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Flood mitigation project gets go-ahead

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By Correne Martin

More than a year and a half after the June 2013 storm that caused flooding and property damage in the city of Prairie du Chien, the common council has approved a preliminary flood mitigation project at the base of the Highway 27 watershed. The Wisconsin DNR has awarded the city a municipal flood control grant for $463,050 toward the project, to which the city must provide a match of about $255,000. The city’s cost share will be funded via a state trust fund loan, payable at about $18,000-$20,000 per year for 15 to 20 years.

“The city’s first documented attempt to mitigate these issues was about 10 years ago. We were unsuccessful in receiving a DNR grant. We attempted to receive a stormwater utility in 2007 and that didn’t work out,” City Administrator Aaron Kramer said at a Tuesday evening public information meeting at city hall. Around 100 letters were sent by the city to community members in the immediate area of the project and approximately 25 attended Tuesday. The meeting took place two hours prior to the council meeting, when the project was officially approved.

Kramer noted that the city has also considered running a pipe from Godden’s Pit to the Mississippi River, to alleviate flooding waters, though that option is determined cost prohibitive at $1.8 million.

In 2013, 47 properties were damaged in the city’s northeastern quadrant due to the storm that brought 10.5 inches of rain over several days (5.5 inches within 24 hours). Also, 171 residential and commercial structures required emergency services for acts such as debris removal and flooded basements.

“We had a lot of water but the key impediment was the debris that washed out of the watershed,” Kramer stated. “Godden’s Pit wasn’t near overflowing, but we had plans in place to evacuate in case it did. It was overwhelming.”

Since that 100-year storm, the ditches along the Highway 27 watershed have been cleaned out, reshaped and reseeded, and trees removed, therefore improving their hydraulic capacity. In addition, Godden’s Pit has been addressed by the city, which spent over $300,000 in 2014 to dredge the pit that Kramer admitted the city had mistakenly neglected over the years. Over 30,000 cubic yards of material was removed and the capacity of the basin was expanded last year. That project was entirely funded by tax increment financing (TIF) dollars.

However, Godden’s Pit has never had the luxury of basins upstream, according to Kramer. With the preliminary flood mitigation project approved by the council, two stormwater detention basins are proposed upstream—one currently on city-owned land northeast of Jackson Street and another on privately-owned property along the Mondell Hill north of Highway 27. Both basins are designed to safely pass a 500-year flood event and control a 50-year storm event. A primary ditch and a secondary bypass ditch south of the Jackson Street basin are also proposed to work in tandem as channels, reducing the risk of future flooding downstream of the basin.

Kurt Muchow, of Vierbicher Associates, the city’s consultant on the project, presented details of the preliminary project plans to those attending the public information meeting. He said a complete analysis of the 2013 storm and flooding was done by September of that same year. Then, Vierbicher came up with four different mitigation options for the city and the council eventually selected what he presented Tuesday.

“The first basin (along Highway 27) incorporates steel I-beams that are designed to catch big debris,” Muchow explained, noting that the I-beams will stick out of the 5- to 6-foot-deep basin by about 1.5 feet. “The second basin also has trash racks to collect for smaller debris. The idea is to trap as much sediment as possible in the two basins and also knock the water flow down.”

Muchow said, under the plans, each basin will be planted with grass, which will be stabilized to avoid erosion. He added that both are considered dry basins, meaning that after 24 hours, they should be drained out and starting to dry up.

After large storm events, Kramer said, city crews will tend to the basins and channels and manually clean the debris catchers.

“The basins are designed so the crews can drive in there with trucks, load the stuff up and get it out,” Muchow said.

The two ditches that are proposed in the project will be 4- to 6-feet deep and slope downward at about 1 percent. “Instead of the water just coming through, we’re widening them so they can act as storage as well,” Muchow noted.

Another main component of the project is an intergovernmental agreement, anticipated between the city, Crawford County, town of Prairie du Chien and the Wisconsin DOT to ensure a cooperative effort is in place for effective maintenance of the new facilities and for emergency response to storm events, debris clearance and damage repair.

“We cannot resolve this without something being done outside the city limits. With the intergovernmental agreement, we can share resources,” Kramer stated, also pointing out that the majority of the project won’t be done until 2016, which falls within the DNR’s grant timeline of December of 2016.

Muchow said some work can be done this fall, including final designs and acquisition of the land. If the owner of the property where the one basin is proposed is not willing to sell, city staff and Vierbicher will come back to the common council and put new options on the table.

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