms continued through the evening thanks to light winds aloft. The result was torrential rainfall, with nearly 15 inches of rain falling in about 6 hours near Nemo, South Dakota. 

Heavy rain and its resulting runoff produced record floods along many creeks in the Rapid City area during the evening. Flood waters first reached Rapid City between 9:30 and 10 p.m. on June 9, carrying large amounts of debris that clogged the spillway of the Canyon Lake Dam. The dam at Canyon Lake eventually failed at about 10:45 p.m. on June 9, unleashing a torrent of water that was carried swiftly through Rapid City at about Midnight on June 10. Unfortunately, this occured while many people were asleep and unaware of the impending flood.

The floods struck quickly and forcefully, leaving behind immense devastation. However, the flooding did not last long as Rapid Creek within Rapid City was back within its banks by 5 a.m. on June 10. The flood was responsible for 238 people dead and 3,057 people injured.

Total damage was estimated in excess of $160 million (about $1.16 billion in 2023 dollars), which included 1,335 homes and 5,000 automobiles destroyed.

After the floods, Rapid City approved a flood-plain management program, which converted most of the flood plain into large parks. While most businesses were granted the right to stay in the flood plain, houses and motels in the floodway were destroyed or moved to new locations. Canyon Lake Dam was redesigned and rebuilt to prevent debris clogs. 

Rapid City and its surrounding communities recovered from the 1972 flood, but this area remains at risk for flash flooding due to heavy rainfall falling over steep terrain, which gives little time for warning residents of flood threats.

Sources: USGS, weather.gov
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Story Image: Flood damage is seen on East Boulevard at Omaha Street in Rapid City, S.D., June 10, 1972. (Courtesy of the Rapid City Journal and the National Weather Service Forecast Office in Rapid City, S.D.)