Woodbury to study storm ponds in light of larger rain events
With a notable increase in large and more frequently-occurring rain storms, Woodbury is among several Midwestern cities taking steps to avoid flooding inside properties.
The Woodbury City Council passed an ordinance at its Feb. 22 meeting after the Federal Emergency Management Agency (FEMA) determined the soon-to-be-built Twenty-One Oaks neighborhood is no longer within a flood zone. The city is also preparing to study about 3,000 storm ponds for potential weaknesses in their overflow systems.
According to the National Oceanic and Atmospheric Administration (NOAA), Minnesota and much of the Midwest has seen an increase in large storm events once thought to occur once every 100 years or so.
Since 1980, Minnesota has seen more than a dozen storms that produce more than six inches of rain. The agency's data also suggests storms are becoming larger than they were in prior decades.
"The data is there. We can argue about what to call it, but the fact is, we are definitely experiencing more severe weather and bigger storms," said Woodbury Engineering and Public Works Director Klayton Eckles. "That's why cities are talking about how to respond."
FEMA requires homeowners to have flood insurance if they live in areas deemed at risk.
They can also opt out of the requirement by requesting a map amendment, which can sometimes require a new survey to be done.
The city council passed a similar ordinance in 2010 that identified 450 properties inside of a flood zone. The state requires cities to pass an ordinance every time FEMA amends its map.
Last year, several multi-inch rain episodes washed out part of the Twin Cities.
Though Woodbury didn't see any significant floods during the state's wettest year on record, new data suggests cities may be forced to make several hard decisions in the coming years.
In 2013, NOAA updated precipitation amounts for the 100-year storm from 6 inches to 7.5 inches.
"Pretty much every state agency has designed their system on the old data," Eckles said. "With this new data, it suggests there may be some problems."
While Woodbury benefits from being a newer city, the city plans to inspect storm ponds to determine how they would hold up during a heavy rainstorm.
The city has about 3,000 storm ponds and each has an emergency outlet. The city plans to inspect all of the ponds to double check that they'll hold up in the event of a big storm.
The outlets can sometimes become blocked when, for example, someone's lawn chair blows away during a storm and clogs it. Homeowners who have done landscaping or alterations to their yards may also be blocking redundant overflow systems that go into the streets.
Ponds built to accommodate a 6-inch rain event might lead to basement floods for homeowners near bodies of water if the city is hit with more than 7.5 inches of rain in a short period of time.
New homes, however, are being built that will include higher flood protection standards, Eckles said.
"I think it's important for our residents to be aware, and it's good for them to know we're thinking about those things," he said. "It's possible they may see us out in their yard doing some survey work in the coming year."
Correction: A previous version of this story misstated the Twenty One Oaks Development is within FEMA's floodplain. The article's headline has also been edited to reflect the correction.