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Crow Wing County Board: Conserving clear and cold Big Trout

The stormwater treatment project proposed by the Crow Wing Soil and Water Conservation District will be installed along County Highway 66, on the eastern shore of Big Trout Lake. Submitted by: Crow Wing SWCD1 / 4
The Downstream Defender vortex separator will be one of two methods used in a proposed system intended to treat stormwater runoff before it enters Big Trout Lake in Manhattan Beach. Submitted by: Crow Wing Soil and Water Conservation District2 / 4
A photo taken in December 2014 shows a heavy flow of stormwater runoff flowing through a culvert into Big Trout Lake in Manhattan Beach. Submitted by: Crow Wing Soil and Water Conservation District3 / 4
The stormwater treatment project proposed by the Crow Wing Soil and Water Conservation District will be installed along County Highway 66, on the eastern shore of Big Trout Lake. Submitted by: Crow Wing SWCD4 / 4

One of the area's clearest, coldest lakes is about to get a protection boost from a recently funded runoff treatment project.

Big Trout Lake, a part of the Whitefish Chain of Lakes and the only lake in the Brainerd area stocked with lake trout, is the intended beneficiary of a proposed system to treat runoff from County Highway 66. The Crow Wing Soil and Water Conservation District project was funded in 2016 with a $310,000 grant from the Clean Water Fund, one of the funds supported by the 2008 Legacy Amendment.

Bill Westerberg is an engineer with the North Central Minnesota Joint Powers Board and designed the project, which will incorporate a vortex separator to remove sediment and a drain field to reduce and cool runoff entering the lake.

"It was determined that the goal was to reduce the suspended sediment and salt entering the lake and provide additional storage and temperature reduction of the runoff before it enters the lake," Westerberg told the Crow Wing County Board May 23. "There's really no treatment other than what's being filtered out in the grass and the drainage ditch."

Rob Hall, assistant county engineer, added the drainage system currently in use was constructed 40 years ago.

Big Trout Lake covers 1,342 acres and is 128 feet deep. The lake is considered "heavily developed" by the county, with 237 homes, two resorts and two camps along its 8.5 miles of shoreline. Along with its lake trout population, Big Trout Lake is a Cisco Refuge Lake, designated by the Minnesota Department of Natural Resources. Cisco are a fish species considered an indicator of environmental stresses, due to its sensitivity to temperature and oxygenation changes.

Big Trout Lake is considered a priority for protection in the Crow Wing County Water Plan due to its recent decline in water clarity and increase in impervious surfaces within its catchment area.

According to statistics gathered by the University of Minnesota, between 1990 and 2000, the amount of land considered urban near Big Trout Lake increased by 15.4 percent, and proportion of area covered by impervious surfaces—such as pavement—increased by 2.5 percent.

Runoff from impervious surfaces can have a detrimental impact on lake water quality. It can increase nutrient loads, introduce toxic pollutants and reduce oxygen levels by increasing temperature.

The Crow Wing SWCD identified an area where stormwater treatment could have the most impact—along the lake's eastern shore in Manhattan Beach. County Highway 66 runs close to the water's edge for about a half-mile, and rainwater and the chemicals, sediment and salt it collects along the way runs almost unabated through culverts into Big Trout Lake.

The Downstream Defender system the SWCD will install uses energy generated by the water's natural flow to create a vortex within a chamber. This forces heavier sediment to settle at the bottom, while oils, garbage and other floating debris are stored at the top. The treated water flows outward from an interior chamber.

A second element of the SWCD's plan is a drain field using perforated plastic pipes. During average, 1-year rain events, the pipes will assist with diverting the stormwater through a rockbed and into the ground. This will reduce the temperature and overall flow of the runoff, Westerberg said. In larger rain events, some runoff will bypass this second stop, although the vortex system will serve as a first line of defense.

Westerberg said property owners along the area where the system will be installed have agreed to temporary easements during construction. The plan includes maintaining two lanes of traffic throughout installation, and concrete barriers along the shoulders will protect motorists from steep embankments while the work is being completed.

"It's going to look like we're mining out there," Westerberg said. "But when we're done, it shouldn't look any different."

The action Hall requested the county board take concerning the project was to agree to a cost-sharing arrangement between all involved entities. The county is involved in the equation because the project will be installed within the right-of-way of County Highway 66, Hall said, and the agreement also includes the SWCD, the city of Manhattan Beach and the Whitefish Area Property Owners Association.

The city and WAPOA agreed to future maintenance, including annual pumping, for the 25 years of life expectancy of the system. The SWCD is responsible for providing the 25 percent funding match, which it is doing so through in-kind staff support. The county will be the owner of the system and will be responsible for future removal or replacement as needed.

The board unanimously approved the memorandum of understanding outlining each agency's responsibility.

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