A City of Grey… What’s the problem?

As a large urban metropolis, New York City is covered in paved surfaces, from streets, to sidewalks, to parking lots, to rooftops.  And as an older American city, NYC has an aging infrastructure, including a Combined Sewer System.  Combined sewer systems (CSSs) are designed to convey all types of wastewater to a treatment plant, including household sewage, commercial and industrial waste, and stormwater resulting from surface runoff.  In cities, like New York, with combined sewer systems, rainfall events overwhelm the storage and treatment capacity of waste water treatment plants. The combined sewage and stormwater are discharged directly into a receiving water body without any treatment.  These events are known as combined sewer overflows (CSOs) (DEP, 2010).

CSOs ultimately happen because impervious cover and paved surfaces create excessive amounts of surface runoff. With point source pollution being controlled and monitored, combined sewer overflows remain as the biggest threat to New York City waterways.  Pathogens, suspended solids, and entreated detergents are all released during these events (DEP, 2010).   


What is Green infrastructure?

According to the New York City Department of Environmental Protection (DEP), green infrastructure is “techniques that detain or retain stormwater runoff from impervious surfaces through capture and controlled release, infiltration into the ground, and/or vegetative uptake and evapotranspiration.”  The primary purpose of green infrastructure is to keep a portion of the city’s rainwater out of the sewer system, so the system does not overflow into our waterbodies (DEP, 2010).

Green infrastructure best management practices (BMPs) include subsurface, surface, and rooftop systems, including bioswales/ vegetated swales, rain gardens, trees and enhanced tree pits, porous pavement, green roofs, blue roofs, rain barrels, and constructed wetlands (DEP, 2010).

Picture2- Source DEP


The Future of Green

Historically, NYC has managed stormwater through a primarily grey system.  Green infrastructure is becoming nationally recognized as an important tool for managing stormwater, which has important environmental and economic co-benefits, and increases the overall sustainability of the urban landscape by adding open space, cooling the city, reducing energy consumption, restoring ecosystems, and improving air quality (DEP, 2010).

In 2010 the DEP launched the NYC Green Infrastructure Plan, a twenty year strategy for implementing green infrastructure to control the first inch of runoff on 10% of impervious surfaces in combined sewer watersheds (DEP, 2010).

Picture3- Source DEP

Source: DEP

El Barrio: Chipping Away at the Concrete Jungle

In 2012, New Yorkers for Parks (NY4P), an independent advocacy nonprofit, released a report called the East Harlem Open Space Index, which analyzes the availability and quality of open space in the area based on fifteen New York City-specific open space targets developed by the organization (NY4P, 2012).  The report analyzes the existing population-adjusted open space measures in East Harlem compared to the citywide targets (NY4P, 2012).

The East Harlem Open Space Index report finds that the East Harlem exceeds OSI standards in several categories including community gardens and permeable surfacing in parks.  East Harlem does not meet OSI standards in many categories including total open space and tree canopy coverage (NY4P, 2012).  It would be challenging to increase the amount of open space in an area as densely populated as East Harlem, with few possibilities for the acquisition of new parkland.  This begs the question of whether a strategy to increase green in East Harlem could be to implement green infrastructure projects in the community.

Picture4- Source NY4P

Source: NY4P

Trees: The Only Infrastructure that Appreciates with Age

Our client, TreesNY, utilizes trees as a vehicle for environmental education.  Not every New Yorker has access to a park, but most New Yorkers have some access to street trees.  Trees are an important component of green infrastructure.  Green infrastructure has the potential to expand the mission of TreesNY, by providing New Yorkers more access to green.

Picture5- Source TreesNY

Source: TreesNY


New York City Department of Environmental Protection (DEP). (2010). NYC Green
Infrastructure Plan: A Sustainable Strategy for Clean Waterways. Retrieved from:
New Yorkers for Parks (NY4P).  (2012). East Harlem Open Space Index.  Retrieved from:


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