Rain Garden Demonstration
Wastewater Division, Public Works Department, City of Superior, Wisconsin
Basin Program Funds:
Impervious surfaces, such as roofs, roads, sidewalks, and parking lots, and storm sewer systems change the natural flow of water across the landscape, virtually eliminating infiltration into the soil and creating flash deposits into waterways, followed by drought-like conditions. These urban flows transport sediment and pollutants directly into waterways.
Rain gardens provide a cost-effective method to help limit quantity and improve quality of surface water flows. Rainwater falls for free, while tap water costs homeowners twice, once coming into the residence and again for wastewater/sewer charges. One inch of rain on a 1,000-ft2 roof yields approximately 625 gallons of water. Keeping water on-site and out of engineered conveyances minimizes pollutant transfer to waterways and maximizes capacity and efficiencies of stormwater and wastewater sewer systems.
More than 40% of water body impairment is attributed to air depositions. Unlike conventional lawns, rain gardens do not require mowing. According to the EPA, a two-cycle lawn mower can contribute 0.3283 pounds of volatile organic compounds (VOCs) and 0.6690 pounds of carbon monoxide per summer day. Gasoline, electric and battery powered tools also emit carbon dioxide (CO2), a major greenhouse gas; nitrous oxides and sulfur dioxide, which react with atmospheric water to form acid rain, and other air toxics such as benzene and particulates.
Native plants help reduce CO2 by storing carbon in plant stems, leaves, roots and soil, have a greater ability to retain and store water, and are more efficient than mowed grass as a carbon sink. The use of native plants reduces or eliminates use of herbicides, pesticides and fertilizers.
The Wastewater Treatment Plant covers nearly 14 acres, all needing on-site stormwater management. By applying rain garden practices at a city facility, we can set an example for stormwater best management practices (BMP’s) that we encourage the community to employ.
The Stormwater Management team demonstrated the viability of rain gardens in Superior starting with two in-house projects at the wastewater treatment plant. In 2002, more than 400 5th and 6th grade students participated in tours and stormwater pollution prevention activities. Additionally, we average 250 high school/college student visitors every year. The newly created demonstration gardens will be included in tours of the wastewater plant. We will also organize public tour events to celebrate Earth Day and National Pollution Prevention Week to increase exposure of the gardens to at least 1,000 citizens in a typical year. A brochure detailing the project, a rain garden display, and on-line information will provide exposure to at least 500 additional citizens.
Each garden area was excavated to 18? then layered with 2? of gravel, 3? of sand, 1? of gravel. A 12? layer of 2:1 peat:topsoil mix along the perimeter will taper down to 6? at the center. Plans to inoculate the area with fungal mycelium were changed. This step would have been too costly and was not allowed by city ordinance. The gardens were mulched with straw, shredded wood or cocoa beans. Two to four weeks later, the first few inches of topsoil were tilled, weed seeds germinate and sprayed with an environmentally safe herbicide, then the site was be planted.
At the Grit Building site, some of the excavated clay was used to construct a berm to deflect roof and parking lot water to the garden. Two enclosed rain barrels capture rainfall from the building, with an overflow valve and tubing emptying at the surface into the rain garden. The 900-ft2 garden will be planted with an 80:20 grass/sedge/wildflower mix in the depression. Chokeberry, a 4'-6' shrub, will screen the railing at the back edge.
A second garden site near the Blower and Chemical Building was divided into four sites, the first three with wildflowers and the fourth planted with native grasses. Site preparation is similar to the Grit Building site.
Two half-day workshops were conducted, one in June 2004 and one in June 2005 to educate the public on the gardens. Approximately 15 to 20 people attend each workshop and received instruction on how to build rain gardens. During the workshops two small gardens were added to demonstrate how rain gardens might be applied in a private residential situation. Newspaper adds, radio spots, and press releases were submitted to area media. Tours were given to interested citizens, and PowerPoint presentations were given to the tours and at garden club meetings.
Contact: Ms. Diane Thompson, 715-394-0392 ex 135