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Rain Gardens: A Solid Environmental Bet

December 26, 2011 By Ryan Sparrow, Macalester College

Today we present another installment in Minnesota 2020’s series of columns focusing on environmental policy issues. It’s part of our continuing collaboration with Macalester College's Environmental Studies Department and its students.

The Twin Cities have been nationally recognized for their sustainability efforts, but that doesn’t change the fact that urban areas cause a lot of severe environmental problems. These problems include air pollution, improper waste management, the urban heat island effect, and river and lake pollution through storm water runoff.

While Saint Paul and Minneapolis have done a lot to mitigate urban environmental consequences, one of the best solutions to some of these problems is often overlooked. A cost effective, easy installation and aesthetically pleasing way to battle urban pollution problems is a bioretention system, otherwise known as a rain garden. A rain garden is a depression in the soil, about 6 inches deep, designed to seize and absorb rainwater coming off a roof driveway, or other hard services.

Development in urban or suburban areas reduces green space by putting impermeable concrete pavement everywhere. Rainwater that would naturally infiltrate through the ground is directed off of building and/or pavement and into to storm drains, which lead to nearby rivers, lakes, and streams.



As the rainwater directs to the storm drains, other chemical, physical, and biological substances are mixed in with the water, heading straight to the drain. This urban and suburban runoff includes a variety of physical, chemical, and biological pollutants from anthropogenic and natural sources, such as dirt particles, oil and grease, carbon, nutrients such as nitrogen and phosphorus, heavy metals, and toxic organics such as pesticides and fuel pathogens. If a building has a nearby rain garden in place, these sources of runoff are instead directed to the rain gardens where the natural biochemical activity in mulch and soil transform the toxins into less harmful compounds.

Rain gardens also have high levels of efficacy. During a 2006 field study about the efficiency of rain gardens, the University of New Hampshire Storm water center reported 97% of total suspended solids removal through a rain garden system. Additionally, field results at the University of Maryland at College Park documented 70-85% phosphorus removal.

Most people are often led to believe that the mitigation of urban pollution is only possible through grandiose projects such as green roofs. Projects like green roofs or the retrofitting of older buildings do provide extensive benefits, but require intensive labor and generous funding. Newer buildings better allow for retro fits, part of the reason why Minneapolis has been slightly better suited for green roofs.

Rain gardens, on the other hand, can be placed in almost any area where there is space, they can still function in winter, and they create green space for native plants that would have been present if not for the city itself. The installation of a rain garden also gives businesses some green credibility. According the Journal of Environmental Engineering, similar to green roofs, rain gardens are also identified as a site practice for green building design, and leadership in energy and environmental design (LEED) certification.

Since rain gardens have all these great aforementioned benefits, it is important that more businesses and residents in the Twin Cities install rain gardens. Commercial businesses take up a large fraction of space in urban and suburban areas, therefore contributing a substantial amount of the environmental damage caused by storm water runoff. Rain gardens are a low-development, low-cost way to offset these damages, and businesses should take initiative to make our cities cleaner.

The Cities of Saint Paul and Minneapolis both actively promote rain gardens’ installation, and provide further information to help businesses or citizens install them. There are even organizations within Saint Paul/Minneapolis, such as the Ramsey-Washington Metro Watershed District, that provide financial assistance or guidance in the installation of a rain garden.

Residential properties also take up a big portion of space in cities and suburbs, and homes also play a huge role in urban pollution. Runoff from residential properties is especially dangerous because some homes use significant amounts of fertilizers and pesticides to keep their gardens and lawns beautiful. Planting rain gardens will help these homeowners offset the negative environmental effects. The splendor of rain gardens could also be considered a benefit for their lawns as well.

Rain gardens are easy fixes to be more widely utilized throughout the twin cities. Whether it is in a parking lot of a local grocery store, or on a residential home, rain gardens can be placed to help protect our water sources.

Ryan Sparrow is a Macalester sophomore majoring in environmental studies and economics.

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