Introduction - Living Roofs in Integrated Urban Water Systems - page 3

regularly causes CSOs (NY/NJ Baykeeper.org 2013). Philadelphia is served by 164
permitted CSO discharge points, serving 48 percent of the city (PWD 2011).
While larger storms cause the greatest volume of CSO, smaller storms create the
greatest number of CSO events. In many areas of the United States, these sorts
of discharges are in violation of the 1972 Clean Water Act and its amendments
(including the 1994 Combined Sewer Overlow Control Policy) and/or the Wet
Weather Water Quality Act of 2000. In the Paciic Northwest, CSOs and runoff
contaminants including the elevated temperature of untreated stormwater runoff
threaten salmonids protected by the 1973 Endangered Species Act. Environmen-
tal regulation and impending lawsuits and/or ines, exacerbated by shifting public
awareness and opinion, is causing municipalities and water utilities to invest sig-
niicant resources in reducing the frequency and volume of CSOs, and restoring
degraded waterways.
Upgrading buried infrastructure is increasingly found to be uneconomical and
impractical compared to surface-level action. Rigid grey infrastructure (pipes,
pumps, tanks and centralized treatment plants) lacks resilience. Alternatively,
small and large cities around the world are developing or are already implement-
ing green infrastructure (GI) solutions for stormwater management. Although
many deinitions of GI have been proposed, a useful compilation is “Natural and
engineered ecological systems which integrate with the built environment to
provide the widest range of ecological, community, and infrastructure services”
(greeningofcities.org 2012). The term green stormwater infrastructure (GSI) is
speciically used to identify approaches for runoff management.
Decisions defending GI and GSI adoption cite economics, inability to achieve
technical objectives using grey infrastructure, and multi-functionality over and
above provision of ecosystem services, particularly with respect to human health
and social capital. Across the world, the two largest municipal investments in GSI
were recently introduced in Philadelphia and New York City, speciically to
address CSO control and receiving water quality improvement. After a compre-
hensive alternatives analysis, the Philadelphia Water Department (PWD) deter-
mined that traditional grey infrastructure would be “cost prohibitive while also
missing the restoration mark.” Instead, the PWD is investing US$1.2 billion (2009
net present value) in GSI and in excess of US$3 billion in GI over 25 years
“towards greening the city as a means to provide speciic beneits . . . while
meeting ecological restoration goals” (PWD 2011: 3). Implementing GI across
New York City is projected to eliminate $1.4 billion and defer $2 billion from the
municipal government's budget for state-mandated grey infrastructure projects
(City of New York 2012).
On a smaller scale, site or block-level initiatives are often instigated by munici-
palities in response to neighborhood complaints. Many successful stories and/or
pilot projects are emerging from Seattle, Portland, Lancaster (Pennsylvania), New
York City and Washington, DC where GI solutions for stormwater are integrated
into street or intersection redevelopment to improve trafic and pedestrian safety.
Addressing runoff problems at - or close to - the source with GI eases the