Keeping rain out of the drain

Shoemaker Green, three acres of green space on Penn’s campus, is more than just a nice place to have lunch. Formerly home to tennis courts, the space was revamped in 2012 and now includes garden beds with native plantings, benches, and shaded walkways.

But all that conceals what is perhaps the most unusual facet of the Green—an underground cistern capable of holding 20,000 gallons of water.

The site represents one example of how the University is increasingly incorporating design features into campus buildings and landscapes to manage stormwater. From green roofs and rain gardens to buried storage tanks and water-reuse systems, Penn is playing a leading role in the city’s efforts to keep runoff from overwhelming the sewer system. All significant new building projects at Penn are designed to meet the Philadelphia Water Department goal of managing the first inch and a half of rain that falls on impervious surfaces. 

“That means that the first inch and a half of water that falls from the sky literally can’t go down the drain as runoff,” says Bob Lundgren, Penn’s landscape architect. “That regulation dictates how we do a lot of projects here. We do green roofs, we do cisterns, we do permeable paving, so the rain can soak into Mother Earth or sit somewhere and then drain slowly or be reused.”

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The rationale behind all of this attention on stormwater management is tied intimately with Philadelphia’s older infrastructure. In many parts of the city, the pipes that carry stormwater are connected to those that carry sewage. When a rainstorm sends a deluge into the storm drains, the overflow from these pipes goes directly into waterways, such as the Schuylkill and Delaware rivers, instead of routing to wastewater-treatment plants. These so-called “combined-sewer overflow” (CSO) events degrade the environment, make the rivers unsafe for recreation, and increase the cost of treating the water. 

Lundgren notes that managing runoff has been part of campus design strategy since long before the city required it. The late Penn landscape architect Ian McHarg, lauded as an innovator in ecological design, incorporated such elements into campus plans half a century ago.

“When he designed Woodland Walk in the 1950s,” Lundgren says, “he disconnected the drainage system from the sewer line, used permeable paving—cobbles over gravel—and put in native species. He was one of the first to be taking that approach.”

And though Penn has been a leader in environmental design since McHarg’s tenure, Philadelphia’s 2006 Stormwater Management Regulations and 2011 launch of “Green Cities, Clean Waters” prompted a closer look at management efforts. 

The “Green Cities” plan in particular places emphasis on green infrastructure—increasing permeable surfaces—over traditional infrastructure like larger stormwater pipes and storage tanks. The 25-year initiative, which emerged under the leadership of Howard Neukrug, then-commissioner and CEO of Philadelphia Water and now a professor of practice and executive director of the Water Center at Penn, aims to reduce stormwater pollution entering city waterways by 85 percent. The plan includes provisions to encourage large property owners to take on the brunt of the responsibility in reducing CSOs.

“Residential and smaller commercial landowners can take steps to address stormwater on their properties and the government can manage runoff from roads, but we won’t solve our problems unless large property owners do their part,” says Neukrug. “When we are talking about a 50-acre or larger property in the middle of the city, economies of scale make the cost and impact of the project that much more important.”

The University has taken up the reins on this issue. A Stormwater Master Plan for Penn published in 2013 identifies areas where stormwater management is already succeeding, and pinpointed opportunities to extend this influence to new areas. 

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Penn Park represents perhaps the largest project that has conferred stormwater management benefits to campus. Constructed in 2011, the site was overhauled from a series of paved parking lots and other impervious surfaces to a 24-acre multi-use complex with turf playing fields, tennis courts, grass playing fields, picnic areas, and an orchard. The site includes a cistern with a 300,000-gallon capacity so stored rainwater can later be used for irrigation, as well as several large natural areas, including six acres of native-grass meadows that serve to collect rainwater and allow it to soak slowly into the ground. 

“One of Penn’s first projects, Penn Park, became the model for how private landowners can respond to stormwater issues and gain additional benefits at the same time,” Neukrug says. “The ecological, economic, and recreational co-benefits of green stormwater infrastructure to Penn and Philadelphia as a whole speak for themselves.”

Some green infrastructure helps on a small scale: Tree pits and trenches, for example, can intercept runoff from paths and sidewalks before it reaches a storm drain. But large-scale projects make even more of a difference. At Penn, every recent significant building project has some stormwater-management elements. The Singh Center for Nanotechnology, New College House, and Golkin and Fagin halls have green roofs that function not only to keep rain from entering the sewer system but in some cases provide green spaces to eat lunch or take a study break. 

“We have 1.4 acres of green roofs on campus,” says Lundgren. “By the time New College House West comes out, we’ll have close to two acres. That’s a pretty big deal.”

While green infrastructure confers a variety of benefits, it also comes with challenges. The spaces around porous pavers must be kept clear in order to allow rainwater to seep into the ground. Underground cisterns with pumps for irrigation require significant upkeep and technical skills to operate. 

“It can be a learning curve,” says Lundgren.

That’s part of the reason why, when Shoemaker Green was installed, provisions were made to carefully monitor its systems as well as conduct research aimed at improving it and other future stormwater-management projects. 

David Vann, a research coordinator in the Department of Earth and Environmental Science in the School of Arts and Sciences, has led efforts to study and monitor those systems for several years. Partly as a component of a course on bioremediation and partly as independent research projects, Vann has worked with students to measure how much water the system is taking in, how fast or slow it drains, and how the plants and trees planted on the Green itself contribute to water management through evapotranspiration, the process by which water is taken up by plants and then evaporates from their leaves. 

“We have found the system is doing pretty faithfully what it was designed to do: Regulate the stored water and permit it to drain slowly in the two or three days after a rain event,” says Vann. “One thing we’re looking at is whether, as the trees and plants grow, the contribution of evapotranspiration will increase.”

When Shoemaker Green was redesigned, care was taken to preserve six mature London planetrees in front of the Palestra, each estimated to be roughly 80 years old. As the largest trees at the site, their contribution to evapotranspiration is significant. Vann and colleagues have found that, in summer, evapotranspiration causes roughly 2,000 gallons per day to leave the system. As the Green’s younger bald cypress, red maple, swamp white oak, and other trees continue to mature, that figure may grow, leaving room in the cistern to capture additional rainfall.

Recently, Vann has identified places to drop down equipment that can measure the flow of water more precisely than the system’s original sensors. “With these wells, we’ll be able to measure the quantity of water in each of the catchment areas, so we can more or less understand where the water is at all times,” Vann says.

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Beyond the quantity of water, Vann is also monitoring the quality of the water entering the cisterns. Though an environmentally friendly salt substitute is used to keep walkways on campus ice-free in the winter, Vann is concerned that rock salt used on the adjacent road may be infiltrating and building up in the system. 

In the future, Vann would like to incorporate studies of the ecology and sociology of the space. “It’s not my area but there is interest in understanding how the space is being used by insects, birds, and even people,” he says. “Is it being integrated into the campus as intended, being used as a place where people can rest, relax, play soccer?”

Armed with data from such experiments, Lundgren hopes the University will continue to push the boundaries of designing with ecology and sustainability in mind. “The ecological health of a place is pretty much the highest thing on my list,” he says, “and that feeds right into stormwater management.”

Bob Lundgren is University landscape architect in Facilities and Real Estate Services.

Howard Neukrug is executive director of the Water Center at Penn and a professor of practice in the School of Arts and Sciences’ Department of Earth and Environmental Science.

David Vann is a research coordinator in the School of Arts and Sciences’ Department of Earth and Environmental Science.