Pint-Sized Parks Make Safer Streets and Cleaner Rivers

The Greenstreet at 110th and Amsterdam helps keep sewage out of city rivers and features a beefed-up, traffic-calming "blockbuster."

It rained yesterday, sending stormwater streaming down New York City streets and through sewer grates. The runoff mixed with wastewater in the system and overloaded treatment facilities, causing raw sewage to spill into the city’s waterways.

Sound like an ecological disaster? It can be triggered by as little as one tenth of an inch of rainfall in one hour. Called Combined Sewer Overflow (CSO), this toxic broth also contains chemicals leached from roofs and pavement. 27 billion gallons of CSO pour into city rivers and bays every year. Until recently, there was no concerted effort to prevent it.

One of the more unsung PlaNYC initiatives aims to drastically reduce CSO, in part by managing streets more wisely. Certain traffic calming measures, it turns out, can not only make streets more ped-friendly, but also help make the city’s rivers clean enough to swim in. To accomplish this, PlaNYC calls for retooling the Parks Department’s Greenstreets program, and we are starting to see the results.

At their best, Greenstreets — the pint-sized green spaces that Parks began planting in 1996 — have served as modest traffic-calming measures, displacing asphalt with patches of greenery that send cues to slow down. The new breed goes a few steps further: They combine advanced stormwater capture techniques with more overt traffic-calming devices, like neckdowns and bulb-outs.

You can find one of the first new Greenstreets at 110th and Amsterdam in Morningside Heights. It occupies a long, wedge-shaped sidewalk extension along the southwest side of Amsterdam, widening from mid-block to occupy two traffic lanes at the intersection. This feature is called a "blockbuster," and it prevents southbound traffic from driving the wrong way down Amsterdam, which runs one-way below 110th.

Stormwater is captured by a drainage pipe on the north side of the blockbuster (right), where it is channeled under the sidewalk and into the soil of the planting bed. Any excess is stored in a chamber beneath the soil, where the plants can soak it up in times of drought.

"That’s less water that our sewer system has to deal with," says Bram Gunther, the head of Forestry and Horticulture at Parks, who has been instrumental in implementing the new Greenstreets. He points out that by storing the water for later use, this Greenstreet won’t require Parks to send a water truck out on the street to keep it maintained. "Anytime you get to recycle water, that’s a good thing."

Gunther’s team began work on stormwater-capturing Greenstreets about two years ago. When PlaNYC was announced in 2007, he says, "it dovetailed perfectly, and the scope of [the project] increased by an order of magnitude."

Because stormwater capture requires construction that goes deeper than previous Greenstreets — and because the new Greenstreets entail more sidewalk extensions — a host of city agencies have to cooperate, including Parks, DOT, Environmental Protection, and Design and Construction. The PlaNYC mandate minimized red tape and allowed construction to ramp up.

The site at 110th and Amsterdam before the Greenstreet was built.

"It’s kind of exceptional," says Dr. Paul Mankiewicz of the Gaia Institute, an expert on stormwater capture who has consulted for the city. "You’ve got real cooperation between the agencies."

This spring Mankiewicz will lead an evaluation of the first batch of "greener" Greenstreets, measuring just how well they capture runoff. There are now between 10 and 20 of them to look at, with 30 to 50 more in development.

Mankiewicz says Greenstreets will play a big part in the city’s overall stormwater capture strategy, which also includes building green roofs, laying down permeable pavement, and planting a million trees. By his estimates, Greenstreets could eventually handle "somewhere greater than 10 percent of all excess stormwater, maybe much more."

Chicago Green Alley Brochure
In addition to Greenstreets, new surfaces can absorb stormwater and mitigate the urban heat island effect, which reduces condensation and runoff (image from Chicago DOT’s Green Alley Handbook).

The program has been lauded by environmental advocates. Carter Craft, director of programs and policy at the Waterfront Alliance, thinks the early returns are promising.

"Tying stormwater capture with traffic-calming makes absolute sense," he said, "because you won’t get another chance [to tear up the street] for five to ten years."

Craft has been helping the Office of Long-Term Planning and Sustainability determine sites that can be used to intercept runoff. While pleased with the progress on stormwater capture to date, he’s reserving final judgment. "It’s a success story if all the public agencies can maintain their focus and keep it going. Many of us are optimistic, but it’s too early in the implementation phase to judge."

As we were reminded this morning, not every neighborhood welcomes a new Greenstreet. But the City Council took a big step toward advancing the concept two weeks ago, when it passed a resolution to create a citywide stormwater management plan based on the outline in PlaNYC. Mayor Bloomberg is expected to sign the bill into law.

New York still has a lot of ground to cover to catch cities like Seattle, which captures 90 percent of its excess stormwater. Although we get hit by bigger storms, explains Mankiewicz, we also enjoy a geological advantage. "There are huge amounts of sand and gravel under the soil," he said, perfect for absorbing stormwater. "We need to make a connection between the surface and the deeper soil beneath."

Daniel Simon contributed material for this story.

Photos: Ben Fried

  • rlb

    Greenstreets is admirable for their environmental efforts. Calling them pint-sized parks is inaccurate, however, as I can think of no greenstreets that allow for their use by human beings. On the contrary, they frequently occupy valuable sidewalk space and leave very little for the pedestrian. The most frustrating example of this which comes to mind is the large greenstreet on Houston between first and A. What would have been an ideal place for a plaza like setting is instead an oppressively fenced in mini jungle which leaves behind narrow isolating sidewalks on either side of it. It may be environmentally sound, but it mars the pedestrian experience.
    Let’s see if we can do both, Greenstreets.

  • Does a mere 0.1 inches of rain really trigger CSO (Combined Sewer Overflow)? And isn’t it a question of *rate* as well as *volume*, thus making this statement problematic unless a time period is also specified?

  • ps

    greenstreets should go big and convert three parking spaces on every block in the city into pocket parks. and while we are on the topic, PlaNYC’s 1 million new trees initiative is great, but since most of them are being planted on sidewalks, that is thousands of acres of precious sidewalk space lost. why not plant trees in parking spaces instead?

  • Ben Fried

    “Does a mere 0.1 inches of rain really trigger CSO (Combined Sewer Overflow)? And isn’t it a question of *rate* as well as *volume*, thus making this statement problematic unless a time period is also specified?”

    Some of the literature I came across said that as little as 1/20th of an inch can trigger it. But I didn’t take rate into account, so you’re right, perhaps “every time” should be amended.

  • Jonathan

    ps, excellent idea!

  • For what it’s worth, here’s Portland’s web page on Green Streets. It includes engineering drawings, site evaluations, photos, and everything else you’d ever want to know about Green Streets in Portland.


  • ps

    thanks Jonathan. it’s important not to miss the forest for the combined sewer overflow (CSO)

  • The numbers i’ve seen are a rate of “as little as 1/10 inch per HOUR.” Obviously this varies according to what sewershed you are in. NYC has 14 different sewersheds-each feeding to one of the 14 sewage treatment plants in the 5 boros. Places like the north shore of Staten Island it may take a lot more to trigger an overflow becasue the landcover in that area may be 50-70% vegetation. In places like along the Bronx River it could be a smaller amount because so much of the surrounding area is a) rooftops and b) streets and sidewalks. A LOT of Manhattan actually sends its sewage over to Brooklyn, pumping it under the East River to the Newtown Creek facility…. Check out this guide at the Lower East Side Ecology Center:

    Also The Riverkeeper report at has more information too…

  • Mitch

    In my part of the world, rain gardens are pretty hot; they are green spaces that are specifically engineered to channel runoff into the soil. There is one example not far from my house where several gardens were put into the strip between the sidewalk and the street. I haven’t gone out during a rainstorm to verify that the gardens divert rain from the storm sewers, but as far as I know, they do reduce runoff.

  • ln

    There’s training available from the parks dept that will make you legally able to garden in greenstreets. However, theres no help or support to actually carry it out, no way to have compost or woodchips delivered, no offers of plants, tools or seeds, and no easy way to make these greenstreets more green or facilitate a way to make these greenstreets ‘belong’ to community caretakers.

    Instead the parks dept hires outside contractors (over $2000 a tree!) to dump in soon to be rat infested ivy, toss in baby trees into some terrible dirt with no thoughts of follow up or maintainance. If this was done in partnership with communities, teaching them gardening and giving the materials to maintain the greenstreets, they could be success. Its next to impossible for a community group to green their neighborhood without corporate sponsorship, which isnt available to all ‘hoods.

  • This is a fantastic idea. Combining high-albedo pavement with these drainage programs would be perfect for tropical and sub-tropical cities.

  • dbs

    Great piece.

    Stormwater capture has multiple benefits that deserve greater exploration. One additional benefit of improving stormwater capture is reduced flooding risk, not only on streets and in homes, but on our subterrain transportation network.

    As the August 8, 2007 Storm Report ( points out, the following green technologies need to be explored to prevent future flooding:
    • Blue roofs/green roofs to capture and/or detain runoff from buildings adjacent to the identified sites
    • Tree pits designed to retain water for absorption by trees
    • Greening and use of porous pavement in area parking lots
    • Possible enhancement of nearby green spaces to retain more storm water

  • City Council’s passage of the resolution to create a citywide sustainable stormwater plan marks a significant win for Storm Water Infrastructure Matters (SWIM), a coalition of more than 50 organizations dedicated to ensuring swimmable waters around New York City through natural, sustainable storm water management practices in our neighborhoods.

    To learn more about SWIM or to get involved, check out

    Great piece!

  • Tommy

    The story does take rate of rainfall into account. Second paragraph, second sentence: ” It can be triggered by as little as one tenth of an inch of rainfall IN ONE HOUR.” (Caps are mine, obviously.)

  • That’s a great idea. It hadn’t occurred to me to actually build these pocket parks or greenstreets with the storm water runoff considerations built in.

  • [NYC stands to get a piece of this R&D pie if it passes through full House and Senate…]
    Posted Tue, 03/04/2008

    Thanks to leadership by Congressman David Wu, a new bill has passed through the House Science and Technology Committee to expand funding for green streets research throughout Portland and the rest of the country.

    H.R. 5161, also known as The Green Transportation Infrastructure Research and Technology Transfer Act, will authorize research and educational programs on green infrastructure, such as bioswales, curb extensions, and sidewalk planters, which catch and filter runoff, naturally removing pollutants and recharging groundwater.

    This bill will fund research and educational programs at select University Transportation Centers, such as the Oregon Transportation Research and Education Consortium (OTREC), a partnership between Portland State University, Oregon State University, University of Oregon, and the Oregon Institute of Technology.

    Portland has won national praise for its innovative green streets designs that minimize the harmful effects of stormwater runoff and combined sewer overflows. Currently there are over 600 green streets facilities throughout the city.

    Congressman David Wu, chair of the Subcommittee on Technology and Innovation for the House Science Committee, met with Sam in April to tour several of Portland’s innovative green streets. Sam was invited by the Congressman to testify at a subcommittee hearing last May to share Portland’s success with sustainable stormwater practices.



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