Philly’s long-term flooding plan could involve relocating parts of neighborhoods

Rising sea levels are a serious threat to low-lying areas of the city.

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Mark Henninger / Imagic Digital
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As a city located between two rivers, rising sea levels are a serious threat to Philadelphia. Luckily, officials are already working on a plan.

“We’re going to have to start making substantial investments, and they may not be all that fun,” said Marc Cammarata, the Philly Water Department’s deputy commissioner of planning and environmental services. “Relocation, buyouts. People need to start expecting that.”

No reason to start packing your bags just yet. Officials are just starting to mull the idea as a long-term solution.

“We’re thinking our sea level will rise by two meters by the start of 2100,” Cammarata said. “This is a burden on our system like no other.”

This winter is Philadelphia’s 19th wettest in almost 150 years, per National Weather Service spokesperson Brian Haines. Since the start of 2020, the NWS has issued nine flood warnings in the region.

When it rains, water pools all over Philly — in some areas worse than others. Along riverside roadways like Kelly Drive, for example, and Columbus Boulevard, or in low-lying neighborhoods like East Germantown and the former marshlands that now form Eastwick.

The Water Department conducted a study in Germantown to figure out how much it would cost to replace existing water pipes with underground tunnels and tanks, which would increase their capacity to hold water and hopefully alleviate flooding in the area.

“We found it would cost $500 to $800 million to mitigate flooding for 2,000 or so properties,” Cammarata said. Even that expense wouldn’t be foolproof. “That may work for a 10-year storm, but if a 50-year storm hits, you’re still getting flooding.”

Hence, the relocation idea. Should it become really necessary, Cammarata said Philly is looking to Milwaukee for inspiration. The Midwestern city flooded so badly in 1993 that 50 people died and there were $15 billion in damages.

Some Milwaukee neighborhoods were so damaged as to be irreparable, so Wisconsin created a buyout program. From 2002 to 2018, the state paid 140 property owners to move elsewhere, and also created jobs by paying for some new construction. The original homes were converted back into wetlands that could better drain water from the region.

Similar buyout programs have been conducted in New Jersey and Delaware.

“They used it as a pretty good tool,” Cammarata said. “It’s something that the community at large is thinking about, because it may be a heck of a lot more cost effective than trying to mitigate flooding.”

Warning from a Founding Father

Climate change or not, Ben Franklin warned us this would happen.

Franklin wrote in 1789 that by “covering a ground plot with buildings and pavements, which carry off most of the rain and prevent its soaking into the Earth and renewing and purifying the springs … the water of wells must gradually grow worse, and in time be unfit for use.”

Sure enough, the city is now covered with “buildings and pavement.” Instead of grass or small creeks, we’re mostly covered in concrete, which can’t absorb water very well. Meanwhile, our sewer system is hundreds of years old. As our population grows, the capacity of the pipes wanes.

The city’s in the middle of a 25-year plan to create more stormwater infrastructure that could absorb rainfall.

There’s the option to replace Philly’s older pipes with tunnels and tanks to increase underground water storage. Although costly, it’s on the table.

Next, PWD wants to increase capacity at Philly’s wastewater treatment plants. If those can hold more water at a time, Cammarata said, then PWD can pump more excess water away from neighborhoods — nipping a potential flood in the bud.

They’re also debating requiring private developers to incorporate more porous materials into their projects, creating more surface area for water to drain.

And then there’s relocation, which Cammarata understands would be a controversial undertaking.

“Relocation, it’s a scary word,” he said. “In a city where people already have affordable housing crises, it’s not fun to talk about. But neither is having someone die in an extreme weather event.”

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