An analysis of flood-related complaints in New York City received via the 311 hotline has found that the majority come from just seven distinct neighborhoods scattered across priority watersheds in the Bronx, Queens, and Staten Island. That is the conclusion of Nette Compton, director of green infrastructure, and her staff at the city’s parks department.
With funding from the American Recovery and Reinvestment “stimulus” Act, Compton has led the successful Greenstreets program over the past two years, building stormwater capture sites in 28 locations crucial to alleviating storm sewers and addressing flood problems. AN caught up with Compton to talk about her creative problem solving and get a sneak peek at what
This is a city infrastructure project, so what’s the parks department’s involvement?
Over the past 16 years our office has been in partnership with the Department of Transportation (DOT) to design and build Greenstreets. My office works to modify street geometry and transform streets into greener, safer, and more ecologically functional areas. While each site as a whole does not appear as grandiose as a waterfront or park, this approach to landscape design is a crucial piece to how we can meet the goals and challenges of 21st century cities, which will be hotter, wetter, and more crowded. Our work also informed the parks department’s designs for the future as we improved soil types, plant selection, and inlet design. All 28 sites are now complete and include monitoring equipment.
What makes a green infrastructure system truly green?
“Green infrastructure” has been defined in many ways, sometimes simply because it’s not gray infrastructure—that is, all of the purely man-made, engineered solutions used to manage the city’s water and sewer needs. At Parks, we look at this much more comprehensively, starting with a shift in thinking about water as an asset rather than a waste product. Green infrastructure can transform unused space, such as overly-wide sidewalks and roads, stripped-off roadway, and awkward intersections. In its place we install healthy plantings fed by the additional stormwater entering the site. There are other benefits, too, such as calmer traffic, since vehicles travel more slowly down tree-lined streets. On a larger scale we’re creating a network of green spaces that shade pavements, provide habitat, and beautify entire neighborhoods. The combined size of New York City’s Greenstreets is 85 acres, almost all of which would otherwise be impervious surfaces.
How do you redirect the 5.6 million gallons of stormwater collected at the 28 sites?
The water is diverted into planting beds, where it is absorbed into the soil or used by the plants. Any overflow exits the Greenstreet and enters the sewer to eliminate the risk of standing water or flooding in the area. These sites are specially designed to handle this amount of water through deeper excavation and specially-designed soil and stone layers. This allows the system to move large volumes of water quickly while still holding on to some for the plants.
Citywide, we estimate that our 2,536 Greenstreets capture 105 million gallons of water per year. What’s even more exciting is that they’re influencing the city’s hydrology beyond their borders. A 1,000-square-foot Greenstreet, for example, can handle runoff from a 3,000- to 10,000-square-foot area.
Is filtering and reusing the collected stormwater an option?
Filtering and reusing the stormwater for other purposes can be complicated, in order to meet city health codes. The easiest use of stormwater is to direct it into planting beds, as it requires very little pre-treatment and is immediately available to plants and eventually to the ground water.
Now that a year or two have passed since many of these sites have been built, what’s working and what have you learned?
The main lessons we learned are to make the inlet wider than you think it needs to be, to make the design and maintenance as simple as possible, and to pre-treat your runoff before it enters the main planting area, which helps trap sediment and trash in one concentrated place, preserving the rest of the area and making cleanup simpler.
The systems piloted here are now being used in many of our designs with the Department of Environmental Protection (DEP). Whenever possible, these are at the surface, so their function is visible to the public and maintenance crews.
So you’re working on a project with DEP now?
Yes, DEP has identified priority sewersheds throughout the city that are in the greatest need of sustainable stormwater infrastructure. Sewersheds are essentially the network of sewers that drain into a particular area or water body, much like a watershed, though they aren’t always the same. Parks, along with DOT and several other city agencies, has partnered with DEP to build green infrastructure on a massive scale in these sewersheds. This will include stormwater Greenstreets, such as bumpouts, neckdowns, and swales, as well as DEP’s Right-of-Way Bioswales (ROWB), which were designed by DEP with input from DOT and Parks. At first glance they look like large tree pits with a surrounding fence and understory plantings. However, there is much more going on underground, with two feet of engineered soil and two feet of open-graded stone, allowing ROWBs to capture up to 250 cubic feet of runoff for every one-inch storm.
This fall, Parks will construct 121 bioswales and 17 greenstreets in the Bronx and Flushing. We’ll expand in the spring, with an estimated 72 bioswales and 12 greenstreets in the Bronx and Flushing, and over 200 sites by summer 2013, with many more to come. This work will be funded by DEP, including maintenance, which is exciting for two big reasons. One is that dedicated maintenance by trained personnel will ensure that these sites work better and last longer. On a larger scale it indicates that green infrastructure is not considered solely for its aesthetic or “feel-good” attributes, but that it’s a respected method for managing large volumes of stormwater in a cost-effective manner. As a city, we would never build a waste water treatment facility without also expecting to fund the maintenance. The fact that we are funding green infrastructure in a similar way indicates that it has graduated into a field of trusted engineering.