Keeping Stormwater at Bay: a Brooklyn Green Roof Offers a Look at a Climate Resilient Future

NEW YORK—Every Friday afternoon, the Kingsland Wildflower Green Roof opens its doors to the local community. Tall grass and brightly-colored flowers greet visitors after their four-floor trek to the top of the building—a green oasis in Brooklyn, surrounded on all sides by heavy industrial activity.

Just across the street, the Newtown Creek Wastewater Treatment Plant’s gargantuan “digester eggs” treat millions of gallons of sewage every day. 

Despite the visual incongruity of this scene, both the garden and the treatment plant work to stop contaminated water from flowing into the city’s waterways during heavy rainfall. 

The rooftop garden sits on a building on Kingsland Avenue owned by the production company Broadway Stages. Two well-tended sections contain a variety of plants and flowers native to the area, like strawberries and camassias. A garden on a lower roof is made up largely of sedum, a small succulent-type plant. 

The garden is under the purview of the Newtown Creek Alliance, a local organization that works to improve the environment around the creek, which is a tributary of the East River and forms the border between Brooklyn and Queens. 

Teresa Herrera, a graduate student, and her sister, Lele, have never been to the roof. They’re welcomed by Newtown Creek Alliance’s horticulturist, Brenda Suchilt, who explains that some plants on the roof are actually in a phase of “accelerated bloom.” They are blooming early because of the roof’s position in an urban heat island, surrounded by industrial buildings and a lack of green spaces.

“I feel very calm up here,” said Lele Herrera, who lives in the Upper East Side. “You don’t see gardens like this in the city.”

Seven years ago, the green roof was born of a partnership between the Newtown Creek Alliance, the NYC Bird Alliance, formerly NYC Audubon, Broadway Stages and Alive Structures, a landscaping firm that specializes in roof gardens. The installation was funded by the Greenpoint Community Environmental Fund, a $19.5 million payment to the New York State Department of Conservation (NYSDEC) in a settlement with ExxonMobil over their contamination of Newtown Creek. 

In 1979, an investigation by the Department of Conservation found that ExxonMobil, which had historically operated oil refineries and fuel storage spaces along the creek, had spilled an estimated 17 million gallons of oil into the water—one of the largest terrestrial oil spills in the country’s history. Although ExxonMobil has been working for decades to remediate the problem through groundwater treatment, the creek remains an extremely contaminated Superfund site and is still on the National Priorities List of the nation’s most hazardous toxic waste areas. 

A former wetland, much of the creek’s natural borders have been reconstructed for industrial operations, like oil refineries and petrochemical plants. 

Much of the area surrounding Newtown Creek is located on a 100-year floodplain, which means that every year there is a 1 percent chance of an extreme flood event. Due to the weaknesses in New York’s sewage infrastructure, extreme rainfall constitutes a threat not just to the residents living near Newtown Creek, but also to the biodiversity within the creek and the flora that surrounds it. 

When extreme rainfall takes place in New York City, the sewage system is often overwhelmed. Around 60 percent of the city has a “combined” sewer system, which means that stormwater enters the same pipes as sewage and both flow to wastewater treatment plants. When the combined volume of rainfall and sewage overwhelms the system, the excess is redirected out to rivers and creeks in what is called combined sewer overflows. Every year, the city releases an estimated 27 billion gallons of combined sewer overflow into the Hudson River according to Riverkeeper, an organization dedicated to safeguarding New York’s waterways. Newtown Creek receives around 1.2 billion gallons of that contaminated water. 

“[Newtown Creek] doesn’t get flushed with the tides as much as it once did, and because it’s confined, the impact of stormwater and combined sewer overflows are magnified,” said Robert Pirani, the program director for the New York-New Jersey Harbor & Estuary Program, an organization dedicated to restoring the Harbor Estuary.  

The Newtown Creek Alliance and other environmental justice organizations have been working to use green infrastructure like the rooftop garden to mitigate these pressures on the city’s sewer system, both to increase the water quality in the creek and to help communities better understand the impact of stormwater on their environment.

“There’s nothing that any resident can do to directly impact the historic toxins that are at the bottom of the creek. We can’t go and clean that stuff up,” said Willis Elkins, executive director of the Newtown Creek Alliance. “Whereas, if you don’t flush your toilet when it rains, you’re basically saving pollution from going to the waterway—it’s directly connected.”

Green infrastructure like roof gardens retain stormwater that would otherwise be destined for the city’s sewer systems. The substrate used in roof gardens, the surface on which the plants grow, is engineered to be both lightweight and water retentive. The layers of material underneath the substrate are also designed for water retention. They take in stormwater and then slowly release it, limiting the water entering the sewer systems during a rainfall event. 

The main garden at Kingsland Avenue is defined as an intensive green roof—the substrate is deeper than six inches, and there is high plant diversity. As a result, it can take in large volumes of stormwater and better serve the wildlife and pollinators in the area. 

The lower sedum roof is an extensive roof, which means the plants must be grown in a small amount of substrate, and thus there is less biodiversity. Though sedum roofs retain less stormwater, they are more lightweight than intensive gardens, which means that buildings without the structural capacity to hold the weight of a larger amount of soil can still grow them. 

“I think that green roofs are really a win for everyone,” said Dustin Partridge, director of the Green Roof Researchers Alliance and of conservation and science at the NYC Bird Alliance. “They’re so important for a climate-impacted future–they help people, they help the city, and they help wildlife. It’s amazing what can happen when you install a green roof on a building in New York City. We have now, probably over 80 bird species observed on green roofs throughout the city, and thousands of insects.”

Today, the Newtown Creek Alliance uses the gardens for much of its educational programming about climate resilience through green infrastructure. 

“It wasn’t just about doing ecological work, it was also about providing a benefit to the community,” said Elkins. “We have educators on staff, and we tapped into the demand for more environmental education-based field trips.”

“They’re so important for a climate-impacted future–they help people, they help the city, and they help wildlife.”

The alliance maintains this green roof with Broadway Stages, while also tending to 15 rain gardens across the area surrounding the creek through a partnership called the RAIN Coalition. Maintenance is a main concern when it comes to the city’s green infrastructure because trash very often accumulates in rain gardens, brought in by stormwater, or by residents. 

“Once, someone left a cooler full of rotten crabs,” said Gus Perry, the greenspace steward for Newtown Creek Alliance. He tends to the rain gardens once a week. 

Perry and horticulturist Suchilt use plants from their own nursery, also located in the Kingsland building, to maintain the rain gardens, though they lament the difficulties of finding native plants that are also locally adaptive to New York’s many microclimates. 

The city’s Department of Environmental Protection has identified green infrastructure as an important tool for climate resilience, particularly since Hurricane Ida in 2021 highlighted the city’s weaknesses in stormwater mitigation. They are trying to incentivize more private property owners to install green roofs through their Green Infrastructure Grant Program, which reimburses for the cost of installation, and the city’s Green Roof Tax Abatement, which offers a one-time property tax reduction for installing a green roof on one’s property. 

Despite these incentives and the many ecological benefits of green infrastructure projects like the Kingsland green roof, few have been installed on private property. The cost and maintenance of a green roof often dissuades property owners from investing in one, even though they can often help cool a building in the summer and reduce the chances of roof leaks, according to Partridge. 

The Waterfront Alliance, an organization dedicated to making the New York and New Jersey Harbors a resource for all residents, believes there is more to be done. Their RAIN Ready New York Act, which was introduced in the New York State Legislature this past session, would give local authorities power over mitigating stormwater, as well as flooding. 

“It would give them legal clarity to, essentially, manage stormwater and sewage water together to create incentive programs for green and gray infrastructure outside of the general city-owned properties,” said Tyler Taba, the director of resilience at the Waterfront Alliance.

Last week, the Newtown Creek Alliance hosted an event to inform the local community about flood mitigation at their boathouse in Queens Landing. Emily Ruby, the advocacy and policy coordinator for Riverkeeper, gave a presentation on the water quality at the creek. Ruby emphasized the impact of combined sewer overflow on the water, and the organization’s goal of making all New York City waters swimmable. 

“Who here would be willing to swim in Newtown Creek today?” Ruby asked near the end of the presentation. 

No one raised a hand.