A storm like June 9, 1972, could happen again.
Experts say if it does, the warning system will be better, the dams engineered smarter and the community more aware that devastating floods can happen in Rapid City.
The 1972 flood killed 238 people, putting Rapid City on the top 10 list of the worst floods in U.S. history.
The massive event 40 years ago is commonly called a “500-year flood.” That means there is a 1 in 500 – a .2 percent – chance that a similar storm could strike again.
“There still needs to be, in my opinion, a heightened awareness of the season when these floods can happen and a heightened awareness that if this is going to happen again, this is going to be after dark,” said Mark T. Anderson, director of the South Dakota Water Science Center.
Anderson, who lived through the 1972 flood, said the devastating event led him into his career as a scientist. He has studied it in detail and has a passion to understand what confluence of events caused the flash flood and deadly wall of water, and why it killed so many Rapid City residents.
“The 1972 flood was a marker event in the history of Rapid City, and there was a tragic amount of death,” he said. “Some of it could have been better if we were better prepared. And that is why we dwell on it.”
On June 9, 1972, winds from the east carried rain clouds into the area. As it hit the Hills, the warm air was forced upward where it built moisture and let loose vicious late afternoon rains. That weather pattern is typical in the region, but usually high altitude winds move the storms away.
Not that night.
There were virtually no high altitude winds, leaving the storm cloud to hover over the foothills, dumping massive amounts of water - and fast.
“What was unusual about this storm was the intensity and duration of it,” said Susan Sanders, warning coordination meteorologist with the National Weather Service in Rapid City. She has extensively studied the weather patterns from that evening.
Johnson Siding, which is 25 minutes west of Rapid City, received 12.6 inches of rain. Nemo took a pounding downpour, collecting an estimated 15 inches. Rain gauges were destroyed in the flood. The airport, however, received just 2.3 inches of rain.
As the sun set and the skies darkened, it was the intense lightning that gave residents flickering images of an increasingly dangerous situation. Water inundated the foothills and rushed downstream, gaining velocity.
“A lot of people lost their lives in cars, and they just got captured on Jackson Boulevard or Omaha and their cars starting floating away and they didn’t know what to do,” Anderson said.
Last year across the nation, 63 percent of all flood deaths happened in a car. Exact numbers from the Rapid City flood are unknown, but a famous photo showing cars stacked along the roadside showed two-ton automobiles had no chance against the rushing wall of water.
The Canyon Lake Dam’s failure around 10:30 p.m. didn’t cause the flood, but it made a bad situation much worse. Anderson said it “spiked the peak.” Since the flood, Anderson said the Canyon Lake Dam has undergone a complete redesign, as have all the bridges in town.
A federal program demanded after the flood that Pactola Dam be raised well beyond any water height ever fathomed in the region. Pactola Dam never failed, nor did the water approach spilling. However, its presence may have contributed to local residents feeling Rapid City would never see a great flood.
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“In terms of complacency, most people were of the opinion that the peak couldn’t happen because Pactola was there,” Anderson said. “How could such a peak happen with just rain in the foothills?”
Today’s emergency warning system is far superior to 40 years ago, Sanders said.
Sophisticated Doppler radar more accurately predicts storms. No five-day forecast existed in 1972. Rainfall and stream gauges are automated. The emergency alert system gives the National Weather Service access to break into live television and radio broadcasts.
In 1972, the warning system meant a call from weather officials to local media. Weather service personnel counted on first-hand accounts from the public to decide when to declare an emergency. The weather service sent out its first warnings at 7:15 p.m., Sanders said.
Whether the warnings reached the public is anyone’s guess. It was a Friday night in the 1970s. People could have been at the movies or out with friends.
“We heard about so many different things going on that night, like a German band concert,” Sanders said.
Robert Holmes, a hydrologist with the U.S. Geological Survey, is among the foremost experts in floods. He has studied the area, traveling here many times, he said.
“Massive devastation in terms of people” is how Holmes remembers the flood. “I remember the pictures of just the cars lined up and stacked up.”
Jerry Mitchell, 75, was a pilot who flew to Pierre around 8 p.m. that day.
“As I took off and looked back to the west, I saw it was coming over the hills in town,” he remembered.
He flew back to Rapid City in the early morning hours, surviving turbulence he now says he wouldn’t test if he had to do it over. At sunrise the next morning, he began looking for bodies.
“That was one of the worst days that I can remember,” Mitchell said.
That day could come again. Anderson said the only more devastating event he could imagine would be a Pactola Dam failure, a situation he said is nearly inconceivable based on its size and capacity.
Some scientists have linked outbreaks in drought, floods and tornadoes nationwide and internationally to global climate change. Sanders said she can’t quite link climate change to any increasing chance for another Black Hills flood.
“You can’t predict that,” she said. “It is hard to blame a large-scale system on something that could happen anytime.”
Holmes said floods will always happen, so society needs to be vigilant.
“We can’t prevent floods, they are a natural phenomenon,” he said. “People just have to be more aware of the flood risk. We in society are being more aware, but we are still not there.”