seen as key to cutting pollution
By Stephanie Hemphill
Minnesota Public Radio
Published June 23, 2004
A good Midwestern summer storm can dump a lot of water
in one place. Sometimes there's so much rainwater, it
floods into sewer lines, and washes untreated sewage into
lakes and rivers. Cities across the country are spending
millions of dollars to solve the problem. In Superior,
Wisconsin, the city is encouraging people to build rain
gardens. The perennial gardens are designed to hold rainwater
and let it seep gradually into the ground.
Superior, Wis. — The sewage treatment plant for the city
of Superior sits right on the waterfront. There are treatment
tanks and pump houses. And lately there are gardens. They're
demonstration plots, showing how homeowners can help solve
a serious problem. Each garden is like a shallow bowl,
about six inches lower than the surrounding ground. The
buildings next to the gardens have downspouts that carry
water from the roofs right into the gardens.
Charlene Johnson is creating these rain gardens. She
dug away the surface soil, added compost, and then planted
native grasses and perennials.
"We've got the golden alexander starting to bloom,"
she says, pointing to the flowers. "This garden has
purple coneflower, green-headed coneflower, cardinal flower,
They're all plants that can live with a lot of water,
or just a little. Johnson says they do a much better job
of holding onto rainwater than a regular lawn, because
they have deep roots.
"The average lawn is about one to two inches,"
she says. "Therefore you'd only have one or two inches
of roots. Roots equal storage capacity. Also as the roots
penetrate through the ground, they die back, and those
holes can also be used for storm water retention."
Johnson would like it if every yard in Superior had a
rain garden. The ideal size depends on the size of the
house and the type of soil in the yard. But typically
they're about the size of a small patio.
Lots of people are building water gardens these days
-- small pools or ponds -- but a rain garden is different.
It's not designed to hold water or goldfish; it's designed
to absorb big rains and let them sink slowly into the
"Plants and soil naturally cleanse pollutants from
water. By the time it recharges into the groundwater aquifers,
the water is essentially clean," Johnson says.
And it's cheaper in the long run than sending it through
a treatment plant. Johnson says rain gardens cost about
the same to build as any other perennial garden - between
$3 and $5 per square foot. Most of that is to buy plants.
This is an expense for homeowners. But Johnson says it
will pay off in the long run, because it'll keep rainwater
out of the sewage treatment system. And that could offset
likely increases in monthly water bills.
On the other side of town, Jan Murphy loves her rain
garden. She built it seven years ago when she built J.W.
Beecroft, a bookstore and coffee shop in Superior. As
the traffic speeds by on the highway, a redwing blackbird
sings from the garden.
"We've had ducks," Murphy says. "It's
been very delightful. We've had lots of little critters
in here from time to time."
Runoff from the parking lot flows into the garden, where
the cattails and other native plants clean it up before
it seeps into the city storm water system. Rain gardens
aren't going to solve every city's problems with storm
water runoff. But they can help.
Kurt Soderberg, who directs the Western Lake Superior
Sanitary District in Duluth, says rainwater picks up all
kinds of pollution as it flows across parking lots, streets,
and yards, and eventually into lakes and rivers.
"Rainwater is a big impact on water quality,"
Soderberg says. "Whether it's sediment washing into
the lake, or fecal coliform going into the creeks and
the lakes, there are a whole lot of reasons why you want
to stop storm water from rushing into the natural bodies
In Duluth, every time it rains hard, the storm water
mixes with sewage and gushes into Lake Superior. The city
and the sanitary district are planning to spend as much
as $30 million to fix the problem. Soderberg says rain
gardens could be part of the solution.