Thirty-five years ago today, storms that dropped 6 inches of rain in about six hours caused Rochester creeks and the Zumbro River to swell and flood the city.
On July 5-6, 1978, water raged down Rochester streets and rushed into people's homes, filling their basements and first floors. Five deaths were tied to the flood, which caused $60 million in damage to homes, buildings and infrastructure.
It led city and county officials to ramp up efforts to obtain funding for the $115 million flood control system that now protects Rochester. Voters here approved a local-option, half-cent sales tax to help pay for the project, of which the final portion was completed in 1996.
Looking ahead
The existing flood control system has done a good job of protecting Rochester from catastrophic flooding, especially considering frequent heavy rainfall in recent years.
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"I believe, in my view, we would have had at least four significant flood events — two of them would have been very damaging — since just probably 2000," saidRochester Assistant City Administrator Gary Neumann.
The flood control project was designed to handle rainfall much greater than what happened in 1978, which was considered a little worse than a "100-year flood," or about 6 inches of rain in a 24-hour period, Neumann said.
Now, the city and county need to assess whether the flood control system needs to be enhanced, given the latest climatology data.
Recent studies by climatologists, such as those at the Minnesota Climatology Working Group, which is part of the Minnesota Department of Natural Resources, find that the "100-year flood" definition likely needs to change.
Until 2007, the record rainfall in the state was 10.84 inches in a 24-hour period. It happened in July 1972 in Crow Wing County, in north central Minnesota. In August 2007, 15 inches of rain fell in a 24-hour period in Houston County in southeastern Minnesota. That year, about 9 inches fell in Rochester.
Complex system
The flood control system includes the massive concrete channel on the Zumbro River and seven reservoirs on four tributary streams in the outskirts of town. The reservoirs hold back water during significant rain events, said Neumann, who managed the project for the city.
There is one reservoir on Silver Creek, one on Bear Creek, two on Willow Creek and three on Cascade Creek. They were designed and constructed by what is now called the Natural Resources Conservation Service, which is part of the U.S. Department of Agriculture.
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The work on the Zumbro River, designed and completed by the U.S. Army Corps of Engineers in 1996, significantly deepened and widened the channel through Rochester. The Corps also completed channel work on Cascade and Bear creeks.
The city was responsible for acquiring land, relocating people and utilities and providing the local financing portion of the costs to design the pedestrian/bike trails, landscaping and other features along the channel.
The city is responsible for the maintenance of the flood control infrastructure, and the city and county, through a joint powers agreement, maintain the reservoirs and their dams, Neumann said.
Before the flood in 1978, city and county planners and officials already realized Rochester needed a flood control system. In fact, working with federal agencies, they developed a flood control plan for Rochester during 1976 and 1977 and submitted a bill to Congress in 1977, Neumann said.
"Everybody thinks (the bill's submission) happened after 1978, but, actually, the plans were done in response to some major floods in the 1960s. There were several huge flooding events in the 1960s here," he said.
