(TNS) — A flaw in the local flood-control system just north of Highway 14 needs to be fixed within the next 18 months, federal officials have told Mankato. And if it's not addressed, a substantial portion of property owners in lower North Mankato could suddenly find themselves living in a designated floodplain and be forced to buy hundreds of dollars of flood insurance each year.
The problematic area is in Mankato's city limits between the Minnesota River and Highway 169 north of the interchange with Highway 14.
"But it's our residents that would be affected," said North Mankato Mayor Mark Dehen.
Neither Dehen nor Mankato City Manager Pat Hentges sees the FEMA-identified flaw as an imminent danger, and Dehen said people shouldn't be alarmed. Their homes won't be underwater the next time the river is high.
At the same time, Dehen said it's important to take FEMA's concerns seriously, and the threat of FEMA remapping the area and putting major portions of lower North Mankato in the flood plain is an immediate worry.
Being in the flood plain would force property owners with a mortgage or other loan against their property to obtain flood insurance, which costs an average of $700 a year nationwide.
"It's an unwanted expense," Dehen said. "When you have the money we've invested in the dike system, to have flood insurance on top of that is an unnecessary expense."
FEMA's concern involves a procedure required under the U.S. Army Corps of Engineers' plan for Mankato's flood system during the very worst floods. When the Minnesota River reaches a certain level, something that last occurred in 1993, a temporary earthen berm must be constructed across Highway 169 north of Highway 14 to keep water from surging back through the Highway 14 overpass.
"That's been OK for 35 years," Hentges said of the contingency, but FEMA and the Corps reconsidered when they did their last re-certification of the flood-control system.
Without that berm — or if it was put in place but failed — extremely high river levels could flow back into the previous river channel past the Hiniker Pond area, through Spring Lake Park and into surrounding neighborhoods.
"It's a fair chunk of lower North Mankato," Dehen said. "So it would affect a large number of our residents."
When the emergency berm has been constructed, the river has never actually reached it, Hentges said. But ever since Hurricane Katrina and the failure of the flood-control system in New Orleans, FEMA has been skeptical of provisions in flood plans that require human action and the possibility of human error.
Hentges, who is encouraging the two cities to push for federal funding for improvements to Highway 169, said the FEMA concern could be addressed as part of a new cloverleaf interchange at Highway 14. And the flood-control issue could make the project eligible for additional funding.
While Dehen favors exploring that possibility, he's inclined to push for a short-term fix to the flood-control issue to ensure that FEMA is satisfied that a solution is in the works when the 2019 deadline arrives.
"I'm fine with that. ... Come up with a plan for the future," he said. "I just don't want to delay that flood mitigation."
A short-term fix could involve raising about 500 feet of Highway 169 and its ditches by seven inches just north of the northside ramps to and from Highway 14. Although the emergency berm would still be needed during the most severe floods, it would be built on a higher foundation and that appears to be a satisfactory plan for FEMA.
MnDOT District Engineer Greg Ous said his agency recognizes the urgency of the situation and is willing to work with the cities on a solution. First, though, an updated analysis of the Minnesota River is needed to reflect changes in recent decades since the last modeling was done, he said. And predicting what a river will do in a major flood is extremely difficult.
"The river is changing," Ous said. "The one thing we know about flood-modeling is we're wrong."
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