Milwaukee pilots a new stormwater management tool.

By Timothy A. Schuler

By August, the faded yellow house at 3930 North 35th Street in Milwaukee will be gone. In its place, invisible to all but the team that designed it, will be a new tool for stormwater management: the “BaseTern.” Conceived by Erick Shambarger, the deputy director of Milwaukee’s Office of Environmental Sustainability, a BaseTern is a basement that’s been converted into a rainwater or stormwater cistern. Milwaukee is completing what is said to be the world’s first such system this month.

The BaseTern concept, which Shambarger trademarked, is simple. Stormwater will be directed to an abandoned or foreclosed property’s basement, which, after the aboveground structure is demolished, is waterproofed and filled with gravel and stormwater-harvesting cells. According to a feasibility study by engineers at HNTB, the system can hold anywhere from 13,000 to 40,000 gallons of water during storms, reducing flooding in adjacent homes.

It’s a clever riff on adaptive reuse, taking advantage of one urban issue—a surplus of city-owned foreclosures—to solve another: the flooding that is increasingly common in dense, impervious neighborhoods like Milwaukee’s Sherman Park, where the pilot project is located.

“A lot of the systems you see on the street, bioswales and stuff, can maybe handle a half inch or an inch of rain,” says Shambarger, who came up with the idea while serving on the mayor’s flooding study task force. “That’s certainly an improvement over just straight-up pavement, but they don’t have the capacity to deal with the megastorms that you worry about with climate change.”

Shambarger used GIS mapping to analyze all reported basement backups and noticed that the most severe flooding occurred in neighborhoods with high rates of foreclosures. The city controls roughly 900 foreclosed properties, many of which it plans to demolish. Shambarger figured the city could preserve the basement structure and put it to use. He commissioned the feasibility study, which concluded that the concept was both sound and cost-effective.

The project has gained the attention of designers around the country, as well as the local landscape architect Jennifer Current, who teaches at both the University of Wisconsin–Madison and the Illinois Institute of Technology (IIT) and runs a small design studio called Freelens. As innovative as the BaseTern was, Current had a hunch that the city would simply cap the BaseTern and plant turfgrass over top, making it indistinguishable from any other vacant lot in the city.

“When there’s something so interesting going on below the surface, there should be something that speaks to that above the surface,” she says. So, with nine of her IIT landscape architecture students, Current began exploring aboveground interventions that would bring attention to the innovative water engineering below the surface.

She and her students came up with three concepts, which they delivered to Shambarger’s office this past May. Of the ideas, which range from a tree nursery to a steel structure with a second-story viewing platform, the one most likely to be implemented is “Splash Garden,” which directs sheet flow from the street and alley into the BaseTern and exposes the engineering underfoot through a series of old-fashioned hand pumps that draw water up from the basin below.

The garden’s design preserves the memory of the house, making visible with hardscape elements the house’s original footprint and limiting rain garden elements to the perimeter. “There’s a history to this,” Current says of the site. “It’s a homestead. People in the neighborhood know the house; they know the people who lived there.” She says it was important not to lose that.

The city, however, plans to “proceed with the basics,” Shambarger says, which means a geotextile layer, a foot of soil, and turfgrass. But he says he was impressed by the students’ understanding of the issues and intends to show their work to the city’s philanthropic partners to find funding for various elements of the Splash Garden concept.

Most eyes are on the BaseTern itself, to see if and how it works. If successful, it will be one more achievement for a city that is becoming known for water research and innovation. Last summer, the University of Wisconsin–Milwaukee opened its $53 million School of Freshwater Sciences, and in September the city became one of four new Regional Innovation Clusters established by the federal Small Business Administration to further develop new water technologies.

Shambarger sees the BaseTern as a cost-effective and replicable solution to urban flooding in any city where basements are common. “Is this the thing? Not by a long shot,” he says. “It’s a thing. It’s one tool in the tool kit we have for trying to manage stormwater in a more sustainable way.”

Timothy A. Schuler, the editor of NOW, is at timothyaschuler@gmail.com and on Twitter, @Timothy_Schuler.

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