Potter helps lead UW-Madison storm water overhaul
“We've disrupted the hydrologic cycle,” he says, “and we have only tinkered with fixing it.”
The good news, Potter says, is that a new storm-water management policy at UW-Madison is a big step toward a real fix. Approved last fall by university officials, the policy calls for redirecting as much storm runoff as possible on the 930-acre campus into the ground rather than into Lake Mendota. Not overnight, but eventually.
You could call it an endorsement of the trickle-down effect.
Potter helped organize a group of faculty and staff members and graduate students that spent much of last year scrutinizing storm-water management on campus. Now they are plotting ways to improve it. Their work is supported by a grant from the Wisconsin Department of Natural Resources to the university's Nelson Institute for Environmental Studies.
Currently, much of the rainfall and snowmelt on developed parts of the campus that does not evaporate or soak into the soil either flows into storm sewers, which empty into Lake Mendota, or runs directly into the lake. Although that simple strategy made sense in the past, today it can backfire.
Under natural conditions, most of the precipitation that fell on what is now Dane County accumulated in natural depressions and seeped into the ground. As farmers converted the land to agriculture, they drained the depressions, compacted the soil and triggered erosion, producing more storm runoff.
More recently, urban and suburban growth has transformed increasing areas of the county into landscapes of buildings, streets, driveways and parking lots. These impervious surfaces seal off the ground beneath them, leaving storm water fewer places to go and creating flooding problems downstream. Detention ponds, built to catch runoff and release it slowly, help somewhat, but they do little to reduce total runoff amounts.
Potter says all this is why heavy spring and summer rains now increasingly cause flooding around the Yahara Lakes, including some parts of campus, often yielding substantial property damage. The solution, he says, is to keep more storm water close to where it falls until it can evaporate or soak into the ground.
Even in dense urban areas, there are many ways to do this. “Rain gardens” — clusters of water-tolerant plants in bowl-like depressions — are one increasingly popular tool. Permeable pavements, such as porous concrete blocks, are another.
“Permeable pavements have been shown to work in places like Sweden, where the climate is similar to ours and they have to contend with snow and ice,” says Potter. “Entire roads of permeable pavements have been built in the Netherlands and Oregon. There's no reason why they can't work here.”
Potter's group has scouted campus for locations where storm water could be better managed with these and other remedies. Their search has turned up some surprises.
“The students found that most green spaces around here are as hard as rock,” says Potter. “On the big lawn in front of the Kohl Center, if you dig down six inches, it's solid clay. That's because when the building site was excavated, the clay was spread in front. Then it was just covered with turf. The students observed that when it rains, the water runs off the lawn instead of sinking in. So you've got a very large green space acting as if it were a roof. We could correct that relatively easily by replacing the compacted ground with soil that absorbs more water.”
Potter believes the gradual redevelopment of the eastern end of the campus called for in the university's long-range plans will provide many opportunities to improve the way storm water is handled in that area. The rapidly growing western portion of the campus presents different challenges because the land is lower and wetter. Nevertheless, Potter sees opportunities there, as well. And staff from the university's Facilities Planning & Management division have been working closely with Potter's students to help integrate some of their ideas on campus.
Instead of flowing into storm sewers, for example, the runoff from the roof of the West Campus Cogeneration Facility, a power plant under construction on Walnut Street, will be piped into the soil beneath nearby athletic fields or stored in surface depressions.
Campus facilities staff are also looking at potential rain gardens, infiltration trenches and “green roof” technologies for new campus buildings to clean up the storm water, slow it down and infiltrate some of the water before it gets to Lake Mendota.
Already, UW-Madison has replaced a deteriorating parking lot at Angler's Cove, a popular fishing spot near Eagle Heights, with a smaller parking area and natural landscaping designed to keep storm water from scouring away the fragile lakeshore. The university also has applied for financial assistance to rebuild a large parking lot near the shore of Lake Mendota so that virtually all of the rainfall on the lot seeps into the ground.
Flood prevention is only one benefit of better storm water management, says Potter. Minimizing runoff also reduces erosion, keeps pollutants on the ground from washing into lakes and streams, helps prevent excessive warming of surface waters in summer, and replenishes the groundwater that serves as the municipal water supply for Madison and surrounding communities.
Potter says continued urban and suburban growth in Dane County will intensify the need for enlightened storm water management.
“Only five to six percent of the Lake Mendota watershed — the land area that drains into the lake — is impervious now,” he notes. “We've only begun to develop it. Most of the watershed north of the lake is still farmland. As that becomes more developed, the problem will only get worse.”
Potter acknowledges that UW-Madison alone cannot solve the problem — that every community in the county must share the responsibility.
“But let's face it,” he says, “the university is a big presence here. We have a lot of impervious surfaces, and for the most part, we have been exempt from storm water regulations that apply in other places. If we can improve things here, we set a new standard for others.”
For more information, visit the Storm Water Runoff Management Project Web site at www.ies.wisc.edu/courses/719_summer_03/.