Jeff Miller-UW Madison
Following torrential rains in June 2008, stormwater runoff from Manitou Way in Nakoma floods a section of the Arboretum’s Viburnum Garden.
When Laurie Elwell was doing naturalist training at the UW Arboretum a few years ago, her class spent a day near a pond near the perimeter of the property.
“We were tromping around. I remember the instructors told the people in the class to stay away from the pond,” Elwell says. “‘This pond is polluted,’ they said. ‘Don’t go near it.’ That left an impression on me.”
The pond in question was in fact designed to collect pollution and keep it from getting into the Arboretum and Lake Wingra.
The Arboretum may seem like a pristine, natural wonder in the middle of a city. But the urban environment regularly influences and changes it. One of the most notable ways it does that is by sending millions of gallons of stormwater — and all of the pollution it contains — to the Arboretum every year. The UW-Madison’s College of Engineering has described Madison as a sink, with the Arboretum as a “drain.”
“Inevitably the stormwater that’s discharged in the watershed ends up going through the Arboretum on its way to Lake Wingra,” says David Liebl, a UW-Madison emeritus engineering professor, who helps the Arboretum deal with all this stormwater. “Some of it comes from quite a distance, as far away as Westgate shopping mall and Fitchburg.”
It’s a large watershed, with 450 million to 500 million gallons of stormwater draining into the Arboretum each year, Liebl says.
In Madison, the stormwater system — the drains on every street — and the sewage system are separate, says Greg Fries, a city of Madison engineer. When you flush your toilet, the water goes to the sewage treatment plant. But when it rains, the water that runs off your roof, down your driveway and into the street ultimately goes, untreated, into a lake or stream.
“A hundred percent goes to some water body,” Fries says. “Whether it’s Door Creek, the Sugar River or the lakes.”
That’s a problem because the stormwater carries with it particles and pollution: oil and salt from streets, dog poop, herbicides used on lawns, pesticides and manure from farm fields, and industrial pollution.
The city has a goal of stopping 40 percent of the particles — sand, grit, salt, dirt, etc. — from getting to a water body.
“Attached to those particles tend to be pollutants you associate with modern life,” Fries says. “The better job you do at collecting particles, the better job you do at collecting pollutants, like cadmium and zinc.”
Nevertheless, a lot of city pollution ends up draining into the Arb. “The Arboretum doesn’t see itself as an ecosystem designed to treat stormwater,” Liebl says. But its stewards have come to accept that since the Arboretum sits at the bottom of the watershed, they will have to deal with the runoff.
Jeff Miller-UW Madison
Liebl: “Stormwater discharged in the watershed ends up going through the Arb on its way to Lake Wingra.”
Liebl says that the city and Arboretum began trying to deal with this stormwater back in the ‘60s, with the creation of runoff ponds. There are six of these today, five of which have been modernized in recent years. The city and town of Madison, Fitchburg, and the state all contribute to the cost of maintaining them.
Ideally, these ponds (including the one Elwell’s teachers warned her about, Pond #2 near the Leopold Pines) are the first stop for much of the runoff that comes into the Arboretum during heavy rain. The ponds hold the water while sediment settles to the bottom. The stormwater then slowly drains out, eventually getting to Lake Wingra.
During extremely heavy rains, the Arboretum can’t absorb the water fast enough, leading to flooding on nearby streets. Manitou Way occasionally floods high enough to kayak on.
Liebl says there’s more that could be done to prevent stormwater from entering the Arboretum, but it’s expensive and politically difficult.
“There are a lot of different steps that could be taken to keep the water up in the watershed. A lot of that would have to be done on private property,” he says. “If everyone had to have a rain garden, for example, that would make a huge difference in the amount of water coming into the lake. It would have the side benefit of recharging the groundwater, which is significantly lower than it was pre-development.”
When the city reconstructs some streets, it does offer to build residents rain gardens for $100, Fries says. These are designed to hold stormwater until the water can be absorbed by the ground, reducing erosion and stopping pollutants from getting into the lakes. The city’s first “rain garden street” was Adams Street near Edgewood College, where nine gardens were built along three blocks in 2005.
But Elwell knows from her naturalist training that there are simpler things that people can do, including keeping yard waste out of the streets, making sure to collect dog poop, limiting use of salt on sidewalks in the winter, and cutting down on the use of pesticides, fertilizers and herbicides.
Elwell, who is on the board of Friends of the Arboretum, helped develop a guide for people who live near the Arboretum for simple ways they can prevent pollution from getting into the Arboretum. It will be distributed through neighborhood groups and at events.
“The idea is for people who aren’t going to spend a lot of time thinking about it, to maybe change a couple of things they do in their yard,” she says. “You care about Lake Wingra when you want to take your grandchildren to swim. So you should care about this.”
This story is part of our Arboretum Issue. Read the rest of our Arb coverage.
