Sustainable Water Management in City Architecture

Author: David Bergman, Yale Class of ‘78
Location: New York, NY

The Action

NYC has an infrastructure problem but it’s not likely to make headlines. Chicago has it, too. So do Philadelphia and Atlanta as well as thousands of smaller cities. It goes by the decidedly unsexy and somewhat gross title of a Combined Sewer System or CSS.

Other cities have separate pipes for sewage and for storm water. In a CSS, they both go down one set of pipes. So when it rains, the pipes and treatment plants can’t handle the combined flow of sewage and storm water, and raw sewage ends up getting dumped into the nearest waterway.

The issue is exacerbated by the fact that stormwater in cities often has no place to go because so much surface area is covered in impermeable streets, sidewalks, parking lots and buildings. It’d cost way too much to rip up every street and rebuild the CSS system. So what’s a city – or its residents – to do?

Taking Action for Environmental Impact

Fortunately, there are a few ways to at least partially address the problem. And they tend to have multiple benefits.

One embraces trees. Their multiple benefits include global warming mitigation by absorbing CO2 and diminishing of the urban heat island effect (in which cities tend to be several degree armer than surrounding areas (Urban Heat Islands). Plus they’re just, well, nice to have in less green urban areas. But they also help with stormwater and runoff issues both by absorbing water themselves and being planted in soil, taking the place of paved areas so the water can be absorbed.

Among other plans to plant massive numbers of trees, NYC has its Million Trees program, which reached its goal a couple of years ago. Scotland has a 22 million tree plan. The Nature Conservancy has its Plant a Billion Trees campaign.

Yet another way to address stormwater runoff is with green roofs. As with trees, green roofs have multiple benefits such as relieving the urban heat island. But the one that’s relevant here is their ability to act like sponges. Both the plants and the soil absorb the rain and release it slowly so as to delay the runoff and spread out the flow in the pipes. As an amenity (another benefit), you can have an “extensive” roof which is covered by a shallow layer of soil for growing sedums and grasses, or, if your roof is strong enough, an ”intensive” version with deeper soil that allows planting of gardens, bushes and even, sometimes, trees.

(In the 100+ year old building I live in, the old wood joists weren’t strong enough to support either type. We looked into building a deck floating above the roof, but the cost for our small former tenement building was prohibitive. An alternative called “sistering” the joists – bolting new joists alongside the existing ones – might have been possible, but we’ve had had to rip up the roof first to get to the joists.)

NYC, by the way, also requires holding tanks, usually underground, for new buildings. A smaller scale version, more suitable for homes and more DIY, is a rainwater barrel connected to the roof gutters. The water is typically used for irrigation. Of course, there are few homes in NYC that can take that approach. But even something as low-tech as that can help alleviate the stormwater runoff problem. And for those of you where water supply is an issue, it makes more sense to use that water than using good potable water for your plants. (Or for that matter, flushing toilets, but that’s another story.)

How to Get Involved

As an individual or small group, In NYC, you can request a street tree in front of your building. Or you can help maintain them. You can join a community garden.

Another approach replaces impermeable or impervious surfaces along streets and sidewalks with planted bioswales. Those are usually constructed by local governments, but on your own property, you can replace paved areas such as driveways or urban back yards with porous surfaces such as pervious paving. You can even plant an “edible estate”: a front yard (as unusual as they may be in dense cities) with fruits and vegetables.