Sarah Madden
June 2010
MIT-DUSP Urban Sustainability Evaluation
Green Infrastructure: Stormwater Management Technical Memo
What Is Stormwater Management, and How Does it Work?
Urban stormwater runoff is an important contributor to water
pollution; it both contaminates and physically harms aquatic
environments. According to the Environmental Protection Agency
(EPA), urban pollutants are the most important contributor to
contamination of the nation’s waters (National Research Council
2009).
Urban stormwater problems arise because urban development
typically involves converting undeveloped areas to impervious,
often paved, surfaces, thereby transforming surfaces that would
have soaked up heavy rains into impermeable land cover that
generates runoff. In natural landscapes, less than 10 percent of
the rainfall volume converts to runoff; instead, rainfall and
snowmelt filter slowly into the ground (EPA 2003). By contrast,
in urban landscapes, roads, parking lots, rooftops, and
compacted soils seal 45 percent to 90 percent of land cover,
preventing the infiltration of rainwater and altering the
hydrology of surrounding ecosystems (Paul and Meyer 2001; Booth,
Hartley, and Jackson 2002; Kloss et al. 2006). In fact,
imperviousness is used as a key indicator for measuring the
impacts of urbanization, and many studies reveal negative
effects on biological diversity in aquatic ecosystems at and
above watershed imperviousness levels of 10 percent (Brabec,
Schulte, and Richards 2002; Clar, Barfield, and O'Connor 2004;
Jacob and Lopez 2009).
During storm events, impervious surfaces cause runoff to rapidly
flow towards receiving pipes or water bodies, all the while
picking up pollutants—including sediment, metals, bacteria,
nutrients, pesticides, trash, and polycyclic aromatic
hydrocarbons—from the surfaces of the city. Those pollutants can
either infiltrate into the ground, potentially degrading the
groundwater, or flow into surface waters, depositing pollutants,
sediments, and debris, while also eroding stream channels,
1
altering sediment loads, and affecting stream temperature (Paul
and Meyer 2001; Roy et al. 2008). Furthermore, impervious
surfaces—especially roads and parking lots—increase the risk of
flooding for downstream regions by increasing water volume and
decreasing travel time, resulting in rapid flood peaks (NRC
2008; Jacob and Lopez 2009). In sum, there is a direct
relationship between land cover and downstream water quality,
and an effective management strategy to mitigate the Urban
Stream Syndrome requires addressing the cumulative impacts of
urbanization, including hydrology, water quality, and habitat
considerations (NRC 2008).
Cities have a variety of infrastructure systems to control the
flow of rainwater and runoff in the city. Many older U.S. cities
use conventional combined sewer systems, which collect both
sewage and stormwater runoff in the same underground pipes. In
such gray infrastructure systems, Combined Sewer Overflow (CSO)
events are a serious problem: during heavy rains, when the sewer
system reaches capacity, excess flows are released directly into
rivers or receiving water bodies. CSOs release an estimated 850
billion gallons per year of a mix of untreated sewage and
stormwater, which contains microbial pathogens, viruses, and
oxygen-depleting substances, in addition to normal stormwater
pollutants. These releases present significant environmental and
health risks (USEPA 2004).
Since the mid-1990s, cities have been installing greeninfrastructure systems to address stormwater in a more
distributed pattern, using landscape interventions instead of
underground pipes. Green infrastructure involves taking a more
environmentally sensitive approach to prevent runoff rather than
treating it down the line—using green roofs, rain gardens, rain
barrels, and porous pavements to filter and absorb rainwater
(Spirn 1984; Hill 2007; Berghage 2009). These more natural
drainage systems are of a comparable cost to underground
concrete sewers, but also provide aboveground benefits and take
much less time to install than gray infrastructure projects.
Each of these engineered solutions or Best Management Practices
(BMPs) has different performance (some are better than others at
removing pollutants), variable water holding capacity,
longevity, cost, climate suitability, and maintenance
requirements.
2
Laws and Institutions to Regulate Stormwater
The federal regulatory history of stormwater control in the U.S.
dates to the 1972 Clean Water Act and the 1990 Phase I
Stormwater Rule, which regulate the discharge of pollutants into
water bodies (NRC 2008; Booth and Bledsoe 2009). Part of the
challenge of stormwater management is that by the time the
stormwater regulations were enacted, cities already had
extensive water infrastructure networks and laws focused more on
flood control and protecting structures than water quality.
Furthermore, cities rely on land-use zoning, building codes and
standards, and infrastructure standards and practices to shape
the built environment, and the “overlapping and conflicting maze
of codes, regulations, ordinances, and standards [have] a
profound influence on the ability to implement stormwater
control measures” (NRC 2008, 72). Because such regulations
affect activities and material choices for land cover in the
public and private realms, they also affect stormwater and
efforts to mitigate its impacts. In order to effectively address
pollution and water quality issues, then, local governments must
coordinate the work of multiple departments, reconnecting landuse planning, regulation, and stormwater management (NRC 2008).
Zoning
Different approaches to zoning affect stormwater runoff in
different ways, potentially influencing the amount of impervious
area on a site as well as on-site stormwater management
opportunities (NRC 2008). Each of the most common types of
zoning—Euclidean, performance, and form-based—could be designed
to encourage improved stormwater management. For example,
Euclidean zoning, which segregates land uses into geographic
districts and dimensional standards, could incorporate a rewardbased incentive system to encourage on-site stormwater control
measures. The more flexible performance zoning could require
development to meet performance standards for stormwater. Formbased zoning, which combines prescriptive and discretionary
criteria and often favors shorter buildings that impede on-site
stormwater management, can be re-designed to encourage small
impervious footprints and preserve open space (NRC 2008).
3
Building Codes
Building codes establish standards for construction, and
sometimes incorporate materials standards that prevent the use
of landscape-based green infrastructure (such as porous
pavements) because of traditional concerns about protecting
structures from water. As technical engineering expertise with
green infrastructure practices improves, cities can update
building codes that currently impede the adoption of innovative
stormwater approaches (such as rules that specify a minimum
distance between a building and an infiltration area, for
example).
Groups such as the American Society of Landscape Architects
(ASLA) are considering how to encourage sustainable site design
among the design and engineering professions. The ASLA devised a
voluntary land- and water-oriented rating system for sustainable
landscapes, The Sustainable Sites Initiative: Guidelines and
Performance Benchmarks 2009 (Sustainable Sites Initiative 2009)
as a landscape parallel to the Leadership in Energy and
Environmental Design Green Building Rating System™ (LEED®) model
for buildings. The system rates criteria related to the site
selection, assessment and planning, design for water, design for
vegetation and soils, materials selection, human health and
well-being, construction, operations and maintenance, and
monitoring and innovation, and outlines a precise system for
sustainable landscape design.
Engineering and Infrastructure Standards and Practices
In the public right-of-way, engineering standards and practices
define how cities address surface drainage, road construction,
grading, pipe size, landscaping, and other requirements that
affect stormwater. Local codes also establish requirements for
stormwater drainage from private homes into the municipal
drainage system, and may conflict with green approaches to
reduce runoff (NRC 2008). Stabilizing dynamics such as path
dependence reinforce the status quo: the many layers of uses in
the modern built environment, including networks of underground
infrastructure, size requirements for emergency vehicles, and
years of refinement and maintenance experience tempt cities to
stay the course, to the detriment of innovative stormwater
management approaches.
4
Innovative Approaches to Stormwater
The optimal approach to stormwater runoff would be
comprehensive, addressing land-use planning and stormwater
management, as well as national regulation of harmful material
uses. According to the National Resource Council (NRC),
In an ideal world, stormwater discharges would be regulated
through direct controls on land use, strict limits on both
the quantity and quality of stormwater runoff into surface
waters, and rigorous monitoring of adjacent waterbodies to
ensure that they are not degraded by stormwater discharges.
Future land-use development would be controlled to prevent
increases in stormwater discharges from predevelopment
conditions, and impervious cover and volumetric
restrictions would serve as a reliable proxy for stormwater
loading from many of these developments. Large construction
and industrial areas with significant amounts of impervious
cover would face strict regulatory standards and monitoring
requirements for their stormwater discharges. Products and
other sources that contribute significant pollutants
through stormwater—like de-icing materials, urban
fertilizers and pesticides, and vehicular exhaust—would be
regulated at a national level to ensure that the most
environmentally benign materials are used when they are
likely to end up in surface waters. (NRC 2008, 101)
The task is to link water management with land-use: “We now
understand, for example, that groundwater and surface water are
really one resource that should be managed conjunctively, the
pollutants should be managed at their source, and that we can
predict, within limits, the consequences of urban development on
the ecological health of urban streams,” and the connections
between these systems adds technical expertise to more
effectively design with nature (Baker, Shanahan, and Holway
2009, 288).
Moving forward, cities must transition away from the solely gray
infrastructure approach. A more sustainable frame of mind would
prioritize the use of green infrastructure in a proactive way,
moving away from treating infrastructure as necessary for damage
control toward a broader view of the potential water quality,
ecological, and social benefits of greener cities.
5
Cities’ options for innovative approaches to stormwater
management initially may be constrained by the existing water
infrastructure, competing land and water uses, water rights,
laws, and institutions. Green infrastructure is an especially
promising approach because it provides an array of environmental
and social benefits to the community that are not provided by
the gray infrastructure approach. The benefits from the green
approach have the potential to ease some of the cost challenges
cities face while also fulfilling the mandates of multiple city
departments.
The NRC (2008) suggests ways that cities can update their
zoning, building codes, and infrastructure and engineering
standards to improve stormwater management:




Separate ordinances for new and infill development. Because
redevelopment is more challenging than new development, and
strict stormwater requirements might hinder redevelopment
in the city core at the expense of undeveloped land at the
fringe, separate ordinance for the two development types
enable cities to align the new stormwater policy with
development goals.
Integrated stormwater management and growth policies. This
approach combines incentives to attract high-density infill
development with performance-based water-quality goals
(i.e. minimizing impervious area, prioritizing swales).
Unified development codes. Consolidate layers of code to
surface any inefficiencies and encourage innovation.
Design review incentives to speed permitting. Incentives
include reduced development fees, preferential review and
approval for innovative plans, reduced stormwater fees, and
other incentives. Chicago’s Green Permit Program and
Portland’s Green Building Program offer developers ways to
save time and money by meeting environmental goals.
Common Program Types
Cities have adopted a variety of different approaches to
stormwater. Because this memo focuses on green-infrastructure
approaches, with an emphasis on the structural investment by the
city, we have categorized these programs as infrastructure
investment (by the city), codes and regulations (including
6
incentives and deterrents), watershed protection and
restoration, and education.
Table 1 summarizes the programs in the 25 project cities, and
assigns an initial rating to the cities’ stormwater efforts
relative to a sustainable stormwater management system. (The
rating system is described in more detail in the Analysis
section.)
Table 1. Components of Cities’ Stormwater Programs.
***DRAFT—April 2010 – if a cell row is blank, that means I still
need to investigate that place or category
REGULATION
CITY
Austin, TX
Boston, MA
Boulder, CO
Cambridge, MA
Chatanooga, TN
Chicago, IL
Denver, CO
Detroit, MI
Houston, TX
Jacksonville, FL
Los Angeles, CA
Milwaukee, WI
Minneapolis, MN
New York, NY
Philadelphia, PA
Pittsburgh, PA
Portland, OR
Salt Lake City, UT
San Diego, CA
San Francisco, CA
Santa Monica, CA
Seattle, WA
Washington DC
Used
for
Direct
CSO
Contr
ol?
Water
shed
Depa
rtmen
t or
Regio
nal
Sewe
rage
Distri
ct
Desig
n
Guide
lines
for
New
Conts
tructi
on &
Retro
fits
Density
bonus
or
require
ments
for
develo
pers,
incentiv
es for
homeo
wners
Y
N
?
Y
Y
N
Y
Y
Y
N
Y
N?
Y
Y
Y
N
N
?
Y
N
Y
Y
Y
Y
N
Y?
N
Y
N
INFRASTRUCTURE
Stor
mwat
er
Utility
and
Fees
base
d on
Imper
vious
Area
Gre
en
Roof
s
Rain
garde
ns/Ve
getat
ed
Swals
&
Land
scape
featur
es
Per
me
abl
e
Pav
em
ent
Down
spout
Disco
nnect
ion/R
ainw
ater
Colle
ction
Overall
rating:
1(begin
ning
stages)
-5
(strong,
compre
hensive
approac
h)
N
N
Gree
nway
s/Wet
lands
/Ripa
rian
Prote
ction/
Urba
n
Fores
ts
Y
Y
N
Y
Y
Y
Y
Y
Y
N
2
1
N
N
N
N
1
?
Y
Y
Y
Y
Y
N
N
N
1.5
N
N
N
N
N
N
N
N
1
Y
Y
N
N
Y
N
Y
N
Y
N
Y
N
N
Y
Y
1
1.5
Y
N
N
Y
Y
N
Y
Y
N
Y
Y
N
Y
N
N
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
N
Y
Y
Y
Y
1
2
1.5
2
N
Y
N
N
N
Y
N
Y
N
Y
N
Y
N
N
N
Y
N
N
N
N?
propo
sed
N
Y
N
Y
N
N
N
N
Y
Y
N
N
Y
Y
Y
N
N
Y
N
Y
N
N
N?
Y
N
1
1
1
2
1
N
Gray
infras
tructu
re:
Deep
stora
ge
tunne
ls
Infrastructure Investment
Infrastructure investment refers to the physical structures that
cities build to manage stormwater. Historically, cities have
used gray infrastructure to rapidly convey water away from the
city; now, more cities are looking towards natural drainage
7
systems as a more sustainable system. In theory, green
stormwater management works because the aggregate of
strategically located systems detain, filter, and slowly release
rainwater, thereby alleviating the rapid conveyance of polluted
runoff towards sewers and, during heavy storms, water bodies. In
other words, green infrastructure for stormwater involves
applying principles of landscape ecology to the urban built
environment (Ahern 2007).
One of the problems that cities struggle with is how to design
for both frequent storms with relatively light levels of
rainfall, and extreme storm events, which test the capacity of
the sewer system and potentially lead to CSO events or flooding.
In many cities that have long deferred investment in sewer
infrastructure, the prospect of installing larger sewers is an
expensive and slow undertaking. By contrast, green
infrastructure approaches provide above-the-ground benefits and,
because the scale of construction is smaller, come on line
sooner. Common green infrastructure interventions include
surface infiltration practices (e.g., infiltration basins),
subsurface infiltration systems (e.g., infiltration trenches),
gravel wetland systems, bioretention systems, water quality
swales, porous pavement systems, wet ponds, and extended dry
detention ponds, all of which the EPA has evaluated for
performance in particular climatic conditions (EPA 2008).
Although green infrastructure approaches, as an alternative, are
ideal for mitigating runoff from small, frequent storm events,
they generally are not sufficient to absorb runoff from extreme
storm events. Under NPDES requirements for long-term CSO
mitigation plans, cities must eliminate 85 percent of CSO
events. To meet this requirement, many cities are exploring
hybrid approaches that mix the known engineering solutions –
increasing storage capacity with pipes or tunnels – to address
the extreme storm events, along with natural drainage systems to
soak up runoff from routine smaller storms.
Many cities are undertaking massive infrastructure projects
oriented towards updating aging sewer infrastructure, and some
are embracing green-infrastructure projects. On one end of the
spectrum is the construction of deep tunnels and reservoirs to
detain stormwater during extreme events. These systems are
designed to hold excesses of stormwater runoff until the
treatment facility is able to treat and release it. Such
8
projects are expensive, and typically preclude significant
investment in green infrastructure systems. Cities often pair
gray infrastructure investment approaches with –such as design
guidelines—to influence on-site stormwater management
approaches, including permeable pavements, rain barrels, green
buildings, and green roofs.
In other cases, notably in the wet climate of the Pacific
Northwest, green infrastructure projects have been successful
for managing street runoff through green street designs and
infiltration planters. Such street-level projects integrate
effective water management with thoughtful and beautiful
designs, and many other U.S. cities are pursing innovative green
street design concepts.
9
10
Regulation: Codes, Fees, and Incentives
Codes and regulations that address stormwater management take a
variety of forms, all aimed at influencing the behavior of
cities, private developers, and individual property owners.
First, many cities have created stormwater utilities, which are
responsible for managing stormwater systems and levying fees
against each property’s contribution of stormwater runoff to the
sewer system. Many cities now calculate these fees according to
the quantity of impervious area per property, because more
impervious area contributes more runoff. When the fees are based
on this area calculation, the distribution of costs is
considered to be more fair than simply levying a fee based on
the total square footage of a property, for example, and also
creates an incentive for property owns to decrease the amount of
impervious cover on their land.
Another common approach is for cities to establish design
guidelines for new development. Cities use design guidelines to
require new construction to manage 100 percent of the stormwater
generated from a site, for example, and might simultaneously
reward the inclusion of green infrastructure elements—such as
green roofs, rain gardens, or permeable pavement—with a zoning
bonus or increased floor-area-ratio (FAR) allowance. Design
guidelines often provide information for developers to learn
about specific green infrastructure interventions and how to
install them. Cities that charge stormwater fees based on
impervious area have an incentive to complement those fees with
information on sensitive water design. Such policies aim to
affect the parcel-by-parcel decision-making of individual
property owners in order to transform the city (Hill 2007).
Many cities are updating their regulations to encourage
innovative approaches to building and redevelopment. For
example, Seattle’s revised (2009) stormwater code requires green
infrastructure to be incorporated into development projects to
the maximum extent feasible, while Philadelphia’s Wet Weather
Source Control Program creates land-based regulations that
require new development to capture the first one inch of
rainfall through the landscapes. Austin’s Stormwater Treatment
Program specifies design guidelines and requires stormwater BMPs
for new development. Los Angeles is currently creating similar
LID-oriented regulations.
11
Rain barrel and downspout disconnection programs are based on an
incentive system to encourage private property owners to
individually contribute to reducing stormwater flows into the
sewer systems. In Philadelphia’s Rain Barrel Program, the city
offered free rain barrels to resident to connect to individual
gutter downspouts. Chicago also encourages homeowners to
disconnect downspouts to reuse water for landscape applications,
while Portland offers a $53 incentive per downspout disconnected
from the combined sewer system. As of 2006, 45,000 households
were participating in the program.
Seattle charges stormwater fees based on the impervious area of
a property; Philadelphia is launching a similar program that
targets commercial users, at first, and will later scale up to
include residential customers. The revenues from these
stormwater utility fees then fund the utility’s operations and
infrastructure projects.
Watershed protection and restoration
Some cities have invested in watershed protection and
restoration, an approach that relies on landscape preservation
for natural drainage, ecological sustainability, and aquatic
health. This approach, while relevant to stormwater management
and water quality, is discussed in more depth in the Landscape
Ecology memo.
In Pittsburgh, a watershed program led by a collaboration
between the city and a non-profit group, the Nine Mile Run
Watershed Association, aims to restore one of the last daylit
streams in the city. The stream is currently heavily degraded by
stormwater discharges. The project involves creating a wetland
buffer to provide habitat and filtration, physically reversing
the channelization of the stream, and taking steps to reduce the
flow of runoff pollution into the waterway. Community groups
commissioned a study that determined that an extensive rain
barrel program would be the most effective approach to reduce
runoff, and, coupled with education about restoration and longterm maintenance, the city aims to create a model for watershed
stewardship.
Philadelphia is also framing much of its localized stormwater
management efforts in terms of watershed protection of urban
streams: this conceptual shift suggests a broader scope for
12
management that locates distributed projects as contributing to
the larger watershed protection goals.
Education
Finally, all programs involve some education component, which
aims to raise awareness about particular programs or
interventions in order to change individual behaviors.
Education-oriented programs take several forms, the most common
of which is Catch Basin Stenciling (Boston, Seattle, Houston),
while Los Angeles launched a marketing campaign that advertised
the city’s Environmental Monitoring and Watershed Protection
divisions in bus shelter ads.
Another aspect of education is monitoring, which is required
under NPDES regulations. Community monitoring by citizens’
groups raises awareness.
Governance
Lastly, cities may make chances in governance procedures or
processes to promote more effective stormwater management.
Cities deserve credit for improving the integration and
coherence of land-use and water-related programs to help promote
holistic and sustainable water management.
Cities typically cede responsibility for water management—
providing drinking water, removing and treating wastewater, and
managing wet weather flows—to a specialized water utility. These
utilities can be a regional water and/or sewage district, multifunctional watershed district, or groundwater management
district, and usually manage several, but not all, aspects of
the urban water environment (Baker, Shanahan, and Holway 2009).
Some utilities do house all municipal water-related functions,
an arrangement that may ease the path towards promoting
innovative green infrastructure programs: the Seattle Public
Utilities and the Philadelphia Water Department, for example,
operate combined drinking water, wastewater, and stormwater
utilities, and both have undertaken ambitious greeninfrastructure projects (PWD 2009; City of Seattle 2010).
Analysis: How Effective Are Cities’ Programs, and Why?
More research is needed to evaluate the long-term performance of
many green infrastructure interventions on their urban
watersheds, and cities are essential partners to enable long13
term comparative studies (Pickett 2009). As the National
Research Council (2008, 7) notes, “Although the state of
knowledge has yet to reveal the mechanistic links that would
allow for a full assessment of that relationship, enough is
known to design systems of SCMs, on a site-scale or local
watershed scale, that can substantially reduce the effects of
urbanization.”
Cities combine strategies in different ways, establishing a
framework for water quality management at a regional level and
via distributed pieces of infrastructure throughout the built
environment. Our analysis seeks to evaluate spatial
characteristics, such as the regional setting, historical
infrastructure (to establish a baseline), and new engineering
efforts, as well as policy incentives, guidelines, or penalties
that affect citizens’ behaviors, and the institutional factors
that make those programs sustainable. Currently, most cities
efforts to adopt green infrastructure approaches to stormwater
are modest. Thus, analysis seeks to develop a the rating system
to credit these promising initial steps and to reflect that the
stormwater plans and programs must be scaled up substantially if
they are to advance cities’ sustainability.
14
References
Ahern, Jack. 2007. Green Infrastructure for Cities : The Spatial
Dimension In Cities of the Future : Towards Integrated
Sustainable Water and Landscape Management, edited by V.
Novotny and P. R. Brown. London: IWA Publishing.
Baker, Lawrence A., Peter Shanahan, and Jim Holway. 2009.
Principles for Managing the Urban Water Environment in the
21st Century. In The Water Environment of Cities, edited by
L. A. Baker. New York: Springer.
Berghage, Robert. Green Roofs for Stormwater Runoff Control.
National Risk Management Research Laboratory, Office of
Research and Development, U.S. Environmental Protection
Agency 2009 [cited. Available from
http://purl.access.gpo.gov/GPO/LPS115140.
Booth, D. B., D. Hartley, and R. Jackson. 2002. Forest Cover,
Impervious-Surface Area, and the Mitigation of Stormwater
Impacts. Journal of the American Water Resources
Association 38:835-846.
Booth, Derek B., and Brian P. Bledsoe. 2009. Streams and
Urbanization. In The Water Environment of Cities, edited by
L. A. Baker. New York: Springer.
Brabec, Elizabeth, Stacey Schulte, and Paul L. Richards. 2002.
Impervious Surfaces and Water Quality: A Review of Current
Literature and Its Implications for Watershed Planning.
Journal of Planning Literature 16 (4):499-514.
City of Seattle. 2010. Seattle Public Utilities: Natural
Drainage Projects 2010 [cited March 25 2010]. Available
from
http://www.seattle.gov/util/About_SPU/Drainage_&_Sewer_Syst
em/GreenStormwaterInfrastructure/NaturalDrainageProjects/in
dex.htm.
Clar, Michael L., Billy J. Barfield, and Thomas P. O'Connor.
2004. Stormwater Best Management Practice Design Guide.
Washington, DC: National Risk Management Research
Laboratory, Office of Research and Development, U.S.
Environmental Protection Agency.
Hill, Kristina. 2007. Urban Ecological Design and Urban Ecology
: An Assessment of the State of Current Knowledge and a
Suggested Research Agenda. In Cities of the Future :
Towards Integrated Sustainable Water and Landscape
Management, edited by V. Novotny and P. R. Brown. London:
IWA Publishing.
15
Jacob, John S., and Ricardo Lopez. 2009. Is Denser Greener? An
Evaluation of Higher Density Development as an Urban
Stormwater-Quality Best Management Practice. Journal of the
American Water Resources Association 45 (3):687-701.
Kloss, Christopher, Crystal Calarusse, Nancy Stoner, and Natural
Resources Defense Council. 2006. Rooftops to Rivers : Green
Strategies for Controlling Stormwater and Combined Sewer
Overflows. New York, NY: Natural Resources Defense Council.
National Research Council (U.S.), and National Academies Press
(U.S.). 2008. Urban Stormwater Management in the United
States. Washington D.C.: National Academies Press.
———. 2009. Urban Stormwater Management in the United States.
Washington D.C.: National Academies Press.
Paul, Michael J., and Judy L. Meyer. 2001. Streams in the Urban
Landscape. Annual Review of Ecology and Systematics 32:333365.
Philadelphia Water Department (PWD). 2009. Green City, Clean
Waters: The City of Philadelphia's Program for Combined
Sewer Overflow Control; a Long Term Control Plan Update.
Philadelphia.
Roy, Allison, Seth Wenger, Tim Fletcher, Christopher Walsh,
Anthony Ladson, William Shuster, Hale Thurston, and Rebekah
Brown. 2008. Impediments and Solutions to Sustainable,
Watershed-Scale Urban Stormwater Management: Lessons from
Australia and the United States. Environmental Management
42 (2):344-359.
Spirn, Anne Whiston. 1984. The Granite Garden : Urban Nature and
Human Design. New York: Basic Books.
Sustainable Sites Initiative. 2009. The Sustainable Sites
Initiative: Guidelines and Performance Benchmarks.
http://www.sustainablesites.org/report.
United States Environmental Protection Agency. 2004. Report to
Congress Impacts and Control of CSOs and SSOs. Washington,
DC: U.S. Environmental Protection Agency, Office of Water.
16