On one of the last warm evenings in October, a small group of homeowners living near Woodbury’s Colby Lake gathered around a driveway lined with plants in four-inch pots.
The group listened attentively as Tara Kline and Andy Schilling, resource specialists from the Washington Conservation District, explained how to follow planting plans created for their newly excavated raingardens.
Altogether, 12 raingardens have been built in the neighborhood this year, and another 13 will be installed next spring. The project is part of an effort led by the South Washington Watershed District to clean up Colby Lake and keep nuisance algae at bay.
Colby is a shallow, 70-acre lake that is fed by runoff from the surrounding Woodbury landscape, as well as overflow from Wilmes Lake to the north. Various agencies and volunteers have monitored the lake since 1994, and in 2006, the Minnesota Pollution Control Agency listed Colby Lake as officially impaired due to excess phosphorus, a naturally occurring element that contributes to algae blooms when there is too much in the water.
After analyzing water monitoring data and other research, South Washington Watershed District determined that three key actions would be needed to nurse Colby Lake back to health. First, the amount of phosphorus reaching Colby from Wilmes Lake would need to be reduced by 71kg per year.
Second, internal loading that occurs when nutrient-rich sediment at the bottom of the lake is stirred up would need to be reduced by 30 kg per year, and finally, the amount of phosphorus being washed into the lake from the surrounding roads and neighborhoods would need to be cut by 55kg per year. This last part of the equation is where the 25 new raingardens on the west side of Colby come into play.
One of the families that came by to pick up plants for a new raingarden this fall were Kevin Cunningham, his wife Chiching and their two little boys. I first met the Cunningham family when Andy and I showed up at their house one evening in April to see if they would be willing to participate in the Colby Lake improvement project.
Though they had a house full of visiting family and dinner on the table, Kevin walked outside with us to talk about where the raingarden would be located, how it would work and how it would help to keep pollution out of Colby Lake. We explained that the garden would be built during the summer while the City of Woodbury was completing a street improvement project, and would be designed so that when it rains, stormwater from the street flows into the garden and soaks into the ground instead of entering the storm sewer system and traveling directly to Colby Lake.
While he was unfamiliar with the South Washington Watershed District’s studies, Kevin was interested in adding a new garden to his yard and supportive of efforts to improve their neighborhood lake.
Over the past 10 years, hundreds of homeowners in Washington County have built raingardens in their yards, some through individual cost-share projects and others through neighborhood-scale efforts like this one in Woodbury. The Colby Lake project is unique because a study conducted by the Washington Conservation District has already identified the best possible places near the lake to capture and treat the most stormwater for the least amount of money and each of the 25 new raingardens is in one of those priority locations.
Funding from the South Washington Watershed District, together with a grant from the Clean Water, Land and Legacy Amendment, have covered all costs for the raingardens’ design and installation, which is a bonus for homeowners like Kevin and Chiching who have volunteered space in their yards to benefit the common good.
In future years, the watershed district will continue to work with landowners and businesses around Colby and Wilmes Lakes to reduce stormwater runoff and will also work with the city to manage curly leaf pond weed, establish native aquatic vegetation, and manage fish populations to reduce rough fish and increase game fish in Colby Lake.
Learn more about the South Washington Watershed District and its projects at www.swwdmn.org.