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Stormwater projects aim to fix Arboretum runoff woes

Anita Weier  —  8/28/2008 2:19 pm

Almost half a billion gallons of urban runoff swamps the UW-Madison Arboretum every year, endangering the restored prairies, savannas and wetlands and gradually overwhelming the stormwater detention ponds that protect the valuable property from erosion.

Five of the six stormwater detention ponds within the 1,260-acre research, conservation, educational and recreational facility have failed, and a concrete gutter that carried stormwater collapsed. As a result, soil has eroded, wetlands have been degraded, and a delta of sediment is settling into Lake Wingra, said David Liebl, the head of a committee that has planned stormwater control improvements at the Arboretum.

Five major projects are planned to help solve the problem over a five-year period, at a cost of $750,000 to $1 million each.

Representatives of the cities of Madison and Fitchburg as well as the town of Madison, the state Department of Transportation and the University of Wisconsin-Madison participated in the planning process. The new facilities will be paid for with a combination of university, city and DOT funds, with the UW contributing extra funds in some cases to support research efforts.

But though an agreement was reached to share costs, it has not yet been signed, according to Liebl, a stormwater management specialist for the UW-Extension.

The public is invited to find out the details of the projects during an open house on Monday, Sept. 8, from 7 to 9 p.m. at the McKay Visitor Center at the Arboretum.

Fixing or replacing the Arboretum's existing stormwater detention ponds and channels is the main goal, but the committee also plans to try solutions other than the detention ponds that slow stormwater flow and let sediments settle.

"The Arboretum is very cognizant that it has a limited parcel of property with a unique research and teaching mission, which means there's a reluctance to trade land for detention ponds if that's all they're going to be," Liebl said.

"So we've tried to meld those missions with what would be considered contemporary stormwater management construction."

For instance, typical detention ponds will be supplemented with shallow areas that completely drain between rainfalls, in which scientists will test how various native plants perform in stabilizing soils, controlling erosion and removing nutrients that stimulate growth of non-native plants.

"Urban runoff is becoming more and more of an issue around the country, so the research that the Arboretum does in conjunction with these projects is going to be used quite widely," said Gary Brown, who oversees Arboretum projects for UW-Madison's Office of Facilities Planning and Management.

The first two projects will be repair and improvements of Johannsen Pond and the Manitou Way/Secret Pond.

Johannsen Pond handles urban runoff from the Arbor Hills neighborhood, Beltline and Todd Drive commercial area. A concrete flume and storm drains carry stormwater to the pond, which lacks sufficient capacity to remove nutrients and sediments before they head downstream to wetlands and Lake Wingra.

The rehabilitation project will include a special trap that collects and cleans heavy sediment such as street sand or spills of petroleum or other chemicals from the highway so they don't enter the main detention pond. Additionally, runoff from a Waste Management tipping yard will be pre-treated by the company to remove oils and greases before discharging into the pond.

The Arboretum also will build a stormwater management research facility upstream from the pond to direct flows into a shallow basin where native plants will be tested for their ability to remove nutrients and let water soak into the ground.

The Manitou Way/Secret Pond handles runoff draining through the Manitou Way outfall from the Nakoma neighborhood and runoff from the Odana Road and Whitney Way areas, to make up about 40 percent of all runoff entering the Arboretum.

A trench currently carries this stormwater through the basin of now-failed Secret Pond and West Wingra Marsh before entering Lake Wingra. Large amounts of sediment come into the lake at this site, and invasive plants have spread.

The project includes building a 1.4-acre detention pond at the outfall adjoining Manitou Way, where it will collect 60 percent of sediments and debris as well as moderating flows downstream. The trench will be replaced with a broad swale -- a wide, shallow depression that carries and slows the water. Faculty and students will use the swale to investigate the ability of various native plants to stabilize soils and reduce erosion.

But Liebl stressed that homeowners and businesses will also have to pitch in to sufficiently control stormwater. Homeowners are urged to build rain gardens, make sure downspouts drain over lawns instead of sidewalks, not use too much salt and keep leaves out of the gutter. Businesses can use engineered rain gardens that have a drain.

Anita Weier  —  8/28/2008 2:19 pm