Like many older cities, Philadelphia relies on a combined sewer system to handle much of its stormwater. The combined sewer system conveys wastewater and rainwater from roof drains and street inlets to sewer treatment plants that filter and purify the water before discharging it to rivers and streams. In dry weather, the system works. However, small amounts of rain can overwhelm the system, allowing rainwater laced with road oil and litter, in addition to bathroom and kitchen wastewater, to gush, untreated, directly into Philadelphia 's streams and rivers, causing bacteria levels to skyrocket.
In 2009, Philadelphia unveiled its 3,369-page plan to transform the city's approach to drainage during the next 20 years. The plan relies on relatively low-tech green infrastructure measures, such as rain gardens, green roofs, thousands of new trees, and porous paving, to manage the billions of gallons of rainwater that overwhelm the city sewer system when it rains.
According to an article in The Philadelphia Inquirer , Jon Capacasa, regional director of the U.S. Environmental Protection Agency (EPA), said that the city's stormwater management plan presents a bold, innovative approach to reducing drainage requirements and improving water quality. He called it “the most significant use of green infrastructure I've seen in the country; the largest scale I've seen." The EPA has the final say on whether the city's plan passes muster.
Philadelphia's plan is a radical departure from the more typical approach to stormwater, which entails expanding sewage plants and adding highly engineered tunnels under streets. Applying such a typical approach in Philadelphia would have required reconfiguring 1,600 miles of pipes and digging up yards, walkways, and streets throughout the city at a cost of billions of dollars.
"Instead of figuring out how to manage this pollution, maybe we should be looking at how to prevent it in the first place," Howard Neukrug, director of the Office of Watersheds in the city's Water Department, told The Philadelphia Inquirer . "Let's break down some of the barriers against nature and deal with rainwater where it lands."
South Philadelphia's Herron Park, designed by Langan Engineering and Environmental Services in 2008, incorporated many of the sustainable urban drainage measures cited in the city's proposed stormwater plan. Langan provided landscape architecture, civil engineering, surveying, and permitting services for restoration of the park for Philadelphia's Department of Public Properties, which renovated the park on behalf of the city's recreation department.
The park features a state-of-the-art sprayground to replace a former swimming pool. A series of age-specific playground equipment, some of which includes computer-generated interactive games, are clustered throughout the park to provide additional play options. Play areas, game tables, and seating and dining areas are defined and shaded by plantings throughout the park. Concrete, gravel, rubberized safety surface, and porous asphalt paving define various use areas, reinforcing the park design while directing and infiltrating stormwater flows.
It is critical that sustainable stormwater elements be an integral part of the site design, not a tacked-on afterthought. To integrate stormwater elements in site design requires thinking about how stormwater can be used as a resource to irrigate landscapes and recharge the water table rather than hustling stormwater down the nearest drain.
At Herron Park, both the site design and material selection reinforce the public and play spaces in the park while serving to control stormwater. Examples include the following:
- A push-button activator for the sprayground elements ensures that water is only on when people are present. This simple activator replaces a typical fountain timer and requires no additional maintenance.
- A porous asphalt basketball court surface allows water to infiltrate to the gravel bed below.
- A springy playground safety surface made from recycled tires meets all playground safety and public accessibility criteria while allowing water to infiltrate through the surface into gravel beds and the water table below the playground.
- More than 80 native and adapted trees, and hundreds of shrubs and grasses, shade the site, reduce reflected glare, and define use areas while breaking the impact of raindrops, absorbing water through their roots, and releasing water vapor back into the atmosphere through their leaves.
- A rain garden uses water-tolerant native and adapted plants with many seasons of interest, which serves to buffer the park from the street and shade play and gathering areas while creating a low point to store initial rainfall and allow particulates to fall out of the stormwater before any overflow is allowed to enter the drainage system.
- A vegetated swale serves as a passive lawn play area while slowing down the flow of stormwater toward drains so it can infiltrate into the ground or be absorbed by plants before stormwater enters the city's drainage system.
- An infiltration trench replaces a traditional solid drain pipe. The trench uses a perforated pipe surrounded by gravel to allow stormwater to infiltrate the soils beneath the porous play surface while ensuring that the playground drains properly.
- Catch-basin traps were constructed in each drainage inlet to allow oil and floatable materials to rise to the top of an inlet, thereby preventing these pollutants from entering the sewer system.
The innovative stormwater design plan for Herron Park garnered the first Green Project Review by the Philadelphia Water Department. Being eligible for this expedited review and permitting process helped to advance the construction schedule, saving the client time and money. The project also received a 2009 Stormwater Best Management Practices Award granted through Villanova University, Temple University, and the Philadelphia Water Department.
Jayne Spector, RLA, LEED AP, and Thomas Spokas, P.E., LEED AP , are with Langan Engineering and Environmental Services. Contact Spector at email@example.com.