Storm-water management efforts deter runoff into Lake Mendota

September 7, 2004 By Tom Sinclair

It was easy to blame last spring’s flooding in Dane County on record-setting rains. But people are as much at fault as the weather, says Ken Potter, civil and environmental engineering professor.

“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, the policy calls for redirecting as much storm runoff as possible on the 930-acre campus into the ground rather than into Lake Mendota.

One could call it an endorsement of the trickle-down effect.

Potter helped organize a group of faculty, staff 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 Gaylord Nelson Institute for Environmental Studies.

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.

As farmers converted the land to agriculture, they drained the depressions, compacted the soil and triggered erosion, producing more storm runoff.

Urban and suburban growth transformed the county into landscapes of buildings, streets, driveways and parking lots. These impervious surfaces seal the ground beneath them, leaving storm water fewer places to go. Detention ponds, built to catch runoff and release it slowly, help somewhat, but they do little to reduce total runoff.

Potter says all this is why heavy spring and summer rains increasingly cause flooding around the Yahara Lakes, including some parts of the UW–Madison campus. The solution, he says, is to keep more storm water close to where it falls until it can evaporate or soak into the ground.

“Rain gardens” — clusters of water-tolerant plants in bowl-like depressions — are a popular tool in urban areas. 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,” Potter says. “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 the campus for locations where storm water could be better managed.

“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 planned for the eastern end of campus will provide opportunities to improve storm water management. The rapidly growing western portion of the campus presents different challenges because the land is lower and wetter. Nevertheless, Potter sees opportunities there. And staff in the Facilities Planning and Management division worked closely with Potter’s students to help integrate their ideas on campus.

Instead of flowing into storm sewers, runoff from the West Campus Cogeneration Facility on Walnut Street will be piped into the soil beneath athletic fields or stored in surface depressions.

FP&M is 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. The university also has applied for financial assistance to rebuild a large parking lot near the shore of Lake Mendota.

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.

Potter says continued urban and suburban growth in Dane County will intensify the need for storm-water management.

“Only 5 to 6 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. 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 UW–Madison Storm Water Runoff Management Project Web site.

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