Rain gardens are sprouting all over Dakota County, cleansing runoff from streets and fertilized lawns and saving big money for some cities.
Hastings and Inver Grove Heights have avoided laying storm water pipes by letting runoff soak into big and small rain gardens, saving millions, city officials said.
Several thousand homeowners from nearly every city have attended dozens of Blue Thumb workshops held by the county's Soil and Water Conservation District over the past four years. With $250 district grants available for home rain gardens, more than 150 have been installed around the county, district urban conservationist Mike Isensee said.
The first inch of rainfall carries the most pollutants -- mostly phosphorus and nitrogen from fertilizer and traces of petroleum products, Isensee said. Home rain gardens can hold a few inches of water, which settle out sediment and filter water into the ground.
City officials noted that a major motivator for the free workshops and grants has been the national Clean Water Act and related state requirements that cities reduce and clean up runoff before it reaches lakes and rivers. A side benefit is that the gardens reduce mosquito breeding because they are designed to dry up within two days, before eggs can hatch.
Ellen Fike of Inver Grove Heights is doing her part to send cleaner water down her 69th Street storm sewers into the Mississippi River.
"We want to help keep the river clean, and this seemed like a good way to do it," Fike said.
Fike is one of more than 40 homeowners in a dozen cities to plant rain gardens this year in Dakota County, Isensee said.
Last week, Isensee dropped off hydrangea, lilies, spirea and other perennials for Fike and her two daughters to plant. In return for the city paying about $2,000 for her 75-square-foot garden by a curb cut, Fike agreed to plant and maintain the garden, which will catch runoff from the street and her roof downspout.
After an extensive study of the cost of a storm drainage system for the glacier-pocked northwest part of Inver Grove Heights, the city estimated a traditional storm sewer system would cost about $10 million, said City Engineer Tom Kaldunski.
"We found out we could do it for half that cost by preserving the regional basins and using infiltration in new construction," he said. A system of rain gardens and retention ponds can handle the first, most polluted inch of rain, absorb it in the sandy soil and reduce the size of regional pipes needed for rains of more than an inch, which account for only about 20 percent of rain storms, Kaldunski added.
"In essence, we are trying to mimic what nature has always done -- that is, to soak the water into the ground and send less to the Mississippi River."
Burnsville, with more than 50 home and public rain gardens, has been a national leader in the practice since it did a four-year experiment comparing runoff in two nearly identical Rushmore Drive neighborhoods, one with rain gardens and one without.
Study results in 2006 showed the neighborhood in which 17 of 25 homes had rain gardens produced far less runoff than the control neighborhood. Storm water draining into Crystal Lake dropped by 90 percent in the second year after the gardens were installed, said Daryl Jacobson, city water resources specialist.
Jim Adams • 952-707-9996