<>EPA
United States
Environmental Protection
Agency
2012 GREEN INFRASTRUCTURE TECHNICAL ASSISTANCE PROGRAM
City of Beaufort, Planning Department
Beaufort, South Carolina
>
X-SSSSSx
Block-Scale Green Infrastructure Design for the
Historic Northwest Quadrant, City of Beaufort
Photo: Morris Street, City of Beaufort
AUGUST 2013
EPA 830R13006
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About Green Infrastructure Technical Assistance Program
Stormwater runoff is a major cause of water pollution in urban areas. When rain falls in undeveloped areas, the
water is absorbed and filtered by soil and plants. When rain falls on our roofs, streets, and parking lots, however,
the water cannot soak into the ground. In most urban areas, Stormwater is drained through engineered collection
systems and discharged into nearby waterbodies. The Stormwater carries trash, bacteria, heavy metals, and other
pollutants from the urban landscape, polluting the receiving waters. Higher flows also can cause erosion and
flooding in urban streams, damaging habitat, property, and infrastructure.
Green infrastructure uses vegetation, soils, and natural processes to manage water and create healthier urban
environments. At the scale of a city or county, green infrastructure refers to the patchwork of natural areas that
provides habitat, flood protection, cleaner air, and cleaner water. At the scale of a neighborhood or site, green
infrastructure refers to Stormwater management systems that mimic nature by soaking up and storing water. These
neighborhood or site-scale green infrastructure approaches are often referred to as low impact development.
EPA encourages the use of green infrastructure to help manage Stormwater runoff. In April 2011, EPA renewed
its commitment to green infrastructure with the release of the Strategic Agenda to Protect Waters and Build More
Livable Communities through Green Infrastructure. The agenda identifies technical assistance as a key activity
that EPA will pursue to accelerate the implementation of green infrastructure.
In February 2012, EPA announced the availability of $950,000 in technical assistance to communities working to
overcome common barriers to green infrastructure. EPA received letters of interest from over 150 communities
across the country, and selected 17 of these communities to receive technical assistance. Selected communities
received assistance with a range of projects aimed at addressing common barriers to green infrastructure,
including code review, green infrastructure design, and cost-benefit assessments.
Through the assistance provided to the City of Beaufort, South Carolina (City), EPA developed block-scale green
infrastructure designs appropriate for the historic residential community located in the City's Northwest Quadrant.
These designs respect the historic character of the neighborhood while enhancing the pedestrian environment,
adding functional open space, and protecting the Beaufort River and marsh.
For more information, visit http://water.epa.gov/infrastructure/greeninfrastructure/gi_support.cfm
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Acknowledgements
Principal EPA Staff
Anne Keller, USEPA Region 4
Katherine Snyder, USEPA Region 4
Tamara Mittman, USEPA
Christopher Kloss, USEPA
Community Team
Lauren Kelly, City of Beaufort
Isiah Smalls, City of Beaufort
Libby Anderson, City of Beaufort
Monica Holmes, The Lawrence Group
Consultant Team
Jason Wright, Tetra Tech
Merrill Taylor, Tetra Tech
Garrett Budd, Tetra Tech
Neil Weinstein, Low Impact Development Center
Doug Davies, Low Impact Development Center
MI
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Contents
1. Introduction 1
1.1. Benefits of Green Infrastructure 2
2. 3BGI Northwest Quadrant Project Site 4
2.1. Existing Site Conditions 5
2.2. Proposed Site Design 8
3. Goals 8
3.1. Project Goals 8
3.2. Design Goals 9
4. Green Infrastructure Toolbox 9
4.1. Vegetated Green Infrastructure Practices 9
4.2. Permeable Pavement 11
4.3. Stormwater Wetland 12
5. Green Infrastructure Design 13
5.1. Design Elements 13
5.2. Analytical Methods 14
5.3. Recommended Sizing and Layout 15
6. Green Infrastructure Practice Technical Specifications 21
6.1. Common Elements 21
6.2. Bioretention 22
6.3. Permeable Pavement 24
6.4. Vegetated Infiltration Basin 25
6.5. Stormwater Wetland 27
6.6. Stormwater Diversion 29
7. Operations and Maintenance 30
8. Green Infrastructure Practice Cost Estimates 33
9. References 35
Appendix A - Conceptual Design Layouts
Appendix B - EPA SWMM Design Parameters
Appendix C - Charrette Process Review Memo
IV
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Tables
Table 1-1. Studies estimating percent increase in property value from green infrastructure 4
Table 5-1. Subcatchment delineations and runoff volumes 15
Table 5-2. Available area for green infrastructure practices 15
Table 5-3. Green infrastructure practices proposed for redevelopment of Duke Street to treat the 1.95 inch eventl?
Table 5-4. Green infrastructure practice proposed for the southeast corner of Hamar and Prince Street 19
Table 7-1. Vegetated green infrastructure practice operations and maintenance considerations 31
Table 7-2. Permeable pavement operations and maintenance considerations 32
Table 7-3. Stormwater wetland operations and maintenance considerations 32
Table 8-1. Duke Street cost estimate 33
Table 8-2. Vegetated infiltration basin cost estimate1 34
Table 8-3. Annual maintenance cost estimate 34
Figures
Figure 1-1. Site location map 2
Figure 2-1. Northwest Quadrant boundary 5
Figure 2-2. Contributing drainage areas and existing conditions 7
Figure 2-3. 3BGI green street site, east side 8
Figure 2-4. 3BGI vegetated infiltration basin site 8
Figure 4-1. Bioretention incorporated into a parking lot 10
Figure 4-2. Bioretention incorporated into a right-of-way 10
Figure 4-3. Vegetated infiltration basin incorporated into an open space park 11
Figure 4-4. Grass paver parking stalls 12
Figure 4-5. Permeable Interlocking Concrete Paver parking stalls 12
Figure 4-6. Stormwater wetland 13
Figure 5-1. Available green infrastructure practice area on Duke Street 16
Figure 5-2. Required green infrastructure practice area on Duke Street to treat the 1.95 inch event 18
Figure 5-3. Hamar and Prince Street vegetated infiltration basin layout 20
Figure 6-1. Typical bioretention configuration 24
Figure 6-2. Permeable interlocking concrete pavers 25
Figure 6-3. Pervious concrete 25
Figure 6-4. Typical vegetated infiltration basin configuration 27
Figure 6-5. Plan view of the Stormwater wetland zones 28
Figure 6-6. Profile view of the Stormwater wetland zones: (I) Deep Pool, (II) Transition, (III) Shallow Water, (IV)
Temporary Inundation, and (V) Upper Bank 28
Figure 6-7. Typical diversion structure 30
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1. Introduction
In Beaufort, South Carolina, the pristine beauty of the Beaufort River and marsh are essential to the City's
economy and livelihood. In order to ensure that future generations are able to appreciate and experience
Beaufort's natural beauty, City staff and leadership consider the principles of preservation, growth, and
sustainability in each development and infrastructure decision. This commitment to preserving
Beaufort's natural resources for future generations has led the City to embrace the concept of green
infrastructure for stormwater management. In developing their stormwater management program, the
vision of Beaufort's Public Works and Planning Departments is to implement appropriate, low-cost green
infrastructure practices to filter and clean stormwater.
To implement appropriate green infrastructure practices within Beaufort's Northwest Quadrant, the City
has conceived of the Block by Block Green Infrastructure (3BGI) program. The Northwest Quadrant is a
historic residential community with a rich history of planning that seeks to preserve the historic feel of the
community, enhance community amenities, and provide sustainable stormwater management. The City
articulated its vision for maintaining the historic feel of the Northwest Quadrant in the preservation
guidelines adopted in 1999. The goals stated in the guidelines include:
Maintaining the traditional character of the block;
Maintaining the informal nature of the streets, lanes, and gardens where they exist;
Maintaining the soft edges found along neighborhood streets; and
Encouraging informal gardens throughout the neighborhood.
The Neighborhood Strategic Plan, adopted in 2008, includes goals related to stormwater management in
the community. The plan highlights the goals of:
Encouraging the use of rain barrels and greywater recycling;
Supporting community gardens; and
Identifying future pocket park locations.
Given the aesthetic, social, and environmental goals identified for the Northwest Quadrant, the City
determined that block-scale green infrastructure practices would be most appropriate for this community,
and developed the concept of the Block by Block Green Infrastructure (3BGI) program. The US EPA
recognized the unique opportunity to address historic preservation, community open space, and water
quality goals in the Northwest Quadrant and selected the City to receive technical assistance. Through
this technical assistance, EPA developed conceptual designs for two block-scale green infrastructure
interventions in the Northwest Quadrant. One design was developed for the redevelopment of Duke Street
between Ribaut Road and Bladen Street, and a supplementary second design was developed for the
underutilized open space at the southeast intersection of Hamar Street and Prince Street. The project area
is illustrated in Figure 1-1 and will be referred to as the 3BGI Northwest Quadrant Project Site. The
City's vision for the 3BGI Site is to develop a green street corridor along Duke Street as well as a
supplemental vegetated infiltration basin within the open space parcel that preserve the historic feel of the
neighborhood.
This project will provide community space that serves as a stormwater facility, an amenity, and an
educational opportunity for the entire community. The project will serve as a model for other existing
neighborhoods in Beaufort, as well as other historic communities, and will provide a range of appropriate
green infrastructure tools that can be implemented citywide.
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Beaufort Northwest Quadrant
ProjectLocation
Beaufort \
Legend
| Project Location
~^\ Northwest Quadrant Boundary
| | City of Beaufort Limits
Highway
Major Road
Railroads (Local)
Lake/Pond/Stream/River
Swamp/Marsh
Cities
Parris Island
City of Beaufort
South Carolina
Project Location
Figure 1-1. Site location map.
1.1. Benefits of Green Infrastructure
Green infrastructure restores the natural hydrologic processes of infiltration, percolation, and
evapotranspiration to reduce the adverse effects of urban stormwater runoff on receiving water bodies.
Green infrastructure practices have been shown to cost-effectively reduce the impacts of stormwater
runoff; reduce maintenance requirements; and provide multiple environmental, social and economic
benefits (Kloss 2006). The 3BGI program therefore has the potential to provide a cost savings to the City
of Beaufort, while advancing many of the goals articulated in the Preservation Guidelines and
Neighborhood Strategic Plan. Some of the additional environmental, social, and economic benefits of
green infrastructure include:
Increased enjoyment of surroundings: A large study of inner-city Chicago found that one-third of the
residents surveyed said they would use their courtyard more if trees were planted (Kuo 2003). Residents
living in greener, high-rise apartment buildings reported significantly more use of the area just outside
their building than did residents living in buildings with less vegetation (Hastie 2003; Kuo 2003).
Research has found that people in greener neighborhoods judge distances to be shorter and make more
walking trips (Wolf 2008). Implementing green infrastructure practices to enhance vegetation, preserve
parking within the right-of-way, and add open or park space through the 3BGI project will help to create a
more pedestrian friendly environment that encourages walking and physical activity. Green infrastructure
practices can also be incorporated into future community gardens and pocket parks, enhancing and
increasing the enjoyment of the neighborhood.
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Increased safety and reduced crime: Researchers examined the relationship between vegetation and
crime for 98 apartment buildings in an inner city neighborhood and found the greener a building's
surroundings are, the fewer total crimes (including violent crimes and property crimes), and that levels of
nearby vegetation explained 7 to 8 percent of the variance in crimes reported by building (Kuo 2001a). In
investigating the link between green space and its effect on aggression and violence, 145 adult women
were randomly assigned to architecturally identical apartment buildings but with differing degrees of
green space. The levels of aggression and violence were significantly lower among the women who had
some natural areas outside their apartments than those who lived with no green space (Kuo 200Ib). The
stress-reducing and traffic-calming effects of trees are also likely to reduce road rage and improve the
attention of drivers. Green streets can also increase safety. Generally, if properly designed, narrower,
green streets decrease vehicle speeds and make neighborhoods safer for pedestrians (Wolf 1998; Kuo
200 la).
Increased sense of well-being: There is a large body of literature indicating that green space makes
places more inviting and attractive and enhances people's sense of well-being. People living and working
with a view of natural landscapes appreciate the various textures, colors, and shapes of native plants, and
the progression of hues throughout the seasons (Northeastern Illinois Planning Commission 2004). Birds,
butterflies, and other wildlife attracted to the plants add to the aesthetic beauty and appeal of green spaces
and natural landscaping. "Attention restorative theory" suggests that exposure to nature reduces mental
fatigue, with the rejuvenating effects coming from a variety of natural settings, including community
parks and views of nature through windows; in fact, desk workers who can see nature from their desks
experience 23 percent less time off sick than those who cannot see any nature, and desk workers who can
see nature also report a greater job satisfaction (Wolf 1998).
Increased property values: Many aspects of green infrastructure can increase property values by
improving aesthetics, drainage, and recreation opportunities that can help restore, revitalize, and
encourage growth in some of the economically distressed areas in the City of Beaufort. Table 1-1
summarizes the recent studies that have estimated the effect that green infrastructure or related practices
have on property values. The majority of these studies addressed urban areas, although some suburban
studies are also included. The studies used statistical methods for estimating property value trends from
observed data.
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Table 1-1. Studies estimatin
reen infrastructure
Source
Value6""
Ward et al. (2008)
Shultz and Schmitz
(2008)
Wachter and Wong
(2006)
Anderson and Cordell
(1988)
Voicu and Been (2008)
Espey and Owasu-Edusei
(2001)
Pincetletal. (2003)
Hobden, Laughton and
Morgan (2004)
New Yorkers for Parks
and Ernst & Young
(2003)
3.5 to 5%
0.7 to 2.7%
2%
3.5 to 4.5%
9.4%
11%
1.5%
6.9%
8 to 30%
Estimated effect of green infrastructure on adjacent
properties relative to those farther away in King County
(Seattle), WA.
Referred to effect of clustered open spaces, greenways and
similar practices in Omaha, NE.
Estimated the effect of tree plantings on property values for
select neighborhoods in Philadelphia.
Estimated value of trees on residential property (differences
between houses with five or more front yard trees and those
that have fewer), Athens-Clarke County (GA).
Refers to property within 1,000 feet of a park or garden and
within 5 years of park opening; effect increases over time
Refers to small, attractive parks with playgrounds within 600
feet of houses
Refers to the effect of an 11% increase in the amount of
greenery (equivalent to a one-third acre garden or park)
within a radius of 200 to 500 feet from the house
Refers to greenway adjacent to property
Refers to homes within a general proximity to parks
2. 3BGI Northwest Quadrant Project Site
The Northwest Quadrant is a historic neighborhood established following the Civil War by freed slaves
looking for work and stability. Between downtown Beaufort and the Boundary Street Redevelopment
District, the Northwest Quadrant is a diverse neighborhood that is part of the larger Beaufort National
Historic Landmark District. The historically African American neighborhood consists of simple one- and
two-story houses built from 1865 to 1950. In recent years the Northwest Quadrant has experienced a
resurgence due to its location, culture, diversity, and character. Preserving this diversity and character is
the impetus for appropriate new green infrastructure investments.
The Northwest Quadrant Neighborhood is adjacent to the pristine marsh of the Beaufort peninsula in the
Low country of South Carolina (Figure 2-1). The elevation ranges from approximately 10 to 25 feet,
with several gradual topographic depressions throughout. These topographic depressions result in several
places in the neighborhood that collect water instead of conveying runoff to the marsh. The standing
water results in safety issues and can cause building damage. Pollutants from urban land uses, including
bacteria, nutrients, and heavy metals, also create a hazard for the Beaufort River ecosystem.
Using green infrastructure concepts at the block scale in the Northwest Quadrant will preserve the small
single family lots and provide opportunities for additional urban housing, while also improving water
quality and drainage in a manner appropriate for the historic neighborhood. In addition, the community
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could experience several other benefits often associated with green infrastructure, including increased
property values, enhanced enjoyment of surroundings, a greater sense of well-being and reduced crime.
Following this project, the City hopes to apply block-scale green infrastructure interventions to other
urban neighborhoods. The City may be able to leverage private investment in the neighborhood to build
these green infrastructure interventions.
Legend
i Streets
J Northwest Quadrant Boundary
A
200 400
800
Feet
City of Beaufort
South Carolina
Northwest Quadrant
TETRATECH
Figure 2-1. Northwest Quadrant boundary.
2.1. Existing Site Conditions
The Northwest Quadrant is primarily residential and traditionally has very few streets with curb and
gutter. Stormwater typically surface-drains directly into the sandy/loamy soils through a system of state-
owned, poorly maintained swales and roadsides. During small rain events, the soil quality of the
Northwest Quadrant typically allows for rainwater to filter into the sandy soils. In larger rain events
(typical of spring and summer), however, standing water tends to collect in numerous locations. The
neighborhood has a low to medium density configuration with small houses on small- to medium-sized
lots that are close to the street and often lack yard space for conventional stormwater treatment. The
inadequate space and urban setting requires a more comprehensive strategy that evaluates the drainage on
a "block-by-block" approach. To address these issues, the City recently implemented multiple pilot
projects incorporating permeable pavement within the parking lanes along Bladen Street and is interested
in implementing additional pilot projects in the neighborhood. The 3BGI Northwest Quadrant Project Site
(the area of interest for this project) spans Boundary Street to King Street and Union Street to Bladen
Street and encompasses approximately 36 acres as shown in Figure 2-2.
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An analysis of the existing utilities and site topography indicated that surface water generally flows north
to south on the site. The Department of Social Services is located within the 3BGI site area and manages
its own stormwater runoff by providing treatment with a dry extended detention basin. Because of the
onsite stormwater treatment at the Department of Social Services, it was excluded in the delineation of the
contributing areas to the proposed green infrastructure practices, as indicated in Figure 2-2. The existing
stormwater drainage network currently outfalls to the Beaufort River which was listed with an approved
total maximum daily load (TMDL) for dissolved oxygen in April 2006.
The predominant soil type in the City is sandy with a hydrologic soil group classification of Type A,
indicating the potential for high infiltration rates. There are no known potential soil contamination issues
(including leaking underground storage tanks) within the project contributing area. The area is not
designated as a groundwater recharge area. There are no environmentally sensitive areas within the
project limits and project efforts will improve the stormwater impact to the downstream receiving waters
and wetlands.
The Duke Street location right of way, shown in Figure 2-3, is owned and maintained by the South
Carolina Department of Transportation, but the City of Beaufort could assume ownership in the future.
The proposed vegetated infiltration basin site, shown in Figure 2-4, is comprised of multiple privately-
owned parcels with an area maintained as open space (open space parcel). Rights to the parcels must be
secured prior to project design.
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HllBAGGETT,ST
Department
«y,n ^
_ T-< I / . I
Social
/IPBSL *5' '* «" '
Legend
> Storm Sewers
- Streets
Duke Street Catchment
Basin Catchment
Parcels
Elevation, ft
5
10
15
.)(«R-; Elementary^
City of Beaufort
South Carolina
Project Contributing Areas
Figure 2-2. Contributing drainage areas and existing conditions.
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Figure 2-3. 3BGI green street site, east side.
Figure 2-4. 3BGI vegetated infiltration basin site.
2.2. Proposed Site Design
In November 2012, a team consisting of City Staff, EPA Region 4, and multiple consultants participated
in the Northwest Quadrant Stormwater Charrette for the 3BGI project. The goal of the design charrette
was to evaluate the neighborhood to identify potential implementation sites and types of green
infrastructure practices that could be incorporated into these sites. Through the course of the charrette,
participants identified two locations for green infrastructure conceptual designs: a two-block segment of
Duke Street, and an open space parcel at the southeast corner of Hamar and Price Streets. Participants
identified green street design elements as appropriate practices for the Duke Street location, and a
vegetated infiltration basin as an appropriate practice for the open space parcel.
The overall vision for stormwater management discussed at the design charrette was to incorporate a
variety of green infrastructure techniques into the conceptual designs at different spatial scales, from a lot
level to a neighborhood level. These techniques would be transect-specific, relating to their surrounding
context. A memo describing the charrette process was delivered on December 12, 2012 and is included in
Appendix C. See Section 5 for more detail regarding the conceptual design of the stormwater control
measures.
3. Goals
Beaufort County has been at the forefront of adopting green infrastructure standards for new
development. However, the toolset is lacking for existing urban development. The Northwest Quadrant
project will be the first in the county to explore an urban toolset applying green infrastructure concepts to
an existing historic neighborhood on a block-by-block scale. This block scale application could also
create opportunities for the addition of dense infill development that drains to a series of block- and
neighborhood-scale green infrastructure practices. The proposed framework will provide flexible
treatment solutions that can be adapted to the goals and standards of a range of existing development
types, including historic residential areas, while maintaining the character of the neighborhood.
3.1. Project Goals
While allowing for full development of the 3BGI site, green infrastructure concepts and practices are
intended to approximate the hydrologic conditions of the site prior to development through infiltration,
evaporation, and detention of stormwater runoff. Matching natural hydrologic conditions will improve
drainage, reduce local flooding, and improve water quality. Secondary goals of the project are to improve
the aesthetic appeal of the neighborhood while maintaining the historic character of the area and to
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reinforce the right-of-way to prevent vehicles from negatively impacting the vegetation on the edge of the
road. These goals will be accomplished through implementation of permeable pavement and bioretention
along Duke Street and a vegetated infiltration basin at the southeast corner of Hamar and Prince Street. It
is feasible that a stormwater wetland could be effective at this location; however, a vegetated infiltration
basin will provide greater volume reduction due to the infiltration capacity of the native soils and is
recommended for the site. Use of these practices will allow the existing community to achieve the
desired additional on-street parking and landscaping while still protecting and improving water quality.
3.2. Design Goals
Stormwater management design criteria for the City of Beaufort are provided in the Beaufort County
Manual for Stormwater Best Management and Design Practices (2012). According to the Design Criteria
Manual, stormwater measures must be designed to capture the 1.95 inch, 24-hour Type III storm event.
To simplify the design process, the manual requires that the volume sizing of the green infrastructure
practice be the greater of 0.5 inch of runoff over the entire contributing area or 1.5 inches of runoff over
the impervious area. Additional design criteria as identified in the Beaufort County Best Management
Practices Manual are summarized as specifications in Section 6 of this report.
In addition to sizing practices to manage the specified design storms, modeling was performed to estimate
the maximum storm size that could be captured if all of the available space for green infrastructure were
utilized.
4. Green Infrastructure Toolbox
Green infrastructure typically incorporates multiple practices utilizing the natural features of the site in
conjunction with the goal of the site development. Multiple controls can be incorporated into the
development of the site to complement and enhance the proposed layout while also providing water
quality treatment and volume reduction. Green infrastructure practices are those methods that provide
control and/or treatment of stormwater runoff on or near locations where the runoff initiates, thus
providing water quality improvement and volume reduction. Typical large scale practices include
approaches such as vegetated infiltration basins and stormwater wetlands. Smaller scale practices
typically include approaches such as permeable pavement and bioretention facilities. The green
infrastructure practices identified as appropriate for the Beaufort region included vegetated green
infrastructure practices, permeable pavement, and stormwater wetlands. To assist the City in
incorporating green infrastructure practices into the project locations, the following discussion addresses
constraints and opportunities associated with each green infrastructure practice.
4.1. Vegetated Green Infrastructure Practices
Vegetated green infrastructure practices are vegetated, depressed areas with a fill soil (often engineered
soil media) that remove pollutants through a variety of physical, biological, and chemical treatment
processes. Vegetated green infrastructure practices can be large-scale controls treating several acres or
small-scale controls placed in parking medians, right of ways, and other locations within impervious
areas. The following sections discuss two types of vegetated green infrastructure practices; bioretention
areas and vegetated infiltration basins. Each provides a similar water treatment mechanism but provides
different scales of treatment. Bioretention areas are typically designed to treat watersheds of less than 5
acres, whereas vegetated infiltration basins are designed to provide treatment for much larger areas.
Bioretention: Bioretention typically consists of vegetation, a ponding area, mulch layer, and planting or
engineered soil media. The depressed area is planted with small- to medium-sized vegetation including
trees, shrubs, grasses and perennials and may incorporate a vegetated groundcover or mulch that can
withstand urban environments and tolerate periodic inundation and dry periods. Runoff intercepted by the
practice is temporarily captured in the depression and then filtered through the soil (often engineered soil)
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media. Pollutants are removed through a variety of physical, biological, and chemical treatment
processes. Pretreatment of stormwater flowing into the bioretention area is recommended to remove large
debris, trash, and larger particulates. Pretreatment may include a grass filter strip, sediment forebay, or
grass swale. Ponding areas can be designed to increase flow retention and provide flood control.
Bioretention is well suited for removing stormwater pollutants from runoff, particularly for smaller (water
quality) storm events. Bioretention can be used to partially or completely meet stormwater management
requirements on smaller sites. Bioretention areas are best suited for areas that would typically be
dedicated to landscaping and can be designed to capture roof runoff, parking lot runoff, or sidewalk and
street runoff (as shown in Figure 4-1 and Figure 4-2).
Figure 4-1. Bioretention incorporated into a parking Figure 4-2. Bioretention incorporated into a right-of-
lot. way.
Vegetated Infiltration Basin: A vegetated infiltration basin is a constructed depression designed to provide
temporary storage of stormwater for subsequent infiltration into the underlying soil. Vegetated surfaces
along the bottom and sides of the infiltration basin allow for pollutant removal and treatment of
stormwater within the basin through a variety of physical, biological, and chemical treatment processes
before it infiltrates into the groundwater. Amended or engineered soils and plant selection differentiate
the vegetated infiltration basin from other County infiltration measures including trenches and wells. A
vegetated infiltration basin consists of a ponding area and vegetated surface. Infiltration basins, in
general, are commonly used as water quality controls with additional benefits such as storage and
groundwater recharge. Large scale vegetated infiltration basins typically require large open parcels and
can be configured to provide multi-use benefits including use as parks between rain events, such as the
one shown in Figure 4-3, or outdoor classrooms.
10
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Figure 4-3. Vegetated infiltration basin incorporated into an open space park.
4.2. Permeable Pavement
Conventional pavement results in increased surface runoff rates and volumes relative to pre-developed
conditions. Permeable pavements, in contrast, work by allowing streets, parking lots, sidewalks, and other
impervious surfaces to retain the underlying soil's natural infiltration capacity while maintaining the
structural and functional features of the materials they replace. Permeable pavements contain small voids
that allow water to drain through the pavement to an aggregate reservoir and then infiltrate into the soil. If
the native soils below the permeable pavements do not have enough percolation capacity, underdrains can
be included to direct the stormwater to other downstream stormwater control systems. Permeable
pavement can be developed using modular paving systems (e.g., concrete pavers, grass-pave, or gravel-
pave) or poured-in-place solutions (e.g., pervious concrete or permeable asphalt).
Permeable pavement reduces the volume of stormwater runoff by converting an impervious area to a
treatment unit. The aggregate sub-base can provide water quality improvements through filtering and
enhance additional chemical and biological processes. The volume reduction and water treatment
capabilities of permeable pavements are effective at reducing stormwater pollutant loads.
Permeable pavement can be used to replace traditional impervious pavement for most pedestrian and
vehicular applications. Composite designs that use conventional asphalt or concrete in high-traffic areas
adjacent to permeable pavements along shoulders or in parking areas can be implemented to provide a
cost effective solution to meet both transportation and stormwater management requirements. Permeable
pavements are most often used in constructing pedestrian walkways, sidewalks, driveways, low-volume
roadways, and parking areas of office buildings, recreational facilities, and shopping centers (Figure 4-4
and Figure 4-5).
11
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Figure 4-4. Grass paver parking stalls.
4.3. Stormwater Wetland
Figure 4-5. Permeable Interlocking Concrete Paver
parking stalls.
A stormwater or constructed wetland is a constructed basin designed to treat Stormwater by temporarily
storing runoff to allow for pollutant removal and water quality improvement. Stormwater wetlands
employ a combination of physical, chemical, and biological processes to remove multiple pollutants
carried by stormwater runoff including sediment, metals, motor oil, pathogens and nutrients. Wetland
plants help to slow incoming runoff, allowing sediment and other particles to fall out of suspension and
settle in the wetland. Stormwater wetlands consist of varying ponding depths, or zones, including deep
pools, shallow water, and areas of temporary inundation. The variable depths allow for ample and diverse
vegetation that remove nitrogen and phosphorus through direct uptake to fuel their own growth. Bacteria
living with wetland plants and sediment are especially important in providing water treatment services by
breaking down hydrocarbons, such as oil, and removing excess nitrogen from the water through a process
called denitrification. The distinction should be made that a stormwater wetland does not divert runoff
into a natural, existing wetland but rather creates a new, distinct engineered wetland designed with the
intent of controlling and treating stormwater. Stormwater wetlands are most effective in conditions where
infiltration is not feasible. Infiltration provides the greatest water quality benefit; however, pending the
results of a full geotechnical investigation, if infiltration is proven to be infeasible at the open space parcel
at Hamar Street and Prince Street, then a stormwater wetland will be an appropriate green infrastructure
practice.
In addition to pollutant reduction, stormwater wetlands can provide important habitat for plants, insects,
amphibians, birds, and other animals that is otherwise lacking in most urban landscapes, contributing to
greater biologic diversity in urban and suburban areas. Biodiversity is an important part of most
ecosystems as it underpins the provision of many other ecosystem services. For instance, diverse plant
and benthic macroinvertebrate communities may improve nutrient cycling and removal in stormwater
wetlands and have increased resilience against disturbances such as drought or disease. Stormwater
wetlands can support a diverse community of aquatic insects and fish that prey upon mosquito larvae,
providing control of mosquitoes. Stormwater wetlands can provide a place for community members to
participate in recreational activities and be incorporated as an amenity in community parks and open
space like the stormwater wetland shown in Figure 4-6. Many wetland plants produce colorful flowers
that attract dragonflies, butterflies, and birds, making stormwater wetlands an ideal place to observe
wildlife within urban and suburban areas. Walking trails and boardwalks can be installed in stormwater
wetlands treating runoff from neighborhoods to provide community members a place to stroll and enjoy
the aesthetic component of these constructed ecosystems. Stormwater wetlands are complex ecological
12
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systems that can also be utilized as an educational amenity providing a site for hands-on learning.
Educational signs can be placed at any stormwater wetland to inform the public about the beneficial suite
of services these ecosystems provide.
Figure 4-6. Stormwater wetland.
5. Green Infrastructure Design
This section addresses the selection, layout, and design of the green infrastructure practices for the 3BGI
site in Beaufort. The selection and proposed layout of the controls are based on discussions during the
charrette as detailed in Section 2.2. The conceptual layout and sizing of green infrastructure practices to
meet the water quality objectives are discussed in Section 5.3. Details on design information are
summarized and presented in Section 6 to assist with final design of the green infrastructure practices.
5.1. Design Elements
The selection and proposed layout of the stormwater control measures are based on discussions during the
charrette where improving water quality on the site; incorporating and preserving vegetated areas; and
preserving the historic character of the neighborhood were emphasized as high priorities. The sites were
selected based on multiple factors including the potential to improve drainage or reduce flooding,
potential water quality improvement based on treatment volume, potential for green infrastructure
practice demonstration, multi-use benefit for the surrounding neighborhood, and ancillary benefits such as
aesthetic improvement. The potential for green infrastructure practice demonstration was evaluated based
on the proximity to parks, schools, or other BMPs that would attract the public.
13
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Duke Street is in close proximity to permeable pavement implemented along Bladen Street and Duke
Street east of Bladen Street. While the right-of-way between the curb and sidewalk is not designated or
delineated for parking, current residents are parking in the space impacting the grass and destabilizing the
area causing a potential for erosion. Permeable pavement implemented in the right-of-way on Duke
Street west of Bladen Street would stabilize the right-of-way and bioretention could add additional
opportunities for landscaping enhancing the current efforts by providing additional treatment and
opportunity for demonstration in the Northwest Quadrant.
A stormwater diversion structure implemented in the right of way at Prince Street and Hamar Street
would divert flow from the stormwater drainage network to the undeveloped, open space parcel at the
intersection of Hamar Street and Prince Street prior to discharging to the Beaufort River, thus providing
water quality treatment and protecting the quality of the river. The parcel is directly adjacent to the
Beaufort Elementary School, providing educational opportunities for the students and teachers. A green
infrastructure practice installed at the site could also provide multi-benefit uses to the surrounding
residents, serving as an open space park in addition to providing water quality treatment. All of these
benefits were emphasized and expressed as critical elements of the goals of the City of Beaufort during
the charrette process. For additional details on the charrette process and the selection of the green
infrastructure practices, see Appendix C.
5.2. Analytical Methods
The Beaufort Design Manual allows stormwater controls to be sized to capture the greater of 1.5 inches
over the impervious area or 0.5 inches over the entire drainage area. The greatest amount of runoff was
produced by 1.5 inches of rainfall over the entire impervious area in the drainage areas of interest, and
was therefore selected as the design target for this analysis.
EPA's Storm Water Management Model (SWMM) was used to assess the existing runoff conditions and
evaluate green infrastructure opportunities in the project area (USEPA 2004). SWMM is a dynamic
precipitation-runoff simulation model designed for discrete event or continuous representation of
hydraulics, hydrology, and water quality in urbanized catchments. SWMM represents land areas as a
series of subcatchments, with properties that define retention and runoff of precipitation, infiltration,
percolation to a shallow aquifer, and discharge from the aquifer. Subcatchments are connected to the
drainage network, which may include natural watercourses, open channels, culverts and storm drainage
pipes, storage and treatment units, outlets, diversions, and many other elements of an urban drainage
system.
The subcatchment areas for the proposed green infrastructure practices were derived from LIDAR
topographic data and field visits (Figure 2-2). Note that these data will need to be validated as part of the
final design. The drainage areas were represented as a residential land use per the land use map generated
by the City. The imperviousness was calculated at 50% for Duke Street and 32% for the vegetated
infiltration basin catchment using the building footprint and road area data made available. The soil was
represented as a high-infiltrating sandy soil (Hydrologic Soil Group A) per the Natural Resources
Conservation Service Soil Survey and field observations.
Green infrastructure practice improvements were represented using the low impact development (LID)
components recently introduced in SWMM 5. LID is modeled in SWMM using a layered configuration
that allows a great deal of flexibility in representing various types of practices, including bioretention,
swales, infiltration devices, permeable pavement, rain barrels, and cisterns. Horton or Green-Ampt
infiltration parameters can be defined for filtering media, and the model tracks evaporation and soil
moisture, allowing infiltration rates during runoff events to be dynamic. Green infrastructure practices are
sized by assuming an equivalent depth and calculating the surface area required to treat the design storm.
14
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To size the design elements in the project area, bioretention and permeable pavement were incorporated
into the Duke Street sub-catchment, while a storage basin model was incorporated into the basin sub-
catchment to represent the vegetated infiltration basin. Table 5-1 shows the volume of runoff produced by
the 1.5 inch design target that must be treated by the green infrastructure practices. All of the detailed
SWMM modeling assumptions used in this study can be found in Appendix B.
Table 5-1. Subcatchment delineations and runoff volumes.
Subcatchment Volume of water
drainage 1.95 inch, 24-hour Type III
Subcatchment (acres) (cu ft)
Duke Street -
Green Street
Vegetated
Infiltration Basin
1.5
36.3
4,140
82,200
Volume of water
25-year, 24-hour Type III
(cuft)
26,790
553,210
5.3. Recommended Sizing and Layout
The conceptual layout and sizing of the green infrastructure practices with in the right-of-way along Duke
Street and at the corner of Prince and Hamar Streets are discussed in this section.
Green Street: Green infrastructure BMPs could be implemented in the right-of-way in the eight feet of
pervious area between the edge of the curb and the sidewalk for the length of Duke Street to treat the
runoff from the adjacent parcel and one driving lane of Duke Street. The available area and green
infrastructure practice dimensions of bioretention and permeable pavement along Duke Street are shown
in Table 5-2 and Figure 5-1. A bioretention area of 1,453 square feet with an equivalent depth of
approximately 1.4 feet (providing a storage volume of 2,034 cubic feet) and a permeable pavement area
of 2,906 square feet with an equivalent depth of approximately 0.3 feet (providing a storage volume of
872 cubic feet) will be required to treat the design storm. The primary design parameters for bioretention
conceptual sizing included the surface storage depth, planting soil depth and void space ratio, and native
soil infiltration rate. The primary design parameters for permeable pavement conceptual sizing included
the surface storage depth, pavement thickness, aggregate base depth, void space ratio, and native soil
infiltration rate. The water storage volume is the product of the area and equivalent storage depth.
Equivalent storage depth is the sum of the surface ponding depth and the product of the soil depth and
porosity. Storage volume indicates the green infrastructure practice volume required to treat the design
storm. Because infiltration is accounted for in the design, the water storage volume will be less than the
required treatment volume allowing for smaller green infrastructure practices to treat equivalent volumes.
Each of the primary design parameters can vary in the final design and the design goals will be met as
long as the water storage volume capacity is maintained. Utilizing all of the area available for
implementation (6,717 square feet of bioretention and 13,434 square feet of permeable pavement) will
provide treatment for the runoff generated by the 5.97 inch event (approximately a 5 year event),
substantially more than is required by the current design storm. The analysis indicates that approximately
one-quarter of the available area would be required to treat the runoff generated from the 1.95 inch event,
as shown in Table 5-3 and Figure 5-2. Additional analysis, including the cost estimate, will focus on
treating the design storm.
Table 5-2. Available area for green infrastructure practices.
Green Infrastructure
Practice
Bioretention
Green
Infrastructure
Practice Width Length Surface Area Water Storage
Location (ft) (ft) (soft) Volume (cuft)
Right-of-way
8
840
6,717
9,404
Permeable Pavement
Right-of-way
8
1,680
13,434
4,030
15
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Legend
Catch Basins
» Storm Sewers
Streets
Bioretention
Permeable Pavement
N
50 100
200
i Feet
City of Beaufort
South Carolina
Available Implementation Area
TETRATECH
Figure 5-1. Available green infrastructure practice area on Duke Street.
16
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Table 5-3. Green infrastructure practices proposed for redevelopment of Duke Street to treat the 1.95 inch
event
Green Infrastructure
Bioretention
Green
Infrastructure
Practice Width Length Surface Area Water Storage
Location (ft) (ft) (sqft) Volume (cu ft)
Right-of-way
8
182
1,453
2,034
Permeable Pavement
Right-of-way
8
363
2,906
872
17
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Legend
Catch Basins
Storm Sewers
Streets
Bioretention
Permeable Pavement
City of Beaufort
South Carolina
1.95 inch Event Area
TETRATECH
Figure 5-2. Recommended green infrastructure practice area on Duke Street to treat the 1.95 inch event.
18
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Vegetated Infiltration Basin: The dimensions of the vegetated infiltration basin proposed for the southeast
corner of Prince and Hamar Streets are presented in Table 5-4 and Figure 5-3. The width and length are
limited by the available area and current grading of the parcel. A vegetated infiltration basin with a
surface area of 15,700 square feet and storage volume of 20,880 cubic feet would provide treatment for
the runoff generated by the 1.22 inch event. While this is less than the design storm, an infiltration basin
at this site will provide significant volume reduction and water quality treatment for the watershed. The
primary design parameters for the vegetated infiltration basin conceptual design included contributing
volume, available surface area, and native soil infiltration rates. Side slopes are also accounted for where
applicable. A stormwater wetland could be an appropriate control for the site if the benefits of a
stormwater wetland are preferred. Performance specifications for a stormwater wetland are provided in
section 6.1.5. In order to maintain a permanent pool within the stormwater wetland, infiltration must be
limited or prevented. It was determined, due to the lack of infiltration, that a stormwater wetland can only
treat the runoff from the 0.45 inch event, providing significantly less treatment than a vegetated basin that
utilizes the infiltration capacity of the native soils. Because of the significantly greater treatment capacity,
the vegetated infiltration basin is recommended and will be the focus of the remaining analysis including
the cost estimate.
Table 5-4. Green infrastructure practice proposed for the southeast corner of Hamar and Prince Street
Vegetated
infiltration Basin
Additional design details for each green infrastructure practice are included in Appendix A.
19
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"Ts InJetf&JMpn itpri ng: Point
Legend
Catch Basins
Diversion Structure
O Inlet & Monitoring Point
Streets
Storm Sewers
Proposed Inlet Line
Parcels
Top Footprint
Banks - 2:1 Sideslope
Banks - Steps
Bottom Footprint
N
A
0 15 30
60
i Feet
City of Beaufort
South Carolina
Implementation Areas
TETRATECH
Figure 5-3. Hamarand Prince Street vegetated infiltration basin layout.
20
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6. Green Infrastructure Practice Technical
Specifications
The purpose of this section is to provide guidance for designing the green infrastructure practices during
final design. Design guidance for each applicable green infrastructure practice is presented in a table with
an accompanying figure showing a cross-section of atypical design.
6.1. Common Elements
Soil Media
Based on the soil type of the native soils, it is anticipated that infiltration capacity of each site is
appropriate for infiltration. However, if the results of the geotechnical investigation (described below)
show that the infiltration rate is less than 0.5 in/hr or reveal that infiltration is not feasible for the native
soil at either site, an engineered soil media will be necessary. The soil media is typically specified to meet
the growth requirements of the selected vegetation while still meeting the hydraulic requirements of the
system. Recognizing that there are many possible variations in soil media, the following is one example:
The engineered soil mixture is a blend of loamy soil, sand, and compost that is 20-30 percent compost (by
volume). The expected infiltration rate should range from 1 to 2 in/hr.
A particle gradation analysis of the blended material, including compost, should be conducted in
conformance with ASTM Cl 17/C136 (AASHTO Tl 1/T27). The gradation of the blended material should
meet the following gradation criteria:
Sieve Size
1 inch
#4
#10
#40
#100
#200
Percent Passing
100
75-100
40-100
15-50
5-25
5-15
Soil media must have an appropriate amount of organic material to support plant growth. Organic
matter is considered an additive to help vegetation establish and contributes to sorption of pollutants
but generally should be minimized (5 percent). Organic materials will oxidize over time, causing an
increase in ponding that could adversely affect the performance of the bioretention area. Organic
material should consist of aged bark fines, or similar organic material. Organic material should not
consist of manure or animal compost. Newspaper mulch has been shown to be an acceptable additive.
pH should be between 6-8, cation exchange capacity (CEC) should be greater than 5 milliequivalent
(meq)/100 g soil.
High levels of phosphorus in the media have been identified as the main cause of bioretention areas
exporting nutrients. All bioretention media should be analyzed for background levels of nutrients.
Total phosphorus should not exceed 15 ppm.
Underdrain
If the infiltration rates require an engineered soil media, an underdrain will be required and should meet
the following criteria:
21
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The type of perforated pipe is not critical to the function of the green infrastructure practice as long as
the total opening area exceeds the expected flow capacity of the underdrain and does not limit
infiltration through the soil media. The perforations can be placed closest to the invert of the pipe to
achieve maximum potential for draining the facility. If an anaerobic zone is intended, the perforation
can be placed at the top of the pipe.
Place the underdrain on a minimum 3-foot-wide bed of drainage stone 6 inches deep and cover with
the same drainage stone to provide a 16-inch minimum depth around the bottom, sides, and top of the
slotted pipe.
The underdrain should drain freely and discharge to the existing storm water infrastructure.
Alternatively, the underdrain outlet can be upturned to provide an internal sump (internal water
storage) to improve infiltration and water quality. The elevation of the underdrain invert should be no
less than 1.5 feet from the surface of the basin to provide an aerobic root zone for plants and to
prevent previously-sorbed pollutants from mobilizing.
Plant Selection
For the green infrastructure practice to function properly as stormwater treatment and blend into the
landscape, vegetation selection is crucial. Appropriate vegetation will have the following characteristics:
1. Plant materials must be tolerant of drought, ponding fluctuations, and saturated soil conditions
for 10 to 48 hours.
2. It is recommended that a minimum of three tree, three shrubs, and/or three herbaceous
groundcover species be incorporated to protect against facility failure from disease and insect
infestations of a single species.
3. Native plant species or hardy cultivars that are not invasive and do not require chemical inputs
are recommended to be used to the maximum extent practicable.
4. The following site provides assistance in choosing appropriate native species:
Beaufort County Manual for Stormwater Best Management and Design Practices (BMP)
(http://www.bcgov.net/departments/Engineering-and-Infrastructure/stormwater-
management/documents/beaufort_manual_mar2012 .pdf)
Geotechnical Investigation
A full geotechnical investigation is necessary to characterize the soils prior to final design. Pertinent
information includes permeability at each site, hydrologic soil group type, depth to water table, and the
presence of expansive soils. If expansive soils are present, green infrastructure practice design should
include underdrains and impermeable barriers where the controls are adjacent to infrastructure such as
roads and buildings. Drainage should always be directed away from building foundations and road
subgrades.
6.2. Bioretention
Generally, bioretention areas should have the following design features:
For unlined systems, maintain a minimum of 5 feet between the green infrastructre practice and
any adjacent buildings and at least 10 feet between the green infrastructure practice and any
adjacent basement.
22
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Dewater surface in a time of no greater than 24 hours and subsurface within 72 hours either
through infiltration with soils of sufficient percolation capacity or with an underdrain system and
outlet to a drainage system. Use of an underdrain system is very effective in areas with low
infiltration capacity soils.
Planted with native and noninvasive plant species tolerant of urban environments, frequent
inundation, and Beaufort's humid subtropical climate (per Koppen Climate Classification).
Inclusion of an overflow structure with a non-erosive overflow channel to safely pass flows that
exceed the capacity of the facility or design the facility as an off-line system where only the
design volume enters the bioretention area.
Inclusion of a pretreatment mechanism such as a grass filter strip, sediment forebay, or grass
swale upstream of the practice to enhance the treatment capacity of the unit.
If the infiltration rates are greater than 0.5 in/hr and infiltration is feasible, the growing layer, filter layer,
and drainage layer will not be necessary. Native material will be appropriate for the entire Vertical
Component.
1. Siting Setbacks
Pavement
Building
Property lines/ROW
2. Volume
Bottom slope
Side slopes
Freeboard
3. Vertical Component
Ponding Area
Soil Media Layer
Filter Layer
Drainage Layer
Native Material
4. Drainage
No requirement
No requirement with lined
bottom; otherwise,
Basement: > 10 feet
No Basement: > 5 feet
> 2 feet / >0 feet
Flat
2H: IV or flatter
6 inches
6 inches
> 24 inches soil media;
3 inches of mulch, min
2 to 4 inches of clean
medium sand (ASTM c-33)
over 2 to 3 inches of #8 or
#78 washed stone when
drainage layer is used
Recommended 12 to 30 in. of
clean coarse aggregate
AASHTO #4, #5, or
equivalent
Test infiltration; >0.5 in/hr if
designing with infiltration
Inlet
Outlet
Overflow
Infiltration
Dewatering
5. Composition
Surface Treatment
Soil Media
Side Slopes
Mulch
6. Pollutant
Pretreatment
7. Maintenance
Curb inlet; sheet flow
through grass filter strip;
downspout w/ energy
dissipation
Required to meet release
rates
Downstream inlet or catch
basin set 6 inches above soil
surface and connected to
storm drainage network
Meet water quality volume
requirement
Surface: < 24 hours
Sub-surface: < 72 hours
Vegetation and mulch
Meets dewatering
requirement; supports plant
growth
Grass or mulch
Triple-shredded hardwood
Required. May include grass
filter strip, stone trench,
forebay, sump inlets
Access
Able to be accessed by a
vehicle
Requirements
Designed and maintained to
improve water quality;
Maintenance plan should be
in place
23
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(Filter strip)
soil
Figure 6-1. Typical bioretention configuration.
6.3. Permeable Pavement
General guidelines for applying permeable pavement are as follows:
Permeable pavements can be substituted for conventional pavements in parking areas, low-
volume/low-speed roadways, pedestrian areas, and driveways if the grades, native soils, drainage
characteristics, and groundwater conditions of the paved areas are suitable.
Permeable pavement is not appropriate for stormwater hotspots where hazardous materials are
loaded, unloaded, or stored, unless the sub-base layers are completely enclosed by an
impermeable liner.
The granular capping and sub-base layers should provide an adequate construction platform and
base for the overlying pavement layers.
If permeable pavement is installed over low-permeability soils or temporary surface flooding is a
concern, an underdrain should be installed to ensure water removal from the sub-base reservoir
and pavement.
The infiltration rate of the soils or an installed underdrain should drain the sub-base within 24 to
48 hours.
An impermeable liner can be installed between the sub-base and the native soil to prevent water
infiltration when clay soils have a high shrink-swell potential or if a high water table or bedrock
layer exists.
Measures should be taken to protect permeable pavements from high sediment loads, particularly fine
sediment, to reduce maintenance. Typical maintenance includes removing sediment with a vacuum truck.
If the infiltration rates are greater than 0.5 in/hr and infiltration is feasible, the base layer may be reduced
to 6 inches.
24
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1. Siting Setbacks
Pavement
Building
Property lines/ROW
2. Volume
slope
Side slopes
Freeboard
3. Vertical Component
Surface
Layer
Growing Layer
Bedding
Structural Layer
No requirement
No requirement with lined
bottom; otherwise,
Basement: > 10 feet
No Basement: > 5 feet
> 2 feet / >0 feet
Less than 0.5 percent
Not applicable
Not applicable
Interlocking Concrete Pavers;
Concrete Grid Pavers; Plastic
Grid Pavers; Concrete; Asphalt
Not applicable
Undisturbed Base Soil
1) Perm. Interlocking Cone.
Pavers: 1.5 to 3 inches of #8 or
#78 washed stone
2) Concrete and Plastic Grid
Pavers: 1 to 1.5 inches of
bedding sand
3) Pervious Concrete and
Asphalt: None
12 to 30 in. of clean aggregate
AASHTO #56 or equivalent;
thickness depends on
strength/storage needed; install
30 mil geotextile liner where
aggregate meets soil
Compacted as sub-base
4. Drainage
Inlet
Outlet
Overflow
Infiltration
Dewatering
Pavement surface
Required to meet release
Downstream inlet
rates
Meet water quality volume
requirement
< 72 hours
5. Composition
Surface Treatment
For interlocking or grid-type
pavers use fine aggregate,
coarse sand, or top soil & grass
in openings
6. Pollutant
Pretreatment
Divert runoff from sediment
sources away from pavement
7. Installation and Maintenance
Installation
Per manufacturer's
recommendation
Load Bearing
Designed for projected traffic
loads using AASHTO
methods
Requirements
Designed and maintained to
improve water quality;
Maintenance plan should be in
place
Notes: A reinforced concrete transition width (12-18 inches)
is required where permeable pavement meets adjacent non-
concrete pavement or soil.
Permeable !i^ter
ete Paver (PICP)
Filler Material
(gravel orSa^d)
,^- Cpi^crete Trai/vsitiofi* .strip
Bedeli^£) Layer
(gravel or
.structural Layer
(washed no 5? stoi/v
geotextile
(As Required)
urbed "Base soil
Pervloks Concrete
C-oi^rete TrflKsltloiA, strip
Layer
l, washed no 2 stoi
-------
Dewater surface in a time of no greater than 24 hours and subsurface within 72 hours either
through infiltration with soils of sufficient percolation capacity or with an underdrain system and
outlet to a drainage system. Use of an underdrain system is very effective in areas with low
infiltration capacity soils.
Planted with native and noninvasive plant species tolerant of urban environments, frequent
inundation, and Beaufort's humid subtropical climate (per Koppen Climate Classification).
Inclusion of an overflow structure with a non-erosive overflow channel to safely pass flows that
exceed the capacity of the facility or design the facility as an off-line system where only the
design volume enters the bioretention area.
Inclusion of a pretreatment mechanism such as a grass filter strip, sediment forebay, or grass
swale upstream of the practice to enhance the treatment capacity of the unit.
If the infiltration rates are greater than 0.5 in/hr and infiltration is feasible, the growing layer, filter layer,
and drainage layer will not be necessary. Native material will be appropriate for the entire Vertical
Component.
1. Siting Setbacks
Pavement
Building
Property lines/ROW
2. Volume
Bottom slope
Side slopes
Freeboard
3. Vertical Component
Ponding Area
Growing Layer
Filter Layer
Drainage Layer
Native Material
4. Drainage
No requirement
No requirement with lined
bottom; otherwise,
Basement: > 10 feet
No Basement: > 5 feet
> 2 feet / >0 feet
Flat
2H: IV or flatter
6 inches
2-10 ft typical
> 12 inches soil media;
3 inches of mulch, max
2 to 4 inches of clean
medium sand (ASTM c-33)
over 2 to 3 inches of #8 or
#78 washed stone when
drainage layer is used
Recommended 12 to 30 in. of
clean coarse aggregate
AASHTO #4, #5, or
equivalent
Test infiltration; >l/2 in/hr if
designing with infiltration
Inlet
Outlet
Overflow
Infiltration
Dewatering
5. Composition
Surface Treatment
Soil Media
Side Slopes
Mulch
6. Pollutant
Pretreatment
7. Maintenance
Observation Wells
Access
Requirements
Curb inlet; sheet flow
through grass filter strip;
downspout w/ energy
dissipation
No requirement, infiltration
shall meet release rates
Downstream inlet or catch
basin set 6 inches above soil
surface and connected to
storm drainage network
Meet water quality volume
requirement
Surface: < 24 hours
Sub-surface: < 72 hours
Vegetation and mulch
Meets dewatering
requirement; supports plant
growth
Grass or mulch
Triple-shredded hardwood
Required. May include grass
filter strip, stone trench,
forebay, sump inlets
Perforated PVC pipe 4- to 6-
inches in diameter with a
tamper-proof lockable cap in
center of trench
Able to be accessed by a
vehicle
Designed and maintained to
improve water quality;
Maintenance plan should be
in place
26
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(Filter strip)
Figure 6-4. Typical vegetated infiltration basin configuration.
6.5. Stormwater Wetland
Generally, stormwater wetlands contain five zones: the forebay, deep pools, shallow water, temporary
inundation, and upland zones. These zones are generally differentiated by water level, and each has a
specific role in the wetland's intended function. The zones should have the following design features:
The forebay should be armored to prevent erosion and disperse flow as much as possible. The
forebay should represent 10% to 15% of the total area of the stormwater wetland.
Deep pools (I) are approximately 2 to 2.5 feet deep and connected with shallow water channels
no more than six inches in depth. The temporary inundation zone is no more than six inches
above the top of the shallow water channels. Deep pools generally represent 20% to 25% of the
wetland area, in addition to the forebay, and are deep enough to retain water during droughts
(usually at least 18-in deep).
Deep to Shallow Water Transitions (II) provide a connectin between the deep pools and the
shallow water at a slope no steeper than 1.5h: Iv.
Shallow water (III) generally represents 30% to 40% of the total wetland surface area and are
typically 6 inches in depth (2 to 4 inches will support a more diverse plant community).
Temporary inundation (IV) zones provide storage above the permanent pool to capture a
required volume of stormwater runoff and represents 30% to 40% of the total stormwater wetland
area. This temporary inundation zone is temporarily submerged during runoff events and then
dries over a period of 2 to 5 days as runoff is slowly discharged from the wetland. Because it is
not permanently inundated, a greater variety of vegetation is adapted to life in this zone.
The upper bank (V) region of the wetland is the area that surrounds the temporary inundation
zones, and is sloped as needed to tie the wetland into the surrounding landscape. This area is not
typically inundated, and can support a variety of upland plants.
27
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SHALLOW
WATER
DEEP POOL
FOREBAY
UPPER
BANK
Source: NCSU BAE
Figure 6-5. Plan view of the stormwater wetland zones.
I
TEMPORARY
INUNDATION
ZONE
IV
Source: NCSU BAE
Figure 6-6. Profile view of the stormwater wetland zones: (I) Deep Pool, (II) Transition, (III) Shallow Water, (IV)
Temporary Inundation, and (V) Upper Bank
28
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If infiltration rates are greater than 0.01 in/hr, a hydraulic restriction layer will be required to maintain a
permanent pool within the wetland area. The infiltration rates of the existing site will make maintaining a
permanent pool impractical; therefore, a vegetated infiltration basin is more appropriate for the site.
1. Siting Setbacks
Pavement
Building
Property Lines/ROW
Groundwater/Karst/Bedrock
Septic System/Wells
> 10ft
Basement: > 10 ft
>10ft/>50ft
>2ft
>50/>100ft
2. Volume
Internal slope
Side slopes
Permanent Pool Depth
Inundation Zone Depth
1.5H: IV or flatter
3H: IV or flatter
30 inches minimum
0 to 12 inches above
permanent pool depth
3. Vertical Component
Inundation Storage
0 to 12 inches above
permanent pool depth
Permanent Pool Storage
The mean depth shall be 30
inches
Native Material
Test infiltration; > 0.5 in/hr if
designing with infiltration
4. Drainage
Inlet
Include sediment removal
device and diversion structure
6.6. Stormwater Diversion
Underdrain
Outlet
Overflow
Infiltration
Dewatering
5. Pollutant
Pretreatment
6. Maintenance
Observation well
Access
Requirements
No requirement
No requirement, infiltration
shall meet release rates
Back-up above ground; Weir;
Standpipe
Meet water quality volume
requirement
Per allowable release rate
Required; May be SCM,
prefabricated device, or
forebay
Perforated PVC pipe 4- to 6-
inches in diameter with a
tamper-proof lockable cap in
center of trench
Able to be accessed by a
vehicle
Designed and maintained to
improve water quality;
Maintenance plan should be
in place
To divert runoff from the storm drainage system running along Hamar Street into the green infrastructure
practice at Prince Street and Hamar Street, a diversion structure should be installed just south of the catch
basins on the south side of the intersection. The diversion structure should be sized to limit erosive flows
entering the vegetated infiltration basin while allowing peak flows that exceed the treatment pipe capacity
to bypass the control entirely. Figure 6-7 shows an example of a typical diversion structure that can be
retrofitted into the existing storm sewer system.
29
-------
PLAN VIEW
I 1^TO TREATMENT STRUCTURE
DESCRIPTION
OUT SIDE WIDTH OF DIVERT ER T5OX
INSIDE WIDTH- OF DIVERTER B.OX
INSIDE WIDTH- OF UIVERTBR-BOX
OHTSI&B WIDTH- OF DIVERTED "B.OX
DIAMETER OF OUTLET PIPE
DIAMETER OF INLETPIPE
WIDTH OF DROP INL6T
-------
The following tables outline the required maintenance tasks, their associated frequency, and notes to
expand upon the requirements of each task.
Task Frequency Maintenance notes
Monitor infiltration and
drainage
Pruning
Mowing
Mulching
Mulch removal
Watering
Fertilization
Remove and replace
dead plants
Inlet inspection
Outlet inspection
Miscellaneous upkeep
1 time/year
1-2 times/year
2-12 times/year
1-2 times/ year
1 time/2-3 years
1 time/2-3 days for first
1-2 months; sporadically
after establishment
1 time initially
1 time/year
Once after first rain of
the season, then
monthly during the rainy
season
Once after first rain of
the season, then
monthly during the rainy
season
12 times/year
Inspect drainage time (12-24 hours). Might have
to determine infiltration rate (every 2-3 years).
Turning over or replacing the media (top 2-3
inches) might be necessary to improve infiltration
(at least 0.5 in/hr).
Nutrients in runoff often cause bioretention
vegetation to flourish.
Frequency depends on the location, plant
selection and desired aesthetic appeal.
Recommend maintaining l"-3" uniform mulch
layer.
Mulch accumulation reduces available water
storage volume. Removal of mulch also increases
surface infiltration rate of fill soil.
If drought conditions exist, watering after the
initial year might be required.
One-time spot fertilization for first year
vegetation.
Within the first year, 10% of plants can die.
Survival rates increase with time.
Check for sediment accumulation to ensure that
flow into the retention area is as designed.
Remove any accumulated sediment.
Check for erosion at the outlet and remove any
accumulated mulch or sediment.
Tasks include trash collection, plant health, spot
weeding, and removing mulch from the overflow
device.
31
-------
Table 7-2. Permeable pavement operations and maintenance considerations
Impervious to Pervious
interface
Once after first rain of
the season, then monthly
during the rainy season
Check for sediment and debris accumulation to
ensure that flow onto the permeable pavement
is not restricted. Remove any accumulated
sediment, vegetative debris, or trash. Stabilize
any exposed soil.
Vacuum street sweeper
Twice per year as needed
Portions of pavement should be swept with a
vacuum street sweeper at least twice per year or
as needed to maintain infiltration rates.
Replace fill materials
(applies to pervious
pavers only)
1-2 times per year (and
after any vac truck
sweeping)
Fill materials will need to be replaced after each
sweeping and as needed to keep voids with the
paver surface.
Miscellaneous upkeep
4 times per year or as
needed for aesthetics
Tasks include trash collection, sweeping, and
spot weeding.
Table 7-3. Stormwater wetland operations and maintenance considerations
Forebay cleanout
Invasive species/tree
control
Bank mowing and
stabilization
Outlet inspection and
cleanout
Trash removal
Rodent & mosquito
management
Frequency
As needed, typical 5-10
years
Semi-annual
Monthly or as needed
Monthly and after storms
greater than 2 inches
As needed
As needed
Maintenance notes
Check for sediment accumulation to ensure that
flow into the retention area is as designed.
Remove any accumulated sediment.
Within the first year, 10% of plants can die.
Survival rates increase with time.
Frequency depends on the location, plant
selection and desired aesthetic appeal.
Check for erosion at the outlet and remove any
accumulated mulch or sediment.
Remove accumulated debris throughout the
area.
Inspect for signs of vector control issues. Proper
eradication measures should be used.
32
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8. Green Infrastructure Practice Cost Estimates
The estimates for implementing the green infrastructure practices at the 3BGI project site are found in
Table 8-1 and Table 8-2. Duke Street costs are estimated based on the existing site conditions and
providing treatment of the 1.95 inch 24-hour Type III distributed storm per requirements. The vegetated
infiltration basin costs are estimated based on the existing site conditions and providing treatment of the
1.22 inch 24-hour Type III distributed storm per maximum available implementation space. It is assumed
that all construction is a retrofit.
Table 8-1. Duke Street cost estimate
Item No
1
2
3
4
5
7
8
9
10
11
12
13
14
15
16
17
21
22
23
' f
Preparation
Traffic Control
Temporary Construction Fence
Silt Fence
Site Preparation
Curb and Gutter Removal
Excavation and Removal
Traditional Bioretention
Fine Grading
Soil Media
Filter Layer (sand and No. 8 stone)
Vegetation
Mulch
Curb and Gutter
Permeable Pavement
Curb and Gutter
Permeable Pavement
Structural Layer (washed no 57 or no 2 stone)
Concrete Transition Strip
Utility Conflicts
Construction Subtotal
Bond (5% of subtotal)
Mobilization (10% of subtotal)
Construction contingency (20% of subtotal)
Quantity Unit Unit Cost Total
15
545
545
545
296
1,453
162
18
1,453
14
278
363
2906
54
363
1
day
LF
LF
LF
CY
SF
CY
CY
SF
CY
LF
LF
SF
CY
LF
LS
$1,000.00
$2.50
$3.00
$3.30
$45.00
$0.72
$40.00
$45.00
$4.00
$55.00
$22.00
$22.00
$12.00
$50.00
$4.00
$10,000.00
Construction Total
24
Design (40% of Construction Total)
$15,000
$1,363
$1,635
$1,799
$13,320
$1,046
$6,480
$810
$5,812
$770
$6,116
$7,986
$34,872
$2,700
$1,452
$10,000
$111,160
$5,558
$11,116
$22,232
BfHIjTO
| $60,026 |
Total Cost
$210,093
33
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Table 8-2. Vegetated infiltration basin cost estimate1
Quantity Unit Unit Cost Total
Preparation
Traffic Control
15
Day
$1,000.00
$15,000
Temporary Construction Fence
500
LF
$2.50
$1,250
Silt Fence
500
LF
$3.00
$1,500
Site Preparation
Excavation and Removal
775
CY
$45.00
$34,875
Clearing and Grubbing
15,700
SF
$0.75
$11,775
Vegetated Infiltration Basin
Fine Grading
15,700
SF
$0.72
$11,304
Inlet Diversion Structure
LS
$15,000
$15,000
Vegetation
15,700
SF
$4.00
$62,800
Construction Subtotal
Bond (5% of subtotal)
Mobilization (10% of subtotal)
11
Construction contingency (20% of subtotal)
12 I Design (40% of Construction Total)
Total Cost
1. Cost estimate does not include the cost of acquiring the property currently held by private individuals
Typical annual routine maintenance costs are included in Table 8-3. Costs were adapted from WERF
estimates to account for the scale of the green infrastructure practice (WERF 2009). Typical routine
maintenance is similar to maintenance for landscape areas, parks, or standard asphalt streets. Maintenance
activities for the proposed green infrastructure practices may already be accounted for in existing budgets
for current maintenance and upkeep activities.
Table 8-3. Annual maintenance cost estimate
Green Infrastructure Practice
Bioretention
Permeable pavement
Vegetated Infiltration Basin
Area Unit Cost
1,453
2,906
15,700
$2.28
$0.67
$1.91
Routine Maintenance
(monthly to 2 years)
$3,312.84
$1,947.02
$29,987.00
34
-------
9. References
Anderson, L., and H. Cordell. 1988. Influence of Trees on Property Values in Athens, Georgia (USA): A
Survey on Actual Sales Prices. Landscape and Urban Planning 15(1-2): 153-164.
Beaufort County. 2012. Manual for Stormwater Best Management and Design Practices (BMP). March
2012. Available at http://www.bcgov.net/departments/Engineering-and-
Infrastructure/stormwater-management/index.php. Accessed December 2012.
Espey, M., and K. Owusu-Edusei. 2001. Neighborhood Parks and Residential Property Values in
Greenville, South Carolina. Journal of Agricultural and Applied Economics 33(3):487-492.
Hastie, C. 2003. The Benefit of Urban Trees. A summary of the benefits of urban trees accompanied by a
selection of research papers and pamphlets. Warwick District Council. Available at
http://www.naturewithin.info/UF/TreeBenefitsUK.pdf Accessed September 2010.
Hobden, D., G. Laughton. and K. Morgan. 2004. Green Space Bordersa Tangible Benefit? Evidence
Kloss, C., and C. Calarusse. 2006. Rooftops to Rivers - Green strategies for controlling stormwater and
combined sewer overflows. Natural Resource Defense Council. June 2006. Available at
http://www.nrdc.org
Kou, F., and W. Sullivan. 200la. Environment and Crime in the Inner City: Does Vegetation Reduce
Crime. Environment and Behavior 33(3):343-367.
Kuo, F., and W. Sullivan. 200 Ib. Aggression and Violence in the Inner City: Effects of Environment via
Mental Fatigue. Environment and Behavior 33(4):543-571.
Kuo, F. 2003. The Role of Arboriculture in a Healthy Social Ecology. Journal of Arboriculture 29(3).
New Yorkers for Parks and Ernst & Young. 2003. Analysis of Secondary Economic Impacts Resulting
from Park Expenditures. New Yorkers for Parks, New York, NY.
Northeastern Illinois Planning Commission (NIPC). 2004. Sourcebook on Natural Landscaping for Local
Officials.
http://www.chicagowilderness.org/files/4413/3087/4878/natural_landscaping_sourcebook.pdf.
Accessed December 2012.
Pincetl, S., J. Wolch, J. Wilson, and T. Longcore. 2003. Toward a Sustainable Los Angeles: A Nature's
ServiceslApproach. USC Center for Sustainable Cities, Los Angeles, CA.
Shultz, S., andN. Schmitz. 2008. How Water Resources Limit and/or Promote Residential Housing
Developments in Douglas County. University of Nebraska-Omaha Research Center, Omaha, NE.
http://unorealestate.org/pdf/UNO_Water_Report.pdf. Accessed September 1, 2008.
United States Environmental Protection Agency (USEPA). 2004. Storm Water Management Model
(SWMM). User's Manual Version 5.0. Lewis A. Rossman. November 2004. Available at
http://www.epa.gov/nrmrl/wswrd/wq/models/swmm/. Accessed December 2012.
Voicu, I., and V. Been. 2009. The Effect of Community Gardens on Neighboring Property Values. Real
Estate Economics 36:2(241-283).
Wachter, S. M. and G.W. Bucchianeri. 2008. What is a Tree Worth? Green-City Strategies and Housing
Prices. Real Estate Economics, Vol. 36, No. 2, 2008. Available at SSRN:
http://ssrn.com/abstractM084652
Ward, B., E. MacMullan, and S. Reich. 2008. The Effect of Low-impact Development on Property Values.
ECONorthwest, Eugene, Oregon.
Water Environment Research Foundation (WERF). 2009. User's Guide to the BMP and LID Whole Life
Cost Models. SW2R08. Version 2.0. Alexandrian, VA.
35
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Wolf, K. 1998. Urban Nature Benefits: Psycho-Social Dimensions of People and Plants. Human
Dimension of the Urban Forest. Fact Sheet #1. Center for Urban Horticulture. University of
Washington, College of Forest Resources.
Wolf, K. 2008. With Plants in Mind: Social Benefits of Civic Nature. Winter 2008. Available at
http://www.MasterGardenerOnline.com. Accessed December 2012.
36
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Appendix A - Conceptual Design Layouts
-------
Appendix B - EPA SWMM Design Parameters
-------
Beaufort EPA SWMM Parameter Tables - Duke Street
Rain Gages 24-hour Type
Subcatchment (Bioretention)
Area
Width
% Slope
% Imperv
N-lmperv
N-Perv
Dstore-lmperv
Dstore-Perv
%Zero-lmperv
Subarea Routing
Percent Routed
Infiltration
0.5
1000
0
50
0.012
0.1
0.05
0.3
0
Outlet
100
Morton
acres
ft
in
in
Subcatchment (Permeable Pavement)
Area
Width
% Slope
% Imperv
N-lmperv
N-Perv
Dstore-lmperv
Dstore-Perv
%Zero-lmperv
Subarea Routing
Percent Routed
Infiltration
1
1000
0
50
0.012
0.1
0.05
0.3
0
Outlet
100
Morton
acres
ft
in
in
Morton Infiltration Parameters
Max Infil. Rate
Min Infil. Rate
Decay Constant
Drying Time
Max Volume
3
0.5
4
7
0
in/hr
in/hr
1/hr
days
in
Bioretention
Surface
Storage Depth
Vegetative Cover Fraction
Surface Roughness (Mannings n)
Surface Slope
SON
Thickness
Porosity
Field Capacity
Wilting Point
Conductivity
Conductivity Slope
Suction Head
6
0.05
0.1
0.0
36
0.4
0.25
0.1
2
10
3.5
in
%
in
in/hr
in
Storage
Height
Void Ratio
Conductivity
Clogging Factor
Underdrain
Drain Coefficient
Drain Exponent
Drain Offset Height
0.1
0.4
2
0
0
0.5
0
in
in/hr
in/hr
in
B-l
-------
LID Controls
Permeable Pavement
Surface
Storage Depth
Vegetative Cover Fraction
Surface Roughness (Mannings n)
Surface Slope
Pavement
Thickness
Void Ratio
Impervious Surface Fraction
Permeability
Clogging Factor
1
0.0
0.014
0.0
6
0.15
0
100
0
in
%
in
in/hr
Storage
Height
Void Ratio
Conductivity
Clogging Factor
Underdrain
Drain Coefficient
Drain Exponent
Drain Offset Height
6
0.4
2
0
0
0.5
0
in
in/hr
in/hr
in
Routing
Permeable Pavement --> Bioretention --> Outlet
B-2
-------
Beaufort EPA SWMM Parameter Tables - Basin
Hydrology
Rain Gages 24-hour Type III Distribution
Subcatchment
Area
Width
% Slope
% Imperv
N-lmperv
N-Perv
Dstore-lmperv
Dstore-Perv
%Zero-lmperv
Subarea Routing
Percent Routed
Infiltration
36.29
1500
0.5
32
0.012
0.1
0.05
0.3
0
Outlet
100
Morton
acres
ft
in
in
Morton Infiltration Parameters
Max Infil. Rate
Min Infil. Rate
Decay Constant
Drying Time
Max Volume
3
0.5
4
7
0
in/hr
in/hr
1/hr
days
in
Storage Units
Max Depth
Initial Depth
Ponded Area
Evap Factor
Infiltration
Storage Curve
1
0
0
0
Yes
Functional
«
ft
ft2
Storage Infiltration Parameters
Green-Ampt
Suction Head
Conductivity
Initial Deficit
1.93
3
0
in
in/hr
B-3
-------
Functional Curve Parameters
Coefficient
Exponent
Constant
17000
0
0
B-4
-------
Appendix C - Charrette Process Review Memo
-------
City of Beaufort Design Charrette
Design Charrette Summary
On November 13, 14, and 15, 2012 the EPA project team facilitated a design charrette intended to
identify potential green infrastructure retrofit projects in the North West Quadrant neighborhood in the
City of Beaufort, SC. The design charrette provided the opportunity for the EPA project team to
coordinate and interact with planning and public works staff from the City of Beaufort to determine the
most beneficial and cost-effective strategy for implementing green infrastructure. The intent of this memo
is to document and present the results from the design charrette.
Dayl
Day 1 began with an introductory meeting with Lauren Kelly (City Planner), Isaiah Smalls (Public Works
Director), Monica Holmes (Planning consultant), Katherine Snyder (EPA Region IV), and other members
of the project team. The city team discussed their goals for the project and provided some background
information on current projects. The city is currently implementing a green street along Bladen Avenue,
which incorporates permeable pavement in the parking lanes. Additionally, the project team provided an
introductory presentation discussing the concepts of LID and green infrastructure focusing on
implementing permeable pavement and bioretention in the right-of-way. Given the multiple definitions
and perceptions of LID and green infrastructure, it was important to present some of the basic concepts to
ensure that the city team was using similar terminology in describing green infrastructure and specific
Stormwater Control Measures (SCM).
For the remainder of the first day, Lauren Kelly and Monica Holmes led the team on a tour of the
downtown Beaufort area and the Northwest Quadrant neighborhood. Anne Keller (EPA Region IV)
joined the team in the tour of the neighborhood. Lauren and Monica provided details on the unique
climate and topography in the historic neighborhood and identified potential areas for SCM
implementation. Lamar Taylor (City of Beaufort Public Works) joined the tour of the Northwest
Quadrant Neighborhood to identify known problem areas where SCMs could possibly be implemented to
alleviate flooding issues. Lamar also provided details on the green streets currently being implemented on
Bladen and Duke Streets (Figure 1 and Figure 2). Multiple approaches to SCM implementation with
multiple site configurations were discussed throughout the tour of the neighborhood. Projects were
discussed based on a parcel approach with SCMs that could be implemented to treat larger drainage areas
or SCMs that could be implemented in the right-of-way. Seven potential sites were identified through the
course of the field tour with multiple options for improvement or SCM implementation.
-------
Figure 1. Permeable pavement on Bladen Street.
Figure 2. Green street construction on Duke Street.
Day Two
Day two focused on refining the potential sites and recommended options for improvement or SCM
implementation. Figure 3 shows the location of the seven potential sites and Table 1 presents potential
sites and recommended improvements in order of feasibility or preference. Projects were evaluated based
on implementation on a full parcel or block scale and implementing SCMs within the right-of-way or
street scale. Each identified site was evaluated for potential to improve drainage or reduce flooding,
potential water quality improvement based on treatment volume, potential for SCM demonstration, multi-
use benefit for the surrounding neighborhood, and ancillary benefits such as aesthetic improvement. The
potential for SCM demonstration was evaluated based on the proximity to parks, schools, or other BMPs
that would attract the public. Integration into the transects is discussed in the following sections. Full
conceptual designs will be developed for the top two sites. Additional details and recommendations for
the remaining 5 sites are presented below.
-------
Candidate Sites
Street Scale
5 - Pilot Street betwen Prince and North St.
6 - Duke and Prince St. Conection
7 - Duke St. from Bladen to Pilot St.
Figure 3. Potential sites for SCM implementation or improvement.
Table 1. Candidate sites
7
2
3
4
5
6
1
Candidate
Project/Tra n sects
Duke Street from Bladen to
Pilot Street
Private Lot at intersection
of Prince and Hamar
Glebe Street Extension
Stormwater Dry Pond
Hamar and Washington
Green Street along Pilot
from Prince to North Street
Connection of Duke and
Princeton
Section 8 Housing Church
and Washington Streets
Candidate Improvements
Bump Outs for Tree Space
Vegetated Curb Extensions
Residential on-lot
Permeable Pavement
Drainage
Improvement
o
o
o
*
*
Water
Quality
w
w
w
Integration of
Transects
o
w
o
o
w
w
Demonstration
of Technology
w
.
V
,
,
O
w
w
w
Neighborhood
Benefit
w
*
*
Ancillary
Benefits
w
-------
Glebe Street Extension
The catch basin at the low point of Prince Street between Pilot Street and Euhaw Street is continually
clogged causing flooding on Prince Street (Figure 4). Drainage collecting in the low point along Prince
Street could be diverted to a bioswale implemented in the city controlled right-of-way intended to extend
Glebe Street to Prince Street shown in Figure 5. A SCM at this location would treat runoff from a small
and isolated drainage area. Some of the flooding could potentially be alleviated by cleaning the catch
basin on Prince Street. Therefore, this project was given a lower priority.
Figure 4. Clogged catch basin.
verti.cn I T^i
overflow
Armored
Cucrb Cut
soil Medi
Figure 5. Right-of-way extending Glebe Street to Prince Street.
Layer
Soil Mtdla B-flmer
width (mm 2', IM.RX. S'
li/up) (y)
Figure 6. Example bioswale.
-------
Figure 7. Example of a bioswale in the right-of-way.
Stormwater Dry Pond at Hamar Street and Washington Street
A dry pond or infiltration basin is currently treating the runoff from the parcel owned by the Department
of Social Services at 1905 Duke Street (Figure 8). This pond could benefit from some aesthetic
improvements and could benefit from conversion to a bioretention area (Figure 9) or could potentially be
converted to a stormwater wetland (Figure 10). It is possible that some additional runoff could be
converted from the surrounding parcels and Washington or Hamar Streets to increase the water quality
treatment benefit. The design treatment capacity of the dry pond should be verified before additional
runoff is diverted for treatment. Because the existing dry pond is already providing treatment and the as
build design plans are not available, this potential project was given a lower priority.
-------
Figure 8. Dry pond at Hamar and Washington Streets.
Figure 9. Example bioretention area.
-------
Figure 10. Example stormwater wetland.
Green Street along Pilot from Prince to North Street
Implementing permeable pavement in the parking stalls and bioretention in the right-of-way would
provide treatment for the runoff from Pilot Street and provide a demonstration project and outdoor
classroom for the students at Beaufort Elementary. Concepts similar to those already implemented along
Bladen Street incorporating permeable pavement could be utilized along Pilot Street.
Connection of Duke and Prince Streets
Utilizing the four vacant lots surrounding 1880 Prince Street to connect Prince Street and Duke Street will
provide an additional avenue for traffic around Beaufort Elementary School. The area within the right-of-
way can then be utilized for parking with permeable pavement parking stalls, similar to the concepts
incorporated along Bladen Street and at city hall, to provide treatment for runoff from Prince and Duke
Streets. Given the close proximity to Beaufort Elementary School, this project could also serve as an
excellent demonstration opportunity. Because the project would require acquiring the parcels and the
limited treatment that would be provided, this project was given a lower priority.
-------
Figure 11. Permeable pavement parking stalls.
Section 8 Housing Church and Washington Streets
Bioretention and permeable pavement could be incorporated into the landscaping and parking areas of the
public housing located at 1200 Washington Street. This area is a low spot and known to flood. Therefore,
incorporating LID SCMs concepts into the site could provide water quality improvement as well as
reduce the flooding in smaller storm events. Because of the extreme flooding and potential for vandalism,
this site was given a lower priority.
-------
-^
Figure 12. Residential bioretention with permeable pavement
Figure 13. Bioretention at a residence.
It was determined, through discussion with the city team including the public works director, that the
potential sites at Hamar Street and Prince Street and the right-of-way along Duke Street best fit the needs
-------
of the city by providing the greatest potential for drainage improvement, water quality benefit, SCM
demonstration, mutil-use opportunities, and aesthetic enhancement. Once the top two sites had been
determined the team returned to the neighborhood to perform additional field reconnaissance and further
refine the approach to implementing green infrastructure at each site. While in the field the team took
additional photos, noted the approximate drainage area, the existing drainage network and drainage
patterns, existing conditions of each potential site, and discussed possible multiple uses and community
benefit.
The team then returned to the town hall with the additional information for each site and began compiling
the relevant information gathered during the field reconnaissance. Concepts were developed illustrating
potential SCM configuration at each site. It was determined that a green street concept would be
implemented along Duke Street, utilizing bioretention, to treat the runoff before entering the catch basin
closest to the intersection with Bladen Street. Grass pavers could be implemented in the right-of-way west
of Bladen Street to stabilized the shoulder and maintain a healthy patch of grass. The gutter in that section
would be reconfigured to allow sheet flow onto the shoulder. Figure 14 and Figure 15 show rough
concepts for a green street on Duke Street.
Figure 14. Bioretention on Duke Street.
10
-------
x \ V
Figure 15. Green street on Duke Street.
The vacant portion of the parcels closest to 1798 Prince Street could be developed as a neighborhood park
incorporating stormwater treatment. A diversion structure placed just south of the catch basin closest to
Hamar and Prince would divert flow from the storm drain running along Hamar Street for treatment in the
park. A stormwater wetland or bioretention area, depending on the depth to the water table and infiltration
capacity, could be used for water quality treatment similar to the concepts shown in Figure 16 and Figure
17.
Figure 16. Concept for Hamar and Prince.
11
-------
Figure 17. Potential SCM configuration for Hamar and Prince.
In addition to the plan for a conceptual design for each site, the team discussed possible opportunities for
developing tools to incorporate into the Regulating Plan for the City of Beaufort. Transects describing
typical street sections in the City of Beaufort with the typical neighborhood setting, average street
configuration, and level of urbanization were developed for the Regulating Plan. Concepts for integrating
green infrastructure into each transect were developed that could possibly be integrated into the
Regulating Plan.
Day three
The information gathered during the site visits in day one and day two, the concepts developed for each
transect for the Regulating Plan, and the concepts developed for both potential sites was compiled into a
presentation. The presentation was then delivered by the city team to the director of public works, the
planning director, and the city engineer outlining the charrette process and the conceptual plan for each of
the two potential sites. The presentation is included as an attachment.
Next Steps
The EPA project team will incorporate the knowledge gained from the charrette and the conceptual plan
for the two sites in the Northeast Quadrant into a full conceptual design for each site. The conceptual
design will provide additional details for incorporating stormwater management into the features of the
site that utilize green infrastructure concepts. The sketches and renderings developed during the charrette
will be modified to show additional details for the green infrastructure practices including the appropriate
depths and materials. Performance specifications will be included for each SCM including the
approximate square footage of each SCM and SCM type required to meet multiple treatment goals.
12
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