Green Roofs - Living Architecture Monitor - Spring 2018 - 34

ON SPEC

MAKING STORMWATER MARKETS:

HOW CITIES CAN SPUR VOLUNTARY
GREEN STORMWATER MANAGEMENT
ON PRIVATE LAND
BY ALISA VALDERRAMA

The twin challenges of modern-day stormwater management and
climate resilience require cities to depart from traditional approaches
to a new view on water infrastructure.

T

o address these challenges, many cities are incorporating
decentralized "green infrastructure (GI)" approaches, into
their water infrastructure planning. As U.S. cities plan to
spend tens of billions on green infrastructure in the coming
years, it will be crucial for them to invest in projects that provide
the maximum social benefit per dollar spent. In many cases,
managing stormwater on private land can provide a vast and
largely untapped opportunity for these lower-cost multi-benefit
projects. However, capturing those opportunities will require
cities to implement new policies and programs to motivate
private property owners to act.
Of the cities that have large-scale GI commitments, most are
currently relying heavily on building green infrastructure on
publicly-owned land and in the public right-of-way. However,
public space is limited: over 50 per cent or more of impervious
area in any given city may be privately owned. Cities are finding
that very low-cost green stormwater management opportunities
exist on private land. For example, in 2013 the City of Philadelphia was paying approximately $250,000 per acre to capture
stormwater from one impervious acre in the public right-of-way.
By creating incentive programs that offer $100,000 toward the
cost of a "greened acre" on private property, the City has managed to spur private property owners to green their own parcels,
and thereby greatly reduce the City's overall costs.
Private property GI incentive programs are important beyond providing water quality benefits. They can also be targeted
to motivate greening in the areas of a city that would stand to
benefit most from GI's advantages such as temperature regulation, improved air quality, green jobs, or beautification.
Incentive programs work best when coupled with area-based
stormwater billing systems, where property owners' stormwater
LIVING ARCHITECTURE MONITOR / SPRING 2018 / 34

fees are correlated with how much stormwater is generated onsite.
When an area-based fee system is in place, a green infrastructure
retrofit can result in substantial stormwater fee savings, a source of
revenue that property owners could put toward long-term GI asset
maintenance. Incentive programs can also work well with credit
trading programs, which enable property developers to comply
with onsite stormwater management rules; in part by buying
stormwater capture credits from owners who voluntarily retrofit. In
Washington D.C.'s stormwater credit trading program, for example,
the city has committed to buy nearly $12 million in stormwater
retention credits - setting a "price floor" - which effectively creates
an incentive program similar to the one in Philadelphia.
For cities that successfully use incentive programs, payoffs
can be substantial. Not only can decentralized GI on private land
cost less and deliver more benefits; but creating a market for
private property retrofits also widens the range of available private
financing mechanisms. These can be structured so that the city
pays based not only on project completion but on measured project performance (e.g., gallons of stormwater reduced).
The more that cities embrace stormwater management on
private property, the more we will have a cleaner, greener future
where cities are able to better manage risks, keep water rates
low, and provide the widest possible range of environmental,
economic, and social benefits from each public infrastructure
dollar spent.
Alisa Valderrama is Founder of Neptune Street Environmental Markets
Advisors. Previously, she was Director of Water Infrastructure Finance
at the Natural Resources Defense Council and co-author of "Catalyzing
Green Infrastructure on Private Property: Recommendations for a Green,
Equitable, and Sustainable New York City (2017)."
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