1. Chapter 7
Green Infrastructure
A. Introduction
“Green infrastructure” refers to natural and engineered ecological systems
that act as living infrastructure, integrating natural vegetation and soils into a
community’s infrastructure through a variety of techniques, approaches,
technologies, and practices. Green infrastructure is planned and managed primarily
for stormwater control, but it also provides additional social, economic, and
environmental benefits. It can be a useful tool for communities that are looking to
protect their natural water resources and stormwater management systems from
the impacts of development and urbanization. Green infrastructure methods can be
implemented practically anywhere soil and vegetation can be worked into a
landscape.
Source: Southeast Watershed Forum
Figure 7-1: Bioretention is one typical method used in green infrastructure.
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2. B. Types of Green Infrastructure
Communities may choose from a wide variety of green infrastructure
techniques. The choice of which techniques to employ and where to locate them is
dependent on site specifications and the goals the community wishes to accomplish.
Specific types of green infrastructure include:
1. Green Roofs
Green roofs are roofs of buildings that are covered with vegetation and soil,
either partially or completely. Green roofs are layered systems, with a waterproof
membrane, drainage mat, root barrier, growing medium, and vegetation.
Evaporation of water occurs due to the exposure of the plants and growing medium
to wind and sun, and the plants transpire moisture into the air. This helps to cool
the roof. It is vital that plants are chosen for the environment in which the roof is
located. It is also important to promote slow to moderate growth of the plants, so
that they are in balance with their root systems during dormant winter periods.
Green roofs can aid in stormwater management and can save energy. They are also
aesthetically pleasing.
Source: Louisville Metro Development Center
Figure 7-2: Green Roof Design
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3. 2. Rain Gardens
Rain gardens, also called bioretention basins, are planted topographic
depressions that are designed to absorb rainwater that drains from impervious
areas, such as roofs, parking areas, streets, walkways, and compacted lawn areas.
Rain gardens reduce runoff because the stormwater soaks into the ground instead
of flowing into storm drains and surface waters. This can help decrease erosion,
water pollution, and flooding, and can help to recharge groundwater sources. The
Rain Garden Network provides a 10‐step synopsis of how to build a rain garden.
This information is available at http://www.raingardennetwork.com/build.htm.
Additionally, Burnsville, Minnesota has implemented a plan to install a rain garden
system to infiltrate stormwater runoff that serves as an excellent example of
utilizing this type of green infrastructure (City of Burnsville 2006).
Source: Southeast Watershed Forum
Figure 7-3: Rain Garden.
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4. 3. Porous and Pervious Pavements
Porous and pervious pavements, also called permeable pavements, are
paving methods that allow rainwater to infiltrate through them into the soil below.
These pavements can be used for roads, parking lots, and walkways instead of
traditional impervious pavements, which increase flow velocity of stormwater
runoff. Porous asphalt, concrete, paving stones, and bricks are examples of pervious
pavements.
Source: Southeast Watershed Forum
Figure 7-4: Pervious Pavement.
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5. 4. Vegetated Swales
Vegetated swales, also known as bioswales, are wide, shallow channels that
are covered on the side slopes and bottom by a dense stand of native vegetation.
Vegetated swales are designed to promote infiltration, reduce the flow velocity of
stormwater runoff, and trap particulate pollutants and silt. They can be either
natural or constructed, and are often used around parking lots so that pollution
from automobiles that is picked up in stormwater can be treated before entering the
watershed.
Source: Southeast Watershed Forum
Figure 7-5: Vegetated Swale.
5. Pocket Wetlands
Pocket wetlands receive, retain, and treat stormwater that has drained from
a limited impervious area. Not only do they reduce stormwater runoff, but they also
provide for the filtering of pollutants. Additionally, pocket wetlands are
aesthetically pleasing and can even serve as a small wildlife habitat. Pocket
wetlands do not require as much space as other stormwater treatment, so they can
be very helpful in congested urban areas.
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6. 6. Planter Boxes
There are two types of planter boxes, contained planters and infiltration
planters. Contained planters are planter boxes that are placed over impervious
surfaces. They hold trees, shrubs, and ground cover. Infiltration planters are
containers or structures with open bottoms that contain a layer of gravel, soil, and
vegetation. They are designed to allow stormwater runoff to temporarily pool on
top of the soil and then slowly infiltrate into the ground. Stone, concrete, brick,
plastic lumber, or wood can all be used to construct infiltration planters. Portland,
Oregon provides an excellent example of utilizing planter boxes for stormwater
management (City of Portland, 2004, pp. 49‐60).
7. Green Parking
Green parking refers to parking lot design that incorporates green
infrastructure instead of only considering purely functional requirements. Green
parking involves managing stormwater on‐site, providing generous landscaped
areas, planting trees, enhancing pedestrian and cycling infrastructure, and reducing
the urban heat island effect. Toronto has implemented a plan for “greening” surface
parking lots (City of Toronto 2007).
Source: Rosetta Fackler
Figures 7-6 to 7-9: A green parking lot design at a Walmart in Nashville, TN.
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7. 8. Rain Barrels
Rain barrels, also called rainwater tanks, are water containers that are used
to collect and store rain water. The rainwater is usually collected from rooftops via
rain gutters. Rain barrels help to reduce the amount of untreated stormwater runoff
into wastewater systems and surface waters. The water stored in rain barrels can
be recycled for many uses, including water gardens, washing cars, agriculture, and
home use. They can also simply store stormwater to be released at a future time.
9. Downspout Disconnection
Downspout disconnection systems redirect stormwater from traditional
collection systems to vegetated areas. By doing so, green infrastructure components
can manage the runoff and stormwater volume is removed from collection systems.
10. Community Forestry and Trees
Trees and forests are essential elements of a community’s green
infrastructure. These include not only public and private forest lands but also
community forests: the canopy of trees in our communities’ yards, parks, roadsides
and streetscapes, commercial centers, common areas, and public spaces. They
provide many environmental and economic benefits to property owners,
communities, and watersheds. The benefits of trees and community forests to water
resources include:
“Tree root networks filter contaminants in soils producing clean
water.
Trees prevent erosion by trapping soil that would otherwise
become silt. Silt destroys fish eggs and other aquatic wildlife and
makes rivers and streams shallower, causing more frequent and
more severe flooding. Trees along streams also hold stream banks
in place to protect against flooding.
Trees reduce topsoil erosion, prevent harmful land pollutants
contained in the soil from getting into our waterways, slow down
water runoff, and ensure that our groundwater supplies are
continually being replenished. For every 5% of tree cover added
to a community, stormwater runoff is reduced by approximately
2%.
Studies that have simulated urban forest effects on stormwater
report annual runoff reductions of 2‐7%.
In one study, a 32‐foot tall tree intercepting rainfall reduced
stormwater runoff by 327 gallons.” (Southeast Watershed Forum,
p. 2)
In addition to water‐based benefits, trees and community forests provide air
quality, climate moderation, energy conservation, and wildlife habitat benefits
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8. (Southeast Watershed Forum, pp. 2‐3). “According to USDA Forest Service, trees
and vegetation reduce stormwater discharge by up to 40%, reduce home heating
and cooling costs by up to 30%, increase the value of property by up to 20%, and
reduce particulate airborne pollution by up to 80%.” (Stormwater Manager’s
Resource Center 2006) In particular, the economic benefits are many. These
economic benefits to property owners, businesses, and communities, according to
studies, include:
“Trees enhance community economic stability by attracting
businesses and tourists.
People linger and shop longer along tree‐lined streets.
Apartments and offices in wooded areas rent more quickly and
have higher occupancy rates.
Businesses leasing office space in developments with trees find
their workers are more productive and absenteeism reduced.
Three trees located strategically around your house can cut air
conditioning bills in half. On a larger scale, the cooling effects of
trees can save millions of energy dollars.
Property values of homes with trees in the landscape are 5% to
20% higher than equivalent properties without trees.” (Southeast
Watershed Forum, p. 1)
Moreover, studies show that the benefits of large trees are 4 to 16 times the benefits
of small trees, depending on whether the benefits are analyzed over a short term or
a long term and whether only benefits to the landowner are analyzed or whether
benefits to the entire community are analyzed (Southeast Watershed Forum, p. 3).
Communities can do many different things to establish or protect trees as
green infrastructure. First, communities can establish a tree canopy goal as part of
their comprehensive plan. Studies recommend that healthy cities should seek to
have at least 40% tree coverage, which is an average of 20 large trees per acre, in
order to achieve ecological, economic, and social sustainability (Southeast
Watershed Forum, p. 1). Second, communities should establish a community
forestry program that supports both public and private efforts to provide, maintain,
and manage local tree canopies. Whether or not a part of a community forestry
program, government agencies should landscape public lands and facilities with
watershed‐sustaining trees and invest in maintaining those trees. Third,
communities can use their codes and ordinances to protect existing trees and
require tree planning and maintenance on development sites. Fourth, communities
can establish watershed reforestation projects that prioritize sites for reforestation
under a comprehensive watershed forest management plan (Stormwater Manager’s
Resource Center 2006).
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9. Case Study in Community Forestry: Fayetteville, Arkansas
(Source: NALGEP et al. 2003, p. 21)
“A number of communities across the nation are partnering with groups like
American Forests to identify how the “green infrastructure” of trees can help reduce
stormwater runoff and nonpoint source pollution, protect the quality of surface and
groundwater, save localities millions of dollars in gray infrastructure costs, and
meet the regulatory mandates of storm‐water and TMDL rules. One such
community is the fast‐growing City of Fayetteville, Arkansas, where American
Forests recently released a study demonstrating the environmental and economic
benefits of maintaining – and increasing – local tree cover.
In Fayetteville, rapid
growth and development has led
to an 18 percent decline of
heavy tree canopy in the last 15
years. American Forests
recently conducted an “Urban
Ecosystems Analysis” using
satellite and aerial imagery,
Geographic Information System
technology, scientific research,
and the organization’s
CITYgreen® computer software
to calculate the benefits trees
provide to Fayetteville’s urban
environment. The findings
show that the City of
Fayetteville’s existing tree cover
currently reduces stormwater
runoff by 50 million cubic feet
during a storm event. The study
also noted that, if the tree
canopy in Fayetteville were
increased from 27 to 40 percent,
the environmental benefits
Source: Tony Arnold
would be significant and the cost‐
saving benefits of stormwater Figure 7-10: Forest in Kentucky.
reduction alone would be $135
million.” (NALGEP et al. 2003, p.
21)
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10. 11. Protecting Riparian Lands, Wetlands, Floodplains, and Native Landscapes
Nature has already provided much of the green infrastructure that we need
in the forms of riparian zones (often with trees and other vegetation), wetlands,
floodplains, and native vegetation. Forest, discussed above, and native grasslands
also are naturally provided green infrastructure. Unfortunately, much of it has been
lost to human land‐alteration activities and what remains is at risk of alteration or
degradation. Therefore, a critical green infrastructure strategy is to preserve and
protect nature’s green infrastructure, while also restoring that which has been lost.
Source: Linda Pearsall
Figures 7-11 and 7-12: Wetland and Riparian Zone.
12. Specific Examples of Green Infrastructure Features
in Particular Development Settings
The following provides some examples of how these types of green
infrastructure can be utilized in particular settings (WERF 2007):
Streetscape and roadway projects
- Add tree boxes or infiltration gardens to capture street runoff.
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11. - Design medians as infiltration areas.
- Use porous pavement for parking lanes.
Commercial areas with significant parking
- Drain roofs to gardens, planters, or parking islands and
medians.
- Use permeable pavement in low‐traffic areas.
- Drain parking to grass buffers and vegetated swales.
Small infill building sites or retrofits
- Install a green roof for buildings and parking structures.
- Install permeable pavement in courtyards and plazas.
- Drain roofs to grass buffers or swales.
Residential areas
- Drain roofs to rain gardens, grass swales, and grass buffers.
- Drain driveways, walkways, and patios to adjacent rain
gardens or grass buffers.
- Construct driveways using permeable pavement.
Examples of green infrastructure and policies supporting green
infrastructure can be found on the following websites:
Center for Neighborhood Technology, Green Infrastructure,
http://greenvalues.cnt.org/green‐infrastructure
State Environmental Resource Center, Green Infrastructure Policy Issues
Package, http://www.serconline.org/grInfrastructure/index.html
U.S. Environmental Protection Agency, Managing Wet Weather with
Green Infrastructure,
http://cfpub.epa.gov/npdes/home.cfm?program_id=298
Water Environment Research Foundation, Livable Communities,
http://www.werf.org/livablecommunities
C. Choosing Green: The Benefits of Green Infrastructure
Green infrastructure can provide a variety of environmental, economic, and
social benefits. These benefits can be especially pronounced in developed area
because environmental damage is usually greater and green space more limited in
these locales. The benefits of green infrastructure include:
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12. 1. Green infrastructure improves water quality.
Green infrastructure reduces the concentration of pollutants in stormwater
runoff. It does so by causing runoff to infiltrate close to its source, thus helping to
prevent pollutants from being transported to surface waters. Additionally, plants
and microbes can naturally filter and breakdown stormwater pollutants in
infiltrated runoff.
2. Green infrastructure reduces and delays stormwater runoff volumes.
Green infrastructure utilizes the natural retention and infiltration
capabilities of vegetation and soils to naturally retain and absorb stormwater, thus
reducing the volume of stormwater runoff, as well as reducing stormwater runoff
peak flows. Green infrastructure also increases the amount of pervious ground
cover, which in turn increases stormwater infiltration rates. This also reduces the
volume of runoff. By reducing runoff volumes and peak flows entering surface
water bodies and wastewater systems, green infrastructure limits the frequency of
flooding and system overflow events.
3. Green infrastructure improves air quality.
Green infrastructure contributes to improved air quality. Vegetation and
trees absorb pollutants from the air, thus filtering many airborne pollutants. They
also cool the air, leading to decreased ground‐level ozone pollution.
4. Green infrastructure enhances water supplies.
Green infrastructure increases natural infiltration, thus improving the rate at
which groundwater aquifers are replenished. Improved groundwater recharge can
enhance private and public drinking water supplies, and can help to maintain
normal base flow rates for streams and rivers. In addition, green infrastructure
techniques that capture and use stormwater help to conserve water supplies.
5. Green infrastructure reduces energy demands
and increases energy efficiency.
The increased amounts of green space and vegetation provided by green
infrastructure in developed areas can reduce energy demands because they mitigate
the urban heat island effect, thus lowering temperatures. This can also lower the
demand for air conditioning energy, thus decreasing power plant emissions. If
incorporated on and around buildings, green infrastructure can help with shade and
insulation, thus decreasing the energy that is needed for heating and cooling.
Additionally, diverting stormwater from wastewater systems reduces the energy
needed to pump and treat the water. All of this reduces energy costs to businesses,
governments, and community residents.
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13. 6. Green infrastructure improves human health.
Green infrastructure can play a vital role in improving human health. A large
number of studies show that green space and vegetation can positively impact
human health, including reduced levels of inner‐city crime, a stronger sense of
community, and reduced symptoms associated with attention deficit and
hyperactivity disorders (U.S. EPA 2009).
7. Green infrastructure enhances communities and neighborhoods.
Green infrastructure can improve the aesthetics of a community because of
the increase in trees and plants. It also provides increased access to recreational
space and wildlife habitats, thus improving community livability. Community
cohesiveness can be enhanced by involving residents with the planning,
implementation, and maintenance of green infrastructure sites. Additionally, a
number of studies show that green infrastructure can increase the property values
in the surrounding area (U.S. EPA 2009).
8. Green infrastructure moderates the impacts of climate change.
Green infrastructure can benefit adaptability for a wide range of
circumstances that result from climate change impacts. This adaptability is possible
because green infrastructure can conserve and reuse water, promote groundwater
recharge, and reduce surface water discharges that can cause flooding. Additionally,
the vegetation utilized in green infrastructure can serve as sources of carbon
sequestration, thus capturing carbon dioxide from the atmosphere.
9. Green infrastructure saves money.
Green infrastructure can save capital costs associated with building,
operating, and maintaining traditional forms of infrastructure. The costs of
repairing damage caused by stormwater can also be avoided.
D. Implementing Green Infrastructure in Projects
Once a community has decided that utilizing green infrastructure may be an
option, it must then assess if this is the best option. One method that can be used
when determining whether, or where, to incorporate green infrastructure is “value
engineering.” This approach allows for a comparison of the costs and values of green
infrastructure with that of traditional infrastructure. “Value engineering” enables a
community to consider the relative costs and benefits of the components of a
project, and then suggests where changes may be made to provide more value for
less cost.
The “value engineering” approach involves the following steps (WERF 2007):
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14. Identify elements of value or benefit that can be used to measure and
compare project components. Factors that can be considered when
identifying elements of value or benefit are land area requirements
for flood storage and water quality treatment, allowable or desired
runoff volume, on‐site water use requirements, groundwater recharge
needs, landscape amenities opportunities, creation of habitat, and
recreation opportunities.
Develop a schematic of the project using traditional forms of
infrastructure, and estimate the value or benefit provided, along with
capital and life cycle costs.
Develop an alternative schematic of the project using green
infrastructure, and estimate value and costs of each component.”
Compare the two different approaches to identify which provides the
best value. This is not strictly a cost‐based analysis.
Once it is decided that a green infrastructure approach will be utilized, and
projects begin to be planned, the following principles and practices can help to
ensure that a green infrastructure project succeeds:
Establish an interdisciplinary team at the beginning of the project.
This group should include, among others, community leaders, the
project owner, review agencies, engineers, and landscape architects.
Work to ensure that this team remains together through
implementation of the project.
Understand the regulatory and development review environment.
Understand which Best Management Practices work best in which
development settings.
Understand the context in which the project will be placed. The type
of project, as well as its aesthetic qualities, should reflect surrounding
land uses and neighborhood character.
Design the project to mimic the natural environment.
Design sustainable projects that can be easily maintained (WERF
2007).
E. Implementing Green Infrastructure in Local Policies and Codes
Green infrastructure is a matter of public policy, as well as landowner and
developer choices. In general, when a community has determined that green
infrastructure would be beneficial, certain policy recommendations can be used to
encourage the use of green infrastructure:
get development right the first time;
incorporate green infrastructure into long‐term control plans for
managing combined sewer overflows;
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15. revise state and local stormwater regulations to encourage green
design;
establish dedicated funding for stormwater management that rewards
green design;
provide incentives for residential and commercial use of green
infrastructure;
review and revise local development ordinances;
preserve existing trees, open space, and stream buffers;
encourage and use smart growth; and
get the community involved (NRDC 2006, pp. 13‐15).
More specifically, though, incorporating green infrastructure into wet growth
policies requires attention to local codes and ordinances. Although some of a
community’s green infrastructure will result from public projects (e.g., government
buildings and facilities, landscape design and management along roads and
highways, and wetlands or stream restoration initiatives) or from the management
of public lands (including parks, nature areas, and recreational facilities, wet growth
policies also include the creation of green infrastructure on private lands.
Community officials and stakeholders should analyze their local codes and
ordinances to determine whether they:
allow green infrastructure as part of new or existing land uses;
encourage green infrastructure as part of new or existing land
uses; and
require green infrastructure as part of new or existing land uses.
First, a community’s land development codes and ordinances might directly
or indirectly prohibit landowners and developers from using green infrastructure
and therefore need to be changed. Examples might include: 1) minimum lot sizes or
setback requirements that prevent clustering of structures and preservation of
existing natural features of development sites; 2) barriers to shared ownership and
management of swales, wetlands, and other green infrastructure; 3) requirements
that structures connect downspouts directly to the stormwater sewer system; 4)
roof design or structural requirements that do not allow for green roofs; or 5)
parking requirements that prevent green parking lot design, among other
regulatory requirements. These provisions should be analyzed and amended to
allow green infrastructure.
Second, a community’s land development codes and ordinances can actually
facilitate decisions by landowners and developers to use green infrastructure.
These might include density bonuses or other development bonuses (e.g., parking
bonuses, height bonuses, streamlined/fast‐track permitting processes) for certain
especially valuable or extensive green infrastructure features of a development
project beyond normal requirements. They might include rebates of or reductions
in stormwater or sewer service or hook‐up fees for certain green infrastructure
features that minimize runoff. They might include relief from landscaping
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16. requirements if existing mature trees and other existing natural landscape features
are retained. Local communities should analyze their codes and ordinances for
opportunities to add incentives that encourage green infrastructure.
Third, communities should consider requiring landowners and developers to
use green infrastructure features, especially for new development. Examples
include 1) tree preservation ordinances; 2) minimum tree canopy and/or
landscaping requirements; 3) prohibitions on development of wetlands, riparian
buffer zones, natural forests, native grasslands, or similar watershed‐supporting
lands; 4) maximum site coverage ratios; and 5) requirements that developers select
from a menu of green‐infrastructure best management practices (BMPs) in
designing and developing sites, among other possible regulatory requirements.
Protecting or requiring green infrastructure by regulation can be necessary, because
developed sites without adequate stormwater management are imposing the costs
and harms of their land uses onto neighbors, other property owners, businesses,
government agencies, taxpayers, and the public. Private property rights, even from
highly libertarian or free‐market perspectives, have never allowed landowners to
use their land in ways that harm others or transfer the costs of their land uses to
others (i.e., known by economists as “negative externalities”), which is what is
happening when developed land has high quantities, velocities, and/or pollution‐
levels of runoff flow. However, protections of existing green infrastructure and
regulations requiring harm‐preventing green infrastructure – especially when
landowners can choose among a variety of green infrastructure methods – are
cheaper, more efficient, and more effective at preventing harms (and externalized
costs) for all relevant parties than the alternative ways of remedying these harms:
litigation or fines. Regulatory methods and examples are discussed further in
Chapter 12. In addition, Chapter 5 explores how green infrastructure might be
incorporated into low impact development standards.
Sources:
Center for Neighborhood Technology. Green Infrastructure. Available at
http://greenvalues.cnt.org/green‐infrastructure.
City of Burnsville, Minnesota. 2006. Burnsville Stormwater Retrofit Study.
Available at http://www.ci.burnsville.mn.us/DocumentView.asp?DID=449.
City of Portland, Oregon. 2004. 2004 Stormwater Management Manual, Chapter 2,
Stormwater Management Facility Design. Available at
http://www.portlandonline.com/shared/cfm/image.cfm?id=55791&#page=49.
City of Toronto. 2007. Design Guidelines for “Greening” Surface Parking Lots.
Available at
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