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Rain gardens help preserve water quality

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Detroit Lakes, 56501
Detroit Lakes Minnesota 511 Washington Avenue 56501

Unless they have a soggy basement after a hard rain or a front yard that floods every spring, most people are completely unaware of the problems caused by storm water runoff.

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But here are just a few examples of its environmental impact:

• One quart of motor oil, when allowed to run off a paved driveway down into a storm drain, can contaminate 250,000 gallons of water.

• One pound of phosphorus, when allowed to contaminate the water that runs off lawns and discharges into a nearby lake or river, can create 500 pounds of algae.

And those are just some of the more obvious examples of storm water contamination, according to Gregg Thompson, an urban conservation specialist with the Association of Metropolitan Soil and Water Conservation Districts in St. Paul.

What many people are unaware of, Thompson said, is that "gunk" which is allowed to run down into a storm drain discharges directly into a wetland or water body. Unlike wastewater that discharges from homes and businesses, the water that flows into a storm drain is not filtered through a sewage or wastewater treatment facility before it is released back into the environment.

Thompson was in Detroit Lakes this past week for a workshop on rain gardens and storm water management at Minnesota State Community & Technical College.

One way to prevent contaminated water from discharging directly into a wetland, lake or river is by creating a rain garden, which takes rainwater from a household gutter, roof, driveway or other impermeable surface and filters it naturally through the soil and back into the water table below.

The size of a rain garden should be approximately "10 percent of the size of the drainage area that feeds it," said Thompson.

Each garden should consist of shallow depressions, between 4-12 inches deep, that can absorb rainwater runoff from a typical storm in 48 hours or less.

According to Thompson, building a rain garden can also lessen the need for irrigation, by not only "keeping more water on site," but also by making the soil more permeable and able to absorb the rainwater naturally.

The problem in many communities, Thompson said, is that "Right now, there's no economic incentive to do anything with (storm water) runoff."

In Minneapolis, however, landowners are charged a storm water utility fee, based on the amount of hard, impermeable surfaces they have on their property. Credits, however, are given for land management practices that reduce the amount of runoff that leaves their property.

"I think that (practice) is going to come everywhere eventually, because it's the fairest system," Thompson said.

If a landowner is given a way to reduce their fee by, say, building a rain garden, it will have not only an economic benefit for them, but the environmental benefit of "extending the life of a lake (or other water body)."

If storm water contamination runs unchecked, however, it will eventually build up to the point where a lake can no longer absorb it -- "and so you get huge amounts of algae, and the quality of the lake drops," Thompson said.

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