The Black Hills Flood of 1972

1972 Flash Flood Event Time Line

June 9, 1972

All times are Mountain Daylight Time

900 am - The National Severe Local Storm Forecast Center (now known as the Storm Prediction Center) advised that isolated thunderstorms approaching severe limits (hail larger than ¾” and wind gusts stronger than 60 mph) were expected in western South Dakota during the late afternoon and evening.

Noon - The Rapid City National Weather Service (NWS) office predicted isolated thunderstorms approaching severe limits (hail larger than ¾” and wind gusts stronger than 60 mph) in the afternoon and evening in their release to the media.

130 pm – Thunderstorms over the Black Hills are detected on Ellsworth Air Force Base (AFB) weather radar.

300 pm - A line of thunderstorms develops southeast of Rapid City and moves west-northwest.

340 pm – The Ellsworth AFB weather radar observer notified the NWS of precipitation over the Black Hills.

500 pm - Rain begins at Pactola Reservoir.

600 pm - State Radio Dispatch requested commercial radio and television stations to announce that motorists should avoid Boulder Canyon because of high water between Deadwood and Sturgis.

615 pm - State Radio advised the NWS of 12 inches of water over the highway west of Sturgis and heavy rain southwest of Rapid City.

630 pm – The South Dakota School of Mines and Technology (SDSMT) radar operator told the NWS about strong thunderstorms in the Hermosa area.

630 pm – The Pennington County Civil Defense Director calls the Rapid City police to report three inches of rain at Pactola Dam and Rapid Creek rising rapidly.

645 pm – The National Guard Commander was informed of water over the road in Boulder Canyon by the Lawrence County Sheriff.

650 pm - The SDSMT radar operator advises the NWS of heavy rain from Piedmont to the northern Hills with radar indications of rain falling at the rate of two inches per hour.

700 pm – The NWS receives a report of four inches of rain since 500 pm at Galena southeast of Deadwood.

715 pm - The NWS issues a flash flood warning for the northern Black Hills.

730 pm – Rapid City Mayor Don Barnett is notified of the flash flood warning and the National Guard and local law enforcement called to duty.

730 pm –National Guard personnel are recalled to duty.

730 pm –KOTA receives a call from the dam tender at Pactola of rapid rises along several creeks.

745 pm - A person in Nemo informs the NWS that Box Elder Creek was flooding, two dams upstream had broken, and low-lying areas of Nemo had been evacuated.

800 pm - The NWS expands the flash flood warning to include Rapid Creek and Box Elder Creek.

800 pm - The Rapid City-Pennington County emergency operations center opens.

840 pm – The Ellsworth AFB radar observer reports heavy precipitation over the central Black Hills.

900 pm - Commercial phone service at the NWS office at the Rapid City airport becomes intermittent and unreliable.

930 pm - NWS informs radio and television stations that the heavy rain will continue until about midnight.

1010 pm - Brookdale residential area (near the Central States Fairgrounds) is evacuated.

1030 pm - In a television and radio broadcast, Mayor Don Barnett urges immediate evacuation of low-lying areas.

1045 pm MDT - Canyon Lake Dam fails, adding to the flood waters rushing through Rapid City. 

June 10, 1972

1215 am  - A flood crest estimated at 50,000 cubic feet per second reaches downtown Rapid City.

500 am  - Rapid Creek is once again within its banks.

Debris and damaged bridge, Rapid Creek (photo courtesy of the Journey Museum).
Debris and damaged bridge, Rapid Creek
(photo courtesy of the Journey Museum).

 Flood Statistics

  • As much as 15 inches of rain fell near Nemo and Sheridan Lake, with an average of 10 inches over 60 square miles.
  • The heaviest rainfall in Rapid City occurred between 1030 pm on June 9 and 1 am June 10.
  • Peak flow on Rapid Creek 50,600 cubic feet per second, more than 10 times greater than the previous flood of record. 
  • During the flood, water rose as fast as 3.5 feet in 15 minutes.
  • Flood debris clogged the Canyon Lake spillway and temporarily raised the pool 11 to 12 feet deeper than normal. 
  • 238 people were killed; 8 of the deaths in Keystone.
  • 3,000 people were injured.
  • 1,335 homes were destroyed.
  • 5,000 automobiles were destroyed.
  • $160 million damage (1972 dollars, $644 million in 2002 dollars)
  • 15 of the 23 bridges over Rapid Creek were destroyed.
  • 754 acres were developed as a floodway.

Back to the Black Hills Flood of 1972

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