October 8, 2009

Construction Corner | Korky Koroluk

Philly’s bold stormwater management plan leads the way

As our climate slowly changes and extreme weather events become more common, cities will have to change the ways in which they manage stormwater.

It’s not common yet, but cities will have to begin specifying larger storm sewers, making greater use of stormwater management ponds, promote greater use of green roofs and rain gardens, and use pervious pavements to allow more stormwater to seep into the ground.

Most cities still have combined sewers in their older areas — usually the downtown core and inner neighbourhoods, and there are thoughts about separating them to prevent overflows of raw sewage into nearby rivers during and after heavy rains. But such work is costly enough to scare many off.

Now Philadelphia, a city not much larger than Greater Toronto, has hatched a stormwater management plan that combines many methods.

It’s a US$1.6 bllion plan to transform the city over the next 20 years by managing and using storm water instead of just sending it streaming into sewers and rivers as fast as possible.

State regulators and environmental experts are still evaluating the scheme — no small task since it is a 3,369-page document.

The plan reimagines the city as an oasis of rain gardens, green roofs, permeable pavements, thousands of additional trees, and more. The idea is to turn the city into a giant sponge to absorb as much rainwater as possible and delay the rest in its journey to the nearby Delaware and Schuykill rivers.

When city officials began working on the plan 12 years ago, separating sewers was quickly ruled out. It would have involved reconfiguring 1,600 miles of pipe and digging up every front yard and front walk in 60 per cent of the city, a prospect that would have been so expensive nobody looked seriously at it.

Massive enlargements of the city’s three sewage plants, or building immense underground storage tunnels was also ruled out, as both inefficient and too expensive. So all that was left was a combination of everything else.

The new plan announced last month would “peel back” a lot of the city’s concrete and asphalt and replace them with plants — rain gardens, green roofs, landscaped swales in parking lots, heavily planted boulevards, and small wetlands.

As impervious paving comes due for replacement it will be placed with pervious paving to let rainwater flow through without leaving puddles. That will apply to the running surfaces of streets, sidewalks, parking lots, even neighbourhood basketball courts.

New and novel uses will be sought for green roofs. A recent one is on the parking garage at the Philadelphia Museum of Art. It supports five feet of soil, and is home to a sculpture garden.

Residents will be encouraged to install downspouts and rainbarrels to collect rainwater for watering flower beds.

None of the ideas are new. What’s new is the scale proposed, and that has large cities across North America watching closely.

The city has been shopping the plan around to neighbourhood groups and, while they met with some opposition, they were astounded to find a high level of enthusiasm for it. There are long-term savings to be had, so residents — so far, at least — seem willing to pay the additional $8 per month per household to pay for it.

Ken Kirk, executive director of the National Association of Clean Water Agencies, said the plan is “very compelling.”

“It may take a little longer, but at the end of the day, they will be using a lot less energy, they will be using the water resources more efficiently, they will be capturing and recharging groundwater under the city, (and) they’ll have less pollution of the rivers.”

From a lot of different perspectives, he said, “this is the way we need to go.”

Korky Koroluk is an Ottawa-based freelance writer. Send comments to editor@dailycommercialnews.com

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