City of Benson prepares for flooding, just in case
BENSON -- A project in the 1950s to straighten the Chippewa River channel at Benson made the threat of spring flooding a problem of the past for the Swift County community.
Or did it?
"There's a certain conviction out there that we haven't had it before and likely won't have it again. But sometimes, you come up with snake eyes,'' said City Manager Rob Wolfington.
The city is doing a lot of work to prepare for the possibility that Mother Nature could roll the wrong dice this year.
It's hard to know the risk of flooding this far in advance, but the stage is certainly being set with the heavy snowpack and the high water content it represents in the upstream watershed, he noted.
The city of Benson has been working in recent weeks to encourage people to consider purchasing flood insurance as their first defense against flooding. A few years ago the Federal Emergency Management Agency developed digital maps of the elevations within the community. They show that about 25 percent of the community is within the zones for 100-year and 500-year flood events.
The previous maps did not show any flood zone areas. Consequently, many people likely purchased their homes without any idea that they lie within an area that could experience flooding.
The homes considered most vulnerable are among the newest. They are built near the Chippewa River along the golf course. The Chippewa River rose to the edge of the golf course roadway in 1997. Some 25 to 30 homes could be flooded if waters top the roadway.
The city has developed contingency plans to erect an emergency clay dike along 1,800 to 2,400 feet of the roadway if necessary. It's a very costly undertaking, and would only be done if it appears likely waters will rise over the roadway.
Unfortunately, knowing how high waters might rise is a very big challenge for the community. At best, the city might have two to six days of advance notice that a certain level of flooding can be expected, Wolfington said.
There are no automatic gauges upstream of the city to provide real-time data on water levels and flows in the approximately 810,000 acre watershed that drains to the community.
The Chippewa River is considered one of 82 "minor'' tributaries in the state. Much of the state's attention -- and resources -- are focused on major rivers like the Red, Minnesota and Mississippi.
As in a game of dice, Benson must also deal with variables that are impossible to predict. The Minnesota Highway 9 and Burlington Northern Sante Fe Railway bridges over the Chippewa River are two "choke'' points. They restrict the flow of water during flood conditions by the limitations of their size.
More worrisome, they raise the risk for sudden flooding caused by ice jamming. The railroad bridge -- with multiple piers in the channel -- presents the greatest ice jamming risk.
The city has plans to close storm sewer lines to prevent water from backing up if the river rises, but that does not guarantee flooding won't occur. If a rain event occurred during flood conditions, water would certainly pond in the city.
Benson is preparing for the potential of flooding knowing that the city will likely bear the costs and responsibilities on its own, Wolfington said. Only if a presidential disaster declaration is made would a portion of the city's costs be reimbursed.