As the first great snow melt of winter hits NYC, let's look ahead to the big Spring Thaw and what comes with it: combined
sewer overflows (CSO). CSOs are one of the City's most pressing environmental problems. Every year, 27 billion gallons of untreated sewage (that’s
41,000 Olympic-size swimming pools for those watching Sochi) is diverted into
New York City’s waterways—from Flushing Bay and Newtown Creek to the Hudson
River and New York Harbor.
CSOs occur
when the City’s sewer system is overwhelmed by rainwater/snow melt—which
unfortunately, doesn’t take much. Indeed, as little as a tenth of an inch of
rain can render most of the waterfront and its
beaches unsafe for recreation.
Today, I
want to look at what New York City is doing to address the problem, focusing on
permeable pavement, and offer an additional policy initiative that should
supplement the City’s plans.
Permeable
pavement is an evolving technology that allows storm water to soak through the
surface and be captured in underground reservoirs that feed back into the soil
(see photo at left).
The New York
State Environmental Facilities Corporation recently awarded a $1.2 million grant to NYC Department of
Transportation for a pilot of permeable pavement in College Point, Queens. The
project is set to be installed in April and will include three types of
permeable pavement, which will be compared to standard asphalt for their
relative benefits.
If the pilot
proves successful, the City will move ahead with implementing 80 sites by 2020
and 400-800 by 2030, in accordance with PlaNYC, which also includes the installation
of inflatable dams in Red Hook and Williamsburg, bioswales, and other
“green” infrastructure.
New York is
a clear leader among American cities in addressing CSO’s, but I think New York
City needs go beyond what is currently planned as part of the PlaNYC effort to
address the significant percentage of non-permeable surfaces that exist on private property. As shown in the chart
at right, while one-third of the City’s impervious surface area are
publicly-controlled streets and sidewalks, nearly half the area is buildings,
most of which are privately owned.
To that end,
I want to plug an idea developed by a colleague of mine at the NYC Comptroller’s
office, Dr. Stephen Corson. Steve’s idea is for the City to develop a series of incentives to nudge private property
owners to install new permeable surfaces on residential or commercial lots.
This could have a transformational effect on the City’s CSOs, helping to divert
billions of gallons of runoff from our waterways.
Sustainable Yards NYC, with assistance from the City
of New York’s Institute for Sustainable Cities, found
that NYC has 52,236 acres (304 sq miles) of residential yard space—more than a
quarter of New York City’s total land area. Many of these yard spaces are located between row houses,
away from street views.
Heretofore, there has been no effort undertaken to
measure how much of this space (or other surface areas) is paved and how much
is permeable. However, a study conducted by Sustainable Yards NYC and CUNY on
one UWS residential block provides a preview of what such a survey might find.
Only 35
percent of the residential yard space measured on the one block (containing 44
rowhouses, 5 apartment buildings and 7 flats) was found to be permeable. Nevertheless, even that modest amount
of permeable space was estimated to have diverted over 50,000 gallons of rainwater
from the sewer system in 2009 (in addition to trapping 8822 pounds of carbon
dioxide that would have otherwise been released into the atmosphere).
Step one in this effort would be for the City to
commission a study that will identify all privately owned non-permeable
surfaces areas in the five boroughs. Following that study, the City should work
with the State to develop tax-incentive programs to use carrots and sticks to
nudge private property owners to do their part to reduce CSOs and make NYC a
model for other cities to follow.
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