1. A run on rain gardens -- Wisconsin Natural Resources magazine, February 2003 Page 1 of 5
February 2003
A run on rain gardens
Capturing water and attracting wildlife.
Natasha Kassulke
Rain gardens made one Maryland community
famous
Contents
The term “rain garden” is catchy Where the law meets the land
enough to intrigue garden clubs and
Cities on the spot
scientists alike.
On the home front
Rain gardens don't require much Stem stormwater from the start
space, can be built in various shapes
and readily added to existing A run on rain gardens
buildings. The gardens fill with a few
inches of rain and allow the water to
slowly filter into the ground rather than run into a storm sewer. A
rain garden allows about 30 percent more water to soak into the
ground compared to a conventional lawn.
Roger Bannerman, a DNR nonpoint source monitoring researcher
and rain garden advocate, is working on at least eight rain garden
designs. His passion for these gardens has made him a popular
speaker on the topic. Neighborhood groups have adopted his rain
garden enthusiasm. Groups like the Friends of Pheasant Branch
and Friends of Lake Wingra host workshops.
The result is that rain gardens are growing up and out. Gardens
have been installed in Poynette. The city of West Bend has a large
residential area rain garden.
A home in the Savannah Village development of Waunakee has a
rain garden that was featured in a Parade of Homes.
Rain gardens planted at Edgewood College and the Willy Street Co-
op grocery store in a Madison residential neighborhood are good
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4. A run on rain gardens -- Wisconsin Natural Resources magazine, February 2003 Page 4 of 5
pattern. An outlet furrow to your garden can direct excess water to a
safe location.
But rain gardens are not appropriate for every lawn. Soil type
makes a difference. Some soils hold water creating a mosquito
breeding grounds. Sand drains the fastest with ponding limited to a
few hours. Clay soils drain slow and may stay wet for days. To test
the infiltration, dig a hole, fill it with water and time how long the
water sits. If the water is still there after 24 hours, it may not be the
right site for a rain garden.
Once you have an idea of how your site drains, you can work with
what you've got or increase your soil's permeability.
"Mixing compost or mulch into your soil," says Bannerman, "really
increases the infiltration later."
If you want to work with poor drainage conditions, you should
choose highly water-tolerant plants and make your depression
shallower so that it doesn't retain as much water.
Bannerman also warns against planting a rain garden on top of a
septic tank drainfield, which could overload the system. He
recommends keeping a 10-foot distance from the foundation to
avoid flooding your basement.
For new developments, rain gardens can be built into the design
plan and the cost comes down when plants are bought in bulk. An
added benefit is that rain gardens reduce the amount of lawn to
mow.
Rain gardens made one Maryland
community famous
Somerset, an 80-acre subdivision in Prince George’s County, Md., features
about 200 homes on 10,000-square-foot lots, with prices starting around
$160,000. Roads here blend into grassed swales. Landscaping contrasts with
the curbs, gutters, and sidewalks of neighboring communities.
But Someset’s unique character really revolves around rain gardens -- each lot
has a 300- to 400-foot rain garden -- located at low lot points.
“It (rain gardens) was an innovative idea when we started it 11 years ago,”
explains Larry Coffman, associate director for programs and planning with Prince
George’s County Department of Environmental Resources.
Coffman is widely regarded as the “father of rain gardens” and Somerset is often
cited as an example of storm water management at work.
For years, bioretention for storm water management was acceptable at
commercial and industrial sites with limited space, and in places where installing
and maintaining oil and water separators and storm water ponds would have
been expensive. Using bioretention in residential locations, was a newer
concept.
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5. A run on rain gardens -- Wisconsin Natural Resources magazine, February 2003 Page 5 of 5
Coffman helped design a plan to replace the ponds, curbs, gutters, and
sidewalks with gardens on each lot and create open drainage swales. Hanifin
Associates, consultants to Prince George's County, dubbed the storm water
facilities "rain gardens."
Each garden costs about $500 -- $150 for excavation and $350 for plants. About
$100,000 was needed to install rain gardens at Somerset, in comparison to
nearly $400,000 -- not including the expense of curbs, gutters, and sidewalks --
for conventional detention ponds.
“We built a couple hundred rain gardens and about 98 percent of them are still
there,” Coffman says.
Flow monitoring at Somerset shows that the gardens curbed runoff.
For small storms we’ve seen a 75 to 80 percent reduction in flow,” Coffman says.
He would now like to see a wider suite of low impact design (LID) measures
installed at Somerset.
Coffman also speculates that the gardens have helped sell homes. Research
shows that LID designed lots elsewhere demand $10,000 more per lot compared
to conventional lot designs. LID designs also save in terms of maintenance
costs.
“The houses at Somerset are sold-out and continue to sell quickly when on the
market,” he says. “Nature sells.”
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http://www.wnrmag.com/supps/2003/feb03/run.htm 1/30/2004