May 13, 2013 — Residents on the south side of Chattanooga, Tenn., celebrated the new year with a new playground meant for adults. Main Terrain, a park situated on an abandoned railroad lot, features a running track, cross-training equipment and interactive sculptures.

The park is a welcome patch of green space in a neighborhood transitioning from light industrial to a mixed-use community of retail, residences and industry, says Mike Fowler, a principal of Ross/Fowler Architecture and Landscape Architecture, the firm that consulted with the city on designing the space. “It is an intensely paved environment, and Main Terrain is a green respite.”

The park offers respite of a less visible sort to Chattanooga’s stormwater management system. Beneath the lush turf is a mix of topsoil, sand and gravel, specially designed to filter stormwater runoff. After a heavy rain, two retention ponds in the park hang onto runoff for eight to 10 hours; a system of drain tiles moves the rainwater to a nearby underground storage tank, where it ultimately serves as irrigation water for the park.

Stormwater management is one of those vital necessities of the built environment that remain invisible unless it fails.

Main Terrain is one of a growing number of urban developments that mix stormwater management with recreational facilities. A rail yard in Milwaukee has been redeveloped as a mixed-use industrial park with picnic areas, athletic fields and a stormwater system that filters pollutants out of runoff. In Neu Ulm, Germany, a public plaza designed by landscape architecture firm Atelier Dreiseitl uses a filtration device and public fountains to sequester urban runoff from the main stormwater system. And the Qunli Stormwater Park, a project in Haerbin City, China, won last year’s Award of Excellence from the American Society of Landscape Architects. One of the driving forces among all of these experiments is a radical rethinking of how we manage urban runoff.

Sea Change for Stormwater

For many of us, our interest in stormwater management began and ended around age 10, when we would put on swimsuits, run out into the rain and race pinecones down the street until they disappeared into the maw of a cast-iron sewer drain. But the fact is that stormwater management is one of those vital necessities of the built environment that remain invisible unless it fails, causing damaging floods to low-lying neighborhoods.

For most U.S. cities, those cast-iron openings along the curb represented the primary method of stormwater management when they were constructed: Rain fell on the roofs and pavement of the city, ran downhill to the nearest gutter, coursed into the underground sewer system, and dumped into the nearest body of water.

The idea was to “get it the hell away from here as fast as possible,” says Thomas Ballestero, director of the University of New Hampshire Stormwater Center in Durham. That strategy worked pretty well for the “here” — by preventing urban floods — but not so well for the “there.” Every storm dumped litter and pollutants into the watershed, and the volume of water concentrated from even small rainstorms caused erosion downstream. Worse, many municipal systems combined stormwater and human waste in one sewer system. Rainstorms would overcome those systems and wash raw sewage into the watershed.

The Clean Water Act was designed to correct these shortcomings. In its latest incarnation, the federal legislation requires municipalities and new developments to incorporate more nuanced forms of managing stormwater.

These new strategies include a wide range of possibilities, according to Reid Christianson, a water resources engineer for the Center for Watershed Protection, a Maryland-based nonprofit organization that helps municipalities design and site stormwater treatment facilities. Some strategies, such as rain barrel and rain garden programs, prevent runoff in the first place. Others, such as the retention ponds at Main Terrain, use green space to hold runoff long enough to allow the soil to absorb the pollutants it contains.

In dense urban areas, green space can be hard to come by — hence the drive behind mixed-use projects like Main Terrain. Originally, Chattanooga’s department of public works had proposed the entire Main Terrain site be used as a holding pond for stormwater runoff. “We heard a strong voice from the community in favor of green space that incorporates fitness and art,” Fowler says. “A simple retention basin would have consumed the entire site, and people wouldn’t have been able to use it for recreation at all.”

Partial Solution

Just how effective are projects like Main Terrain at keeping pollutants out of the watershed? “The most accurate answer is that it hasn’t been studied enough,” says Jonathan Scott, communications director for the nonprofit organization Clean Water Action. “These projects are coming online rapidly, and they barely have enough funding for the project itself, much less the science.”