When it rains, it’s porous: New ‘green’ streets to stem Philly’s flooding woes

The Philadelphia Water Department has launched the Green City, Clean Waters program to cut down on asphalt, plant trees, build parks, and change the way they handle stormwater run-off.

For most people, the sound of an approaching thunderstorm might mean relief from the summer heat, water for the garden or a reminder to roll up the car windows. But for Kate Houstoun and her South Philadelphia neighbors, it has an entirely different meaning.

“We get a huge gush of storm water that comes in the front drain in everyone’s basement. And it can leave anywhere between 3 inches of combined sewer or maybe just rush in and rush out,” Houston says.

While it happens quickly, the aftermath is a challenge, especially for her senior citizen neighbors.

“It’s really tough for them to get into their basement and sop up the mess afterwards. I mean, I don’t like it, but it certainly breaks my heart to see older folks struggling with that, Houston says.

The Philadelphia Water Department thinks it has an answer. It recently unveiled its first porous green street on Percy Street in South Philadelphia. The pavement looks like any other block, except when it rains.

“Rather than it running down the gutter, this is like having a big black lawn out in the street,” says Peter Reilly, a civil engineer and one of the green street designers. “The water just percolates through the surface and goes right into the soil.”

On the regular asphalt, the water lands and runs off the surface, collects in the gutters and then gets deeper and deeper in the gutters until it runs down into the inlets.

Reilly explains that with the porous surface, nothing runs down the gutters.

“It’s designed to accept the full rainfall and take it right off the surface. So it will look wet, but with no standing water at all,” Reilly says.

Percy Street is first step

Tiny Percy Street, barely 6 feet wide, is part of a much larger plan drafted by the water department, called “Green City, Clean Waters,” says Deputy Mayor Rina Cutler.

“We have agreed to green one-third of the city in the next 25 years. Which, for a city our size, has never happened before,” Cutler says. “We decided we would try to do this with green infrastructure instead of gray infrastructure, which are sewer pipes under the ground that nobody sees.”

Green infrastructure can include green roofs on bus stops, rows of trees connected by underground water-catching trenches, rain barrels and other devices.

“There are a lot of tools in the toolbox for how we are going to get to that one-third green city. And porous streets is one component of that overall big picture,” she said.

With nearly 20,000 acres of pavement in Philadelphia, it’s a very big picture. Cutler says the benefits will be big, too.

“We will actually reduce the amount of stormwater runoff that ends up in the sewer system, decreasing flooding and really greening the city in a way that has not really been thought about before,” Cutler says.

She envisions more trees, more spaces for parks and less asphalt, which will make things cooler.

“I think there are a lot of economic and quality-of-life benefits that hit every family in Philadelphia at a level they will understand when they see it,” Cutler says.

When taxpayers hear about new city programs, they see dollar signs. However, Cutler has good news: The water department isn’t going to spend more; it’s just going to spend smarter.  She says porous pavement costs about the same as traditional asphalt, as long as you were already planning to rip up the old road.

Cost-effective investment

“Instead of spending essentially the same $2 billion to build a sewer system underneath the streets, we’re going to take that $2 billion and really invest it in green infrastructure,” she says.

Back on Percy Street, Reilly notes another way they’re saving money.

“We’re implementing this along with any water and sewer work that will be done. So wherever we have a job out, we’ll be looking to add a green component to manage stormwater on site,” Reilly says. “This street was getting the sewer fully replaced and we took this as a test location.”

While Percy Street is just one block among thousands, each street that removes stormwater from the system will be an improvement, Reilly says.

“Each little bit helps not only recharge the groundwater, which helps the plants alongside it, but it does take it out of our system, which is really our end goal,” he says.

Of course, on an individual level, it can make a huge difference for residents such as Kate Houstoun and her South Philadelphia neighbors.

“Please let my block be chosen!” she says.

Since such a project has never been undertaken in a city as large as Philadelphia, the EPA and others are watching, said Cutler, who said she feels the weight of that scrutiny.

“I’m sure they view us very much as a pilot program of a brand new way of doing stormwater management in this country. And so we feel like there are a lot of eyes on us and we’re very clear that failure is not an option,” she said.

Want a digest of WHYY’s programs, events & stories? Sign up for our weekly newsletter.

It will take 126,000 members this year for great news and programs to thrive. Help us get to 100% of the goal.