Combating Flooding and Water Pollution in New York City through Green Infrastructure
A beautiful and functional bioswale along a bike path in Queens (Source: Clarence Eckerson Jr.)
In June 2022, New York City completed a $13 million green infrastructure project in Brooklyn and Queens to bolster the city’s resilience against flooding and water pollution. Sponsored by the New York Governor’s Office of Storm Recovery (GOSR) and the Dormitory Authority of the State of New York (DASNY), the project was designed by Stantec, a global leader in sustainable engineering solutions, to help improve water quality and manage water runoff.
The key component of this effort included the installation of 120 bioswales in low-middle income communities throughout South Brooklyn and South Queens, including Canarsie, Gravesend/Bensonhurst, Midwood/Flatlands, Idlewild, and Rockaway. Following guidance from the NYC Department of Environmental Protection Green Infrastructure Design Manual to identify locations to maximize stormwater capture, the Stantec team arranged bioswales around these communities to optimize their efficiency while minimizing the impact on businesses and pedestrians. Each bioswale was designed to avoid property entrances and utilities while planting projects were determined according to anticipated sun exposure.
Another major component of this project was the development of a multifunctional and educational green infrastructure installation at Catherine & Count Basie Middle School 72 in South Jamaica, Queens. The school’s front yard was transformed from a fully paved lot into a multi-use community garden that includes several rain gardens and rainwater collection devices to be used for gardening. Surrounded by educational signage, the gardens contain resilient plantings that were selected due to their drought tolerance, low maintenance, and ability to welcome local pollinators and wildlife.
GOSR Executive Director Katie Brennan shared this statement regarding the impact of this project: “Green infrastructure helps New Yorkers both mitigate climate change and adapt to its effects. We are proud that this innovative project is making historically underrepresented communities in Brooklyn and Queens more resilient and better able to withstand future storms.”
Together, the bioswales and rain gardens play crucial roles in capturing rainwater while diverting stormwater to relieve pressure on the city’s overburdened storm infrastructure and roads that are subject to frequent flooding.
An illustration of how bioswales temporarily hold and filter rainwater before it is captured into the ground.
(Source: Alyssa Crozier)
The Runoff Problem
Heavy rain events are known to directly translate to increased flooding, runoff, and erosion. Rainfall that hits soil or natural landscapes is absorbed into the ground, while rainfall that hits impervious surfaces, such as concrete and asphalt, runs off into storm sewers rather than soaking in. As the water runs along the pavement, it picks up anything it runs through, carrying motor oil, road salts, and garden chemicals into storm sewers. This untreated water ultimately spills out into freshwater bodies of water and pollutes local rivers and streams. One can see how this problem is amplified in urban environments that are covered in miles of pavement and littered sidewalks.
The issue of water runoff is particularly threatening for communities that utilize combined sewer overflows, such as Indianapolis, which convey both stormwater and wastewater (sewage) into one piping system. When heavy rainfall events cause the sewers to receive more runoff than they can handle, combined sewer runoff floods the sanitary sewer, causing unprocessed sewage to be pushed into our waterways, sometimes even backing up into our basements. As such, strategic management of runoff and flooding mitigation are key components to improving water quality, avoiding water pollution, and preserving public health.
Rainscaping with Bioswales and Rain Gardens
Rainwater runoff can have nasty effects as it travels from the point of rainfall into sewers that can capture it. The solution to mitigating this issue is to increase the capacity for rainfall to be absorbed back into the ground as quickly as possible. Green infrastructure tools to achieve this include:
Rainscaping – any combination of plantings, water features, catch basins, permeable pavement, and other activities that manage stormwater as close as possible to where it falls, rather than moving it someplace else.
Bioswales – vegetated, shallow, landscaped depressions designed to capture, treat, and infiltrate stormwater runoff as it moves downstream.
Rain Gardens – small, natural areas, typically located on a sidewalk near a stormwater catch basin.
Rainscaping
Traditionally, communities relied on the use of pipes, French drains, and other expensive, high-infrastructure strategies to manage water by moving it away from our houses. Rainscaping utilizes sustainable landscape design to allow rainfall to be absorbed as close to the source as possible, offering a cheaper and more earth-friendly solution.
Bioswales
A public bioswale made of drought-resistant plants, grasses, rocks, and mulch.
Due to their proximity to sidewalks, bioswales are known as the “first flush,” which is the first and often most polluted volume of water resulting from a storm event. According to the National Association of City Transportation Officials, bioswales are the most effective type of green infrastructure facility in slowing runoff velocity and cleansing water while recharging the underlying groundwater table. They are composed of diverse, native vegetation that considers minimum irrigation requirements and the potential for wildlife habitat creation. Bioswales are often used to direct water to a rain garden. In properties without rain gardens, bioswales can bring water directly into existing drainage or storm systems.
Rain Gardens
A commercial rain garden used to prevent rainwater runoff during storms.
Rain gardens temporarily hold and filter water, removing contaminants as it infiltrates into the soil and reducing storm runoff into waterways. Utilizing extremely porous engineered soil, rain gardens contain a variety of plants that are specifically chosen for their ability to absorb water and thrive in an urban environment. They are planted with native plants that foster biodiversity by attracting birds and pollinators. Rain gardens also utilize porous concrete to divert stormwater from streets and draw it into the ground. By reducing sewage overflow in local waterways, they can increase a street’s drainage capacity and reduce the risk of flooding. Rain gardens are estimated to collect around 8 million gallons of water per year, according to the New York City Department of Environmental Protection (DEP).
A Safer City
While managing water runoff in urban environments can be a challenge, rainscaping strategies offer cost-effective and sustainable solutions. Rain gardens and bioswales reduce toxins and other pollutants in the water, allowing streets to become more resilient to high rainfall events, particularly in low-lying, flood-prone areas. With strategic planning, cities can improve water quality and preserve public health while creating visually appealing green infrastructure that has minimal disturbance to businesses and utilities. Reduction of sewer overflow, health, and environmental risks, and the improvement of water quality are just a few of the benefits that rain gardens and bioswales offer as green infrastructure strategies. As a result of these rainscaping techniques, more people can be drawn to the water for activities like kayaking, swimming, and going to the beach, with greater confidence in their safety.
References
https://www.nyc.gov/site/ddc/resources/features/2017/08/bioswales.page
https://spottsgardens.com/rainscaping-manage-rainwater-rain-garden-drainage-bioswale/
https://spottsgardens.com/rain-gardens-bioswales-rainscaping/
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