LID-ManualGuidance
Manual
Low Impact
DeveLopment
Funding provided by a NOAA grant through North
Carolina Coastal Nonpoint Source Program // Division
of Water Quality // North Carolina Division of Coastal
Management // North Carolina Coastal Federation
2
.
i
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This guidance document is part of an ongoing effort to encourage and allow for Low Impact
Development (LID) technologies as an alterna�ve and voluntary op�on for developers to sa�sfy
stormwater requirements and watershed goals. The project was funded by a grant secured by the
North Carolina Coastal Federa�on (NCCF) from the Na�onal Oceanic and Atmospheric Administra�on
(NOAA) and includes several public and private partners including New Hanover County, City of
Wilmington, North Carolina Coastal Nonpoint Source Pollu�on Program of the Division of Water
Quality, and NCCF. Larry Coffman, a na�onal LID consultant, provided the ini�al technical support for
the project and prepared the first dra�s of the LID guidance manual. NCCF worked jointly with the
consultant to provide technical support for the project.
The scope of the project included the following:
1. Review of current ordinances to determine roadblocks.
2. Comprehensive review of LID principles and prac�ces to determine appropriateness
for coastal applica�on.
3. Guidance on LID technologies compliant with local and State requirements.
4. Prepara�on of an LID manual and resolu�on to enable developers to use LID on a
voluntary basis.
5. Distribu�on of educa�onal and outreach materials.
6. Development of an LID spreadsheet modeling tool to aid engineers, planners, and
developers with design and permi�ng of LID projects.
A���������������
NCCF and County staff took the lead role in facilita�ng the County project team, organizing logis�cs
for mee�ngs, and workshops. Special acknowledgment should be given to Shawn Ralston, Senior
Environmental Planner for New Hanover County Planning Department for all of her technical support
and organiza�on for the mee�ngs. Special thanks must also be given to Lauren Kolodij, Program
Director of NCCF, for all her work to obtain grant funding and then to provide technical support
throughout the project. Special thanks also to Phil Prete, City of Wilmington Planning Department, for
his technical support and edi�ng assistance.
The Technical Advisory Commi�ee (TAC) for the project included mul�ple stakeholders with
representa�ves from various County, City, and State agencies as well as environmental groups and
private engineering, consul�ng, and development firms. The TAC played a vital role in the project with
their comments and par�cipa�on.
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T�������� A������� C�������� M������
Benjamin Adei, City of Wilmington Stormwater Services
Jennifer Braswell, New Hanover Soil and Water Conserva�on District
Sam Burgess, New Hanover County Planning
Richard Collier, McKim and Creed
Melanie Cook, Coastal Carolina Tomorrow
Jane Daughtridge, New Hanover County Planning
Carey Disney-Ricks, Wilmington Regional Associa�on of REALTORS
Bryan Greene, Cape Fear Commercial
Don Hamilton, Southwind Surveying & Engineering
Bill Hart, New Hanover Soil and Water Conserva�on District
Ann Hines, New Hanover County Zoning
Patricia Hughes, NCDENR, Coastal Nonpoint Source Pollu�on Program
Jim Iannucci, New Hanover County Engineering
Lauren Kolodij, North Carolina Coastal Federa�on
Lisa Manning, Cavanaugh and Associates, P.A.
David Mayes, City of Wilmington Stormwater Services
Shelly Miller, New Hanover Soil and Water Conserva�on District
Tyler Newman, Wilmington-Cape Fear Home Builders
Chris O’Keefe, New Hanover County Planning
Phil Prete, City of Wilmington Environmental Planning
Shawn Ralston, New Hanover County Planning
Sco� Stewart, Demarest Landing/Devaun Park Developments
Steven S�ll, New Hanover County Zoning
Spruill Thompson, Cape Fear Commercial
Cameron Weaver, NCDENR - DWQ
Kenneth Wells, New Hanover County Coopera�ve Extension
Cindee Wolf, Withers & Ravenel
Kenneth Wrangell, Wrangell Homes
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T���� �� C�������
Chapter 1 - Introduc�on to LID ...................................................................................1
1.1 Purpose and Applica�on of the Manual
Chapter 2 - LID Planning and Design Guidance ..........................................................4
2.1 Considera�ons in Coastal Situa�ons
2.2 Basic Site Planning Principles for Residen�al Development
2.3 LID Site Design for High Density and Commercial Development
Chapter 3 - Urban Retrofit and Redevelopment .......................................................16
3.1 General
3.2 LID Retrofit Case Studies
Chapter 4 - Road and Driveway Design .....................................................................24
4.1 Open Road Design
4.2 Urban Road Design
4.3 Driveway Design
4.4 Sidewalks and Bike Paths
4.5 Addi�onal Sources for Informa�on
Chapter 5 - LID BMPs General Design Guidance .......................................................31
5.1 Introduc�on
5.2 Bioreten�on
5.2.1 General
5.2.2 Performance
5.2.3 Applica�ons and Advantages
5.2.4 General Design Guidance
5.2.5 Site and Construc�on Considera�ons for Non-tradi�onal
Bioreten�on
5.2.6 Inspec�on and Maintenance Requirements
5.2.7 Example Bioreten�on Design Details
5.3 Vegetated and Grassed Swales
5.3.1 General
5.3.2 Performance
5.3.3 General Design Guidance
5.3.4 Inspec�on and Maintenance Requirements
5.3.5 Example Swale Design Details
5.4 Permeable Pavement Systems
5.4.1 General
5.4.2 Performance
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5.4.3 General Design Guidance
5.4.4 Open-Cell and Open-Joint Block Pavers
5.4.4.1 General
5.4.4.2 Applica�ons and Advantages
5.4.4.3 Limita�ons
5.4.4.4 General Design Guidance
5.4.4.5 Inspec�on and Maintenance Requirements
5.4.5 Porous Concrete and Asphalt
5.4.5.1 General
5.4.5.2 Applica�ons and Advantages
5.4.5.3 Limita�ons
5.4.5.4 Si�ng Criteria
5.4.5.5 General Design Guidance
5.4.5.6 Inspec�on and Maintenance Requirements
5.4.6 Porous Turf Pavement
5.4.6.1 General
5.4.6.2 Applica�ons and Advantages
5.4.6.3 Limita�ons
5.4.6.4 Si�ng Criteria
5.4.6.5 General Design Guidance
5.4.6.6 Inspec�on and Maintenance Requirements
5.4.7 Porous Gravel Pavement
5.4.7.1 General
5.4.7.2 Applica�ons and Advantages
5.4.7.3 Limita�ons
5.4.7.4 Si�ng Criteria
5.4.7.5 General Design Guidance
5.4.7.6 Inspec�on and Maintenance Requirements
5.4.8 Open-Celled Plas�c Grids
5.4.8.1 General
5.4.8.2 Applica�ons and Advantages
5.4.8.3 Limita�ons
5.4.8.4 Si�ng Criteria
5.4.8.5 General Design Guidance
5.4.8.6 Inspec�on and Maintenance Requirements
5.5 Rain Water Catchment Systems
5.5.1 General
5.5.2 Applica�ons and Advantages
5.5.3 Limita�ons
5.5.4 Si�ng Criteria
5.5.5 General Design Guidance
5.5.6 Inspec�on and Maintenance Requirements
5.6 Tree Box Filters
5.6.1 General
5.6.2 Performance
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5.6.3 Applica�ons and Advantages
5.6.4 General Design Guidance
5.6.5 Stormwater Planters
5.7 Surface Sand Filters
5.7.1 General
5.7.2 Applica�ons and Advantages
5.7.3 Limita�ons
5.7.4 Si�ng Criteria
5.7.5 General Design Guidance
5.7.6 Inspec�on and Maintenance Requirements
5.8 Green Roof
5.8.1 General
5.8.2 Performance
5.8.3 General Design Guidance
5.8.4 Applica�ons and Advantages
5.8.5 Limita�ons
5.8.6 Inspec�on and Maintenance Requirements
5.9 Stormwater Wetlands
5.9.1 General
5.9.2 General Design Guidance
5.9.3 Design and Maintenance Requirements
5.10 Infiltra�on Trenches and Basins
Chapter 6 - Pu�ng LID Into Prac�ce .........................................................................79
6.1 Introduc�on
6.2 Permi�ng LID Projects Using “LID-EZ”
6.3 Construc�ng LID Projects
6.3.1 Training
6.3.2 Communica�on
6.3.3 Erosion and Sediment Control
6.3.4 Tree Protec�on
6.3.5 Construc�on Sequence
6.3.6 Construc�on Administra�on
6.4 Maintenance
A���������
Appendix I - Sample Maintenance Agreement
Appendix II - Suggested Plant List
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C������ 1 - I����������� �� LID
Water quality that meets the designated standards and thriving fisheries are important factors in
sustaining quality of life, the unique character of our community and con�nued economic growth.
While protec�ng water resources is a difficult challenge, the City and County are commi�ed to
implemen�ng their stormwater management policies as well as the Coastal Area Management Act
(CAMA) Land Use Plan as a means to maintain and restore water quality.
Development prac�ces increase impervious areas. The increase in the amount of impervious area
reduces the ground surface available for precipita�on to infiltrate into the ground, increases pollutant
loads in stormwater runoff, and typically shortens the dura�on of �me it takes for stormwater runoff
to reach receiving waters. Riparian buffers and wetlands are o�en diminished, thereby reducing the
likelihood of stormwater filtra�on through na�ve
vegeta�on.
Though the magnitude of the result is site-specific,
the increased volume of runoff and peak discharges
can be substan�ally greater than predevelopment
condi�ons, as shown in Figures 1 and 2. The
increased and new pollutant quan��es that are
carried by stormwater enter into receiving waters.
These pollutants include bacteria, nutrients and
metals. Over �me, as impacts con�nue, the
receiving waters will experience diminished water
quality and lost habitat, thereby drama�cally
altering the hydrology of receiving waters.
Ironically, many of these adverse impacts are not
inevitable, but occur as a result of the methods
we choose to collect, convey, concentrate
and treat runoff in a manner that creates a
highly efficient drainage paradigm. The more
efficiently the drainage system moves water
away from the site, the higher the cumula�ve
impacts o�en can be seen. These cumula�ve
impacts o�en lead to flooding, erosion and
water quality degrada�on. As urbaniza�on
increases, it is now clear that conven�onal
stormwater treatment technology alone is
not enough to prevent con�nued degrada�on
of water quality or prevent adverse impacts
to the ecological integrity of our waters and
its designated uses. Low impact development (LID) technology provides addi�onal tools designed to
op�mize the use of the urban landscape to reduce and treat runoff and be�er meet water quality
protec�on goals.
Figures 1 & 2. Runoff increases drama�cally with the amount
of urbaniza�on. Source Prince George’s County, MD
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LID is a comprehensive stormwater management technology, first described in 1999 in the Prince
George’s County, Maryland, Low-Impact Development Design Strategies, An Integrated Design
Approach. LID is an approach to site development and stormwater management that minimizes
development impacts to the land, water and air. LID may be incorporated into site design with site
level planning, design, and control techniques that are focused toward restoring and op�mizing
the land’s ability to absorb water, capture pollutants and process pollutants in the landscape. This
is accomplished through site design techniques that preserve, minimize or restore the landscaped
capacity in order to restore vital ecological processes to the fullest extent prac�cal.
LID is comprised of stormwater management principles and prac�ces that u�lize a wide range of
site planning and treatment techniques to manage both runoff volume and water quality. The LID
approach emphasizes the integra�on of site design and planning techniques that conserve natural
systems and the hydrologic func�ons of a site. LID is not a land use control approach that reduces
development poten�al - it is a stormwater technology that may be integrated into development to
reduce environmental impacts. It is a decentralized approach (as opposed to an end-of-pipe approach)
where small-scale techniques are distributed and integrated throughout the site to retain, detain, treat,
and u�lize runoff in a manner that more closely mimics the natural water balance of the land in its
pre-developed condi�on. Coastal areas are o�en par�cularly suitable for LID. In coastal areas, the land
is rela�vely flat, the soils are sandy and developable land is located in close proximity to ecologically
sensi�ve resources. While these condi�ons present difficul�es for tradi�onal designs, they present
opportuni�es to develop an LID site design.
The following are the basic principles of LID:
1. Op�mize Conserva�on. Conserve natural resource areas, sensi�ve areas, vegeta�on and
soils and wisely use them to reduce and treat runoff to maintain the site’s ability to retain
and detain runoff.
2. Mimic the Natural Water Balance. Infiltrate water at the same manner and rate as
predevelopment water infiltra�on. This requires careful evalua�on of the soils onsite, taking
par�cular no�ce of the sandier soils. Evaluate where the most permeable, sandy soils are
located – these areas are most o�en the most appropriate for LID control strategies.
3. Decentralize and Distribute Controls. The more LID techniques applied to a site, and the
more uniformly those techniques are distributed throughout the landscape, the more
effec�ve LID will be. By making the landscape more amenable to filter and treat runoff, it will
take longer for stormwater runoff to leave the site. Increasing runoff �me of travel
significantly reduces the flows and discharges.
4. Disconnect Impervious Surfaces. Impervious surfaces should be disconnected, rather then
connected. The runoff characteris�cs of the site are completely changed when impervious
surfaces are disconnected and drain to a landscape feature or LID prac�ce. This approach
prevents the adverse cumula�ve effects of concentrated flows.
5. Create Mul�func�onal and Mul�purpose Landscapes. Many features of the urban landscape
can be designed in a way to provide more func�onality and reduce impacts. Every landscape
feature should be designed with some beneficial hydrologic or water quality to store, retain
detain or treat runoff.
6. Think Small Scale. Integrate mul�ple, small systems into numerous aspects of the site. The
most efficient use of the landscape is to design smaller more numerous techniques. With
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several LID techniques, the stormwater system is not likely to fail. The disconnec�on of one
or two rain gardens will only have a minor impact on the effec�veness of the en�re system.
Contrast this with using one large stormwater pond if that fails the en�re system fails.
7. Ins�ll Pollu�on Preven�on Programs. All efforts should be made to reduce the introduc�on
of pollutants into the environment. This includes those pollutants generated from
construc�on ac�vi�es and human ac�vi�es. LID also includes effec�ve public educa�on
and outreach to help ensure proper use, handling and disposal of possible pollutants.
8. Account for Cumula�ve Impacts. Usually, there is not one single LID technique that is more
important. Reliance on any one LID technique for stormwater management ignores the
cumula�ve beneficial impacts of an array of LID planning and design techniques. By
combining a series of LID techniques, post-development condi�ons will be closer to mimicking
the natural hydrologic regime.
The ul�mate goal of LID is to maintain and restore a watershed’s hydrologic regime by changing
conven�onal site design to create an environmentally and hydrologically func�onal landscape that
mimics natural hydrologic func�ons. This is accomplished through the cumula�ve effects of various
LID techniques and prac�ces. The more techniques applied, the closer one can come to replica�ng the
natural sponge capacity of the landscape and its ability to capture and cycle pollutants. The uniform
distribu�on of LID controls throughout a site increases runoff �me of travel, thus drama�cally reducing
site discharge flow. All components of the urban environment have the poten�al to serve as an LID
prac�ce. This includes roo�ops, streetscapes, parking lots, driveways, sidewalks, medians and the open
spaces of residen�al, commercial, industrial, civic, and municipal land uses.
1.1 Purpose and Applica�on of the Manual
A responsibility of local government is to protect, restore and sustain the environmental integrity and
uses of waters – this is especially true in the coastal region. As urbaniza�on increases, conven�onal
stormwater treatment may not be enough to prevent con�nued degrada�on of water quality or
prevent adverse impacts to the ecological integrity of our waters and their designated uses.
Therefore, the City and County encourage the use of LID to protect or even enhance the overall
environmental quality and character of established communi�es and developing areas. This document
provides technical guidance on the applica�on of LID principles, planning, and prac�ces as an
acceptable approach to mee�ng stormwater management objec�ves.
Being that LID is a fairly new method of trea�ng stormwater runoff, an addi�onal tool has been
developed to assist with the integra�on of LID into projects within the City of County. In an effort to
aid engineers, planners, and developers with design and permi�ng of LID projects, a stormwater
management tool that quan�fies the effect of the structural and non-structural BMPs on the overall
hydrology of residen�al and commercial developments has been developed. The spreadsheet tool,
known as LID-EZ, is described in more detail in Chapter 6.2 of this manual.
While reading this manual, it is important to note that all local and state standards must be met during
the permi�ng of any project in the City or County. The purpose of this manual is not to supersede any
local or state ordinances or regula�ons.
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C������ 2. LID P������� ��� D����� G�������
When incorpora�ng LID into a site, the design represents a philosophy in which stormwater is used as
a resource. Hydrology is the organizing principle which requires designing and engineering a site in a
way that a�empts to maintain natural water balance and ecological processes. The goal is to minimize
development impacts, mimic the natural hydrology, and restore vital ecological processes necessary
to restore and maintain the integrity of our waters. A well-designed site can minimize the volume of
runoff that is generated, and maximize the treatment capabili�es of the landscape, while controlling
runoff as close to the source as possible. If designed properly, individual LID techniques can be
aesthe�cally pleasing and complement the primary use of the property.
2.1 Considera�ons in Coastal Situa�ons
Most coastal areas are rela�vely flat, the soils are sandy, and there is poten�al for heavy rainfall from
coastal storms and seasonal storms. In addi�on, many development projects are within close proximity
to environmentally sensi�ve ameni�es such as wetlands, estuaries, and surface water bodies. These
condi�ons present difficul�es for conven�onal site designs but can present opportuni�es for the
introduc�on of LID.
Many areas of the coast considered to be the most developable will have rela�vely sandy soils. In
natural condi�ons, sandy coastal soils generate very li�le runoff and provide ample ground water
recharge. Areas which have deep, sandy soils present a greater opportunity to infiltrate runoff close
to the source. However, while sandy soils drain quickly, this short dura�on drainage decreases the
filtering capacity of the soil. Before runoff is allowed to be infiltrated in these areas, runoff should be
routed through vegetated areas such as grassed swales, bioreten�on areas, filter strips and buffers
(discussed in Chapter 6) in order to aid in pollutant removal.
While less common, some coastal areas have rolling topography, shallow groundwater, and dense sub-
soils with confining layers of clay or hardpan. Typically, the steeper slopes are the result of relic dune
ridges, escarpments, or river deposits. Coastal soils which have confining layers such as hardpans or
dense clay subsoil will typically be found in areas which present other problems as well. This type of
coastal soil is usually found in areas with a shallow fluctua�ng water table, rela�vely flat topography,
or in areas which were previously much we�er and have been drained over the years. In these areas,
preventa�ve conserva�on measures and filtra�on systems such as bioreten�on and sand filters are
the most beneficial LID concepts. These methods will reduce both quan�ty of runoff and the amount
of pollutants generated. The use of addi�onal smaller, vegeta�ve LID techniques may be incorporated
throughout the site to enhance the quality of stormwater runoff.
In areas with a high groundwater table, incorpora�ng LID may be more challenging and may require
addi�onal site engineering and crea�ve grading to take advantage of swales, bioreten�on, sand
filters, and infiltra�on devices for filtra�on of pollutants. In these situa�ons, it may be more feasible
to rely on preventa�ve conserva�on to the greatest extent possible. This approach will also reduce
both quan�ty of runoff and the amount of pollutants generated. If vegeta�ve LID prac�ces are to be
used, they should be at least 2 feet above seasonal high ground water levels. The top two feet is the
biologically ac�ve zone of a plant and soil complex and is where most of the physical, chemical, and
biological pollutant removal occurs. Addi�onally, plants that tolerate wet condi�ons should be installed
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with these LID prac�ces. While infiltra�on may not be prac�cal in these areas, bioreten�on systems
designed for water filtra�on are s�ll viable op�ons. Soils and groundwater challenges may make it
more a�rac�ve to rely on conserva�on of natural vegeta�on and use of conserva�on areas to filter
runoff prior to discharging to sensi�ve waters.
One important considera�on in developing a site located within coastal areas is the protec�on of
environmentally sensi�ve wetlands, estuaries, groundwater, and surface waters. Many of the coastal
waters are degraded by high levels of fecal coliform. In coastal waters where bacteria control is
important advanced bioreten�on, filtra�on / infiltra�on, or preven�on techniques would be most
appropriate. They have been shown to be the most effec�ve prac�ces to remove bacteria from runoff.
In high ground water areas infiltra�on may not be prac�cal so bioreten�on systems designed for
filtra�on and vegeta�ve filtra�on would be the best choices.
2.2 Basic Site Planning Principles for Residen�al Development
The most important goal of LID is to mimic the predevelopment hydrology. Therefore, the most
effec�ve LID projects require a thorough understanding of the site’s soils, drainage pa�erns, and
natural features. To op�mize an LID design, it is important to consider a number of site planning
principles and follow a systema�c design process from the very beginning. Each site has a unique
set of characteris�cs and will require the use of a unique blend of site-specific LID planning and
treatment techniques. The integra�on of LID techniques into every facet of the project will require an
interdisciplinary approach.
There are several basic LID planning principles that must be followed throughout the site planning and
design process. These principles require a different way of thinking about site design. For example,
detaining and retaining water on the site and using the landscape to treat runoff without causing
flooding problems or interfering with the typical use of the property is in contrast to the current
prac�ce of grading plumbing a site to quickly remove water.
The following is a step-by-step site planning process that factors in the basic LID site design principles
and works to allow the landscape to remain a vital, func�oning part of the ecosystem. To minimize
the runoff poten�al of the development, hydrology is employed as a design element, and a
hydrologic evalua�on would be an ongoing part of the design process. It is important to note that an
understanding of site drainage can suggest loca�ons both for green areas and for poten�al building
sites. In addi�on, an open drainage system can help integrate the site with its natural features, crea�ng
a more aesthe�cally pleasing landscape.
Step 1 - Define Project Goals and Objec�ves
Iden�fy the ecological needs of the site- not just the regulatory needs. These would include the
following fundamental aspects of stormwater control:
• Runoff volume
• Peak runoff rate
• Flow frequency and dura�on
• Water quality
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Determine the feasibility for LID techniques to address volume, flows, discharge frequency, discharge
dura�on and water quality. Priori�ze and rank objec�ves, and define the hydrologic controls
required to meet objec�ves such as infiltra�on, filtra�on, discharge frequency, discharge volume, and
groundwater recharge.
It is not necessary to use or rule out a par�cular style of site development such as tradi�onal
neighborhood design, conven�onal grid pa�erns, cluster development, conserva�on design, or new
urbanism. LID techniques can be used on all different types of development styles as discussed in the
next step.
Step 2 - Thoroughly Evaluate Site’s Poten�al for LID
A site evalua�on will facilitate LID design by providing site details that will help the design team
choose the best LID techniques for each project. Special considera�on must be given for the individual
constraints of each site and the goals for the receiving waters. This step should be completed before
any site layout begins. The following are important elements of an evalua�on.
1. Conduct a detailed inves�ga�on of the site using available documents such as drainage maps,
u�li�es informa�on, soil maps, land use maps and plans, GIS data, and aerial photographs.
2. Evaluate key characteris�cs that could nega�vely affect use of LID techniques. These
characteris�cs could include available space, soil infiltra�on, water table, slope, drainage
pa�erns, sunlight, wind, cri�cal habitat, circula�on, and underground u�li�es.
3. Iden�fy protected areas, setbacks, easements, topographic features, sub drainage divides,
floodplains, slopes, wetlands, and other site features that should be protected.
4. Delineate the watershed and micro-watershed areas. Take into account previously modified
drainage pa�erns, roads, and stormwater conveyance systems.
There may be many more unique site features that influence the site design including historical
features, viewsheds, clima�c factors, energy conserva�on, noise, watershed goals, onsite wastewater
disposal, and off site flows. All of these factors help to define the building envelope and natural
features to be integrated into the LID design.
Step 3 - Maximize the Use of Natural Features and Open Space
It is important to conserve and protect natural drainage corridors, such as dry channels that convey
water during storm events, areas of na�ve vegeta�on, and open space. There are many ways to
increase the amount of open space within a project. Conserving natural features do not only reduce
impacts but they may also preserve natural ecological process and func�ons that can help maintain the
sites water balance and treat runoff.
The most successful LID designs begin with an understanding of the site’s natural resources and an
evalua�on of ways to save these features and incorporate them into the stormwater management
system. The goal is to use these features in your stormwater plan by con�nuing to direct water to the
natural features in the same manner as the predevelopment condi�ons. The major challenge with LID
is to carefully consider how best to make use of the exis�ng soils, topography and natural features to
help reduce and control runoff. The greater the use of the natural features the less clearing and grading
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that will be needed and more natural process that will be preserved. Figures 2-1 and 2-2 contrast a
conven�onal design with a conserva�on design where natural features have been saved to reduce
impacts and allow for greater use of those features to treat runoff. To the extent prac�cable wetlands,
trees, natural drainage pa�erns, swales, topography pervious soils, and depressions are conserved.
This helps to retain areas to store water and maintain the ability of the landscape to infiltrate and
treat water. Integra�ng natural features into the site plan will improve aesthe�cs and long-term
sustainability as well as minimize the cost of clearing and grading.
Op�mizing the site’s green space requires an ability to lay out the site infrastructure in a way that saves
sensi�ve natural features. Loca�ng site infrastructure away from surface waters and direc�ng runoff to
buffers, vegeta�ve filters, and exis�ng drainage features will help to reduce the quan�ty of runoff and
improve the quality of surface runoff. Integra�ng small-scale stormwater management features into
the open space and site landscape elements allows mul�func�onal use of the landscape and improves
the efficiency of stormwater management systems. This approach reduces the disturbance of the
natural soils and vegeta�on, allows for many more areas for surface runoff absorp�on, and slows water
down to increase the contact �me of water with the landscape. The basic strategy is shown in Figures
2-3 and 2-4.
Figure 2-1: Conven�onal site design with li�le
vegeta�on preserved. Source, Phil L. Stuepfert.
Figure 2-2: Conserva�on Design with preserved
vegeta�on. Source, Phil l. Stuepfert, SEC Planning.
Figures 2-3 and 2-4 demostrate conserva�on site design.
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In order to conserve natural features and promote the use of open space, several strategies should be
included in the design. These strategies include:
1. Minimize grading and site clearing only for roadways and building pads;
2. Conserve soils that infiltrate well and place LID techniques in these areas (e.g. hydrologic soil
groups A and B);
3. Construct impervious surfaces on less pervious soil groups (e.g. hydrologic soil groups C and
D);
4. Disconnect impervious surfaces by draining them to natural features; Save natural buffer
areas and use to treat runoff;
5. Increase open space.
Tradi�onal Neighborhood Developments
Most tradi�onal neighborhood developments
conserve natural features external to the lots
(Figures 2-5 & 2-6). This results in much larger
common open spaces. Lots are clustered together
which can make the addi�on of LID techniques
more challenging and expensive. Most LID
techniques will have to be highly engineered to fit
in the more densely built areas. These techniques
may include bioreten�on planter boxes along the
roadway, expanded use of porous pavements, and
underground deten�on and infiltra�on systems. In
most tradi�onal neighborhood developments, it is
likely that there will be insufficient internal space
to create enough storage for stormwater, thereby
crea�ng the need for a stormwater pond.
Figure 2-6 is a schema�c of Cline Village in Conover,
North Carolina. This neighborhood design is a good
example of how tradi�onal neighborhood developments can
be designed so that built areas are clustered and larger natural
areas are conserved. The result is that, these large conserva�on
areas can be used for mul�ple LID techniques.
Coving
There are various design methods that can be u�lized to
conserve natural features. Coving is one of those methods.
Coving is an innova�ve approach to save open space wherein
lots sizes are averaged in order to comply with zoning
restric�ons. Figure 2-7 contrasts a tradi�onal grid lot layout
with Figure 2-8, which is a coving lot layout. The natural
features are saved internally to create larger lots and common
Figure 2-5: Tradi�onal neighborhood design with external
open space and limited internal open
Figure 2-6 Clustered lots with large areas of
open space.
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spaces. In this example, when the coving design is compared to the grid design, the result was that
there was 42% less roadway, the average lot sizes increased, and there was a 31% increased lot yield.
The benefit of this style is that lots sizes are usually larger allowing for more space for the use of lot
level LID techniques such as swales and bioreten�on areas.
Step 4 - Minimize Impacts at the Lot Level
At the individual lot level, impacts should be minimized. In general, conserve wetlands, trees, natural
drainage pa�erns, swales, topography pervious soils and drainage depressions. This retains areas to
store water and maintain the landscape’s ability to infiltrate and treat water and can minimize the cost
of clearing and grading.
Once conserva�on and integra�on of the natural features in the overall stormwater management
strategy for the site have been op�mized, more can be accomplished at the lot level to further minimize
impacts and increase func�onality. The key to preven�ng excessive runoff from being generated is to
slow down veloci�es by direc�ng it toward areas where it can be absorbed. The reliance on many small
measures used throughout the site will serve this purpose be�er than a single large control measure.
There are many lot level planning and site design techniques that should be considered including
the following. It is cri�cal to ensure that these techniques are addressed in homeowners associa�on
documents, easements, and covenants to specify who is responsible for maintenance and enforcement
in order to ensure sustained opera�onal effec�veness.
• Employ a variety of professionals such as botanists, biologist, arborists, and landscape
architects when designing the site.
• Design sites in a way so that development fits into exis�ng contours. Follow exis�ng contours
and avoid stands of trees and other valuable vegeta�on when loca�ng temporary roadways.
• Maintain exis�ng topography, drainage divides, and dispersed flow paths.
• Consider plant and tree health, age, species, space required for growth, aesthe�c values, and
habitat benefits when loca�ng structures and.
• Design new landscaping to provide consistency with exis�ng vegeta�on.
• Increase (or augment) the amount of vegeta�on on the site.
• Restrict ground disturbance to the smallest possible area.
• Minimize compac�on or disturbance of highly permeable soils.
Figure 2-7 Standard Design Figure 2-8 Coving Design
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• Direct flows from paved areas to stabilized vegetated areas or other permeable surfaces such
as open spaces. Encourage sheet flow in these areas.
• Lengthen and increase the number of flow paths. Modify drainage flow paths to increase
�me of concentra�on (Tc).
• Make use of an open swale systems.
• Reduce paving and locate paved areas and structures on clay soils.
• Reduce the use of turf and apply more natural land cover.
• Disconnect roof drains.
Step 5 - U�lize Engineered LID Techniques
LID integrated prac�ces are techniques used to store or treat addi�onal volume needed to meet
regulatory needs or receiving water goals that were not obtained during the site planning process. In
some instances, the soils may be sandy or loamy and due to their depth will provide an opportunity for
infiltra�on if the velocity of runoff can be kept in check.
If site planning is not sufficient to meet the regulatory objec�ves, addi�onal hydrologic control needs
may be addressed through the use of engineered LID prac�ces. Evaluate supplemental needs. If
supplemental control for either volume or peak
flow is s�ll needed a�er the use of LID prac�ces,
selec�on and lis�ng of addi�onal management
techniques should be considered. For example,
where flood control or flooding problems are key
design objec�ves, or where site condi�ons, such
as poor soils or a high water table, limit the use
of LID prac�ces, addi�onal conven�onal end-
of-pipe methods, such as large deten�on ponds
or constructed wetlands, should be considered.
In some cases their capacity can be reduced
significantly by the use of LID upstream. It may
be helpful to evaluate several combina�ons of LID
features and conven�onal stormwater facili�es
to determine which combina�on best meets the stated objec�ves. Use of hydrologic evalua�ons can
assist in iden�fying the alterna�ve solu�ons prior to detailed design and construc�on costs.
One important goal of LID is to create addi�onal storage volume to meet regula�ons. This can be
achieved in many cases by increasing the treatment capacity of the landscape using infiltra�on where
feasible. Use of aesthe�cally pleasing landscape features to store runoff makes mul�func�onal use
of the green space. There are a wide range of engineered LID techniques than can be used to treat
the required water quality volume or design storm. The North Carolina stormwater management
regula�ons encourage the use of infiltra�on, basins/ponds, swales, and vegeta�ve filters. Most LID
prac�ces use these same basic principles. However, rather than using these types of prac�ces on a
large scale at the end of pipe, LID uses prac�ces on a much smaller scale some�mes integrated into
each site as in the sketch in figure 20. If the conserva�on and minimiza�on techniques do not allow
you to provide for the proper surface storage and infiltra�on methods to capture runoff it will be
necessary to engineer more storage and treatment capacity into the site using the LID prac�ces found
in Chapter 6.
Figure 2-9 Comparison of pre- and post-development
hydrographs. CWP 1992.
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Step 6 - Create an LID Master Plan
An overall design sketch of the site is an important tool to ensure
that all aspects of LID have been employed in a manner that
op�mizes conserva�on and the number, types, and placement
of LID control prac�ces. It is important to keep all land areas as
mul�func�onal as possible to provide some type of infiltra�on,
filtra�on, or reten�on. The master plan helps to iden�fy all key
control issues (water quality, water quan�ty, water conserva�on)
and implementa�on areas. The Plan specifies selected LID
technologies and any connec�ons they have to stormwater
overflow units and sub-surface deten�on facili�es. In order to
minimize the runoff poten�al of the development, a hydrologic
evalua�on should be an ongoing part of the design process. An
understanding of site drainage can suggest loca�ons both for
green areas and for poten�al building sites. An open drainage
system can help integrate the site with its natural features,
crea�ng a more aesthe�cally pleasing landscape. Integra�on of LID techniques into every aspect
requires an interdisciplinary approach.
• U�lize exis�ng drainage pa�erns
• Route flow over longer distances
• Use overland sheet flow
• Maximize runoff storage in natural depression
• Fla�en slopes where possible
• Re-vegetate cleared and graded areas
Step 7 – Incorporate a Pollu�on Preven�on Plan
Another important part of LID that is o�en overlooked is that of pollu�on preven�on. Developers,
property owners, and property managers all play a role in helping to reduce the introduc�on of
pollutants into the environment and the proper opera�on and maintenance of LID techniques.
Developers are encouraged to work with poten�al property owners to educate them on the role and
func�on of the LID techniques in their development and located on their property. The ecologically
based approach and greater use of conserva�on and landscaped based prac�ces of LID may be an
effec�ve marke�ng tool. O�en developers have found it possible to obtain lot premiums for the
landscape ameni�es of an LID design.
Below is a list of ac�vi�es to promote pollu�on preven�on:
• Create an environmental stewardship mission statement for the development
• Explain the benefits of low impact development on the surrounding proper�es
• Provide interpre�ve signage or informa�on for historical and cultural
resources.
• Post the mission statement at the main entrance to the development
Figure 2-10 LID master plan showing overall
LID techniques including
conserva�on areas.
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• Publicize the environmental benefits of project (e.g., protec�on of natural space,
wildlife and habitat protec�on, water quality)
• Incorporate environmental benefits in marke�ng literature
• Ac�vely par�cipate with builders in si�ng and landscaping of individual lots
• Install pet waste sta�ons and educa�onal
signage about the natural features and/or
best management prac�ces
• Provide interpre�ve facili�es that assist in
educa�ng residents and visitors about the
natural features of the site
• Develop a program to inform property
owners on how to maintain LID prac�ces;
conserva�on areas; use of na�ve plants;
water conserva�on, and the proper use
handling and disposal of household
hazardous waste, lawn care products, and car
care chemicals.
• Publicize the financial and community benefits of low impact development such as aesthe�cs,
passive open space, rain gardens, wildlife conserva�on, reduced lawn care, maximum tree
cover, energy and water savings, and improving water quality.
• Include informa�on about proper use of fer�lizers, pes�cides, and herbicides and pet waste
management.
• Provide informa�on about the importance of proper maintenance of LID techniques by the
homeowners or homeowners associa�on.
• Promote the proper use of rain barrel for water conserva�on and to help promote rainwater
as a resource.
Step 8 – Develop an Opera�on and Maintenance Plan
The first steps in ensuring the long-term effec�veness of any LID prac�ce are the proper selec�on,
loca�on, and design of the prac�ce. Equally important are the construc�on and long-term
maintenance prac�ces and techniques. It should be noted that while these elements are cri�cal to the
effec�veness of any stormwater prac�ce, the distributed and small-scale nature of LID prac�ces and
techniques make them especially vulnerable to impacts from mass grading, construc�on prac�ces and
maintenance opera�ons. Long-term neglect of LID BMPs that require intensive maintenance is a major
concern and must be addressed during the permit phase.
Proper planning for loca�on and design of LID prac�ces includes a sequence of construc�on. The
sequence of construc�on is cri�cal because some LID prac�ces cannot be built un�l the contribu�ng
drainage area has been stabilized. Similarly, if certain areas of the site are to be preserved for
post-construc�on LID prac�ces, the site design must account for adequate access to the proposed
construc�on areas without impac�ng those protected areas. Impacts to protected areas, even if only
temporary, can cause compac�on of the natural soil horizon or contamina�on with silt, thus reducing
the effec�veness and long term func�on of the prac�ce. If impac�ng a select area is unavoidable, the
plans should include provisions for restora�on and prepara�on of the area for the post-construc�on
use. Therefore, the construc�on drawings must reflect areas to be preserved and include adequate
Figure 2-11 Examples of public educa�on brochures.
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erosion and sediment control measures to protect those areas, especially since those areas may serve
as natural drainage paths.
The sequence of construc�on should be prominently displayed on the plans as a cri�cal element to the
site design, and reflect the mul�ple phases of the construc�on as related to the implementa�on of the
designed LID prac�ces within the overall construc�on ac�vity. Interim inspec�on should be provided
by the project engineer to ensure proper construc�on and adherence to approved design standards of
the various LID prac�ces.
Post-construc�on inspec�ons and maintenance of LID structural and non-structural prac�ces are
important to ensure effec�veness. Annual inspec�ons are recommended at a minimum, with more
frequent inspec�ons during the first year or growing season for vegetated prac�ces, or as required
by any permit condi�ons. Some LID prac�ces may require more frequent inspec�ons, (e.g. a�er
significant rain events, quarterly, during property transfers, etc.). More informa�on about inspec�ons
and maintenance is located a�er each associated LID technique in Chapter 5, as well as in Chapter 6.3.6
and 6.3.7. A sample maintenance agreement can be found in Appendix I.
2.3 LID Site Design for High Density and Commercial Development
The same basic site planning considera�ons detailed in the steps above can also apply to high density
and commercial development. With high density and commercial development, it remains important
to conserve natural resources and soils and minimize impacts internal to the site. Grading should
be conducted in a manner that ensures runoff will be dispersed and directed to the LID features as
opposed to inlets and pipes. In most instances, LID techniques can be incorporated into the site
design without significant altera�ons of traffic flow, parking capacity or building footprint / capacity
poten�al. Not only are the LID techniques effec�ve in mee�ng stormwater management objec�ves
there are other ancillary benefits, such as heat island reduc�on, water conserva�on, and aesthe�cs.
The mul�func�onal use of landscape for stormwater control does not increase maintenance burdens.
Bioreten�on islands and tree box filters require no more
maintenance than typical landscape features.
The selec�on and sizing of LID techniques depends upon
a wide range of factors, including unique site constraints
(soils, high ground) and water quality treatment
objec�ve. The typical LID techniques used for
high-density developments include perimeter buffers,
swales and bioreten�on systems; parking lot bioreten�on
/ deten�on islands, planter boxes, green roofs, porous
pavers / pavement, and infiltra�on devices. Runoff can
also be stored, detained, and / or infiltrated under the
parking lot using porous pavement with subsurface
gravel storage areas.
Figure 2-12 shows a town house development in the
Chesapeake Bay watershed. Infiltra�on devices have
been constructed under the buildings and parking lots,
Figure 2-12 This high-density residen�al community
in the Chesapeake Bay watershed is a zero-discharge
design that was constructed for sandy soils and a high
ground water table. The design included infiltra�on
devices under the buildings, parking lots, and side-
walks; conserva�on and buffers areas to treat runoff;
rain gardens and porous pavements.
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alterna�ve paving surfaces such as gravel sidewalks, take the place of paved paths, bioreten�on
areas have been included and several conserva�on areas have been designated. As a result, the
development generates zero discharge and is used as a model for developments discharging to
sensi�ve waters.
The following figure demonstrates how LID can be incorporated into a site developed for an office or
retail use. The use of several engineered LID prac�ces can be designed to meet both water quality
and water quan�ty requirements. LID features such as buffers, swales, and bioreten�on areas are
incorporated on site. Proper grading is required to ensure that runoff is dispersed and directed to
the various LID landscape features. This design is in contrast to typical site grading where runoff is
concentrated and directed to inlets, pipes and a deten�on pond.
Figure 2-13 LID Design for an Office Project. This figure
shows how several engineered LID techniques were
incorporated into the site.
Bioretention
Porous Pavers
Buffer Bioretention Swales
Buffer / Swale
Planter Boxes
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The next figure demonstrates how a “big-box” retail store could incorporate LID into the site. Swales,
bioreten�on, buffers, and infiltra�on prac�ces are incorporated throughout the site. The LID devices
are incorporated into the landscape islands and used for filtra�on, infiltra�on, and water volume
storage. The selec�on and sizing of the LID techniques that are ul�mately chosen will depend upon a
wide range of factors, including high ground water tables, soil consistency, and proximity of sensi�ve
water bodies.
The final two figures demonstrate a residen�al or commercial high-rise building and a townhouse
development where LID has been incorporated into the parking area and perimeter buffer areas.
Figure 2-14 LID Design for a “Big Box” Commercial Site. This
figure shows swales, bioreten�on areas, buffers and infiltra�on
prac�ces. The bioreten�on islands in the parking lots could be
used for filtra�on, infiltra�on and volume storage.
Figure 2-15 LID Design for a High Density Residen�al
Site – This figure shows a residen�al high-rise
development where LID techniques were applied
throughout the parking area and perimeter landscape
features.
Figure 2-16 LID Design for a Townhouse Development –
This figure shows a residen�al townhouse development
where LID techniques are integrated into the site’s
green space and common areas
Buffers
Bioretention / Detention
Bioretention
Islands
SwalesSwales
Infiltration
Trench
SwalesSwales
SwalesSwales
SwalesSwales
Buffers
Bioretention
Bioretention / Rain Gardens
Buffers (Natural) Bioretention
Swales
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3.1 General
Efforts to protect or improve water quality cannot be directed toward new development alone as much
of Wilmington and New Hanover County is already developed. Impacts from exis�ng stormwater
pollu�on sources must be addressed as well. LID retrofi�ng can be an effec�ve approach to control
stormwater pollu�on in exis�ng urbanized communi�es and commercial developments. With LID
retrofit projects, micro-scale management techniques are introduced into the exis�ng urban landscape
(roads, sidewalks, parking areas, buildings, landscaped areas, etc.) to reduce pollu�on from exis�ng
sources.
The most economical way to retrofit exis�ng development is to ensure that infill development,
redevelopment, and reconstruc�on projects include the use of LID prac�ces. Over �me as urban areas
are redeveloped and rebuilt with LID prac�ces more of the previously untreated urban runoff can be
treated thereby reducing water quality degrada�on. Retrofi�ng over �me through the redevelopment
process combined with targeted capital improvement projects can have a significant impact, but it
takes �me.
Several LID techniques may be used for retrofit and redevelopment. Selec�on should be made on the
level of desired pollutant removal as well as the unique constraints of the site. When selec�ng the
most appropriate LID techniques it is important to match the op�mum LID technique to meet the goals
of the receiving waters.
Figure 3-1 Example of mul�ple LID retrofit techniques. Source LID Center.
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3.2 LID Retrofit Case Studies
Example #1 Bioreten�on - Prince Georges County, Maryland
Parking lot landscape islands can be converted into LID retrofit
projects, as shown in Figures 3-2 through 3-4. This landscape
island was excavated and an underdrain system was installed
to discharge into an inlet structure. The structure was then
filled with a high flow-rated, engineered media, planted, and
mulched. The landscape island has the same dimensions and
serves the same aesthe�c purpose but it now has the added
benefit of removing pollutants from stormwater runoff.
This facility was constructed in 1993 as one of the first retrofit
projects in Prince Georges County, Maryland. It treats approximately 90% of the total annual runoff
volume from the one-acre parking lot draining into it. To maintain the site, annual landscape care and
mulching is required. Approximately every five years the top 3 to 4 inches of sediment must also be
removed to prevent the island from blocking the flow of water entering the curb cut.
Example #2 Bioreten�on - Port City Java, Wilmington, N.C.
The parking lot at the Port City Java Corporate Headquarters in
Wilmington was once a large paved area with no landscape islands.
The stormwater from the 15,450 square foot parking area drained
directly into Burnt Mill Creek with no treatment or deten�on.
To retrofit the parking area, a loca�on between wheel stops was
retrofi�ed with two bioreten�on cells. The two bioreten�on cells
measured 1180 square feet and were installed to intercept stormwater.
To construct the bioreten�on cells, the exis�ng asphalt was removed.
Exis�ng soil was excavated to an appropriate depth, and underdrains
were installed in order to facilitate water movement and allow for
water quality monitoring at the outlet pipe. The exis�ng sandy soil
proved ideal as fill material and was able to be u�lized for the project.
Na�ve plants were installed within the bioreten�on areas, as well as an
access bridge and educa�onal signs.
Figure 3-2 Excava�on of a landscape island to
create a bioreten�on cell. Source Larry Coffman.
Figure 3-3. Urban retrofit showing construc�on
of underdrain system and gravel infiltra�on reservoir.
Source Larry Coffman.
Figure 3-4. Completed bioreten�on cell with plant-
ings. Source Larry Coffman. High Rate
Bio-filtration
Figure 3-5. Port City Java parking
lot prior to retrofit. Source NCSU.
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Example #3 Bioreten�on and Porous Pavement - Wilmington Family YMCA
Wilmington, N.C.
An area at the Central YMCA on Market Street in Wilmington used primarily for overflow parking
was once covered with gravel and did not contain any
landscaping. Although the gravel was ini�ally par�ally
pervious, the parking area became impermeable over �me
as a result of compac�on. Roo�op runoff from part of the
YMCA roof was also directed into the parking lot, causing
runoff from rain events to wash a substan�al amount of
sediment and gravel into the storm drain system.
Two LID retrofits were designed for the site to control and
treat stormwater runoff. Porous pavement was installed to
stabilize the parking area, prevent con�nued erosion, and
allow for infiltra�on of stormwater. A bioreten�on area
was also constructed to filter pollutants from stormwater
runoff through plant uptake. Overflow from the rain garden
is channeled into the concrete parking area to maximize
storage capability.
Figure 3-6 Underdrain installa�on at Port
City Java. Source NCSU.
Figure 3-7 Completed Port City Java
bioreten�on cells with plan�ngs. Source
NCSU.
Figure 3-8 YMCA overflow parking area prior to
retrofit. Source NCSU.
Figure 3-9 Completed porous parking
and bioreten�on area at YMCA. Source NCSU.
Figure 3-9 Completed porous parking
and bioreten�on area at YMCA. Source NCSU.
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Example #4 Bioreten�on - Gregory Elementary School
A bioreten�on area was installed at Gregory Elementary
School in Wilmington to capture and treat runoff from the
9,000 square foot parking lot which is located between the
school and Ann Street. Exis�ng soil was excavated 10 inches
below the lowest point in the parking lot. Two inches of
topsoil was then mixed into the top eight inches of exis�ng
soil. Three inches of mulch was spread in the bioreten�on
area and na�ve vegeta�on was planted.
A grassed forebay with a level spreader was used to slow the
runoff from the parking lot and evenly disperse it into the
bioreten�on area. The banks of the bioreten�on area were
covered with sod and a berm was constructed to divert the
runoff from the stormwater drain into the bioreten�on area.
Overflow from the bioreten�on area is routed back into the
exis�ng storm drain.
A rain catchment device, or cistern, was also installed at
Gregory Elementary School. The cistern will func�on as a
source of water for the landscaping around the building and
will decrease the amount of roof runoff from the building.
Example #5 Bioreten�on – Trask Middle School
Wilmington, N.C.
With grant funding provided through an Environmental
Protec�on Agency (EPA) coopera�ve agreement grant, two
low impact development techniques were constructed in
the Smith Creek watershed in Wilmington. The first loca�on
chosen for retrofit was a semi-grassed swale that drains
the northern side of Trask Middle School. Runoff from the
surrounding faculty parking lot and roof entered this swale,
Figure 3-12. Completed Gregory Elementary
bioreten�on area. Source NCSU.
Figure 3-13. Installa�on of cistern at Gregory
Elementary School
Figure 3-11. Gregory Middle school landscape
area before retrofit. Source NCSU.
Figure 3-13. Grass swale at Trask Middle School
before installa�on. Source NCSU.
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carrying pollutants from the parking lot, sediment from areas
surrounding the parking lot, and the eroding swale, into a
drainage ditch.
A bioreten�on area was designed to capture 1 inch of rainfall.
The bioreten�on area was designed so that stormwater
runoff would be detained in the area and vegeta�on would
filter pollutants. The bo�om of the bioreten�on area was
mulched and the banks were sodded. A variety of na�ve,
drought-tolerant plants were installed within, and several
flowering varie�es were included to improve aesthe�cs. A
grassed forebay was installed to dissipate energy, capture
sediment, and disperse flow more evenly across the mulched
por�on of the bioreten�on area.
Example #6 Constructed Wetland – Laney High School, Wilmington, N.C.
The second project constructed with the EPA coopera�ve agreement grant was a wetland at Laney
High School. The wetland was constructed within an exis�ng drainage ditch in order to reduce the
volume of stormwater runoff and associated pollutants
from entering into Smith Creek. The watershed draining
into the constructed wetland is comprised of athle�c fields,
parking lots, and roo�ops. The runoff flows into a pipe which
emp�es into the exis�ng ditch system.
To construct the wetland, a 0.2-acre area was excavated. The
wetland design includes deep pools (11% of the wetland
area), shallow water areas (39% of the wetland), and shallow
or emergent land areas (50% of the wetland). The pools were
designed to trap sediment, provide anaerobic condi�ons via
nitrate removal for most of the year, and to provide habitat
diversity for wetland plants, amphibians, and fish. An outlet
weir was constructed at the ou�low of the wetland to handle
the 25-year storm.
Since the wetland has been constructed, it has been
monitored by North Carolina State, the N.C. Division of Water
Quality, and students at Laney High School. The wetland also
serves as an outdoor living laboratory that is u�lized by Laney
High School earth science and biology students.
Figure 3-14. Completed Trask bioreten�on area.
Source New Hanover County Planning.
Figure 3-15. Drainage ditch at Laney High
School prior to wetland construc�on. Source
NCSU.
Figure 3-16. Laney constructed wetland a�er
comple�on. Source New Hanover County
Planning.
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Chap3:Pg21
Example #7 Constructed Wetland - Stonesthrow Townhomes, Wilmington, N.C.
The Stonesthrow Townhomes are located in the headwaters
of the Burnt Mill Creek watershed in Wilmington. The site
consists of a 5-acre mul�-family residen�al development
which drains into a ditch towards the rear of the property.
The wetland was sized at half of the area that would be
required to store and treat one inch of rainfall due to site
constraints. Site constraints included the loca�on of an inlet
pipe, a property boundary on one side, and a u�lity pole and
u�lity lines on the other side.
The wetland was designed with 24% pools, 48% shallow land,
and 28% shallow water. The pools were 2.5 feet deep and
were designed to store sediment, provide anaerobic
condi�ons to improve nitrogen removal, and provide habitat
diversity for wetland flora and fauna. Shallow water areas
were intended to have six inches of water at normal pool
(the water level between storms) and serve to connect the
pools, provide diversity, and allow sunlight penetra�on for
bacteria removal. Shallow water areas were intended to dry
out between storms as water leaves the wetland through
drainage and the process of evapo-transpira�on. The level of
the water in the wetland was controlled by a variable outlet
control structure.
Example #8 Bioreten�on - U.S. Navy Yard, Washington, D.C.
This project is one of many LID techniques constructed at the U.S. Navy Yard in Washington, D.C.
Within this exis�ng parking lot, there were no landscape islands. To retrofit the parking lot, a
bioreten�on cell was created between exis�ng wheel stops. Figure 3-19 shows the parking lot prior
to retrofit. Figure 3-20 shows the excavated trench in the parking lot with the under drain system and
engineered media. Figure 3-22 shows the finished project.
As runoff sheet flows across the parking lot, water is intercepted and captured by the bioreten�on area.
Runoff flows through the media plant complex for treatment discharging to the underdrain pipe which
Figure 3-17. Wooded area at Stonewthrow
Townhomes prior to retrofit. Source NCSU.
Figure 3-18. Stonesthrow constructed wetland
a�er comple�on. Source NCSU.
Figure 3-19 U.S. Navy Yard parking lot prior
to retrofit. Source LID Center.
Figure 3-20 Excava�on of bioreten�on cell
with concrete and plas�c liner at Navy Yard.
Source LID Center.
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
Chap3:Pg22
then flows into an exis�ng storm drain system.
Because the Navy Yard was covered by over 98% impervious surfaces there was not an available
area for a stormwater pond, and the use of LID retrofit techniques was the only feasible op�on. As
buildings, parking lots, roofs, sidewalks, and roadways con�nue to be replaced or maintained, LID
techniques are integrated in to each project. The goal of the Navy is to retrofit the en�re installa�on
with LID prac�ces.
Example #9 Bioreten�on and Green Roof – Portland, OR
The City of Portland, OR has undertaken an LID retrofit program.
The City is now controlling stormwater using LID landscape-level
techniques and green roofs rather then tradi�onal stormwater
techniques such as pipe and pond controls. Plants and soils are
being u�lized to slow, cleanse, and infiltrate runoff.
LID techniques are required under the City’s current stormwater
management regula�ons and are designed to enhance the city’s
aesthe�cs, improve air quality, and reduce energy consump�on.
Figure 3-23 shows a bioreten�on and deten�on facility that was
required by the City as part of a redevelopment project located in a
courtyard of a residen�al development.
Figures 3-24 and 3-25 show residen�al streets where bioreten�on and infiltra�on devices were
constructed as retrofit projects by the City.
Figure 3-21 Disconnected gu�er and
bioreten�on area at Navy Yard. Source
LID Center.
Figure 3-22. Completed bioreten�on cell
at Navy Yard. Bioreten�on cell used for
filtra�on only. Source LID Center.
Figure 3-23 Center landscape feature is a
bioreten�on cell with deten�on. Source
Portland, OR BES.
Figure 3-24 Street retrofit with
bioreten�on cell on both sides of road.
Source, Portland, OR BES.
Figure 3-25 Bioreten�on planter boxes.
Source Portland, OR BES.LID Center.
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Figure 3-26 shows a green roof which is part of the City of Portland ongoing green roof program.
Example #10 Bioreten�on - Sea�le, WA
In Sea�le, Washington, the City has an ongoing program to retrofit residen�al streets in order to
protect the Puget Sound. Figures 3-27 (before) and 3-28 (a�er) depict a residen�al roadway that was
transformed by construc�ng a series of bioreten�on areas and deten�on cells in the public right-of-
way. The LID landscaping is maintained by individual homeowners.
Figure 3-27 Sea�le street prior to
retrofit. Source Larry Coffman.
Figure 3-28 Completed Sea�le
retrofit streetscape. Source Larry
Coffman.
Figure 3-26 Green Roof. Source Portland,
OR BES.
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C������ 4 - R��� ��� D������� D�����
The majority of impervious surfaces associated with urban development are found within the vehicular
travel system including roadways and parking surfaces. These impervious surfaces prevent infiltra�on,
but are also part of a drainage paradigm that conveys, collects, and concentrates runoff to pipes and
ponds. To maximize the poten�al that LID could have on water quality, various LID techniques can be
incorporated into overall road design. The chosen techniques will depend on the soils, development
density, zoning, and use of the receiving water. However, there are several ways to include LID in road
design.
When implemen�ng LID in road designs, the goal is not just to reduce impervious surface, but to avoid
using the roadway surfaces to collect, concentrate, and covey the runoff. Specific focus should be on
offloading the runoff (disconnec�ng and de-concentra�ng) into LID treatment systems such as swales,
bioreten�on, buffers, and infiltra�on devices.
4.1 Open Road Design
The simplest way to disconnect a roadway is to use an open
sec�on grass swale roadway design, rather than curb and
gu�er, when engineering a road for a rural or suburban
subdivision. Generally, shallow and broad swales are the
best design for open roads as they provide more surface
area to treat and absorb runoff. The performance of the
swales can be enhanced where you have soils that do not
filter well. Figure 4-1 shows an example of a way to design
a swale to enhance its ability to treat runoff. In this case,
several features have been incorporated into the design,
including a culvert as a weir for deten�on control; check
dams to increase reten�on �me and decrease veloci�es;
and a trench drain along the bo�om of the swale to
encourage infiltra�on and increase runoff storage in the engineered soil. Swales should be designed so
that they are shallow with under drains to encourage good drainage and discourage standing water.
If it is possible to reduce road width, there is an opportunity to increase the available green space to be
used for a wider open swale sec�on to help achieve greater filtra�on, infiltra�on, or storage. Where
allowed open-sec�on roadways can reduce the need for costly curb
and gu�er sec�ons and encourage the filtering and infiltra�on of storm
water. Open sec�on roadways consist of a variable-width gravel or
grass shoulder, usually wide enough to accommodate a parked car,
and an adjoining grassed swale that collects, conveys, stores, detains,
and treats storm water. Even a narrow street width of 22 feet can s�ll
accommodate parking on one side of the roadway and leave ample
room for a safe travel lane that is generous enough to accommodate
most fire trucks, school buses, and garbage trucks. However, it is
possible to design a road sec�on with curb and gu�er and s�ll have
ways to disconnect the roadway runoff. Figure 4-2 shows an open
flume from a curb and gu�er sec�on offloading runoff into an adjacent
swale.
Figure 4-1 Example of a dry swale. Source Mary-
land Department of Environment.
Figure 4-2 Open flume on curb and
gu�er sec�on. Source NC DOT
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Figure 4-3 shows a table with recommenda�ons for a narrower roadway design to allow for the
addi�on of wider swales and reduce pavement
width.
Figure 4-4 shows a standard 60’ roadway design with sidewalks on both sides. The important LID
feature is the use of wider swales for treatment and control. No�ce that the swales are located
between the road surface and sidewalks providing greater protec�on to pedestrians.
Figure 4-5 shows a narrow road sec�on with sidewalks, shallow swale, and porous pavement shoulders.
The paver blocks provide a rough surface to alert drivers if their �res leave the road surface. The pavers
also protect the edge of the asphalt surface form braking off.
Figure 4-3 Narrow roadway designs allow for the use of wider swales and
treat runoff more efficiently. Source Residen�al Streets, NAHB.
Figure 4-4 Suggested design
standard for a rural 60’ wide road
sec�on. Source Logan, Utah.
Figure 4-5 Narrow road sec�on
with a shallow swale, sidewalk, and
porous paver shoulder.
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
Chap4:Pg26
4.2 Urban Road Design
In residen�al se�ngs it is possible to incorporate LID techniques into road design. For example,
Figure 4-6 shows two different types of roadway bioreten�on filtra�on systems for high-density urban
development. Neither system provides infiltra�on due to poor soils and high ground water. Where
flow, volume and water quality controls are required or desired and the soils permit both systems could
be designed as filtra�on and infiltra�on systems.
The following are the main concepts to consider when designing roads to incorporate LID.
• Maximize natural drainage. Preserve natural drainage pa�erns and avoid loca�ng streets in
low areas or highly permeable soils. When si�ng streets, consider natural drainage pa�erns and
soil permeability.
• Remove curbs from roads. Where feasible, build roads without curbs, using vegetated swales as an
alterna�ve.
• U�lize an urban curb cut and swale system. In this case runoff
runs along a curb and enters a surface swale via a curb cut instead
of entering a catch basin to the storm drain system.
• Incorporate a dual drainage system. This is a pair of catch basins
with the first sized to capture the water quality volume into a
swale while the second collects the overflow into a storm drain.
• Build concave medians. With concave medians, the median is
depressed below the adjacent pavement and designed to receive
runoff by curb inlets or sheet flow. The median can then be
designed as a landscaped swale or bioreten�on area.
• Minimize right-of-way. The right-of-way should reflect the
minimum size required to accommodate the travel lane, parking, sidewalk, and vegeta�on, if
present.
• Construct with permeable materials. These materials are especially beneficial for use in alleys and
on-street parking, par�cularly pull out areas.
A typical right-of-way creates wide and o�en visually unappealing streets that promote speeding
and undermine safety. Bioreten�on can be placed in the right-of-way providing a dual func�on of
stormwater treatment and traffic-calming. By strategically placing bioreten�on cells, traffic can be
funneled into a narrower road sec�on forcing motorists to slow down.
Figure 4-6 Bioreten�on planter boxes. Sources City of Port-
land, OR BES and Ocean City, MD Filterra TM
Figure 4-7: Bioreten�on cells used
for stormwater runoff and traffic
calming in Demarest Landing in
Wilmington, NC.
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Chap4:Pg27
Figure 4-8 shows how bioreten�on cells can be integrated into an
urban se�ng for treatment of roadway runoff and to provide traffic
calming. This project was constructed in Portland, Oregon as a
retrofit. Infiltra�on was not possible in this circumstance, therefore
the bioreten�on systems were constructed only as filtra�on devices
that discharge through an under drain into the nearby storm drain
system.
Figure 4-9 also shows an example of a filtra�on bioreten�on cell.
In this applica�on, a�en�on must be given to the inlet structures.
Generally it is desirable to avoid high veloci�es of water
flowing through the bioreten�on cell, so in this case, a mini
deten�on flow restric�on device was used to reduce veloci�es
(highlighted).
When curb and gu�er is desired or required, it is s�ll possible
to incorporate LID. O�en there is space between the curb and
sidewalk that can be used to treat road runoff.
Figure 4-10 shows an example of the curb cut that allows
water to drain into the green space. If this approach is used it
is important that the curb cut is made wide enough to prevent
clogging by trash and debris. Generally curb cuts become blocked
with sediment over �me so they need to be cleaned periodically and if
possible designed with sufficient slope to help create enough velocity to
flush sediment into the grass area.
The main issue with LID road design is that trash and debris are highly
visible and can become unsightly if not rou�nely removed. Since the
treatment area is in the public right-of-way, responsibility for rou�ne
maintenance becomes an issue. Typically this area is maintained
by the State or City, however, it is possible through easement
and covenants to assign the maintenance responsibility to a
property owner or homeowners associa�on. It is rela�vely easy
for an associa�on to maintain this type of system. In some cases
individual property owner’s agreements can be made. Assigning
property owners with maintenance responsibility for some features
of the public rights-of-way is analogous to mowing the grass area
between the curb and sidewalk.
Figure 4-11 shows a fully contained bioreten�on system where trash
and debris are hidden from view. Runoff carrying trash and debris
enters the unit inlet on the curb face deposi�ng it on the surface of
the filter media. Treated water is infiltrated or discharged via an
under drain to a pipe or other appropriate ou�all. Maintenance is
performed periodically (semi-annually) and involves removing the
grate to access the trash and replacing the mulch. Inspec�on and
maintenance is rela�vely easy and safe.
Figure 4-9 Example of a bioreten�on cell
within the road right-of-way. Source
Portland, OR.
Figure 4-8 Bioreten�on cells used
for both stormwater treatment and
traffic calming. Source Portland.
Figure 4-10 Curb cut in Mayfaire in
Wilmington, NC. Photo taken a�er
rain event evidencing where water
entered the bioreten�on area.
Figure 4-11 Bioreten�on system
in a concrete box and used as
an infiltra�on system. Source
Americas Filterra.
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Chap4:Pg28
Another way to incorporate LID into urban road design is
to include it in a cul-de-sac. Depending on a subdivision’s
lot size and street frontage requirements, five to ten
houses can be located around a standard cul-de-sac
perimeter. The bulb shape allows vehicles up to a certain
turning radius to navigate the circle. To allow emergency
vehicles to turn around, cul-de-sac radii can vary from as
narrow as 30 feet to upwards of 60 feet, with right-of-way
widths usually extending ten feet beyond these lengths.
Figure 4-12 shows how cul-de-sacs can be designed to
incorporate a bioreten�on area in the center for roadway
runoff. The table in figure 4-13 below shows the rela�ve
difference in impervious surface area for various turnaround
configura�ons.
Figure 4-13: Impervious surface area coverage for selected turnaround op�ons
Turnaround Op�on Impervious Area (square feet)
40-foot radius cul-de-sac 5,024
40-foot radius with island 4,397
30-foot radius 2,826
30-foot radius with island 2,512
Hammerhead 1,250
4.3 Driveway Design
Driveways add a significant amount of impervious coverage to a community and are an element of a
site’s design that can be altered to minimize total impervious coverage. Driveways o�en slope directly
to the street and storm drain system. The runoff reaching the storm drain system then contributes to
storm water pollu�on. There are several strategies that can be implemented to reduce this impact.
• U�lize shared driveways to provide access to several homes.
• Reduce driveway width by allowing tandem parking (one car in front of the other).
• Install a narrowed driveway with a flared entrance for mul�-car garage access.
• Disconnect the driveway by direc�ng surface flow from the driveway to a permeable landscaped
area, such as a below grade bioreten�on basin.
• U�lize porous surfaces such as porous concrete or asphalt, permeable pavers, or crushed aggregate
(Figure 4-14)
• Install ribbon driveways, which consist of two strips of pavement with grass or some other
permeable surface in between the strips (Figure 4-15).
Figure 4-12 Example of Cul-de-sac design using
bioreten�on. Source-Schuler 1995 and ASCE 1990.
of-way. Source Portland, OR.
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Chap4:Pg29
4.4 Sidewalks and Bike Paths
Sidewalks and bike paths can be another source of impervious coverage. Several management
opportuni�es and strategies are available to reduce this impact.
Figure 4-16 and Figure 4-17 show two different strategies for sidewalk design. One shows the sidewalk
adjacent to the roadway the other shows the swale between the roadway and sidewalk. Figure 4-16
also shows a narrow road sec�on with sidewalks, shallow swale and porous pavement shoulders. The
paver blocks provide a rough surface to alert drives if their �res leave the road surface. The pavers also
protect the edge of the asphalt surface from breaking off.
Some things to remember when incorpora�ng LID into sidewalk design:
• Reduce sidewalks to one side of the street where allowed.
• Disconnect bike paths from streets. Bike paths separated from roadways by vegetated strips reduce
runoff and traffic hazards.
• U�lize pervious materials to infiltrate or increase �me of concentra�on of stormwater flows.
• Reduce sidewalk width when possible.
• Direct sidewalk runoff to adjacent vegeta�on to capture, infiltrate, and treat runoff.
• Install a bioreten�on area or swale between the street and sidewalk and grade to direct runoff from
the sidewalk to these areas.
• Plant trees between the sidewalk and streets to capture and infiltrate runoff.
Figure 4-14 Porous Pavers in driveway at
Preserva�on Park in Wilmington, N.C.
Figure 4-15 Ribbon driveway in De-
marest Village in Wilmington, N.C.
Figure 4-16 Narrow road sec�on with a
shallow swale, sidewalk, and porous paver
shoulder.
Figure 4-17 Example of a shallow roadside swale
system with under drains to facilitate drainage
and reduce ponding �me. Source, Portland, OR. .
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Chap4:Pg30
4.5 Addi�onal Sources for Informa�on
• Center for Watershed Protec�on. Be�er Site Design Fact Sheet: Narrower Residen�al Streets.
• Gibbons, Jim.1999. Nonpoint Source Educa�on for Municipal Officials: Roads.
• Metropolitan Council Environmental Services. 2003. Urban Small Sites Best Management Prac�ce
Manual.
• Milwaukee River Basin Partnership. Protec�ng Our Waters: Streets and Roads.
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
Chap5:Pg31
C������ 5 LID BMP� G������ D����� G�������
5.1 Introduc�on
Chapter 3 provided guidance on general site planning for conserva�on and impact minimiza�on. This
chapter provides general guidance for effec�ve use of several of the most commonly used LID prac�ces
on a well-planned site. The reader is reminded that this document is intended as a technical guide and
that all local, state, and federal permi�ng requirements must s�ll be complied with when using these
techniques.
When designing LID techniques, the primary natural processes that are applied include infiltra�on,
evapotranspira�on, and vegeta�ve intercep�on. The combina�on of BMPs selected for any given site
is based on a number of site-specific factors and the desired stormwater controls. Storage is a key LID
func�on. Storing runoff reduces the runoff volume and peak flow rate. It also improves water quality
by allowing pollutant removal through se�ling, absorp�on, biological processes, and physical filtering.
Most LID techniques use a combina�on of two types of storage – reten�on and deten�on.
Reten�on causes water to remain on site through infiltra�on or absorp�on of water in the treatment
media. Retained water never enters the storm drain system. Between storms, water is lost through
infiltra�on, evapora�on, and transpira�on and the available storage volume is restored. Infiltra�on
may contribute to groundwater recharge.
Deten�on temporarily stores water on site for later release into the storm drain system, through an
underdrain or other device. Par�al pollutant removal can occur – primarily through se�ling with rate of
removal depending on deten�on �me.
The sizing and placement of an LID technique is fundamentally different from conven�onal stormwater
controls such as ponds. Stormwater ponds are typically placed at the outlet of a drainage network for
a rela�vely large area. By contrast, LID techniques treat drainage areas that are each a small por�on
of the total site, ranging in size from ¼ acre to a small roof or driveway and are placed as close to the
source of runoff as possible. Consequently, these LID techniques are distributed throughout the site,
providing decentralized stormwater treatment that mimics the rela�vely even distribu�on of natural
features in an undeveloped site. This distribu�on of LID techniques throughout the site changes the
�me of concentra�on of the runoff and reduces flow volumes to each technique. LID techniques are
generally sized to capture the required water quality volume coming from each drainage area.
Figure 5-1: LID BMP Functions. Source – LID Center
LID Technique Slows
Runoff
Infiltration Retention Detention Water Quality
Control
Bioretention X X X X
Vegetative or Curb outlet Swale/ X X
Permeable Pavement X X X
Cisterns and Rain Barrels X
Tree Box Filters and Planters X
Surface Sand Filters
Green Roofs X X X
Constructed Wetland X X X X
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
Chap5:Pg32
5.2 Bioreten�on
5.2.1 General
Bioreten�on systems consist of a shallow depressed vegetated
area with porous engineered soils designed to capture
and treat urban runoff and infiltrate treated water to the
subsurface where exis�ng soil condi�ons allow. Bioreten�on
systems are also known as bioreten�on cells, landscape
deten�on, rain gardens, bio-filters, tree box filters, and
stormwater planters. This type of LID prac�ce is very versa�le
and can be implemented in most areas where landscaping is
to be incorporated into new development or redevelopment
projects. By capturing, detaining, and retaining runoff,
bioreten�on cells reduce the runoff volume, peak flow rate,
and pollutant loading. A bioretention cell mimics the ecological
func�ons of an upland forest floor through the use of specific vegeta�on, mulch, and soils. It is an
aerobic plant soil complex system as opposed to anaerobic wetland systems. Figure 5-2 shows a
typical cross-sec�on of a bioreten�on system. It is composed of a surface storage area (1 to 2 feet),
appropriate plants, mulch (3 inches), engineered soil mixture (1 to 3 feet),
an underdrain system and an infiltra�on gallery.
5.2.2 Performance
Bioreten�on systems are very effec�ve at reducing the volume and removing
pollutants from urban runoff because they u�lize a combina�on of porous
engineered soils, plants, and their root systems (see figure 5-3). The volume
of urban runoff is reduced by reten�on in the soil, plant uptake,
evapotranspira�on and infiltra�on. Pollutants are effec�vely removed by a
number of processes including physical filtering, ion exchange, adsorp�on,
absorp�on, biological degrada�on, and uptake. Bioreten�on systems can
be installed into exis�ng soils or within concrete enclosures, and with or
without underdrains.
5.2.3 Applica�ons and Advantages
Bioreten�on systems can be incorporated into many aspects
of urban and suburban development, including residen�al,
commercial, municipal, and industrial areas. They are well-
suited for planters along buildings (see figure 5-4), within street
median strips, parking lot islands, and roadside areas where
landscaping is planned. In addi�on to providing significant
water quality benefits, bioreten�on systems can provide shade
and wind breaks, absorb noise, improve an area’s aesthe�cs,
reduce irriga�on needs, and reduce or eliminate the need for
an underground storm drain system. Bioreten�on systems can
Figure 5-2 Typical cross sec�on of a
bioreten�on cell.
Figure 5-3 Bioreten�on
performance. Source: CASQA
2003.
Figure 5-4 This bioreten�on cell intercepts
downspout and walkway runoff. Note the
overflow. Source LID Center.
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Chap5:Pg33
be integrated into a site’s overall landscaping plan to maintain the volume, rate of flow, and pollutant
loading of runoff to pre-development levels.
Examples of bioreten�on applica�ons include:
• Tree wells, tree box filters (boxed bioreten�on cells) placed
at the curb, depressed street median, driveway perimeters,
or within cul-de-sacs;
• Landscaped areas in apartment complexes, mul�family
housing, commercial, industrial, and municipal
developments (see figure 5-5);
• Individual bioreten�on or rain gardens on residen�al lots;
• Planter boxes at roo�op eaves and roo�op gardens
par�cularly on large commercial structures and parking
garages.
5.2.4 General Design Guidance
A typical bioreten�on system design includes a depressed ponding area (at a grade below adjacent
impervious surfaces), an engineered soil mix, and o�en an underdrain system where exis�ng soils have
slow infiltra�on rates. The ponding area is designed to capture, detain, and infiltrate the desired water
quality volume into an engineered soil mix consis�ng of a well-mixed combina�on of topsoil, clean
sand, and cer�fied compost and/or peat moss.
Bioreten�on cells are excavated to a minimum depth of 1 to 3 feet, depending on the infiltra�on
rate, depth to the seasonal high groundwater table or bedrock, and volume to be captured. Deeper
excava�on allows for addi�onal storage in the soil or gravel layers. When exis�ng soils are excavated
and replaced with engineered soils to create a bioreten�on system, a layer of pea gravel (not filter
fabric) should be used at the base of the excavated pit. Although generally not considered necessary,
a geotex�le filter fabric or an impermeable liner can be placed along the sides of the excava�on to
separate the engineered soils from the exis�ng site soils.
Generally runoff is ponded to a depth of approximately 6 to 12 inches and then gradually filters through
the engineered soils mix, where it is retained in the porous soils, u�lized by plants, evapotranspired,
and either infiltrated into the underlying soils, or drained into an underdrain system over a period
of hours. Erosion control and energy dissipa�on features should be provided where runoff enters
bioreten�on systems (e.g. cobbles or riprap beneath a curb-cut opening or a splash block beneath
a roof drain downspout). In addi�on, vegetated swales or filter strips can be added to the design to
provide pretreatment (e.g. for sediment reduc�on).
Bioreten�on areas are designed to capture the water quality volume, storing it in surface ponding
and voids in the soil media and gravel layers. Any stormwater volume greater than the water quality
volume can be detained by providing addi�onal ponding and/or subsurface storage; this reduces the
runoff volume and peak flow rate for larger storms. For instance, the depth of the gravel layer may be
increased to add addi�onal storage. The depths of ponded water generally can be increased provided
it does not cause excessive ponding. The bioreten�on area should be designed so that ponded water
completely drains into the soil within 12 hours (and drains to a level 24 inches below the soil surface
Figure 5-5 Grass-lined bioreten�on cell. This
cell has greater storage depths of 2.5 feet for
addi�onal storage. Source Larry Coffman.
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
Chap5:Pg34
in a maximum of 48 hours). The temporary ponding area in bioreten�on systems should be designed
to retain the volume necessary to meet water quality requirements. Exfiltra�on into the subsoil can
poten�ally reduce the volume of stormwater that ul�mately enters the conveyance system. The
amount of volume reduc�on depends on the available storage in the gravel layer and ponding area,
the maximum flow rate into the subsoil, and the flow rate into the cell, which is related to the storm
intensity and drainage area size.
A gravel layer provides temporary storage of stormwater, which will exit through the underdrain and/or
through exfiltra�on into the subsoil. If an underdrain is present, the gravel layer should surround the
underdrain pipe to minimize the chance of clogging. Bioreten�on soil media occupies the remaining
excavated space, leaving room for the desired amount of surface ponding (6 – 12 inches). The area is
then mulched and planted with shrubs, perennials, grasses, and small trees. When shrubs and flowers
are used as the plant material, a 2 to 3 inch layer of mulch is used on top of the media. The mulch acts
as a pretreatment device to protect the underlying media and helps to retain some water in the media
for the health of the plant.
When exis�ng soils are unsuitable for proper drainage (permeability less than 0.5 in/hr.) or will not
support plant material (improper pH or nutrients), an engineered soil mix of primarily course sand
and peat moss must be used to ensure proper
drainage, prevent excessive ponding that could
encourage mosquito breeding, help improve
plant produc�vity, and retain water. If the
engineered soil mix is not properly designed (see
figure 5-6), it may leach nutrients and salts into
the groundwater or the treated effluent that
discharges to an underdrain system. Leaching
of nutrients and salts may only occur during the
first year when the plants and soil system are
becoming established.
Where underlying exis�ng soils have rela�vely slow infiltra�on rates (less than 2 in/hour), an
underdrain system consis�ng of a perforated pipe in a gravel layer should be included in the
design to facilitate proper drainage. Underdrains are o�en
recommended in areas with low subsoil permeability (e.g.
compacted or clay soils) or shallow soil profiles. Underdrains
must �e into an adequate conveyance system. The underdrain
system should consist of a 3 to 4 inch diameter perforated pipe
inside the bioreten�on system, surrounded by an envelope
of clean coarse aggregate and pea gravel. Discharge from
the underdrain pipe can be routed to a down gradient storm
drain pipe or channel or another BMP device. The underdrain
pipe system should have a ver�cal solid sec�on that extends
above the surface of the ponding area in the basin to provide a
monitoring well and clean out access port (see Figure 5-7).
Figure 5-6 Bioretention media specifications by particle size. Source, Larry Coffman.
• Peat 15 to 20% by volume • Clay <5% (<0.002 mm)
• Silt <5% (0.002-0.05 mm)
• Very Fine Sand 5-10% (0.05-0.15 mm)
• Fine Sand 15-20% (0.15-0.25 mm)
• Medium to Coarse Sand 60-70% (0.25-1.0 mm)
• Coarse Sand 5-10% (1.0-2.0 mm)
• Fine Gravel <5% (2.0-3.4 mm)
Figure 5-7 Bioreten�on cell under construc-
�on in a parking lot showing underdrains.
Source Bill Hunt, NCSU.
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
Chap5:Pg35
Depending on space constraints and drainage area characteris�cs, a pretreatment device - most
commonly a forebay or vegetated filter strip - can be provided to intercept debris and large par�cles. If
a pretreatment device is to be installed, a minimum of 2 feet between the bo�om of the cell and the
seasonal high groundwater table or bedrock must be present and will depend on the soil structure,
water table, and other site condi�ons.
Bioreten�on systems should include design features that allow flows from rela�vely large storm events
to either bypass the system or overflow to a conven�onal storm drain structure such as a channel, a
curb and gu�er system, or a storm drain inlet. An off-line design is preferred and is best accomplished
when only one inlet is present in the bioreten�on unit. Once the bioreten�on cell is full, the high
flows would bypass the inlet (see Figure 5-8). Bypass flows or overflows can also be routed to another
downstream stormwater treatment system such as a vegetated swale or an extended deten�on basin.
Bioreten�on can also be installed within exis�ng natural areas (see Figure 5-9). Generally this is
feasible with very sandy soils with permeability rates above 4 in/hr. It is important that natural
bioreten�on areas be designed so they drain within 4 to 6 hours, to avoid a poten�al nuisance for the
property owner. To ensure a fast draining system, it is best to reduce the drainage area and size the
system for the permeability of the soils.
The plant selec�on and layout should consider aesthe�cs, maintenance, na�ve versus nonna�ve,
invasive species, and regional landscaping prac�ces. A comprehensive list of plants recommended for
bioreten�on areas is provided in Appendix II.
Addi�onal Considera�ons when designing and construc�ng a bioreten�on area:
• Bioreten�on systems should include an engineered soil mixture consis�ng of a well-mixed
combina�on of 50-60% clean sand, 20-30% topsoil, and 5-20% cer�fied compost and/or peat
installed to a minimum depth of 18 inches beneath the temporary ponding area.
• Filter fabric should not be installed at the base of bioreten�on systems because it can be prone
to clogging. Therefore, filter fabric liners should not be placed at the bo�om of excavated basins
to separate engineered soils from exis�ng site soils or at the bo�om of a concrete box that includes
drainage holes to facilitate infiltra�on into exis�ng site soils.
Figure 5-8 Off Line Design – Runoff enters
the curb cut. When the cell is full, water by-
passes the bioreten�on area and enters the
storm drain. Source, Larry Coffman.
Figure 5-9 Conserva�on of exis�ng vegeta-
�on to create a natural bioreten�on cell.
Source University of Florida.
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
Chap5:Pg36
• Layout should be determined based on site constraints such as loca�on of u�li�es, underlying soil
condi�ons, exis�ng vegeta�on, and drainage pa�erns.
• Whenever possible, avoid the use of heavy equipment during construc�on on areas where
bioreten�on systems are to be installed. If soils are compacted, addi�onal ripping may be
necessary to re-establish soil permeability
• A�er basin excava�on, do not compact the na�ve underlying soils. When installing the engineered
soil mix, drop it from the bucket and do not compact it.
• An impermeable liner and an underdrain system should be installed in areas where exis�ng soils are
expansive clays or where there is outdoor storage or use of chemicals or materials within
the drainage area that could threaten groundwater quality if a spill were to occur.
5.2.5 Site and Construc�on Considera�ons for Non-tradi�onal Bioreten�on
Below are addi�onal s for applica�ons where tradi�onal bioreten�on may be prohibi�ve.
• Loca�ons where seasonally high groundwater table is within 1 – 2 feet of the ground surface:
In Figure 5-10 a proprietary bioreten�on system was installed. In this instance, bioreten�on
should not be installed unless enclosed within an impermeable liner or a concrete box with an
underdrain system such as the proprietary device shown in this
figure.
• Areas where high sediment loads in the runoff causes clogging
within the bioreten�on area: In this case, up-gradient
pretreatment may be required with sediment traps and/or
vegetated swales or filter strips.
• In the vicinity of ac�ve construc�on sites: sediment controls and
fencing should be installed to prevent clogging and compac�on
of engineered and exis�ng site spoils from heavy equipment.
The LID construc�on should be sequenced with site stabiliza�on
to prevent sediment loading from ac�ve construc�on.
5.2.6 Inspec�on and Maintenance Requirements
One of the major advantages of bioreten�on over any underground BMP is that inspec�on is easy since
the system is in full view to inspect the health of the plants and amount of debris or sedimenta�on.
Once plants are established, only minimal plant maintenance and occasional removal of sediment and
debris is necessary. The media should never have to be removed, but mulch should be replaced on an
annual basis. Other considera�ons include:
• Upon installa�on and during the first year, landscape deten�on basins should be inspected monthly
and a�er rela�vely large storm events for poten�al erosion and/or extended ponding.
• Key inspec�on/maintenance areas include inlet and overflow areas for poten�al erosion, the
ponding area in basin for trash and debris, and the monitoring well/clean out port for poten�al
early signs of stagnant water in the system if an underdrain system is included.
• Inspec�ons can be reduced to a semi-annual schedule once the landscape deten�on basin has
proven to work properly and vegeta�on is well established.
• An evalua�on of the health of the trees and shrubs should be conducted biannually.
Figure 5-10 Proprietary bioreten�on
system. Source Americast, Filterra.
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Chap5:Pg37
• Pruning, weeding and trash removal should be conducted as necessary.
• Mulch replacement is generally required every year.
• If ponding is observed to exceed 72 hours, par�cularly during the primary mosquito breeding
season (June through October), the cause may be clogged filter fabric (if used, which is not
recommended), compacted soils from construc�on ac�vi�es, improper placement and compac�on
of the engineered soil mix, or surface clogging with fines from a heavy loading source in
the drainage area (e.g. a dirt lot or a construc�on site without erosion control). The reason for the
extended ponding should de determined and mi�gated (e.g. removal of filter fabric, cleaning of the
underdrain system, replacement of engineered soils, and/or ripping of underlying na�ve soils to
re-establish permeability).
• If a spill occurs and hazardous materials contaminate soils in landscape deten�on areas, the
affected materials should be removed immediately and the appropriate soils and materials replaced
as soon as possible.
5.2.7 Example Bioreten�on Design Details
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References
California Stormwater Quality Associa�on (CASQA), 2003. California Stormwater Best
Management Prac�ce Handbook, New Development, and Redevelopment.
Cheng, Mow-Soung, 2003. Somerset Subdivision Monitoring Program (LID). Maryland Water Monitoring Council
Programma�c Coordina�on Newsle�er.
Dietz, M.E. and J.C. Clausen, 2006. Satura�on to Improve Pollutant Reten�on in a Rain
Garden. Environmental Science & Technology, Vol. 40, No. 4, 2006, pp 1335-1340.
Dietz, M.E. and J.C. Clausen, 2005. A Field Evalua�on of Rain Garden Flow and Pollutant Treatment. Water, Air, and Soil
Pollu�on (2005) 167: 123-138.
Guille�e, Anne, 2005. Low Impact Development Technologies. Whole Building Design Guide.
Hager, Mary Catherine, 2003. Low-Impact Development: Lot-level approaches to stormwater management are gaining
ground. Stormwater: The Journal of Surface Water Quality Professionals, Vol. 4 (1).
Hunt, W.F., Jarre�, A. R., Smith J. T, and L. J. Sharkey, 2006. Evalua�ng Bioreten�on
Hydrology and Nutrient Removal at Three Field Sites in North Carolina. Journal of
Irriga�on and Drainage Engineering, November/December 2006.
Idaho Department of Environmental Quality, 2001. Catalog of Stormwater Best Management Prac�ces for Idaho Ci�es and
Coun�es. BMP #44 – Bioreten�on Basin
Kennedy/Jenks Consultants, 2004. Truckee Meadows Structural Controls Design Manual prepared for the Truckee Meadows
Regional Storm Water Quality Management Program.
Maryland Department of the Environment (MDE), 2000. Maryland Stormwater Design Manual
Prince Georges County, Maryland. 2002. Bioreten�on Manual.
U.S. EPA Stormwater Technology Fact Sheet: Bioreten�on
U.S. Department of Transporta�on, Federal Highway Administra�on, Stormwater Best
Management Prac�ces in an Ultra-Urban Se�ng: Selec�on and Monitoring, Fact Sheet Bioreten�on.
Urban Drainage and Flood Control District (UDFCD), 1999. Urban Storm Drainage Criteria Manual, Volume 3 – Best
Management Prac�ces. Denver, Colorado.
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5.3 Vegetated and Grassed Swales
5.3.1 General
Vegetated swales are broad, shallow channels designed to convey,
filter, and infiltrate stormwater runoff. They handle runoff from small
drainage areas at low veloci�es. The bo�om and sides of the swale
are vegetated, with side vegeta�on at a height greater than the
maximum design depth (see Figure 5-11).
Vegetated swales are also known as biofilters, biofiltra�on swales,
landscaped swales, and grass swales. Stormwater runoff is conveyed
along the length of the low slope channel, and the vegeta�on traps
sediments, decreases the velocity of overland flows, and reduces
erosion. Vegetated swales treat runoff by filtering sediments and
associated pollutants through the vegeta�on and by infiltra�on into
underlying soils.
5.3.2 Performance
Figure 5-12 shows the range of removal for various pollutants as
reported in the literature. The large range in pollutant removal
efficiencies reflects differences in design, variable influent concentra�on
levels and flow rates, variability in vegeta�on types, and the permeability
of underlying soils. Bacteria removal data is limited; however, most
reports show very li�le, if any bacteria removal.
Generally, pollutant removal and treatment efficiency improve as
the contact �me and infiltra�on rate increases. Pollutant removal
efficiencies can be increased if the underlying soils allow infiltra�on
through fla�er slopes or broader swales.
5.3.3 General Design Guidance
To provide adequate conveyance of larger storms, the cross-sec�on should be sized to accommodate
the peak flow from the design storm (Figure 5-13). In addi�on, subsurface storage may be provided in
a gravel layer under the swale.
Figure 5-11 Vegetated swale in a
roadway median. Source LID Center
Figure 5-12 Vegeta�ve Swale
Performance. Source: CASQA 2003.
Figure 5-13 Vegetated swale with broad flat
grades to slow flow. Source, Portland, OR.
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
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Swales should be located on hydrologic soil group A and B soils unless an adequate permeability rate
can be demonstrated elsewhere. Soil amendments can be used to increase permeability. The side
slopes of the swale should be no steeper than 3H:1V.
Longitudinal slopes should be 5% or less. Vegeta�on should be selected in order to provide sufficient
surface roughness for filtering and slowing runoff, ensure swale stability (e.g. resistance to erosion), and
ensure con�nued vegeta�ve coverage through dry spells.
Check dams (stone, biologs, wood, or concrete) may be used in swales to act as flow spreaders,
inducing sheet flow along the swale. They may also be used as a stormwater deten�on mechanism to
encourage infiltra�on and sedimenta�on and to reduce runoff velocity. Check dams allow installa�on
of swales in areas of slopes greater than 5% by crea�ng individual drainage sec�ons with shallower
slopes (see Figure 5-14). Check dams may complicate swale maintenance ac�vi�es such as mowing.
Swales sited on exis�ng clay or high silt soils with low infiltra�on rates (less than 0.5 in/hr or 120 min/
in) should also include underdrain systems. Underdrains may also be used to ensure posi�ve drainage.
Figure 5-14 Cross sec�on of swale with check dam
(adapted from Maryland Department of Natural
Resources, 1984).
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Swales can provide desirable open space buffers between developed impervious surfaces, the storm
drain system, and receiving water bodies. Wherever possible, swales should be incorporated into
natural drainage channels. Swales can be accessed by grade design, and curb cuts, or they can replace
curbs, gu�ers, and subsurface storm drain pipe systems and municipal land uses. Vegetated swales can
be used to convey and treat runoff from parking lots, buildings, roadways, and residen�al, commercial,
industrial, and municipal land uses. They are typically located in parks, parkways or private landscaped
areas and public right-of-ways. They can also be used as pretreatment devices for other structural
treatment controls.
5.3.4 Inspec�on and Maintenance Requirements
With proper inspec�on and maintenance, vegetated swales can last indefinitely. Proper maintenance
includes mowing, weed control, removal of trash and debris, and reseeding of non-vegetated areas.
Inspect swales at least twice annually for damage to vegeta�on, erosion, and sediment accumula�on.
Periodic li�er removal is necessary if the swale is located adjacent to a main road or other public use
area. Sediments should be removed when depths exceed 3 inches. If hazardous materials spill and
contaminate soils in vegetated swales, the affected soils should be removed, properly disposed of, and
replaced.
5.3.5 Example Swale Design Details
Figure 5-15 Infiltra�on Swale. Source, Maryland 2000 Design Manual.
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
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Figure 5-16 Example of a Vegeta�ve Swale. Source, City of Salinas.
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
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References
California Stormwater Quality Associa�on (CASQA), 2003. California Stormwater Best
Management Prac�ce Handbook, New Development, and Redevelopment.
City of Livermore, 2003. South Livermore Valley Specific Plan, Residen�al Street Parkway, and Swale Area Plan�ng Policies
and Standards.
City of Livermore, 2005. Bioswale Design Guidance Standard Detail No. L-21.
City and County of Sacramento, 2000. Guidance Manual for Onsite Stormwater Quality Control Measures, Sacramento
Stormwater Management Program.
Minton, G.R., 2006. Stormwater Treatment, Biological, Chemical, and Engineering Principles. Stormwater Quality Design
Manual for the Sacramento and South Placer Regions, February 2007 Public Review Dra�.
Urban Drainage and Flood Control District (UDFCD), 1999. Urban Storm Drainage Criteria Manual, Volume 3 – Best
Management Prac�ces. Denver, Colorado.
Maryland 2000 Stormwater Management Design Manual
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
Chap5:Pg44
5.4 Permeable Pavement Systems
5.4.1 General
Permeable pavement includes a wide range of paved or load-bearing surfaces that allow water to
pass rapidly through the surface and into the sub-grade that serves as a reservoir, a filter bed, and a
load-bearing layer. Permeable pavement decreases the runoff volume and peak flow rate, captures
pollutants, and may be used to recharge groundwater. These systems allow for infiltra�on of
stormwater while providing a stable load-bearing surface for walking and driving.
Porous pavement deten�on can be used as a subs�tute for conven�onal pavement, but should be
limited to parking areas and low traffic volume roadways where li�le to no truck traffic is an�cipated.
Example applica�ons include residen�al driveways, residen�al street parking lanes, parking stalls in
commercial or retail parking lots, overflow parking areas, maintenance walkways/trails, emergency
vehicle and fire access lanes, stopping lanes on divided highways, equipment storage areas, and
pa�os. Permeable pavement treats rainfall that falls directly on the surface, as well as runoff from
adjacent impervious areas. These systems contain void spaces to provide infiltra�on of runoff into
their underlying engineered porous materials and then into exis�ng site soils. Generally, underlying
engineered materials consist of clean sands or gravels separated from exis�ng site soils by a synthe�c
filter fabric. Underlying engineered materials detain and filter pollutants prior to infiltra�on into
underlying soils or discharge to a conven�onal storm drain system through an underdrain system. With
these systems, it is important to note that the load-bearing sub-grade must be sufficiently thick to
support the design load from the intended use and provide storage for volume or deten�on control.
Porous paving systems can preserve natural drainage pa�erns, enhance groundwater recharge and
soil moisture, and can help establish and maintain roadside vegeta�on. Although a good subs�tute for
conven�onal concrete and asphalt, porous paving systems are typically not suitable in high-traffic areas.
The technology for permeable pavement con�nues to progress and alterna�ves may be able to handle
heavy traffic situa�ons in the future. There are several different types of permeable pavement systems
(Figure 5-17) including:
• Open-Celled Block Pavers
• Open-Jointed Block Pavers
• Porous Asphalt Pavement
• Porous Concrete Pavement
• Porous Turf
• Porous Gravel
• Open-Celled Plas�c Grids
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
Chap5:Pg45
Figure 5-17: Various Permeable Pavement Systems. Source – NC State University.
Figure 5-18 Cross sec�on of Permeable pavement Parking Lot Design. Source Cahill and Associates.
Figure 5-19 Cross-sec�ons of typical permeable pavement installa�ons. Source, City of
Sacramento
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Chap5:Pg46
5.4.2 Performance
Effec�veness for removal of various pollutants by permeable pavement
systems is shown in Figure 5-21.
Because permeable pavement reduces the runoff volume and peak flow
rate by temporarily storing runoff in the sub-grade and allowing it to
infiltrate into the subsoil, the storage volume is determined by the sub-
grade thickness. The thickness of the aggregate sub-grade depends on
several factors including the desired reten�on volume, the surface area
of the permeable pavement, the surface area collec�ng rainwater, the
flow rate into the pavement surface, and the exfiltra�on rate into the soil.
Areas with lower soil permeability will require a greater subsurface storage
volume. Infiltra�on rates as low as 0.1 – 0.5 inches/hour are acceptable, as
long as adequate storage capacity is provided. The pavement material
itself should never become saturated. To avoid this problem, provide a
catch basin with an outlet pipe at an eleva�on approximately 2 inches
higher than he pavement surface. The sub-grade should fully drain
within 72 hours. Permeable pavement can treat runoff from adjacent
impervious areas, but the ra�o of impermeable to permeable surface area should not exceed 5:1.
5.4.3 General Design Guidance
Permeable and conven�onal pavements are similar for both asphalt and concrete in that materials
and construc�on techniques are the same. Design differs with regard to the depth of the aggregate
sub-grade, the thickness of the pavement to achieve the same
design strength, and the use of a geotex�le liner below the
sub-grade.
The aggregate sub-grade consists of uniformly graded stone in
order to maximize the void ra�o. The stone should be crushed
and clean washed. The sub-grade is typically divided into
upper and lower filter courses, comprised of fine and larger
aggregate, respec�vely. Geotex�le fabric is placed beneath
the sub-grade to separate the aggregate from the underlying
soil. Perforated pipes may be placed in the sub-grade to allow
runoff from adjacent impervious areas to enter the stone bed
directly.
Permeable pavement should be placed on soils that are not compacted and steps should be taken to
ensure that soil is not compacted during the construc�on process. Erosion control techniques should
remain in place around the permeable pavement area un�l the site has fully stabilized (e.g. vegeta�on
becomes established) to avoid influxes of sediment onto the permeable surface.
Overland runoff should be prevented from entering the parking lot in order to decrease the sediment
loading, reduce maintenance requirements, and maximize the performance and lifespan of the
Figure 5-21 Performance. Source
CASQA 2003.Pavement Systems.
Source – NC State University.
Figure 5-20 Porous concrete in parking stalls at
Costco in Wilmington. .
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
Chap5:Pg47
permeable pavement. This can be accomplished by efficient grading techniques and the installa�on of
a perimeter berm or filter strip.
Si�ng Criteria
• Porous pavement deten�on installa�ons should be installed in areas that are flat in all direc�ons
(i.e. 0% slope).
• If designed to infiltrate stormwater into underlying soils, porous pavements are considered
indirect infiltra�on systems. Therefore apply site screening, infiltra�on tes�ng, separa�on, and
setback standards for indirect infiltra�on systems.
Design and Construc�on Criteria
• Follow pavement manufacturer’s specifica�ons and recommenda�ons for design, construc�on, and
maintenance.
• Registered professional civil engineers should design the porous pavement system.
• Sub-base layers should be capable of bearing an appropriate load without deforming.
• Permeable pavements should be installed during the final phase of construc�on or redevelopment.
• Use an open-graded aggregate base course to provide a permeable reservoir.
• When designing the base course, or base reservoir to detain the water quality volume, select the
appropriate porosity value for the material used.
• Strength and durability of materials under saturated condi�ons must be considered.
• When installing the base course, it must be compacted as it is placed in li�s.
• A bedding layer should be laid over the base course as level bedding for the blocks consis�ng of
rela�vely small open-graded aggregate mee�ng criteria for a filter layer, or “choke layer”.
• Appropriate grada�ons of aggregate material must be used to prevent migra�on of par�cles from
one layer to the next.
• An overflow, possibly with an inlet to a storm sewer, should be installed at 2 inches above the level
of the porous pavement surface.
• Direct sediment-laden runoff away from the porous pavements.
• Filter fabrics should be placed on the bo�om and sides of the sub-base layer.
• An impermeable liner should be installed under the base course to inhibit infiltra�on when
installing over expansive soils or if the tributary area contains ac�vi�es that store, manufacture, or
handle fer�lizers, chemicals, or petroleum products.
• To allow infiltra�on and prevent clogging, the filter fabric should be woven geotex�le fabric layer
such as SI Corpora�on Geotex 117F or an approved equivalent.
• During construc�on, do not allow construc�on or heavy vehicles to traverse excavated recharge
beds or areas of completed porous pavement.
• Once porous pavement is in place, ensure contribu�ng drainage areas of the construc�on site have
erosion and sediment control measures in place and are maintained un�l the site is stabilized.
• The storage capacity of the stone reservoir beneath porous pavements depends upon local
deten�on requirements and can be sized to capture, detain and filter the water quality volume.
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Chap5:Pg48
References
Balades et al., 1995. Permeable Pavements: Pollu�on Management Tools, Water Science and Technology. Vol. 32, No. 1, pp.
49-56, 1995.
California Stormwater Quality Associa�on (CASQA), 2003. Stormwater Best Management Prac�ce Handbook – New
Development and Redevelopment.
City and County of Sacramento, 2000. Guidance Manual for Onsite Stormwater Quality Control Measures.
Legret and Colandini, 1999. Effects of a Porous Pavement with Reservoir Structure on Runoff Water: Water Quality and Fate
of Heavy Metals, Water Science and Technology. Vol. 39, No. 2, pp. 111-117, 1999.
Newman et al., 2002. Oil Bio-Degrada�on in Permeable Pavements by Microbial Communi�es, Water Science, and
Technology. Vol. 45, No. 7, pp. 51-56, 2002.
Pra� et al., 1999.
Mineral Oil Bio-Degrada�on within a Permeable Pavement: Long Term Observa�ons, Water Science and Technology. Vol. 39,
No. 2, pp. 103-109, 1999.
Urban Drainage and Flood Control District (UDFCD), 2005. Urban Storm Drainage Criteria Manual, Volume 3 – Best
Management Prac�ces.
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Chap5:Pg49
5.4.4 Open-Cell and Open-Joint Block Pavers
5.4.4.1 General
Open-celled block pavers, also known as modular block
pavers, consist of block or slabs made of concrete or brick
with open voids that penetrate their surface refer to Figure
5-22 and 5-17b). The modular blocks are placed over a porous
sub-base and the openings within and between the blocks are
filled with pervious materials (e.g. open-graded aggregate).
Porous materials such as clean gravels placed below the porous
pavement detain and filter pollutants prior to infiltra�on into
underlying soils or discharge to drainage to a conven�onal
storm drain system. This type of surface reduces runoff from
paved areas and the ponding that typically occurs in parking
lots during and a�er storm events.
Open-jointed block pavers consist of solid block units made of concrete, clay, or stone that form an
interlocking, flexible pavement surface (refer to Figure 5-17b). Open voids are created, by beveling
the corners of each block or crea�ng wider spacing between the blocks. The blocks themselves also
commonly contain small voids to increase permeability. The modular blocks are placed over a porous
sub-base and the openings within and between the blocks are filled with pervious materials (e.g. clean
sand). The pavers are placed on a gravel sub-grade to detain and filter pollutants prior to infiltra�on
into underlying soils or discharge to drainage to a conven�onal storm drain system. This type of surface
reduces runoff from paved areas and reduces the ponding that typically occurs in parking lots during
and a�er storm events.
5.4.4.2 Applica�ons and Advantages
Open-celled and open-jointed block pavers may be used as a subs�tute for conven�onal pavement,
but should be limited to parking areas and low traffic volume roadways where li�le to no truck traffic
is an�cipated. Examples include residen�al driveways, residen�al street parking lanes, parking stalls
in commercial or retail parking lots, overflow parking areas, maintenance walkways/trails, emergency
vehicle and fire access lanes, stopping lanes on divided highways, equipment storage areas, and pa�os
as well as alterna�ve to conven�onal paving in areas where tree protec�on and preserva�on is a
concern. The storage capacity of the base reservoir beneath porous pavements depends upon local
deten�on requirements and can be sized to capture, detain and filter the water quality volume.
5.4.4.3 Limita�ons
• Not to be applied in high traffic areas or where speeds exceed 30 miles per hour.
• Care must be taken when installing in commercial or industrial areas.
• Maintenance costs can be rela�vely high if the blocks frequently become clogged with sediment
from offsite sources. Care must be taken during installa�on to ensure that the surface does not
become clogged with sediment.
• Porous pavements may cause uneven driving surfaces and may be problema�c for high heel shoes.
Figure 5-22 Open-celled block pavers
within overflow parking area at Best Buy
in Wilmington.
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
Chap5:Pg50
• May not be suitable for areas that require wheelchair access because of the pavement texture.
• Porous pavement can be problema�c with regard to snow and ice removal. Snow removal may be
difficult since plows may damage blocks if they are not installed correctly or if plow blade is not
raised above the block surface. During ice and snow events, sand applica�on can result in clogging
and use of salt can result in groundwater contamina�on.
5.4.4.4 General Design Guidance
• All installa�ons should be designed and constructed to pavement manufactures specifica�ons.
• Permeable pavement should be installed on flat surfaces adjacent to gently sloping conven�onal
pavement surfaces. The completed installa�on should be installed at a grade less then 0.5%.
• Ini�al installa�on should not occur during rain or heavy snowfall or when the ground is frozen.
• If designed to infiltrate stormwater into underlying soils, permeable pavements are considered
indirect infiltra�on systems. Therefore apply site screening, infiltra�on tes�ng, separa�on, and
setback standards for indirect infiltra�on systems.
• Installa�on is to be accomplished by a qualified contractor experienced in paver applica�ons.
• During construc�on, do not allow construc�on equipment or heavy vehicles to traverse excavated
recharge beds or areas of completed porous pavement.
• Sub-base layers should be capable of bearing an appropriate load without deforming.
• Permeable pavements should be installed during the final phase construc�on or redevelopment.
• Block pa�erns should have a minimum surface area void space of 20 percent for open-cell and 8%
for open-joint.
• An open-graded aggregate base course should be installed to provide a permeable reservoir.
• In order to detain the water quality volume, when designing the base course or base reservoir,
select the appropriate porosity value for the material used.
• Strength and durability of materials under saturated condi�ons must be considered.
• When installing the base course, it must be compacted as it is placed in li�s.
• A bedding layer should be installed over the base course as level bedding for the blocks consis�ng
of rela�vely small open-graded aggregate mee�ng criteria for a filter layer, or “choke layer”.
• Appropriate grada�ons of aggregate material must be used to prevent migra�on of par�cles from
one layer to the next. If this cannot be achieved, a woven geotex�le should be used under the
bedding layer above the base course to prevent migra�on. A woven geotex�le fabric layer such as SI
Corpora�on Geotex 117F or equal can be installed.
• Open-celled block pavers must be vibrated into place within the bedding layer.
• Filter fabrics should be placed on the bo�om and sides of the base layer.
• An impermeable liner should be installed under the base course to inhibit infiltra�on when
installing over expansive soils or in an area that contains ac�vi�es that store, manufacture, or
handle fer�lizers, chemicals, or petroleum products.
• Edge restraints should be installed on compacted subgrade or base material, not on the bedding.
• For aggregate fill in the cells, material should consist of open-graded sand and can be the same
material as the bedding material.
• Do not use concrete sand, which is tradi�onally used for interlocking concrete pavement bedding
layer construc�on and has been shown to have low permeability.
• Do not sweep sand into the joints a�er the pavers are installed to fill joints as this can compromise
the permeability and porosity of pavers.
• A concrete perimeter wall should be installed to confine the edges of the block installa�on. The
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Chap5:Pg51
perimeter wall should be 6 inches thick and should extend to 6 inches deeper than the base course.
• Lateral-flow cut-off barriers should be installed using a 16-millimeter or thicker PE or PVC
impermeable membrane liner or concrete walls installed normal to flow. This prevents flow of
water downstream from disrup�ng block installa�on.
• The distance between cut-off barriers shall not exceed: LMAX = D/(1.5*So)
LMAX = Max distance between cut-off barriers normal to flow (�)
D = Depth of the aggregate base course (�/�)
So = Slope of the base course (�)
• An underdrain should be installed where impermeable liners are installed or when soils inhibit
proper infiltra�on rates. Locate each underdrain pipe just upstream of the lateral flow cut-off
barrier.
• For roo�ng vegeta�on in the joints, plan�ng medium should be sandy and open-graded. In bedding
and base course, a limited amount of plan�ng medium could be mixed into open-graded aggregate
to deepen roo�ng.
• Cut pavers with a paver spli�er or masonry saw. When cut, pavers should be no smaller than one-
third of the full unit size along edges subject to vehicular traffic.
• Plant grass in open-joints as plugs or broadcast seed at a reduced rate to account for concrete grids.
• Follow pavement manufacturer’s specifica�ons.
• Direct sediment-laden runoff from adjacent areas away from the porous pavements.
• Once permeable pavement is in place, ensure contribu�ng drainage areas of the construc�on site
have erosion and sediment control measures in place and are maintained un�l the site is stabilized.
Figure 5-23 Porous Paver Block Design. Source Boulder
Stormwater Management Plan
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
Chap5:Pg52
5.4.4.5 Inspec�on and Maintenance Requirements
• Open-celled block pavers should not be washed to remove debris and sediment in the openings
between pavers, rather sweeping with vacuum should be u�lized annually. Replace lost sand infill.
• Joints between block pavers may require occasional weed suppression.
• Pavers can be removed individually and replaced when u�lity work is needed.
• Top course aggregate can be removed or replaced in pavers if they become clogged or
contaminated.
• Replace surface filter layer by vacuuming out sand media from blocks when it becomes evident that
runoff does not rapidly infiltrate into the surface.
• For pavers planted with turf, regular turf maintenance will be necessary. However, pes�cides,
fer�lizers and other chemicals can have adverse effects on concrete products and will infiltrate into
the system, so their use should be restricted.
• If soils swell or subside, blocks can be removed individually, the base leveled, and blocks reset.
References
Balades et al., 1995. Permeable Pavements: Pollu�on Management Tools, Water Science and Technology. Vol. 32, No. 1, pp.
49-56, 1995.
California Stormwater Quality Associa�on (CASQA), 2003. Stormwater Best Management Prac�ce Handbook – New
Development and Redevelopment.
City and County of Sacramento, 2000. Guidance Manual for Onsite Stormwater Quality Control Measures.
Ferguson, B., 2005. Porous Pavements. Boca Raton, FL: CRC Press.
Legret and Colandini, 1999. Effects of a Porous Pavement with Reservoir Structure on Runoff Water: Water Quality and Fate
of Heavy Metals, Water Science and Technology. Vol. 39, No. 2, pp. 111-117, 1999.
Newman et al., 2002. Oil Bio-Degrada�on in Permeable Pavements by Microbial Communi�es, Water Science, and
Technology. Vol. 45, No. 7, pp. 51-56, 2002.
Pra� et al., 1999. Mineral Oil Bio-Degrada�on within a Permeable Pavement: Long Term Observa�ons, Water Science and
Technology. Vol. 39, No. 2, pp. 103-109, 1999.
Urban Drainage and Flood Control District (UDFCD), 1999. Urban Storm Drainage Criteria Manual, Volume 3 – Best
Management Prac�ces.
Florida Department of Environmental Protec�on. 1988. Florida Development Manual: A Guide to Sound Land and Water
Management Volume 2, Chapter 6.
City and County of Sacramento, 2000. Guidance Manual for Onsite Stormwater Quality Control Measures.
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
Chap5:Pg53
5.4.5 Porous Concrete and Asphalt
5.4.5.1 General
Porous concrete and asphalt both make a con�nuous, smooth paving surface like their impervious
counterparts. However, they are made by binding open-graded aggregate, and therefore contain void
spaces that allow water to pass through to a permeable sub base layer. Porous materials such as clean
gravels placed below the porous concrete or asphalt detain and filter pollutants prior to infiltra�on into
the underlying soils or discharge to an underdrain and the conven�onal storm drain system (see Figure
5-24 and 5-17c&d)
5.4.5.2 Applica�ons and Advantages
Porous concrete and asphalt are ideal for light to medium duty
applica�ons such as residen�al access roads, residen�al street
parking lanes, parking lot stalls in parking lots, overflow parking
areas, u�lity access, sidewalks, bike paths, maintenance
walkways/trails, residen�al driveways, stopping lanes on
divided highways, and pa�os. However, porous asphalt has
also been used in heavy applica�ons such as airport runways
and highways because it has been found that its porosity
creates a favorable driving surface in rainy weather. Porous
concrete and asphalt may also reduce icing hazards during
winter freeze and thaw cycles as runoff will tend to infiltrate
rather than freeze onto the surface of roadways, parking lots,
driveways and sidewalks.
5.4.5.3 Limita�ons
• Porous concrete and asphalt typically should not to be installed on streets where speeds exceed 30
mph or streets that experience high-traffic loads.
• Not recommended for slopes over 0.5%.
• Not recommended where the seasonal high groundwater table is less than 2 feet below the bo�om
of the gravel sub-base.
• Sand and salt applied to porous roadways, parking lots, and sidewalks in winter can clog void spaces
and render permeability ineffec�ve if not removed annually.
• Porous concrete may experience raveling if not properly installed.
• Porous asphalt and concrete may become clogged if not protected from nearby construc�on
ac�vi�es, bare soil without landscaping, down slope of steep, erosion-prone areas, or when not
maintained appropriately.
• Installa�ons that include underdrain systems are typically more expensive than conven�onal
asphalt and concrete.
• Do not install over frozen base materials.
Figure 5-24 Close-up of porous concrete at
Costco in Wilmington.
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
Chap5:Pg54
5.4.5.4 Si�ng Criteria
• Ideally, permeable pavement should be installed on flat surfaces adjacent to gently sloping
conven�onal pavement surfaces. They can also be installed on gentle slopes that do not exceed
0.5%.
• Do not use in areas where the poten�al for spills is high (e.g. near service/gas sta�ons, truck stops
or industrial sites). The seasonal high water table eleva�on should a minimum of 2 feet below the
bo�om of the gravel sub-base. Care must also be taken when installing in commercial or industrial
areas.
• Not to be installed in drainage areas where ac�vi�es generate highly contaminated runoff.
• Not to be installed in areas where wind erosion supplies significant amounts of windblown
sediments.
• Snow and ice control with sand applica�on can result in clogging and use of salt can result in
groundwater contamina�on.
• If designed to infiltrate stormwater into underlying soils, porous pavements are considered indirect
infiltra�on systems. Apply site screening, infiltra�on tes�ng, separa�on, and setback standards for
indirect infiltra�on systems.
5.4.5.5 General Design Guidance
• Follow pavement manufacturer’s specifica�ons and recommenda�on for design construc�on and
maintenance.
• Registered professional civil engineers should design porous pavements system.
• Avoid installing in high traffic areas.
• Slopes should be flat or very gentle (less than 0.5%).
• Direct sediment-laden runoff from adjacent areas away from the porous pavements.
• Pretreatment can be used to treat runoff from surrounding areas.
• Filter fabric should be placed on the bo�om and sides of the sub base reservoir.
• Impermeable liner should be installed under the base course to inhibit infiltra�on when installing
over expansive soils or if the tributary area contains ac�vi�es that store, manufacture, or handle
fer�lizers, chemicals, or petroleum products.
• To allow infiltra�on and prevent clogging, the filter fabric should be woven geotex�le fabric layer
such as SI Corpora�on Geotex 117F or an approved equivalent.
• Use an open-graded aggregate to provide open voids in the gravel sub base.
• Erosion and sediment introduc�on from surrounding areas must be strictly controlled during and
a�er construc�on to prevent clogging of void spaces in base material and permeable surface.
• Install porous asphalt and concrete towards the end of construc�on ac�vi�es to minimize sediment
problems.
• Once porous pavement is in place, ensure contribu�ng drainage areas of the construc�on site have
erosion and sediment control measures in place and are maintained un�l the site is stabilized.
• During construc�on, do not allow construc�on equipment or heavy vehicles to traverse excavated
recharge beds or areas of completed porous pavement.
• During emplacement of porous concrete, boards should be used to separate individual pours and to
produce uniform seams between adjacent pours.
• The surface of each pour should be finished as soon as possible as porous concrete can set up very
rapidly in our local arid environment.
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Chap5:Pg55
• Overall project cost savings can be realized where porous asphalt or concrete is installed in well
draining soils (e.g. infiltra�on rates of 0.5 in/hr (120 min/in) or greater), and conven�onal
stormdrain pipes and catch basins can be reduced.
• Care should be taken during installa�on of permeable concrete and asphalt to make sure surface is
not “smoothed over” during or a�er installa�on before having a chance to set as this could close
some of the surface porosity.
5.4.5.6 Inspec�on and Maintenance Requirements
• The overall maintenance goal is to avoid clogging of the void spaces.
• Remove accumulated debris and li�er as needed.
• Inspect porous asphalt and concrete several �mes during the first few storms to insure proper
infiltra�on and drainage. A�er the first year, inspect at least once a year or as otherwise directed
by regulatory requirements.
• Permeable pavements and materials should be cleaned with a vacuum-type street cleaner a
minimum of twice a year (before and a�er the winter).
• Maintenance such as running a vacuum sweeper is required to prevent clogging of the pervious
surface.
• Hand held pressure washers can be effec�ve for cleaning the void spaces of small areas and should
follow vacuum cleaning.
• Maintenance personnel must be instructed not to seal or pave with non-porous materials.
References
Bay Area Stormwater Management Agencies Associa�on (BASMAA). 1999. Start at the Source: Design Guidance Manual for
Stormwater Quality Protec�on. Prepared by Tom Richman& Associates.
Briggs, J.F., Houle, J.P., Roseem, R.M., and Ballestero, T.P. 2005. Hydraulic and Hydrologic Performance of Porous Asphalt
Pavement. StormCon 2005.
EPA. 1999. Storm Water Technology Fact Sheet: Porous Pavement. Office of Water, Washington, D.C.
Hun-Dorris, Tara. 2005. Advances in Porous Pavement. Stormwater, March/April, volume 6(2).
Puget Sound Ac�on Team. 2005. Low Impact Development: Technical Guidance Manual for Puget Sound. Olympia, WA.
Tool Base Services. Permeable Pavement.
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
Chap5:Pg56
5.4.6 Porous Turf Pavement
5.4.6.1 General
Porous turf pavement is a stabilized grass surface that can support intermi�ent pedestrian or vehicular
traffic, underlain by an open-graded (single-sized) sandy root zone, and a permeable aggregate base
course. Porous turf pavement systems should be installed when the appearance of grass is desired, but
a load bearing capability of a pavement surface is needed. The turf surface can be either reinforced or
unreinforced. Reinforced turf contains synthe�c reinforcement that assists the turf in resis�ng wear
and compac�on and allows the turf to bear a heavier traffic load. Advantages of porous turf pavement
include the appearance of a “green space” when not used for parking, as well as the benefit of a living
surface which ac�vely cools by transpira�on counterac�ng the urban heat island effect.
5.4.6.2 Applica�ons and Advantages
Porous turf pavement is suitable for parking areas where parking frequency is up to once per week.
Ideal se�ngs are sports fields, overflow parking areas, church and football stadium parking lots, event
parking, roadway shoulders, parking lanes, crossover lanes on divided highways, flea market or other
large event parking, and maintenance roads and trails. Porous turf applica�ons can also be mul�use
facili�es - for example, a sports field that also serves as a special event parking lot.
Ideally, the porous turf pavement would lead the driver a porous turf surface constructed of another
type of material such as porous concrete or asphalt pavement (i.e. porous turf parking pads with
porous concrete or asphalt lanes). This reduces grass wear from excessive traffic on the porous turf
surface, which could decrease the porosity and increase maintenance requirements.
5.4.6.3 Limita�ons
• Not to be applied in heavily trafficked areas.
• Surface cannot be used un�l grass is established.
• Requires supplemental irriga�on.
• A uniformly graded vegeta�ve cover is required to func�on properly.
• Excessive traffic can cause soil compac�on and reduce infiltra�on.
• Weed invasion can result from thinning grass cover.
• Turning ac�on of vehicles can be problema�c for porous turf, damaging the structure of the leaves
and some�mes causing root damage.
• May be problema�c for high-heeled shoes and smooth-soled shoes (which can slip on wet grass).
5.4.6.4 Si�ng Criteria
• Do not use in areas where the poten�al for spills is high (e.g. near service/gas sta�ons, truck stops
or industrial sites).
• Must be installed only in se�ngs that will be free of traffic on a predictable schedule for
maintenance.
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Chap5:Pg57
5.4.6.5 General Design Guidance
• Turf should be installed by laying sod, seeding, or sprigging.
• Root zone material should be tested by a qualified lab and soil treated with appropriate lime or
fer�lizer as recommended for establishment success.
• Proprietary meshes, mats, and fibers are available for reinforcing turf root zones.
• Once porous pavement is in place, ensure contribu�ng drainage areas of the construc�on site have
erosion and sediment control measures in place and are maintained un�l the site is stabilized.
• Allow turf at least one full growing season to establish before use.
• If seeding, seed in the fall or early spring to avoid heat stress.
• Grass species should be selected based on wear tolerance and irriga�on needs.
• Grass selec�on, traffic control, and good maintenance are required for health of the turf grass.
5.4.6.6 Inspec�on and Maintenance Requirements
• Porous turf requires the regular maintenance that is associated with typical lawn turf such as
irriga�on, mowing, fer�liza�on, aera�on, topdressing, over-seeding, disease control, insect control,
and weed management.
• Soil tes�ng should be conducted at least once every other year to determine proper fer�liza�on,
which will help to maintain turf stress tolerance.
• Rou�ne mowing will be required in the growing season.
• Above ground biomass is important in the tolerance of the turf, therefore mowing with a raised
blade can increase resistance to traffic stress. Mowing pa�erns should also be altered regularly
to limit wear from repe��ve wheel ac�on.
• Reseeding may be required to maintain a uniform turf cover.
• Topdressing material should be at least as coarse and open-graded as root zone.
• Water is required consistent with typical landscape care.
• Traffic routes can be spread out or rotated to give the turf �me to recover between uses. Traffic
control can also divert traffic away from areas showing signs of wear.
References
Bay Area Stormwater Management Agencies Associa�on (BASMAA). 1999. Start at the Source: Design Guidance Manual for
Stormwater Quality Protec�on. Prepared by Tom Richman & Associates.
Ferguson, B. 2005. Porous Pavements. CRC Press, Florida.
Hun-Dorris, Tara. 2005. Advances in Porous Pavement. Stormwater, March/April, volume 6(2).
Post, C. and M. Mills. 2002. The All Seeing All Knowing Lawn Care Manual. University of Nevada Coopera�ve Extension SP-
93-02
Puget Sound Ac�on Team. 2005. Low Impact Development: Technical Guidance Manual for Puget Sound. Olympia, WA.
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
Chap5:Pg58
5.4.7 Porous Gravel Pavement
5.4.7.1 General
Porous gravel pavement, or crushed aggregate, consists of a loose gravel-surface paving placed over
a porous sub-base. Porous materials (such as clean gravels) that are placed below porous pavement
detain and filter pollutants prior to stormwater infiltra�on into underlying soils. This type of pavement
reduces runoff from paved areas and the ponding that typically occurs in parking lots during and a�er
storm events.
5.4.7.2 Applica�ons and Advantages
Porous gravel pavement can be used as a subs�tute for conven�onal pavement. It is most appropriate
for industrial sites, storage yards or for vehicle parking. Other examples or porous gravel pavement
applica�on include residen�al driveways, residen�al street parking, low vehicle movement zones such
as parking lots and maintenance roads, maintenance walkways/trails, and stopping lanes on divided
highways.
5.4.7.3 Limita�ons
• Not to be applied in heavily trafficked areas or where speeds exceed 30 miles per hour.
• Care must be taken when applying in commercial or industrial areas.
• May become clogged if not properly installed and maintained.
• Porous pavements may cause uneven driving surfaces and may be problema�c for high heel shoes.
5.4.7.4 Si�ng Criteria
• Ideally, pervious gravel pavement should be installed on flat surfaces adjacent to gently sloping
conven�onal pavement surfaces. However they can also be placed on gentle slopes that do not
exceed 0.5%.
• Do not use in areas where the poten�al for spills is high (e.g. near service/gas sta�ons, truck stops
or industrial sites).
• The seasonal high water table should be a minimum of 2 feet below the bo�om of the permeable
pavement sub-base.
5.4.7.5 General Design Guidance
• Once porous pavement is in place, ensure contribu�ng drainage areas of the construc�on site have
erosion and sediment control measures in place and are maintained un�l the site is stabilized.
5.4.7.6 Inspec�on and Maintenance Requirements
• Remove accumulated debris and li�er as needed.
• Maintenance is required to prevent clogging of the pervious surface.
• Occasional weed suppression may be required.
• Periodic replenishing and/or raking of displaced gravel may be required.
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Chap5:Pg59
• Frequently inspect the pavement to insure proper infiltra�on and drainage during the first wet
season, and then once a year following that �me.
• Inspect surface gravels once a year. When inspec�ons show accumula�on of sediment and debris
on top of gravel or slow infiltra�on, remove and replace top few inches of gravel.
References
Balades et al., 1995. Permeable Pavements: Pollu�on Management Tools, Water Science and Technology. Vol. 32, No. 1, pp.
49-56, 1995.
California Stormwater Quality Associa�on (CASQA), 2003. Stormwater Best Management Prac�ce Handbook - New
Development and Redevelopment.
City and County of Sacramento, 2000. Guidance Manual for Onsite Stormwater Quality Control Measures.
Legret and Colandini, 1999. Effects of a Porous Pavement with Reservoir Structure on Runoff Water: Water Quality and Fate
of Heavy Metals, Water Science and Technology. Vol. 39, No. 2, pp. 111-117, 1999.
Newman et al., 2002. Oil Bio-Degrada�on in Permeable Pavements by Microbial Communi�es, Water Science, and
Technology. Vol. 45, No. 7, pp. 51-56, 2002.
Pra� et al., 1999. Mineral Oil Bio-Degrada�on within a Permeable Pavement: Long Term Observa�ons, Water Science and
Technology. Vol. 39, No. 2, pp. 103-109, 1999.
Urban Drainage and Flood Control District (UDFCD), 1999. Urban Storm Drainage Criteria Manual, Volume 3 – Best
Management Prac�ces.
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
Chap5:Pg60
5.4.8 Open-Celled Plas�c Grids
5.4.8.1 General
Open-celled plas�c grids, also known as geocells, are manufactured plas�c la�ces which can be filled
with aggregate or topsoil and planted with turf (see figure 5-17e). Many of these systems are made
from recycled plas�cs. The grid systems contain hollow rings or hexagonal cells from 1-2 inches thick
and a few inches wide. Since the cells occupy very li�le surface area, they appear as a turf or gravel
surface. Some models are also joined at the bo�om by either a perforated plas�c sheet or geotex�le
fused to the bo�om of the grid which is placed on the underlying base course. It is important that this
area is open for roo�ng of grasses. Most open celled grid systems are flexible, so they are tolerant of
swelling or freezing soils and are applicable on uneven sites.
5.4.8.2 Applica�ons and Advantages
Open-celled grids should be limited to low intensity use and areas with low traffic speeds. Examples
include driveways, residen�al street parking lanes, parking stalls in commercial or retail parking lots,
overflow parking areas, maintenance walkways/trails, u�lity access, ATV and off-road bike trails, golf
cart paths, emergency vehicle and fire access lanes, loading areas, and alleys.
5.4.8.3 Limita�ons
• Sharp turning on grids should be avoided.
• May be problema�c for high-heeled shoes.
• Irriga�on of porous turf installa�on in open-celled grids has the poten�al to require heavier
irriga�on than normal due to the low water holding capacity of the soil in grids.
• Slopes should not exceed 0.5%.
• Not to be applied in heavily trafficked areas or where speeds exceed 20 miles per hour.
5.4.8.4 Si�ng Criteria
• Ideally, permeable pavement should be installed on flat surfaces adjacent to gently sloping
conven�onal pavement surfaces. However, they can also be placed on gentle slopes that do not
exceed 0.5% percent.
• If designed to infiltrate stormwater into underlying soils, porous pavements are considered
indirect infiltra�on systems. Therefore apply site screening, infiltra�on tes�ng, separa�on, and
setback standards for indirect infiltra�on systems.
5.4.8.5 General Design Guidance
Open-Celled Plas�c Grids Filled with Aggregate
• Follow the standard design and construc�on criteria for general permeable pavement systems.
• La�ces come in pre-assembled panels or rolls in various dimensions, from a few square feet to rolls
that can be spread out to cover large areas.
• Grids need to be anchored to the base in some applica�ons (depending on the model) to prevent
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Chap5:Pg61
being jarred by moving traffic. Anchors may consist of plas�c spikes, pins, or rods, or even boulders,
logs, or wheel stops over the surface.
• A se�ng bed of smaller aggregate may be needed over the base course to make a uniform surface
for the open-celled grids.
• Woven filter fabrics should be placed on the bo�om and sides of the base course layer.
• An impermeable liner is required under the base course when installing over expansive soils or if
the tributary may have ac�vi�es that store, manufacture, or handle fer�lizers, chemical, or
petroleum products.
• To allow infiltra�on and prevent clogging, the filter fabric should be woven geotex�le fabric layer
such as SI Corpora�on Geotex 117F or an approved equivalent.
• Underdrains are required for installa�ons over NRCS type D soils or when an impermeable
membrane liner is needed.
• Aggregate fill must be open-graded, with common installa�on sizes.
• Aggregate is compacted into place with a vibra�ng plate or roller.
Open-Celled Plas�c Grids Planted with Turf
• The plan�ng medium should be se�led into cells by vibra�ng or watering.
• The plan�ng medium should consist of open-graded fine aggregate.
• Sod should only be installed with thin-walled grid systems.
• Sod can be installed by pressing into empty cells. Sod should be cut to a depth of the grid system.
• Anchoring may protect growing grass roots and promote deeper roo�ng, which will add strength to
pavement structure.
• If filter fabric is needed on top of the base course, an open-graded aggregate filter layer may be
used instead.
• Traffic should not be allowed on the surface un�l a�er turf is established.
• Sec�ons can be removed and replaced for u�lity access and pavement repair.
• Remove and replace grid segments where three or more adjacent rings are broken or damaged.
5.4.8.6 Inspec�on and Maintenance Requirements
Open-Celled Plas�c Grids Filled with Aggregate
• Remove accumulated debris and li�er as needed.
• Maintenance is required to prevent clogging of the pervious surface.
• Occasional weed suppression may be required.
• Periodic replenishing and/or raking of displaced gravel may be required.
• Inspect surface gravels once a year. When inspec�ons show accumula�on of sediment and debris
on top of gravel or slow infiltra�on, remove and replace top few inches of gravel.
Open-Celled Plas�c Grids Planted with Turf
• For open-celled grids filled with turf, mechanical aera�on of must be avoided, as this can damage
the plas�c material.
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Chap5:Pg62
References
Ferguson, B. 2005. Porous Pavements. Boca Raton, FL: CRC Press.
Hun-Dorris, T. 2005. Advances in Porous Pavements. Stormwater, March/April, volume 6(2).
Puget Sound Ac�on Team. LID Technical Guidance Manual for the Puget Sound.
Urban Drainage and Flood Control District (UDFCD), 2005. Urban Storm Drainage Criteria Manual, Volume 3 – Best
Management Prac�ces.
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Chap5:Pg63
5.5 Rain Water Catchment Systems – Cisterns and Rain Barrels
5.5.1 General
Cisterns and rain barrels are designed to capture roof runoff for reuse. Cisterns reduce the runoff
volume and may reduce the peak flow rate for small, frequently occurring storms. Water quality
benefits will depend on the end use of collected water. Cisterns are especially useful in areas where
domes�c water is at a premium and where high real estate prices, poor soil infiltra�on capacity, or li�le
available open space preclude the use of infiltra�on techniques such as bioreten�on.
Landscape irriga�on can account for as much as 40% of domes�c water consump�on. An advantage
of roof water recycling is that roof water is rela�vely clean, compared to pavement surface runoff, and
can provide a source of chemically untreated “so� water,” free of most sediment and dissolved salts.
Cisterns or rain barrels can serve as a secondary source of water for applica�ons that do not require
potable water, poten�ally lowering a building’s potable water demand (and water bill). Uses for the
water may include: landscape irriga�on, air condi�oner coolant, vehicle washing, clothes washing,
toilet flushing, and swimming pool makeup.
For any storm, the runoff volume will be reduced by an amount equal to the available volume of the
cistern which may be less than the total storage capacity. The peak discharge rate may be delayed
or a�enuated, depending on captured volume. Cistern sizing depends on the water demand and the
collec�on volume: in other words, an analysis of the water input and output. Addi�onal storage may
be needed if cistern water is not completely drawn down between storms. Per-capita use of cistern
water (e.g. toilet flushes per person per day) can be used to calculate the demand or the cistern
ou�low rate.
5.5.2 Applica�ons and Advantages
Cisterns or rainwater catchment systems can provide a stormwater management solu�on where
impervious surfaces are unavoidable and site constraints limit the use of other LID prac�ces. Such
situa�ons may include highly urbanized areas (such as downtown centers), or dense housing
developments without adequate space for stormwater infiltra�on or deten�on, or where soil
and groundwater condi�ons do not permit infiltra�on. In addi�on to stormwater management
benefits, rainwater catchment systems can be u�lized as a sustainable building approach to reduce a
development’s dependence on municipal water supplies.
5.5.3 Limita�ons
There are several management and maintenance factors for the rain water catchment system that
should be considered such as the following:
• The storage capacity needs to be available to catch the next storm event’s flow. For example, if the
water in the storage tank is only used for landscape irriga�on and the need for irriga�on water
during the rainy season is minimal, the tank may fill a�er the first few storms and overflow during
subsequent storms. Therefore, rainwater catchment systems that are only used for landscape
irriga�on may not be effec�ve for stormwater management during the rainy season. Development
of a water budget should be conducted prior to permi�ng.
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• Water standing for more than 72 hours can provide mosquito breeding habitat. To prevent
mosquitoes from breeding in rainwater catchment systems, the storage tanks and cisterns need to
remain �ghtly sealed and screened. Mosquitoes can fit into holes as small at 1/16 inch in diameter.
5.5.4 Si�ng Criteria
• The tanks need to be placed on level pads in areas not vulnerable to se�ling, erosion or slope
failure.
• Underground tanks (Figure 5-26) should be located at least 10 feet from a building to avoid
founda�on damage if the tank leaks (unless secondary
containment and/or founda�on waterproofing is provided).
• In addi�on to storing water, tanks can serve mul�ple func�ons
such as shading, providing visual screens, and modera�ng hot
and cold temperature extremes within a building.
• The higher above-ground tanks are located, the more gravity-
feed pressure will be available. Water can also be distributed
by gravity flow or by a booster pump via hoses, irriga�on
systems, channels, or perforated pipes.
• The interior space of the tanks will need to be easily accessible
for regular maintenance.
• If a system is to be installed in a basement, a case pumping
system will be required.
• Flow spli�ers can be used to divert a por�on of the roof runoff
(e.g. the water quality volume) to the cistern.
• If the structural capacity exists, cisterns can be placed on roo�ops and drained by gravity.
5.5.5 Design, Construc�on, and Materials
• Cisterns may be constructed from raw materials, but prefabricated systems may offer more
reliability and greater ease of integra�on with the building’s plumbing system. Prefabricated tanks
include those made of plas�c, metal, or concrete.
• Water use will determine the design of the system. The size of the storage tanks, the shape and
placement of impervious surfaces, soils composi�on, slopes, and water use will direct the
placement of the of the rainwater catchment system.
• Though rainwater catchment systems can be designed with various materials and configura�ons,
components of a basic system should consist of the following:
• An impervious surface to collect runoff (e.g. roofs or elevated paved surfaces);
• Devices to collect and convey water from the impervious surfaces (e.g. gu�ers, and
downspouts);
• A debris screening device (also known as a “First Flush” or “Foul Flush” filter);
• Pipes located at least 10feet from the building’s founda�on to carry the water to the tank
(e.g. fill pipe);
• A locking, removable lid or entry port;
• An overflow pipe;
• An exit point to distribute the harvested rainwater (e.g. hose bib);
• A booster pump if gravity alone cannot deliver the water to its des�na�on
Figure 5-26: Underground Cistern
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• Tanks should be securely capped with opaque material to prevent evapora�on, mosquito breeding,
and algae growth. Lock all caps and entry ports for safety.
• Downspouts, inlets and outlets must be screened to keep mosquitoes, animals and debris out of
the tank.
• Outlet pipes should be posi�oned several inches above the bo�om of the tank to allow sediment to
se�le in the bo�om.
• All tanks require an overflow pipe of equal or greater capacity than the fill pipe
• Overflow pipes must be able to operate passively (i.e. not be dependent on a pump).
• Below-ground tanks save land area, but typically require substan�ally more construc�on and
booster pumps to supply the water to its intended uses.
• A booster pump can be added to increase water pressure. Tank water should be filtered before it
enters supply pipes, par�cularly to keep debris from plugging the irriga�on system and prior to
entering interior building pipes that supply water to toilets.
• Overflow water should be routed into a bioreten�on basin, adjacent tank, French drain, or other
loca�on away from buildings.
• Water in above-ground tanks should be delivered by gravity flow to low-pressure uses.
• Tanks can be constructed individually or in a series with the overflow from one tank filling the
adjoining tank, or connected at the bo�om to maintain the same water level in all tanks.
• Avoid placing vegeta�on with intrusive roots near or on top of below-ground tanks
5.5.6 Inspec�on and Maintenance Requirements
Regular maintenance is cri�cal to any dependable rainwater catchment system. The following
inspec�on and maintenance prac�ces are recommended.
• Clean out gu�ers, inflow and ou�low pipes of leaves and debris as needed.
• Gu�ers and downspouts must be free of debris prior to the rainy season.
• The “first flush”, or the runoff created by the first storm event a�er a long dry spell, will need to be
carefully monitored to ensure that the system is working properly.
• Inspect water tanks periodically and remove debris and sediment that may interfere with the
proper func�on of the system.
• Inspect inlet and outlet pipe screening to insure the system is closed to mosquitoes. No opening
should be greater than 1/16 inch in diameter on systems where water will be retained for more
than 72 hours.
• Cap and lock tanks for safety. Caps should have access ports for interior inspec�on and
maintenance.
• A�er the system has stabilized, inspec�on and maintenance might be needed several �mes a year
par�cularly prior to the rainy season and a�er heavy rainfall events.
• The interior of the storage tank should be accessible for periodic inspec�on and maintenance.
References
American Rainwater Catchment Systems Associa�on
City of Tucson Water Harves�ng Guidance Manual, 2005.
Portland Bureau of Environmental Services. Stormwater Management Manual 2004. Rainwater Harves�ng. Rainwater
Harves�ng for Drylands
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5.6 Tree Box Filters
5.6.1 General
Tree box filters are bioreten�on systems enclosed in concrete
boxes that drain runoff from paved areas via a standard storm
drain inlet structure. They consist of a precast concrete
container, a mulch layer, bioreten�on media mix, observa�on
and cleanout pipes, under-drain pipes, a street tree or large
shrub, and a grate cover. The filters are precast or cast-in-place
concrete boxes filled with bioreten�on soil media installed
below grade at the curb line. For low to moderate flows,
stormwater enters the tree box inlet, percolates through
the media, and exits through an underdrain into the storm
drain. For high flows, stormwater bypasses the tree box filter
once it becomes full and flows directly to the downstream curb
inlet. As a media-based filter, tree box filters remove pollutants
through the same physical, chemical, and biological processes as
bioreten�on cells. Under normal condi�ons, pretreatment is not necessary.
Tree box filters are typically located upstream of a conven�onal storm drain inlet (see Figure 5-27)
and should not be located in sump areas (e.g. topographic low points). Where exis�ng site soils are
sufficiently permeable (infiltra�on rates > 0.5 in/hr), tree box filters can be designed to drain directly to
underlying soils via drain holes installed in the base of the concrete box.
Where slow draining na�ve soils exist, tree box filters should be designed with an underdrain pipe,
which is typically connected to the conven�onal storm drain system in the street. Most of the general
design standards noted previously for vegetated swales and bioreten�on areas also apply to tree box
filters. Tree box filters should generally be designed per the bioreten�on system design criteria and
engineered soils tes�ng requirements.
5.6.2 Performance
Tree box filters provide the same water quality benefits as
conven�onal bioreten�on designed for filtra�on (see Figure 5-29). The
engineered soil has much higher flow rates than typical bioreten�on
media, thus allowing a much smaller footprint.
The primary goal of a tree box filter is to reduce the annual pollutant
loadings, rather than control the quan�ty of runoff. Tree box filters
can reduce the runoff volume and peak flow rate for small storms by
capturing the water quality volume if designed to infiltrate runoff, but
this is not their primary purpose. Larger runoff volumes will o�en
bypass the tree box filter.
Figure 5-27 Tree Box Filter Upstream of
Conven�onal Storm Drain. Source, Larry
Coffman.
Figure 5-29 Tree box filter
performance. Source CASQA 2003.
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5.6.3 Applica�ons and Advantages
Tree box filters can be installed throughout the urban
landscape to treat parking lots, streets, sidewalks, and roof
runoff (Figure 5-28). The concrete container provides the
necessary structural integrity to allow the device to be
constructed in and around buildings and streets without
impacts. This system is ideal for urban retrofits and in areas
with clay soils.
Tree box filters are well-suited for planters along buildings,
street median strips, parking lot islands, and roadside areas.
In addi�on to providing significant water quality benefits, they
can provide shade and wind breaks, absorb noise, improve
aesthe�cs, reduce irriga�on needs, and reduce or eliminate
the need for an underground storm drain system. Bioreten�on
systems should be integrated into the overall landscaping of
the site to reduce the volume, rate and pollutant loading of
urban runoff to pre-development levels.
5.6.4 General Design Guidance
Due to the high flow rate media to treat 90% of the annual
runoff volume, the tree box filter surface area should be approximately 0.33% of the drainage area.
Tree boxes must be regularly spaced along the length of a corridor as appropriate to meet the annual
treatment target. Safe overflow relief is required to handle overflows when the high storm flows
exceed the design flows of the tree box. Tree box filters are off-line devices and should never be placed
in a sump posi�on (i.e. low point). Instead, runoff should flow across the inlet. Tree box filters are
intended for intermi�ent flows and must not be used as deten�on devices.
5.6.5 Stormwater Planters
Stormwater planters, also known as infiltra�on planters or flow through planters, are also bioreten�on
systems in enclosed in concrete structures. They can be designed to drain runoff from paved areas via
curb inlet structures or pipes, or they can be located under roof drain downspouts for treatment of roof
runoff. Where exis�ng site soils are sufficiently permeable (infiltra�on rates > 0.5 in/hr), stormwater
planters can be designed as infiltra�on systems with concrete walls on four sides and no floor (Figure
5-30). This type of system drains directly to underlying soils and should consider the setbacks when
located next to buildings and other structures. When slow draining na�ve soils exist, they should be
designed with an underdrain pipe.
Waterproofing should be incorporated into the designs of stormwater planters sited near buildings and
other structures. When designed with underdrains and waterproofing, stormwater planters typically
do not need to apply the setback standards and infiltra�on tes�ng requirements. Most of the general
design standards noted above for landscape deten�on basins also apply to stormwater planters. For
example, the ponding area in stormwater planters should be designed to detain the water quality
volume. Plants can also be selected from the bioreten�on plant list in Appendix II.
Figure 5-28: Example box filter
applica�ons. Source – Filterra.
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References
California Stormwater Quality Associa�on (CASQA), 2003. California Stormwater Best Management Prac�ce Handbook,
New Development and Redevelopment.
Cheng, Mow-Soung, 2003. Somerset Subdivision Monitoring Program (LID). Maryland Water Monitoring Council
Programma�c Coordina�on Newsle�er.
Dietz, M.E. and J.C. Clausen, 2006. Satura�on to Improve Pollutant Reten�on in a Rain Garden. Environmental Science &
Technology, Vol. 40, No. 4, 2006, pp 1335-1340.
Dietz, M.E. and J.C. Clausen, 2005. A Field Evalua�on of Rain Garden Flow and Pollutant Treatment. Water, Air, and Soil
Pollu�on (2005) 167: 123-138.
Guille�e, Anne, 2005. Low Impact Development Technologies. Whole Building Design Guide.
Hager, Mary Catherine, 2003. Low-Impact Development: Lot-level approaches to stormwater management are gaining
ground. Stormwater: The Journal of Surface Water Quality Professionals, Vol. 4 (1).
Hunt, W.F., Jarre�, A. R., Smith J. T, and L. J. Sharkey, 2006. Evalua�ng Bioreten�on Hydrology and Nutrient Removal at
Three Field Sites in North Carolina. Journal of Irriga�on and Drainage Engineering, November/December 2006.
Idaho Department of Environmental Quality, 2001. Catalog of Stormwater Best Management Prac�ces for Idaho Ci�es and
Coun�es. BMP #44 – Bioreten�on Basin
Kennedy/Jenks Consultants, 2004. Truckee Meadows Structural Controls Design Manual prepared for the Truckee Meadows
Regional Storm Water Quality Management Program.
Maryland Department of the Environment (MDE), 2000. Maryland Stormwater Design Manual. Prince George’s County,
Maryland. 2002. Bioreten�on Manual.
U.S. EPA Stormwater Technology Fact Sheet: Bioreten�on
U.S. Department of Transporta�on, Federal Highway Administra�on, Stormwater Best Management Prac�ces in an Ultra-
Urban Se�ng: Selec�on and Monitoring, Fact Sheet – Bioreten�on.
Urban Drainage and Flood Control District (UDFCD), 1999. Urban Storm Drainage Criteria Manual, Volume 3 – Best
Management Prac�ces. Denver, Colorado.
Figure 5-30: Stormwater Planters
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5.7 Surface Sand Filters
5.7.1 General
Surface sand filters, also known as Aus�n sand filters, are a type
of media filter that applies a combina�on of sedimenta�on,
filtra�on, and adsorp�on to remove sediment and associated
pollutants. The surface sand filter is constructed of an
upstream bypass structure (e.g. a weir), a sedimenta�on
chamber, a flow distribu�on cell, and a sand filter bed (See
Figure 5-31, 5-33, and 5-34). The purpose of the sedimenta�on
chamber is to remove floatables and heavier suspended
sediments. The sand filter bed removes lighter suspended
sediments and addi�onal contaminants. This BMP is widely
used across the country. Site design configura�ons can vary
significantly depending on local condi�ons and site constraints.
5.7.2 Applica�ons and Advantages
Surface sand filters can be applied to drainage areas ranging between
0.5 and 50 acres and containing both pervious and impervious
surfaces. Surface sand filters are commonly installed at transporta�on
facili�es, large parking areas, and around commercial developments.
They can also be installed in highly developed areas, on sites with
steep slopes, and to retrofit exis�ng sites. However, sand filters should
not be installed where high sediment loads are expected unless a
pretreatment device is to also be installed. Figure 5-32 shows the
pollutant removal effec�veness of sand filters.
5.7.3 Limita�ons
• Can frequently become clogged in areas with highly erodible or unstable soils
• Clogging of the sand media in surface sand filters installed along roadways commonly occurs 2 – 10
years a�er installa�on, if not properly maintained
• Can only be used in areas where sufficient ver�cal relief in the land topography is available to allow
the system to drain by gravity
5.7.4 Si�ng Criteria
• Sufficient ver�cal relief in land topography is required to allow the system to drain by gravity.
• Rela�vely large drainage areas require large surface sand filters. Therefore, a significant amount of
available open space may be required.
• A minimum distance of 2 feet should exist between the seasonal high water table eleva�on and the
bo�om of the filter bed.
• Surface sand filters should not be installed in areas with highly erodible or unstable soils.
Figure 5-31: Sand filter installa�on
Figure 5-32 Performance for Surface
Sand Filter. Source CASQA.
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Chap5:Pg70
5.7.5 General Design Guidance
• Registered professional civil engineers should design
surface sand filters.
• Sand and gravel should be rinsed with water prior to
installa�on and construc�on of the sand filter. Sand
and gravel should not be washed with recycled wash
water, which typically includes sediment, dissolved
pollutants and a high pH.
• In areas where large sediment loads in runoff are
present, a pre-treatment BMP should be installed
upstream of the surface sand filter.
• In areas of shallow groundwater, a liner may need to
be installed below the sand filter to prevent poten�al
groundwater contamina�on.
• An upstream diversion structure should be used. The
diversion structure should effec�vely isolate
the water quality volume and convey flows greater
than the water quality volume past the basin.
• The sedimenta�on basin should be sized to capture
and detain the water quality volume - plus a
minimum freeboard of 0.5 �.
• Minimum depth of the sedimenta�on basin is 3 feet.
• The sedimenta�on basin length to width ra�o should be a minimum of 2 to 1.
• The sedimenta�on basin should drain in no less than 24 hours but no more then 40 hours.
• The minimum surface area of the sedimenta�on basin (AS) should be determined using the
following equa�on: AS = WQV / df
AS = Surface area of the sedimenta�on basin in �2
WQV = Water Quality Volume in �3
df = Sediment basin depth in feet
• A trash rack should be provided around the outlet structure from the sedimenta�on basin.
Similar to infiltra�on trenches, wells, and basins, the NC DENR Stormwater BMP Manual (2007)
Figure 5-33: Plan View Schema�c of Surface
Sand Filter. Source: Washington.
Figure 5-34: Sec�on View Sand Filter Schema�c. Source Washington
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• Openings in the trash rack should not exceed 1/3 the diameter of the ver�cal riser pipe. The trash
rack should be made of a durable rust resistant material.
• The primary design parameter of the sand filter basin is the surface area, which is a func�on of the
sand permeability, the sand bed depth, the hydraulic head and the expected sediment loading.
5.7.6 Inspec�on and Maintenance Requirements
• Inspect the system at least 3 �mes a year, once at the beginning of the rainy season and a�er major
storm events to remove li�er and debris and to keep the filter from clogging.
• Access should be provided for maintenance and repairs.
• Excess plant growth within the filter is not recommended.
• Rake the top 3 – 5 inches of sand once per year or when drainage begins to slow or pond. Remove
sediments when accumula�on exceeds 0.5 inches.
• If a sand filter does not drain within 40 hours, maintenance is required.
• The vegeta�ve cover should be removed for maintenance of the sand filter every 2-5 years.
• Sand and gravel filter media may need to be replaced every 3 to 5 years.
References
California Stormwater Quality Associa�on (CASQA), 2003. California Stormwater Best
Management Prac�ce Handbook, New Development and Redevelopment.
City of Aus�n, 2003. Environmental Criteria Manual.
City and County of Sacramento, 2000. Guidance Manual for Onsite Stormwater Quality Control Measures, Sacramento
Stormwater Management Program.
Idaho Department of Environmental Quality, 2001. Catalog of Stormwater Best Management Prac�ces: For Idaho Ci�es and
Coun�es. BMP #40 – Sand Filter.
Stormwater Technology Fact Sheet, Sand Filters, U.S. Environmental Protec�on Agency,
Stormwater Management Fact Sheet: Sand and Organic Filter, The Stormwater Manager’s Resource Center
Urban Drainage and Flood Control District (UDFCD), 1999. Urban Storm Drainage Criteria Manual, Volume 3 – Best
Management Prac�ces. Denver, Colorado.
U.S. Department of Transporta�on, Federal Highway Administra�on, Stormwater Best
Management Prac�ces in an Ultra-Urban Se�ng: Selec�on and Monitoring, Fact Sheet
– Surface Sand Filters
Washington State Department of Ecology. 2000. Stormwater Management Manual for Western Washington, volume V:
Runoff Treatment BMPs Final Dra�. Olympia.
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5.8 Green Roofs
5.8.1 General
A green roof is a vegetated roofing system. Green roofs typically consist of a number of layers: a
waterproofing membrane, a drainage system, root protec�on, growing media (soil) and vegeta�on.
Green roofs provide numerous environmental benefits and offer a
valuable tool for integrated stormwater management. Green roofs
may cover all or part of a building’s roof. Areas for u�lity access and
recrea�on are not affected. Green roofs retain rainfall from small,
frequently occurring storms through storage in the soil. In turn, this
water is lost to evapora�on or transpira�on by plants. For larger
storms, the runoff volume and peak flow rate is reduced because of
percola�on and temporary storage in the soil. Green roofs improve
water quality through a variety of physical, biological and chemical
processes in the soil (see Figure 5-35).
Structurally, there are two types of green roofs: extensive and
intensive. Extensive green roofs are lightweight vegetated roofs
consis�ng of 4-8 inches of growth media (or soil), planted with
hardy, drought-tolerant species to minimize addi�onal irriga�on,
maintenance, cost and weight. They typically require supplemental
irriga�on to support growth during ini�al establishment of
vegeta�on and during extended dry periods. Modular green roof
systems are available that can come pre-planted in ready-to-install
blocks. Alterna�vely, intensive green roofs can be designed to support lawns, trees, and create a
useable outdoor garden space; o�en referred to as roof gardens. While these ameni�es do not
preclude environmental benefits of green roofs, they do require extra structural support, cost, and
have func�onal goals in addi�on to stormwater management objec�ves. They also typically require
supplemental irriga�on systems.
Green roofs have been a popular sustainable building prac�ce to improve urban environments in
Europe since the 1970s. However, it is s�ll an immature market and evolving prac�ce in the United
States. Many terms may be used to describe green roof systems. The list below describes some of the
related terms:
• Ecoroof is used to describe lightweight extensive type roof systems, implemented as a sustainable
building technique that limits impacts on the natural environment.
• Roof garden is a term generally describes a useable garden space that includes some vegeta�on.
This type of intensive roof system typically requires extra structural support and consequently,
costs more to build.
• Vegetated roof is a general term that may describe a number of Green roof objec�ves.
• Living roof is a general term that may describe a number of green roof objec�ves.
The most commonly used green roof plants are hardy, self-sustaining, drought-resistant plants mainly
from the genera Sedum and Delosperma, and are available from a variety of vendors. They are
Figure 5-35: Green Roof Performance.
Source – CASQA
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characterized by mat-like growing habits, as shown in figure 5-35 and fibrous shallow roots. Extensive
roofs employ a thin vegetated sheath of hardy, self-sufficient mosses, sedums, and small shrubs. The
plants are able to survive daily and seasonal varia�ons in temperature and moisture on roo�ops. Their
low profile allows them to be added to exis�ng buildings, including those with sloping roofs. Extensive
roofs are well-suited to both retrofit projects and new
construc�on. Intensive roofs are integral to the roof structure,
permi�ng the use of trees and walkways. A greater depth of
media and a greater roof structural capacity may be required
to accommodate larger vegeta�on and other ameni�es such as
walkways and benches.
5.8.2 Performance
Green roofs store rainwater in the soil layer, reducing the
volume and peak flow rate of roof runoff. A por�on of the
stored runoff will be retained and lost to evapotranspira�on.
The remainder will percolate through the soil layer and
ul�mately drain to the downspouts. Green roofs can capture
on the order of 0.5 inch of rainfall. The exact amount depends
on design variables such as the thickness and composi�on
of the soil media, type and health of vegeta�ve cover, type
of geotex�le material, roof slope and ou�low design, and
climac�c condi�ons.
Green roofs provide small-scale decentralized controls that
collect, absorb, and increase the evapotranspira�on rates of
rainfall. Addi�onally, green roofs are effec�ve in reducing
the heat island effect of urbanized areas containing large
impervious surfaces. By reducing the temperatures of the
runoff, the thermal impacts of urban runoff on local waterways
are reduced.
5.8.3 General Design Guidance
Green roofs consist of several layers. A drainage layer may not be necessary for sloped roofs. A leak
detec�on layer is op�onal at addi�onal cost, but it may save on maintenance and repair costs. A
modular green roof has the benefit of easier removal of a block sec�on for inspec�on and repair of
the roof membrane. In all cases, a well-qualified contractor with experience in the type of green roof
constructed, is a necessary component of project success. The decision of whether to construct an
intensive or extensive roof may be influenced by the property owner’s desired maintenance level and
the structural capacity of the roof. Soil depth is another cri�cal design variable that strongly influences
the rainfall reten�on capacity.
Green roofs can be incorporated into new construc�on or as a retrofit to exis�ng buildings. Though
several site factors will need to be considered, such as the posi�on of the roof, the microclimate of
the site, prevailing winds and the building’s func�ons, most factors can be accommodated in an
Figure 5-34: Wayne Community College
Green Roof in Goldsboro one year a�er
plan�ng (May 2003). Source: NCSU
Figure 5-35 Typical green roof design ele-
ments. Source, LID Center.
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Chap5:Pg74
appropriate green roof design. Extensive green roof systems are composed of several layers. The roof
systems may be modular interlocking components or each layer may be installed separately. Either way
an extensive green roof is constructed with the following basic layers (star�ng at the bo�om): structural
support, a waterproof roofing membrane
(including flashing), a root barrier, drainage,
a filter fabric (for fine soils), growing medium
(soil) and plant materials and mulch (see
figure 5-35 and 5-36). Materialfor the growing
medium must be weed seed free and the proper
material and depth for the par�cular roof style.
Generally, a building’s structure must be able to
support an addi�onal 10-25 pounds per square
foot of weight, depending on the growth media
and vegeta�on used. For new construc�on,
the load requirement of the green roof can
be addressed as part of the building’s design
process. Addi�onal structural support may be
necessary for a retrofit project; however, many
exis�ng buildings are constructed with adequate structural support to accommodate a green roof.
Green roofs can be designed by experienced architects, landscape architects, and building contractors.
Green roofs may require maintenance beyond standard roof care, though such care is likely similar in
cost. Long-term management should be factored into appropriate si�ng and design of green roofs.
5.8.4 Applica�ons and Advantages
Green roofs provide numerous environmental, economic, and social benefits including:
• Absorbs rainfall at the source - 10-100% of roof runoff is absorbed and u�lized by the vegeta�on
(peak stormwater flow rates are also reduced).
• Improves building insula�on, thereby reducing hea�ng and cooling costs and energy consump�on.
• Reduces heat island effect and the associated effects on waterway temperatures.
• Increases wildlife habitat for birds and insects that is o�en scarce in urban areas.
• Absorbs noise pollu�on through soils, plants, and trapped layers of air.
• Reduces glare that affects adjacent buildings and habitat.
• Can double life span of roof by protec�ng the roof’s structural elements from UV rays, wind and
temperature fluctua�ons.
• Improves air quality by reducing air temperatures, filtering smog, binding dust par�cles, and
conver�ng carbon dioxide to oxygen through photosynthesis.
• Provides an a�rac�ve roof - in urbanized areas, green roofs integrate living systems into the built
environment; in less urbanized areas, green roofs can help blend a structure into the surrounding
landscape.
Figure 5-36 Typicagreen roof design cross-sec�on. Source, LID
Center.
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5.8.5 Limita�ons
• Ini�al costs can be prohibi�ve, especially for re-roofing a standard roof. However, extensive green
roofs can be cost-compe��ve on a life cycle basis.
• Specific maintenance, such as irriga�on and cleaning out drainage features will need to be factored
into the long-term building maintenance schedule.
• Untradi�onal design and installa�on may prolong the permi�ng process.
• Green roof systems are s�ll an evolving market and prac�ce that may need economic or policy
incen�ves to support further development.
• Not always the best choice if nutrient removal is a major concern.
5.8.6 Inspec�on and Maintenance Requirements
• Upon installa�on, the green roof system should be inspected monthly for the first year and a�er
each large storm event for erosion, plant survival, proper drainage, and waterproofing.
• Inspec�ons can be reduced to a quarterly schedule once the green roof system has proven to work
properly and vegeta�on is established.
• If necessary, irrigate in short bursts only (3-5 minutes) to prevent runoff. Irriga�on frequencies
should be established by the designer using an automated system.
• Clean out drain inlets as needed.
• Weeding and mulching may be necessary during the establishment period, depending on the
plan�ng design.
• Replace or fill in vegeta�on as needed.
• Inspect soil levels semi-annually to ensure plant survival and rainfall absorp�on.
• If the vegeta�on used is flammable during the dry season, it should be mowed or watered as
needed to prevent fire.
References
Cahill, Tom. Sustainable Site Design – A PowerPoint Presenta�on presented at CASQA Conference 2006, September 25,
2006. Sacramento, California.
Eisenman, Theodore. “Raising the Bar on Green Roof Design.” Landscape Architecture Magazine. November 2006: 22-29.
Green Roofs for Healthy Ci�es. 2006. Website resource: h�p://www.greenroofs.net
Rosenzweig, C., S. Gaffin, and L. Parshall, (Eds.) 2006. Green Roofs in the New York Metropolitan Region; Research Report.
Columbia University Center for Climate Systems Research and NASA Goddard Ins�tute for Space Studies. New York. 59
pages.
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5.9 Stormwater Wetlands
5.9.1 General
The most common reason a stormwater wetland is used on
an LID site is the presence of high water tables in places most
suitable for trea�ng stormwater. Very few LID prac�ces func�on
appropriately when there is a shallow seasonal high water table.
In these situa�ons, a shallow backyard wetland is open the most
appropriate BMP.
The stormwater wetland should be designed so that it intersects
the seasonal high water table and possibly also the seasonal low
water table. If the difference between the seasonal high and
seasonal low water table is substan�al, then a drier stormwater
wetland will be created, which is reasonable as long as plant
selec�on reflects the hydrology.
It should be noted that stormwater wetlands are more tolerant
of excessive off-site sediment loads, because they are not
predicated on infiltra�on to func�on. This does not absolve the
contractor from verifying that the upslope is stable or at least
protected.
5.9.2 General Design Guidance
Plants for backyard wetlands usually need to be aesthe�cally appealing and mosquito-resistant. Please
see Appendix II for a list of appropriate plants for constructed wetlands. At normal pool, Ca�ails
(Typha spp.) are conspicuously absent from any constructed wetland plant list. While na�ve, ca�ails
are well adapted to develop monocultures that shelter mosquitoes from their predators. In short, if
a stormwater wetland is to be located near a popula�on center, such as a commercial center parking
lot or a residen�al neighborhood, it is advised to keep ca�ail popula�ons under control. If more than
15% of a stormwater wetland (that is located near people) is populated by ca�ails, it is recommended
to remove the majority – if not all – of the ca�ails present. However, if stormwater wetlands are to be
constructed in rural areas, such as along highways in eastern North Carolina, it is reasonable to allow
ca�ail growth, as these plants are tolerant of rela�vely high pollutant loads and propagate easily.
Stormwater wetlands do have evapotranspira�on and infiltra�on losses. The exact amount of each
has not been well quan�fied. As water ponds in a stormwater wetland immediately following a storm,
the level of water is usually above that of the surrounding groundwater table. Along the perimeter
of a stormwater wetland, some post-storm infiltra�on loss would be expected to occur. The volume
of water lost from a given storm event would be the result of the height above the water table of the
water ponded inside the wetland, the residence �me of water inside the wetland, and the surrounding
soil’s permeability.
There are evapotranspira�on losses from the stormwater wetland between rainfall events. This
amount varies by vegeta�on type and �me of year. A preliminary study revealed that the amount
Figure 5-37: Performance of Constructed
wetlands
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of infiltra�on loss and evapotranspira�on loss annually may range from 22 to 26% and 11 to 26%,
respec�vely.
One common concern among designers is the ability of
shallow water plants to survive during a drought. As Figure
5-38 shows, once established, shallow water plants can
tolerate being dry (i.e., not inundated) during drought periods.
Remember that naturally occurring wetlands also become dry
occasionally. In fact, we�ng and drying cycles are key to the
wetland’s ability to treat many pollutants effec�vely. Even
during droughts, soils within the wetland remain moist within
a foot of the surface. As long as wetland plant roots are able
to reach these moist soils, the wetland plants can survive
during droughts.
A study was conducted in the mid 2000’s in North Carolina
showing that, typically, mosquitoes were not present in high numbers at the majority of stormwater
wetlands and wet ponds surveyed. However, it was found that mosquitoes can survive and thrive in
wetlands with certain characteris�cs, namely overgrown by monocultures of ca�ails, heavily wooded,
or containing significant algal mats, floatage, and debris. It was found that providing habitat for
predators and keeping “mosquito habitat” to a minimum that mosquito popula�ons can be mi�gated.
One major conclusion of the study was to design several small deep pools throughout a stormwater
wetland. These pools can provide refuge for mosquito predators like Gambusia affinis (mosquito fish).
If a stormwater wetland is quite small (such as many will be in LID applica�ons) then either one deeper
pool (18 inches of water) or none will be used. A second design recommenda�on was to include
flowering species of vegeta�on that a�ract other mosquito predators like dragonflies.
5.9.3 Design and Maintenance Requirements
Some considera�ons unique to stormwater wetlands include:
• Excava�on: If the water table to intersect is near the surface, then very li�le excava�on is required.
• Plant spacing: Many designers desire the minimum spacing - plants on 36-inch centers. However,
this spacing will leave the wetland with a barren look for at least a year, and opens the door
to ca�ail infesta�on. A more densely planted wetland (e.g. one plant on 24-inch centers) results in
a be�er-looking wetland in the short term. A �ghter spacing usually results in less maintenance
and unwanted species removal
• Outlet Construc�on. Small “pocket” wetlands may have very simple outlets such as pre-treated
lumber.
• Required Aesthe�cs. If the wetland is “front and center” it needs to be more a�rac�ve and
therefore specific plan�ng plans must be followed. Maintenance becomes more important.
In addi�on to design, stormwater wetlands must be maintained to keep mosquitoes from becoming a
problem. Some common “mosquito maintenance” requirements include:
• Removing unwanted trees and shrubs. An abundance of woody species was found to provide
Figure 5-38 A stormwater wetland in
Durham during the drought of 2002.
Source, Larry Coffman.
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a safe harbor for mosquitoes. It is reasonable to have a limited number of woody species (one
recommenda�on is 1 tree per 3,000 square feet of wetland) but others will volunteer.
• Removing ca�ails. Ca�ails, as discussed earlier, are very aggressive and can out-compete other
vegeta�on if given enough �me. Removing ca�ails as they arrive in the wetland is an annual to
semi-annual process which need not be �me consuming.
• Removing trash and other floatables. Pocket wetlands, like all BMPs, receive water from a larger
watershed meaning that not only does water come to the wetland, but everything in or carried
by the water, as well. Trash will inevitably collect in a wetland if there is a human popula�on in
or adjacent to the wetland’s drainage catchment. Floa�ng trash provides mosquitoes an area free
of many predators.
• Trash removal from outlet. In addi�on to being unsightly, trash can also clog a wetland’s outlet. A
clogged outlet will necessarily raise the eleva�on of the water inside the wetland, which may cause
desirable vegeta�on to die. Into these voids of dead vegeta�on the hardier species (like ca�ails)
take over.
5.10 Infiltra�on Trenches and Basins
For a thorough review of Infiltra�on Wells, Trenches and Basins,
please see the Stormwater BMP Manual (NCDENR 2007). Many of
the concepts discussed in the bioreten�on sec�on of this chapter
also apply to infiltra�on trenches and basins, par�cularly that
deeper and oversized basins will “convert” a much higher fac�on of
inflow to infiltra�on. Also, infiltra�on trench and basin hydrology
is impacted by the geometry of the prac�ce. Maximizing the
perimeter to surface area ra�o of the prac�ce will improve the
infiltra�on basin’s performance.
References
Hunt, W.F., C.S. Apperson, S.G. Kennedy, B.A. Harrison, and W.G. Lord. 2006b. Occurrence and rela�ve abundance of
mosquitoes in stormwater reten�on facili�es in North Carolina, USA. Water Science and Technology, 52(6-7): 315-321.
Figure 5-39: Performance of Infiltra�on
Basins and Trenches.
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C������ 6. P������ LID ���� P�������
6.1 Introduc�on
LID involves the use of many prac�ces. Each LID prac�ce requires careful planning and careful
construc�on. Even the best designs can result in failures if the LID prac�ces are improperly
constructed. Each LID prac�ce has its own specific permi�ng and construc�on requirements. Many
of these requirements are discussed in Chapter 3. This chapter deals with the more general permi�ng
and construc�on issues that should be followed for a successful LID project.
6.2 Permi�ng LID Projects Using “LID-EZ”
New Hanover County and the City of Wilmington, in a collabora�ve effort with Brunswick County, N.C.
Coastal Federa�on, and N.C. Division of Water Quality, have developed a stormwater management tool
to aid engineers, planners, and developers with design and permi�ng of LID projects.
The tool, LID-EZ, quan�fies the effect of the structural and non-structural BMPs on the overall
hydrology of residen�al and commercial developments. LID-EZ requires the user to enter basic pre
and post development informa�on into the so�ware. The so�ware then computes required storage
volumes necessary to meet local and state stormwater regula�ons. The user then inputs all proposed
structural storage devices and iden�fies the non-structural devices, such as disconnected impervious
areas. The resul�ng calcula�ons then quan�fy the impacts of all LID components on the post
development condi�ons as they relate to required water quality storage volumes and peak flow rates.
While small scale structural and non-structural BMPs can be used to meet many state and local
regula�ons, o�en the engineer or developer may need to incorporate addi�onal storage areas to fully
comply with the regula�ons. The importance and the benefit of the small scale LID devices cannot
be overlooked. If a hybrid approach is used, LID-EZ should s�ll be used to compute the effec�ve post
development curve numbers, which can then be used to determine actual volume requirements of the
large scale deten�on structures. In many cases, the size of the large scale devices may be significantly
reduced.
If the user chooses to use a hybrid approach to stormwater management and includes large structural
BMPs, such as a wetland or wet pond, addi�onal deten�on system rou�ngs and analysis may be
required.
LID-EZ is available free of charge from the City of Wilmington or New Hanover County. Contact either
of these planning departments for more informa�on.
6.3 Construc�ng LID Projects
6.3.1 Training
It is very important that contractors, vendors, and inspectors be properly trained in the design
specifica�on and construc�on requirements for all LID prac�ces employed. The success of many of
the LID techniques depends on accurately following the grading plan; the use of proper materials and
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the appropriate loca�on of prac�ces. Due to the complexi�es of the prac�ce, it may be necessary for
vendors, contractors, and permi�ers to par�cipate in cer�fica�on training. For example, the design and
construc�on of bioreten�on cells requires the knowledge of several disciplines including engineering,
landscape architecture, and soil science to ensure the proper design and construc�on of the project.
North Carolina Coopera�ve Extension, through the N.C. State Biological and Agricultural Engineering
Program, offers a stormwater BMP inspec�on and maintenance cer�fica�on program. The purpose
of the workshop is to offer instruc�on of BMP construc�on and maintenance ac�vi�es. Professional
development hours are offered for professional engineers and surveyors. More informa�on about the
cer�fica�on program may be found at h�p://www.bae.ncsu.edu/stormwater or by contac�ng the N.C.
State Biological and Agricultural Engineering Stormwater Program.
6.3.2 Communica�on
LID uses innova�ve techniques, unique strategies and various combina�ons of prac�ces. Consequently,
each development results in a unique design with its own set of issues and challenges. It is vital
that everyone involved in the LID project (contractors, vendors, design engineers, and inspectors)
understands the unique details of the LID project. A pre-construc�on mee�ng is the most useful
approach to ensure that the project goals and issues are effec�vely communicated. Ideally the permit
reviewer, contractor, vendor, design engineer, and inspector should hold a mee�ng to go over the plans
and discuss all aspects of the project. During the pre-construc�on mee�ng, the inspector may evaluate
the proposed sequence of construc�on, sediment control requirements, and indicate when inspec�on
points during construc�on of the LID prac�ces are required as iden�fied in the design manual.
Throughout the construc�on process, there must be effec�ve communica�on. No construc�on project
takes place without unforeseen problems and the need to make some field adjustments. Proper lines
of communica�on must be in place throughout the construc�on phase between the general contractor,
site engineer, inspector, and permit staff to address required changes. A�er construc�on, a final
inspec�on and walk-through of each LID prac�ce is necessary to ensure its proper func�on.
6.3.3 Erosion and Sediment Control
One of the major advantages to an LID design is that it allows for clearing and grading in stages. Since
LID can be a lot-specific approach to stormwater management, it is not necessary to completely clear-
cut and regrade the site to establish the drainage system. A development can be constructed on a
lot-by-lot basis. This can greatly reduce the amount of sediment generated, thus reducing possible
damage to LID designated areas.
Proper erosion and sediment control during construc�on is vital for LID prac�ces. If exis�ng vegeta�on
is to be used for treatment, (bioreten�on, swales or buffers) then these areas must be protected
from sedimenta�on. A thin layer of sediment over the root system is enough to suffocate a plant
or tree. Addi�onally, areas that may be used for infiltra�on must be protected to prevent sediment
from clogging soils with silts and clays. Preven�ng damage from sedimenta�on is less expensive than
cleaning or rehabilita�ng an area.
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6.3.4 Tree Protec�on
Care must be taken to protect tree conserva�on areas during construc�on. Tree conserva�on areas are
ineffec�ve if the trees die shortly a�er the project is completed. Trees can be damaged in a number
of ways during the construc�on process, therefore it is recommended that a cer�fied arborist be
employed during the construc�on process.
In order to effec�vely protect trees, it is important to consider the following during any construc�on
process:
• All types of construc�on equipment can cause mechanical injury to roots, trunks, or branches. This
can weaken a tree’s resistance to a number of diseases and insect infesta�on. Trees should be
clearly marked and given wide clearance. Excava�on around trees should not be within the drip
line of the tree.
• Soil compac�on squeezes the air and water out of the soil making it difficult for a tree to absorb
oxygen and water. No construc�on equipment should be allowed to run over the roots within the
drip line of the tree.
• Grading prac�ces that deposit soil over the roots of trees eventually suffocates those roots. More
than an inch or two of soil over the roots is enough to poten�ally suffocate the roots of trees and
compromise the health of the tree. Measures can be taken to improve soil aera�on around tree
roots if it is necessary to add fill within the cri�cal root zone (see Figure 6-1).
• Grading prac�ces that divert too much runoff to a mature stand of trees can result in damage. As
a tree matures its ability to adapt to changes decreases. Addi�onally, if a stand of trees is located
in a normally dry area that suddenly becomes very wet, the addi�onal water may kill the trees.
An arborist should be consulted these situa�ons to determine the trees’ tolerance to a change in
hydrology.
• A tree protec�on plan with wri�en recommenda�ons
for the health and long-term welfare of the trees during
the pre-construc�on, demoli�on, construc�on, and
post-construc�on development phases, should be
developed. The tree protec�on plan should include
specifics about avoiding injury, informa�on about
treatment for damage and specifics about required
inspec�ons of protected trees. The tree protec�on plan
should also provide informa�on about caring for
damaged trees.
6.3.5 Construc�on Sequence
Construc�on sequencing is important to avoid problems
while construc�ng LID projects. Proper sequencing
decreases the likelihood of damage to the BMP during
construc�on and helps to ensure op�mal performance of
the BMP. Each LID prac�ce is somewhat different, therefore
informa�on should be provided to the contractor on the
proper sequencing.
Figure 6-1: Radial Root Aera�on System
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Conserva�on areas must be iden�fied and protected before any major site grading takes place. Most
of the engineered LID prac�ces (bioreten�on, infiltra�on trenches, and infiltra�on swales) should
be constructed at the end of the site development process, and preferably when most of the site is
stabilized. Any LID prac�ce that relies on filtra�on or infiltra�on must be protected throughout the
construc�on phase from sedimenta�on and should not be ac�vated un�l the contribu�ng drainage
area is stabilized. For example, bioreten�on areas should be constructed at the �me of final grading
and landscaping, and these areas should be protected from sedimenta�on un�l the drainage routes to
the facility are stabilized.
6.3.6 Construc�on Administra�on
Proper oversight is important to the success of an LID design. Each engineered LID prac�ce should
be inspected at the �me of installa�on. The general contractor should have their engineer on site
during cri�cal periods during the construc�on process, and the site manager should follow up with the
engineer to ensure proper installa�on.
Inspectors not only need to be well informed about design and construc�on specia�on of all LID
techniques, they also need adequate enforcement tools. Occasionally, it is necessary to stop work and
force contractors and vendors to remove and replace improper materials or install prac�ces. It may not
be possible to have the project manager on site at all �mes to make field adjustments. Therefore, it
may be necessary to empower inspectors with the ability to make minor field adjustments in order to
prevent unnecessary construc�on delays.
6.4 Maintenance
As with any stormwater management technique, maintenance is essen�al with LID BMPs to ensure
that the designed stormwater benefits con�nue. Post-construc�on inspec�ons and maintenance
are important to ensure that each technique is func�oning effec�vely. Annual inspec�ons are
recommended, with more frequent inspec�ons during the first year to ensure that vegeta�on is
thriving.
Inspec�on and maintenance of structural LID prac�ces such as cisterns, vegetated roofs, permeable
pavements, infiltra�on structures, and manufactured proprietary devices should follow local
health department, state or local stormwater minimum standards, as well as manufacturer’s
recommenda�ons for maintenance or repair. Any under-drains or ou�all structures should be
inspected on a regular basis and cleaned out or repaired as necessary.
The primary maintenance requirement for vegeta�ve LID structural and non-structural prac�ces
is inspec�on and periodic repair or replacement of the treatment area’s components. This o�en
includes the maintenance of the vegeta�ve cover (pruning), replacing mulch, removing weeds, and
possibly removing sediment to preserve the prac�ce’s hydraulic proper�es. For many LID prac�ces,
this generally involves li�le more than the rou�ne periodic landscape type maintenance. Maintenance
requirements are further discussed in Chapter 5 with each associated LID technique.
To ensure con�nued long-term maintenance, all affected landowners should be made aware of their
individual or collec�ve maintenance responsibili�es through legal instruments such as maintenance
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agreements and maintenance easements that convey with the property. Outreach materials, such as
LID brochures or facts sheets that explain the func�on of prac�ces and the an�cipated maintenance
responsibili�es for homeowners, should be included in se�lement or homeowner associa�on
documents. The developer should prepare a maintenance plan that provides clear guidance and
instruc�ons to the property owner property manager or property owners associa�on about the annual
maintenance needs of each LID technique. See Appendix I for an example of a sample maintenance
easement agreement.
Maintenance Agreement
The developer should record, and reference on the recorded plat, a maintenance agreement, or
restric�ve covenant that sets forth the con�nuing responsibili�es of the property owners associa�on or
lot owner for maintenance, including specifying how cost will be appor�oned among lot owners when
maintenance is provided by a homeowners associa�on. The maintenance agreement should provide
that the associa�on and its individual members are jointly and severally liable for maintenance (see
Appendix I for an example of a maintenance agreement).
Maintenance Easements
Where necessary the developer must record easements for access, maintenance, and inspec�ons
by any property owners associa�on and by the regula�ng jurisdic�on. Where natural features
and conserva�on prac�ces are used the maintenance easement should also include conserva�on
easements with appropriate limita�ons to restrict destruc�on of the conserva�on areas.
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Appendix I
Sample Maintenance Agreement
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Sampl
e
Return to: Thomas L. Horstman, CPESC
Erosion Control Supervisor
New Hanover County
230 Government Center Drive
NORTH CAROLINA
WAKE COUNTY
STORMWATER CONTROL STRUCTURE AND ACCESS
EASEMENT AND AGREEMENT (Corporate)
THIS STORMWATER CONTROL STRUCTURE AND ACCESS EASEMENT AND AGREEMENT, made this
day ___ of ____________, 20___, (DATE OF AGREEMENT) by 2 (NAMEOF OWNER), a North Carolina
corpora�on whose principal address is 2a , (herea�er “Grantor”), with, to, and for the benefit of the
Town of Cary, a municipal corpora�on of the State of North Carolina, whose address is P.O. Box 8005,
Cary North Carolina 27512-8005 (hereina�er “Grantee” or “Town”).
W I T N E S S E T H:
WHEREAS, Grantor is the owner in fee simple of certain real property, situated in the Town of
Cary, County of Wake, North Carolina and more par�cularly described as follows:
3 (LEGAL DESCRIPTION OF PROPERTY)
It being the same land conveyed to the Grantor by deed recorded in Book 3a at page 3a in the
Office of the Register of Deeds for Wake County (herea�er referred to as “Property”); and
WHEREAS, the property is located within the planning jurisdic�on of the Town of Cary, and is
subject to certain requirements set forth in the Land Development Ordinance of the Town, (herea�er
“Cary LDO”), as such may be amended from �me to �me; and
WHEREAS, one of the condi�ons for development of Property is the gran�ng or dedica�on of
a Stormwater Control Structure easement, which includes the implementa�on of certain stormwater
prac�ces such as, but not limited to, the construc�on, opera�on and maintenance of engineered
stormwater control structure(s) as provided in Cary LDO; the dedica�on of an access easement for
inspec�on and maintenance of the Stormwater Control Structure easement area and engineered
structures; and the assump�on by Grantor of certain specified maintenance and repair responsibili�es;
and
WHEREAS, this Easement and Agreement has been procured in accordance with the
requirements of N.C. G.S. Sec 143-211 et. seq. and Chapter 4, Part 4.6 of the Cary LDO.
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Sampl
e
NOW, THEREFORE, for a valuable considera�on, including the benefits Grantor may derive
therefrom, the receipt of which is hereby acknowledged, Grantor has dedicated, bargained and
conveyed and by these presents does hereby dedicate bargain, sell, grant and convey unto the
Grantee, its successors and assigns, a perpetual, and irrevocable right and easement in, on, over, under,
through and across Property (1) for a STORMWATER CONTROL STRUCTURE easement (“herea�er SCS
Easement”) of the nature and character and to the extent hereina�er set forth, more par�cularly
shown and described on A�achment 4 (NAME OF AS BUILT DRAWING) which is a�ached hereto and
incorporated herein by reference; upon which Grantor shall construct, maintain, repair and reconstruct
stormwater control structure(s), including deten�on pond(s), pipes and water control structures, berms
and dikes, and shall establish and maintain vegeta�ve filters and groundcovers; and (2) an access
easement more par�cularly shown and described on A�achment 4a (ATTACHMENT NUMBER 1 OR 2),
, for the purpose of permi�ng Town inspec�on and, if necessary, maintenance and repair of the SCS
Easement and engineered structure(s) as more fully set forth herein and in Cary LDO.
The terms, condi�ons, and restric�ons of the Stormwater Control Structure Easement and
Access Easement are:
1. The requirements pertaining to the SCS Easement are more fully set forth in Chapter 4, Part 4.6 of
Cary LDO and the ”Opera�on and Maintenance Manual for 5 (herea�er “Opera�ons and Maintenance
Manual”), Cary, NC, prepared by 5a, and dated 5b a copy of which is on file in the Town of Cary
Engineering Department. Grantor further agrees Grantor shall perform the following, all at its sole cost
and expense:
I. Monthly or a�er every runoff producing rainfall, whichever comes first:
a. Remove debris from trash rack.
b. Check and clear orifice of any obstruc�ons.
c. Check pond side slopes; remove trash, repair eroded areas before next
d. rainfall.
II. Quarterly
a. Inspect the collec�on system (i.e., catch basin, piping, grassed swales) for proper
func�oning. Clear accumulated trash from basin grates, and basin bo�oms, and check
piping for obstruc�ons.
b. Check pond inlet pipes for undercu�ng. Repair if necessary.
c. Repair any broken pipes.
d. Replace rip rap that is choked with sediment.
e. Reseed grassed swales twice yearly. Repair eroded areas immediately.
III. Semi-Annually
a. Remove accumulated sediment from bo�om of outlet structure.
b. Check available ponding depths at several loca�ons. If depths are reduced to 75% of
original design depths, remove sediment to original design depth.
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App1:iv
Sampl
e
IV. General
a. Mow side slopes according to the season and species of vegeta�on.
b. Ca�ails and other invasive species shall be removed when they cover the en�re surface
area of bioreten�on area.
c. All components of the engineered structures are to be kept in good working order.
d. In case the ownership of the Stormwater Control Structure transfers, the current owner
shall, within thirty (30) days of transfer of ownership, no�fy the Town of Cary
Engineering Department, Stormwater Management Division of such ownership transfer.
e. This property and structure are also subject to the Opera�on and Maintenance Manual
filed with the register of deeds.
2. Grantor represents and warrant that Grantor is financially responsible for construc�on, maintenance,
repair and replacement of all stormwater control structures, appurtenances and vegeta�on, including
the impoundment. Grantor agrees to perform the maintenance as outlined above and in the Opera-
�ons and Maintenance Manual in considera�on of the Cer�ficate of Compliance with stormwater
regula�ons received for Property.
3. If Grantor fails to comply with these requirements, or any other obliga�ons imposed herein, in Cary
LDO or Opera�ons and Maintenance Manual the Town of Cary may perform such work as Grantor is
responsible for and recover the costs thereof from Grantor.
4. This Easement and Agreement gives the Grantee the following affirma�ve rights: Grantee, its officers,
employees, and agents may enter Stormwater Control Structure and Access Easement whenever
reasonably necessary for the purpose of inspec�ng same to determine compliance herewith, to
maintain same and make repairs or replacements to the engineered stormwater control structure(s)
and appurtenances and condi�ons as may be necessary or convenient thereto in the event Grantor
defaults in its obliga�ons and to recover from Grantor the cost thereof, and in addi�on to other rights
and remedies available to it, to enforce by proceedings at law or in equity the rights, covenants, du�es,
and other obliga�ons herein imposed.
The Grantor shall in all other respects remain the fee owner of Property and area subject to
these easements, and may make all lawful uses of Property not inconsistent with these easements.
The Grantee does not waive or forfeit the right to take ac�on to ensure compliance with the
terms, condi�ons and purposes of this Easement and Agreement by a prior failure to act.
The Grantor agrees that the terms, condi�ons and restric�ons of this easement will be
inserted by Grantor in any subsequent deed or other legal instrument by which he divests himself of
either the fee simple �tle to or possessory interests in the subject property. The designa�on Grantor
and Grantee shall include the par�es, their heirs, successors and assigns.
TO HAVE AND TO HOLD the aforesaid rights, privileges, and easements herein granted to
the Grantee, its successors and assigns forever and the same Grantor does covenant and that Grantor is
seized of said premises in fee and has the right to convey the same, that except as set forth below the
same are free from encumbrances and that Grantor will warrant and defend the said �tle to the same
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App1:v
Sampl
e
against claims of all persons whosoever.
The covenants agreed hereto and the condi�ons imposed herein shall be binding upon the
Grantor and its agents, personal representa�ves, heirs and assigns and all other successors to Grantor
in interest and shall con�nue as a servitude running in perpetuity with the above described land.
IN WITNESS WHEREOF, the Grantor has caused this instrument to be signed in its corporate
name by its duly authorized officers and its seal to be hereunto affixed by authority of its Board of
Directors, the day and year first above wri�en.
____________________________________
(Grantor)
____________________________________
President
A�est:
__________________________________
_____________Secretary (Corporate Seal)
NORTH CAROLINA
WAKE COUNTY
I, the undersigned Notary Public, do hereby cer�fy and State aforesaid, do hereby cer�fy that
personally appeared before me this day and acknowledged the execu�on of the foregoing instrument.
Witness my hand and official seal this ____day of__________________ , 20____ .
My commission expires_______________________:
_____________________________________
Notary Public
[Official Seal]
ckc
Easement&Deed/Corporate.doc
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
Appendix II
CONTENTS
Water Use Zones
Hardiness Zones
Recommended Plants for New Hanover County Landscapes
Plants for Rain Gardens
Wetland Plants for Coastal NC
Salt Tolerant Plants
Compiled lists by Charlotte Glen, Urban Horticulture Agent, NC Cooperative Extension
54
WATER USE ZONES
The following pages list plants that are suitable for Southeastern North Carolina landscapes. The plant tables
make reference to “hardiness zones” and “water use zones” which are discussed on the following pages.
Water Use Zones
Water use zones refer to a plant’s water needs. Some plants
need more water than others. By grouping plants together that
have similar water needs, less water is wasted to irrigate mixed
plantings when half the plants don’t need the extra water.
The philosophy is to only use high water use plants
(most annuals, roses, some ornamentals) close to a house
for impact. High water use plants need weekly irrigation
throughout the growing season. The rest of the landscape
should feature medium and low water use plants - medium
use plants would need watering during drought, and low
water use plants should thrive under natural rainfall except
during times of extended drought. You can easily create these
water use zones in your yard.
The placement of plants is a key element in efficient water
use. Many of our common southern landscape plants survive
drought and disease conditions. Once they are established,
plants such as Crape Myrtle, Elaeagnus, Chinese Hollies,
Glossy Abelia and Juniper can survive weeks without
watering.
Turf (grass) requires much more care than landscaping
with native plants. Turf is only practical in areas where it
serves a function such as in recreational areas, on certain
slopes to control erosion or where it lends aesthetic value.
When you begin planning your landscape, locate plants
according to their water needs. Create these water use zones in your yard: low water use zones (3), medium
water use zones (2) and high water use zones (1). Remember, it is best to create a landscape of low (3) and
medium (2) water use plants! Additional information can be found on the web at:
http://www.bae.ncsu.edu/programs/extension/ag-env/publicat/turf.html
http://www.ces.ncsu.edu/depts/hort/consumer/hortinternet/
Appendix
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-1
55
HARDINESS ZONES
Weather varies significantly from one part of
North Carolina to another. Plants that flourish in one
part of the state may do poorly or fail in another part
of the state. The primary guide to determine plant
hardiness is the USDA Hardiness Zone Map which
is divided into ten zones based on average minimum
temperatures. Each zone is further divided into states.
In North Carolina the zones tend to be aligned
more East and West instead of North and South. A
plant is said to be hardy if it can tolerate the lowest
average winter temperatures that usually occurs in a
zone. There is not a clear cut line between zones. A
given location can be warmer or colder than the rest
of a zone because of air drainage or elevation. Some
plants can be grown in isolated areas north of their
designated zone but may suffer from winter injury. A
plant can often be grown in a warmer zone if growing
conditions (rainfall, soil, summer heat) are comparable.
In some cases, the hardiness zones listed by a
reference book are conservative and are a full one
half zone farther south than the plant is known
to survive. Hardiness is affected by duration and
intensity of sunlight, length of growing season,
amount and timing of rainfall, length and severity
of summer drought, soil characteristics, proximity
to a large body of water, slope, frost occurrence,
humidity and cultural practices. (The USDA
Hardiness Zone Map was revised in 1990. You will
probably find older reference books that provide
information on hardiness that differs from recent
publications).
Plants can be classified as either hardy or non-hardy, depending upon their ability to withstand cold
temperatures. Winter injury can occur to non-hardy plants if temperatures are too low or if unseasonably low
temperatures occur early in the fall or late in the spring. For more information visit:
http://www.ces.ncsu.edu/depts/hort/consumer/weather/hardiness_zones.html
http://www.usna.usda.gov/Hardzone/ushzmap.html
*This section adapted from Erv Evans, Consumer Horticulturalist, NC Cooperative Extension.
NC has three hardiness zones (6,7 and 8) based on the
average minimum temperature. Wilmington is situated in
Hardiness Zone 8A.
Appendix
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-2
56 Appendix
Recommended Plants for New Hanover County Landscapes
Compiled by Charlotte Glen, Urban Horticulture Agent, NC Cooperative Extension
The following lists are plants recommended for landscape use in the New Hanover County area. All plants are hardy to Zone 8a
(minimum temperature of 10-15 degrees Fahrenheit), perform well in local climate conditions, are relatively easy to grow, and are
available at most local nurseries and garden centers. Plant lists are arranged with common names listed first, however plants are arranged
in alphabetical order according to scientific name. Several information codes accompany each plant list. They are explained below:
NATIVE PLANT (*)
A plant native to SE USA implies a plant endemic to the Southeastern portion of the United States, from Virginia to Eastern Texas.
WATER USE ZONES (see also page 54)
These zones indicate the water needs of a plant. 1 = High Water Use Zone, 2 = Medium Water Use Zone, 3 = Low Water Use Zone
For more info including Water-Wise Use in Landscaping and How to Plan and Design a Water-Wise Use Landscape, visit
http://www.bae.ncsu.edu/bae/programs/extension/publicat/wqwm/usewtr.html
EXPOSURE
Exposure refers to the amount of sunlight a site receives:
• Full sun indicates a site that receives at least 8 hours of direct sun each day.
• Light Shade indicates a site that is shaded less than half of the day by a light high shade, such as that cast by pine trees.
• Part Shade indicates a site that is shaded for half the day by a dense shade, such as that cast by buildings or shade trees.
• Full Shade indicates a site that is in the shade all day.
SOIL
Soil refers to soil condition at the site as follows:
• Wet indicates a site that stays moist most of the time and receives periodic flooding.
• Moist indicates a site that is moist most of the time with brief (less than 12 hours) periods of standing water.
• Well Drained indicates a site where water drains freely and rarely stands.
• Xeric indicates a site that is extremely dry and sandy with very little ability to hold water.
DROUGHT-TOLERANT PLANTS
Extremely drought-tolerant plants are marked with an underline. When planted in their preferred soil type, these plants are able to
withstand extended periods of drought (4-6 weeks) without supplemental irrigation once established. Most trees and shrubs take two
to three seasons to become bully established. Perennials, grasses, and groundcovers usually require one to two seasons to become
established.
MATURE SIZE
Mature sizes of all plants are given as height x width, though many may take several years to reach these dimensions. Mature size can
vary depending on growing conditions.
RECOMMENDED VARIETIES
For many plants, recommended varieties are given. These are selections of that plant that either perform better in our area or are more
suitable to landscape use than the plain species. Plant varieties, also known as cultivars, are listed using single quotes.
•
NHC COOPERATIVE EXTENSION WEBSITE
For more detailed information about each plant and to see images, visit the Plant Fact Sheets on the NC Cooperative Extension Consumer
Horticulture website: http://www.ces.ncsu.edu/depts/hort/consumer/index.html.
VISIT THE COOPERATIVE EXTENSION
To see many of these plants growing in a landscape setting, visit the NHC Arboretum, which is part of the NHC Cooperative Extension. The
Arboretum is located at 6206 Oleander Drive and is open seven days a week during daylight hours, free. To find out more, call 798-7660 or visit
http://newhanover.ces.ncsu.edu/.
PLANT INFORMATION CLINIC
If you have questions about plant selection and maintenance, lawn care, vegetable gardening or plant pest problems, call or visit the Cooperative
Extension Plant Information Clinic. The Plant Clinic is open from 9am - 3pm, Monday-Friday and is staffed by trained Master Gardener
volunteers and Extension Horticulture agents. Call direct at 798-7680 or stop by during operating hours.
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-3
Water Use Zones: 1 - High Water Use Zone, 2 - Medium Water Use Zone, 3 - Low Water Use Zone
57 Appendix
GROUNDCOVERS
* = Indicates a plant native to the Southeastern USA
Underline = Indicates an extremely drought-tolerant plant
Colors = W-white, Y-yellow, O-orange, B-blue, Pu-purple,
P-pink, R-red, L-lavender
COMMON NAME BOTANICAL NAME WATER
USE ZONE
RECOMMENDED
VARIETIES
HEIGHT
(IN)
TYPE OF
PLANT
GROWTH
RATE EXPOSURE SOIL CONDITIONS
SHADE – PART TO FULL
Carpet Bugle Ajuga reptans 1,2 4 - 8 Evergreen
Perennial Moderate Part to Full
Shade Moist to Well Drained
Pussytoes*Antennaria
plantaginifolia 1,2,3 4 - 8 Evergreen
Perennial Moderate Light to Full
Shade Well Drained
Japanese Ardisia Ardisia japonica 1,2 4 - 8 Evergreen
Perennial Moderate Part to Full
Shade Well Drained
Green and Gold*Chrysogonum
virginianum 1,2 6 - 8
Semi-
Evergreen
Perennial
Moderate Light to Part
Shade Moist to Well Drained
Holly Fern Cyrtomium falcatum 1,2,3 24 - 30 Evergreen
Fern Moderate Part to Full
Shade Well Drained
Dwarf Gardenia Gardenia jasminoides
‘Radicans’1,2 12 - 24 Evergreen
Shrub Moderate Light to Part
Shade Well Drained
Algerian Ivy Hedera canariensis 1,2,3 12 Evergreen
Vine
Moderate to
Fast
Light to Full
Shade Well Drained
English Ivy Hedera helix 1,2,3 6-12 Evergreen
Vine
Slow to
Moderate
Part to Full
Shade Well Drained
American Alumroot*Heuchera americana 1,2,3Many Available6 - 12
Semi-
Evergreen
Perennial
Moderate Light to Part
Shade Well Drained
Hosta Hosta species and
hybrids 1,2,3Many Available12 - 24 Herbaceous
Perennial Moderate Part to Full
Shade Well Drained
Liriope Liriope muscarii 1,2,3 Many Available12 - 18 Evergreen
Perennial Moderate Light to Full
Shade Moist to Well Drained
Creeping Jenny Lysimachia nummularia 1,2 ‘Aurea’2
Semi-
Evergreen
Perennial
Fast Light to Full
Shade Moist to Well Drained
Mondograss Ophiopogon japonicus 1,2 6 - 10 Evergreen
Perennial
Slow to
Moderate
Part to Full
Shade Well Drained
Creeping Raspberry Rubus calycinoides 1,2 6 - 12 Evergreen
Shrub Moderate Light to Part
Shade Well Drained
Sweetbox Sarcococca hookeriana
var. humilis 1,2 36 Evergreen
Shrub Moderate Light to Full
Shade Well Drained
Strawberry Begonia Saxifraga stolonifera 1,2 12 Evergreen
Perennial Fast Light to Full
Shade Moist to Well Drained
Asiatic or Star Jasmine Trachelospermum
asiaticum 1,2,3 6 - 8 Evergreen
Vine
Fast to
Moderate
Light to Part
Shade Well Drained
Common Periwinkle Vinca minor 1,2,3 5-6 Evergreen
Vine Fast Light to Full
Shade Well Drained
Christmas Fern*Polystichum
acrostichoides 1,2 12 - 18 Evergreen
Fern Moderate Part to Full
Shade Moist to Well Drained
Autumn Fern Dryopteris erythrosa 1,2 18 - 24 Evergreen
Fern Moderate Part to Full
Shade Moist to Well Drained
Japanese Painted Fern Athyrium nipponicum 1,2 12 - 18 Herbaceous
Fern Moderate Light to Full
Shade Moist to Well Drained
Spreading Liriope Liriope spicata 1,2,3 8-15 Evergreen
Perennial Moderate Light to Full
Shade Moist to Well Drained
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-4
Water Use Zones: 1 - High Water Use Zone, 2 - Medium Water Use Zone, 3 - Low Water Use Zone
58 Appendix
GROUNDCOVERS
* = Indicates a plant native to the Southeastern USA
Underline = Indicates an extremely drought-tolerant plant
Colors = W-white, Y-yellow, O-orange, B-blue, Pu-purple,
P-pink, R-red, L-lavender
COMMON NAME BOTANICAL NAME WATER
USE ZONE
RECOMMENDED
VARIETIES
HEIGHT
(IN)
TYPE OF
PLANT
GROWTH
RATE EXPOSURE SOIL CONDITIONS
SUN
Beach Wormwood*Artemisia stelleriana 2,3‘Silver Brocade’6 - 12 Evergreen
Perennial ModerateFull SunWell Drained to Xeric
Hardy Ice Plant Delosperma cooperi
Delosperma nubigenum 2,3 4 - 6
Semi
– Evergreen
Perennial
ModerateFull SunWell Drained to Xeric
Cheddar Pinks, Dianthus
Dianthus
gratianopolitanus and
hybrids of this species
2,3
‘Bath’s Pink’
‘Firewitch’
‘Greystone’
4 - 8 Evergreen
Perennial ModerateFull Sun Well Drained
Weeping Love Grass Eragrostis curvula 2,3 24 - 36 Clumping
Grass ModerateFull SunWell Drained to Xeric
Daylily Hemerocallis hybrids 1,2,3Many Available18 - 48 Herbaceous
Perennial Moderate Full Sun to
Part Shade Moist to Well Drained
Atlantic St. John’s Wort*Hypericum reductum 2,3 8 - 12
Semi-
Evergreen
Shrub
Moderate Full Sun Well Drained to Xeric
Candytuft Iberis sempervirens 1,2,3 6 - 8 Evergreen
Perennial Moderate Full Sun to
Light Shade Well Drained
Shore Juniper
Juniperus conferta
2,3 ‘Blue Pacific’12-18 Evergreen
Conifer Fast Full Sun Well Drained to Xeric
Blue Rug Juniper
Juniperus horizontalis
‘Wiltonii’2,3 4-6 Evergreen
Conifer ModerateFull SunWell Drained to Xeric
Andorra Juniper Juniperus horizontalis
‘Plumosa’2,3 24 Evergreen
Conifer ModerateFull SunWell Drained to Xeric
Creeping Juniper*Juniperus horizontalis 2,3
‘Bar Harbor’
‘Blue Chip’10 - 12 Evergreen
Conifer Moderate Full Sun Well Drained to Xeric
Dwarf Nandina Nandina domestica 1,2,3
‘Harbor Belle’
‘Harbor Dwarf’
‘San Gabriel’
24 - 36 Evergreen
Shrub ModerateFull Sun Well Drained
Moss Phlox or Thrift* Phlox subulata 1,2,3 Many4 - 6 Evergreen
Perennial Moderate Full Sun to
Light Shade Well Drained
Orange Coneflower*Rudbeckia fulgida 1,2,3‘Goldsturm’24 - 30
Semi-
Evergreen
Perennial
Moderate Full Sun to
Part Shade Moist to Well Drained
Stonecrops
Sedum reflexum
Sedum album
Sedum tetractinum
1,2,3 ‘Blue Spruce’
‘Murale’4 - 6 Evergreen
Perennial Moderate Full Sun to
Light Shade Well Drained
Wooly Stemodia*Stemodia tomentosa 1,2,3 4 - 6 Evergreen
Perennial ModerateFull SunWell Drained
Prostrate Germander Teucrium chamaedrys 1,2,3 ‘Prostratum’
‘Nanum’6 - 8 Evergreen
Perennial ModerateFull SunWell Drained
Many ornamental grasses, perennials and low growing shrubs will make good groundcovers when planted in mass. View those
lists for more possibilities. Evergreen plants retain enough foliage to remain dense and full during winter. Semi-evergreen plants retain
at least half of their foliage through winter, but are not as dense as evergreens. Herbaceous plants go dormant during winter, losing all
of their foliage.
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-5
Water Use Zones: 1 - High Water Use Zone, 2 - Medium Water Use Zone, 3 - Low Water Use Zone
59 Appendix
VINES
* = Indicates a plant native to the Southeastern USA
Underline = Indicates an extremely drought-tolerant plant
Colors = W-white, Y-yellow, O-orange, B-blue, Pu-purple,
P-pink, R-red, L-lavender
COMMON NAME BOTANICAL NAME WATER
USE ZONE HEIGHT FLOWER COLOR/
TIME OF BLOOM CLIMBING TYPE SOIL EXPOSURE
EVERGREEN
Evergreen Clematis Clematis armandii 1,220’White/SpringTendrilsWell Drained Sun to Pt.
Shade
Climbing Fig Ficus pumila 1,2 30’+Grown for foliage Clinging Well Drained Sun to Shade
Carolina Jessamine* Gelsemium
sempervirens 1,2,3 10’-20’Yellow/Spring Twining Moist to Well Drained Sun to Pt.
Shade
English Ivy Hedera helix 1,2,350’+Grown for foliageClinging Well Drained Sun to Shade
Coral Honeysuckle*Lonicera
sempervirens 1,2,3 10’-20’Orange-Red-Yellow/
Spring Twining Moist to Well Drained Sun to Pt.
Shade
Goldflame Honeysuckle Lonicera x heckrottii 1,210’-20’Pink/Spring TwiningMoist to Well Drained Sun to Lt.
Shade
Confederate Jasmine Trachelospermum
jasminoides 1,2,3 15’White/Summer Twining Well Drained Sun
Evergreen Wisteria Milletia reticulata 1,210’+Purple/Summer Twining Well DrainedSun
Fatshedera X Fatshedera lizei 1,28’Grown for FoliageScramblerMoist to Well Drained Pt. Shade to
Shade
Greenbriar Smilax laurifolia
Smilax smallii 1,215’+Grown for FoliageScramblerMoist to Well DrainedSun to Shade
DECIDUOUS
Climbing Aster*Aster carolinianus 1,210’Lavender-Pink/FallScramblerMoist to Well Drained Sun to Lt.
Shade
Fiveleaf Akebia Akebia quinata 1,2,3 30’+Purple/summer Twining Well Drained Sun to Pt.
Shade
Cross Vine*Bignonia capreolata
‘Tangerine Beauty’1,230’+Orange/SpringTendrils and ClingingMoist to Well Drained Sun to Lt.
Shade
Large Flowered
Clematis Clematis hybrids 1,2 10’Purple, pink, white/Spring Tendrils Well Drained Sun to Pt.
Shade
Climbing Hydrangea*Decumaria barbara 1,220’White/Summer ClingingMoist to Well Drained Lt. Shade to
Shade
Virginia Creeper* Parthenocissus
quinquefolia 1,2,3 30’+Grown for foliage Tendrils and Clinging Moist to Well Drained Sun to Shade
Boston Ivy Parthenocissus
tricuspidata 1,2,3 30’+Grown for foliage Tendrils and Clinging Well Drained Sun to Shade
Passionflower
Passiflora x alato-
caerulea
Passiflora x ‘Incence’
1,210’+Purple/Summer Tendrils Well Drained Sun to Lt.
Shade
Lady Banks’ Rose Rosa banksiae ‘Lutea’1,2,3 20’Yellow/Spring Scrambler Well Drained Sun to Lt.
Shade
Climbing Rose Rosa species 1,2 10’Many colors/Spring Sprambler Well Drained Sun to Lt.
Shade
Japanese Hydrangea
Vine
Schizophragma
hydrangeoides 1,220’-30’White/Summer Clinging Well Drained Pt. Shade to
Shade
American Wisteria* Wisteria frutescens 1,2,3 20’-30’Lilac/Spring Twining Moist to Well Drained Sun
“Climbing Form” refers to the way a vine climbs and helps determine the type of support structure needed:
Tendrils – Tendrils are short curly stems that wrap around narrow structures like wire or bamboo. These vines need a support structure
with small diameter elements and do very well on chain link fences or wires.
Clinging – Clinging vines produce short root-like growths that act like adhesive pads. They easily climb trees, walls and wood fences
with little assistance.
Twining – Twining vines climb by wrapping their stems around and through their support structure. They grow well on lattice, chain link
fence, or any structure they can weave through, but usually need a little help getting started.
Scrambler – Scrambling vines produce long, supple stems that can be woven through the same type of support structures as twining
vines. They generally need to be trained to climb up and through their support structure.
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-6
Water Use Zones: 1 - High Water Use Zone, 2 - Medium Water Use Zone, 3 - Low Water Use Zone
60 Appendix
ORNAMENTAL GRASSES
* = Indicates a plant native to the Southeastern USA
Underline = Indicates an extremely drought-tolerant plant
Colors = W-white, Y-yellow, O-orange, B-blue, Pu-purple,
P-pink, R-red, L-lavender
COMMON NAME BOTANICAL NAME WATER USE
ZONE
RECOMMENDED
VARIETIES
HEIGHT AND
SPREAD SOIL EXPOSURE
Feather Reed Grass Calamagrostis
brachytricha 1,2,3 4’ x 3’Moist to Well
Drained Sun to Pt. Shade
Japanese Sedge Carex morrowii 1,2 ‘Goldband’
‘Variegata’
1’ x 1’
1’ x 1’
Moist to Well
Drained Lt. Shade to Shade
Weeping Japanese Sedge Carex oshimensis 1,2 ‘Evergold’1’ x 2’Moist to Well
Drained Lt. Shade to Shade
Chinese Sedge Carex phyllocephala 1,2 ‘Sparkler’2’ x 2’Moist to Well
Drained Lt. Shade to Shade
River Oats* Chasmanthum latifolium 1,2,3 4’ x 2’ Wet to Well DrainedSun to Shade
Pampas Grass Cortaderia selloeana 1,2,3 8’ x 6’ Moist to Well
Drained Sun
Maiden Grass Miscanthus sinensis 1,2,3
‘Adagio’
‘Cosmopolitan’
‘Morning Light’
‘Strictus’
4’ x 3’
8’ x 4’
6’ x 4’
6’ x 3’
Moist to Well
Drained Sun – Lt. Shade
Muhly Grass*Muhlenbergia capillaris 2,3 3’ x 3’Well Drained to
Xeric Sun
Panic Grass*Panicum virgatum 1,2,3
‘Cloud Nine’
‘Northwind’
‘Shenandoah’
8’ x 5’
5’ x 3’
4’ x 2’
Moist to Well
Drained Sun to Lt. Shade
Fountain Grass Pennisetum
alopecuroides 1,2,3 ‘Hameln’3’ x 2’ Moist to Well
Drained Sun – Lt. Shade
Tall Fountain Grass Pennisetum orientale 1,2,3 ‘Tall Tails’6’ x 4’Moist to Well
Drained Sun
Indian Grass*Sorghastrum nutans 1,2,3 6’ x 3’Moist to Well
Drained Sun
TURFGRASSES
* = Indicates a plant native to the Southeastern USA
Underline = Indicates an extremely drought-tolerant plant
Colors = W-white, Y-yellow, O-orange, B-blue, Pu-purple,
P-pink, R-red, L-lavender
COMMON
NAME
BOTANICAL
NAME
WATER
USE
ZONE
RECOMMENDED
VARIETIES
SHADE
TOLERANCE PROPAGATION RATE OF
ESTABLISHMENT
FERTILIZER
(LBS OF
NITROGEN/
1,000 SQ. FT./YR)
MOWING
Frequency
MOWING
HEIGHT
Centipede Eremochloa
ophiuroides 1,2,3 Common
‘TifBlair’Moderate Seed for common,
Plugs, Sod for both Slow 0.5 Low1”
St.
Augustine
Stenotaphrum
secundatum 1,2
‘Raleigh’
‘Mercedes’
‘Palmetto’
Very Good Plugs, Sod Moderate2 to 3Medium-high2” to 3”
Zoysia Zoysia hybrids 1,2,3
‘Emerald’, ‘Meyer’
‘El Toro’, ‘Zenith’
‘Crowne’, ‘Empire’
‘GN-Z’
Good
Only ‘Zenith’ can be
grown from seed. All
other varieties must be
established by sprigs,
plugs, or sod.
Very Slow
to Moderate
depending on
variety
2 to 4
depending on
variety
Low-medium
0.75” to
1.5”
depending
on variety
Common
Bermuda
Cynodon
dactylon 1,2,3 ‘Princess’
‘Jack Pot’Very Poor Seed. Springs, Plugs,
Sod Fast 4.5Medium-high 1.0” to
1.5”
Hybrid
Bermuda
Cynodon
dactylon
hybrids
1,2,3
‘Tifway’,
‘Tifsport’,
‘Vamont’, ‘GN-1’
‘Celebration’
‘Tifton-10’
Very PoorSprings, Plugs, SodModerate5 to 6Very high 0.75” to
1.5”
All of the above are warm season grasses listed in order from low to high maintenance. Warm season grasses are well adapted
to areas with hot summers and mild winters. They actively grow during spring, summer and fall and are dormant during winter. The
best time to sow seed for these grasses is from spring to early summer (March/April-July). Plugs, sprigs, and sod establish best when
planted in spring and summer (March-July).
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-7
Water Use Zones: 1 - High Water Use Zone, 2 - Medium Water Use Zone, 3 - Low Water Use Zone
61 Appendix
PERENNIALS
* = Indicates a plant native to the Southeastern USA
Underline = Indicates an extremely drought-tolerant plant
Colors = W-white, Y-yellow, O-orange, B-blue, Pu-purple,
P-pink, R-red, L-lavender
COMMON NAME BOTANICAL NAME
WATER
USE
ZONE
RECOMMENDED
VARIETIES HEIGHT COLOR TIME OF
BLOOM EXPOSURE SOIL
SHADE–PART TO FULL
Bear’s Breeches Acanthus species and
hybrids 1,2‘Summer Beauty’3 – 4 ftPuSummer Light to Part
Shade
Moist to Well
Drained
Carpet Bugle Ajuga reptans 1,2 4 – 8 inB,W,Pu Spring Light to Full
Shade
Moist to Well
Drained
Eastern Columbine*Aquilegia canadensis 1,2,3 2-3 ft R/Y Spring Light to Part
Shade Well Drained
Cast Iron Plant Aspidistra elatior 1,2,3 2 – 3 ftFoliageEvergreen Part to Full
Shade Well Drained
Japanese Painted Fern Athyrium nipponicum 1,2 18 inFoliage Light to Full
Shade
Moist to Well
Drained
Hardy Begonia Begonia grandis 1,2 15 in PSummer Light to Full
Shade Well Drained
Green and Gold*Chrysogonum virginianum 1,2 8 – 12 inYSpring Light to Full
Shade
Moist to Well
Drained
Southern Shield Fern*Dryopteris ludoviciana 1,2 3 ftFoliage Part to Full
Shade
Moist to Well
Drained
Lenten Rose Helleborus x hybridus 1,2 12-15 in W,P,L Winter/
Spring
Part to Full
Shade Well Drained
American Alumroot*Heuchera americana 1,2,3 Many Available8 – 12 in W,P,R Spring Light to Full
Shade Well Drained
Hosta Hosta species and hybrids 1,2.3 1-3 ft Foliage Spring/
Summer
Part to Full
Shade Well Drained
Leopard Plant Ligularia tussilaginea 1,2 18 – 24 inYFall Part to Full
Shade
Moist to Well
Drained
Creeping Jenny Lysimachia nummularia 1,2 ‘Aurea’2 inFoliageEvergreen Light to Full
Shade
Moist to Well
Drained
Woodland Phlox*Phlox divaricata 1,2 8 – 12 inB,W,LSpring Light to Part
Shade
Moist to Well
Drained
Variegated Solomon’s
Seal
Polygonatum odoratum
‘Variegatum’1,2,3 18 – 24 inWSpring Light to Full
Shade
Moist to Well
Drained
Strawberry Begonia Saxifraga stolonifera 1,2 12 inWSpring Light to Full
Shade
Moist to Well
Drained
Indian Pink*Spigelia marilandica 1,2 12 – 18 inR/YSpring Light to Part
Shade Well Drained
Toad Lily Tricyrtis formosana 1,2 12 – 24 inW/Pu/LFall Light to Part
Shade
Moist to Well
Drained
SUN – FULL TO PART
Yarrow Achillea millefolium 1,2,3 2 - 3 ft W,P,Y,O Summer Sun Well Drained to
Xeric
Anise Hyssop Agastache foeniculum 1,2,3‘Blue Fortune’2 – 3 ftBSummer SunWell Drained
Arkansas Blue Star*Amsonia hubrichtii 1,2,3 3 – 4 ftBSpringSunWell Drained
Blue Star*Amsonia tabernaemontana 1,2,3 3 – 4 ftBSpring Sun to Part
Shade
Moist to Well
Drained
‘Powis Castle’
Artemisia Artemisia x ‘Powis Castle’2,3 2 – 3 ftFoliageEvergreenSun Well Drained to
Xeric
Butterfly Weed* Ascelpias tuberosa 1,2,3 1-2 ft O,Y Summer Sun Well Drained to
Xeric
Swamp Milkweed*Asclepias incarnata 1,2 ‘Cinderella’
‘Ice Ballet’3 ftW,PSummer Sun to Part
Shade
Moist to Well
Drained
Heath Aster*Aster ericoides 1,2,3 ‘Monte Cassino’
‘Pink Star’2 – 4 ftW,PFallSun Well Drained to
Xeric
Aromatic Aster*Aster oblongifolius 1,2,3 ‘Fanny’
‘October Skies’2 – 4 ftB,PFallSunWell Drained
False Wild Indigo*
Baptisia australis
Baptisia alba
Baptisia sphaerocarpa
Baptisia hybrids
1,2,3 ‘Carolina Moonlight’
‘Purple Smoke’2 - 3ft B,W,Y,L Spring Sun/Partial
Shade
Moist to Well
Drained
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-8
Water Use Zones: 1 - High Water Use Zone, 2 - Medium Water Use Zone, 3 - Low Water Use Zone
62 Appendix
PERENNIALS
* = Indicates a plant native to the Southeastern USA
Underline = Indicates an extremely drought-tolerant plant
Colors = W-white, Y-yellow, O-orange, B-blue, Pu-purple,
P-pink, R-red, L-lavender
COMMON NAME BOTANICAL NAME
WATER
USE
ZONE
RECOMMENDED
VARIETIES HEIGHT COLOR TIME OF
BLOOM EXPOSURE SOIL
Canna Lily Canna hybrids 1,2Many Available2 – 6 ftP,R,O,YSummer Sun to Part
Shade
Moist to Well
Drained
Leadwort Ceratostigma
plumbaginoides 1,2,3 12 inBFall Sun to Part
Shade
Moist to Well
Drained
Turtlehead*Chelone glabra
Chelone obliqua 1,2 2 – 3 ftW,PFall Sun to Part
Shade
Moist to Well
Drained
Mouse Ear Coreopsis*Coreopsis auriculata 1,2 ‘Nana’1 – 2 ftYSpring Sun to Part
Shade
Moist to Well
Drained
Threadleaf Coreopsis*Coreopsis verticillata 1,2,3 ‘Golden Showers’
‘Zagreb’1 - 2 ftYSummerSunWell Drained
Crinum Lily Crinum species and hybrids 1,2,3 2 – 4 ftW,P Summer Sun to Part
Shade
Moist to Well
Drained
Hardy Ice Plant Delosperma cooperi
Delosperma nubigenum 2,3 6 inP,YSpringSun Well Drained to
Xeric
Cheddar Pinks,
Dianthus Dianthus gratianopolitanus 1,2,3
‘Bath’s Pink’
‘Firewitch’
‘Greystone’
8 – 12 inW,PSpringSun Well Drained to
Xeric
Hummingbird Plant Dicliptera suberecta 1,2,3 12 – 18 inOSummer Sun Well Drained
Purple Coneflower* Echinacea purpurea 1,2,3 ‘Bravado’, ‘Kim’s Knee High’
‘White Swan’, ‘Magnus’3-5 ft P,W Summer Sun/Partial
Shade Well Drained
Joe Pye Weed*
Eupatorium fistulosum
Eupatorium dubium
Eupatorium maculatum
1,2 4 – 6 ftPFall Sun to Light
Shade
Moist to Well
Drained
Blanket Flower,
Gaillardia Gaillardia x grandiflora 1,2,3 ‘Goblin’
‘Fanfare’1 - 2 ftY,R,O Summer-
Fall Sun Well Drained to
Xeric
Gaura*Gaura lindheimeri 2,3 ‘So White’
‘Pink Cloud’2 – 3 ftW,PSummerSun Well Drained to
Xeric
Hardy Ginger Lily Hedychium species and
hybrids 1,2 4 – 6 ft.W,Y,O,Summer
- Fall
Sun to Part
Shade
Moist to Well
Drained
Swamp Sunflower*Helianthus angustifolius 1,2 6 ftYFall Sun to Light
Shade
Moist to Well
Drained
Daylily Hemerocallis species and
hybrids 1,2,3 Many Available1-4 ft Y,O,R,W,PSummer Sun/Partial
Shade
Moist to Well
Drained
Red False Aloe Hesperaloe parviflora 2,3 3 – 4 ftRSummerSun Well Drained to
Xeric
Hardy Hibiscus*
Hibiscus moscheutos
Hibiscus coccineus
Hibiscus hybrids
1,2
‘Anne Arundel’
‘Blue River II”
‘Moy Grande’
4 – 5 ftR,P,WSummer Sun to Light
Shade
Moist to Well
Drained
Confederate Rose Hibiscus mutabilis 1,2 5 – 6 ftPFall Sun to Light
Shade
Moist to Well
Drained
Evergreen Candytuft Iberis sempervirens 1,2,3 12 in W Spring Sun to Part
Shade Well Drained
Bearded Iris Iris hybrids 1,2,3 3 ftP,O,Y,W,L,Pu,Spring Sun to Light
Shade Well Drained
Siberian Iris Iris sibirica 1,2 2-4 ft W,Y, B, Pu, LSpring Sun to Part
Shade
Moist to Well
Drained
Japanese Aster Kalimeris pinnatifida 1,2,3 2 ftWSummer Sun to Light
Shade Well Drained
Red Hot Poker Kniphofia species and
hybrids 1,2,3 2-4 ft R,O,Y Summer Sun Well Drained
Seashore Mallow*Kosteletzkya virginica 1,2 4 – 5 ftP,WSummer Sun to Par
Shade
Moist to Well
Drained
Lantana Lantana camara
Lantana montevidensis
Lantana hybrids
2,3
‘Miss Huff’
‘Tangerine’
‘New Gold’
‘Radiation’
2 – 4 ft W,L,P,Y,O,R Summer to
Fall Sun Well Drained to
Xeric
Cardinal Flower*Lobelia cardinalis 1,2 3 ftRFall Sun to Part
Shade
Moist to Well
Drained
Garden Phlox*Phlox paniculata 1,2
‘Robert Poore’
‘David’
‘Laura’
3 – 4 ft W,P,L Summer Sun to Part
Shade
Moist to Well
Drained
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-9
Water Use Zones: 1 - High Water Use Zone, 2 - Medium Water Use Zone, 3 - Low Water Use Zone
63 Appendix
PERENNIALS
* = Indicates a plant native to the Southeastern USA
Underline = Indicates an extremely drought-tolerant plant
Colors = W-white, Y-yellow, O-orange, B-blue, Pu-purple,
P-pink, R-red, L-lavender
COMMON NAME BOTANICAL NAME
WATER
USE
ZONE
RECOMMENDED
VARIETIES HEIGHT COLOR TIME OF
BLOOM EXPOSURE SOIL
Moss Pinks, Thrift*Phlox subulata 1,2,3Many Available6 – 12 inW,P,L,BSpring Sun to Light
Shade Well Drained
Rudbeckia, Orange
Coneflower*Rudbeckia fulgida 1,2,3 ‘Goldsturm’3 ftYSummer Sun to Part
Shade
Moist to Well
Drained
Dwarf Mexican Petunia Ruellia brittoniana ‘Katie’1,2,3 6 in W,P,PuSummer Sun to Light
Shade Well Drained
Autumn Sage
Salvia greggii
Salvia microphylla
and hybrids
1,2,3 2 – 4 ftR,P,W,Pu Spring and
Fall
Sun to Light
Shade Well Drained
Anise Sage Salvia guaranitica 1,2‘Black and Blue’3 – 4 ftB,Pu Summer Sun to Part
Shade
Moist to Well
Drained
Mexican Bush Sage Salvia leucantha 1,2,3‘San Carlos Festival’3 – 5 ftPuFallSunWell Drained
Sedum Sedum hybrids 1,2,3 ‘Matrona’
‘Autumn Fire’2 –3 ftP, RFall Sun to Light
Shade Well Drained
Purple Heart Setcreasia pallida 1,2,3 12 – 15 inPuSummer Sun to Light
Shade Well Drained
‘Fireworks’
Goldenrod*
Solidago rugosa
‘Fireworks’1,2,3 1-3 ft Y Fall Sun to Part
Shade
Moist to Well
Drained
Stokes Aster* Stokesia laevis 1,2 Several Available1 –2 ftB, L, W, YSummer Sun to Part
Shade
Moist to Well
Drained
Verbena* Verbena canadensis 1,2,3 ‘Homestead Purple’
‘Snowflurry’8 – 12 inW,B,L,P Spring and
Summer
Sun to Light
Shade
Moist to Well
Drained
Creeping Veronica Veronica peduncularis 1,2‘Georgia Blue’8 inBSpring Sun to Part
Shade Well Drained
Rain Lily Zephyranthes species and
hybrids 1,2Several Available1 ftW,Y,P Summer
and Fall
Sun to Part
Shade
Moist to Well
Drained
ANNUALS
* = Indicates a plant native to the Southeastern USA
Underline = Indicates an extremely drought-tolerant plant
Colors = W-white, Y-yellow, O-orange, B-blue, Pu-purple,
P-pink, R-red, L-lavender
COMMON NAME BOTANICAL NAME WATER USE
ZONE
HEIGHT
(INCHES)COLOR EXPOSURE
COOL SEASON ANNUALS
Snapdragon Anthirrhinum majus 1,2 6-36 All but B Sun
English Daisy Bellis perennis 1,26 - 12 P, R, W Sun to Pt. Shade
Swiss Chard Beta vulgaris 1,2 24 Foliage Sun
Ornamental Cabbage and Kale Brassica oleracea 1,2 12 Foliage Sun
‘Giant Red’ Mustard Brassica species ‘Giant Red’1,2 18 Foliage Sun
Calendula Calendula officinalis 1,2 12 - 24 Y,O Sun
Bachelor’s Buttons Centaurea cyanus 1,212 - 30 B, W, P Sun
Cardoon Cynara cardunculus 1,2,3 36 Foliage Sun
Chinese Forget-me-not Cynoglossum amabile 1,2 12 B Sun to Pt. Shade
Delphinium Delphinium x elatum 1,236 - 48W, B, Pu, L, P Sun to Pt. Shade
Sweet Williams Dianthus barbatus 1,212 - 24 R, P, W Sun to Pt. Shade
China Pinks Dianthus chinensis 1,28 - 12 R, P, W Sun
Foxglove Digitalis purpurea 1,212-60 All but B Sun to Pt. Shade
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-10
Water Use Zones: 1 - High Water Use Zone, 2 - Medium Water Use Zone, 3 - Low Water Use Zone
64 Appendix
ANNUALS
* = Indicates a plant native to the Southeastern USA
Underline = Indicates an extremely drought-tolerant plant
Colors = W-white, Y-yellow, O-orange, B-blue, Pu-purple,
P-pink, R-red, L-lavender
COMMON NAME BOTANICAL NAME
WATER USE
ZONE
HEIGHT
(INCHES)COLOR EXPOSURE
Wallflower Erysimum cheiri 1,2 12 All but B Sun to Pt. Shade
California Poppy Eschscholzia californica 1,2,3 12-24 All but B Sun
Dame’s Rocket Hesperis matronalis 1,2 36 Pu, W Sun to Pt. Shade
Annual Candytuft Iberis umbellata 1,2 12 P, Pu, L, W Sun
Sweet Alyssum Lobularia maritima 1,2 6 W,P,L Sun to Pt. Shade
Stock Matthiola incana 1,212 - 15W, P, R, Pu Sun
Forget-me-nots Myosotis sylvatica 1,2 12 B Sun to Pt. Shade
Parsley Petroselinum crispum 1,2 12 Foliage Sun
Dusty Miller Senecio cineraria 1,2,3 6-12 Foliage Sun
Pansy Viola x wittrockiana 1,2 6 All Sun to Pt. Shade
WARM SEASON ANNUALS - SHADE
‘Dragonwing’Begonia Begonia x ‘Dragonwing’1,2 15 R,P Sun to Shade
Wax Begonia Begonia x semperflorens 1,2,3 6-12 W,P,R Sun to Shade
Caladium Caladium bicolor 1 12 - 36 Foliage Pt. Shade to Shade
Coleus Solenostemon scutellarioides 1,2 24 - 36 Foliage Sun to Shade
Polka Dot Plant Hypoestes phyllostachya 1,215 - 24 Foliage Pt. Shade to Shade
New Guinea Impatiens Impatiens hawkeri 1 12 - 36 O,R,P Pt. Shade to Shade
Impatiens Impatiens wallerana 1 12-36 All but B Pt. Shade to Shade
Yellow Shrimp Plant Pachystachys lutea 1,224 - 30 Y Pt. Shade to Shade
Wishbone Flower Torenia fournieri 1,2 12 W,B,Pu,P Pt. Shade to Shade
WARM SEASON ANNUALS - SUN
Ageratum Ageratum houstonianum 1,2 8 - 24 W,B,Pu Sun to Pt. Shade
‘Purple Knight’ Alternanthera Alternanthera dentata 1,224 - 30 Foliage Sun to Pt. Shade
Joseph’s Coat Alternanthera ficoidea 1,28 - 12 Foliage Sun to Pt. Shade
Angelonia Angelonia angustifolia 1,224 - 36 W,Pu,P Sun to Pt. Shade
Tropical Milkweed Asclepias curassavica 1,236 - 48 O,R,Y Sun
Asparagus Fern Asparagus densiflorus 1,2,3 18 - 24 Foliage Sun to Pt. Shade
Wax Begonia Begonia semperflorens 1,2,3 12 R,W,P Sun to Shade
Dragonwing Begonia Begonia x ‘Dragonwing’1,2 15 R,P Sun to Shade
Million Bells Calibrachoa x hybrida 1,2,36 - 12All but B Sun
Ornamental Pepper Capiscum annum 1,2,3 12 - 18 Fruit Sun
Madagascar Periwinkle Catharanthus roseus 1,2,3 6 - 18 W,P,L,Pu Sun
Cockscomb Celosia cristata 1,2,3 6 - 30 All but B Sun
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-11
Water Use Zones: 1 - High Water Use Zone, 2 - Medium Water Use Zone, 3 - Low Water Use Zone
65 Appendix
ANNUALS
* = Indicates a plant native to the Southeastern USA
Underline = Indicates an extremely drought-tolerant plant
Colors = W-white, Y-yellow, O-orange, B-blue, Pu-purple,
P-pink, R-red, L-lavender
COMMON NAME BOTANICAL NAME
WATER USE
ZONE
HEIGHT
(INCHES)COLOR EXPOSURE
Spider Plant Cleome hasslerana 1,2,3 24 - 48W,P,L Sun
Cosmos Cosmos bipinnatus 1,2,318 - 48 P, R, W Sun to Pt. Shade
Mexican Heather Cuphea hyssopifolia 1,2,3 12 Pu Sun to Lt. Shade
Mexican Cigar Plant Cuphea ignea 1,2 12 R Sun
Blue Daze Evolvulus pilosus 1,2,36 - 8 B Sun
Blanket Flower Gaillardia pulchella 1,2,3 12-30 Y,O,R Sun
Globe Amaranth Gomphrena globosa 1,2,38 - 24 W,P,L,Pu Sun
Ornamental Sweet Potato Ipomoea batatas 1,2 12 Foliage Sun to Pt. Shade
Lantana Lantana camara 1,2,3 12 - 36 Y,O,P,R Sun
Trailing Lantana Lantana montevidensis 1,2,3 12 L,W Sun
Melampodium Melampodium paludosum 1,2,3 18 - 30 Y Sun to Pt. Shade
Cat’s Whiskers Orthosiphon stamineus 1,2 24 Pu,W Sun to Lt. Shade
Red Fountain Grass Pennisetum setaceum ‘Rubrum’1,2,3 24 - 36 Foliage Sun
Pentas Pentas lanceolata 1,2,3 12 - 24R,P,W,L Sun to Lt. Shade
Petunia Petunia x hybrida 1,2 6-12 All Sun to Pt. Shade
Cuban Oregano Plectranthus amboinicus 1,2 24 - 30 Foliage Sun
Silver Plectranthus Plectranthus argenteus 1,2 24 Foliage Sun
‘Mona Lavender’ Plectranthus Plectranthus x ‘Mona Lavender’1,2 24 L Sun to Lt. Shade
Moss Rose Portulaca grandiflora 1,2,3 4 - 6 All but B, Pu Sun
Purslane Portulaca oleracea 1,2,3 6 All but B, Pu Sun
Texas Sage Salvia coccinea 1,2,318 - 24 R,P,W Sun to Lt. Shade
Mealycup Sage Salvia farinacea 1,2,3 12 - 24 B,W Sun to Lt. Shade
Scarlet Sage Salvia splendens 1,2,3 12 - 18 R,W,O,Pu Sun to Pt. Shade
Fan Flower Scaevola aemula 1,2 8 W,Pu Sun to Lt. Shade
Sun Coleus Solenostemon scutellarioides 1,2 24 - 36 Foliage Sun to Shade
Persian Shield Strobilanthus dyerianus 1,2 24 Foliage Sun to Pt. Shade
Marigold Tagetes erecta,
Tagetes patula 1,2 12 – 30 Y,R,O Sun
Mexican Sunflower Tithonia rotundifolia 1,2,3 36 - 48 O,Y Sun
Verbena Verbena x hybrida 1,2 6-12 All but Y Sun to Lt. Shade
‘Profusion’ Zinnia Zinnia elegans 1,2 12 W,O,P,R Sun
Creeeping Zinnia Zinnia linearis 1,2,3 12 - 18 Y, O, W Sun
All annuals grow best in a well-prepared soil with good drainage. Cool season annuals should be planted from October through
mid-November. Warm season annuals are best planted from mid-April through May.
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-12
Water Use Zones: 1 - High Water Use Zone, 2 - Medium Water Use Zone, 3 - Low Water Use Zone
66 Appendix
SMALL SHRUBS (2-4 feet)
* = Indicates a plant native to the Southeastern USA
Underline = Indicates an extremely drought-tolerant plant
Colors = W-white, Y-yellow, O-orange, B-blue, Pu-purple,
P-pink, R-red, L-lavender
COMMON NAME BOTANICAL NAME WATER
USE ZONE
RECOMMENDED
VARIETIES
HEIGHT
X SPREAD
(FT.)
ORNAMENTAL
CHARACTERISTICS SOIL EXPOSURE
EVERGREEN SHRUBS
‘Rose Creek’ Abelia Abelia x ‘Rose Creek’1,2,32-3 x 2-3
Clusters of small white bell-
shaped flowers summer and
fall
Well DrainedSun
Dwarf Aucuba Aucuba japonica 1,2,3 ‘Nana’3-4 x 2-3 Large, evergreen leavesWell Drained Part to Full
Shade
Poet’s Laurel Danae racemosa 1,2,3 2-4 x 3-5 Graceful habit and handsome
foliage. Slow growing Well Drained Part to Full
Shade
Creeping Gardenia Gardenia radicans 1,2 2-3 x 3-4 Fragrant white flowers in
summer Well Drained Sun to Part
Shade
Chinese Holly Ilex cornuta 1,2,3 ‘Carissa’
‘Rotunda’3-4 x 4-5 Very tough. Glossy dark green
foliage Well Drained Sun to Light
Shade
Dwarf Yaupon Holly* Ilex vomitoria 1,2,3
‘Bordeaux’
‘Schillings’
‘Nana’
3-4 ft Extremely tough. Small
leaves, fine texture
Well Drained
to Xeric
Sun to Part
Shade
Winter Jasmine Jasminum nudiflorum 1,2,3 3-4 ft Yellow flowers in early springWell Drained Sun to Part
Shade
Chinese Juniper Juniperus chinensis 2,3
‘Old Gold’
‘Gold Lace’
‘Pfitzeriana’
2-3 x 4-5
3-4 x 5-6
3-5 x 5-10
Many varieties have golden
foliage, others have bluish
needles
Well Drained
to Xeric Sun
Dwarf Nandina Nandina domestica 1,2,3
‘Firepower’
‘Moon Bay’
‘Gulf Stream’
‘Harbor Dwarf’
2-3 ft
All but ‘Firepower’ eventually
produce red berries. Attractive
foliage, red in winter
Well Drained Sun to Part
Shade
Dwarf Pittosporum Pittosporum tobira 1,2,3 ‘Wheeler’s Dwarf’
‘Cream de Mint’3-4 ft Attractive foliage, ‘Cream de
Mint’ is variegated
Well Drained
to Xeric
Sun to Part
Shade
Indian Hawthorne Rhaphiolepis indica 1,2,3
‘Olivia’
‘Eleanor Taber’
‘Indian Princess’
‘Gulf Green’
2-4 ft
White or Pink flowers in May.
These varieties have good
resistance to leaf spot disease
Well DrainedSun
Azaleas Rhododendron hybrids1,2 Satsuki Varieties
‘Gumpo’ Varieties 2-3 x 3-4 Later flowering than most
Azaleas Well Drained Light to Part
Shade
‘Conoy’ Viburnum Viburnum x utile
‘Conoy’1,2 3-5 x 5-8 Fragrant white flowers in
spring Well Drained Sun to Part
Shade
Adam’s Needle Yucca*Yucca filamentosa 1,2,3
‘Color Guard’
‘Garland Gold’
‘Bright Edge’
2-4 x 2-4 Interesting texture, all of these
varieties have gold variegation
Well Drained
to Xeric Sun
DECIDUOUS SHRUBS
Japanese Barberry Berberis thunbergii 1,2,3 ‘Crimson Pygmy’2-3 x 3-4 Crimson foliage throughout
growing season Well Drained Sun to Light
Shade
Sweet Pepperbush,
Clethra*Clethra alnifolia 1,2 ‘Hummingbird’
‘Sixteen Candles’2-3 x 4-6 Fragrant white flowers in mid-
summer, yellow fall color
Moist to Well
Drained
Sun to Part
Shade
Dwarf Fothergilla*Fothergilla gardenii 1,2 3-4 x 3-4 White flowers in spring, nice
fall color
Moist to Well
Drained
Sun to Part
Shade
‘Pia’ Hydrangea Hydrangea
macrophylla ‘Pia’ 1,2 2-3 x 2-3 Pink or blue mophead flowers
in summer Well Drained Sun to Part
Shade
Virginia Sweetspire*Itea virginica 1,2,3 ‘Little Henry3-4 x 3-5 White flowers in spring, good
autumn color
Moist to Well
Drained Sun/Shade
Japanese Spirea Spirea japonica
Spirea x bumalda 1,2,3
‘Anthony Waterer’
‘Goldflame’
‘Shirobana’
‘Gold Mound’
‘Little Princess’
2-4 x 2-4 Pink flowers in summer. Some
varieties have golden foliage Well Drained Sun to Light
Shade
‘Snowmound’ Spirea Spirea nipponica
‘Snowmound’1,2,3 3-5 x 4-5 White flowers in spring, bluish
foliage in summer Well Drained Sun to Light
Shade
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-13
Water Use Zones: 1 - High Water Use Zone, 2 - Medium Water Use Zone, 3 - Low Water Use Zone
67 Appendix
MEDIUM SHRUBS (4-8 feet)
* = Indicates a plant native to the Southeastern USA
Underline = Indicates an extremely drought-tolerant plant
Colors = W-white, Y-yellow, O-orange, B-blue, Pu-purple,
P-pink, R-red, L-lavender
COMMON NAME BOTANICAL NAME
WATER
USE
ZONE
RECOMMENDED
VARIETIES
HEIGHT
X SPREAD
(FT.)
ORNAMENTAL
CHARACTERISTICS SOIL EXPOSURE
EVERGREEN SHRUBS
Abelia Abelia x grandiflora 1,2,3 4-8 x 4-6 Small white flowers in summer
and fall, attracts butterflies
Well
Drained
Sun to Part
Shade
Japanese Aucuba Aucuba japonica 1,2 5-8 x 4-6 Large, thick leaves. Some
varieties spotted in gold
Well
Drained
Part to Full
Shade
Wintergreen Barberry Berberis julianae 1,2,3 6-8 x 6-8 Yellow flowers in spring, leaves
turn bronze to burgundy in winter
Well
Drained Sun
Bottlebrush Callistemon rigidus 1,2,3‘Woodlander’s Hardy’5-6 x 5-6Unusual red flowers in spring Well
Drained Sun
Japanese Camellia Camellia japonica 1,2Many Available6-12 x 4-8 Red, Pink, White or Rose flowers
in winter and early spring
Well
Drained
Light to Part
Shade
Sasanqua Camellia Camellia sasanqua 1,2Many Available6-10 x 4-8 Red, White, Pink or Rose flowers
in fall and winter
Well
Drained
Light to Part
Shade
Dwarf Hinoki Cypress Chamaecyparis obtusa
‘Nana Gracilis’1,2 4-6 x 3-4 Unusual foliage texture, often
seen in Japanese Gardens
Well
Drained
Sun to Part
Shade
Mediterranean Fan Palm Chamaerops humilis 1,2,3 5-6 x 5-6 Beautiful texture, very slow
growing
Well
Drained
Sun to Light
Shade
King Sago
Emporer Sago
Cycas revoluta
Cycas taitungensis 1,2 4-8 x 6
4-6 x 10
Unique textural effect, both are
slow growing palm like plants
Well
Drained
Sun to Part
Shade
Fatsia Fatsia japonica 1,2 6-8 x 6-8 Large, glossy lobed leaves give a
tropical effect
Well
Drained
Part to Full
Shade
Pineapple Guava Feijoa sellowiana 1,2,36-10 x 5-8 Pink and crimson flowers in
spring, gray foliage
Well
Drained Sun
Gardenia Gardenia jasminoides 1,2
‘Kleim’s Hardy’
‘Mystery’
‘August Beauty’
4-8 x 4-8 Extremely fragrant white flowers
in summer, glossy green leaves
Well
Drained
Sun to Light
Shade
Chinese Holly Ilex cornuta,1,2,3 ‘Dwarf Burford’5-7 x 6-8 Glossy green leaves, red berries in
fall and winter
Well
Drained
Sun to Light
Shade
Inkerry Holly* Ilex glabra 1,2,3 ‘Shamrock’5-8 x 5-8 Small, dark green leaves, similar
to boxwood
Moist
to Well
Drained
Sun to Light
Shade
Chinese Juniper Juniperus chinensis 2,3‘Sea Green’4-6 x 6-8 Fountain like, arching branches,
mint green foliage
Well
Drained
to Xeric
Sun
Japanese Privet Ligustrum japonicum 1,2,3
‘Recurvifolium’
‘East Bay’
‘Lake Tresca’
5-6 x 4-6 Tough evergreen shrub, dark
green glossy foliage
Well
Drained
Sun to Light
Shade
Loropetalum Loropetalum chinense 1,2 ‘Ruby’
‘Burgundy’
4-6 x 4-6
6-8 x 6-8
Hot pink fringy flowers in spring,
burgundy foliage throughout the
season
Well
Drained
Sun to Light
Shade
Leatherleaf Mahonia Mahonia bealei 1,2,3 6-8 x 3-4 Upright shrub with coarse spiny
leaves. Very shade tolerant
Well
Drained
Part to Full
Shade
Banana Shrub Michelia figo 1,2,3 6-8 x 6-8
Glossy dark green leaves. Small
cream colored, banana scented
flowers in spring
Well
Drained
Sun to Part
Shade
Nandina,
Heavenly Bamboo Nandina domestica 1,2,3 5-8 x 3-4 Graceful foliage, large clusters of
red berries in fall
Well
Drained
Sun to Part
Shade
Oleander Nerium oleander 1,2,3Several Available6-10 x 4-8
Red, white, pink or salmon
flowers in summer. All parts of
this plant are poisonous
Well
Drained
to Xeric
Sun
Pittosporum Pittosporum tobira 1,2,3 ‘Louisiana Compact’
‘Variegata’6-8 x 6-8 Small white fragrant flowers in
spring
Well
Drained
to Xeric
Sun to Part
Shade
Firethorn, Pyracantha Pyracantha coccinea
Pyracantha koidzumii 1,2,3Many Available6-10 x 4-8 Clusters of red or orange berries
in fall and winter
Well
Drained
Sun to Light
Shade
Needle Palm Rhapidophyllum
hystrix 1,2,3 5-10 x 5-10Slow growing, hardy palm Well
Drained
Sun to Part
Shade
Azaleas - Southern Indica
Varieties Rhododendron hybrids1,2
‘Formosa’
‘G.G.Gerbing’
‘George Tabor’
6-8 x 6-8 Large growing, tough azaleas with
white, magenta or pink flowers
Well
Drained
Light to Part
Shade
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-14
Water Use Zones: 1 - High Water Use Zone, 2 - Medium Water Use Zone, 3 - Low Water Use Zone
68 Appendix
MEDIUM SHRUBS (4-8 feet)
* = Indicates a plant native to the Southeastern USA
Underline = Indicates an extremely drought-tolerant plant
Colors = W-white, Y-yellow, O-orange, B-blue, Pu-purple,
P-pink, R-red, L-lavender
COMMON NAME BOTANICAL NAME
WATER
USE
ZONE
RECOMMENDED
VARIETIES
HEIGHT
X SPREAD
(FT.)
ORNAMENTAL
CHARACTERISTICS SOIL EXPOSURE
Rosemary Rosmarinus officinalis 2,33-6 x 3-6 Blue flowers in spring, culinary
herb
Well
Drained
to Xeric
Sun
Dwarf Palmetto*Sabal minor 1,2,3 4-6 x 4-6Hardy, shrub like palm
Moist
to Well
Drained
Sun to Part
Shade
Sandwanka Viburnum Viburnum suspensum 1,2,34-8 x 4-8 Leathery, dark green foliage.
White flowers in spring
Well
Drained
to Xeric
Sun
Tinus Viburnum,
Laurustinus Viburnum tinus 1,2
‘Eve Price’
‘Compactum’
‘Spring Bouquet’
5-7 x 5-7 Dark green foliage, pink flower
buds open to white in spring
Well
Drained
Sun to Part
Shade
DECIDUOUS SHRUBS
‘Brilliant’ Chokeberry*Aronia arbutifolia
‘Brilliantissima’1,2,3 6-8 x 6-8
White flowers in early spring, red
berries persist all winter, excellent
fall color
Moist
to Well
Drained
Sun to Light
Shade
Butterfly Bush Buddleia davidii 1,2,3Many Available4-8 x 4-6
White, Purple, Lavender, Rose,
or yellow flowers in summer.
Extremely fragrant, attracts lots
of butterflies
Well
Drained
Sun to Light
Shade
American Beautyberry*Callicarpa americana 1,2,3 4-6 x 4-6 Vibrant purple berries in fall,
attracts songbirds
Moist
to Well
Drained
Sun to Part
Shade
Sweetshrub,
Carolina Allspice*Calycanthus floridus 1,2,3‘Michael Lindsey’6-8 x 6-8 Very fragrant maroon flowers in
late spring
Moist
to Well
Drained
Sun to Part
Shade
Sweet Pepperbush, Clethra*Clethra alnifolia 1,2,3 ‘Ruby Spice’
‘Chattanooga’4-8 x 3-6 Extremely fragrant white or pink
in summer. Yellow fall color
Moist
to Well
Drained
Sun to Part
Shade
Dwarf Burning Bush Euonymous alatus
‘Compactus’1,2,3 6-8 x 6-8Excellent red fall color Well
Drained Sun
Bigleaf Hydrangea Hydrangea
macrophylla 1,2 Many Varieties
Avaliable 4-6 x 4-8
Large clusters of pink or blue
flowers in summer. Flower color
will vary depending on soil pH
Well
Drained
Light to Part
Shade
Oakleaf Hydrangea* Hydrangea quercifolia 1,2 ‘Alice’6-8 x 6-8 Large panicles of white flowers in
summer, excellent fall color
Moist
to Well
Drained
Sun to Part
Shade
Virginia Sweetspire, Itea*Itea virginiana 1,2,3‘Henry’s Garnet’4-6 x 4-8 White flower s in spring.
Excellent fall color
Moist
to Well
Drained
Sun to Part
Shade
Japanese Kerria Kerria japonica 1,2 4-6 x 4-6 Bright yellow flowers in springs,
green stems in winter
Well
Drained
Light to Full
Shade
Double Reeves Spirea Spirea cantoniensis
‘Lanceata’1,2,3 4-6 x 4-6 Abundant white flowers in early
spring
Well
Drained Sun
Vanhoutte Spirea Spirea x vanhouttei 1,2,3 6-8 x 8-10 Abundant white flowers in early
spring
Well
Drained Sun
Possumhaw Viburnum*Viburnum nudum 1,2‘Winterthur’6-8 x 6-8
White flowers in spring followed
by pink and blue berries in fall.
Good fall color
Moist
to Well
Drained
Sun to Part
Shade
‘Mohawk’ Viburnum Viburnum x burkwoodii
‘Mohawk’1,2 6-8 x 6-8 Red buds open to pink blossoms,
very fragrant
Well
Drained
Sun to Part
Shade
Weigela Weigela florida 1,2‘Wine and Roses’4-6 x 4-6 Cherry pink flowers in spring,
purple foliage all season
Well
Drained
Sun to Light
Shade
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-15
Water Use Zones: 1 - High Water Use Zone, 2 - Medium Water Use Zone, 3 - Low Water Use Zone
69 Appendix
LARGE SHRUBS (8 feet and up)
* = Indicates a plant native to the Southeastern USA
Underline = Indicates an extremely drought-tolerant plant
Colors = W-white, Y-yellow, O-orange, B-blue, Pu-purple,
P-pink, R-red, L-lavender
COMMON NAME BOTANICAL NAME
WATER
USE
ZONE
RECOMMENDED
VARIETIES
HEIGHT
X SPREAD
(FT)
ORNAMENTAL
CHARACTERISTICS SOIL EXPOSURE
EVERGREEN SHRUBS
Hedge Bamboo Bambusa multiplex 1,2,315-20 x 6-10
Clump forming bamboo,
interesting textural and vertical
effect
Well Drained Light to Part
Shade
Pindo Palm, Jelly Palm Butia capitata 1,2,3 10-15 x
10-15
Bluish palm with long arching
leaves Well DrainedSun
Elaeagnus Elaeagnus pungens
Elaeagnus x ebbingii 2,3 10-15 x
10-15
Very tough, rapidly growing
shrubs, tolerant of salt spray
Well Drained
to Xeric
Sun to Part
Shade
Chinese Holly Ilex cornuta 1,2,3
‘Burford’
‘Fineline’
‘Needlepoint’
8-15 x 6-12 Dark green glossy leaves, red
berries in fall and winter Well Drained Sun to Light
Shade
Yaupon Holly* Ilex vomitoria 1,2,3 8-15 x 6-10 Translucent red or orange
berries in fall and winter Moist to Xeric Sun to Part
Shade
‘Nellie Stevens’ Holly Ilex x ‘Nellie R. Stevens’1,2,3 15-25 x
10-15 Red Berries in Fall/Winter Moist to Well
Drained
Sun to Part
Shade
Anise Tree*Illicium parviflorum 1,2,3 8-12 x 6-10 Large, olive green leaves.
Vigorous, evergreen shrub
Moist to Well
Drained
Sun to Part
Shade
Chinese Juniper Juniperus chinensis 2,3
‘Spartan’
‘Hetzii
Columnaris’
12-20 x 3-6 Upright, columnar shrubs with
bright green needles
Well Drained
to Xeric Sun
Hollywood Juniper
Juniperus chinensis
‘Kaizuka’ also known as
‘Torulosa’
2,3 15-25 x 8-15
Branches grow in upright
twisting pattern, resulting in
architectural, Japanese effect
Well Drained
to Xeric Sun
Loropetalum Loropetalum chinense 1,2‘Zhuzhou Fuchsia’10-15 x 8-12
Hot pink fringy flower in early
spring, maroon-purple foliage
in summer
Well Drained Sun to Light
Shade
Southern Waxmyrtle* Myrica cerifera 1,2,3 8-15 x 8-15 Tough, fast growing shrub with
olive green foliage Moist to Xeric Sun to Part
Shade
Tea Olive, Osmanthus Osmanthus fragrans
Osmanthus x fortunei 1,2,3 10-15 x
10-15
Dark green foliage,
exceptionally sweetly scented
white flowers in fall
Well Drained Sun to Part
Shade
Chinese Podocarpus Podocarpus macrophyllus
var. maki 1,2 10-15 x 4-6 Dark green, narrow foliage,
upright habit Well Drained Sun to Part
Shade
‘Majestic Beauty’ Indian
Hawthorn
Rhaphiolepis umbellata
‘Majestic Beauty’1,2,3 8-10 x 8-10 Clusters of pink flowers in
early summer Well DrainedSun
Cleyera Ternstroemia gymnanthera 1,2 8-12 x 5-6 Very dark green, shiny leaves,
upright shrub Well Drained Sun to Full
Shade
‘Emerald’ Arborvitae*Thuja occidentalis
‘Emerald’1,2,3 10-15 x 3-4
Bright emerald green foliage
held in vertical sprays, holds
color in winter
Moist to Well
Drained Sun
‘Chindo’ Viburnum Viburnum awabuki
‘Chindo’1,2,3 10-15 x 6-8 Dark green, glossy leaves,
upright habit Well Drained Sun to Part
Shade
DECIDUOUS SHRUBS
Flowering Quince Chaenomeles speciosa 1,2,3 6-10 x 6-10
Early spring flowers in shades
of red, pink, orange and white.
Dwarf varieties are available
Well Drained Sun to Light
Shade
Forsythia Forsythia x intermedia 1,2,3 8-12 x 8-12 Bright yellow flowers in early
spring Well Drained Sun to Light
Shade
Rose of Sharon Hibiscus syriacus 1,2,3
‘Aphrodite’,
‘Diana’, ‘Helene’,
‘Minerva’
8-12 x 6-10 White, purple, or pink flowers
in summer Well DrainedSun
Winterberry*Ilex decidua 1,2‘Winter Red’6-10 x 6-10 Branches covered in red
berries in fall
Moist to Well
Drained
Sun to Light
Shade
Chinese Snowball Bush Viburnum macrocephalum 1,2,3 12-15 x
10-15
Large, globe shaped clusters of
white flowers in spring Well Drained Sun to Light
Shade
Doublefile Viburnum Viburnum plicatum var.
tomentosum 1,2,3 ‘Shasta’
‘Mariesii’8-10 x 8-10 Horizontal branches covered
with white flowers in spring Well Drained Sun to Part
Shade
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-16
Water Use Zones: 1 - High Water Use Zone, 2 - Medium Water Use Zone, 3 - Low Water Use Zone
70 Appendix
SMALL TREES (10-30 feet tall)
* = Indicates a plant native to the Southeastern USA
Underline = Indicates an extremely drought-tolerant plant
Colors = W-white, Y-yellow, O-orange, B-blue, Pu-purple,
P-pink, R-red, L-lavender
COMMON NAME BOTANICAL NAME
WATER
USE
ZONE
RECOMMENDED
VARIETIES
FLOWERS/FRUIT/
FALL COLOR
HEIGHT/
SPREAD (FT)
GROWTH
RATE SOIL EXPOSURE
EVERGREEN TREES
Loquat Eriobotrya japonica 1,2,3
Fragrant W Flowers
in Fall/Winter
Edible Y Fruit in
Spring
15-20/15-20 Medium Well Drained Sun to Light
Shade
Lusterleaf Holly Ilex latifolia 1,2,3 R Berries in Fall/
Winter 20-25/15-20 Medium Well Drained Sun to Part
Shade
American Holly* Ilex opaca 1,2,3 R Berries in Fall/
Winter 20-30/15-20 Slow Moist to Well
Drained
Sun to Part
Shade
Yaupon*Ilex vomitoria 1,2,3
‘Hoskin’s Shadow’
‘Kathy Ann’
“Katherine’
R,O,or Y Berries in
Fall/Winter 15-20/10-15 Medium to
Fast Moist to Xeric Sun to Light
Shade
Topel Holly*Ilex x attenuata 1,2,3
‘Savannah’,
‘Fosters’,
‘Greenleaf’
R Berries in Fall/
Winter 20-30/10-15 Medium Moist to Well
Drained
Sun to Part
Shade
‘Nellie Stevens’ Holly Ilex x ‘Nellie R. Stevens’1,2,3 R Berries in Fall/
Winter 15-25/10-15 Medium Moist to Well
Drained
Sun to Part
Shade
‘Little Gem’ Magnolia*Magnolia grandiflora
‘Little Gem’1,2,3 Fragrant W Flowers
in Summer 20-25/10-15 Slow to
Medium
Moist to Well
Drained
Sun to Part
Shade
Sweet Bay* Magnolia virginiana 1,2 Fragrant W Flowers
in Spring 20-30/10-20 Medium to
Fast
Moist to Well
Drained
Sun to Part
Shade
Waxmyrtle*Myrica cerifera 1,2,3
Blue-Black Berries
on Female Plants in
Winter
10-20/10-20FastMoist to Xeric Sun to Light
Shade
Carolina Cherrylaurel* Prunus caroliniana 1,2,3 W Flowers in Spring20-30/15-20 Fast Well Drained
to Xeric
Sun to Light
Shade
Anise Tree*Illicium parviflorum 1,2,3 Insignificant Flowers
in Spring 10-15/10-15Fast Moist to Well
Drained
Sun to Part
Shade
Palmetto Palm*Sabal palmetto 1,2,3 W Flowers in
Summer 10-30/10-15Slow Moist to Well
Drained
Sun to Part
Shade
DECIDUOUS TREES
Southern Sugar Maple*Acer barbatum 1,2,3 Y,O Fall Color20-25/15-20Medium Moist to Well
Drained
Sun to Light
Shade
Trident Maple Acer buergerianum 1,2,3 Y,O,R Fall Color20-25/10-15 MediumWell DrainedSun
Japanese Maple Acer palmatum 1,2Many AvailableR Fall Color 15-25/10-20SlowWell Drained Sun to Part
Shade
Red Buckeye*Aesculus pavia 1,2 R flowers in Spring10-20/10-15Slow Moist to Well
Drained
Sun to Part
Shade
Serviceberry*Amelanchier arborea 1,2‘Autumn Brilliance’
W flowers in Spring,
R fruit in Summer,
Y,O Fall Color
20-25/10-15Medium Moist to Well
Drained
Sun to Part
Shade
Pawpaw*Asimina triloba 1,2 Edible Fruit in Fall15-20/10-15Medium Moist to Well
Drained
Sun to Part
Shade
Ironwood* Carpinus caroliniana 1,2 Interesting Bark20-30/15-25 Slow Wet to Well
Drained
Sun to Part
Shade
Redbud* Cercis canadensis 1,2,3
‘Forest Pansy’
‘Royal White’
‘Oklahoma’
P or W Flowers in
Spring 20-30/20-25 Medium Moist to Well
Drained
Sun to Part
Shade
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-17
Water Use Zones: 1 - High Water Use Zone, 2 - Medium Water Use Zone, 3 - Low Water Use Zone
71 Appendix
SMALL TREES (10-30 feet tall)
* = Indicates a plant native to the Southeastern USA
Underline = Indicates an extremely drought-tolerant plant
Colors = W-white, Y-yellow, O-orange, B-blue, Pu-purple,
P-pink, R-red, L-lavender
COMMON NAME BOTANICAL NAME
WATER
USE
ZONE
RECOMMENDED
VARIETIES
FLOWERS/FRUIT/
FALL COLOR
HEIGHT/
SPREAD (FT)
GROWTH
RATE SOIL EXPOSURE
Chinese Fringetree Chionanthus retusus 1,2,3 W Flowers in Spring15-25/15-25SlowWell Drained Sun to Part
Shade
Fringe Tree* Chionanthus virginicus 1,2 W Flowers in Spring 10-20/15-20 Slow to
Medium
Moist to Well
Drained
Sun to Part
Shade
Flowering Dogwood*Cornus florida 1,2 ‘Cloud 9’
‘Cherokee Princess’
W Flowers in Spring,
Red Berries in Fall,
Burgundy Autumn
Color
15-25/10-20 Slow to
Medium
Moist to Well
Drained
Sun to Part
Shade
Kousa Dogwood Cornus kousa 1,2 W Flowers in Spring20-30/20-30 Slow to
Medium Well Drained Sun to Light
Shade
Washington Hawthorn*Crataegus phaenopyrum 1,2,3
W Flowers in Spring,
R Fruit in Fall,
Thorny
25-30/20-25Medium Moist to Well
Drained
Sun to Light
Shade
Carolina Silverbell* Halesia tetraptera 1,2,3 W Flowers in Spring20-30/15-20 Medium Moist to Well
Drained
Sun to Part
Shade
Possumhaw* Ilex decidua 1,2,3 ‘Warren’s Red’
‘Council Fire’
R berries in Fall and
Winter 15-20/10-15 Medium Moist to Well
Drained
Sun to Light
Shade
Crape Myrtle Lagerstroemia hybrids 1,2,3
‘Osage’ ‘Sioux’
‘Natchez’
‘Tuskegee’
‘Biloxi’
‘Miami’
‘Lipan’
W, P, L, Pu, or R
Flowers in Summer
depending on Variety.
15-30/10-25
Depending on
Variety
Fast Well DrainedSun
Star Magnolia Magnolia stellata 1,2,3 W or P Flowers in
Spring 15-20/10-15Slow Well Drained Sun to Light
Shade
Saucer Magnolia Magnolia x soulangiana 1,2,3 P to L Flowers in
Spring 20-30/15-25 Medium Well Drained Sun to Light
Shade
Sourwood* Oxydendrum arboreum 1,2,3 W Flowers in
Summer, R Fall Color 25-30/15-20 Slow Well Drained Sun to Part
Shade
‘Okame’ Cherry
‘Dreamcatcher’ Cherry
Prunus campanulata
hybrids 1,2,3 P Flowers in Spring20-30/15-20MediumWell Drained Sun to Light
Shade
Japanese Flowering
Apricot Prunus mume 1,2 P,R, or W Flowers in
Winter 15-25/15-25MediumWell Drained Sun to Light
Shade
Japanese Flowering
Cherry Prunus serrulata 1,2 ‘Kwanzan’P Flowers in Spring20-30/20-30 Medium Well Drained Sun to Light
Shade
Higan Cherry Prunus subhirtella 1,2‘Autumnalis’P Flowers in Spring
and Fall 20-30/15-25MediumWell Drained Sun to Light
Shade
Yoshino Cherry Prunus x yedoensis 1,2 Light P Flowers in
Spring 15-25/15-25 Medium Well Drained Sun to Light
Shade
Japanese Snowbell Styrax japonicus 1,2 ‘Emerald Pagoda’
‘Pink Chimes’
W or P Flowers in
Spring 20-30/20-30MediumWell Drained Sun to Part
Shade
Blackhaw Viburnum*Viburnum prunifolium 1,2
W Flowers in Spring,
Edible Black Fruit
in Fall
10-20/10-15Medium Moist to Well
Drained
Sun to Part
Shade
Chastetree Vitex agnus-castus 1,2,3 Pu,P, or L Flowers in
Summer 15-20/10-15 Medium Well DrainedSun
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-18
Water Use Zones: 1 - High Water Use Zone, 2 - Medium Water Use Zone, 3 - Low Water Use Zone
72 Appendix
LARGE TREES (30 feet and up)
* = Indicates a plant native to the Southeastern USA
Underline = Indicates an extremely drought-tolerant plant
Colors = W-white, Y-yellow, O-orange, B-blue, Pu-purple,
P-pink, R-red, L-lavender
COMMON NAME BOTANICAL NAME WATER
USE ZONE
RECOMMENDED
VARIETIES
ORNAMENTAL
FEATURES
HEIGHT/
SPREAD
(FT)
GROWTH
RATE SOIL EXPOSURE
EVERGREEN TREES
Deodar Cedar Cedrus deodora 1,2,3
Grayish to Bluish
Needles, Interesting
Texture and Form
50-70/50-70MediumWell DrainedSun
Atlantic White Cedar*Chamaecyparis
thyoides 1,2,3 Evergreen Needles40-60/10-20Medium Moist to Well
Drained Sun
Japanese Cedar Cryptomeria japonica 1,2,3 ‘Yoshino’
‘Radicans’Interesting Texture40-60/20-30Medium Moist to Well
Drained Sun
Eastern Red Cedar*Juniperus virginiana 2,3Extremely Tough30-50/10-20Medium Well Drained to
Xeric Sun
Southern Magnolia* Magnolia grandiflora 1,2
‘Alta’, ‘Hasse’,
‘D.D. Blanchard’,
‘Claudia
Wannamaker’
Large, Fragrant W
Flowers in Summer 60-80/30-50 Slow to
Medium Well Drained Sun to Part
Shade
Longleaf Pine* Pinus palustris 1,2,3 Long Needles, Large
Pinecones 50-60/15-20 Medium Well DrainedSun
Loblolly Pine* Pinus taeda 1,2,3 Fast Growth60-90/20-30 Fast Moist to Well
Drained Sun
Laurel Oak*Quercus
hemisphaerica 1,2,3‘Darlington’Small Leaves, Fine
Texture 40-60/30-40MediumWell DrainedSun
Live Oak* Quercus virginiana 1,2,3 Wide Spreading,
Drooping Branches 60-80/60-80 Medium Well Drained to
Xeric Sun
DECIDUOUS TREES
Red Maple* Acer rubrum 1,2 ‘October Glory’
‘Red Sunset’O to R Fall Color40-50/25-35 Medium Moist to Well
Drained
Sun to Light
Shade
River Birch* Betula nigra 1,2,3 ‘Heritage’
‘Dura-heat’White Bark40-70/40-60 Fast Moist to Well
Drained Sun
Sugarberry* Celtis laevigata 1,2,3Smooth Gray Bark60-80/50-70 Medium to
Fast
Moist to Well
Drained Sun
American Beech*Fagus grandifolia 1,2,3 Smooth Gray Bark, Tan
Leaves in Winter 50-70/40-60SlowWell DrainedSun
Green Ash* Fraxinus
pennsylvanica 1,2,3 Y Fall Color50-60/40-50 Fast Moist to Well
Drained Sun
Ginkgo, Maidenhair
Tree Ginkgo biloba 1,2,3 ‘Autumn Gold’Y Fall Color50-70/30-40 Slow Well DrainedSun
Japanese Crape Myrtle Lagerstroemia fauriei 1,2,3 ‘Fantasy’
‘Townhouse’
Dramatic Cinnamon
Bark, Small W Flowers
in Summer
30-40/25-35MediumWell DrainedSun
Dawn Redwood Metasequoia
glyptostroboides 1,2 Ferny Foliage, Rusty
Fall Color 60-100/20-25 Fast Moist to Well
Drained Sun
Black Gum*Nyssa sylvatica 1,2,3 R Fall Color30-50/20-30 Slow to
Medium
Moist to Well
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Water Oak* Quercus nigra 1,2,3 Very Tough50-80/30-60 Medium to
Fast
Moist to Well
Drained Sun
Nutall Oak*Quercus nutallii 1,2,3 R Fall Color40-60/30-50Medium Moist to Well
Drained Sun
Willow Oak* Quercus phellos 1,2,3 Dark Green Foliage,
Fine Texture 80-100/40-50 Medium Moist to Well
Drained Sun
Pond Cypress*Taxodium ascendens 1,2,3 Unusual Texture60-80/15-20Medium Moist to Well
Drained Sun
Bald Cypress* Taxodium distichum 1,2,3 Lacey Foliage50-70/20-30 Medium Wet to Well
Drained Sun
Lacebark Elm Ulmus parvifolia 1,2,3 ‘Bosque’, ‘Allee’,
‘Athena’
Bark Flakes in Patterns
Exposing White,
Brown, Green
40-50/30-40 Fast Well DrainedSun
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-19
Plants for Rain Gardens
Soil conditions in rain gardens alternate between wet and dry, making them tough places
for many plants to grow. The following plants are adapted to these conditions, though
some plants will tolerate more moisture than others. Each plant is marked according to its
flooding tolerance, with 3’s being tolerant of longer flooding, 2’s only tolerating brief
flooding, and 1’s indicate plants that tolerant extended drought once established.
All of these plants are native to the southeastern United States in wetland habitats and
most are readily available at local nurseries. Wetland plants can generally grow well in
moist or well-drained soils, whereas plants adapted to dry soils rarely survive in soggy
conditions. How wet a rain garden stays will vary considerably depending on the site
where it is installed. Rain gardens created on sandy soils will rarely hold water for more
than a few hours. On these sites it is most important to choose plants for their drought
tolerance. Rain gardens created on loamy or silty soils could pond water for 2-4 days (if
your site ponds water for more than 5 days, you should consider creating a wetland). On
these sites, choosing plants tolerant of extended flooding is critical to success.
Remember you are not limited to planting just within the excavated area! Extending
plantings around this area will help the rain garden to blend in with the overall landscape.
Any plants adapted to the site conditions can be used outside of the excavated area.
Large Trees (over 30’ tall)
Deciduous
Red Maple (2) – Acer rubrum
River Birch (1,3) – Betula nigra
Green Ash (3) – Fraxinux pennsylvanica
Black Gum (2) – Nyssa sylvatica
Willow Oak (1,2) – Quercus phellos
Willows (3) – Salix species
Bald Cypress (1,3) – Taxodium ascendens
Nutall Oak (1,2) – Quercus nuttalii
Evergreen
Atlantic White Cedar (1,3) – Chamaecyparis thyoides
Southern Magnolia (1,2) – Magnolia grandiflora
Longleaf Pine (1,2) – Pinus palustris
Swamp Laurel Oak (3) – Quercus laurifolia
Small Trees (under 30’ tall)
Deciduous
Redbud (1,2) – Cercis canadensis
Fringe Tree (2) – Chionanthus virginicus
Washington Hawthorn (3) – Crataegus phaenopyrum
Possumhaw (1,3) - Ilex decidua
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-20
Evergreen
American Holly (1,2) – Ilex opaca
Red Cedar (1,2) – Juniperus virginiana
Sweet Bay (3) – Magnolia virginiana
Red Bay (1,2) – Persea borbonia
Evergreen shrubs that can be grown as small trees include Yaupon, Wax Myrtle, and
Anise Shrub.
Shrubs
Deciduous
Chokeberry (1,3) – Aronia arbutifolia
Beautyberry (2) – Callicarpa americana
Sweet Shrub (2) – Calycanthus floridus
Buttonbush (3) – Cephalanthus occidentalis
Pepperbush (2) – Clethra alnifolia
Fothergilla (2) – Fothergilla gardenii
Winterberry (3) – Ilex verticillata
Virginia Willow (3) – Itea virginica
Possumhaw (3) – Viburnum nudum
Evergreen
Inkberry (2) – Ilex glabra
Yaupon (1,2) – Ilex vomitoria
Anise Shrub (1,2) – Illicium parviflorum
Wax Myrtle (1,2) – Myrica cerifera
Dwarf Palmetto (3) – Sabal minor
Perennials
Blue Star (3) – Amsonia tabernaemontana
Swamp Milkweed (3) – Asclepias incarnata
Climbing Aster (3) – Aster carolinianus
False Indigo (1,2) – Baptisia species
Boltonia (3) – Boltonia asteriodes
Turtlehead (3) – Chelone glabra
Tickseed (1,2) – Coreopsis lanceolata
Joe Pye Weed (3) – Eupatorium dubium
Swamp Sunflower (3) – Helianthus angustifolius
Swamp Mallow (3) – Hibiscus moscheutos
Texas Star (3) – Hibiscus coccineus
Seashore Mallow (3) – Kosteletskya virginica
Gayfeather (2) – Liatris spicata
Cardinal Flower (3) – Lobelia cardinalis
Garden Phlox (2) – Phlox paniculata
Rudbeckia (1,2) – Rudbeckia fulgida
Green Headed Coneflower (3) – Rudbeckia laciniata
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-21
Goldenrod (3) – Solidago rugosa
Stoke’s Aster (2) – Stokesia laevis
Ironweed (3) – Vernonia novaboracensis
Verbena (1,2) – Verbena canadensis
Ornamental Grasses
River Oats (1,3) – Chasmanthium latifolium
Muhly Grass (1,2) – Muhlenbergia capillaris
Panic Grass (1,3) – Panicum virgatum
Indiangrass (1,2) – Sorghastrum nutans
Non-native perennials and ornamental grasses suitable for rain gardens include: Liriope
(1,2) (Liriope muscarii and L. spicata), Siberian Iris (2) (Iris sibirica), Daylily (1,2)
(Hemerocallis hybrids), Rain Lilies (3) (Zephyranthes species), Crinum Lilies (3)
(Crinum species), and Maiden Grass (1,2) (Miscanthus cultivars).
1 = Plants that once established* can withstand considerable drought ( 3-4 weeks without
rainfall)
2 = Plants that grow best in moist to average soils and will only tolerate short periods (1-
2 days) of flooding.
3 = Plants that will tolerate longer periods of flooding (3-5 days), but will also grow in
moist to average soils.
*Establishment usually takes 1-2 years for trees and shrubs and 1 year for perennials.
Prepared by:
Charlotte Glen, Urban Horticulture Agent – Arboretum Coordinator
North Carolina Cooperative Extension – New Hanover County Center
Distributed in furtherance of the acts of Congress of May 8 and June 30,1914. North Carolina State University and North Carolina
A&T State University commit themselves to positive action to secure equal opportunity regardless of race, color, creed, national
origin, religion, sex, age, or disability. In addition, the two Universities welcome all persons without regard to sexual orientation.
North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments
cooperating.
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-22
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Development Guidance Manual
Ap
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II
-
3
0
NC STATE UNIVERSITY
North Carolina Cooperative Extension
SALT TOLERANT PLANTS
Recommended for New Hanover County Landscapes
New Hanover County Cooperative Extension Urban Horticulture Factsheet 14
Coastal Challenges
Plants growing at the beach are subjected to environmental conditions much
different than those planted further inland. Factors such as blowing sand, poor soils,
high temperatures, and excessive drainage all influence how well plants perform in
coastal landscapes, though the most significant effect on growth is salt spray. Most
plants will not tolerate salt accumulating on their foliage, making plant selection for beachfront
landscapes particularly challenging.
Salt Spray
Salt spray is created when waves break on the beach, throwing tiny droplets of salty water into the air.
On-shore breezes blow this salt laden air landward where it comes in contact with plant foliage. The
amount of salt spray plants receive varies depending on their proximity to the beachfront, creating
different vegetation zones as one gets further away from the beachfront. The most salt-tolerant species
survive in the frontal dune area. As distance away from the ocean increases, the level of salt spray
decreases, allowing plants with less salt tolerance to survive.
Natural Protection
The impact of salt spray on plants can be lessened by physically blocking salt laden winds. This occurs
naturally in the maritime forest, where beachfront plants protect landward species by creating a layer of
foliage that blocks salt spray. It is easy to see this effect on the ocean side of maritime forest plants,
which are “sheared” by salt spray, causing them to grow at a slant away from the oceanfront. Removal
of this “shear zone” during construction opens holes that allow salt spray to blow through, damaging
plants that were previously protected.
Manmade Protection
Buildings, fences and other structures that block salt laden winds also allow plants with less salt
tolerance to grow landward of a structure. Homes near the ocean will have two distinct
micro-environments based on salt spray. The side of the house facing the ocean will require landscape
plants with high salt tolerance. The landscape area on the landward side that is protected from salt
spray may be planted with species having little or no salt tolerance depending upon the degree they are
protected from blowing winds. Frequent overhead irrigation rinses salt accumulations off plant foliage,
reducing the impact to less salt-tolerant species.
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-31
Landscaping at the Beach
The following plant lists have been compiled to assist homeowners and landscape professionals to
choose appropriate plants for coastal landscapes. The lists are divided by plant type (trees, shrubs,
vines, groundcovers, etc.) and three levels of salt tolerance (high, moderate, slight) and have been
compiled from the references listed on the last page as well as personal observation.
Properties within at least one-eighth of a mile of the oceanfront should be landscaped with plants
known to have some level of salt tolerance. Properties along or near brackish water estuaries should
also be landscaped with plants possessing some degree of salt tolerance, though not necessarily as high
as those on the oceanfront. During hurricanes and coastal storms, salt laden winds extend further inland
than normal. This causes damage to plants that are not salt tolerant, though they generally recover
following the storm event.
Other factors to take into consideration when choosing plants for coastal landscapes include soil pH,
which can be determined by sending a soil sample to the NC Department of Agriculture (boxes, forms
and instructions are available from your local Cooperative Extension office); sun and wind exposure;
and soil type. Incorporating composted organic matter into the soil will greatly increase the soil’s
ability to hold moisture and improve plant growth. Applying two to four inches of mulch will also help
plant growth by reducing soil temperature and conserving moisture. Organic mulches such as pine
straw or shredded bark mulches decompose over time, adding to the organic matter content of the soil.
Dune Preservation and Vegetation Restoration:
Preservation of the natural dune system and its native vegetation is critical to protecting both natural
and manmade coastal landscapes. More information about the natural dune system and restoring its
vegetation is available online as follows:
• Restoration and Management of Coastal Dune Vegetation, from the NCSU Soil Science
Department: http://www.soil.ncsu.edu/lockers/Broome_S/ram.html
• The Dune Book, by David Nash and Spencer Rogers, available from NC Sea Grant at:
http://www.ncseagrant.org/files/dune_booklet.pdf
2
Table of Contents:
Key . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Small Trees . . . . . . . . . . . . . . . . . . . . 4-5
Large Trees . . . . . . . . . . . . . . . . . . . . 5-6
Shrubs . . . . . . . . . . . . . . . . . . . . . . . . 6-9
Vines . . . . . . . . . . . . . . . . . . . . . . . . . 9
Palms . . . . . . . . . . . . . . . . . . . . . . . . . 9
Ornamental Grasses . . . . . . . . . . . . . . 10
Perennials . . . . . . . . . . . . . . . . . . . . . . 10-12
Turf Grasses . . . . . . . . . . . . . . . . . . . . 12
Annuals . . . . . . . . . . . . . . . . . . . . . . . 13
Groundcovers . . . . . . . . . . . . . . . . . . . 14
References . . . . . . . . . . . . . . . . . . . . . 15
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-32
Key to Plant Lists
Highly Salt Tolerant
Plants tolerant of the direct salt spray such as that received along dunes and immediately adjacent to the
oceanfront.
Moderately Salt Tolerant
Plants tolerant of moderate levels of salt spray, such as that received in landscapes adjacent to the beach front,
but which are sheltered by other plants, structures or natural dunes.
Slightly Salt Tolerant
Plants with the lowest level of tolerance to salt spray. These plants should be used only in areas receiving some
protection from direct salt spray, either from a building or other vegetation. In areas that are completely
sheltered, plants with no known salt tolerance can be grown.
Underlined Plants
Plants that are extremely tolerant of growing in sandy, poor soils and display extreme drought tolerance once
established.
* Native
Plants that are native to the coastal plains of the southeast USA, ranging from New Jersey south along the
Atlantic Seaboard through Florida and along the Gulf Coast to East Texas.
‘Cultivar Names’
Cultivar names are written in single quotes. Cultivars, or varieties, are plants that have been selected because
they display desirable characteristics such as larger flowers, different color foliage, more compact growth, etc.
Cultivars are propagated vegetatively (cuttings, division, tissue culture) so they are genetically identical to
each other.
Evergreen/Deciduous
E or D refers to whether a plant is evergreen (retains its foliage all year) or deciduous (sheds its foliage each
fall and grows new leaves in spring).
Exposure
Refers to the amount of sunlight a site receives as follows:
• Full sun indicates a site that receives at least 8hrs of direct sun each day.
• Light Shade indicates a site that is shaded less than half of the day by a light high shade such as that cast
by pines.
• Part Shade indicates a site that is shaded for half the day by a dense shade like that cast by buildings or
shade trees.
• Full Shade indicates a site that is in shade all day.
Soil
Refers to soil condition at the site as follows:
• Wet indicates a site that stays moist most of the time and receives periodic flooding.
• Moist indicates a site that is moist most of the time with brief (less than 12hrs) periods of standing water.
• Well Drained indicates a site where water drains from the surface and rarely stands.
• Xeric indicates a site that is extremely dry and sandy with very little ability to hold water.
3
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-33
SMALL TREES, 10’ – 30’ Tall
Common Name Botanical Name
Height x
Spread (ft)
Evergreen/
Deciduous Soil Exposure
Yaupon* Ilex vomitoria 15-20 x 10-15 E Moist to Xeric Sun to Light Shade
Waxmyrtle* Myrica cerifera 10-20 x 10-20 E Moist to Xeric Sun to Light Shade
Devilwood* Osmanthus ameri-
canus 15-25 x 10-20 E Moist to Well
Drained Sun to Light Shade
Redbay* Persea borbonia 20-30 x 15-25 E Moist to Xeric Sun to Light Shade
Japanese Black Pine Pinus thunbergii 20-40 x 15-25 E Well Drained to
Xeric Sun
Chinese Podocarpus Podocarpus macro-
phyllus ‘Maki’ 20-30 x 10-15 E Well Drained Sun to Part Shade
Sand Live Oak* Quercus geminata 20-30 x 30-40 E Well Drained to
Xeric Sun
Small Trees—Moderately Salt Tolerant
Common Name Botanical Name
Height x
Spread (ft)
Evergreen/
Deciduous Soil Exposure
Trident Maple Acer buergerianum 20-25 x 10-15 D Well Drained Sun
Arizona Cypress Cupressus arizonica 10-30 x 8-20 E Well Drained Sun
Italian Cypress Cupressus sempervirens 20-30 x 4-8 E Well Drained Sun
Loquat Eriobotrya japonica 15-20 x 15-20 E Well Drained Sun to Light
Shade
Eucalyptus Eucalyptus cinerea 15-30 x 10-20 E Well Drained Sun
Dahoon Holly* Ilex cassine 20-30 x 8-15 E Moist to Well
Drained Sun
Myrtle Leaf Holly* Ilex cassine variety myrtifolia 10-20 x 8-12 E Well Drained Sun
American Holly* Ilex opaca 20-30 x 15-20 E Moist to Well
Drained
Sun to Part
Shade
Foster’s Holly* Ilex x attenuata ‘Fosters’ 20-30 x 10-15 E Moist to Well
Drained
Sun to Part
Shade
‘Nellie Stevens’ Holly Ilex x 'Nellie R. Stevens' 15-25 x 10-15 E Moist to Well
Drained
Sun to Part
Shade
Hollywood Juniper
Juniperus chinensis
‘Kaizuka’ also known as
‘Torulosa’
15-25 x 8-15 E Well Drained
to Xeric Sun
Crape Myrtle Lagerstroemia hybrids –
many varieties available
15-30 x 10-25
Depending on
Variety
D Well Drained Sun
‘Little Gem’
Magnolia*
Magnolia grandiflora
‘Little Gem’ 20-25 x 10-15 E Moist to Well
Drained
Sun to Part
Shade
Sweet Bay* Magnolia virginiana 20-30 x 10-20 Semi-E Moist to Well
Drained
Sun to Part
Shade
4
Small Trees—Highly Salt Tolerant
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-34
Small Trees—Moderately Salt Tolerant, continued
Common Name Botanical Name
Height x
Spread (ft)
Evergreen/
Deciduous Soil Exposure
Sourwood* Oxydendrum arboreum 25-30 x 15-20 D Well Drained Sun to Part
Shade
Carolina
Cherrylaurel* Prunus caroliniana 20-30 x 15-20 E Well Drained
to Xeric
Sun to Light
Shade
Japanese Snowbell Styrax japonicus 20-30 x 20-30 D Well Drained Sun to Part
Shade
Tamarix Tamarix ramosissima 10-20 x 8-12 D Well Drained
to Xeric Sun
Chastetree Vitex agnus-castus 15-20 x 10-15 D Well Drained Sun
LARGE TREES, Over 30’
Common Name Botanical Name
Height x
Spread (ft)
Evergreen/
Deciduous Soil Exposure
Thornless Honeylocust* Gleditsia triacanthos 40-60 x 20-40 D Well Drained Sun
Eastern Red Cedar* Juniperus virginiana 30-50 x 10-20 E Well Drained
to Xeric Sun
Southern Magnolia* Magnolia grandiflora 60-80 x 30-50 E Well Drained Sun to Part Shade
Willow Oak* Quercus phellos 80-100 x 40-50 D Moist to Well
Drained Sun
Live Oak* Quercus virginiana 60-80 x 60-80 E Well Drained
to Xeric Sun
Large Trees - Moderately Salt Tolerant
Common Name Botanical Name
Height x
Spread (ft)
Evergreen/
Deciduous Soil Exposure
River Birch* Betula nigra 40-70 x 40-60 D Moist to Well
Drained Sun
Atlas Cedar Cedrus atlantica 40-60 x 30-40 E Well Drained Sun
Deodar Cedar Cedrus deodora 50-70 x 50-70 E Well Drained Sun
Sugarberry* Celtis laevigata 60-80 x 50-70 D Moist to Well
Drained Sun
Ginkgo, Maidenhair Tree Ginkgo biloba 50-70 x 30-40 D Well Drained Sun
Black Gum* Nyssa sylvatica 30-50 x 20-30 D Moist to Well
Drained Sun
Laurel Oak* Quercus hemi-
sphaerica 40-60 x 30-40 E Moist to Well
Drained Sun
Water Oak* Quercus nigra 50-80 x 30-60 D Moist to Well
Drained Sun
5
Large Trees—Highly Salt Tolerant
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-35
Common Name Botanical Name
Height x
Spread (ft)
Evergreen/
Deciduous Soil Exposure
Shumard Oak* Quercus shumardii 40-60 x 40-60 D Moist to Well
Drained Sun
Black Locust* Robinia pseudoacacia 30-50 x 20-35 D Moist to Xeric Sun
Lacebark Elm Ulmus parvifolia 40-50 x 30-40 D Well Drained Sun
Large Trees—Moderately Salt Tolerant, continued
Large Trees—Slightly Salt Tolerant
Common Name Botanical Name
Height x
Spread (ft)
Evergreen/
Deciduous Soil Exposure
Japanese Cedar Cryptomeria japonica 40-60 x 20-30 E Moist to Well
Drained Sun
American Beech* Fagus grandifolia 50-70 x 40-60 D Well Drained Sun
Baldcypress* Taxodium distichum 50-70 x 20-30 D Wet to Well
Drained Sun
SHRUBS
Common Name Botanical Name
Height x
Spread (ft.)
Evergreen/
Deciduous Soil Exposure
Century Plant Agave americana 5-7 x 8-12 E Well Drained to
Xeric Sun
Elaeagnus Elaeagnus pungens
Elaeagnus x ebbingii 10-15 x 10-15 E Well Drained to
Xeric
Sun to Part
Shade
Dwarf Yaupon Holly* Ilex vomitoria ‘Nana’,
‘Bordeaux’, ‘Schilling’s’ 3-4 x 4-5 E Well Drained to
Xeric
Sun to Part
Shade
Oleander Nerium oleander 6-10 x 4-8 E Well Drained to
Xeric Sun
New Zealand Flax Phormium tenax 4-6 x 4-6 E Well Drained Sun
Pittosporum Pittosporum tobira 6-8 x 6-8 E Well Drained to
Xeric
Sun to Part
Shade
Dwarf Pittosporum
Pittosporum tobira
‘Wheeler’s Dwarf’,
‘Mojo’, ‘Cream de Mint’
3-4 x 3-5 E Well Drained to
Xeric
Sun to Part
Shade
‘Majestic Beauty’ Indian
Hawthorn
Rhaphiolepis umbellata
‘Majestic Beauty’ 8-10 x 8-10 E Well Drained Sun
Rugosa Rose Rosa rugosa 3-5 x 4-6 D Well Drained Sun
Rosemary Rosmarinus officinalis 3-6 x 3-6 E Well Drained to
Xeric Sun
Butcher’s Broom Ruscus aculeatus 2-3 x 2-3 E Well Drained Part Shade to
Shade
Sandwanka Viburnum Viburnum suspensum 4-8 x 4-8 E Well Drained to
Xeric Sun
Yucca* Yucca gloriosa
Yucca aloifolia 6-8 x 4-8 E Well Drained to
Xeric Sun
6
Shrubs—Highly Salt Tolerant
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-36
Shrubs—Moderately Salt Tolerant
Common Name Botanical Name
Height x
Spread (ft.)
Evergreen/
Deciduous Soil Exposure
Japanese Aucuba Aucuba japonica 5-8 x 4-6 E Well Drained Part to Full
Shade
Dwarf Aucuba Aucuba japonica ‘Nana’ 3-4 x 2-3 E Well Drained Part to Full
Shade
Hedge Bamboo Bambusa multiplex 15-20 x 6-10 E Well Drained Light to Part
Shade
Wintergreen Barberry Berberis julianae 6-8 x 6-8 E Well Drained Sun
Bottlebrush Callistemon rigidus 5-6 x 5-6 E Well Drained Sun
Flowering Quince Chaenomeles speciosa 6-10 x 6-10 D Well Drained Sun to Light
Shade
Sweet Pepperbush,
Clethra* Clethra alnifolia 4-8 x 3-6 D Moist to Well
Drained
Sun to Part
Shade
Dwarf Sweet Pepperbush,
Clethra*
Clethra alnifolia
‘Hummingbird’, ‘White
Doves’, ‘Sixteen Candles’
2-3 x 4-6 D Moist to Well
Drained
Sun to Part
Shade
Fragrant Daphne Daphne odora 2-3 x 2-3 E Well Drained Part Shade
Japanese Euonymus Euonymus japonicus 4-10 x 3-6 E Well Drained Sun to Shade
Fatsia Fatsia japonica 6-8 x 6-8 E Well Drained Part to Full
Shade
Pineapple Guava Feijoa sellowiana 6-10 x 5-8 E Well Drained Sun
Forsythia Forsythia x intermedia 8-12 x 8-12 D Well Drained Sun to Light
Shade
Rose of Sharon Hibiscus syriacus 8-12 x 6-10 D Well Drained Sun
Bigleaf Hydrangea Hydrangea macrophylla
Many varieties available 4-6 x 4-8 D Well Drained Light to Part
Shade
‘Carissa’ Holly Ilex cornuta ‘Carissa’ 3-4 x 4-5 E Well Drained Sun to Part
Shade
‘Rotunda’ Holly Ilex cornuta ‘Rotunda’ 3-4 x 4-5 E Well Drained Sun to Part
Shade
‘Needlepoint’ Holly Ilex cornuta ‘Needlepoint’ 8-15 x 6-12 E Well Drained Sun to Light
Shade
Inkerry Holly* Ilex glabra 5-8 x 5-8 E Moist to Well
Drained
Sun to Light
Shade
Chinese Juniper Juniperus chinensis
Many varieties available
2-12 x 4-8 de-
pending on vari-
ety
E Well Drained
to Xeric Sun
Texas Sage Leucophyllum frutescens 4-6 x 4-6 E Well Drained Sun
Japanese Privet Ligustrum japonicum 6-12 x 5-10 E Well Drained Sun to Light
Shade
Leatherleaf Mahonia Mahonia bealei 6-8 x 3-4 E Well Drained Part to Full
Shade
Firethorn, Pyracantha Pyracantha coccinea 6-10 x 4-8 E Well Drained Sun to Light
Shade
Indian Hawthorne Rhaphiolepis indica 2-4 x 3-5 E Well Drained Sun
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New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-37
Shrubs—Moderately Salt Tolerant, continued
Common Name Botanical Name
Height x
Spread (ft.)
Evergreen/
Deciduous Soil Exposure
Azaleas -
Southern Indica Varieties
Rhododendron
‘Formosa’, ‘G.G. Gerbing’,
‘George Tabor’
6-8 x 6-8 E Well Drained Light to Part
Shade
Satsuki Azaleas Rhododendron Satsuki
Varieties, ‘Gumpo’ Series 2-3 x 3-4 E Well Drained Light to Part
Shade
Stinking Viburnum Viburnum odoratissimum 8-15 x 6-12 E Well Drained Sun to Part
Shade
Adam’s Needle Yucca* Yucca filamentosa 2-4 x 2-4 E Well Drained
to Xeric Sun
Shrubs—Slightly Salt Tolerant
Common Name Botanical Name
Height x
Spread (ft)
Evergreen/
Deciduous Soil Exposure
Abelia Abelia x grandiflora 4-8 x 4-6 E Well Drained Sun to Part
Shade
‘Brilliant’ Chokeberry* Aronia arbutifolia
‘Brilliantissima’ 6-8 x 6-8 D Moist to Well
Drained
Sun to Light
Shade
Japanese Barberry Berberis thunbergii 2-3 x 3-4 D Well Drained Sun to Light
Shade
Butterfly Bush Buddleia davidii 4-8 x 4-6 D Well Drained Sun to Light
Shade
American Beautyberry* Callicarpa americana 4-6 x 4-6 D Moist to Well
Drained
Sun to Part
Shade
Japanese Camellia Camellia japonica
Many varieties available 6-12 x 4-8 E Well Drained Light to Part
Shade
Sasanqua Camellia Camellia sasanqua 6-10 x 4-8 E Well Drained Light to Part
Shade
Gardenia Gardenia jasminoides 4-8 x 4-8 E Well Drained Sun to Light
Shade
Winterberry* Ilex verticillata 6-10 x 6-10 D Moist to Well
Drained
Sun to Light
Shade
Banana Shrub Michelia figo 6-8 x 6-8 E Well Drained Sun to Part
Shade
Nandina, Heavenly
Bamboo Nandina domestica 5-8 x 3-4 E Well Drained Sun to Part
Shade
Dwarf Nandina
Nandina domestica
‘Firepower’, ‘Moon Bay’,
‘Harbor Belle’
2-4 x 1-3 E Well Drained Sun to Part
Shade
Tea Olive, Osmanthus Osmanthus fragrans
Osmanthus x fortunei 10-15 x 10-15 E Well Drained Sun to Part
Shade
Double Reeves Spirea Spirea cantoniensis
‘Lanceata’ 4-6 x 4-6 D Well Drained Sun
Cleyera Ternstroemia gymnanthera 8-12 x 5-6 E Well Drained Sun to Full
Shade
Walter’s Viburnum* Viburnum obovatum 4-12 x 4-10 E Moist to Well
Drained Sun
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New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-38
Common Name Botanical Name
Height x
Spread (ft)
Evergreen/
Deciduous Soil Exposure
Tinus Viburnum,
Laurustinus Viburnum tinus 5-7 x 5-7 E Well Drained Sun to Part
Shade
Weigela Weigela florida 4-6 x 4-6 D Well Drained Sun to Light
Shade
Shrubs—Slightly Salt Tolerant, continued
VINES
Common Name Botanical Name Height
Evergreen/
Deciduous Soil Exposure
Climbing Fig Ficus pumila 30’+ E Well Drained Sun to Shade
Carolina Jessamine* Gelsemium sempervirens 10’-20’ E Moist to Well Drained Sun to Pt. Shade
English Ivy Hedera helix 50’+ E Well Drained Sun to Shade
Coral Honeysuckle* Lonicera sempervirens 10’-20’ E Moist to Well Drained Sun to Pt. Shade
Goldflame Honeysuckle Lonicera x heckrottii 10’-20’ E Moist to Well Drained Sun to Lt. Shade
Virginia Creeper* Parthenocissus quinquefolia 30’+ D Moist to Well Drained Sun to Shade
Lady Banks’ Rose Rosa banksiase ‘Lutea’ 20’ D Well Drained Sun to Lt. Shade
Confederate Jasmine Trachelospermum
jasminoides 15’ E Well Drained Sun
Fatshedera X Fatshedera lizei 8’ E Moist to Well Drained Pt. Shade to Shade
PALMS
Common Name
Botanical Name Height x Spread (ft.) Soil Exposure
Dwarf Palmetto* Sabal minor 4-6 x 4-6 Moist to Well Drained Sun to Part Shade
Cabbage Palm, Palmetto* Sabal palmetto 10-20 x 10-15 Well Drained Sun
Saw Palmetto* Serenoa repens 3-5 x 4-8 Moist to Well Drained Sun to Part Shade
Palms—Moderately Salt Tolerant
Common Name
Botanical Name Height x Spread (ft.) Soil Exposure
Pindo Palm, Jelly Palm Butia capitata 10-15 x 10-15 Well Drained Sun
Mediterranean Fan Palm Chamaerops humilis 5-6 x 5-6 Well Drained Sun to Light Shade
King Sago
Emporer Sago
Cycas revoluta
Cycas taitungensis
4-8 x 6
4-6 x 10 Well Drained Sun to Part Shade
Needle Palm* Rhapidophyllum hystrix 5-10 x 5-10 Well Drained Sun to Part Shade
Chinese Windmill Palm Trachycarpus fortunei 10-20 x 6-12 Well Drained Sun to Part Shade
9
Vines—Moderately Salt Tolerant
Palms—Highly Salt Tolerant
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-39
ORNAMENTAL GRASSES
Common Name
Botanical Name Height x Spread Soil Conditions
Exposure
Pampas Grass Cortaderia selloeana 8’ x 6’ Moist to Well Drained Full Sun
Lyme Grass Leymus arenarius 2’ x 4’ Well Drained to Xeric Full Sun
Maiden Grass Miscanthus sinensis 4’-8’ x 3’-6’ Moist to Well Drained Full Sun
Muhly Grass* Muhlenbergia capillaris 3’ x 3’ Well Drained to Xeric Full Sun
Bitter Panicum* Panicum amarum 3’ x 2’ Well Drained to Xeric Full Sun
Sand Cordgrass* Spartina bakeri 3’ x 3’ Well Drained Full Sun
Ornamental Grass—Slightly Salt Tolerant
Common Name
Botanical Name Height x Spread Soil Conditions
Exposure
Panic Grass* Panicum virgatum 4’-8’ x 2’-4’ Moist to Well Drained Full Sun
Fountain Grass Pennisetum alopecuriodes 3’ x 2’ Moist to Well Drained Full Sun
PERENNIALS
Common Name Botanical Name
Height x
Spread (ft.) Exposure Soil
Blanket Flower, Gaillardia* Gaillardia pulchella 1-2 x 1-2 Sun Well Drained to Xeric
Daylily Hemerocallis species
and hybrids 1-4 x 1-4 Sun/Partial
Shade Moist to Well Drained
Lantana Lantana camara
Lantana montevidensis 2-4 x 3-6 Sun Well Drained to Xeric
Prickly Pear Cactus* Opuntia compressa 1-2 x 2-3 Sun Well Drained to Xeric
Lavender Cotton Santolina
chamaecyparissus 1-2 x 2 Sun Well Drained
Seaside Goldenrod* Solidago sempervirens 4-6 x 3-4 Sun Well Drained to Xeric
Perennials—Moderately Salt Tolerant
Common Name Botanical Name
Height x
Spread (ft.) Exposure Soil
Fern Leaf Yarrow Achillea filipendulina 3-4 x 2-3 Sun Well Drained
Common Yarrow Achillea millefolium 2-3 x 3 Sun Well Drained to Xeric
Agapanthus Agapanthus africanus 2-4 x 2 Sun to Part
Shade Well Drained
10
Ornamental Grasses—Highly Salt Tolerant
Perennials—Highly Salt Tolerant
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-40
Common Name Botanical Name
Height x
Spread (ft.) Exposure Soil
Sea Thrift Armeria maritima 1 x 1 Sun to Part
Shade Well Drained
Butterfly Weed* Ascelpias tuberosa 2-3 x 2-3 Sun Well Drained to Xeric
Asparagus Fern Asparagus densiflorus
‘Sprengeri’ 2-3 x 2-3 Sun to Part
Shade Well Drained
Crinum Lily Crinum species and hybrids 2-4 x 2-4 Sun to Part
Shade Moist to Well Drained
Mexican Heather Cuphea hyssopifolia 1 x 2 Sun Well Drained
Hardy Ice Plant Delosperma cooperi
Delosperma nubigenum 6” x 1-2 Sun Well Drained to Xeric
Cheddar Pinks, Dianthus Dianthus gratianopolitanus 6”-1 x 1-2 Sun Well Drained to Xeric
Hummingbird Plant Dicliptera suberecta 1-2 x 3-4 Sun Well Drained
Firebush* Hamelia patens 3-5 x 3-4 Sun Well Drained
Hardy Ginger Lily Hedychium species and hybrids 4-6 x 3-5 Sun to Part
Shade Moist to Well Drained
Candytuft Iberis sempervirens 6”-1 x 2-3 Sun Well Drained
Red False Aloe Hesperaloe parviflora 3-4 x 2-4 Sun Well Drained to Xeric
Turk’s Cap* Malvaviscus drummondii 3-4 x 3-4 Sun Well Drained
Nippon Daisy Nipponanthemum nipponicum 2-3 x 2-3 Sun Well Drained
Seashore Mallow* Kosteletzkya virginica 4-6 x 3-4 Sun to Part
Shade Moist to Well Drained
Firecracker Plant Russelia equisetiformus 3-4 x 3-4 Sun Well Drained
Purple Heart Setcreasia pallida 1 x 2 Sun to Light
Shade Well Drained
Hen and Chicks Sempervivum tectorum 6”-1 x 1 Sun Well Drained to Xeric
Society Garlic Tulbughia violacea 1 x 1 Sun Well Drained
Perennials—Moderately Salt Tolerant, continued
Perennials—Slightly Salt Tolerant
Common Name Botanical Name
Height x
Spread (ft.) Exposure Soil
Angel’s Trumpets Brugmansia 4-6 x 4-6 Sun to Part Shade Well Drained
Canna Lily Canna hybrids 4-8 x 2-6 Sun to Part Shade Moist to Well Drained
Holly Fern Cyrtomium falcatum 1-2 x 1-2 Part Shade to Shade Moist to Well Drained
Golden Dewdrop Duranta erecta 3-5 x 3-5 Sun to Part Shade Well Drained
Purple Coneflower* Echinacea purpurea 3-5 x 2-4 Sun to Part Shade Well Drained
Hardy Hibiscus*
Hibiscus moscheutos
Hibiscus coccineus
Hibiscus hybrids
4-6 x 4-6 Sun to Light Shade Moist to Well Drained
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New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-41
Common Name Botanical Name
Height x
Spread (ft.) Exposure Soil
Hosta Hosta species and hybrids 1-3 x 1-3 Part to Full Shade Well Drained
Red Hot Poker Kniphofia species and hy-
brids 2-4 x 1-3 Sun Well Drained
Daffodil Narcissus 1 x 1 Sun to Part Shade Well Drained
Leadwort, Blue jasmine Plumbago auriculata 3-4 x 3-4 Sun Well Drained
Dwarf Mexican Petunia Ruellia brittoniana ‘Katie’ 6” x 1 Sun to Light Shade Well Drained
Autumn Sage* Salvia greggii
Salvia microphylla 2-4 x 2-4 Sun to Light Shade Well Drained
Princess Flower Tibouchina urvilleana 3-5 x 3-5 Sun to Light Shade Well Drained
Common Thyme Thymus vulgaris 1 x 1 Sun Well Drained
Verbena* Verbena canadensis 1 x 2-3 Sun to Light Shade Moist to Well Drained
Perennials—Slightly Salt Tolerant, continued
TURF GRASSES
Common
Name
Salt
Tolerance
Drought
Tolerance
Shade
Tolerance
Maintenance
Level
Fertilizer
Requirements
Wear
Tolerance
Centipede
Slight – high soil pH
often a problem for
centipede in coastal sites
Moderate Poor Low Very Low Good
St.
Augustine Moderate Low Very Good Low - Moderate Moderate Good
Zoysia High High Good Moderate Moderate Excellent
Common
Bermuda High High Very Poor High High Excellent
Hybrid
Bermuda High High Very Poor Very High Very High Excellent
Seashore
Paspalum
Very High – tolerates
irrigation w/ saline water Moderate Poor Moderate Moderate Good
For more information about Seashore Paspalum see the following online factsheet:
Seashore Paspalum for Florida Lawns— http://edis.ifas.ufl.edu/EP059
For complete information about turf grass care and selection, see the individual lawn maintenance calendars and other
publications available from North Carolina Cooperative Extension at your local NC Cooperative Extension office or the
NCSU TurfFiles website: www.turffiles.ncsu.edu
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New Hanover County - City of Wilmington Low Impact Development Guidance Manual
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Drought Tolerant Perennials
The following drought tolerant perennials perform well in sandy, poor soils. Though they are not known to tolerate salt
spray, they are recommended for coastal gardens when planted in sites sheltered from salt spray.
Common Name Scientific Name ‘Blue Fortune’ Hyssop Agastache x ‘Blue Fortune’
Arkansas Blue Star* Amsonia hubrichtii
Texas Firecracker* Anisacanthus wrightii
‘Powis Castle’ Artemisia Artimisia x ‘Powis Castle’
False Wild Indigo* Baptisia species and hybrids
Wine Cups* Callirhoe involucrata
Threadleaf Coreopsis* Coreopsis verticillata
Gaura* Gaura lindheimeri
Russian Sage Perovskia hybrids
Moss Pinks* Phlox subulata
‘Goldsturm’ Rudbeckia* Rudbeckia fulgida ‘Goldsturm’
Mexican Bush Sage Salvia leucantha
‘Indigo Spires’ Salvia Salvia x ‘Indigo Spires’
Stonecrops Sedum species
Lamb’s Ear Stachys byzantina
Salt Tolerant Annuals
Most annuals do not tolerate salt spray but the following have proven to tolerant moderate levels. Most are perennials in
warmer climates but are usually killed by the average winter temperatures in this area and so are best grown as annuals.
In addition to those listed below, Allamanda, Bouganvilla and Mandevilla vines all tolerate moderate levels of salt spray,
though are not hardy in this climate (USDA Hardiness zone 8a).
Common Name Scientific Name
Baby Sun Rose Aptenia cordifolia
Blue Daze Evolvulus glomeratus
Joseph’s Coat Alternanthera ficoidea
Vinca, Periwinkle Catharanthus roseus
Pentas Pentas lanceolata
Moss Rose Portulaca grandiflora
Coleus Solenostemon hybrids
Drought Tolerant Annuals
The following annuals do not have any known salt spray tolerance but do grow well even in sandy, poor soils and are
therefore recommended for planting in coastal gardens in sheltered sites.
Common Name Scientific Name
Wheat Celosia Celosia spicata
Globe Amaranth Gomphrena globosa
Melampodium Melampodium padulosum
Porterweed Stachytarpheta jamaicensis
Mealycup Sage* Salvia farinacea
Mexican Sunflower Tithonia rotundifolia
Narrow Leaf Zinnia Zinnia angustifolia
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New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-43
GROUNDCOVERS
Common Name
Botanical Name Height Exposure
Soil Conditions
Winter Creeper Euonymous fortunei 6”-2’ Full Sun to Full Shade Well Drained
‘Blue Pacific’ Juniper Juniperus conferta ‘Blue Pacific’ 12”-18” Full Sun Well Drained to Xeric
Spreading Liriope Liriope spicata 12” Full Sun to Full Shade Moist to Well Drained
Mondograss Ophiopogon japonicus 6”-10” Part to Full Shade Well Drained
Creeping Rosemary Rosmarinus officinalis ‘Prostratus’ 12”-18” Full Sun Well Drained to Xeric
Golden Stonecrop Sedum acre 4”- 6” Full Sun to Light
Shade
Well Drained
Groundcovers—Moderately Salt Tolerant
Common Name
Botanical Name Height Exposure
Soil Conditions
Beach Wormwood* Artemisia stelleriana 6”- 12” Full Sun Well Drained to Xeric
Silver and Gold Chrysanthemum pacificum 12”-18” Full Sun Well Drained
Algerian Ivy Hedera canariensis 12” Light to Full Shade Well Drained
English Ivy Hedera helix 6”-12” Part to Full Shade Well Drained
Creeping Juniper* Juniperus horizontalis 10”-12” Full Sun Well Drained to Xeric
Liriope Liriope muscarii 12”- 18” Light to Full Shade Moist to Well Drained
Star Jasmine Trachelospermum asiaticum 6”-8” Light to Part Shade Well Drained
Groundcovers—Slightly Salt Tolerant
Common Name
Botanical Name Height Exposure
Soil Conditions
Cast Iron Plant Aspidistra elatior 3’ Part to Full Shade Well Drained
Beach St. John’s Wort* Hypericum reductum 12” Full Sun Well Drained to Xeric
Periwinkle, Vinca Vinca minor 6” Light to Full Shade Moist to Well Drained
For More Information About Listed Plants
For more information about each plant, including recommended varieties for New Hanover County landscapes, visit the
Recommended Plants Lists on the New Hanover County Cooperative Extension website, www.gardeningnhc.org.
Click on the plant information link to access the lists.
Or visit the NCSU Urban Horticulture website, www.ncstate-plants.net and click on the Plant Fact Sheets link to
access hundreds of fact sheets with complete details about each plant, including images.
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Groundcovers—Highly Salt Tolerant
New Hanover County - City of Wilmington Low Impact Development Guidance Manual
App II-44
REFERENCES
Black, R.J. “Salt Tolerant Plants for Florida.” 26 Oct. 2004.
http://edis.ifas.ufl.edu/BODY_EP012
Black, R.J. and Edward Gilman. Landscape Plants for the Gulf and South Atlantic Coast.
Gainesville: University Press of Florida, 2004
Chaplin, Lois Trigg. The Southern Gardeners Book of List: The Best Plants for All Your Needs,
Wants and Whims. Dallas: Taylor Publishing, 1994.
Dirr, Michael A. Dirr’s Trees and Shrubs for Warm Climates. Portland: Timber Press, 2002.
Graetz, Karl E. Seacoast Plants of the Carolinas. Raleigh: Sea Grant Publication, 1974.
Hansen, Keith. “Landscape Development for Texas Coastal Areas.” 26 Oct. 2004. http://aggie
horticulture.tamu.edu/southerngarden/coastplants.html
Kowalsick, Tom. “Seashore Plantings.” 26 Oct. 2004.
http://www.cce.cornell.edu/suffolk/grownet/treselect/seashore.html
Sullivan, Barbara J. Garden Perennials for the Coastal South. Chapel Hill: University of
North Carolina Press, 2003.
Prepared by:
Charlotte Glen, Urban Horticulture Agent,
North Carolina Cooperative Extension – New Hanover County Center
With contributions and assistance from the following:
Matthew Martin, Area Specialized Agent – Turfgrass
David Nash, Area Specialized Agent – Coastal Management
Distributed in furtherance of the acts of Congress of May 8 and June 30,1914. North Carolina State University and North Carolina A&T State University commit
themselves to positive action to secure equal opportunity regardless of race, color, creed, national origin, religion, sex, age, or disability. In addition, the two
Universities welcome all persons without regard to sexual orientation. North Carolina State University, North Carolina A&T State University,
U.S. Department of Agriculture, and local governments cooperating.
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