Because of our dense development patterns in NYC, ~72% of our landmass is impervious. This means that, during wet weather, large volumes of stormwater (rain and snowmelt) runs off most of our hard surfaces (i.e. pavement, asphalt, rooftops) and, rather than get absorbed back into the ground, it runs off our streets into two different conveyance systems underneath our streets. Stormwater runoff is a root cause of a whole host of challenges in NYC such as sewage pollution in our waterways, flooding in our streets, erosion of our fragile shorelines, and deterioration of our overburdened sewer infrastructure.
NYC's stormwater runoff runs to drains on our streets (or floods our streets when the drains get clogged) and through a labyrinth of pipes underneath our streets. Depending on which part of the city it falls, stormwater is transported through either our Combined Sewer System (CSS) or the Municipal Separate Storm Sewer System (MS4). Here is a map of these two systems.
The MS4 system captures ~ 30-40% of the city's polluted stormwater runoff and discharges it, untreated, directly into our waterways. Stormwater picks up all manner of debris and unsavory material. After a rain our local waterways look like someone dumped tons of trash in them.
The Combined Sewer System transports ~ 60% of our stormwater runoff and all of the city's wastewater (sewage) through the same set of pipes and out to one of 14 wastewater treatments plants. When this system becomes overwhelmed during wet weather events ( ~20-30 times per year) the combined untreated wastewater and polluted stormwater are released directly into our waterways. These events are called Combined Sewer Overflows (CSO).Every year, NYC discharges ~20 billion gallons of polluted stormwater and wastewater into our waterways. The City's plans to reduce this pollution (CSO Long Term Control Plans) aim to reduce CSO discharges by 1.67 billion gallons by the year 2030.
The next decade is crucial in terms of how we address our stormwater and climate change related challenges in NYC. According to the NYC Panel on Climate Change, our region can expect to see a 1 – 8% increase in precipitation in the 2020s, and 4 – 11% increase by the 2050s. More precipitation means more stormwater runoff! NYC will have to carefully evaluate our building and zoning policies to ensure that the impact of more impervious surfaces is mitigated.
NYC has initiated a series of programs to reduce the large volumes of runoff that inundate our overburdened infrastructure and local waterways.
The plans, which have specific goals they have to reach by the year 2030, aim to reduce stormwater pollution from the city's municipal separate storm sewer system (MS4) and combined sewer overflow pollution from our antiquated combined sewer system. See a map of both systems here.
Below is a list of the key plans and programs underway or coming to fore:
CSO Long Term Control Plans:
The Combined Sewer Overflow Long Term Control Plans aim to use a combination of grey and green infrastructure methods to reduce the ~ 20 billion gallons of CSO pollution that discharge into our waterways each year. The plans must explore and identify specific actions to reduce sewage pollution in individual waterbodies.
We are concerned that these plans, once completed, will not meet the 2030 goals because they will still leave ~16-18 billion gallons of CSO pollution in our waters every year. The rainfall data they are modeled on (2008) and the water quality criteria they are assessed with are both out of date and do not align with the standards mandated by the Federal Environmental Protection Agency, nor do the plans consider the impacts of sea level rise. Here is a link to details about these plans and our concerns.
Green Infrastructure Plan:
NYC's GI plan has a goal of managing the first inch of stormwater runoff on 10 % of NYC's impervious surfaces (within the combined sewer area of the city) through green infrastructure solutions by 2030. This translates into a goal of "greening" 8,000 impervious acres.
So far, we've greened ~1230 acres, mostly on publicly owned property. Nearly half of the 8000 impervious acres are on privately owned property. Several milestones for the plan have been missed. Here is a link to our concerns about this plan.
Incentive programs for GI on private property:
DEP's GI Grant program has not yielded as much GI on private property as anticipated. They recently revamped the program to focus solely on green roof retrofits to help support two new sustainable roof laws that went into effect in early 2020. Scroll down to see more about the sustainable roof laws.
NY State Green Roof Tax Abatement program that has recently been renewed and updated to identify priority areas where the abatement amount is much higher in order to incentivize more green roofs in areas where they are needed most. SWIM is part of a Green Roof Tax Abatement Working Group that helped inform the updates to the program. You can find our recent public hearing testimony on the criteria for designating the priority areas here.
DEP is initiating a new grant program to support installation of GI practices on large private properties (50,000 sq ft and above) citywide. The program will go into effect in 2021.
Sustainable Rooftop Laws
In 2019, as part of the City Council Climate Mobilization Act, two new
Sustainable Roof Laws require new and retrofitted roofs to install
either a vegetated roof system or solar system or both.
Stormwater Management Plan for the Municipal Separate Storm Sewer System
In 2017/18, under a permit agreement between the city and the state, a Stormwater Management Plan (SWMP) for the city's Municipal Separate Storm Sewer System (MS4) was initiated to develop a series of programs that will help reduce contaminants in stormwater runoff from properties in the MS4 portion of the city and to track down illegal discharges.
The program got underway in 2018 and the city recently issued a 2019 annual report on their progress for this plan. So far, the plan seems to be on track.
2021 Unified Stormwater Rule
In late 2020, by order of the Mayor, the city council passed a bill (Intro 1851) granting the NYC Department of Environmental Protection the authority to enact a new stormwater management rule. In 2021, the city will introduce the draft rule at a public hearing for comment. SWIM testified at the hearing for Intro 1851 and provided an initial set of comments for what the new rule should entail. Here is a link to our recent blog post about the rule and our comments.
SWIM Coalition members have monitored and informed most of these programs and we are in an ongoing and productive dialogue with the city and state to ensure that the plans stay on track and adapt to new information and regulations as we evolve into the city's climate resilience planning. Sign up for our e-blasts and join us at out quarterly public meetings to get updates.