Cities Use Design to Tackle Stormwater Runoff
In Northeast Philadelphia, along busy Kensington Avenue, sits a small park. What used to be flat ground is now sloping terrain that contains a low-lying area intended to gather and funnel storm water.
At the park’s southern end is a depression lined with well-arranged plants—a new landscape carefully engineered to change how water flows through the area.
This is Womrath Park, one of a handful of “green infrastructure” projects Philadelphia has begun—with many more to come—aimed at tackling a widespread urban environment problem. Ten trillion gallons of rainwater per year flow over rooftops and roads around the U.S., picking up contaminants that include bacteria, oil and grease, metals, pesticides, and many others. When a rainstorm is big enough, the runoff causes overflows from outdated sewer systems that combine both raw sewage and stormwater in a single pipe. This tide of pollutants ends up in surrounding waterways that serve as drinking water sources and recreational areas.
“Stormwater runoff is one of the largest water pollution issues facing the U.S. today,” says Larry Levine, a senior attorney in the Natural Resource Defense Council’s water program.
Now, however, numerous cities around the country—including Philadelphia, New York, Washington, Portland, and Seattle—have embarked on innovative stormwater runoff fixes that rely not so much on the old “gray infrastructure” of huge, piped systems and sewage treatment plants, but rather on new green infrastructure techniques to collect and treat stormwater at the street level.
Green infrastructure mimics how nature handles rainwater through the use of porous surfaces, rather than impervious surfaces like roadways. These techniques are decentralized. Instead of one facility or large underground tank to store water when a big storm hits, the idea is to eliminate the need for such storage through the use of green rooftops, roadside plantings, carefully landscaped parks, rain gardens, rain barrels, and other swatches of nature dropped down inside the landscape of modern cities.
The plants and soils collect water during a storm, preventing it from either running into sewer systems at all, or at least slowing it down to prevent overflows. Green infrastructure can also help clean some pollution from the water and can even be used to gather water for re-use.
“The green infrastructure approach says, ‘Let’s get the water out of those sewer systems in the first place before it has a chance to convey all that pollution into our waterways,’” says Levine. “And the way to do that is to put back into our built environment features that mimic the way nature handles rainwater in the natural water cycle. It doesn’t necessarily mean replacing a paved street with a park, but it means putting enough green space into the design of your roadway that you can capture runoff from that paved space.”
These types of green projects carry numerous ancillary benefits, Levine notes, from improving surrounding property values, to reducing in the urban heat island effect, to lowering asthma rates.
Green stormwater infrastructure means thousands of individual projects in big cities like New York or Philadelphia. The price tag—Philadelphia is spending around $3 billion, and the country as a whole needs something like $63 billion just in fixes to stormwater-related sewage overflows—is high. But advocates say going green is eventually a far more cost-effective method than constructing large wastewater treatment plants. Philadelphia and other cities are using city and federal funding to finance these green infrastructure projects.
Valessa Souter-Kline, a representative of the Philadelphia Water Department, says the decentralized concept of green infrastructure development represents a major challenge. “No one is saying ‘no’ to the idea,” says Souter-Kline, standing at the bottom of the rain garden in Womrath Park. “The issue is the scale. You just need so much of this.” On any given project, she says, the Philadelphia Water Department will likely have to work with the streets department, parks and recreation, utility companies, and other stakeholders.
Levine and others say the new methods of stormwater runoff control deal with a key flaw in the landmark 1972 Clean Water Act—“nonpoint source” pollution.