Stemming the Tide

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A redesigned courtyard at Pace University, designed by AECOM, was rebuilt to capture stormwater through permeable pavement and an advanced cellular support system.
Courtesy AECOM

Overflows from New York City’s combined sewer system are among the greatest threats to our environment. Each year, more than 27 billion gallons of raw sewage and polluted stormwater are discharged into the city’s harbor from around 460 Combined Sewer Overflows (CSOs). These malodorous events occur during heavy rain storms and snowmelts when stormwater runoff contaminated with waste, such as auto fluids, plastic bags, cigarette butts and raw sewage overwhelms city wastewater treatment plants unable to handle flows more than twice design capacity. With the system overload, the excess wastewater is released into the city’s waterways where it kills off marine life, leads to beach closings, and befouls the air with waterborne vapors linked to diseases.

Thanks to a landmark 2012 settlement with state environmental officials, New York City finally is taking major steps to manage stormwater near contaminated waterways that don’t comply with the Clean Water Act, such as the Gowanus Canal and Newtown Creek. The initiative includes an ambitious plan to spend $2.4 billion on green infrastructure, which can include streetscapes designed with materials such as structural soil and permeable pavers.

 
 

However, for some New York City designers, planners, and neighborhood leaders, the multi-billion dollar stormwater infrastructure plan does not go far enough, and they are hammering away at the city’s bureaucracy for approvals and funding to install green infrastructure on streets and public plazas outside of the city’s designated priority stormwater areas.

New York City used to have a dedicated funding source through PlanNYC for building stormwater “Greenstreets” outside of the priority areas but the funding ran out. “There are a whole lot of reasons that it is important to do green infrastructure everywhere—it is inefficient to have stormwater run into your sewage treatment plant,” said Jeanette Compton, former director of the New York City Parks Department’s Green Streets program. But city funds are limited, noted Compton, currently associate director of City Park Development at The Trust for Public Land, adding that outside of the priority areas, “these types of projects aren’t part of proving to the state regulators that we are complying with our water regulations.”

 

Another obstacle is that green stormwater infrastructure is still a relatively new concept for many city agencies. “It took quite a bit of doing to get the City’s Department of Transportation (DOT) and the Public Design Commission to agree that permeable pavement could be a standard,” said Signe Nielsen, principal in Mathews Nielsen Landscape Architects, who was instrumental in getting several green storm water infrastructure guidelines written into the city’s Green Codes, approved in 2012.

Despite the new guidelines, it is still challenging to get city agencies and private property owners to commit to building green stormwater infrastructure in neighborhoods outside the priority areas, because it demands more upkeep than typical hardscapes. “It requires a maintenance agreement and that means participation by private property owners or a business improvement district association,” said Nielsen, adding, “Sidewalks are the responsibility of the property owners, and with permeable materials it is a bit of a learning curve to get everyone to agree that this is not the world’s hugest burden, and the benefits are so valuable that they should be willing to take it on.”

 
New streetscapes in Hudson Square designed by Mathews Nielsen have permeable pavers and trenches with structural soil that will capture millions of gallons of run-off.
Ted Tarquino
 

Currently Nielsen is designing green infrastructure for the flood-prone Hudson Square neighborhood in Lower Manhattan as part of a $27 million streetscaping initiative, which includes a $3.2 million contribution from the city for the first phase of construction. Nielsen’s environmentally enlightened client, The Hudson Square Connection, a new business improvement district organization, has a five-year plan to plant 300 new trees in the neighborhood. In addition, the plan calls for one quarter of this former industrial neighborhood’s sidewalks to be made permeable so that stormwater can seep through and be absorbed by soil underneath.

As opposed to treating stormwater as a waste product at hugely expensive sewage treatment plants, green infrastructure transforms it into a resource for growing plants. In Hudson Square this is accomplished in part by means of subsurface tree trenches composed of structural soil and covered by permeable concrete pavers built adjacent to new oversize tree pits. “The trees get more water and they develop better and more robust root systems,” said Nielsen, “So they are less likely to get blown over by the wind, and they are also more resistant to disease.”

Altogether, the 300 new street trees being planted at Hudson Square are expected to capture 2.5 million gallons of stormwater per year, an amount equal to that used by 25 households annually. The auxiliary benefits of these new storm resistant trees include providing shade, reducing the heat island effect and improving air quality by capturing carbon dioxide and transforming it into oxygen.

 
Astor Place and Cooper Square are being redesigned with massive bioswales and large tree pits.
Courtesy WXY
 

Another part of Manhattan that is being dramatically transformed with green infrastructure is the area around Astor Place and Cooper Square. Here construction is underway on a major redesign by WXY Architecture + Urban Design, and a team that includes landscape architecture firm Quennell Rothschild & Partners, garden designer Piet Oudolf, and environmental engineering firm eDesign Dynamics. As part of the plan, city streets are being realigned, existing public spaces are being redesigned and new ones are being built, including a pedestrian plaza between Astor Place and Cooper Square. The green infrastructure for this $18 million project, which is being funded by the New York City DOT, includes more than 60 new street trees and about 17,000 plantings. Many of the trees will be planted in enlarged tree pits with cobblestone surrounds to increase permeability; beds of structural soil running underneath sidewalks will allow root expansion.

To make the project more environmentally sustainable and to provide additional greenery for the space the design team also pushed to have ten enormous bioswales installed. These landscape features, which measure 10 feet by 20 feet, are designed to capture large amounts of stormwater and to slowly release it into the ground where it is put to use irrigating plants. In addition to introducing new types of materials to the city’s street, green infrastructure often requires particular plant . “There may be times when there is standing water in the bioswales,” said Quennell Rothschild & Partners managing partner Andrew Moore, “so the plants have to be varieties that can withstand that, and other times they may have to withstand drought conditions.”

The new Liberty Park Plaza, adjacent to the World Trade Center site, also designed by AECOM, will also incorporate advanced stormwater retention systems.
Courtesy AECOM
 

As opposed to a typical stretch of New York City sidewalk or a typical tree pit, bioswales and permeable pavers also require more maintenance to keep them free of litter and debris that can interfere with their drainage. To this end, local stakeholders including the Grace Church School and the Village Alliance have been enlisted as partners to help the City’s Department of Transportation keep the plazas clean. Such partnerships with local community groups or BIDs are critical to winning approval for many green infrastructure projects from the New York City Department of Environmental Protection (DEP), the agency in charge of approving projects that deal with stormwater. “Unless there is something in writing that shows how they will maintain it, we have no guarantee that those pavers will be maintained,” said DEP Assistant Commissioner for Green Infrastructure Magdi Farag. “You have to vacuum around it and pick up the fine particles between one paver and another.”

 
 

However, in the long haul green infrastructure pays off by extending the life of trees and even sidewalks. Many significant landscape designs from other eras that once looked good have not aged well. The 8,000-square-foot Pace University Courtyard off Spruce Street in Lower Manhattan is a case in point. Designed by the firm Eggers & Higgins in 1968, the Dogwood trees that were planted became deformed because they were confined to small tree pits with no room for their roots to expand. “They didn’t grow beyond four to six feet, and their bark lost its aesthetic quality over time,” said Gonzalo Cruz, design director of AECOM’s Landscape Architecture Studio in New York. “They tried to grow toward the sun, but they couldn’t do it because there was not enough soil around their roots.”

 

To improve the ecology of the courtyard, AECOM is ripping out the old plaza and starting fresh with birch trees that are planted in an integrated tree and stormwater management system called Silva Cell. This new system, which is a more expensive alternative to structural soil, consists of a modular suspended paving system that protects large amounts of lightly compacted soil contained in a cellular like support structure underneath, and allows ample room for tree roots to expand. “It is basically a self-irrigating system,” said Cruz. “Almost 60 percent of the plaza will be covered with these cells—the water will stay in place nurturing the trees.”

Many designers are hoping that green stormwater infrastructure will someday be a standard component of streetscapes through the entire city. “Even if it is not a priority in terms of a certain program, there are many other metrics that show the benefits of green infrastructure,” said Claire Weisz, principal in WXY Architecture + Urban Design. “If you look at the High Performance Infrastructure Guidelines that Design Trust produced and the High Performance Park Guidelines, they all recommend green infrastructure across the board, not just in one area over the other.”

Despite the advantages of stormwater green infrastructure, under the current fiscal realities it will be institutions and environmentally enlightened communities with access to private sector funds that are best positioned to build such projects outside the designated priority areas. However, we undoubtedly require a more robust response to relieve our overburdened combined sewer system. “We are a city that is growing and increasing the source of the problem,” said Compton. “We are adding a million more New Yorkers, increasing density to fit these people, and therefore increasing impervious surfaces and the amount of effluent coming from all of those new residents.”

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