&EPA
United States
Environmental Protection
Agency
Office of Water
(4502F)
Washington, DC
EPA-843-B-96-001
October 1996
Protecting Natural
Wetlands
A Guide to Stormwater
Best Management Practices
Internet Address (URL) http://www.epa.gov
Recycled/Recyclable Printed with Vegetable Oil Based Inks on Recycled Paper (20% Postconsumer)
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Protecting Natural Wetlands:
A Guide to Stormwater
Best Management Practices
Office of Water (4502F)
United States
Environmental Protection Agency
Washington, DC 20460
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Contents
ACKNOWLEDGEMENTS vi
1. INTRODUCTION 1-1
2. FACTORS TO CONSIDER WHEN SELECTING BMPS 2-1
Introduction 2-1
Wetland Factors 2-2
Wetland Type 2-2
Hydrology 2-3
Biological Functions 2-6
Microbes 2-6
Vegetation 2-6
Animals 2-7
Site-Specific Conditions 2-7
Soils 2-7
Climate - : 2-9
Landscape Position 2-9
Descriptions of Specific Wetland Types 2-10
Pocosin Wetlands 2-10
Cienegas 2-10
Playa Lakes 2-11
Riverine or Riparian Wetland Areas of the Southwest 2-12
Prairie Potholes 2-12
Sand Hills Wetlands..... 2-13
Peatlands of the North-Central States 2-14
Bottomland Hardwoods 2-14
Swamps and Bogs of the Northeast 2-15
Cypress Dome Wetlands 2-16
Permafrost/Tundra Wetlands 2-16
Stormwater Factors 2-17
Stormwater Quantity 2-17
Runoff and Peak Flow 2-17
Rainfall ....2-19
Stormwater Quality 2-19
Overview of BMP Capabilities 2-27
Assessing the Ability of a BMP to Protect a Wetland 2-27
Nonstructural Controls 2-28
Watershed Planning 2-29
Permitting Programs 2-30
Preventive Construction Techniques 2-30
Operation and Maintenance 2-30
Outreach and Educational Programs 2-31
Structural Controls 2-31
BMPs in Series 2-32
BMP Maintenance Requirements 2-32
Page iii
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Maintenance Factors 2-33
Implementation 2-34
Development of an Effective Maintenance Plan 2-35
Components of an Effective Maintenance Plan 2-36
Funding Sources 2-37
Taxes ....2-37
Fees 2-38
Capacity Credits 2-39
Fee-in-Lieu 2-39
Bonds/Debt Financing 2-39
State Revolving Funds 2-40.
Grants 2-40
Leases 2-40
Matching Wetland/Stormwater Factors to BMP Design 2-41
Preliminary Treatment of Stormwater 2-41
Matching Wetland Characteristics to BMP Design 2-41
Hydrology 2-41
Climate ....2-43
Water Quality 2-44
Monitoring 2-44
Summary 2-46
References 2-47
3. CASE STUDIES 3-1
Introduction 3-1
Regional Case Studies 3-5
EPA Region 1 - Narrow River Special Area Management Plan, Rhode Island 3-5
EPA Region 2 - Freshwater Wetlands Protection Act, State of New Jersey 3-8
EPA Region 3 - Watershed Management Study, Prince William County, Virginia 3-11
EPA Region 4 - Hidden River Wetland Stormwater Treatment Site, Tampa,
Florida 3-16
EPA Region 5 - Lake McCarrons Wetland Treatment System, Roseville,
Minnesota 3-17
- The Phalen Chain of Lakes Watershed Project, Ramsey and Washington
Counties, Minnesota 3-20
- The Prairie Wolf Slough Project, Chicago, Illinois 3-23
EPA Region 6 - Tensas Cooperative River Basin Study, Louisiana 3-24
EPA Region 7 - Muiti-Species Riparian Buffer Strips, Bear Creek Watershed, Iowa... 3-30
EPA Region 8 - Watershed Approach to Municipal Stormwater Management,
Fort Collins, Colorado : 3-36
- Lemna Nonpoint Source Treatment System, Chatfield Reservoir, Colorado ..3-41
EPA Region 9 - Lincoln-Alvarado Project, Union City, California 3-46
EPA Region 10 - Riparian Area Wetland Restoration Project, Sawmill
Creek, Idaho 3-46
- Sublett Creek Restoration Project, Idaho 3-47
- Bear Creek Restoration Project, Crook County, Oregon 3-48
-Camp Creek Restoration, Crook County, Oregon 3-50
-The Chewaucan River Project, Lake County, Oregon 3-51
4. BEST MANAGEMENT PRACTICES 4-1
Introduction 4-1
Nonstructural BMPs - Pollution Prevention 4-2
Pageiv
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Contents
Nonstructural BMPs - Watershed Management Plans 4-8
Nonstructural BMPs - Preventive Construction Techniques 4-12
Nonstructural BMPs - Outreach and Educational Programs 4-13
Nonstructural BMPs - Riparian Areas 4-18
Structural BMPs - Infiltration Basins 4-20
Structural BMPs - Infiltration Trenches 4-25
Structural BMPs - Sand Filters 4-29
Structural BMPs - Grassed Swales 4-32
Structural BMPs - Vegetative Filter Strips 4-35
Structural BMPs - Vegetative Natural Buffers 4-38
Structural BMPs - Open Spaces 4-41
Structural BMPs - Extended Detention Dry Basins 4-43
Structural BMPs -Wet Ponds 4-47
Structural BMPs - Constructed Wetlands 4-50
Structural BMPs - Porous Pavement and Concrete Grid Pavement 4-54
Structural BMPs - Oil/Grit Separators or Water Quality Inlets 4-58
Structural BMPs -Level Spreaders 4-61
Structural BMPs - French Drains 4-63
Structural BMPs - Dry Wells or Roof Downspout Systems 4-65
Structural BMPs - Exfiltration Trenches 4-68
BMPs in Series - 4-70
Pagev
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Acknowledgments
Adcnowledh
its
This document was prepared by Tetra Tech, Inc., for the Wetlands Division in EPA's Office of
Wetlands, Oceans and Watersheds. Fran Eargle was the EPA project manager. She was assisted
by Michael Plehn.
Tetra Tech project staff included Shannon Cauley, Jim Collins, Mary Beth Corrigan, Emily
Faalasli, Kelly Gathers, John Hochheimer, Robert Johnson, Marti Martin, Paula Proctor, Dave
Skibiak, Victoria Tanga, and Sharon Thorns. Subcontractual support was provided for several of
the case studies by Gary Bentrup of Aquatic and Wetland Consultants, Inc.
Pagevi
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Introduction
Section 1
introduction
Overview
...wetlands
in urban areas
can be
dramatically
altered by
uncontrolled
Ithough wetlands have long been recognized for their flood control and water quality
improvement functions, there is an increasing concern that unrestricted use of natural
wetlands as receptacles for point and nonpoint sources of pollution, such as urban
stormwater and other diffuse sources of runoff, will have an adverse effect on wetlands and
wetland biota. As a result of this concern, the U.S. Environmental Protection Agency (EPA), in
cooperation with the State of Florida, the Association of State Hoodplain Managers, Inc., and
the Association of State Wetland Managers, sponsored a workshop in January 1992 on wet-
lands and stormwater. The purpose of the workshop was to investigate various issues related to
the management of stormwater and wetlands, explore potential options, and learn from the
experiences of the participants (wetland scientists, engineers, and environmental managers)
about protection of natural wetlands that receive stormwater runoff.
One of the major findings of the workshop was that wetlands in urban areas can be
dramatically altered by uncontrolled runoff resulting from natural drainage or direct discharge
to wetland systems. Consequently, workshop participants included in their final recommenda-
tions a need for guidelines to provide a framework for baseline protection of wetlands that
receive stormwater runoff. This document is a first step toward providing such guidelines. The
purpose of this document is to describe the potential benefits, limitations, and
__^__ appropriate application of best management practices (BMPs)1 that can be
implemented to protect the functions of natural wetlands from the impacts of
urban stormwater discharges and other diffuse sources of runoff. This docu-
ment is not designed to recommend specific management practices that
would be applicable under all circumstances. Instead, it presents information
to assist managers in making informed decisions concerning the appropriate
use of BMPs to protect existing wetland resources.
Land use changes within a watershed that accompany urbanization can
result in a variety of impacts to wetlands and other receiving waters. As the
percentage of impervious surface increases with the building of roads, parking
lots, and buildings, resulting runoff volume, velocity, and pollutant loads can increase dramati-
cally. Increases in impervious surfaces also reduce the opportunity for the rainfall or snowmelt
'BMPs can include planning, schedules of activities, prohibitions of practices, maintenance procedures, and other management
approaches necessary to prevent or reduce the pollution of waters of the United States.
Page 1-1
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
to infiltrate, thereby lowering groundwater levels. The impacts of these changes on wetlands
can be severe, but they will vary depending on a number of factors including the natural
hydrology of the system, the degree of change in the landscape, and the size and type of
wetland being affected.
Where natural wetlands are the ultimate receivers of stormwater, either inadvertently or
by design, the potential for impacts to the wetlands (through changes in hydrology or water
quality) exists, and BMPs may be necessary to minimize these impacts. Existing wetland
characteristics need to be matched with site characteristics as well as stormwater characteristics
when selecting BMPs. Management practices can be designed to preserve existing wetlands in a
watershed in their current state so they can continue to provide water quality improvement
and other functions and/or to restore degraded wetlands. BMPs designed to control stormwater
can result in potential impacts on downstream wetlands as well as the wetlands directly
receiving stormwater discharge. Therefore, the impacts to both onsite and offsite wetlands
should be considered when determining the suitability of wetlands for receiving stormwater
and when selecting and designing stormwater BMPs to protect the functions of natural wet-
lands.
The ecological attributes of natural wetlands can be adversely affected as watersheds
develop and stormwater flows increase. Wetlands tend to exist in dynamic equilibrium with
surrounding conditions when activities in a watershed remain constant. Changes in the
volume or quality of stormwater runoff resulting from changing activities in a watershed can
affect the functions and values of a natural wetland by altering the hydrologic, water quality,
and sediment or soil characteristics of a wetland. Alteration of the physical and chemical
characteristics of a wetland can adversely affect the biological community and result in
negative impacts to the ecological functions of a wetland.
As discussed in Section 2 of this document, the hydrologic conditions in a wetland affect
abiotic factors such as salinity, soil oxygen availability, and nutrient availability. These factors
in turn greatly influence the flora and fauna present in a wetland. Water depth and the natural
hydroperiod in a wetland also directly influence vegetative composition and density, primary
productivity, organic accumulation, nutrient cycling and availability, and the types and density
of aquatic and terrestrial fauna in a wetland. Stormwater inflows to wetlands can directly
affect the natural hydrology of wetlands by changing water depths and altering the
hydroperiod of the systems.
The impacts of stormwater runoff on the water quality in a wetland are dependent on
the volume and composition of the stormwater. Pollutants found in runoff from urban areas
tend to include sediments, oxygen-demanding substances, nutrients, heavy metals, pesticides,
hydrocarbons, increased temperature, and trash and debris (see Section 2). Changes in turbidity,
oxygen levels, and water temperature in a wetland can have direct impacts on the flora and
fauna in the wetland. In addition, the assimilation of heavy metals, pesticides, and hydrocar-
bons associated with stormwater runoff by the flora and fauna' in a wetland can result in
negative impacts to the ecological characteristics of the wetland.
The morphological characteristics of the soils in a wetland can also be changed as a result
of introducing stormwater runoff into a wetland system. Changes in the texture of a wetland
soil can result from changes in the amount or particle size of sediments that enter the wetland
system. Changes in the texture of a wetland soil can affect the hydrology of the system by
changing wetland drainage characteristics. Adsorption of pollutants in stormwater runoff by
suspended sediments can result in the incorporation of heavy metals, hydrocarbons, nutrients,
Page 1-2
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Introduction
and bacteria into the soil when the sediments settle out of suspension. The pollutants can later
reappear throughout the wetland ecosystem via chemical transformations, vegetative uptake, or
resuspension.
The Code of Federal Regulations (CFR) provides definitions of "waters of the United
States" and "wetlands" at 40 CFR 122.2 (a) through (g). Because wetlands are included under
this definition of waters of the United States, their water quality must be protected to meet
the mandate of the CWA articulated in sectionlOl(a) "to restore and maintain the chemical,
physical, and biological integrity of the nation's waters." The protection of water quality must
address not only the water chemistry, but also the multiple elements, including aquatic life,
wildlife, habitat, vegetation, and hydrology, that together make up aquatic systems. Therefore,
relevant issues to address with respect to wetlands protection include the toxicity and
bioaccumulation of pollutants, diversity and composition of aquatic species, entrapment of
pollutants in sediment, habitat loss, and hydrologic changes.
Controlling stormwater runoff into natural wetlands can benefit the ecosystem by
helping to maintain natural conditions in the system. As mentioned, changes in the hydrology,
water quality, and/or soil characteristics of a wetland resulting from stormwater inflows can
result in shifts in the character of the wetland habitat, which in turn changes the overall
ecological characteristics of the system. Maintaining natural conditions in a wetland by
controlling upstream stormwater runoff can mitigate the impacts of a developing watershed
on the ecological attributes of a wetland by helping to maintain predevelopment hydrologic,
water quality, and soil conditions.
Implementation of BMPs to protect wetlands from runoff can include watershed planning
techniques and also site-specific structural approaches. The planning approaches are generally
preferable to the structural practices. However, where planning has failed or is no longer an
option, implementation of structural controls, including retrofitting stormwater management
facilities into BMPs, may be appropriate.
Some general guiding principles to use in protecting wetlands from stormwater and
nonpoint source runoff include the following:
Wetlands serve valuable water quality functions; however, wetlands have a limited
capacity for handling increased flows or additional pollutants.
The use of BMPs specifically designed to mitigate impacts to wetlands might offset
some of the impacts of stormwater runoff by controlling increased volumes and
velocities of runoff. However, BMP discharges to wetland can adversely affect wetland
functions and values.
BMPs have the potential to reduce impacts to downstream wetlands or wetlands
directly receiving stormwater discharges. To reduce the impacts to a receiving wetland,
BMPs should be selected based on site-specific conditions, as well as regional variability
in stormwater characteristics, climate conditions, urban development patterns, soil
types, and wetland types.
There might be opportunities to use degraded urban wetlands or wetlands in arid
areas to provide final polishing treatment or to restore some wetland functions (e.g.,
hydrology), provided there is adequate treatment of the stormwater before it is
discharged to a wetland.
« Stormwater management should be integrated within other programs at the federal,
state, and local levels. Basinwide planning is needed to address stormwater manage-
Page 1-3
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
ment objectives and wetland protection goals (i.e., advance planning, watershed
management plans, state wetlands conservation plans, or other planning tools).
Because wetlands have a limited capacity to mitigate increased flows of stormwater and
increased pollutants, any proposal to use natural wetlands for final polishing of treated
stormwater discharges should include monitoring and maintenance as components of the
plan.
In urbanizing areas, former wetlands whose vegetation has been removed and hydrology-
altered to the extent that they no longer function as wetlands (e.g., prior converted
croplands), can offer valuable opportunities to restore wetland functions.
While additional research is needed, existing studies suggest that constructed wetlands
can provide better pollutant removal and more consistent, predictable filtering of
stormwater than natural wetlands. Constructed wetlands should therefore be located
upstream of natural wetland locations, so their treated discharges can be directed to
natural wetlands or other waters.
Multiple BMPs in series, or the "treatment train" approach, whereby a series of BMPs
provide alternative nonstructural approaches (e.g., watershed planning) or various
structural control techniques (i.e., grassed swales or longer flow paths to settle solids,
regulate flow, and reduce pollutants), may provide greater: protection for natural
wetlands than individual BMPs.
Using This Manual
Although a number of manuals describe best management practices to be used to address
stormwater runoff, this manual is a first attempt at addressing the specific water quality
concerns related to wetlands. It is intended for use by anyone addressing potential impacts to
wetlands from stormwater runoff, and it presents a wide range of planning approaches as well
as specific BMPs that can be employed in a variety of situations. Regardless of what type of
approach is taken, and at what level, this manual should be used as a starting point in a process
to identify and evaluate appropriate BMPs to protect wetland resources (see Figure 1-1).
The information in this document is presented in four sections. Section 2 describes the
factors (wetland and stormwater characteristics) that should be considered when developing
BMPs to protect wetlands and their natural functions from the potential impacts of stormwater
discharges and other diffuse sources of runoff. Wetland factors to consider include wetland type,
Mnm^BMMBMMB^^BBM hydrology, climate, and site-specific conditions. Stormwater factors to
consider include the quantity and quality of runoff and the frequency of
...thlS manual IS 3 runoff events.
starting point
f- fri fffi Although they are described separately, the wetland factors and
LU lUcI ILIiy stormwater factors are closely related. For example, climate influences the
frequency and intensity of storm events; the wetland type affects the
capacity of the wetland to handle a given quantity or quality of stormwater
runoff; and the functional attributes of a particular wetland can be severely
affected by the introduction of even small amounts of certain contaminants.
When deciding what BMPs may be appropriate for a particular situation,
both sets of variables wetland factors and stormwater factors should be considered individually
and in combination. Helpful tables that detail these factors (for example, wetland types or typical
DrOtGCt WOtland
Page 1-4
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Introduction
(Identify/Evaluate desired
natural wetland functions
Identify potential threats
to wetland functions
See discussion of wetland factors
and types (consider wetland
functions, soils, climate,
hydrology, etc.), pp. 2-2 to 2-17.
See discussion of stormwater
factors (land use, climate, etc.)
pp. 2-17 to 2-26.
Identify watershed management
measures to prevent uncontrolled
runoff to wetlands.
Select BMPs to address potential
threats to wetland functions
See benefits to wetland functions
(Table 2-7) p. 2-42.
Are potential
impacts, resource, and maintenance
requirements acceptable?
Implement BMPs
Monitor/Evaluate BMP performance
and wetland functions/'health"
Are BMPs effective?
Are wetland functions
intact?
See description of BMPs and
BMPs in series in Section 4.
Consider potential impacts to
wetland functions, and capital
and maintenance costs.
See Case Studies (Section 3) and
BMP Fact Sheets (Section 4) for
information on implementation
of BMPs.
See page 2-44 for overview of
monitoring.
Figure 1-1. How to me this manual.
Page 1-5
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
pollutants found in stormwater runoff) are provided in Section 2 to assist managers in considering
the factors in depth. A third set of factorsthe characteristics of potential BMPsshould also
be considered in combination with the wetland and stormwater factors. An overview of BMPs
for controlling the effects of stormwater on the functions of natural wetlands is provided in
Section 2; details are provided in the BMP fact sheets in Section 4.
Section 3 of this document presents several case studies that describe examples of situa-
tions where BMPs were used to protect natural wetland functions from the impacts of runoff
and to restore the functional quality of degraded wetlands. Case studies were selected from
both arid and nonarid climates, as well as from temperate and colder climates. Some of the case
studies include an in-depth overview of a particular experience using BMPs to protect wetlands,
whereas others present only anecdotal information. Since states have only recently had
stormwater management programs in place, or will begin implementation of such programs
within the next decade, only a limited number of well-documented case studies show the
effectiveness of stormwater management BMPs and natural wetlands.
Section 4 presents fact sheets describing specific BMPs and their potential relationship to
natural wetlands. For each BMP, a fact sheet is provided with the following information:
definition and purpose of the BMP, its scope and applicability, design criteria considerations,
potential effects on wetlands (i.e., benefits and limitation for use), cost-effectiveness (where
applicable), maintenance, and sources of additional information. BMPs included in this docu-
ment represent examples of some of the more commonly used practices. Numerous BMP
manuals from state and local governments throughout the country were used to gather the
information presented in the fact sheets.
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Jfoctor? tp Consider When Selecting BMPs
Section 2
Factors to Consider
When Selecting BMPs
Introduction
est management practices (BMPs)both structural and nonstructural1 are used to
protect natural wetlands from the impacts of stormwater and other diffuse or nonpoint
sources of runoff,2 including changes in wetland hydrology or water quality. When natural
wetlands are the final discharge point, BMPs maybe used to provide preliminary treatment
of runoff that might impact the receiving natural wetland. Natural wetlands, usually by
virtue of their position in the landscape, directly receive stormwater runoff. In this case, BMPs
should be used to control the runoffoutside the wetlandto maintain the wetland's existing
hydrology and functions. BMPs should be selected after carefully considering the combination of
variables that influence a potentially impacted wetland and the characteristics of the runoff
entering that particular wetland, as well as the capabilities and applicability of the potential
BMPs.
Wetland factors to consider include wetland type, hydrology, biological functions, and site-
specific conditions. A consideration of stormwater factors should consist of an evaluation of the
geographical area producing runoff, including existing and future impervious surfaces and
stormwater infrastructure, quantity and quality of runoff, and the frequency of runoff events.
Factors like zoning and changes in planned land use should also be considered to evaluate the
potential impacts from future development on the quantity and quality of stormwater and the
ability of existing treatment systems to control the runoff adequately. BMP capabilities include
factors such as flood storage; infiltration; and sediment, nutrient, and pollutant removal.
By evaluating the wetland characteristics in concert with the stormwater characteristics,
and applying the appropriate BMPs described in Section 4, the effects on the wetland system can
be minimized. For example, if it is anticipated that a certain type of development will cause
higher sediment loading to receiving waters and the wetland on the site is sensitive to increased
sedimentation, BMPs that control sedimentation should be employed to minimize the effects on
the wetland.
Wetland factors, stormwater factors, and BMP capabilities are described in this section. This
information can be used when evaluating the BMPs presented in Section 4.
'Structural best management practices are those practices which entail construction of human-made structures (USEPA,
1992V). Examples of structural BMPs include infiltration basins, sand filters, vegetated filter strips, and constructed wetlands.
Nonstructural best management practices are regularly scheduled activities or programmatic actions (USEPA, 1992b). Examples
of nonstructural BMPs include pollution prevention, watershed planning, vegetated buffer areas, street sweeping, inspections, and
improved materials-handling practices.
2f or the purpose of this document, the termrano/f should be interpreted to include stormwater discharges and nonpoint
sources of pollution, including urban sources. These other sources of nonpoint pollution can include agriculture, forestry, marinas,
and hydromodification activities. The reader should refer to Guidance Specifying Management Measures for Sources of Nonpoint
Pollution in Coastal Waters (USEPA, 1993) for additional information on all sources of nonpoint pollution.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Wetland Factors
Wetlands are integral parts of a watershed; their position in the landscape is influenced by
and influences the characteristics of a watershed. Wetlands can function as nutrient sinks,
temporary water storage areas, groundwater recharge areas, and critical wildlife habitat. Natural
and anthropogenic (human-induced) activities within a watershed influence the functions of
natural wetlands. When these activities remain relatively constant, the functions of natural
wetlands tend to exist in dynamic equilibrium with the surrounding conditions. However,
changes in the established combination of natural and anthropogenic activities within a
watershed can result in dramatic changes in the functions of natural wetlands.
The physical, chemical, and biological characteristics of natural wetlands combine to
determine unique wetland types. Differences in these characteristics range from subtle to obvious
among different wetland types depending on many factors associated with wetlands that include,
but are not limited to, hydrology, biological functions, site-specific factors, the climate and
geology of the region, landscape position, and soils. These factors are not independent, but form a
complex interrelationship to make each wetland type unique.
An assessment of the current status of these factors for a particular wetland is important to
understand the effects of certain factors, such as increased or decreased quantities of stormwater
runoff, on an individual wetland. Understanding the interactions of a particular wetland with the
other watershed features provides a broader and more comprehensive perspective of impacts of
various activities within the wetland and the watershed as a whole. For example, by changing the
hydrology of a wetland, the water retention and sediment attenuation functions can be lost,
resulting in downstream hydrological and water quality impacts; or vegetative species and
composition within and surrounding a wetland might change, resulting in habitat quality
changes.
Some of the factors affecting wetland type are influenced more by stormwater runoff than
others. For the purpose of this document, hydrology, biological functions, soils, and site-specific
conditions are considered to be factors that can be significantly affected by stormwater runoff.
Other factors, such as climate and landscape position (which might be linked to hydrology), are a
function of the location of a particular wetland. They are not affected by stormwater runoff, but
they contribute significantly to the determination of wetland type.
Selection and design of stormwater BMPs should consider the wetland type, hydrology,
biological functions, site-specific features, and other wetland factors, as well as the relationship
of the wetland to other watershed features, including climate. Additionally, the impacts of a
particular BMP need to be considered in the context of both the individual wetland and the
entire watershed to determine potential impacts on other resources.
Wetland Type
The effects of stormwater on a particular wetland depend, in part, on the type of wetland in
question. Wetland type can be defined as the combination of attributes (e.g., physical, chemical,
and biological) that make a particular wetland different from other wetlands. A wide range of
wetland types, which are the result of the cumulative effect of many environmental variables,
exist in the United States. In an effort to bring precision and standardization to the classification
of wetland types, Cowardin and others (1979) developed Classification of Wetlands and Deepwater
Habitats of the United States for use in the National Wetlands Inventory. Their classification
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Factors to Consider When Selecting BMPs
system breaks wetlands into systems, subsystems, and classes analogous to plant or animal
taxonomic classifications.
The classification system developed by Cowardin and others (1979) is very comprehensive.
However, because it contains too much detail for this document, a simpler classification system,
proposed by Mitsch and Gosselink (1993), is used here.3 In their classification system, Mitsch
and Gosselink (1993) divided wetlands into two major groupscoastal and inlandas shown in
Table 2-1. Some wetlands in the United States are not adequately described by the Mitsch and
Gosselink (1993) classification system, but the system is intended as only a preliminary guide to
evaluate wetlands.
Table 2-1.
types off wetlands
wetlana type
Cawartlln et at., 1O7B Equivalent
coastal Wetlands
Tidal salt marshes
Tidal freshwater marshes
Mangrove wetlands
Estuarine Intertldal emergent, hallne
Estuarlne Intertidal emergent, fresh
Estuarine intertldal forested and shrub, haline
Inland Wetlands
Inland freshwater marshes Palustrine emergent
Northern peatlands Palustrine moss-lichen
Southern deepwater swamps Palustrine forested and scrub-shrub
Riparian wetlands Palustrine forested and scrub-shrub
Source: Adapted from Mitsch and Gosselink, 1993.
Hydrology
Hydrology is described by Mitsch and Gosselink (1986) as probably the most important factor in
the establishment and maintenance of specific types of wetlands and wetland processes. Precipitation,
surface water inflow and outflow, groundwater exchange, and evapotranspiration are the major
factors influencing the hydrology of most wetlands. Figure 2-1 shows a simplified diagram of a
wetland hydrologic cycle.
Mitsch and Gosselink (1986) concluded thathydrologic conditions are extremely important for the
maintenance of a wetland's structure and function, although simple cause-and-effect relationships are
difficult to establish. Hydrologic conditions affect many abiotic factors, including salinity, soil
oxygen levels (which can cause anoxia), and nutrient availability. These abiotic factors, in turn,
determine the flora and fauna that develop in a wetland. Finally, biotic components are active in
altering the wetland hydrology, completing the cycle.
3 The reader should refer to Cowardin and others (1979) if a more detailed classification system is needed.
Page 2-3 .
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
r EVAPORATION
\
Percolation b° <>
Water Table__
Ground Water
Wetland
Figure 2-1. Wetland Hydrological Cycle.
Some wetlands remain permanently inundated or saturated, some are wet for only a short
period during the year; and others may remain dry over periods of several years. The periods of
saturation or dryout in wetlands have strong implications for the characteristic structures that
develop in wetlands (Kadlec and Knight, 1996). Each wetland type exhibits a unique hydroperiod
that is fundamental in the stability of a wetland system. Hydroperiod is defined as the periodic or
regular occurrence of flooding and/or saturated soil conditions (Marble, 1992). Mitsch and
Gosselink (1986) suggested characterizing hydroperiod as the ratio of flood duration divided by
flood frequency over a given period of time. Cowardin and others (1979) provided general
descriptions of hydroperiod for both tidal and nontidal wetland systems (listed in Table 2-2). The
hydroperiod for a particular wetland is a function of the water budget (i.e., inflow and outflow
water balance) and storage capacity, which is affected by the surface contours of the landscape
and subsurface soil, geology, and groundwater conditions (Mitsch and Gosselink, 1986).
Since wetlands typically represent a transition between terrestrial and open-water
ecosystems, the effects of changed hydrology are extremely variable. Several principles outlining
the importance of hydrology to wetlands have been described by Mitsch and Gosselink (1986)
and include the following:
1. Hydrology leads to a unique vegetation composition, but can limit or enhance species
richness. For example, different species of vegetation respond differently to flooding
and large trees tolerate flooding better than seedlings.
2. Primary productivity in wetlands is enhanced by flowing conditions and a pulsing
hydroperiod. Primary-productivity is often depressed by stagnant conditions.
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Factors to Consider When Selecting BMPs
Table 2-2. Definitions of Wetland Hydroperlods
Definition
The substrate is permanently flooded with tidal water.
The land surface is exposed by tides less often than daily.
Tidal water alternately floods and exposes the land surface at
least once dally.
Tidal water floods the land surface less often than dally.
Water covers the land surface throughout the year in all years.
Vegetation is composed of obligate hydrophytes.
Surface water Is present throughout the year except in years
of extreme drought.
Surface water persists throughout the growing season in most
years. When surface water is absent, the water table is usually
at or very near the land surface.
Surface water is present for extended periods, especially early
in the growing season, but is absent by the end of the season
in most years. When surface water is absent, the water table is
often near the land surface.
The substrate is saturated to the surface for extended periods
during the growing season, but surface water is seldom
present.
Surface water Is present for brief periods during the growing
season, but the water table usually lies well below the soil
surface for most of the season. Plants that grow both in
uplands and wetlands are characteristic of the temporarily
flooded regime.
The substrate is usually exposed, but surface water is present
for variable periods without detectable seasonal periodicity.
Weeks, months, or even years may intervene between periods
of inundation. The dominant plant communities under this
regime may change as soil moisture conditions change.
The amount and duration, of flooding are controlled by means
of pumps or siphons in combination with dikes or dams.
Vegetation present cannot be considered a reliable indicator
of water regime.
Tidal Wetlands
Subtidal
Irregularly Exposed
Regularly Flooded
Irregularly Flooded
Nontldal Wetlands
Permanently Flooded
Intermittently Exposed
Semipermanently Flooded
Seasonally Flooded
Saturated
Temporarily Flooded
Intermittently Flooded
Artificially Flooded
Source: Adapted from Mitsch and Gosselink, 4993; Cowardin et al., 1979.
3. Organic accumulation in wetlands is controlled by hydrology through its influence on
primary productivity, decomposition, and export of particulate organic matter.
4. Nutrient cycling and nutrient availability are both significantly influenced by
hydrologic conditions.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Changes in the natural hydrology of a wetland can therefore affect many of the functions of
a wetland. When volumes of stormwater runoff to a wetland increase, or when a wetland is
impounded to treat stormwater runoff, changes to the biotic and abiotic characteristics can occur.
For example, hydrologic disturbance of a wetland can cause a shift from a function as a sink for
nutrients and metals toward a function as a source of these materials, thereby affecting other
functions within the wetland and in downstream communities (Brinson, 1988).
Biological Functions
Because wetlands are transition zones between uplands and aquatic systems, they can serve
as exporters of organic materials and sinks for inorganic matter (Mitsch and Gosselink, 1993).
Because of this transitional position in the landscape, some wetlands have high biodiversity,
whereas others are very productive in terms of biomass. Wetlands typically provide habitat to a
variety of microbial and plant species due to presence of ample water. The diversity of physical
and chemical interactions that occur in wetlands results in a continuum of flora and fauna from
the smallest of microbes to large trees. Interactions resulting from the biological diversity in
wetlands results in greater diversity, more complete utilization of energy inflows, and ultimately
the emergent properties of the wetland ecosystem (Kadlec and Knight, 1996). The biological
communities that become established in wetlands are typically made up of a rich mixture of
microbes, plants, and animals.
The established biological community in a particular wetland exists in a state of dynamic
equilibrium with the physical and chemical properties associated with that wetland. Actions that
upset the established balance found in the biological community, such as changes in the
hydroperiod, volume of runoff, or water quality, lead to significant changes in the functions of a
wetland. For example, increasing the volume of stormwater runoff that enters a wetland can
stress indigenous vegetation and allow more flood-tolerant species of vegetation (e.g., Typho) to
take over a wetland.
Microbes
In wetlands, microbes are major transformers of organic and inorganic materials. The
population of microbes in a wetland varies according to many factors, but usually it is composed
of aerobic species at the surface of the substrate and shifts to anaerobic species as the depth
increases. As facilitators for the many biochemical reactions that occur in wetlands, wetland
microbes have adapted to a wide range of substrate conditions. Aerobic bacteria colonize areas
around plant roots to take advantage of the oxygen-rich rhizosphere surrounding the roots of
wetlands vegetation. Other anaerobic microbes play important roles in the chemical reactions
that produce methane, nitrogen gas, and hydrogen sulfide. Mychorrhizial fungi facilitate nutrient
uptake, reduce stress, enhance salt tolerance, and increase the initial growth and survival of
wetland plants (USDA-SCS, 1992).
Vegetation
Wetland vegetation comes in many forms, including floating, rooted, emergent,
submergent, herbaceous, and woody. Wetland plants transport oxygen from their leaves to the
rhizosphere surrounding their roots. This soil oxygenation process is important for many of the
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Factors to Consider When Selecting BMPs
microbial reactions that take place in wetlands. Other functions of wetland vegetation include
trapping sediment and removing nutrients or other pollutants from the water column and
substrate (USDA-SCS, 1992). Wetland plants provide habitat for a variety of fish and wildlife. All
species of fish and wildlife need habitatfood, water, and coverfor survival. The habitat value
of a particular wetland site depends on the quantity, quality, diversity, and seasonality of the food,
water, and cover that it offers (PSWQA, 1990).
Animals
Wetlands support many different types of animals, including invertebrates, fish,
amphibians, reptiles, birds, and mammals. Because of the transitional nature of wetlands,
both aquatic and terrestrial animals live in wetlands. Wetlands provide food sources,
protection from weather and predators, resting sites, reproductive sites, and molting grounds
for wildlife (Cooper, 1989). Wetlands provide this habitat function for many species of fish
and wildlife, including some that are threatened or endangered. Many species of animals
that are not typically considered to be wetland species spend a part of their life-cycle or
fulfill daily requirements in wetlands. Other species like the beaver and muskrat can alter
wetlands as a result of their activities (USDA-SCS, 1992).
Site-Specific Conditions
Although wetlands in rural or undeveloped areas might be relatively pristine, they can be
affected by agricultural activities, particularly sedimentation and drainage. Wetlands in previously
developed urban areas can be affected by changes in surface water and groundwater hydrology or
water quality. In drier areas, some existing urban wetlands are hydrologically dependent on
treated wastewater inputs, which are subject to variable water use practices. Wetland plant
communities can be altered as a result of hydrologic or physical disturbances. Exotic or invasive
plant species, which become established more easily in disturbed ecosystems, might be present,
affecting the existing plant species and habitat functions of the wetland. Also, .natural buffer
areas surrounding urban wetlands might have been eliminated, lowering the diversity of the
wetland system and reducing areas for wildlife refuge.
Wetlands in temperate climates undergo seasonal variation in biological activity, which is a
major factor in many wetland processes involving the retention or transformation of pollutants.
Some wetland types can serve as a sink for nutrients during the growing season and as a source at
other times of the year (Mitsch and Gosselink, 1986), making consideration of the seasonal
distribution of runoff important.
Soils
Soils and their characteristic properties develop as the result of interactions between parent
material, climate, plant and animal life, relief, and time. The degree of influence of each of the five
factors generally varies from place to place. In a given location one factor can dominate in the
formation of a soil and determine most of its properties (Smith and Matthews, 1975).
Soils that form in a wetland environment are classified as hydric and have morphological
characteristics that result under wet conditions. Hydric soils are defined by the Natural Resources
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Conservation Service (NRCS) as soils that are saturated, flooded, or ponded long enough during the
growing season to develop anaerobic conditions in their upper part. Hydric soils are classified as
either organic or mineral soils based on the percentage of organic material in their upper part (see
Table 2-3). General differences in physicochemical characteristics between organic and mineral soils
include percentage of organic content, pH, bulk density, porosity, hydraulic conductivity, water
holding capacity, nutrient availability, and cation exchange capacity (see Table 2-3).
Changes in the characteristics of a soil during its formation result from processes that include
additions, removals, transfers, and transformations (Hall and Matthews, 1974). Modifying existing
processes by placing BMEs adjacent to or upstream of a wetland can result in changes in wetland soil
characteristics. For example, changes in the textural characteristics of a wetland soil can result from
changes in the amount, type, and/or particle size of sediments that enter a wetland. The modification
of soil textural characteristics can result in changes in the drainage characteristics of the wetland. For
example, the percentage of coarse-grained sediments deposited in a wetland could be reduced by a
stormwater BMP, resulting in a reduction of the soil's permeability over time. The reduced
permeability could result in a reduction in the soil's ability to infiltrate water, thereby
changing the character of the wetland.
The placement of BMPs adjacent to wetlands can result in changes to the chemical
characteristics of the wetland soil if stormwater is not adequately treated prior to its
discharge to the wetland. Suspended organic and inorganic particles tend to adsorb pollutants,
such as heavy metals, nutrients, hydrocarbons, and bacteria (Stockdale, 1991). If the suspended
particles are deposited in the wetland, the pollutants can become incorporated into the soils.
Over a period of time pollutants that have accumulated in the soil can appear throughout the
wetland environment via chemical transformations, vegetative uptake, or resuspension.
Additional changes to the chemical and morphological characteristics of a wetland soil can
occur as the result of alterations to the natural factors affecting the soil's development. Changes
to the natural characteristics (e.g., hydrology or vegetation) of a wetland can result in changes to
Table 2-3. Comparison of Mineral and Organic
Soils in Wetlands
Parameter
Organic Content
pH
Bulk Density
Porosity
Hydraulic Conductivity
Water Holding Capacity
Nutrient Availability
Cation Exchange Capacity
Typical Wetland Type
Mineral soil
Less than 20%-55%
Usually circumneutral
High
LOW (45%-55%)
High (except for clays)
Low
Generally high
Low, dominated by major cations
Riparian forest, some marshes
Organic Soil
Greater than 20%-35%
Acid
Low
High (80%)
Low to high
High
Generally low
High, dominated by hydrogenion
Northern peatland
Source: Adapted from Mltsch and Cosselink, 1993.
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factors to Consider When Selecting BMPs
the chemical transformations and nutrient cycling in a wetland soil. Redox potential, cation
exchange capacity, pH, porosity, hydraulic conductivity, and the organic content of a soil can
change as a result of altering the natural conditions within, or affecting, a wetland. Conversely,
changes in the chemical and morphological characteristics of the soil in a wetland affect the
overall characteristics of the existing wetland habitat.
Climate
Climate is defined as the average state of the atmosphere during a period of timedays,
weeks, years, etc. (Rasmusson et al., 1993). Solar radiation is the primary external source of
energy. However, other external natural events (e.g., volcanic eruptions) and human-induced'
changes (e.g., land surface changes) also can affect climate (Rasmusson et al., 1993). Naturally
occurring quantities and variations in rainfall and runoff are essential to the maintenance of
many wetland types. Both the amount and seasonal distribution of rainfall and resulting runoff
can play a role in determining the species composition, soil characteristics, and ecological func-
tioning of inland wetlands. Factors such as precipitation patterns, including the frequency,
intensity, and duration of storm events, determine the quantity and timing of runoff (Hammer,
1992). Other climatic factors, such as temperature, winds, relative humidity, and incident solar
radiation, also affect wetlands.
Because hydrology is a particularly important factor, wetlands in arid and semiarid climates
require water source investigations before a stormwater pretreatment strategy can be chosen.
Whether wetlands in arid or semiarid climatic regions receive water from groundwater sources or
from surface flows, maintaining adequate and natural inundation periods is crucial to their
survival. Despite the significant reduction of hydrologic flows to wetlands by agricultural
diversions, climate determines the fate of most aquatic habitats in arid and semiarid regions
(Hutchinson et al., 1992). In arid and semiarid regions, precipitation should be considered a
variable rather than a constant when planning surface water controls. Arid and semi-arid climates
are largely responsible for the three distinct types of wetlands found in the American Southwest:
ciengas, playas, and riverine wetlands.
Landscape Position
The location of a wetland in the landscape plays a role in the natural hydroperiod of the
wetland, its retention of pollutants, and the effects of increased stormwater inputs. Brinson
(1988) defined three major geomorphic wetland types based on location in the watershed:
Basin - Wetlands typically in headwater regions that capture drainage from small areas and
may receive precipitation as the primary source of water. Basins are characterized by
fluctuations of the water table, a long hydroperiod, low hydrologic energy, and low nutrient
levels. Plant communities usually consist of concentric zones of similar vegetation. ,
Riverine - Wetlands that occur throughout the landscape and are primarily influenced by
water flowing downstream. Riverine wetlands typically have short hydroperiods, high
hydrologic energy, and high nutrient levels. Plant communities are usually arranged
parallel to the direction of flow.
Fringe - Wetlands that are usually located at the base of a drainage basin and adj acent to a
large body of water, including estuarine areas. They generally have a long hydroperiod,
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
highhydrologic energy, and variable nutrient loads. Fringe wetlands are often influenced
by frequent flushing by bidirectional flow. Zonation of vegetation is usually perpen-
dicular to the direction of water flow.
Descriptions of Specific Wetland Types
Poeosln wetlands
Pocosin wetlands occur along the Atlantic seaboard's lower coastal plain, from southern
Virginia to northern Florida. Approximately 70 percent of pocosins are located in North Carolina.
Pocosin, an Algonquin Indian word, literally means "swamp on a hill," which is an accurate
description because pocosin wetlands are found in ridge and swale topography, as well as in flat
areas of the lower coastal plain, in depressions of the Carolina Bays, in areas of springs and seeps
in the upper coastal plain, and in the floodplains of streams. Pocosins contain dense evergreen
plant communities, consisting of small broad-leaved evergreen trees (pondpine) and scrub shrubs
(fetterbush and inkberry), which can occur either on highly organic soils, such as mucks or peats,
or on very poorly drained mineral soils. Locally, there is wide species diversity. The soils of
pocosins are acidic and low in nutrients and minerals. (Phosphorus is the limiting agent due to
phosphorus-reducing microbes.) Pocosins occur in many different shapes and can vary tremen-
dously in size from less than an acre to several thousand acres. These wetlands are important to
birds and animals such as migratory waterfowl, herons, egrets, and muskrats.
Pocosin wetlands provide very favorable groundwater storage due to the differing
permeability properties of their organic layers. Macropores in the upper layers make the soil
very permeable, allowing for high retention of rainfall. Conversely, the reduced permeability
of the lower layers, due to smaller pore spaces, prohibits the stored rainwater from draining
very quickly. Because the base of a pocosin is not very permeable, the groundwater beneath
the pocosin, which has a high mineral content, does not come into contact with the low-
mineral-content water and soil of the pocosin. Water movement occurs as seepage at the
pocosin's margins that flows to streams, or as direct flow to salt marshes in estuarine areas.
These two principal properties of pocosins attenuation of flow and continuous release of fresh
groundwater are essential to the estuarine ecology of the southeast Atlantic coast. These two
properties also make pocosins particularly vulnerable to the adverse effects of stormwater
discharges in the many areas of the lower coastal plain that are experiencing development.
cienegas
Cienega is a term that usually applies to mid-elevation (1,000 to 2,000 m), or (3,281 to 6,562 ft)
wetlands characterized by permanently saturated, highly organic, reducing soils (Hendricksonand
Minckley, 1984). These warm, temperate habitats were most often termed cienegas by Hispanic and
later explorers and settlers, and appear to be distinctive habitats (Hendrickson and Minckley, 1984).
The word cienega comes from the Spanish den aqua, meaning "hundred waters." Cienegas are
perpetuated by permanent, scarcely fluctuating sources of water, and are rarely subject to harsh
winter conditions.
At mid-elevations of in semidesert grassland, cienegas are usually associated with perennial
springs and headwater streams. They are near enough to headwaters that the probability of
scouring from flood is minimal. Often, many meters of organic sediments have been deposited.
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factors to Consider When Selecting BMPs
These wetlands are dominated by semiaquatic sedges, rushes, and grasses. Trees are scarce and
immediate surroundings are saline as a result of capillarity and evapotranspiration (Hendrickson
and Minckley, 1984). Historically grazed, more than 95 percent of the original cienegas have been
lost (Hendrickson and Minckley, 1984). Many have been drained for development or destroyed
by upstream pumping of the groundwater sources.
Playa Lakes
The teimplayas generally refers to areas occupied by temporary shallow lakes that have
internal drainage, usually in arid to semi-arid regions. They are not part of an integrated surface
drainage system, but are related to geologic fracture areas. Playas are shallow (typically less than 1
1m (3.28 ft) deep), circular basins averaging 15.5 acres (6.3 hectares) in surface area (Haukos and
Smith, 1992). Playa floors are plate-like with relatively constant water depth throughout much of
the basin. Because very few playas are directly associated with groundwater, playas can usually fill
only from precipitation and irrigation runoff. Most playas are dry during one or more periods of
each year, usually late winter, early spring, and late summer. Several wet-dry cycles during one
year are not uncommon for a playa and depend on precipitation and irrigation patterns (Haukos
and Smith, 1992). Soils of the playa are predominantly clays, differing from the loams and sandy
loams of the surrounding uplands (Haukos and Smith, 1992). The climate of the region containing
most of the playa lakes in the United States (southern Great Plains) is semi-arid in the west to
warm temperate in the east. Vegetation in dry playas resembles upland vegetation and includes
species such as summer cypress, ragweed, and various prairie grasses. Moist and flooded conditions
in playas favor vegetation representative of other North American wetlands: barnyard grass,
smartweed, bulrush, cattail, spikerush, arrowhead, toothcup, and dock (Haukos and Smith, 1992).
Although playas occur throughout the West, the following discussion focuses on a group of
playas occurring in the High Plains of eastern New Mexico and northern Texas, and in an area
south of the Arkansas River and north of the Canadian River. The playas in Texas are small marsh-
like basins, 5 to 15 acres (2 to 6 hectares) in size, and are typically underlain by clay or fine sandy
loam soils that are hydric. These shallow, circular lakes have individual watersheds of about 80 to
120 acres; the size of the watershed determines the size of the playa. The topography is flat to
gently rolling, containing approximately 20,000 to 30,000 separate playa watersheds. The "wet"
period of playas is seasonal, and their size and wet period depend on the intensity, duration, and
frequency of precipitation and infiltration. Vegetation is diverse because it is influenced by
varying salinity and depth and duration of saturated conditions. Typically, playas demonstrate a
pattern of concentric plant zonation of submerged and emergent aquatic species, such as
pondweeds, arrowheads, and cattails, and lowland plants in wet meadows that surround the lakes.
Many of these lakes are important migratory bird and songbird habitat.
Precipitation, ranging from 22 to 12 inches from east to west, is the major input since there
are no permanent rivers and streams in the area. Excessive rainfall produces surface runoff in late
spring and early fall. Other inputs, such as groundwater from deep aquifers and irrigation water,
contribute to the permanence of standing water. Such groundwater input is uncommon because
most playas are situated above the regional groundwater table. Because there is no surface water
outflow, playas lose their water by evaporation, seepage, and irrigation use. However, an
abundance of inflow of surface runoff in large enough quantities can result in some recharge to
the High Plains aquifer. This occurs at the margins of the impermeable playas where more
permeable sediments are found.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Since many of the playa watersheds function as cropland and rangeland, their vegetation
serves an important purpose, helping to reduce excess nutrients from runoff and thereby
improving the quality of surface water. In an area where water is not abundant, any addition to
the groundwater will have economic significance, whether it be from irrigation water or recharge.
Where playa watersheds receive Stormwater discharges, the potential exists for adverse impacts to
the playa itself or for degradation of the quality of the local and/or regional groundwater
resources.
Riverine or Riparian wetland Areas of the Southwest
Riverine or riparian wetlands exist along the margins of rivers, behind natural levees, in
oxbows and floodplains. Riverine wetlands in arid climates are limited shoreward by desert and
riverward by water depth and scouring. These wetlands are transitory. They develop rapidly only
to be removed by channel-straightening floods, or proceed toward an upland community after
drying. In the American Southwest, riverine marshes are located in broad alluvial valleys distantly
bounded by mountains. Like cienegas, riparian lands have been impacted by depletion of baseflow
sources or by direct diversions upstream (Hawkins, 1993). A number of riparian wetlands exist,
but some rely on other water sources such as treated upstream wastewater. The quality of the
wastewater discharging to these wetlands plays a more important role in maintaining wetland
functions than do the effects of Stormwater runoff.
Prairie Potholes
The prairie pothole region of the northern United States consists of North Dakota, western
Minnesota, and northeastern South Dakota. This region also extends into southern Canada.
Pothole is defined as a surface depression occurring in glacial sediments, containing water from
precipitation, surface runoff, and groundwater. Vegetation characteristics include cattails and
various species of grasses, sedges, and rushes such as bulrushes. More ephemeral potholes are
characterized by meadow grasses and sedges. Prairie potholes are shallow wetlands in a region
that is fairly flat to rolling; they can occur at many different elevations. These saucer-shaped
depressions have an average depth of about 2 to 5 feet (0.6 to 1.5 m). Their appearance is
dependent on the size and shape of the original stagnant ice block that formed them and on
the effects of wind-induced wave erosion. Individual potholes can range in size from a few
hundred square yards up to several thousand square miles.
Potholes are not usually associated with any regional network of stream channels, but they
are related to local and regional groundwater systems. Water input is from groundwater inflow
(discharge), direct precipitation, and occasionally from surface inflow from excess Stormwater or
snowmelt runoff. The hydroperiods in wetlands range from temporarily to permanently flooded.
These differences cause the development of diverse vegetation zones such as wet meadow,
shallow marsh, and deep marsh. Prairie potholes lose water through evaporation, transpiration,
and seepage to groundwater.
Prairie potholes are extremely important wetland resources in a region with few rivers,
lakes, or other productive wetland types. Approximately 50 to 75 percent of all North
American waterfowl use this region for breeding and for resting during migration. Other
birds and mammals, such as blackbirds and deer, are also common to the pothole region.
Drainage of these wetlands for commercial cropland production threatens them as limited
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factors to Consider When Selecting BMPs
water resources. Degradation of prairie potholes from stormwater discharges is a growing
concern where potholes occur in urban or urbanizing areas.
Sand Hills wetlands
The Sand Hills wetlands account for about 5 percent (1.3 million acres or 0.5 million
hectares) of the Sand Hills area, which consists of central and eastern Nebraska and a portion of
South Dakota. Fifteen percent (28,021 acres or 11,340 hectares) of the original wetlands were lost
before 1970. These wetlands are a result of hilly topography in conjunction with permeable
geologic formations. Small lakes, marshes, and wet meadows occur in the interdune areas.
Approximately 194 species of grasses, sedges, rushes, floating leaved, and submerged plants,
such as Japanese brome, spreading bentgrass, and fox-tail barley (Segelquist et al., 1.990),
dominate these wetlands. These wetlands are important migration sites for waterfowl,
shorebirds, and songbirds. Approximately 80 percent of the Sand Hills wetlands are less than
10 acres in size. The following wetland types are typical:
Seasonally flooded basins are flooded during spring and well drained the rest of the
year.
Fresh (wet) meadows have no standing water but have waterlogged soils and root zone
during the growing season; vegetation consists of sedges and grasses.
Subirrigated meadows have plant roots in contact with the water table. .
Shallow fresh marshes have waterlogged soils for most of the year; marsh areas have
standing water and emergent aquatic vegetation.
Deep fresh marshes have a flooding depth of up to 3 feet in spring and early summer.
Open freshwater lakes and ponds are typically perched above local groundwater
levels, or where topography is below the water table level; a small change in depth yields
a large change in water area because of very shallow lakes. In the westernmost region of
the Sand Hills, lakes and ponds are alkaline and have less diversity of wetland plant
species.
Wind pump wetlands are small wetlands caused by overflowing wind-powered pumps
that tap underlying groundwater.
Most of the wetlands are influenced by local hydrogeology. There is negligible groundwater
inflow from areas beyond the Sand Hills. Annual precipitation ranges from 16 inches in the west
to 24 inches in the east, and is the principal source of water. Highly permeable soils and grassy
dune vegetation promote high rates of water infiltration. Within the interdune valleys, the
accumulation of fine sediments and organic material has reduced permeability. Therefore,
snowmelts and spring rains result in the wetland formations described previously. The hydrology
of each wetland type is dependent on the rate of water input and the rate of downward
infiltration. Other factors influencing groundwater recharge are soil characteristics, geology,
and water table depth. These "subirrigated" meadows are unique because they have more
consistent precipitation and infiltration rates than other wetland types with more seasonal
variations and their water level is almost permanently at ground level. Many have a fairly
constant hydrologic input from groundwater. This constant inflow continues even in drier
years.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
The Sand Hills wetlands are an integral part of the Sand Hills hydrologic system. The
meadowlands have economic significance because of hay production, as well as ecological
significance related to lakes and marshes. Although the wetlands themselves play a relatively
minor role because they constitute only 5 percent of the land surface, the Sand Hills area is
important for recharge of water to the underlying Ogallala High Plains aquifer, which extends
into other portions of Nebraska, as well as parts of Kansas, Oklahoma, and Texas.
Pentlands of the North-Central states
The peatlands of the north-central states include the Red Lakes Peatlands of northern
Minnesota, one of the largest areas of peatlands in the country. Peatlands in this area have low
topographic relief and have a depth ranging from 3 to 10 feet. Peatland describes wetlands that
have soils composed of partially decomposed remains of plants. The decomposition rate is low
because of low oxygen concentrations and saturated soils. Bogs and fens are the predominant
types of wetlands found in the peatlands of the north-central states.
Bogs have acidic, fibrous, spongy, nutrient-poor organic soil (phosphorus and potassium are
the limiting factors), whose organic plant material consists mostly of sphagnum moss. Because of
their location at or above the local groundwater table, bogs acquire most of their water from
precipitation and primarily support the growth of acid-tolerant trees and shrubs such as the
tamarack, the black spruce, and the leatherleaf. Fens represent a transitional stage between
marshes and bogs. Fens obtain water not only directly from precipitation, but also by surface
runoff and groundwater seepage. Fens support diverse plant communities consisting of sedges,
grasses, reeds, and some woody vegetation. Both areas contain a vast number of invertebrates,
insects, and amphibians.
Water chemistry determines the development of different wetland types. Acidic water with
a very low mineral content is typical of bogs, while the fens are characterized by the reverse.
These water chemistry differences are related to water origins. Mineralized fen water originates
from groundwater, whereas precipitation produces the high-acidity, low-mineral water content of
a bog.
Peatlands have a hydrogeologic flow system independent of regional groundwater
movement. Some limited groundwater recharge might occur in the sandy former shorelines
of glacial lakes, where more permeable sediments would permit the percolation of water.
Some examples of particular groundwater interactions are spring fens and groundwater
mounds. The former result from upward seepage of regional groundwater, and the latter are a
result of the mounding of the water table. Also, because of increased elevation of water in
groundwater mounds, a gradient is created, thereby resulting in a return of flow downward.
As a result of increased agricultural cultivation over the last 100 years, many of the
peatlands in the north-central states have been drained. The increase in impervious surfaces that
results from development associated with urbanization has the potential to adversely impact
certain peatlands, particularly fens due to their receiving surface water flows.
Bottomland Hardwoods
Bottomland hardwoods are forested wetlands in the river valley floodplains of the Atlantic
Coastal Plain (extending south from Virginia to Florida), and of the Gulf states of Alabama,
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factors to Consider When Selecting BMPs
Mississippi, and Louisiana. They occupy the broad floodplains, seldom exceeding a width of
5 miles. Since the settling of America, 60 to 80 percent of the original area of these wetlands has
been lost. Bottomland hardwoods consist of flood-tolerant species of oak, gum, cypress, elm, and
ash. These species are adapted for survival in areas that are flooded between 20 to 150 days a year.
Vegetational characteristics are determined by the overall extent of seasonal flooding. This region
is also home to a diverse number of animal and bird species such as deer, raccoons, owls, and
hawks. Forested wetlands like the bottomland hardwoods are important wood duck breeding
habitat. t
This seasonal hydrology also affects surface water and groundwater movement. In drier
seasons, floodwaters and lateral groundwater movement serve as the dominant inputs. Other
input sources include overbank flooding from the main channel, flooding from small tributary
streams, lateral overland flow from valley sides, lateral groundwater flow from valley-side rock
formations, and movements of groundwater parallel to the main river channel. Where there are
permeable rock formations in the local geology like limestone, groundwater helps maintain
wetland characteristics through seepages and springs. Recharge can also occur in the form of bank
storage. As water levels rise, water can move laterally from the channel to the adjacent floodplain.
During floods, bottomland hardwoods trap, filter, and attenuate inputs of sediments and
nutrients. In instances of high rainfall conditions they filter upslope surface runoff. They can also
provide continual recharge to the aquifer, raising groundwater levels up to hundreds of feet away
from the channel.
Swamps and Bogs off the Northeast
Two wetland types common to the Northeast are swamps and bogs. Swamps and bogs occur
in the Northeast in Pennsylvania, New Jersey, New York, and New England. Swamps consist of
woody vegetation occurring on poorly drained lowlands. Generally, they are found in valleys and
valley-side depressions that are periodically flooded. They are associated with surface drainage
systems and periodically can have standing water. Their size ranges from small depressions of less
than an acre to many acres. Northern floodplain swamps have an abundance of hardwoods. Other
swamps, not bordering a river, may contain a mixture of evergreen and deciduous trees. Trees
common to the areas are the white cedar and the red maple. Bogs are a type of wetland dominated
by peat soils, which are nutrient-poor acidic soils dominated by sphagnum moss. Bogs can occur
on flatland, on slopes, or as raised bogs as is the case in northern Maine. Bogs can support only
hardy, acid-tolerant trees and shrubs, heath species, and sedges such as the black spruce, the
tamarack, orchids, and insect-eating plants. Depending on the dominant vegetation, bogs can be
described as forested, scrub-shrub, or moss-lichen types. Both areas in this region harbor animals
and birds such as deer, rabbits, grouse, and owls. In addition, swamps and bogs are home to a
diverse array of rare plants.
The hydrology of swamps and bogs differs greatly. Groundwater, floodwaters, and tidal
innundations provide input to swamps, while rainfall provides hydrologic input to bogs.
Swamps collect groundwater from valley-side seepage, from the soil of downslope depres-
sions, and through fractures in bedrock. Discharge leaves the swamp as stream flow and/or
seepage. Groundwater is not a major hydrologic component of bogs, although the water that
bogs hold is considered groundwater. Bogs in the Northeast are hydrologically self-contained
and are referred to as ombotrophic; there is little inflow or outflow of either surface water or
groundwater. They are isolated from the high mineral content of groundwater and are therefore
Page 2-15
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
very acidic. Although water is not released to stream systems, it can be released as seepage during
times of surplus precipitation. This lateral movement, however, is very slow.
The functions of both wetlands also vary. Water stored in swamps attenuates the movement
of water through the complex integrated hydrological systems involving groundwater, wetlands,
rivers, and lakes. During storm flooding in a dry era, the flooding of a wetland serves as a recharge
source to adjacent aquifers. Bogs, because they retain water so well, act as giant sponges and do
not let much water leave as seepage. What little water is released does not necessarily increase dry
stream flow or recharge aquifers.
Cypress Dome wetlands
Cypress dome wetlands occur in southern Georgia and in the Florida wetlands. The term
cypress dome, also referred to as "cypress pond" and "cypress head," is defined as a hardwood
forested wetland occurring in seasonally or permanently wet saucer-shaped depressions. These
wetlands are small in scope, usually not exceeding 25 acres (10.1 hectares) and are dominated by
pond cypress trees, some of which are over 400 years old. If enough light penetrates the canopy,
understory vegetation like the wax myrtle can grow. Viewed from the side, these trees assume a
characteristic dome-shaped profile, with the smaller trees toward the edges and the larger trees in
the middle. The arrangement of the trees in this manner is due to the occurrence of wildfire,
which often burns only the outer, smaller trees. These domes contain acidic water and organic soil
that is thickest in the middle and thinner toward the edges of the domes. Snakes, alligators, and
nine species of frogs are common in this region.
Cypress domes occur in flat areas where the water table is close to the surface; this surface
water is connected to shallow aquifers. Movement of water from cypress domes proceeds in a
lateral direction. Primary hydrologic inputs to cypress dome wetlands are rainfall and surface
water inflow. Water is lost through evapotranspiration and seepage to groundwater systems. The
deciduous leaves of cypress trees seasonally influence the water budget due to the changes in the
amount of interception of rainfall and transpiration. In the summer months of maximum rainfall,
a net inflow into the wetlands results. The reverse occurs during drier times, providing some ,
recharge. Groundwater recharge/discharge is influenced by the geologic formation beneath the
cypress domes. Cypress dome wetlands located above sinkholes can create permeable pathways
between the wetland and the aquifer and are capable of recharging deeper limestone aquifers.
Cypress dome wetlands have been used for the natural treatment of effluent.
Permafrost/Tundra wetlands
Permafrost/Tundra wetlands are situated in the interior of Alaska and are the western
extension of the wetland complexes of northern Canada. Severe frost is the most important
characteristic that distinguishes the hydrology of these wetlands. Water is frozen in the ground
year-round, resulting in impermeable layers known as permafrost. Permafrost encompasses over a
half-million square miles in Alaska. This condition is continuous in the north, but scattered in
regions farther south. Permafrost areas are very sensitive to minute changes in vegetation cover
and drainage. For instance, color, thickness, and degree of saturation of the wetland determine the
thermal properties of the wetland, which in turn determine summer thaw depth and winter
freeze depth. Thawing occurs at a maximum of 3 feet, and freezing can extend up to hundreds of
Page 2-16
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Factors to Consider When Selecting BMPs
feet. Wetlands produced fay permafrost are seasonal thaw ponds, shallow emergent wetlands,
partially drained lake basins, and wetlands in wet and dry tundra. The term muskeg means
peatland, and it constitutes the organic content of these wetlands. A brief summer growing
season produces limited vegetation consisting of mosses, lichens, and sedges. Mosses fill a particu-
larly important ecological niche because of their role in peat formation; the rate of which is about
one inch per 300 years primarily due to the cold temperatures.
The water budget of the permafrost/tundra wetlands of Alaska varies from site to site.
Precipitation in the Alaskan interior yields less than 12 inches (30.5 cm) per year. However,
because of limited evapotranspiration, there is a net surplus of water available. Both snowmelt
and rainfall are very important water sources for wetlands. Precipitation is the main water input
because of impermeable conditions created by permafrost. Very little water is lost or received to
or from stream and groundwater flow, although there are exceptions. Groundwater recharge can
occur in certain instances where summer snowmelt and precipitation percolate through frozen,
but dry surfaces, or on the warmer southern-facing slopes that have permafrost-free zones
allowing for infiltration. In warmer areas where there is groundwater circulation, more
mineralized water can emerge, resulting in the formation of arctic fenlands. Icings and icy
mounds are wetland features that are the result of springs that continue to flow in early winter.
The timing and amount of summer rain and snowmelt have a significant impact on the
characteristics of individual wetland areas.
Stormwater Factors
Stormwrater Quantity
Changes in land use within a watershed usually result in changes to Stormwater runoff
volume and quality. For example, urbanizing watersheds are characterized by increases in
impervious surfaces, which include roads, sidewalks, parking lots, and buildings, as compared to
rural land uses. Increased imperviousness leads to increased runoff volumes and velocities and
higher pollutant loads. Moreover, natural Stormwater conveyances lend to be replaced with hard
structures such as concrete gutters or swales because of the increases in erosion that often
accompany increased runoff amounts and velocities.
Runoff and Peak Flow
Land use changes alter the established rainfall-runoff relationship that exists in a
watershed. The most common effects are reduced infiltration and subsequent reduction in
the time of concentration (which is the time it takes surface runoff from the most distant
point of a watershed to reach the first swale, gutter, sewer, or channel) (Maidment, 1993).
Travel time, the time it takes flow to move through various conveyance elements to the next
inlet or design point, may also be decreased by urbanization. Both of these factors can
significantly increase peak discharges and runoff (USDA-SCS, 1986). Runoff volumes are
primarily determined by the amount of precipitation and by the infiltration characteristics
of an area. For a given location, some of the factors that determine infiltration characteristics are
more likely to be influenced by human intervention than others. The amount and type of
precipitation for a given location can be quite variable, but are not likely to be modified by
Page 2-17
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Protecting Natural Wetlands: A Guide to Stormwateir Best Management Practices
human actions. The infiltration characteristics are a function of soil type, soil moisture,
antecedent rainfall, cover type, impervious surfaces, and surface retention (USDA-SCS, 1986).
Activities that increase imperviousness, decrease surface retention, or modify cover type can lead
to increases in surface runoff or peak discharge.
As mentioned above, travel time is the time it takes runoff to travel from the point where
sheetflow enters a recognizable conveyance element (e.g., culverts, swales, over land), through the
various conveyance elements, to a specified point in a watershed (Urbonas and Roesner, 1993).
Travel time is principally a function of slope, length of the flow path, depth of flow, and the
roughness of the flow surfaces (USDA-SCS, 1986). As land uses in a watershed become smoother
(e.g., imperviousness increases or forested areas decrease), the velocity of runoff increases, which
decreases the travel time (Urbonas and Roesner, 1993).
Peak discharge changes are often good indicators of changes in land use within a watershed that
will affect the hydrology of natural wetlands. The relationship between runoff volume, watershed
drainage area, relative locations of urbanized areas, effectiveness of flood control structures or other
storage, the time distribution of rainfall during a storm event, and travel time determines peak
discharge (USDA-SCS, 1986). The estimation of peak flows on small (16.1 miles2 or<25.9 km2) to
medium-sized (321.9 miles2 or <518 km2) watersheds is a very common application of stormwater
runoff estimation (Pilgrim and Cordery, 1993).
Mathematical relationships, or models, are used to approximate the relationship of rainfall
to runoff. The results from modeling approximations used to predict runoff from a particular area
are generally much better at indicating changes in runoff, rather than absolute runoff volumes.
For the purpose of determining impacts to wetlands from stormwater runoff, estimating relative
changes in runoff volume and peak discharge is sufficient.
A variety of methods exist to determine runoff volume or peak discharge for sizing and
designing conveyance systems and detention facilities. Pilgrim and Cordery (1993) and
Maidment (1993) describe several different approaches for predicting runoff volume and peak
discharge. Some of the modeling approaches focus on runoff and others on the loss, the part of the
rainfall that does not run off. The assumptions of the different approaches are summarized below:
Loss (and conversely runoff) is a constant fraction of rainfall in each time period, or for
storms with constant rainfall intensity, a simple proportion of the total rainfall. An
example method using these assumptions is the rational formula.
Runoff is the residual after a selected constant loss rate or infiltration capacity is
fulfilled. Examples include use of probable maximum flood computations and the
prediction of hydraulic conductivity (assuming sufficient soils data are available).
Initial loss and continuing constant loss rate index models are similar except that the initial runoff
is zero until an initial loss capacity is met regardless of the rainfall rate; then runoff is a constant
rate.
Runoff is estimated by an equation that represents a function of the capacity rates of loss
decreasing with time. The equations may be based on empirical relationships or
physically based models. An example is the Green and Ampt (1911) equation.
Runoff is represented by,rainfall-runoff relationships, such as the U.S. Soil Conservation
Service TR-55 method, a runoff curve (CN) method.
Page 2-18
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Factors to Consider When Selecting BMPs
Rainfall
Rainfall and snowmelt are the basis for stormwater runoff and are variable in space and
time. In the estimation of runoff or peak flows, rainfall is represented by a hyetograph, which is
the time pattern of rainfall intensity. When data are available, recorded rainfall can be used to
determine the hyetograph, which may be assumed to be constant for the entire watershed if
sufficient spatial data are not available. In the absence of sufficient local data, regional design
rainfall of average intensity (found in national intensity-duration-frequency information) can be
used (Pilgrim and Cordery, 1993). National precipitation data are published mQimatologicalData
and Hourly Precipitation Data by the National Climatic Data Center, which is part of the National
Oceanic and Atmospheric Administration in the Department of Commerce.
Storm frequency refers to the time between rainfall events of equal intensity (return periods).
Storm (and flood) frequency can also be expressed as a probability. For example, a 25-year frequency
storm has a 4 percent chance of happening in any year. Storm intensity is typically defined as a volume
of rain in a given time period. Maps are available that show rainfall for durations from 30 minutes to
24 hours and return periods of 1 to 100 years (Hershfield, 1961). The frequency and intensity of storm
events vary regionally and seasonally. For example, storm events in the central and southwestern
United States typically occur less frequently than those in the East, but may occasionally produce large
volumes of runoff. Some areas may receive the bulk of their annual precipitation as snowfall, and
snowmelt would be a major contributor to streamflow and runoff in such regions. In a summary of
several studies related to urbanization in a watershed, the largest changes in runoff were associated
with 2-year storm events, not 100-year events (Urbonas and Roesner, 1993).
Stormwater Quality
Runoff can be characterized by the use of the land from which the runoff comes. For
example, the constituents of runoff from farmland are likely to be different from those in urban
runoff. Agricultural runoff tends to be high in nitrogen, phosphorus, bacteria, and suspended
sediments. The principal types of pollutants found in urban runoff include sediment, oxygen-
demanding substances, nutrients (phosphorus and nitrogen), heavy metals, pesticides,
hydrocarbons, increased temperature, and trash or debris (Woodward-Clyde Consultants, 1990).
The source of sediments in stormwater might be erosion of bare soil in the watershed or
channel scouring due to increased stormwater volumes and velocities. Sediments in surface water
may settle in wetlands because of the effects of wetland morphology and vegetation on the
lowering of water velocities. Some wetland types, such as tidal and riverine wetlands, might
benefit from settling of some sediments and particulates, while other wetland types might be
adversely affected by even low sediment loadings. High sediment loadings might affect plant
communities or reduce fish spawning habitats in a wetland (Canning, 1988).
Another effect of urbanization is generally higher runoff water temperatures in the summer and
colder temperatures in the winter, primarily because of a reduction in vegetative cover and resulting
rapid drainage (Galli and Debose, 1990). Higher summer water temperatures are associated with
decreased dissolved oxygen levels in surface waters, which affect the aquatic fauna! community.
Pollutants found in stormwater runoff are not transported in the same form; for example,
phosphorus and metals are primarily transported bound to sediments, and nitrogen is often a
dissolved pollutant. Also, the levels of pollutants in runoff can vary according to season and land
use in a watershed (Hickock et al., 1977). Urban wetlands can be affected by increased loadings of
pollutants in runoff in comparison to predevelopment levels.
Page 2-19
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Wetlands that receive stormwater discharges with high sediment levels from sources such as
uncontrolled construction sites can be impacted by excessive silt loads or altered flow patterns.
Large flow volumes, high velocity, and long-term pollutant loads delivered by stormwater dis-
charges can alter or destroy stable wetland ecosystems (USEPA, 1995).
The Nationwide Urban Runoff Program, or NURP (USEPA, 1983), although limited in scope
and purpose, is still considered by the Agency to be the most comprehensive national assessment
of pollutants in urban runoff. The major focus of NURP was to characterize the water quality of
runoff from residential and commercial areas and from industrial park sites. The program
evaluated data from 81 sites in 22 cities and covered more than 2,300 individual storm events.
Because the industrial park category did not include heavy industrial activity, data from the
industrial parks were merged with the data collected from the commercial areas. It should also be
pointed out that the sites evaluated in NURP were selected in part for their low probability to be
influenced by pollutant contributions from construction sites, heavy industrial activities, illicit
connections, or other confounding influences.
The NURP study provides insight on what can be considered background levels of pollutants
for runoff from residential and commercial land uses (USEPA, 1995). The majority of samples
collected under NURP were analyzed for seven conventional pollutants (biochemical oxygen
demand, chemical oxygen demand, total suspended solids, total Kjeldahl nitrogen (TKN), nitrate plus
nitrite, total phosphorus, and soluble phosphorus) and three metals (total lead, total copper, and total
zinc). Median values for the NURP pollutants are reported in Table 2-4, along with their
corresponding coefficients of variation. The original NURP data presented in Table 2-4 are reported
for four land uses: residential, mixed, commercial, and open space. Table 2-5 summarizes the event
mean concentrations as composite results for the same four NURP land use categories.
Because the NURP sites represent average runoff conditions from a mix of residential,
commercial, and industrial park sites, loading estimates based on NURP concentrations will be
influenced by loadings from some of the sources considered in the industrial and commercial
analysis that were located in the catchments monitored (USEPA, 1995). It is, therefore, important
to consider the land use from which runoff originates, as well as other watershed-specific
conditions, when evaluating BMPs to treat stormwater quality for protecting wetlands. Table 2-6
shows different types of land use, the pollutants expected in runoff from those land uses, and the
potential effects of those pollutants on wetlands. This table can be used as a basis to start
evaluating stormwater quality when determining potential impacts to wetlands.
Page 2-20
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Factors to Consider When Selecting BMPs
Table 2-a. Results of the Nationwide Urban Runoff
Program
Meaian Event Moan concentrations for Ml Sites ay tana use Category
aesiaentlal Mixed
Pollutant Median
BOD (mg/L)
COD (mg/L)
TSS (mg/L)
Total Lead (mg/L)
Total Copper (mg/L)
Total Zinc (rng/U
10.0
73
101
144
33
135
TKN(mg/L) 1900
Nitrate plus Nitrite (mg/L)
Total Phosphorus (mg/U
Soluble Phosphorus (mg/L)
736
383
143
Source: USEPA, 1983. Note: CV =
0 x" J J',,'**?''!^> > ">, '" ,*'^' .'VV ^ ^'-A- «,^ ^ot
CV
0
0
0
0
0
0
0
0
0
0
.41
.55
.96
.75
.99
.84
.73
.83
.69
.46
Median
7.8
65
67
114
27
154
1288
558
263
56
CV
0.52
0.58
1.14
1.35
1.32
0.78
0.50
0.67
0.75
0.75
Commercial
Median
9.3
57
69
104
29
226
1179
572
201
80
CV
0
0
0
0
0
1
0
0
0
0
31
39
85
68
81
07
43
48
67
71
Open/
Nonuraan
Median
40
70
30
195
965
543
121
26
CV
0
2
1
0
1
0
1
2
78
92
52
66
00
91
66
11
coefficient of variation.
^ **», "*-v*.
\m ' EBB^unA
from NURP for selected
Composite of Mil i.ana Use
Constituent
BOO (mg/L)
COD (mg/L)
TSS (mg/L)
Total Lead (mg/L)
Total Copper (mg/L)
Total Zinc (mg/L)
TKN (mg/L)
Nitrate plus Nitrite (mg/L)
Total Phosphorus (mg/L)
Soluble Phosphorus (mg/L)
5ta//re: USEPA, 1983. 1995.
Mean
12
94
239
0.24
0.05
0.35
2.3
0.86
0.50
0.15
Categories
Meaian
Site
9
65
100
0.14
0.03
0.16
1.5
0.68
0.33
0.12
oottt
f^f^M^fB^MB&B^UUfp&fVt/B^S
wncdnrBCvons
Pollutants
coefficient of
aercentlle variability
Site
15
140
300
0.35
0.09
0.50
3.3
1.75
0.70
0.21
for Events
0.5-1
0.5-1
1-2
0.5-1
0.5-1
0.5-1
0.5-1
0.5-1
0.5-1
0.5-1
Page 2-21
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Protecting Natural Wetlands: A Guide to Stormwatet Best Management Practices
Table 2-6. effects of Pollutants from DIKFferent
Land uses/Sources on wetlands
tana use/Source
Agricultural runoff (cattle
grazing land, manure)
Agricultural runoff (feedtots)
Commercial stormwater
runoff
Residential stormwater runoff
(low to moderate density)
urban runoff
(developing areas)
Highway stormwater runoff
typical Pollutant*
Bacteria (conform,
streptococcus) .
Sediment
Nutrients
Organic matter
Pesticides, salts
Nitrogen, phosphorus
Total nitrogen
Heavy metals
(Pb, Zn, Cu, Cd)
Petroleum residues
Total nitrogen
Bacteria (coliform)
Heavy metals'
(Pb, Zn, Cu, Cd)
Petroleum residues
Pesticides (diazinon)
Suspended solids
Nitrogen, phosphorus
Lead
BOD
Sheet flow blockage by
embankments
Effect on WtBtiantim
Contamination of shellfish, rendering them
Inedible
Clogged bottom sediments, Interfering
with fish spawning and benthic
Invertebrates
Increased vegetative productivity, resulting
In increased standing stocks of vegetation,
followed by Increased rates of vegetative
decay and higher community respiration
rates
Greater oxygen demand/depletion
Alteration of species distribution
Increased vegetative productivity, resulting
in Increased standing stocks of vegetation
followed by Increased rates of vegetative
decay and higher community respiration
rates
Increased vegetative productivity, resulting
In increased standing stocks of vegetation,
followed by increased rates of vegetative
decay and higher community respiration
rates
Alteration of species distribution
Decreased growth and respiration rates
(chronic toxiclty)
Increased vegetative productivity, resulting
In increased standing stocks of vegetation,
followed by increased rates of vegetative
decay and higher community respiration
rates
Contamination of shellfish, rendering them
Inedible
Alteration of species distribution
Decreased growth and respiration rates
(chronic toxiclty)
Alteration of species distribution
Clogged bottom sediments, interfering
with fish spawning and benthic
invertebrates (smothering)
Increased vegetative productivity, resulting
In Increased standing stocks of vegetation,
followed by Increased rates of vegetative
decay and higher community respiration
rates
Alteration of species distribution; decreased
growth and respiration rates
(chronic toxicity)
Greater oxygen demand/depletion
Sheet flow reduced by embankments,
decreasing the sediment supply to wetlands
and making the waters more likely to stag-
nate when fully flooded.
Page 2-22
-------
factors to Consider When Selecting BMPs
Table 2-6. (continu
Lantf use/Source
Highway stormwater
runoff (cont.)
Multlfamlly residential area
stormwater runoff
,
urban stormwater
runoff (developed)
Pasture stormwater
runoff
Cultivated land
stormwater runoff
industrial area runoff
Sources: USEPA, 1983, 1993,
ecu
typical Pollutants
OH and grease; polyaromatlc
hydrocarbons
Heavy metals (Pb, Zn)
and delcing salt/sand
Nitrogen, phosphorus
Suspended solids
BOD
Bacteria (conform)
Heavy metals
(Cu, Pb, Zn, NI, As, Be)
Organlcs (bls-2-
ethylhexyl phthalate)
Pesticides (a-BHC)
Nitrogen, phosphorus
BOD
Suspended solids
Heavy metals (Pb, Zn, Cu, Cd)
Suspended solids
Nitrogen
Suspended solids
Hydrocarbons
BOD
COD
Suspended solids
1995.
Effect on wetlands
Alternation of the hydrologlc regime, sediment
loading, and direct wetlands removal;
hydrologlc Isolation, decreased salinity In I
tidal marshes, and Increase in vegetative cover;
nutrient retention and signs of eutrophicatlon |
Reduced species diversity
Alteration of species distribution and replace-
ment of sensitive species with tolerant species;
Decreased growth and respiration rates
(chronic toxlclty)
Increased vegetative productivity, resulting In
increased standing stocks of vegetation,
followed by Increased rates of vegetative decay
and higher community respiration rates
Clogged bottom sediments, interfering with j
fish spawning and benthlc Invertebrates
(smothering)
Greater oxygen demand/depletion
Contamination of shellfish, i
rendering them Inedible
Reduced species diversity
Replacement of sensitive species with
tolerant species.
Alteration of species distribution
Decreased growth and respiration rates
(chronic toxlclty) |
Increased vegetative productivity, resulting in
increased standing stocks of vegetation,
followed by increased rates of vegetative decay
and higher community respiration rates
Greater oxygen demand/depletion
Clogged bottom sediments. Interfering with
fish spawning and benthlc Invertebrates
Alteration of species distribution
Clogged bottom sediments, interfering with
fish spawning and benthlc invertebrates
(smothering)
Increased vegetative productivity, resulting In |
increased standing stocks of vegetation,
followed by Increased rates of vegetative decay
and higher community respiration rates
Clogged bottom sediments. Interfering with
fish spawning and benthlc Invertebrates
Reduced species diversity; replacement of
sensitive species with tolerant species; alteration
of species distribution; decreased growth and I
respiration rates (chronic toxlcity) j
Greater oxygen demand/depletion j
Greater oxygen demand/depletion j
Clogged bottom sediments. Interfering with j
fish spawning and benthic Invertebrates I
(smothering) I
I
Page 2-23
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Factors contributing to the variability of pollutant types and loadings from similar land uses
could include the following (Driver and Tasker, 1988):
Physical and Land-Use Characteristics
Total contributing drainage area - a factor in determining the amount of runoff
Percentage of total drainage area that is impervious - a factor in determining the
amount of rainwater that runs off as opposed to being absorbed into the ground
Percentage of total drainage area that is industrialized - a factor in determining the
types of constituents likely to be present in runoff
0 Percentage of total drainage area that is commercialized - a factor in determining
the types of constituents likely to be present in runoff
Percentage of total drainage area that is residential - a factor in determining the
types of constituents likely to be present in runoff
0 Percentage of total drainage area that is nonurban - a factor in determining the
types of constituents likely to be present in runoff
Population density - a factor in determining the amount of pollution per unit area that
might be expected
Stream flow - an influence on the amount of likely dilution
Climatic Characteristics
Total storm rainfall - a factor in determining the amount of rain available to run off
Duration of each storm - a factor affecting the amount of rain running off balanced by
the amount that can be retained in the ground or channeled into another water body in a
given amount of time
2-year maximum daily precipitation - a factor explaining the expected climatic
pattern for a geographic area
Mean annual rainfall - a factor in determining the amount of rain available to run off
Mean annual nitrogen load in precipitation - a factor explaining some of the sources
of pollution to wetlands
Mean annual January temperature - a factor explaining the expected climatic pattern
for a geographic area
Surface water hardness - an influence on the toxicity of certain hazardous substances
(Owe etaL, 1982)
Pollutant loadingsnitrogen, phosphorus, sediment, and leadfrom urban, agricultural,
and open space land uses were evaluated and plotted to aid in the selection of stormwater BMPs.
Figures 2-2 through 2-5 show the median, maximum, and minimum pollutant loadings reported
for several locations around the United States. Although these figures cannot be used to replace a
thorough evaluation of site-specific conditions, they can be used initially to screen BMPs to
shorten a list of potential BMPs to protect a wetland. For example, a wetland that is downstream
from a predominantly urban area could potentially need to be treated for lead, whereas if the
Page 2-24
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factors to Consider When Selecting BMFs
predominant land use were forest, lead would presumably not be a problem. Sediment
loadings would be an important consideration for all land uses, but loading rates can vary
widely within a land use category. The above-mentioned factors could account for the ranges
of pollution from different land uses and from within the same land use category, as shown
in Figures 2-2 through 2-5.
Sediment Loadings
**** Maximum
*-s
?6
TJ-5
i-
10000.000-r
1000.000-
100.000-
10.000-
1.000
II ]
1 1
m
' 1
Minbnun
Median
1
Urban
Agriculture Open Space
Source
Forested
Figure 2-2. Sediment loading rates for various land uses.
Nitrogen Loadings
c o
10000.00 -r
1000.00 -
100.00 -
10.00 -
1.00 --
.10 ..
Urban
Agriculture Open Space
Source
" Maximum
Minimum
Median
I
Figure 2-3. Nitrogen loading rates for various land uses.
Page 2-25
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
0
'en T
£ "Si1
CD 2
II
«£
jg^.
Phosphorus Loadings
"~ Maximum
1000.000 -|
100.000 -
10.000
1.000 -
0.100-
0.010 -
Minimum
m "
Median
iL
'
T
J. P T
1
UAJUI Urban Agriculture Open Space Forested
Source
Figure 2-4. Phosphorus loading rates for various land uses.
Lead Loadings
1*
§ £
10.000 j
1.000--
0.100--
0.010--
0.001
Maximum
Minimum
Median
Uifaan
Agriculture Open Space
Source
Forested
Figure 2-5. Lead loading rates for various land uses.
Sources for Figures for 2-2 through 2-5: Novotny and Chesters, 1981; Shahane, 1982; Sweeten and Melvin. 1985; USEPA, 1983.
Page 2-26
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Factors to Consider When Selecting BMPs
Overview of BMP Capabilities
Assessing the Ability of a BMP to Protect a wetland
Wetlands can provide water quality benefits that should be considered when developing or
implementing watershed planning. However, because natural wetlands are waters of the United
States they must be afforded the same protection from degradation as any other receiving water.
The wide variability of wetland types and the range of potential impacts from runoff make it
very difficult to recommend a particular methodology to protect wetlands. EPA believes, however,
that the use of natural wetlands for control of runoff should be avoided.
Different wetland types vary in their ability to handle the changes caused by stormwater
flows and pollutant levels. Where runoff is specifically channeled or routed to wetlands, BMPs
should be implemented to maintain the natural functions of the wetland. This might require the
use of BMPs for water quality improvement, techniques to minimize changes in the natural
hydrology of a system, or both. The principal question to be answered is whether the BMP is
providing the level of protection necessary to ensure that the wetland retains its natural health
and functions. Therefore, unlike other manuals that use end-of-pipe approaches, this manual
focuses attention on the resource. To the resource manager this approach could be viewed by
standing in the wetlands.
A variety of physical, chemical, morphological, and biological wetland functions could serve
as appropriate indicators of the wetland's continued health and sustainability. These include:
Groundwater quality and recharge
Groundwater discharge
Flood flow alteration
Shoreline stabilization
Sediment/toxicant retention
Nutrient uptake, transformation, and removal
Vegetative diversity, biomass production, and export
Aquatic diversity and abundance
Terrestrial wildlife diversity and abundance for breeding, migration, and wintering
Stable recreational opportunity, uniqueness, heritage
The wetland's continued function and sustainability should be assessed. If it can be
determined that the wetland is healthy, this might also be an indication that the proper BMP has
been selected, has been well designed for the site and specific application, and has been well
maintained (assuming other objectives of the BMP are being achieved, such as water quality). If
there is some problem with the wetland (i.e., its function, health, or sustainability), the cause of
the problem should be evaluated. Any combination of a number of causal factors could be
responsible for the problem. These include, among others, choice of BMP, design, operation, and
maintenance.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
The evaluation should follow a logical, decision-tree-type sequence, working in reverse
order (selection, design, operation, and maintenance). For example, if the improper BMP was
selected for the site, none of the other factors would be likely to solve the problem, although they
might help to some degree. Or, it might be determined that the proper BMP was selected but the
design was not tailored to the site conditions (i.e., considering stormwater discharge factors and
wetland factors like hydrology, soils, and Vegetation). In other cases, an operational flaw might be
altering the wetland's hydrology, or perhaps the BMP is not being maintained in the manner best
suited to ensuring the continued health and function of the wetland.
It is likely that the same decision makers and technical personnel will be responsible for
implementing both stormwater BMPs that discharge to wetlands and BMPs that do not discharge
to wetlands. Therefore, these considerations should be emphasized to the appropriate staff so that
the aspects of stormwater BMP selection, design, operation, and maintenance unique to practices
used to protect wetlands are not inadvertently disregarded.
Although a number of manuals describe BMPs to be used to address stormwater runoff, this
manual is a first attempt at addressing the specific water quality concerns related to wetlands. It
is intended for use by anyone addressing potential impacts to wetlands from stormwater runoff,
and it presents a wide range of planning approaches as well as specific BMPs that can be employed
in a variety of situations. Although these are all discussed as BMPs for the purposes of this manual,
some approaches might be more relevant and useful for large-scale planning efforts, whereas
others are more appropriate for very specific localized problems.
Nonstructural controls
Nonstructural controls are techniques used to manage stormwater runoff that do not
require physical alteration of the land (USEPA, 1993). The prevention and minimization of
pollutant loadings through source reduction and watershed planning are preferred over treating
the unavoidable loadings that occur following urbanization. Watershed planning can help to
reduce the need for expensive construction and maintenance of permanent structures if
development in the watershed is accomplished in an environmentally sensitive manner that
minimizes impacts. Obviously, opportunities for watershed planning will be limited by the
current level and pace of development in a given watershed.
Nonstructural control practices applicable to wetlands include:
Pollution prevention
Watershed planning
Advance identification of wetlands
Permitting programs
Preventive construction techniques (minimal impact development)
Retaining open spaces, vegetated natural buffers, and riparian areas
Inspection and maintenance of existing stormwater and erosion controls
Education programs
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Factors to Consider When Selecting BMPs
Watershed Planning
Watershed planning involves the development of a watershed management plan, often as
part of a comprehensive plan. The watershed management plan that describes existing patterns of
environmental quality and community life in a watershed (including demographic trends,
housing, infrastructure, economic activity, natural resources, and wildlife) and recommends goals
and policies (including protection of drinking water sources and control of land uses) to manage
future development to minimize impacts on water resources. A watershed management plan
consists of maps of the watershed and its resources and text that explicitly addresses conflicts and
trade-offs among development, environmental protection, social issues like as affordable housing,
transportation, and many other factors. Watershed management plans also consider alternative
actions and methods of measuring progress (CTIC, n.d.). Special-purpose planning, e.g., wetlands
management planning, is one component of a watershed plan (USEPA, 1992c). Other components
are wellhead protection and Class V (underground injection) well management.
Resource inventory and information analysis provide the basis of watershed management
planning. For a plan to be effective, it should have measurable goals describing desired outcomes;
for example, "Reduce loads to wetlands and surface waters by 25 percent." The process of
developing a watershed plan should also identify how wetland protection goals and other
concerns of the plan will be addressed, and should identify information gaps. Goal setting must
then be followed by developing means of measuring progress. For example, sediment input and
specific pollutant loads can be assessed to determine whether the plan is being successfully
implemented.
Watershed planning also allows stormwater managers to determine how best to control the
quality and quantity of surface waters within a watershed after development has commenced.
Ideally, this process will attempt to replicate, to the extent possible, the predeveloped hydrology
of the watershed, including how wetlands function for flood storage as well as their water quality
functions. Watershed planning is an opportunity for wetland managers to assess wetland
protection needs, develop wetland restoration goals, plan mitigation strategies, and determine
impacts from land use changes to wetland resources. When wetland resources are identified on a
watershed (or landscape) scale, factors such as location of individual wetlands with respect to
other wetlands, adjacent land uses, or water bodies can be factored into the decision-making
process of a wetland resource assessment and the design of appropriate controls (structural or
nonstructural) for preventing or treating stormwater discharges to natural wetlands.
Some increase in impervious surfaces, resulting hydrological changes, and a related addition
of pollutant sources are inevitable results of urban and suburban development. BMPs attempt to
mitigate these hydrological modifications and pollutant inputs. Without BMPs, wetlands
receiving flows of uncontrolled runoff would likely become severely degraded. Therefore, the
changes in hydrology rather than the BMPs are the cause of the problem. Nonetheless, where .
wetlands occur within a watershed, planning for BMPs needs to consider the impact of each BMP
on wetlands and related groundwater resources.
A modeling mechanism may be incorporated into the watershed management plan. Such a
model shows the cause-and-effect relationships within a watershed and can be used to test various
land use/stormwater control scenarios to determine which option best preserves overall wetland
functions or improves the health of a degraded wetland system.
The Maryland Nontidal Wetlands Program calls for watershed management plans that
contain, at a minimum, a functional assessment of nontidal wetlands within a watershed; the
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
location of potential mitigation sites; and plans for the protection of nontidal wetlands, limiting
cumulative impacts, water supply management, and flood management (MDDNR, 1991). An
effective wetlands watershed management plan may also include wetlands and floodplain
protection ordinances, river corridor programs, sewer overflow provisions and siting controls,
control of septic systems, requirements for pumpout stations for small boats, designing and siting
of wastewater treatment facilities, surface water and groundwater quality controls; and non-
point source pollution controls (USEPA, 1992c).
Once wetland resources and existing land use designations have been identified and the
goals for wetland protection have been determined, implementation strategies can be developed
to guide activities in the watershed. Nonstructural control practices (as opposed to structural
practices) are the preferred technique for protecting wetlands because they are based on pollution
prevention and reduction. Nonstructural control practices can be used within four program areas:
permitted uses, preventive construction techniques, operation and maintenance, and education.
Permitting Programs
The goals of a watershed management plan, such as wetland protection and water quality
improvement, can be implemented through various permitting programs such as land-use
planning and zoning, natural resource/wetland protection ordinances, storm water permitting
programs, and other pollution control programs. Land development regulations may also require
natural performance standards such as limiting rates of runoff, soil loss, or pollutant loadings into
wetlands and the completion of environmental impact assessment statements prior to
construction plan approval.
Preventive Construction Techniques
Stormwater quality and wetland protection can be improved through the implementation
of numerous nonstructural preventive construction techniques for new development and
redevelopment that help to minimize impacts, such as:
Limiting the amount of impervious surf ace
Requiring setbacks from wetlands, riparian areas, and surface waters
Preservation of natural vegetation
Open space requirements and slope restrictions
Siting infrastructure so as not to adversely affect wetland and water resources
Discouraging development in environmentally sensitive areas that are critical to
maintaining water quality
Site plan review procedures
Performance standards for Stormwater and wetlands
Operation and Maintenance
Maintenance of existing Stormwater controls ensures continuing operation, effective
pollutant removal, and the protection of wetland and surface water resources. Maintenance, such
as the removal of sediments from detention and infiltration devices, the replanting of vegetation
as upkeep within buffer and open space areas, and the maintenance of erosion and sediment
control structures, is essential to the success of most structural and vegetation-dependent NFS
Page 2-30
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Factors to Consider When Selecting BMPs
pollution controls. Maintenance programs should require the prior designation of an entity or
individual who is responsible for maintenance, and should stipulate the funding source or sources.
Outreach and Education Programs
Outreach programs can be designed to reduce individual contributions to stormwater
problems and improve program implementation by maintenance personnel and government
officials. Training programs and educational materials for public officials, contractors, and the
public are also crucial to implementing effective urban runoff management programs. Contractor
certification, inspector training, and competent design review staff are important to the success
of a stormwater management program. The states of New Jersey, Virginia, Maryland, Washington,
Delaware, and Illinois; NRCS; and the city of Alexandria, Virginia, have developed manuals and
training materials to assist in implementation of urban runoff requirements and regulations
(USEPA, 1993).
Education programs should be implemented in homes, in residential communities, and at the
workplace. At a minimum, they should educate and encourage the public to participate in and
support local pollution prevention programs. Such programs might include storm drain stenciling,
used oil and hazardous chemical recycling, litter control, street sweeping, lawn management and
landscaping, safe use and disposal of household hazardous materials and chemicals, correct
operation of onsite disposal systems, including the danger of industrial wastewater discharges to
septic systems, proper disposal of pet excrement, and water conservation.
Structural Controls
Structural controls are methods for managing stormwater that involve altering the flow,
velocity, duration, and other characteristics of runoff by physical means (USEPA, 1993).
Structural controls can be used for both stormwater volume control and water quality
improvement. A fundamental consideration for design or selection of a particular BMP is whether
the wetland hydrology is dependent on surface water flow, groundwater flow, or some
combination of the two. Most structural controls are engineered structures that require regular
maintenance. Structural controls that can commonly be used to protect wetlands include:
Infiltration basins
Infiltration trenches
Sand filters
Level spreaders (may be associated with gabions)
French drains
Grassed swales
Vegetated filter strips
Open spaces
Extended detention dry basins
Wet ponds
Constructed wetlands
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Less common controls may be used in special situations and for special purposes, usually to
improve stormwater quality. These controls generally have limitations regarding applicability and
maintenance. For example, untreated stormwater directed to a separator, dry well, or other
shallow disposal system will eventually find its way to a water-table aquifer. Examples of these
less commonly used controls include:
Porous pavement and concrete grid pavement
Oil/grit separators or water quality inlets
Dry wells or roof downspout systems
Exfiltration trenches
BMPS In series
BMPs in series incorporate several stormwater treatment mechanisms in a sequence to
enhance the treatment of runoff where determined necessary. By combining treatment
mechanisms in series rather than using a single method of treatment for stormwater runoff, the
overall levels and reliability of pollutant removal can be improved. Some examples of serial BMPs
include the use of multiple pond systems, the combination of vegetated filter strips with grassed
swales and detention ponds, and the combination of grassed swales or vegetated filter strips with
infiltration trenches. (For more information, see the fact sheet "BMPs in Series" in Section 4 of
this manual.)
BMP Maintenance Requirements
When properly designed and located, BMPs can protect wetlands by providing preliminary
treatment of stormwater to (1) restore or maintain predevelopment hydrology and hydroperiod
by providing a balance between infiltration and detention or retention, (2) reduce fluctuations in
nutrient levels, and (3) remove excessive levels of nutrients and sediments. The ability of
stormwater pretreatment systems to provide these functions depends on both the effectiveness
and reliability of individual BMPs or BMPs in series. Regular inspections and maintenance are
essential to good performance for all BMPs (Washington State Department of Ecology, 1991).
Failure to provide proper maintenance can result in reductions in the pollutant removal
efficiency or reductions in hydraulic capacity of stormwater treatment systems (Washington
State Department of Ecology, 1992).
If stormwater BMPs are not functioning properly due to inadequate maintenance, the result
can be flooding problems and in some cases even an increase in the pollutant load of stormwater
discharges (Washington State Department of Ecology, 1992). Effective maintenance can be
ensured by clearly defining maintenance responsibilities and performing regular inspections to
determine maintenance needs (Washington State Department of Ecology, 1992). Apart from
achieving the required effectiveness and reliability, BMP maintenance and longevity are
important considerations in the selection of a BMP, not only because longevity varies
considerably between treatment options, but also because maintenance costs may be high, in
some cases rivaling construction costs over the design life of the BMP (Schueler et al., 1992).
Page 2-32
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Factors to Consider When Selecting BMPs
Maintenance and maintenance costs can be reduced if maintenance needs are anticipated in
the design stage (Schueler, 1987). The need for incorporation of maintenance provisions in
facility designs is especially important when anticipating removal of sediment and debris from
basins. Two specifics to be incorporated into site plans are access for maintenance equipment and
easements. Easements are necessary around the perimeter of stormwater facilities to allow for
maintenance and to provide a buffer from encroachment (Washington State Department of
Ecology, 1992).
Maintenance is necessary to ensure that the storage and infiltrative capacity of the BMP is
not compromised so that the BMP can effectively buffer wetlands from the detrimental effects of
stormwater. The temporary storage and infiltration functions of pretreating stormwater can be
partially accommodated by the wetland if not provided by the BMP, but not without potential
damage to the wetland. Furthermore, stormwater might not be sufficiently treated before it
enters the wetland. Regular maintenance is used to ensure that the BMP continues to function
according to design specifications. Specific design variables that regular maintenance is intended
to maintain include the detention time of pond systems; the flow path of stormwater to, from,
and within the BMP (preventing erosion); the water level; and vegetative cover in and
surrounding the device. Frequent problems that maintenance is targeted to address include
clogging of infiltrative surfaces; blockage of inlet or outlet structures by debris; erosion of pilot
channels, side slopes, embankments, and emergency spillways; sedimentation; accumulation of
pollutants; overgrown or patchy vegetation; and nuisance insects.
The major mechanism by which pollutants are removed by BMPs is through sedimentation
of sediment particles and pollutants attached to sediments. The more efficient a BMP is at
removing sediments, the more frequently sediments and pollutants that have accumulated in the
treatment device will need to be removed to ensure that the system continues to function
properly (Washington State Department of Ecology, 1992). It is beneficial not to allow sediments
to stand in the system for long because the longer the wastes accumulate in the system the more
likely they are to become contaminated to the point where they might no longer be accepted for
disposal at a landfill (Washington State Department of Ecology, 1992). Frequent sediment
removal from catch basins, detention vaults, pretreatment inlets, oil/grit separators, vegetative
BMPs, and pond forebays prevents sediments from being scoured by storms, which could result in
shock loadings to receiving waters or clogging of a downstream BMP if BMPs occur in series. Pond
systems require less frequent sediment removal; however, flooding can result if pond capacity is
reduced by accumulated sediment. Infiltration devices that become clogged with sediment can
also cause flooding.
Maintenance Factors
The degree and type of maintenance required depend on the BMP type, design, management
objectives, climate, and surrounding land use. For instance, infiltration BMPs, although effective
in removing pollutants, are usually less reliable than other types of BMPs due to poor longevity
(Schueler et al., 1992). Specific management requirements for each of the stormwater
pretreatment systems described in this document are provided in Section 4.
The type of maintenance depends on management objectives. For instance, pond systems
composed of wet meadow or wetland marsh and constructed stormwater wetlands, adjacent to
natural wetlands, may be managed for the dual purpose of promoting wildlife habitat and
removing pollutants. Creation of wetland habitat within a stormwater treatment pond is
Page 2-33
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
especially important in areas where the value of natural wetlands has been diminished by
construction of stormwater treatment systems adjacent to or in natural wetlands (South Carolina
Coastal Council, 1988). Benefits of wetland creation include removal of soluble pollutants,
provision of wildlife habitat, and disguise of unsightly debris and sediment deposits (Schueler,
1987). When a constructed wetland is placed adjacent to a natural wetland, the two wetlands
form an integrated system, the function of which is significantly influenced by the management
of the constructed wetland (DeVoe and Baughman, 1986). Management for waterfowl, the most
common natural habitat objective, may employ some combination of water level manipulation,
bed disturbance, and salinity manipulation in coastal areas. The goal of these practices is to
promote the growth of aquatic plants that attract migrating waterfowl. The degree and timing of
exchange of water between adjacent creeks, the constructed wetland, and the natural wetland
influence dissolved oxygen, temperature, and aquatic species (such as fish and crayfish)
recruitment (DeVoe and Baughman, 1986). Usually water levels of ponds and wetlands
exclusively managed for waterfowl are maintained in the spring and fall for waterfowl migration.
During the late spring, water is drained so the beds can be plowed in June. In October, the beds are
flooded again (DeVoe and Baughman, 1986). There might be conflict of use between the need to
maintain low water levels to capture stormwater and the need to maintain higher water levels to
attract waterfowl. In addition, an objective might be to discourage waterfowl from using the
constructed wetland if pollutant concentrations are expected to be high.
Mosquito control and frequent mowing will not be as important in an area managed for
wildlife as in a residential neighborhood. Mosquitoes are a problem in wet meadows because
rainfall pools in areas, allowing mosquito eggs to develop and hatch. Constructed wetlands and
pond systems can be managed to minimize the production of mosquitoes by maintaining a system
of ditches or canals for drainage. An aquatic weed control program can control mosquitoes by
preventing an overgrowth of vegetation in the pond. Fish stocks can be maintained in the
permanent pool of retention ponds (South Carolina Coastal Council, 1988). A pond that is
scheduled to be filled for waterfowl use can be filled and emptied first to flush out resident
mosquito populations (DeVoe and Baughman, 1986).
Implementation
Frequently, more attention is placed on design and location of structures than on
maintenance. In addition, many jurisdictions do not have required BMP maintenance programs
to ensure the adequate performance of BMPs (Schueler et al., 1992). The lack of routine
inspection and maintenance is especially evident in the case of small, privately owned local
disposal facilities, such as grassed swales, infiltration trenches, and infiltration basins, that are too
small to justify a full-time staff person. The long-term effectiveness and reliability of BMPs can
be enhanced through implementation of a maintenance and operation schedule for each BMP that
explains routine and nonroutine maintenance tasks and identifies the party (or parties)
responsible for performing them (Washington State Department of Ecology, 1991). A
maintenance plan developed for the life of the stormwater treatment facility can be required
before the certification of a project (South Carolina Coastal Council, 1988). Inspectors need to be
trained to know how the stormwater treatment system is designed to function and what the early
warning signs of problems are. In addition to the brief overview of maintenance requirements of
various types of BMPs, specific information is provided in Section 4 for each BMP to assist
managers in developing their operation and maintenance plans.
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Factors to Consider When Selecting BMPs
Development of an Effective Maintenance Plan
Development of an effective maintenance plan requires site-specific information and a
considerable amount of planning and foresight, beginning with the establishment of broad goals
and objectives and ending with the scheduling of staff and equipment. Activities involved in
designing an effective maintenance program include developing goals, reviewing existing policies,
assigning responsibilities, planning the frequency of inspections, scheduling inspections,
determining staffing needs, and determining enforcement procedures (Washington State
Department of Ecology, 1992). Each component of the planning phase is discussed separately.
An effective maintenance plan reflects the specific priorities and goals of the community
served by the stormwater treatment program, as well as watershed characteristics and existing
policies within the jurisdiction (Washington State Department of Ecology, 1992). Therefore,
development of a management plan begins with arriving at policies that outline who should be
responsible for maintaining BMPs on private and public lands and how these policies will be
enforced. The goal-setting stage differs from the final stages of maintenance plan development in
that here utility officials should not constrain themselves to consideration of goals limited by
current practices and policies but rather should consider how maintenance ideally should be
performed, looking beyond the next 5 to 10 years to anticipate how decisions made now will
affect future courses of action and alternatives (Washington State Department of Ecology, 1992).
Existing policies within a jurisdiction can either facilitate or impede an effective
maintenance program. Once the goals of the maintenance program are identified, managers
should review existing statutes, ordinances, and policies to assess how these complement the
established goals of the maintenance program. In this manner, options for revising these policies
where shortfalls are uncovered can be identified early (Washington State Department of Ecology,
1992). Design requirements for maintenance (e.g., access, dean-out traps, sediment disposal areas)
should be included in ordinances and policies.
During the planning stage of the maintenance plan, staffing needs and limitations should be
considered prior to deciding who will be responsible for performing maintenance tasks,
specifically whether they will be performed privately or by the local government. Some
distinctions maybe made between routine and nonroutine maintenance activities or between
facilities located on rights-of-way and those on private lands. If private individuals or
organizations will perform the maintenance, an ordinance that requires owners to be informed of
operation and maintenance frequency, schedules, procedures, responsibilities, and enforcement
will be necessary. For example, an ordinance might require that new owners be notified at the
time of sale that they are owners of a stormwater treatment device and that they be provided
with the operation and maintenance instructions (Urbonas and Stahre, 1993). An ordinance
might not be required if local government will perform the bulk of the maintenance. If an
ordinance is not used to assign responsibilities, consideration should be given to staffing needs
and limitations, merits of alternative funding mechanisms, provisions for intergovernment
cooperation, and specific needs or limitations (Washington State Department of Ecology, 1992).
Maintenance inspections need to be planned, including inspection frequency, scheduling,
and staffing needs. In general, BMPs should be inspected and maintained once a year, at the very
least, to remove debris, sediment, and vegetation that threaten the function or capacity of the
facility and to replant damaged vegetation on grassed swales, vegetated filters, and buffer strips
(Washington State Department of Ecology, 1992). The frequency of inspection depends on the age
of the stormwater BMP, the occurrence of large runoff events that could damage the BMP, the
history of problems encountered, and whether inspectors will perform routine maintenance.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Maintenance inspection programs should be designed with enough flexibility to accommodate
greater frequency of inspection if maintenance records indicate a particular need. Because each
maintenance task has specific personnel and equipment requirements, the scheduling of
maintenance activities should also be considered to-avoid the frustration that goes along with
inefficient implementation (Washington State Department of Ecology, 1992). Routine
maintenance burdens are greater during the rainy season when vegetation grows quickly,
sediments accumulate, and erosion damage from storms threatens to clogBMPs. Nonroutine
maintenance such as sediment removal from basins should be scheduled for the dry season.
Staffing needs become apparent once tentative inspection and maintenance schedules have
been developed. Staffing needs should be assessed early in the planning and budgeting stage of a
project so that inspection and maintenance costs can be included (Washington State Department
of Ecology, 1992). Provisions should be made so that extra staffing is available in times of flooding
or to correct problems promptly when the facility is contributing to a violation of a water quality
criterion. Managers should consider personnel requirements to perform routine operation and
maintenance inspections as well as inspections performed after BMP construction. Although less
staffing is required if much of the routine maintenance, such as mowing and trash removal, is in
the hands of private facility owners, private facilities still require inspection and perhaps
nonroutine maintenance by government-employed staff. Staffing programs must consider the
level of staffing required, training programs, and hiring of skilled inspectors'(Washington State
Department of Ecology, 1992).
Record keeping assists jurisdictions in developing maintenance schedules, identifying
problems, and enforcing maintenance plans. It is recommended that records be maintained for
existing public and private BMPs as well as for new facilities as they are constructed. Existing
facilities should be added to the maintenance schedule as they are encountered (Washington State
Department of Ecology, 1992). Records of new stormwater facilities should include (Washington
State Department of Ecology, 1992):
As-built plans and locations
Findings of fact from any exemption granted by the local government
Operation and maintenance requirements and records of inspections
Maintenance actions and frequencies
Engineering reports, as appropriate
Enforcement provisions must be included in any plan in the event that facilities are not
being maintained by responsible parties. One possibility for enforcement includes billing the
owner for work performed on the facility.
Components of an Effective Maintenance Plan
The following are the essential components of a good maintenance program (South
Carolina Coastal Council, 1988):
Description of required maintenance
Maintenance frequency, schedule, and/or criteria
Maintenance responsibility
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factors to Consider When Selecting BMPs
The tasks required under both routine and nonroutine maintenance should be well defined,
including who is responsible. An operation and maintenance manual should be provided to the
owner or whoever is responsible for maintenance. The manual at the very least should teE the
person responsible for the facility what to watch for and what tasks to perform on a regular basis.
A more complete manual might include copies of the as-built plans, a list of replacement parts,
emergency procedures in case of severe flooding, and contacts for more information (Urbonas
and Stahre, 1993). Routine maintenance activities such as mowing and trash removal should not
be neglected because these will keep the facility in an aesthetically pleasing state, which is
important to the community. A well-maintained appearance also deters vandalism and trash
dumping. The details of specific maintenance tasks are given in Section 4 for each type of BMP.
The maintenance plan should outline the frequency of inspection. Maintenance should be
scheduled so that BMPs will be ready for the next rainy season and will be capable of operating at
full conveyance in time for seasonal flooding. The maintenance scheduling should also include
prompt repair of facilities that are contributing to violations of water quality criteria. The
problem should be corrected and the facility reinspected within one month to ensure that it is
being maintained (Washington State Department of Ecology, 1992).
The primary purpose of the maintenance plan is to define who is expected to provide long-
term maintenance of the stormwater treatment system, whether it is the developer, homeowners'
association, landowner, city, county, or other body (South Carolina Coastal Council, 1988).
Backup procedures should also be specified in the event that the responsible party fails to provide
adequate maintenance (Washington State Department of Ecology, 1992).
Funding Sources
Included in this section are some examples of various traditional and innovative funding
sources for the implementation of environmental programs. Environmental programs are often
implemented to protect natural resources such as wetlands and stormwater. Traditionally, funding
for environmental programs has come from general revenue funds. Now that both state and local
governments are realizing fiscal constraints, alternative sources of funding are becoming
important options for implementing nonpoint source pollution controls. Traditional sources of
funding, such as taxes and bonds, are being supplemented by innovative funding sources like
special license plates and income tax check-offs (USEPA, 1994). This section briefly describes
some traditional and some innovative funding alternatives that could be used to finance
nonpoint source pollution control programs (adapted from A State and Local Government Guide to
Environmental Program Funding Alternatives, USEPA, 1994).
Taxes
Property and sales taxes are charged as a percentage of property value or gross sales and are
imposed at the state and local levels. An innovative example is the Puget Sound, Washington,
proposal to charge landowners an annual nonpoint source pollution control tax, based on
property size and type. Owners with onsite sewage systems, livestock, and parcels in areas
required to develop stormwater management plans would be assessed a surcharge if land uses were
not managed to reduce nonpoint source pollution inputs.
Page 2-37
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Real estate transfer taxes are assessed as a percentage of property values when property is
sold. These taxes are imposed on property buyers, sellers, or both. Funds raised by such taxes can
be dedicated to help purchase environmentally sensitive lands or to support resource conservation
programs.
A. he Prince William County,
Virginia, watershed management
study Is a project that Is attempting
to develop an Innovative
stormwater management plan
through the use of BMPs and the
restoration of riparian habitats. A
5-year, multimillion-dollar program
to study the three urban water-
sheds Is being funded through a
federal-state-local cost-sharing
approach. The Prince William
County government Is funding 50
to 60 percent of the entire
project. The remainder of the
funding Is being provided by the
U.S. Fish and Wildlife Service, the
U.S. Geological Survey, the Army
Corps of Engineers, and the
Environmental Protection Agency.
The Prince William County
government Is helping to fund the
project through a stormwater
utility fee. Utility taxes can be
Imposed on property owners
based on a variety of factors, such
as the amount of runoff gener-
ated on a piece of property. (The
fee can be calculated by the
percent of the property that Is
Impervious.) Impact fees are
usually collected at one time and
can based on factors such as new
land development.
(See case study on P. 3-11 for
more Information.)
Commodity taxes are charged on specific items (commodities) such as
gasoline, liquor, or cigarettes. The money raised could be targeted for
environmental programs or services. A tobacco tax helps finance Washington
State's water quality protection plan.
Tax surcharges are fees added to established tax rates. They are often
used for sudden unforeseen events. A tax surcharge on residential sewer bills,
for instance, might be used to finance the replacement of stormwater
retention basins destroyed during a hurricane.
Stormwater utility taxes are imposed on property owners to pay for
stormwater treatment. The charge can be based on the amount of runoff
generated from the property, the amount of impervious area (hard surfaces)
on the property, or the assessed value of the property. There are more than 100
stormwater utilities in the United States. Methods of determining
stormwater utility charges vary considerably around the country, depending
on local stormwater management goals and conditions. In general, utilities
are either publicly owned and operated enterprises or privately owned
enterprises whose ability to profit from providing public services is regulated
by a public agency. Utilities provide a more reliable source of funds for local
stormwater management than do property taxes.
Tax incentives and disincentives refer to a tax system set up to encourage
or discourage certain behaviors by offering tax reductions or increases.
Incentives often take the form of state tax credits, deductions, or rebates. A tax
credit for the use of low-flow plumbing fixtures, for example, can encourage
water efficiency. Disincentives often take the form of fees, taxes, or price
increases. A tax or fee, for example, can discourage the inefficient use of a
product.
Fees
User fees are the most common way of recovering the costs of providing a service. These
fees can tie directly to the users of a resource or facility (sportfishing license fees, for example).
User fees are particularly useful at the local level, where user groups are easily identified.
An innovative example of a user fee is the State of Maryland's license plate program to fund
its Chesapeake Bay Trust. More than 40,000 Treasure the Chesapeake" license plates have been
sold, raising over $4 million. Baltimore, Maryland, area Ford dealers offered Bay license plates at
no cost to their new cat and truck owners by paying the $10 fee from June through July 1991,
raising $20,000 for the Trust.
Plan review fees are assessed by a local government to conduct a review of development
plans to ensure that they meet certain requirements. This technical review includes determining
Page 2-38
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factors to Consider When Selecting BMPs
the adequacy of stormwater management facilities, setback requirements, and wetland
protection. These fees help cover the cost of conducting plan reviews and inspections.
Onsite inspection fees are charged to cover the costs of activities to make
sure that development plans are properly implemented. These activities can
include erosion and sediment control; IM/1P siting, implementation, and
maintenance; and wetland protection. This approach defrays the cost of
conducting inspections.
JL he myriad programs that have
been established to preserve and
restore wetlands in the Chesapeake
Bay watershed are an example of
a multi-stakeholder federal, state,
local, and private citizen partner-
ship. Private organizations and
public agencies, such as the
Chesapeake Bay Foundation and
the Environmental Protection
Agency and the states of Pennsyl-
vania, Maryland, and Virginia, are,
in certain Instances, pooling their
resources to fund projects and
create policies regarding the
Chesapeake Bay watershed. For
example, the Sea Grant College
Chesapeake Bay Studies Program,
which researches fish stocks, fate
and transport of toxic pollutants,
and remote sensing. Is funded
through a research grant from the
National Oceanic and Atmospheric
Administration. Remote sensing has
been used successfully for
Identifying wetlands and delineat-
ing the wetland/upland boundaries
in the Chesapeake Bay region.
The state governments of Maryland
and Virginia have implemented
license plate programs that provide
part of the proceeds of the plates
to a Chesapeake Bay Trust. Private
citizen associations, such as the
Herring Run Watershed Association
In the Baltimore, Maryland, area
can also receive funding from
beyond their local membership.
The Herring Run restoration
project Is a community, state, and
federal partnership that includes
school curricula for "adopting" and
inventorying land use, planting
trees, and caring for the existing
forest buffers. The Maryland
Department of Natural Resources
recently accepted a grant of
$22,300 from the U.S. Forest
Service's Chesapeake Bay Program
to help fund this effort to Improve
conditions within the Herring Run
watershed.
Impact fees transfer the costs of infrastructure services (roads, sewers,
stormwater treatment) needed for private development directly to
developers or property owners. Unlike user fees, which recover costs over the
life of a project, impact fees are usually collected in one lump sum at the
beginning of a project. These fees are particularly attractive to local
governments because they relieve up-front financing pressures on local
budgets. In California, for example, several wastewater treatment plants have
been financed with fees paid by developers on the basis of the demands for
treatment that their projects are expected to generate. Impact fees could be
used for building regional stormwater management facilities.
Capacity Credits
Capacity credits are a form of financing in which private interests
(usually developers) purchase future capacity in a public facility such as a
stormwater treatment facility. Applicants are guaranteed future access to the
additional capacity of that particular facility. When enough credits have been
sold, work on the project begins.
Pee-ln-Ueu
Fee-in-lieu is a method of easing environmental impacts on a regional or
watershed basis. If a county or municipality determines that wetland
restoration is too costly for an individual site, a fee can be charged to the
property owner in lieu of implementing the restoration. The funds collected
could be used to restore a more valuable wetland elsewhere in the watershed.
Bonds/Debt Financing
Bonds or debt financing raises up-front capital and distributes the
burden of repayment for capital projects over the life span of the project and
among those who benefit from it. Typically, bonds can be used only to
finance projects that have both known and proven life expectancies. Short-
term bonds are usually payable within 1 year. Establishing short-term debt
provides interim funding of projects waiting to receive long-term financing.
Long-term bonds traditionally match the term of financing with the life expectancy of the
project. A stormwater treatment facility, for example, might be expected to perform adequately
for 30 years; therefore, the community could issue up to a 30-year bond.
Page 2-39
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
State Revolving Funds
State Revolving Funds (SRFs), which have been established since the Clean Water Act
Amendments of 1987 by grants from EPA and state matching funds, can provide states with funds
to finance NFS projects. They are generally operated by the state and provide long-term, low-
interest loans to localities for major capital investments, such as stormwater retrofit projects.
SRFs may also provide credit enhancement or, to a limited degree, grants. The designated state
institution receives an initial flow of capital from EPA; local user fees are established to cover
operation and maintenance costs and to repay loans and interest rates. As repayments
accumulate, the SRF is able to make more loans using those repayments. The State of California,
for example, uses its SRF for nonpoint source purposes. The fund is administered by the State
Water Board, which developed a flexible program to evaluate and select for funding a wide variety
of nonpoint source pollution projects. Eligible projects include construction of demonstration
projects, retention/detention basins, and a variety of BMPs to reduce or remove pollutants. The
nonpoint source program for the SRF also permits the establishment of substrate revolving funds
that can provide funding to private individuals to finance new onsite septic systems.
Grants
Grants are sums of money awarded to state and local governments or nonprofit
organizations that do not need to be repaid. Grants are awarded for the purpose of financing a
particular activity or facility. EPA grants are federal grants that provide state and local
governments funding to meet national environmental quality goals. Criteria for receiving grant
money are established by EPA and must be met before the funds can be used for a specific activity
or program. For example, section 6217 of the Coastal Zone Act Reauthorization Amendments of
1990 (CZARA) requires states to establish coastal nonpoint source control programs, which must
be approved by both the National Oceanic and Atmospheric Administration (NOAA) and EPA.
Once approved, the programs will be implemented through changes to the state nonpoint source
pollution program approved and funded by EPA under section 319 of the Clean Water Act and
through changes to the state coastal zone management program approved by NOAA under section
306 of the Coastal Zone Management Act. Section 604(b) of the Clean Water Act requires an
allotment of funds to provide grants to states to carry out water quality management planning.
Section 314 of the Clean Water Act provides funding for project grants to states for assessing the
water quality of publicly owned lakes, developing lake restoration and protection plans,
implementing these plans to restore and preserve the lake, and performing postrestoration
monitoring to determine the longevity and effectiveness of restoration.
Leases
Leases are contracts that allow another person to use land or a building for a specific time,
usually in return for repayment. Leasing obligations are not considered debt in most states and
voter approval for financing is not required. Lease-purchase agreements (municipal lease) give the
person holding the property lease, the lessee, the option of applying lease payments to the
purchase of the facility. The lessee is responsible for paying taxes. These agreements can be used to
finance wetland restoration projects or to purchase riparian areas or other environmentally
sensitive areas. Sale-leaseback arrangements allow private investors to purchase public facilities or
equipment on behalf of the community. Since the investors are entitled to tax benefits, they can
lease the property back to the municipality at a lower cost.
Page 2-40
-------
Factors to Consider When Selecting BMPs
Matching Wetland/Stormwater Factors to BMP Design
Preliminary Treatment of Stormwater
The level of treatment needed to protect a wetland that receives urban Stormwater is
dependent on the type and condition of the wetland; on the quality, quantity, and distribution of
runoff; and on what levels of impacts to the wetland are considered acceptable. Ideally, all
pollutants and sediments not present prior to watershed development should be removed before
the Stormwater is discharged to wetlands; however, some wetland types might be able to
assimilate higher levels of certain pollutants. Some regions, such as southern Florida, parts of New
England, and the Southwest, have soils with high infiltration rates, and a major concern related to
urban Stormwater might be the potential contamination of aquifers. Instituting Stormwater
treatment might be part of a larger effort to protect or restore wetland and downstream
ecosystems and might involve analysis of Stormwater dynamics at the watershed level and a
variety of actions aimed at runoff quality maintenance or enhancement.
Matching Wetland Characteristics to BMP Design
Wetlands should be characterized with a classification system such as that of Cowardin and
others (1979) prior to introducing additional Stormwater or modifying the characteristics of
existing Stormwater inflows with BMPs. The general characteristics of a wetland, used to
determine its placement in a classification system, should be considered when determining the
type and placement of BMPs adjacent to or upstream of a wetland. In addition to considering
general classification characteristics, site-specific evaluations of wetlands should be made. The
modification of existing Stormwater characteristics due to development or the type of BMPs used
should be compatible with the characteristics of the existing wetlands in a system. Table 2-7
shows a general comparison of various BMPs and the benefits to protecting wetland functions
that they might offer. This table is intended to be used as a preliminary screening device to
identify potential wetland protection BMPs to treat Stormwater runoff.
Hydrology
In addition to considering wetland type and conditions, the nature of Stormwater
discharges must be evaluated to determine the best practices for protecting urban wetlands. Both
the quantity and quality of urban runoff are significantly affected by watershed development.
Increased impervious area, removal of trees and other vegetation, and soil compaction in a
watershed can increase runoff volume (Schueler, 1987), altering the natural hydroperiod of
receiving wetlands. Reduced infiltration of Stormwater can reduce baseflow and alter the
groundwater hydrology of some urban wetlands. Known hydrologic impacts to wetlands
associated with increased Stormwater runoff include changes in wetland response time, changes
in water levels in the wetland, and changes in the detention time of the wetland. Increased
runoff volumes are also associated with greater water level fluctuations in receiving wetlands,
which can adversely affect wetland plant and animal communities (Azous, 1991; Cooke, 1991).
Large amounts of water entering a wetland at once can cause disturbance through changes in
circulation and flushing characteristics and through possible erosion of wetland soils.
Page 2-41
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
table 2-7. Potential Benefits to
front various BMPs
^BENEFICIAL
1 =BENEFICIAL WITH
CERTAIN LIMITATIONS
^NEUTRAL
1
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ruiiuuun rievenuuii
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Page 2-42
-------
Factors to Consider When Selecting BMPs
The natural hydrologic characteristics of a wetland are of concern when designing
stormwater management systems. In areas where natural wetlands are relatively unimpacted, the
existing hydroperiod of wetlands should be maintained, while in areas where wetlands have been
deprived of water, BMPs can play a role in enhancing wetland ecosystems through restoration of a
more natural hydroperiod.
The source of water in a wetland is also important in designing a stormwater management
system. In wetlands where the source of hydrology is primarily in the form of surface water
runoff, the use of BMPs that incorporate infiltration into the soil as the method for stormwater
treatment (e.g., infiltration trenches or infiltration ponds) might change the natural hydroperiod
of adj acent or downstream wetlands. As mentioned, changes in the natural hydrologic
characteristics can adversely affect the structure and functions of these wetlands. Stormwater
treatment systems that treat stormwater by temporary detention or retention (e.g., extended
detention ponds, wet ponds), when properly designed, can help to restore the predevelopment
hydrologic conditions in this type of wetland. Conversely, the use of detention or retention
systems adjacent to or upstream of groundwater wetlands can adversely affect their hydroperiod
by altering natural baseflow conditions.
Climate
Local climatic conditions determine the quantity, frequency, and intensity of stormwater
runoff events. Under natural conditions, development of wetland types and functions is based
largely on these climatic conditions. In fact, in the United States, climate variation has
contributed to the formation of distinctly different wetland types, and climate is the second
major controlling factor that leads to the formation of regional wetland types. Therefore, climatic
conditions, precipitation, and storm events all need to be analyzed prior to selecting a
stormwater pretreatment strategy. The placement of BMPs to treat stormwater or to protect
existing wetlands from stormwater impacts can actually harm the systems if the practices are not
designed based on the local conditions and the natural wetland characteristics. Likewise, the
selected BMP type and design should be based on both design storm requirements and adjacent
wetland characteristics.
For example, stormwater in the Southwest is similar to that in other areas of the country.
Some qualifications would include the following: (1) no major sodium chloride components in
runoff from deicing salts as found in snow zones; (2) an increased dust component; (3) higher
first-flush pollutant concentrations arising from a longer accumulation time between storm
events; (4) suspended sediment sources masked by a high natural background; and (5) the
desiccation of organic material on the landscape, especially domestic animal feces (Hawkins,
1993). Many urban areas in the Southwest lack storm sewers; streets and other land surfaces act
as a conduit for stormwater, which enhances street runoff and contact with contaminants
(Hawkins, 1993).
Any BMPs that require regular rainfall or a moist climate would not be appropriate for
southwestern arid land conditions (Hawkins, 1993). Runoff is not frequent, stored stormwater is
subject to high evaporation rates, and cover is naturally sparse. Traditional retention-type BMPs
are used in the region, however, for peak flow reduction. Most of the water quality BMPs being
proposed for southwestern cities stress dust and soil control, catch basin cleaning, debris removal,
street sweeping, hazardous waste disposal, and other similar pollution prevention practices
(Hawkins, 1993).
Page 2-43
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Water Quality
Natural nutrient levels within a particular wetland vary widely among wetland types, and
the potential effects of loadings from stormwater must be evaluated with consideration of the
type of receiving wetland. Wetlands can vary in their ability to absorb or transform these
compounds due to variations in hydrologic, soil, and vegetative characteristics of the wetlands,
and they might be only temporary sinks for some compounds. Although nitrogen can be removed
from wetland soils as nitrogen gas through the process of denitrification, phosphorus can be held
in wetland soils until a wetland's natural storage capacity is reached, beyond which the wetland
might no longer function as a sink or might even become a net exporter of phosphorus to
receiving waters (Richardson, 1989).
Pretreatment of stormwater flow prior to its inflow into existing wetlands can help in
attenuating fluctuations in nutrient levels. The pretreatment of stormwater through the
incorporation of BMPs can also reduce the amount of sediment that enters a wetland. If incoming
sediment loads are high, the wetland's storage capacity could be reduced over time and its ability
to-function could be affected (Marble, 1992). While the increased levels of nutrient and sediment
loading to wetlands associated with stormwater can adversely affect wetland functional
characteristics, the removal of most or all suspended particulates through the placement of BMPs
can also result in wetland degradation. Reductions in the natural levels of sediment deposition in
a wetland can result in the embedding of downstream wetland substrates in some wetland types
or in erosion in other types and potentially in erosion and channel scouring in associated
downstream systems. In some systems the resuspension of downstream floodplain sediments can
occur. Natural soil and sediment conditions should be considered in a wetland or wetland system
when determining the feasibility, design, and types of BMPs to be used.
Monitoring
One strategy for determining the performance of a BMPits effect on the wetland's
water quality, health, and functionsis through monitoring. Even though monitoring is beyond
the scope of this manual, it is worthwhile to discuss the fundamentals of a monitoring project.
During the BMP planning process, the appropriate level of monitoring should be determined so
that resource requirements can be identified and factored into the overall project. Proper
planning targets monitoring efforts at key elements of the project that will indicate the degree
of success and the potential need or opportunity for improvement in a particular system.
A monitoring plan should be developed based on the objectives of the BMP project and on
documented literature or readily available monitoring results of similar projects (Kusler and
Kentula, 1990; USEPA, 1992). The wetland functions of concern should be identified and the
current level of those functions established relative to reference wetlands. For an existing
wetland, functions that might be threatened by stormwater runoff (e.g., sediment retention and
long-term water storage) should be documented. Where stormwater might be used to restore a
severely degraded wetland, the desired functions of the wetland should be evaluated so progress
can be measured.
The first step in any monitoring effort, establishing baseline data, is important in
evaluating the long-term effectiveness of the BMP. Obtaining as much information as possible
about the resource to be protected or restored will allow progress or degradation to be measured.
As soon as construction of the BMP is completed, monitoring of the project should begin. For a
thorough monitoring effort, the boundaries of the watershed in which the BMP was constructed
Page 2-44
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factors to Consider When Selecting BMPs
should be determined and the exact location of the project within that watershed should be
indicated on a map. Variables that might be included in a monitoring effort include the following
(North Carolina Cooperative Extension Service, 1995; USEPA, 1992a):
Morphometry (area, slope, and perimeter-to-area ratio)
Hydrology (water depth, flow rates, flow patterns, and indirect indicators)
Substrate (soil depth, color, texture, source, organic matter, sediment flux)
Vegetation (species, coverage, survivorship)
Fauna (observations, habitat evaluation, species- or community-specific sampling)
Water quality (pH, DO, temperature, metals, turbidity, TSS, BOD, N, P)
Monitoring strategies might range from simple visual assessments of a wetland to full
evaluations including ambient water quality analyses in the wetland and a BMP inlet/outlet
efficiency assessment. In some cases, the simple, visual assessments (e.g., looking at the
vegetation and hydrologic changes) might be enough monitoring to determine whether the BMP
is performing efficiently. When this simple monitoring does not provide adequate information,
more elaborate analysis is needed.
It is advisable to identify and take into account other existing information that might be
available, such as meteorological data, data obtained from monitoring conducted under an
NPDES or state permit, or volunteer monitoring data. A sampling regime including set (or
randomly selected) sampling sites and specific times to repeat the sampling (e.g., in wet and dry
seasons) should be established. A site can be monitored through routine inspections or more
comprehensive, quantitative sampling events. Routine inspections are "spot checks" and are
conducted as often as daily or weekly. These assessments allow the investigator to identify
problems as they develop. Generally, routine inspections are less costly and not as damaging to
the wetland or BMP because these inspections are less intrusive (i.e., they require less data
collection and less equipment to obtain the data).
Quantitative sampling events, in comparison, are periodic assessments conducted annually
for several years after the BMP is constructed. This type of monitoring indicates the degree to
which the goals of the project have been met (Kusler and Kentula, 1990). Comprehensive
assessments typically require more equipment and skilled personnel and therefore are more
costly and often more damaging to the wetland than are routine inspections.
Reports of monitoring efforts should include photographs of each sampling effort, a
description of the project and project site, an explanation of site preparation, and a summary of
what was conducted and the results. These data, once evaluated, will allow for improvements in
design guidelines for future BMP projects.
The data quality of monitoring efforts must be scientifically acceptable. Five quality
assurance components of assessments have been identified: precision of the measurements of the
same variable, accuracy of the measurements, completeness of the collected data versus what was
expected, representativeness of the variable's characteristics, and comparability of one data set to
another (Sherman et al., 1991, cited in USEPA, 1992a).
Page 2-45
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Summary
Best management practices used for the treatment of urban stormwater are commonly
located in low topographic positions adjacent to or within existing wetlands. They can be used
primarily to treat or pretreat stormwater or to protect existing wetlands from the effects of
stormwater runoff. The above examples represent only a few of the variables that should be
considered when placing BMPs within or adjacent to wetland systems. When designing BMPs,
the treatment of stormwater is not the sole consideration. For BMPs that are incorporated into
systems where wetland protection and optimal stormwater treatment are both objectives, the
characteristics, of the existing wetlands must also be considered. It is most desirable to consider
protecting wetland resources from a holistic perspective. This can be accomplished through the
use of a variety of nonstructural BMPs including watershed planning, public education, and
preventive construction techniques.
Page 2-46
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Factors to Consider When Selecting BMPs
References
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Canning, D.J. 1988. Urban runoff water quality: Effects and management options. Shorelands Technical Advisory
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Cooke, S.S. 1991. The effects of urban stormwater on wetland vegetation and soils A long-term ecosystem
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Cooper, D.J. 1989. A citizen's handbook for wetland protection. U.S. Environmental Protection Agency, Region
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Green, WH., and GA. Ampt. 1911. Studies on soil physics 1. Flow of air and water through soils. Journal of
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Hammer, D. 1992. Creating freshwater wetlands. Lewis Publishers, Chelsea, MI.
Haukos, D.A., and LM. Smith. 1992. Waterfowl management handbook: Ecology of playa lakes. Fish and
Wildlife Leaflet 13.3.7. U.S. Department of the Interior, Fish and Wildlife Service, Washington, DC.
Hawkins, R.H. 1993. Draft: Reconnaissance review of "Best Management Practices for Stormwater
Discharges to Natural Wetlands." The University of Arizona, Tucson, AZ.
Hendrickson, DA., and WL. Minckley. 1984. Cienegas vanishing climax communities of the American
Southwest. Desert Plants 6(3):131-175.
Hershfield, D.M. 1961. Rainfall frequency atlas of the United States for durations from -10 minutes to 24 hours and
return periods from 4 to 400 years. Technical Paper 40. U.S. Weather Bureau, Washington, DC.
Hickock, E.A., M.C. Hannaman, and M.C. Wenck. 1977. Urban runoff treatment methods: Vol. I. Non-structural
wetland treatment. EPA 600/2-77-217. U.S. Environmental Protection Agency, in cooperation with Minnehaha
Creek Watershed District.
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Hutchinson, C.F., P. Warshall, E.J. Arnould, and J. Kindler. 1992. Development in arid lands. Environment
34(6):16-43.
Kadlec, R.H., and R.L Knight. 1996. Treatment wetlands. Lewis Publishers, Boca Raton, FL
Kusler, J.A., and M.E. Kentula, eds. 1990. Wetland creation and restoration: The status of the science. Island Press,
Washington, DC.
Maidment, P.R., ed. 1993. Handbook of hydrology. McGraw-Hill, Inc., New York, NY.
Marble, A.D. 1992. A guide to wetland functional design. Lewis Publishers, Boca Raton, FL.
MDDNR. 1991. A guide for developing nontidal wetlands watershed management plans in Maryland. Maryland
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Mitsch, W.J., and J.G. Gosselink. 1986. Wetlands. Van Nostrand Reinhold Co., New York, NY.
Mitsch, W.J., and J.G. Gosselink 1993. Wetlands. 2nd ed. Van Nostrand Reinhold, New York, NY.
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North Carolina Cooperative Extension Service. 1995. Section 319 National Monitoring Program: An overview.
North Carolina State University College of Agriculture & Life Sciences.
Novotny, V, and G. Chesters. 1981. Handbook of nonpoint pollution; sources and management. Van Nostrand
Reinhold Co., New York, NY.
Iverson. 1982. Contaminant levels in precipitation and urban surface runoff. Water Resources Bulletin
18(5):863-869.
Pilgrim, D.H., and I. Cordery. 1993. Flood runoff. In Handbook of Hydrology, ed. D.R. Maidment. McGraw
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PSWQA. 1990. Protecting fish and wildlife habitat in Puget Sound. Puget Sound Water Quality Authority,
Seattle, WA.
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Hydrology, ed. D.R. Maidment. McGraw Hill, Inc., New York, NY.
Richardson, CJ. 1989. Wetlands as transformers, filters and sinks for nutrients. In Freshwater wetlands:
Perspectives on natural, managed and degraded ecosystems. University of Georgia, Savannah River Ecology
Laboratory, Ninth Symposium, Charleston, SC.
Schueler, T.R. 1987. Controlling urban runoff: A practical manual for planning and designing urban BMP's.
Metropolitan Washington Council of Governments, Washington, DC.
Schueler, T.R., P.A. Kumble, and M.A. Harity. 1992. A current assessment of urban best management practices:
Techniques for reducing non-point source pollution in the coastal zone. Prepared for the U.S. Environmental
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6217(g) of the Coastal Zone Management Act.
Segelquist, C.A., WL. Slauson, M.L Scott, and G.T. Auble. 1990. Synthesis of soil plant correspondence data
from twelve wetland studies throughout the United States. FWS Biological Report 90(19). U.S. Fish and Wildlife
Service, National Ecology Research Center, Fort Collins, CO.
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factors to Consider When Selecting BMFs
Shahane, AN. 1982. Estimation of pre- and post-development nonpoint water quality loadings. Water
Resources Bulletin 18(2):231-237.
Sherman, A.D., S.E. Gwin, and M.E. Kentula, in conjunction with WA. Niering. 1991. Quality assurance
project plan: Connecticut Wetlands Study. EPA 600/3-91/029. U.S. Environmental Protection Agency,
Environmental Research Laboratory, Corvallis, Oregon. Cited in USEPA, 1992a.
Smith, H., and E.D. Matthews. 1975. Soil survey of Harford County area, Maryland. U.S. Department of
Agriculture, Soil Conservation Service, in cooperation with the Maryland Agricultural Experiment Station,
Washington, DC.
South Carolina Coastal Council. 1988. Stormwater management guidelines. South Carolina Coastal Council.
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review and annotated bibliography. Washington State Department of Ecology, Olympia, WA.
Sweeten, J.M., and S.W Melvin. 1985. Controlling water pollution from nonpoint source livestock operations.
Urbonas, B., and LA. Roesner. 1993. Hydrologic design for urban drainage. In Handbook of Hydrology, ed.
D.R. Maidment. McGraw Hill, Inc., New York, NY.
Urbonas, B., and P. Stahre. 1993. Stormwater best management practices and detention for water quality, drainage,
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Environmental Protection Agency, Water Planning Division, Washington, DC.
USEPA. 1992a. An approach to approving decision making in wetland restoration and creation. EPA/600/R-92/
150. U.S. Environmental Protection Agency, Washington, DC.
USEPA. 1992b. Storm water management for industrial activities. EPA 832-R-92-006. U.S. Environmental
Protection Agency, Office of Water, Washington, DC.
USEPA. 1992c. Protecting coastal and wetland resources. EPA 842-R-92-002. U.S. Environmental Protection
Agency, Office of Water, Washington, DC.
USEPA. 1993. Guidance specifying management measures for sources of nonpoint pollution in coastal waters. EPA
840-B-92-002. U.S. Environmental Protection Agency, Office of Water, Washington, DC.
USEPA. 1994. A state and local government guide to environmental program funding alternatives. EPA 841-K-94-
001. U.S Environmental Protection Agency, Office of Water, Washington, DC.
USEPA. 1995. Storm water discharges potentially addressed by phase II of the National Pollutant Discharge
Elimination System storm water program: Report to Congress. EPA 833-K-94-002. U.S. Environmental Protection
Agency, Office of Water, Washington, DC.
Washington State Department of Ecology. 1991. Stormwater management manual for the Puget Sound Basin.
Public review draft. Document no. 90-73. Prepared by the Washington State Department of Ecology,
Olympia, WA.
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Washington State Department of Ecology. 1992. Stormwater program guidance manual. Vol. II. Prepared by the
Washington State Department of Ecology, Olympia, WA.
Woodward-Clyde Consultants. 1990. Urban targeting and BMP selection, an information and guidance manual
for state nonpoint source program staff engineers and managers. Prepared for the U.S. Environmental Protection
Agency, Region 5, Water Division, Chicago, IL, and the Office of Water Regulations and Standards,
Washington, DC.
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Case Studies
Section 3
Case Studies
Introduction
o illustrate how BMPs have been incorporated with wetlands into urban stormwater
management systems, several case studies are presented. The purpose of the case studies
is to illustrate measures that can be taken to prevent adverse impacts to wetlands from
stormwater runoff. In most of the case studies, wetlands were incorporated into the
stormwater management system for the site. Generally, some type of treatment was provided to
reduce pollutants in the stormwater before its discharge to natural wetlands. Available water
quality data are presented, as well as information regarding habitat change. The case studies are
presented by EPA Region, and by wetland type and BMP applicability. The following list
correlates BMPs used in the case studies to applicable BMP fact sheets in
Section 4.
Case Study-BMP Fact Sheet Correlation
EPA Region 1
Narrow River Special Area Management Plan
Watershed Management Plans (See BMP Fact Sheet p. 4-8)
Preventive Construction Techniques (See BMP Fact Sheet p. 4-12)
Grassed Swales (See BMP Fact Sheetp. 4-32)
Extended Detention Dry-Basins (See BMP Fact Sheet p. 4-43)
EPA Region 2
Freshwater Wetlands Protection Act
Extended Detention Dry Basins (See BMP Fact Sheet p. 4-43)
Contour Terraces
Grassed Swales (See BMP Fact Sheet p. 4-32)
Watershed Management Plans (See BMP Fact Sheet p. 4-8)
Riparian Areas (See BMP Fact Sheet p. 4-18)
Outreach and Educational Programs (See BMP Fact Sheet p. 4-13)
Pollution Prevention (See BMP Fact Sheet p. 4-2)
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EPA Region 3
Watershed Management Study
Watershed Management Plans (See BMP Fact Sheet p. 4-8)
Vegetated Natural Buffers (See BMP Fact Sheet p. 4-38)
Wet Ponds (See BMP Fact Sheet p. 4-47)
Road Culvert Retrofit
Riparian Areas (See BMP Fact Sheet p. 4-18)
EPA Region 4
Hidden River Wetland Stormwater Treatment Site
Vegetated Natural Buffers (See BMP Fact Sheet p. 4-38)
Construction Sedimentation Basins
Grassed Swales (See BMP Fact Sheet p. 4-32)
EPA Region 5
Lake McCarrons Wetland Treatment System
Construction Sedimentation Pond
Level Spreaders (See BMP Fact Sheet p. 4-61)
Watershed Management Plans (See BMP Fact Sheet p. 4-8)
Constructed Wetlands (See BMP Fact Sheet p. 4-50)
The Phalen Chain of Lakes Watershed Partnership
Watershed Management Plans (See BMP Fact Sheet p. 4-8)
Outreach and Educational Programs (See BMP Fact Sheet p. 4-13)
Grassed Swales (See BMP Fact Sheet p. 4-32)
Open Spaces (See BMP Fact Sheet p. 4-41)
Constructed Wetlands (See BMP Fact Sheet p. 4-50)
Vegetated Natural Buffers (See BMP Fact Sheet p. 4-38)
The Prairie Wolf Slough Project
Watershed Management Plans (See BMP Fact Sheet p. 4-8)
Outreach and Educational Programs (See BMP Fact Sheet p. 4-13)
Constructed Wetlands (See BMP Fact Sheet p. 4-50)
Open Spaces (See BMP Fact Sheet p. 4-41)
EPA Region 6
Tensas Cooperative River Basin Study
Watershed Management Plans (See BMP Fact Sheet p. 4-8)
Vegetated Filter Strips (See BMP Fact Sheet p. 4-35)
Grassed Swales (See BMP Fact Sheet p. 4-32)
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Case Studies
Water and Sediment Control Basins
Vegetated Natural Buffers (See BMP Fact Sheet p. 4-38)
Pollution Prevention (See BMP Fact Sheet p. 4-2)
Constructed Wetlands (See BMP Fact Sheet p. 4-50)
EPA Region 7
Multi-Species Riparian Buffer Strips, Bear Creek Watershed
Vegetated Natural Buffers (See BMP Fact Sheet p. 4-38)
Vegetated Filter Strips .(See BMP Fact Sheet p. 4-35)
Watershed Management Plans (See BMP Fact Sheet p. 4-8)
Pollution Prevention (See BMP Fact Sheet p. 4-2)
Riparian Areas (See BMP Fact Sheet p. 4-18)
Constructed Wetlands (See BMP Fact Sheet p. 4-50)
EPA Region 8
A Watershed Approach to Municipal Stormwater Management
Outreach and Educational Programs (See BMP Fact Sheet p. 4-13)
Watershed Management Plans (See BMP Fact Sheet p. 4-8)
Riparian Areas (See BMP Fact Sheet p. 4-18)
Grassed Swales (See BMP Fact Sheet p. 4-32)
Infiltration Basins (See BMP Fact Sheet p. 4-20)
Constructed Wetlands (See BMP Fact Sheet p. 4-50)
Vegetated Natural Buffers (See BMP Fact Sheet p. 4-38)
Vegetated Filter Strips (See BMP Fact Sheet p. 4-35)
Pollution Prevention (See BMP Fact Sheet p. 4-2)
Lemna Nonpoint Source Treatment System
Wet Ponds (See BMP Fact Sheet p. 4-47)
Watershed Management Plans (See BMP Fact Sheet p. 4-8)
Constructed Wetlands (See BMP Fact Sheet p. 4-50)
EPA Region 9
Lincoln-Alvarado Project
Oil/Grit Separators (See BMP Fact Sheet p. 4-58)
Vegetated Filter Strips (See BMP Fact Sheet p. 4-35)
EPA Region 10
Sawmill Creek
Riparian Areas (See BMP Fact Sheet p. 4-18)
Vegetated Natural Buffers (See BMP Fact Sheet p. 4-38)
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Watershed Management Plans (See BMP Fact Sheet p. 4-8)
Fencing of Riparian Pasture
Upland Water Troughs for Livestock
Planting of Willow Cuttings
Sublett Creek Restoration Project
Watershed Management Plans (See BMP Fact Sheet p. 4-8)
Riparian Areas (See BMP Fact Sheet p. 4-18)
Grazing Allotment Management Plan (AMP)
Planting of Willow Cuttings
Drift Fences
Log Dams
Upland Water Troughs for Livestock
Bear Creek Restoration Project
Sedimentation Basins
Watershed Management Plans (See BMP Fact Sheet p. 4-8)
Riparian Areas (See BMP Fact Sheet p. 4-18)
Fencing Riparian Pasture
Riprap
Upland Spring Sites for Livestock
Camp Creek Restoration
Watershed Management Plans (See BMP Fact Sheet p. 4-8)
Riparian Areas (See BMP Fact Sheet p. 4-18)
Sedimentation Basins
Fencing Riparian Pasture
Planting of Willow Cuttings
Riprap
Low-rock Structures and Gabions
Outreach and Educational Programs (See BMP Fact Sheet p. 4-13)
The Chewaucan River
Watershed Management Plans (See BMP Fact Sheet p. 4-8)
Riparian Areas (See BMP Fact Sheet p. 4-18)
Riprap
Snag Removal
Fencing Riparian Pasture
Planting of Willow Cuttings
Exclusion of Cattle Grazing
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Case Studies
Regional Case Studies
EPA Region 1
Narrow River Special Area Management Plan, Rhode Island
The Narrow (Pettaquamscutt) River watershed is located in southern Rhode Island in the
towns of North Kingstown, South Kingstown, and Narragansett. The watershed drains into
southwestern Narragansett Bay and encompasses several unique water bodies (Figure 3-1).
SILVER SPRING LAKE
SHADY
LEA POND
MATTATUXETT RIVER
PAUSACACO
CCARR)
POND
GILBERT
STUART
STREAM
CPETTA QUAMSCUTT)
UPPER POND
LOWER POND
THE NARROWS
PETTA QUAMSCUTT
COVE
Figure 3-1. Location of the Narrow River watershed study area in the State of Rhode Island.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Known use of the river and its resources extends back to at least 3,000 years ago when
Native Americans hunted and gathered along the river. Other uses of the river have included ship
building, agriculture, dairy farming, summer housing, and permanent homes. The Narrow River
watershed is rich in recreational resources such as boating, camping, hiking, fishing, swimming,
and birdwatching, and the river valley is considered one of Rhode Island's most scenic areas.
Wildlife inhabit Narrow River and its watershed for breeding, nesting, spawning grounds,
and migratory bird routes. Several threatened and endangered species, including species of marsh
grass, osprey, Least Tern, sea cucumber, moonfish, luminescent moss, and several fern species are
known to inhabit the area.
Coastal wetlands in Rhode Island have been altered and destroyed by development
activities, which impact wetlands by filling, removing vegetation, grading, dredging, excavating,
draining, damming, and diverting the hydrologic flows into the wetlands. Alteration of the
adjacent land areas has affected local drainage patterns, thereby altering the sedimentation
processes and salinities of waters that enter wetlands. Building practices, human encroachment,
and other development pressures have caused water quality degradation, impacted critical habitat
areas, reduced public access, and spoiled aesthetic values throughout the watershed.
In response to coastal wetlands loss, the Rhode Island Coastal Resources Management
Council (CRMC) has set goals to protect, preserve, and where possible restore coastal wetlands.
CRMC supports a policy of "no net loss" of coastal wetland acreage and functions and requires a
2:1 mitigation ratio of replacement or creation of coastal wetland to areas permanently altered or
lost. (Wetlands created for stormwater management, erosion control, or waste management are
exempt from mitigation requirements.)
Past management efforts to protect the Narrow River and its watershed were undertaken by
the Narrow River Preservation Association (NRPA), the Narrow River Watershed Advisory
Council, and the Narrow River Land Trust. NRPA, founded in 1970, initiated the first planning
study of the watershed, which resulted in a report describing the development trends and impacts
to the river, and made recommendations for development control. The Narrow River Watershed
Advisory Council, formed in 1981, was a group of representatives from North Kingstown, South
Kingstown, and Narragansett, whose objective was to promote the protection of the watershed's
values. The Council appointed the Narrow River Watershed Advisory Committee, which
developed a watershed program, recommended policies, and collected and analyzed resource data.
The Narrow River Land Trust, created in 1983, is a nonprofit organization that obtains property
and property rights for protection of natural resources.
Special Area Management plans (SAMPs) have been developed at the local and national
levels as management strategies for environmental planning. SAMPs focus the legislative and
regulatory powers of the CRMC to the specific problems of the designated resource. The effort to
create a SAMP for the Narrow River watershed began in September 1985 as an adaptation of the
SAMP that existed for the salt pond region of southern Rhode Island. It resulted from the general
belief that activities in the Narrow River's watershed needed stronger management.
One of the first steps in designing the plan was to create a comprehensive characterization
of the watershed. Available research conducted by consulting firms, students, scientists from the
University of Rhode Island, and state agencies and town records were reviewed to determine past
and present problems in the watershed and to develop management strategies and initiatives to
address those problems.
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Case Studies
At the beginning of the planning process, September 24,1985, CRMC imposed a building
moratorium on all development applications within an area 200 ft (60.96 m) inland of mean high
water, or the inland edge of a wetland, bluff, river bank, or other coastal feature. The moratorium
also applied to all CRMC permits required by facilities requiring a parking area (at least 1 acre in
size) and by subdivisions of six units or more. Applications submitted after the end of the
moratorium, December 31,1986, were subject to the guidelines and regulations set forth in the
SAM plan.
The focus of the SAM plan was to address several problems that had not been adequately
addressed in past management efforts: degradation in water quality, development pressures and
human encroachment into areas unsuitable for building, potential loss of wildlife species and
habitat, and loss of aesthetic values. The SAM plan for the Narrow River watershed regulates the
following:
Land classification for watershed protection
Watershed controls for storm water management
Watershed controls for septic system management
Watershed controls for erosion and sedimentation
Lands requiring special considerations (historic/archaeological value)
Petroleum tanks and oil spills
Community participation
Future research efforts
Stormwater management is highlighted here because the SAM plan regulates stormwater as
a means to protect wetlands. The plan defines stormwater management as the quantitative
control of increased volume or rate of runoff and the qualitative control of runoff through a
system of vegetative and structural measures to prevent pollutants from being transported in
runoff.
Stormwater management is required for all new residential developments six units or more,
all facilities and activities requiring 20,000 ft2 (1,800 m2) or more of impermeable surface area or
resulting in 20 percent or more of the project area being impervious, and all roadway construction
and upgrade projects. Stormwater management is also required for activities that will involve
alteration, maintenance, or improvement to an existing stormwater management structure that
will alter the quality, rate, volume, or location of surface water discharge.
CRMC requires the stormwater management plan to include information on existing
conditions as well as predicted conditions after the activity is implemented. A stormwater
management plan must include maps, charts, graphs, tables, photographs, descriptions, and other
supporting documentation.
The stormwater management plan must provide evidence that structures were planned and
designed and will be constructed to ensure that postdevelopment runoff, hydrodynamic
characteristics of the watershed and groundwater, and wetland functions and values are the same
as predevelopment conditions. Postdevelopment conditions must also prevent increased flooding,
damage, and saltwater intrusion; must protect natural fluctuating levels of salinity in estuarine
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
areas; and must minimize alterations to flora, fauna, and habitat that could result from improper
construction, design, and location of the structures.
Design, construction, and maintenance of stormwater systems may not allow the direct
discharge of runoff into Narrow River and its tributaries. CRMC also prohibits increasing the
volume or rate of runoff or further degrading the quality of existing discharges. Discharges must
be routed through vegetated swales or other structural or nonstructural systems that increase time
of concentration, decrease velocity, increase infiltration, allow suspended solids to settle, and
remove pollutants. These systems should use overland flow and reinfiltration as priority tech-
niques for the treatment of runoff. Detention and retention ponds may not be located in areas
that might cause groundwater contamination.
Stormwater management is only one component of the SAM plan, and CRMC recognizes
that future management improvements and further research efforts are needed to protect the
natural resources of the Narrow River watershed. CRMC has recommended the following areas
for further research:
Monitoring of the river's water quality
Development of a hydrodynamic model of the estuary
Analysis of bottom sediment (distribution, composition, and transport dynamics)
Studies of water quality in the northern regions of the watershed
Determination of the current status of the quality and quantity of groundwater resources
Initiation of water quality testing in the freshwater systems in the northern regions of
the watershed
The state and towns collectively undertaking stormwater management techniques to
upgrade or create programs
References/Additional Information
Howard-Strobel, M.M., T.G. Simpson, and T.P. Dillingham. 1989. The Narrow River special area management
plan. Coastal Resources Management Council, Wakefield, RJ.
Olsen, S., and G.L Seavey. 1993. The State of Rhode Island Coastal Resources Management Program as amended.
Coastal Resources Management Council, Wakefield, RI.
EPA Region 2
Freshwater Wetlands Protection Act, State of New Jersey
The protection of wetlands has long been a priority in the State of New Jersey (NJDEP,
1995). To protect these vital areas, the New Jersey legislature passed the Wetlands Act in 1970 and
the Freshwater Wetlands Protection Act in 1987. These acts and their corresponding regulations
require approval by the New Jersey Department of Environmental Protection (NJDEP) for a
number of proposed activities that could impact wetlands (both freshwater and saltwater). This
discussion focuses on New Jersey's Freshwater Wetlands Protection Act and its subsequent rules
regarding stormwater facilities.
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Case Studies
Wetlands receive the same protection granted surface waters under the state's water quality
standards (N.J.A.C. 13:9B-13 and N.J AC. 7:7A-3.5(a)4). In addition to restrictions protecting the
wetlands themselves, restrictions placed on areas surrounding the wetlands offer further
protection for freshwater wetlands. These areas are designated "transition areas" in the state's
Freshwater Wetlands Protection Act Rules (N.J.A.C. 7:7A-6.1). The Freshwater Wetlands
Protection Act requires a transition area adjacent to wetlands of "exceptional" or "intermediate"
resource value. Freshwater wetlands of "ordinary" resource value, which constitute approximately
5 percent of New Jersey's wetland area, do not require a transition area.
The standard width of the transition area adjacent to a freshwater wetland of intermediate
resource value is 50 ft (15.24 m) and for freshwater wetlands of exceptional value is 150 ft (45.72
m). Wetlands of exceptional resource value require an individual permit, and mitigation must be
provided. Further, applicants for activities proposed in wetlands of exceptional resource value
must demonstrate either that there is a compelling public need for the proposed activity which is
greater than the need to protect the wetland or that denial of the permit would impose
extraordinary hardship.
As defined in the Freshwater Wetlands Protection Act Rules, freshwater wetlands of
exceptional resource value are those which exhibit any of the following characteristics:
Those which discharge into FW-1 waters or FW-2 trout production waters or their
tributaries (FW-1 and FW-2 are water-quality rankings for fresh surface waters in New
Jersey) or
Those which are present habitats for threatened or endangered species, or those which are
documented habitats for threatened or endangered species, and which remain suitable for
breeding, resting, or feeding by these species during the normal period when these species
would use the habitat.
Freshwater wetlands of ordinary resource value are those which (1) do not exhibit the
characteristics above, (2) are isolated wetlands that are more than 50 percent surrounded by
development, and (3) are less than 5,000 ft2 (450 m2) in size including but not limited to drainage
ditches, swales, and detention facilities. Freshwater wetlands of intermediate resource value are
those which are not defined as either exceptional or ordinary.
The Freshwater Wetlands Protection Act Rules also have requirements related to
pretreatment practices for the protection of wetlands (N.J.A.C. 7:7A-9.2(a) 11, v, ix, and x.)
Under the state's general permit requirements, pretreatment of stormwater is required for
stormwater flows entering natural wetlands regardless of resource value. All stormwater
discharged into a freshwater wetland from a stormwater outfall must first be filtered or otherwise
treated outside the freshwater wetland (NJDEPE, 1992). Detention basins, contour terraces, and
grassed swales are examples of predischarge techniques that may be required by the NJDEP. The
general permit does not authorize placement of detention facilities in freshwater wetlands and
requires compensation for disturbance within the wetland transition area (see Figure 3-2). Other
stormwater facility design restrictions include the following:
The total amount of riprap or any other material used for energy dissipation at the end of
the headwall placed in the freshwater wetland cannot exceed 10 cubic yards per outfall
structure.
Excavated areas for the placement of conveyance pipes must be returned to the
preexisting elevation using the original topsoil to backfill from a depth of 18 in (45.72
cm) to the original grade and must be revegetated with indigenous wetland species.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Transition Area Compensation
Transition Area
Reduction
The square footage in the compensation
area is equal to that of the reduction area.
NJDEP, 1995.
Figure 3-2. Example of a transition area reduction and compensation.
Pipes used for stormwater conveyance through the wetlands must be designed not to
exceed the preexisting elevation and properly sealed with anti-seep collars at a spacing
sufficient to prevent drainage of the surrounding wetlands.
If a detention basin is being proposed as the method of pretreatment for water quality,
routing calculations must show that the basin has been designed for the 1-year storm
event according to the New Jersey Stormwater Management Regulations (N.J.A.C. 7:8).
If a swale is being proposed to convey stormwater through the wetlands, profiles from
the outlet to the receiving water body, cross-sections, and design support information
must show that the proposed swale will not result in drainage of the wetlands. Swales in
wetlands are permitted only where onsite conditions prohibit the construction of a
buried pipe to convey stormwater to an outfall.
The NJDEP works with property owners on a case-by-case basis to determine the most
appropriate stormwater treatment method to protect wetlands from both physical disturbance
and potential impacts from stormwater discharges. Where new development is proposed adjacent
to freshwater wetlands and preliminary treatment of stormwater is required to meet state water
quality standards, NJDEP staff make the final decisions on the location and design of each BMP.
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Case Studies
References/Additional Information:
NJDEP. 1995. New Jersey Coastal Nonpoint Pollution Control Program: A plan prepared in satisfaction of section
6Z17 of the Coastal Zone Act Reauthorization Amendments of 1990. Draft. New Jersey Department of
Environmental Protection. April.
NJDEPE. 1992. Freshwater Wetlands Protection Act Rules NJ.A.C 7-7A (amended March
Department of Environmental Protection and Energy.
6, 1992). New Jersey
EPA Region 3
Watershed Management Study, Prince William County, Virginia
Three watersheds in Prince William County, Virginia, are the subject of a 5-year
interdisciplinary, intergovernmental (federal-state-iocal) watershed management study (see
Figure 3-3). The study includes the protection of wetlands through the use of a variety of BMPs
and the restoration of degraded riparian wetlands following the installation of'upstream controls.
The purpose of the project is to develop an innovative stormwater management plan and several
demonstration projects that take a watershed approach to environmentally sensitive decision
making. The headwaters of the three watersheds being studied are located in the Piedmont
physiographic province, cross the fall line, and drain into the tidal portion of the Potomac River
Estuary within the Mid-Atlantic Coastal Plain. The area of study within the watersheds consists
entirely of the portions to the west of Interstate 95 in the Piedmont province.
The northernmost watershed, Neabsco Creek (13,047 acres or 5,284 hectares), experienced
substantial urban/suburban development before stormwater and nonpoint source controls
became a requirement. The large planned community of Dale City is located in the Neabsco Creek
watershed, as is the Potomac Mills shopping complex. The center watershed, Powells Creek
(11,762 acres or 4,764 hectares), is predominantly rural, forested land that is experiencing
development pressure. The southernmost watershed, Quantico Creek (24,636 acres or 9,978
hectares), the majority of which is currently owned by the National Park Service and the U.S.
Marine Corps, is largely undeveloped and is likely to remain so.
All of the watersheds were extensively logged beginning in colonial times, and logging
continued periodically through the 19th century. In addition, the Quantico Creek watershed was
the site of both agricultural activities and active pyrite mining for sulfur into the 20th century.
Nonetheless, the habitat quality of the streams and wetlands is high throughout the upper
watershed and therefore the Quantico Creek watershed has the potential to be used as a control
site during the study. The intention is for the Quantico Creek watershed riparian and wetland
habitats to serve as benchmarks for habitat quality goals established for the Neabsco Creek and
Powells Creek watersheds. Stream rapid bioassessments have been conducted in all three of the
watersheds, allowing comparisons of current habitat conditions. Water quality and quantity
monitoring is also being conducted along all three streams.
Riparian floodplain forests located along the piedmont streams are the dominant nontidal
wetland type that has been identified in the study area to date. National Wetlands Inventory
maps indicate temporarily flooded (PFO1A) and seasonally flooded (PFO1C) palustrine forested
wetland communities. Because much of the land was in agriculture relatively recently (farming
generally ceased between 25 and 60 years ago), the forests range from successional to mature
communities dominated by red maple (Acer rubrum), sycamore (Platanus ocddentalis), and pin oak
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
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Case Studies
(Quercuspalustris). Common understory species include musclewood (Carpinus caroliniana),
spicebush(Lindera benzoin), Japanese honeysuckle (Lonicerajaponica), andgreenbriarfS/m/tof
rotundifolia). Emergent wetland communities that have become established in impounded areas,
such as old farm ponds and some stormwater basins, include cattail (Typka latifolia), smooth alder
(Alnus serrulata), soft rush (Juncus effusus), and wool grass (Scirpus cyperinus).
A federal interagency team consisting of the U.S Army Corps of Engineers (Corps), the U.S.
Fish and Wildlife Service (USFWS), and the U.S. Environmental Protection Agency (EPA)
conducted preliminary wetland assessments in 1992 for portions of the Powells Creek and
Neabsco Creek watersheds. The team focused its assessment on forested wetlands and relied on a
combination of the Army Corps of Engineers' Wetland Evaluation Technique (WET II) and best
professional judgment. Results of the assessment indicated that floodplain forests in both
watersheds have high effectiveness and good potential for floodplain storage, sediment retention,
and nutrient removal functions. Opportunity for these functions to be performed is greater in the
intensely developed Neabsco Creek watershed. Because of the extensive development, the
wetlands in the Neabsco Creek watershed are smaller and more fragmented than those in the
adjacent, relatively undeveloped Powells Creek watershed. The riparian areas and floodplain
wetlands along Powells Creek are larger and more contiguous, providing greater overall wildlife
habitat functions.
The assessment also indicated that deep stream entrenchment caused by increased
frequency, duration, and intensity of stormwater flows in the Neabsco Creek watershed appeared
to be affecting the hydrology of adjacent wetlands. Ironically, despite this degradation, the
Neabsco Creek wetlands were determined to have high educational and recreational value because
of their proximity to population centers. The U.S. Fish and Wildlife Service, in cooperation with
the Prince William County Public Works Department, is working on several stream/wetland
restoration projects along Neabsco Creek.
The structural stormwater management facilities being evaluated as part of the study
include onsite and regional BMPs. Nonstructural BMPs include riparian buffers and stream
restoration techniques. Several of these practices are currently protecting downstream wetlands
from the impacts of urban stormwater discharges.
A regional wet pond is located immediately upstream from a substantial riparian
wetland area along Neabsco Creek adjacent to a shopping center. The BMP pond, which
controls a drainage area of approximately 300 acres (122 hectares), is.intended to protect
the downstream wetlands from erosive velocities and to improve water quality. A
restoration plan has been prepared for approximately 1 mi (1.6km) of stream channel, 6
acres (2.4 hectares) of associated riparian forest, and 20 acres (8.1 hectares) of emergent
wetland habitat, which are located immediately downstream of the regional BMP pond.
A "road culvert retrofit BMP " that essentially functions as an extended detention BMP
facility has been established on an unnamed tributary on Neabsco Creek. The upstream
drainage area is more than 200 acres (81 hectares) and is intensely developed with
residential and commercial land uses. The immediate area includes a shopping center
located adjacent to the stream upstream of the culvert. A riser was initially constructed
upstream of a wing wall (concrete apron) built in front of the existing road culvert (see
Figure 3-4). The design is being modified to incorporate a small permanent pool behind
the wing wall and the use of a hydraulic jump to provide the outlet for the 2-year storm
rather than the use of the riser. The design modifications were necessary because during
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Emergency
Spillway
Existing Road Culvert
BMP Riser
Low Flow Channel
Prince William County, 1994.
Figure 3-4. Isometric view of the Neabsco Creek tributary road culvert retrofit BMP.
the winter of 1994 the riser became clogged with debris and local officials perceived the
ponded area to be too large.
The road culvert retrofit BMP works by ponding the more frequent storms, which cause
sediment-laden water to overflow the stream banks in the backwater area and deposit its
solids load in the riparian floodplain. This BMP protects downstream riparian wetlands
from the erosive peak velocities and durations associated with frequently occurring
storm events. The specific water quality benefits of the BMP are being studied as part of
the comprehensive 5-year watershed program. Automatic sampling and flow-gauging
equipment has been installed and is providing data on hydrology and pollutant transport.
The water quality monitoring information that will be collected and analyzed by the
Virginia Polytechnic Institute and State University (Virginia Tech) includes:
- Flow
- Nutrients: total phosphorus, soluble reactive phosphorus, soluble aluminum, total
Kjeldahl nitrogen, and oxidized nitrogen
- Dissolved oxygen, pH, conductivity, alkalinity, and hardness
- Trace metals
- Biochemical oxygen demand and chemical oxygen demand
- Total suspended solids
- Total organic carbon
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Case Studies
Prince William County intends to install additional road culvert retrofit BMPs in other
areas of the county during the program. Watersheds of about 80 acres (32 hectares) are being
targeted for these BMPs. The BMPs will allow the floodplain forests that are inundated to realize
the high potential effectiveness for sediment retention and nutrient removal functions identified
by the WET II/BPJ analysis described above. Another potential benefit of this innovative BMP is
to minimize the impact on wetlands. If provided in series throughout a watershed, these BMPs
have the potential to provide substantial water quality improvements and possible wetland
protection with a minimum of disruption to the natural ecosystem (i.e., displacement of natural
wetlands by large stormwater management ponds).
Riparian wetland areas have been identified and delineated in the Powells Creek watershed.
BMPs designed for the improvement of water quality and the protection of riparian wetlands
have been planned and installed to protect some of these wetland areas. These include numerous
onsite BMP ponds in residential and commercial developments throughout the watershed, a
regional pond currently in design, stream restoration plans, and two farm pond retrofit projects.
The multiple stakeholders, the interdisciplinary approach, and the long-term aspects of the
program are unique. The comprehensive approach being taken in the project contains elements
that cut across traditional federal and local roles. For example, program elements include flood
protection, stormwater management, erosion and sediment control, wetland preservation, water
quality, and terrestrial as well as aquatic habitat quality. Prince William County is funding more
than 50 percent of the project. The U.S. Geological Survey (USGS) is involved in the stream
gauging and water quality monitoring components of the project. In addition to the USGS, the
Corps, the USFWS, and EPA are providing federal agency involvement and funding to varying
degrees. The Virginia Department of Environmental Quality and the Chesapeake Bay Local
Assistance Department (a state agency that implements Virginia's Chesapeake Bay Preservation
Act) are providing funding and/or monitoring and other technical support. Two state universities,
George Mason and Virginia Tech, are providing technical support in the form of bioassessments
and water quality monitoring, respectively.
Initial data collection for the project will continue through 1997. An environmental history
of the watersheds will be compiled using baseline water quality monitoring data, land use
information, and an evaluation of data collected on terrestrial and aquatic resources. Traditional
and innovative BMPs for stormwater and nonpoint source controls will be tested and evaluated.
The design of stormwater management facilities will attempt to replicate the hydrologic
characteristics of the watershed based on modeled predevelopment conditions. (These results
could ultimately be compared to field data collected in the Quantico Creek watershed, for the
"predeveloped case.") Ultimately, the project is attempting to document the cumulative impacts
that result as urbanization degrades water resources and ways in which sound watershed
management might mitigate water quality problems and related habitat problems. The results of
this comprehensive approach to preserving the environmental integrity of a developing watershed
should be useful to all stakeholders. Prince William County will benefit by being able to use the
data to determine the best approach for managing its other watersheds.
References/Additional Information:
Everett, R., and T. McCandless. 1994. New watershed approach in Prince William County. In Watershed
Events, Summer 1994, pp. 9-12. EPA 840-N-94-002. U.S. Environmental Protection Agency, Office of Water,
Washington, DC.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Getlein, S., R.S. Karalus, A Spingam, and F. Pasquel. 1993. Balancing development, water quality, and
wetlands protection in a Mid-Atlantic watershed. In Proceedings of Watershed '93, A National Conference on
Watershed Management, March 21-24, 1993, Alexandria, VA, p. 823. EPA 840-R-94-002. U.S. Environmental
Protection Agency, Office of Water, Washington, DC.
Pasquel, RJE, M.R. Mohan, and S.P. Getlein. 1993. Comprehensive Stormwater management planning. In
Engineering Hydrology, Proceedings of the American Society of Civil Engineers Hydrology Symposium, July 25-30,
1993, San Francisco, CA, pp. 832-837.
EPA Region 4
Hidden River Wetland Stormwater Treatment Site, Tampa Florida
Hidden River Wetland is a natural wetland located in the Hidden River Corporate Park in
Tampa, Florida. The 3-acre (1.2 hectares) wetland receives runoff from a mostly impervious
drainage basin approximately 15 acres (6 hectares) in size that includes an office park complex,
parking lots, and a central roadway. The wetland-to-upland ratio of the Stormwater treatment site
is approximately 1:5 or 20 percent (i.e., about 80 percent of the treatment site is upland). Annual
precipitation in the region is about 52 in (132.08 cm) per year. Water leaving the wetland flows
into the Hillsborough River via an alluvial floodplain. Water quality of the Hillsborough River is
good near Hidden River; however, it becomes degraded downstream at Tampa because of factors
not related to this site.
Hidden River Wetland is a freshwater, herbaceous marsh, classified as a palustrine emergent
wetland. In southwest Florida there are many isolated wetlands of this type, known locally as
Florida flag marshes. These wetlands have highly reduced organic soils. Hidden River Wetland has
95 percent vegetation cover; the plant community is dominated by maidencane (Panicum
hemitomom), pickerelweed (Pontederia cordata), and waterlily (Nymphaea odorata). The wetland was
undisturbed prior to site development. Construction of a roadway filling a portion of the south
end of the marsh necessitated the construction of a small mitigation area to the east side of the
marsh. The north rim of the marsh is protected by a buffer of native vegetation.
Runoff enters the system through two inlets and undergoes preliminary treatment in two
sedimentation basins that were built in 1987 as part of the Stormwater management system to
protect the wetland. The east sediment basin consists of approximately 0.2 acre (784.08 m2) of
open water, while the west basin, which is usually dry, covers about 0.07 acre (274.43 m2) and is
vegetated with cattails (Typka latifolia) and other plant species. The west basin has a very wide,
brief water level fluctuation. Rain events of over 0.5 in (1.27 cm) generally produce flows into
the wetland for less than a day; however, discharges from the wetland do not occur until July and
then are continuous until September. Wetland outflow is treated in a grassed swale before it
enters a lower detention pond. After passing through a forested alluvial floodplain, the outflow
enters the Hillsborough River.
After several years of use, Hidden River Wetland continues to have a beneficial effect on
water quality. Generally, inorganic nitrogen, phosphorus, and suspended solid concentrations are
lower in the wetland outflow than in the inflows. Water in the wetland maintains lower pH,
dissolved oxygen, and reduction/oxidation potential than the inflowing waters. Fluctuations in
water quality are much greater in the sedimentation basins than in the wetland. Water tempera-
tures in the wetland are as much as 10 degrees Celsius lower than those in the sedimentation
basin.
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Although a plant survey was not conducted prior to sedimentation pond construction and
site development, a comparison of aerial imagery from 1984 and 1992 suggests that the discharge
of pretreated stormwater to the wetland has caused a reduction in open water area of the wetland
but has had little effect on which plant species are present. The typical seasonal variation of water
level in Florida flag marshes, including a dry winter period, has been maintained. The pH of the
wetland is slightly acidic rather than the circumneutral pH typical of Florida flag marshes, which
might be due to acidic groundwater influences. Conductivities are also lower than usual for flag
marshes. Where the edge of the wetland vegetative community was disturbed by landscaping
activities, cattails (Typha latifolia) and primrose willow (Ludwigia peruviana) have invaded.
Sedimentation of the preliminary treatment pond has not yet been a problem, possibly as a result
of the close attention paid to construction-related sediment control and site landscaping.
Continuing research on the Hidden River Wetland Treatment Site will include
investigations into the wetland's hydrologic interactions with groundwater, analyses of soils and
sediments, and continued analyses of water quality at wetland inlets and the outlet.
References/Additional Information:
Rushton, B. 1991. Variation in field parameters in a native wetland used for stormwater treatment. In
Statewide Stormwater Management Workshop, October 2, 4991, ed. B. Rushton, J. Cunningham, and C.
Dye. Southwest Florida Water Management District, Brooksville, FL
Rushton, B. 1992. Evaluation of a wetland used for stormwater treatment: Preliminary data. Southwest
Florida Water Management District, Brooksville, FL. Unpublished report.
Rushton, B. Southwest Florida Water Management District. Interview, November 1992.
Rushton, B., and C. Dye. 1991. Hidden River stormwater treatment. In Annual report for Stormwater
Research Program, fiscal year 1989-1990. Southwest Florida Water Management District, Brooksville, FL.
EPA Region 5
Lake McCarrons Wetland Treatment System, Roseville, Minnesota
The Lake McCarrons Wetland Treatment System was built in 1985 in Roseville, Minnesota,
a suburb of St. Paul. About 85 percent of the runoff in the Lake McCarrons watershed is routed to
the wetland for treatment prior to discharge to the lake. The portion of the Lake McCarrons
watershed draining to the wetland is approximately 636 acres (258 hectares) in size with
17 percent impervious surface. Normal annual precipitation in the area is about 26 in (66.04 cm).
Lake McCarrons is a eutrophic lake with a surface of 81 acres (33 hectares) and a mean depth of
25 ft (7.62 m). In summer the dominant phytoplanktori are blue-green bacteria and the lake's
deeper waters become anoxic.
The two goals of the project are the improvement of the quality of stormwater runoff
entering Lake McCarrons and the restoration of an existing degraded palustrine wetland. A
sedimentation pond upstream of the wetland serves both as a moderator of stormwater peak
flows to the wetland and as a primary pollutant removal system for water entering the wetland.
The baseflow in the pond/wetland system was recorded as between 0.05 and 0.20 ft3/s (0.0014
and 0.0057 m3), derived from groundwater inflows including natural springs and some storm
sewer leakage. The sediment basin was intended to reduce pollutant and sediment loads to the
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
wetland, allowing the wetland to serve a "polishing" function and to restore some of the original
wetland functions.
Low berms (12 to 18 in (30.48 to 45.72 cm) high with 12-in culverts) were installed,
dividing the wetland into five consecutive chambered wetlands between the sedimentation pond
and Lake McCarrons (see Figures 3-5 and 3-6). An entrenched channel in the wetland, a result of
increased runoff volume and velocity due to urbanization of the watershed, was filled. These
modifications brought the wetland's hydrology closer to a natural state and allowed stormwater
entering the wetland to spread out as sheet flow through wetland vegetation and over the peat/
mineral soils for greater removal of pollutants. The resulting wetland is described as a palustrine
emergent marsh similar to the original marsh with a smaller palustrine scrub/shrub border than
that present before construction.
IBerm
Sedimentation Basin
Spillway
Outlet
Wetland
McCarrons
Blvd.
To Lake
Figure 3-5. Lake McCarrons Wetland Treament System.
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1200 1300
Vertical exaggeration approximately 7x
2000 2100
Figure 3-6. Cross section of Lake McCarrons wetland treatment system.
Lower pollutant removal efficiencies were recorded for the wetland than for the sediment
pond, probably because of removal of the most easily settled particulates in the pond and the high
sorption capacity of newly exposed peat soils in the pond. Table 3-1 shows the results of water
quality monitoring for the pond, wetland, and combined system. Although the pond-to-watershed
area ratio is only 0.5 percent, the pond performed well in the reduction of pollutants monitored.
The pond/wetland treatment system did result in substantial reductions in phosphorus loadings
to Lake McCarrons. However, no change in lake water quality has been detected, probably
because of the high internal phosphorus loadings that remain in the lake.
Table s-i .
Pollutant
Total Suspended Solids
Total Phosphorus
Total Kjeldahl Nitrogen
Total Lead
inflow vs.
Events
fontl
91
78
88
85
Outflow
Load Reductions:
over 21 Rainfall
Wetlana comulnea System0
87
36
26
68
94
78
85
90
"Some runoff enters the lower wetland with no pretreatment, explaining combined reductions lowerthan
pond reductions.
1
;/--
11
K
*5
r-
f
8
Among problems encountered are the loss of effective pond treatment when the pond is
ice-covered and washouts of wetlands directly below the culverts through berms. Over a 7-year
period (1985-1992) there was a loss of pond storage capacity due to sedimentation, with pond
depth decreasing from 6 to 2 ft (1.83 to 0.61 m). In retrospect, a design including a drain valve for
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
easier pond maintenance and graveled spillways over wetland berms Would have been desirable.
Wildlife was described as abundant and the plant community was found to be very diverse in the
modified wetland after 3 years; after 7 years cattails (Typha sp.) had increased substantially.
Since the completion of the original study in 1988, a sedimentation pond has been added to
provide preliminary treatment of runoff entering the lowest wetland chamber. Some road runoff
that previously entered the wetland as sheet flow over a grassed area, however, has now been
routed directly to the wetland without preliminary treatment. A report presenting the results of a
renewed 2-year study on the Lake McCarrons Wetland Treatment System will be completed in
the spring of 1997.
References/Additional Information:
Oberts, G.L. Metropolitan Council of the Twin Cities Area. Interview, November 1992.
Oberts, G.L, and R A Osgood. 1988. Lake McCarrons Wetland Treatment System: final report on the function of the
wetland treatment system and the impacts on Lake McCarrons. Publication no. 590-88-095. Metropolitan
Council of the Twin Cities Area, St. Paul, MN.
Oberts, G.L, and R-A. Osgood. 1991. Water-quality effectiveness of a detention/wetland treatment system
and its effect on an urban lake. Environmental Management 15(1):131-138.
Wotzka, P., and G. Oberts. 1988. The water quality performance of a detention basin-wetland treatment
system in an urban area. In Nonpoint pollution: 4988Policy, economy, management, and appropriate
technology, pp. 237-247. American Water Resources Association, Edina, MN.
The Phalen Chain of Lakes Watershed Project, Ramsey and Washington
Counties, Minnesota
The Phalen Chain of Lakes watershed covers about 23 mi2 (36.8 km2) in Ramsey and
Washington Counties. It includes five major lakes, 950 acres (385 hectares) of wetlands, and
several connecting creeks called county ditches.
The watershed is the land area that drains to the five major lakesKohlman, Gervais, Keller,
Round, and Phalen. The watershed includes parts of seven communities (Figure 3-7)Little
Canada, Maplewood, North St. Paul, and smaller portions of Oakdale, St. Paul, Vadnais Heights,
and White Bear Lake. The lakes follow the ancient bed of the preglacial St. Croix River. The area is
considered unique and is heavily used for its recreational resources by local residents and the East
Metro area. The Chain of Lakes watershed is also part of a major flyway for migratory waterfowl
and songbirds, and it provides significant habitat for other birds and wildlife in an urban setting.
From settlement in the 1850s until World War II, the watershed was dominated by
vegetable and dairy farming. Farmers drained wetlands, channelized creeks, and constructed early
roads. In the 1970s, construction of Interstate 35E and large commercial areas like Maplewood
Mall accelerated urban development in the watershed.
Urbanization has affected natural resources in the watershed in many ways. First,
settlement has nearly eliminated the native vegetation of the area, replacing it with buildings,
paved surfaces, and lawns. Habitat diversity and the varieties of birds and animals that inhabit the
area have been much reduced because of these changes. Non-native species like loosestrife have
also gained a foothold in the watershed and become problems.
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Phalen Chain of Lakes Watershed
JR
Phalen Chain of Lakes
Watershed
Major Minnesota Watersheds
Figure 3-7. Phalen Chain of Lakes watershed.
Second, the natural drainage in the watershed has been altered. Soils, vegetation, and
wetlands present at settlement easily absorbed much of the water that fell on the land. Urban
development has increased soil compaction, paved surfaces, channelized creeks, and eliminated
over half the wetlands in the watershed. These changes cause more water to run off the land at a
faster rate, creating flooding and erosion problems.
Higher volumes of runoff carry pollutants and nutrients to lakes, wetlands, and creeks,
causing declines in water quality, and a reduction in the quality of fish and wildlife habitat. Algae
blooms on area lakes are evidence of these changes. It is apparent that without conscious efforts
to manage land and water resources differently, ongoing development in the watershed will
continue the following trends:
Increasing volumes of stormwater runoff, with additional sediments and nutrients
transported to wetlands, creeks, and lakes.
Loss of aquatic vegetation and reduced habitat for fish and other aquatic organisms.
Increasing fragmentation of upland and wetland habitat and loss of plant and animal
diversity.
Loss of open space.
In early 1993, a partnership was formed to address concerns about declining natural
resources in the watershed. The partnership included local city governments, developers and
businesses, the University of Minnesota, and the Minnesota Department of Natural Resources.
The partnership received a grant to develop a comprehensive plan for the watershed. A Steering
Committee, including representatives of all interested groups in the watershed, completed the
plan in April 1994.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
The comprehensive watershed plan includes seven major goals, BMPs, and many
recommended action steps to protect, restore, and manage natural resources in the watershed in
the short term and long term. Major goals of the seven-point Action Plan for the Watershed
include the following:
Improve, restore, and protect surface water quality.
Restore, enhance, and protect wetlands and creeks.
Protect the groundwater resources of the watershed.
Develop and support a connected system of "green corridors" to protect water resources,
enhance fish and wildlife habitat, and provide natural resources recreation and education
opportunities.
Restore and expand forest cover and diverse native vegetation.
Increase public awareness and involvement in natural resources management in yards,
public and private lands, and all of the watershed.
Establish a local natural resources board to coordinate implementation of the watershed
plan.
During the summer of 1994, the Watershed Project partners, local residents, cities,
businesses, and others in the watershed improved natural resources through a variety of projects,
including the following:
Developing an innovative BMP to control stormwater in Maplewood. It will let
stormwater infiltrate within a neighborhood and eliminate the need for new storm
sewers that would empty into Lake Phalen. This neighborhood will serve as a model for
stormwater management in other urban areas.
Working with the City of St. Paul and District 2 community to obtain funding for the
Phalen Wetland Park restoration as part of the Phalen Village Small Area Plan.
Implementing projects to restore aquatic shoreline vegetation, and working with parks
departments and landowners to manage vegetation and use BMPs around wetlands and
lakes to benefit fish, wildlife, and water quality.
Completing a watershed-wide wetlands plan, based on the functions and values of
wetlands in the watershed, that will help the watershed district and local governments
set priorities for purchase, protection, or management of wetlands.
Completing field work to identify the remaining natural areas and prairie fragments,
and inventorying open-space areas to assist in development of the "green corridors"
network for the watershed.
Completing restoration projects at the H.B. Fuller Company Willow Lake Nature
Preserve to restore aquatic vegetation and other natural communities.
Developing a workshop for teachers in five local school districts on watershed issues and
identifying student proj ects to benefit natural resources.
Working with neighborhood and citizen groups on creative plantings and projects to
benefit natural resources in parks and residential areas of'the watershed.
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Case Studies
The Phalen Project Committee will continue to work with local governments, businesses,
citizens, and natural resources agencies to identify projects and opportunities to benefit land,
water, plants, animals, and local communities.
The Prairie Wolf Slough Project, Chicago, Illinois
The Prairie Wolf Slough is one of several projects aimed at addressing natural resource issues
along the 156-mile-long (249.6-km) Chicago River corridor. The 25-acre (10.1-hectare) project
involves the ecological restoration of a wetlands/prairie/savanna complex along the Middle Fork
of the North Branch of the Chicago River and the creation of an interpretive nature trail.
The key component of the restoration is the creation of a wetland vegetation complex that,
in the past, was drained by an agricultural drainage tile system. Sediments and other
contaminants used to enter the stream via a gully created by the outlet of the drainage system.
After the tiles were removed and the gully was filled, water naturally returned to the floodplain.
The restored wetlands help to eliminate sediments, nutrients, and residues from farm chemicals
used on the property, which is leased by a local farmer for row crops.
Water drains onto the site from a corporate complex and a shopping center, which
contribute pollutants typical of urban runoff, such as lawn chemicals, road salts, and oil and
grease. Ponds just downstream provide some physical removal of sediment, but most of the
organic toxics and dissolved nutrients are not removed. The project diverts water from the two
upstream sources into the wetland system, which provides secondary biological treatment of the
runoff. The water from the site will eventually percolate back into the river, but it will have been
purified by the restored wetland, absorbing waterborne sediments and nutrients that reach the
river. The native wetland vegetation will also function as a filter medium to assist in removal of
deleterious waterborne metals.
The restored wetlands will have a beneficial impact during flood events. By restoring a
cover of dense native vegetation to the 25-acre (10.1 hectare) parcel, many beneficial wetland
functions would be restored. These include an improvement in the retention of precipitation. A
dense matrix of native plants would filter and hold more water than would a traditional crop
field. Increased water retention time translates into an increased ability for soil water absorption
and, therefore, decreased surface erosion.
The restoration will benefit many surrounding jurisdictions. The communities will benefit
from the enhanced site aesthetics, improved wildlife habitat, and increased recreational
opportunities for walking and nature observation. The parcel of land is a logical link with a
proposed riverside trail system and is also a part of a larger greenway that follows the Middle Fork
of the North Branch of the Chicago River. This corridor provides vital habitat, foraging sites, and
nesting locations for neotropical migratory birds, in addition to providing habitat for migratory
waterfowl. Local grade and high schools and a nearby college will also use the site for
environmental education activities and the promotion of environmental awareness. The
beneficial qualities of the wetlands will also be used by the Friends of the Chicago River to help
focus public attention on the importance of water quality, fisheries, wildlife habitat, and open
spaces along the river. The volunteer and environmental education components will build
interest and a constituency for protecting the river and its upper reaches.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
EPA Region 6
Tensas Cooperative River Basin Study, Louisiana
Background
The cumulative impacts of human activities have led to the reduction of bottomland
hardwood forests and wetlands, and their associated wildlife habitat, in the Tensas River
Basin in northeastern Louisiana. Historically, over 90 percent of the 718,000-acre
(290,790 hectares) basin was forested with bottomland hardwoods. Approximately 350,000
of these acres (141,750 hectares) were irregularly to permanently flooded forested wetlands.
Today, an estimated 85 percent of these forests have been cleared and converted to row crop
agriculture, and the basin now contains only 135,000 acres (54,675 hectares) of bottomland
hardwood forests. The accelerated conversion of forestland to cropland during the 1960s and
1970s has resulted in increased environmental and social problems in the basin. The natural
ecosystem can no longer sustain acceptable water quality levels, provide adequate flood
storage functions, or offer the habitat diversity needed for many wildlife species.
In November 1991, various agencies met with the Natural Resources Conservation Service
to devise a strategy for resolving water quality impairment and wetland habitat loss and decline.
The group determined that an overall plan was needed for the entire basin to avoid a "piecemeal"
approach to protecting the area's natural resources. As the main sponsor of the study, the Natural
Resources Conservation Service realized that for the study to be effective, a broad selection of
participants should be included in the process. Participants in the study included the following:
U.S. Environmental Protection Agency; U.S. Fish and Wildlife Service; U.S. Army Corps of
Engineers; U.S. Geological Survey; U.S. Forest Service; Louisiana Department of Agriculture and
Forestry; Louisiana Nature Conservancy; Louisiana Cooperative Extension Service; Louisiana
Office of Soil and Water Conservation; East Carroll, Madison, Tensas-Concordia, and Northeast
Soil and Water Conservation Districts; Fifth Louisiana Levee District; National Fish and Wildlife
Foundation; and farmers of the Tensas Basin. The study began in October 1992.
The objectives of the study were to facilitate and coordinate the orderly conservation and
management of the basin's land and water resources, particularly bottomland hardwood
wetlands. Specific objectives include:
Describe the ecological, economic, cultural, and social resources of the Tensas River Basin.
Provide a broad-scale analysis of ecological, economic, cultural, and social problems in the
basin.
Describe solutions to the basin's problems that are environmentally, economically, and
socially sound and acceptable to local residents.
Identify various federal, state, and local agencies and organizations that provide
technical and financial assistance for implementing solutions to water and related land
resource problems.
Physical Setting
The study area is located in northeastern Louisiana in portions of East Carroll, Madison,
Tensas, and Franklin Parishes and encompasses the watershed of the Tensas River from Lake
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Case Studies
Providence to its confluence with Bayou Macon. The Tensas River Basin is in a subtropical,
transitional climatic region that is affected alternately by cool, dry air flowing southward and
warm, moist air flowing northward. Winters are usually mild with an average temperature of 47
degrees Fahrenheit (°F), and the average summer temperature is 81 °E The average annual
precipitation is 55 in (139.7 cm), most of which occurs between December and May.
The Tensas River Basin is located in the Mississippi River alluvial valley, which was formed
during the early Pleistocene epoch. Following the glacial retreat of the epoch, the Mississippi
River became deeply incised within the basin area, creating a broad, entrenched valley that
gradually filled with alluvial deposits. Elevations average from about 100 ft (30 m) above sea level
along the northern boundary to less than 50 ft (15 m) along the southern boundary. The major
landforms resulting from meanders in the course of the Mississippi River can be divided into five
categories: abandoned courses, abandoned channels, natural levees, point bars, and back swamps
(see Figure 3-8). Forested wetlands can be found in all of the major landforms except the natural
levees, which are elevated above the floodplain.
Abandoned courses are lengthy segments of a river abandoned when the stream forms a
more hydrologically efficient course in the floodplain. They can vary from a few miles to
tens of miles in length, but they always contain more than one meander loop. The
abandoned courses gradually fill in with sediment and are often occupied by a smaller
stream or bayou.
Abandoned channels are cut-off bends of meandering streams, commonly called oxbow
lakes. A sediment plug forms in the abandoned channel immediately below the point of
cutoff. If the parent stream remains in close proximity, the oxbow quickly becomes
partially or wholly filled with fine-grained sediments and is replaced by vegetated
wetlands in a few centuries. If the river channel rapidly meanders far away from the
oxbow, however, sediment filling is slow and open water conditions often prevail.
Point bars are crescent-shaped ridges consisting principally of sand and silt on the inside
of meander loops as the stream migrates toward the concave bank. As the process
continues, a succession of bars can be formed, the height of which can be as much as 10 ft
above the mean low water level. The shape tends to conform to the curvature of the
channel in which they were created. The low areas between point bars constitute what
are known as swales. They develop dense willow growth that traps fine sediments, and
in time they are filled with silts and clays. Many of the remaining regularly flooded
forested wetlands in the basin occur in swales.
Backswamps are low, flat, featureless areas bordering natural levees and point bars.
Backswamp deposits consist of fine-grained sediments laid down in broad, shallow
slackwater basins during stream flooding. Historically, backswamps would remain
flooded for months during high river stages and periods of heavy rainfall due to
inefficient channels and low gradients. Today, most of these areas have been converted to
row crop farms.
The regularly or permanently flooded bottomland hardwood forests are composed of
baldcypress (Taxodium distichum), drummond red maple (Acer rubrum drummondii), swamp
blackgum (Nyssa sylvatica), and buttonbush (Cephalanthus ocddemalis). Seasonally and irregularly
flooded bottomland hardwood forests are composed of overcup oak (Quercus lyrata), bitter pecan
(Carya aquaticd), green ash (Fraxinus pennsylvanica), willow oak (Quercus phellos), cedar elm
(Ulmus crassifolia), waterlocust (Gleditsia aquatica), boxelder (Acer negundo), and hackberry (Celtis
laevigata).
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
TENSAS BASIN
Geomorphologic
Features
Legend:
Abandoned Channels
Abandoned Courses
fTTTTTn Point Bar
Backswamp
Project Boundary
Acreage (Percentage)
Water 9,562.89 (1.33%)
Non-Agland 65,502.38 (9.11%)
Forest 133,565.36 (18.58%)
Agland 510,113.93 (70.97%)
Criteria Not Met 1.54 (0.01%)
Base Sauce: USCA-NCRS Digital STATSGO data. USGS 7.5' Base
Quads. Universal Transverse Mercator Projection; Ellipsoid -
Qarto66. received bactewamp data, modified canal systems,
and WUoJIfe Management Areas from the SIS Coordinator.
Mississippi River Alluvial Ptaln Project. The Nature Conservancy.
General landuse data (1992) obtained from The Nature
Conservancy was originally sampled by the LA. Dept. of
Note: Some of the data provided to the USDA Natural Resources
Conservation Service may not meet National Map Accuracy
standards. In the case of raster data, ground truth was not
available to support a comprehensive accuracy assessment.
Figure 3-8. Geomorphologic features in Tensas Basin.
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Case Studies
The social and economic resources of the Tensas River Basin were also reviewed and
incorporated into the study. The economy of the region is based primarily on row crop agriculture
(see Figure 3-9). Timber harvesting has diminished since there have been no large reforestation
efforts. The area experiences chronic unemployment problems and lack of job diversity and,
consequently, has been undergoing an emigration of people in search of job opportunities. For
example, prices for farm inputs have increased 46 percent more than prices received for raw
agricultural products, and unemployment in the basin ranges from 10.7 to 24.1 percent. These
combinations result in fewer dollars being circulated in the local economy and thus reduced job
opportunities in the retail and service industries in the rural, farm-based economies.
Problem Identification and Treatment Options
A series of public meetings were held throughout the basin to identify problems and
potential solutions. Problems identified include long-term viability of row crop production,
bottomland hardwood wetland decline, impaired water quality, flooding, limited recreational
opportunities, reduced fish and wildlife habitat, and socioeconomic concerns. Regarding the
bottomland hardwood wetland decline, the major sources of problems are habitat fragmentation,
excessive sediment loading, and nutrient and pesticide loading. Throughout the analysis and
planning process, it became apparent that the problems were usually interrelated. Water quality
was also being impaired due to excessive sediment loading and nutrient and pesticide loading,
which was reducing the profit margin for the agricultural operations. Limited recreational
opportunities and reduced fish and wildlife habitat were tied to the forested wetland decline.
Flooding is also a major problem because there are fewer wetlands to provide floodwater storage
and control.
Based on the identified problems, two primary methods for addressing these issues were
evaluated: BMPs and bottomland hardwood restoration. Due to the agricultural nature of the
region, row crop BMPs were determined to be the most effective. Only BMPs deemed by the
study group to be cost-effective, efficient, and acceptable to the residents were included in the
final plan. Row crop BMPs are categorized as follows: (1) soil management, (2) water
management, and (3) nutrient and pesticide management.
Soil Management BMPs
Soil erosion was determined to be linked to many of the problems identified in the basin,
including the decline of bottomland hardwood wetlands. Soil particles often act as carriers of
nutrients and pesticides, which further add to water pollution problems. Soil erosion can be
reduced by maintaining a protective cover of plants or plant residue, reducing the number of
tillage operations, and improving soil structure. The following BMPs were determined by the
Tensas River Basin study to be the most effective measures in reducing soil erosion: (1) chiseling
and subsoiling, (2) conservation cropping sequences, (3) conservation tillage systems, (4) contour
farming, (5) cover crop, and (6) crop residue use.
Water Management BMPs
Water management practices are applied in the fields where the crops are grown and at the
field edges where water enters and exits a field. BMPs applied in the crop field to facilitate plant
growth and to reduce sediment and water from leaving the fields include (1) land leveling,
(2) irrigation water management, and (3) crop row arrangement. BMPs applied to minimize
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
TENSAS BASIN
Landuse
Legend:
Water
Non-Hydrte Soils
Forest
Agricultural Land
Project Boundary
SWUTCMUS
4 4 KLCME1ERS
Acreage (Percentage)
Water 9,562.89 (1.33%)
Non-Agland 65,502.38 (9.11%)
Forest 133,565.36 (18.58%)
Agland 510,113.93 (70.97%)
Criteria Not Met 1.54 (0.01 %)
Base Source: USDA-NCRS Digital SIAJSGO data, LEGS 7.5' Base
Quads. Universal Transverse Mercator Projection; Ellipsoid
Clartce66, received backnvomp data, modified canal systems,
and Wildlife Management Areas from (he GIS Coordinator,
Mississippi River Alluvial Plain Project, the Nature Conservancy.
General landuse data (1992) obtained from The Nature
Conservancy was originally sampled by the LA Dept. cf
Note: Some of the data provided to the USDA Natural Resources
Conservation Service may not meet National Map Accuracy
Standards. In the case of raster data, ground truth was not
available to support a comprehensive accuracy assessment.
Figure 3-9. Main land uses in Tensas Basin.
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Case Studies
environmental impacts before or after water reaches a field are (1) filter strips, (2) grassed
waterways, (3) irrigation tailwater recovery, (4) water and sediment control basins, and
(5) water control structures.
Nutrient and Pesticide Management BMPs
Nutrient and pesticide runoff is closely tied to soil and water management. However, in
many instances excess nutrients and pesticides do not need to be applied. Prudent application of
nutrients and pesticides enables the producer to reduce expenses while having a positive impact
on the surrounding wetlands. Proper nutrient management requires periodic soil testing and use
of fertilization rates within-a recommended range. Pesticide management requires the use of field
scouting, safe handling and mixing procedures, and nematode assay to determine if and when
pesticides should be applied.
Bottomland Hardwood Restoration
Approximately 350,000 acres (141,750 hectares) of hydric soils occur in the Tensas River
Basin. On some hydric soils, profitable row crop production might be limited over the long term
and therefore the most prudent land use for these soils would be hardwood production because it
would allow the floodplain to function naturally. Bottomland hardwood restoration would
reduce the impacts of flooding and would improve water quality. It would improve fish and
wildlife habitat while providing a higher economic return. Although not always considered a
BMP to protect natural wetlands, the restoration of the forested wetlands would enhance the
existing wetlands by enlarging the resource as well as providing additional buffer zones.
Implementation ;
The Natural Resources Conservation Service will use the Tensas River Basin Study to
develop detailed watershed plans for implementation of BMP measures and to target potential
bottomland hardwood restoration sites. Solving the environmental and social problems of the
Tensas River Basin will require a concerted effort by private landowners, federal and state
agencies, local governments, and organizations. Implementation of land treatment options, to a
large extent, is dependent on the voluntary efforts of local landowners. However, by
demonstrating that protection and restoration of bottomland hardwood wetlands not only will
improve environmental quality but also will provide economic and social benefits for the
landowners, this transition should be more easily accomplished. Probably the most beneficial
aspect of the basin study was the consensus building. The diversity of the participants ensured
that a variety of viewpoints were considered, and the result is a plan that relates protection of
bottomland hardwood wetlands to the overall health of the watershed, including the
socioeconomic health.
References/Additional Information:
USDA/NRCS. 1995. Tensas Cooperative River Basin Study. U.S. Department of Agriculture, Natural
Resources Conservation Service, Alexandria, 1A.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
EPA Region 7
Multi-Species Riparian Buffer Strips, Bear Creek Watershed, Iowa
Background
Most agricultural landscapes are a mosaic of croplands and residences superimposed on areas
that were previously natural prairie, wetland, and forest ecosystems. In the Corn Belt of the
midwestern United States, most of these natural ecosystems have been cleared for agricultural
purposes. In Iowa, for example, 99 percent of the prairie and wetlands have been converted to
other uses. Many of the remaining riparian wetland systems are heavily impacted by nonpoint
source (NFS) pollution. BMPs in the Midwest that include the protection of riparian wetlands as
an objective must also address enhancement and restoration of riparian wetlands. An example of
this type of BMP is a multi-species riparian buffer strip (MSRBS) system designed and placed
along Bear Creek in central Iowa by the Iowa State Agroforestry Research Team.
The Bear Creek Watershed is located in north-central Iowa within the Des Moines Lobe, the
depositional remnant of Wisconsinan glaciation in Iowa. Bear Creek is 2.16 mi (34.8 km) long,
with 17.27 mi (27.8 km) of major tributaries. The creek empties into the Skunk River. The
watershed drains 18,386.4 acres (7,446 hectares) of farmland, most of which has been subjected
to field tile drainage during the last 40 years. About 87 percent of the watershed is devoted to corn
and soybean agriculture.
Two different levels of research activity are taking place in the Bear Creek Watershed. The
Leopold Center for Sustainable Agriculture's Agroecology Issue Team (ATT) is using the watershed
to study the condition of riparian zones at the watershed level. The AIT is developing a model to
identify critical riparian reaches along the creek that need protection and restoration. The long-
term goal of the project is to help farmers who own land along Bear Creek and other streams to
develop riparian zone management systems that protect riparian wetlands and water quality by
removing sediment and agricultural chemicals.
The Iowa State Agroforestry Research Team (IstART) has been working on one farm in the
watershed to develop the MSRBS model system for use along the critical reaches of Bear Creek.
This model has been developed by an interdisciplinary team of researchers with specialists in
forage crops, soils, hydrogeology, forest hydrology, forest ecology, wetland ecology, economics,
biometrics, wildlife management, and extension. The model can be adapted to other waterways
in Iowa and the Midwest.
The MSRBS system is a filter strip 65.62 ft (20 m) wide consisting of three vegetative zones.
The first zone consists of four to five rows of fast-growing trees planted adjacent to the stream.
The second, or central, zone consists of two rows of shrubs. The third zone, planted on the outer
edge of the riparian buffer, consists of a strip of switchgrass 22.97 ft (7 m) wide. The MSRBS
design takes advantage of the different aboveground and belowground structures of each species
to provide maximum year-round interception of sediment and agricultural chemicals from surface
runoff and subsurface water movement. One of the innovative aspects of this design is the use of
fast-growing tree species that can be used as a short-rotation woody crop system. These systems
can produce biomass for energy in 5 to 8 years and timber products in 15 to 30 years. The frequent
harvests help to maintain active nutrient and pesticide sequestering by the woody plant
community. The selected species do not have to be replanted for three to four harvests because the
species reproduce vegetatively by stump or root sprouts. The large root systems allow very rapid
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Case Studies
regrowth, which provides continuity in water and nutrient uptake and physical stability of the
soil throughout the life of the stand.
The MSRBS systems also include native shrubs, which can provide biomass if harvested and
demonstrate coppice regeneration. The shrubs increase species diversity and wildlife habitat,
provide yet another rooting pattern that will hold soil, intercept shallow groundwater nutrients,
and provide organic matter for soil microbes. Finally, the addition of native prairie grasses such as
switchgrass will provide additional species diversity, a very high frictional surface for
intercepting surface runoff, and a deep and fibrous root system that will play an important role
in improving soil quality.
Study Design
The MSRBS system lies along a 3,281-ft (1,000-m) reach of Bear Creek on a private farm
(see Figure 3-10). At this location, the creek is a third-order stream with average discharge rates
varying between 10.59 and 49.44 fts/s (0.3 and 1.4m3/s). During the past 5 years, pesticides
applied on the farm have included chlomazone, atrazine, cyanazine, and the herbicide EPTC.
During the past 12 years, impregnated urea pellets have been applied at the rate of 122.83 Ib/acre
(134 kg/hectare).
The reach of the creek under study was divided into three blocks: inside bend, outside bend,
and straight reaches. Five 295.29-ft (90-m) plots were located within each block. Treatments
consisting of three combinations of planted trees, shrubs, grass, and two controls were randomly
assigned to the plots within each block. The planted treatments consisted of five rows of trees
planted closest to and parallel to the creek with a 5.91-ft (1.8-m) spacing between rows.
Different species of trees were used in each of the three treatments. One treatment consisted of a
Shrubs
Trees \ Grass
Stream
Wetland
at end of
field tile
Willows
in
Streambank
Poplar G. Ash
Willow Oak
Silver Maple Walnut
Ninebark
Chokecherry
Osier Dogwood
2 Rows 0.9 x 1.8 m
Figure 3-10. Multi-species Riparian Buffer Strip System.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
poplar hybrid (Populus X euramericana Eugenei) that has been extensively tested and is readily
available in Iowa. The second treatment contained green ash (Fraxinus pennsylvanica), and the
third treatment contained a mixture of four rows of silver maple (Acer saccharinum) with a center
row of black walnut (Juglans ttigra). Upslope from the trees, a row of red-oiser dogwood (Cornus
stolonifera) and a row of ninebark (Physocarpus opulifolius) were planted. The shrubs were planted
with 3.94-ft (1.2-m) spacing between rows. Finally, a strip of switchgrass 23.95 ft (7.3 m) wide
(Panicum virgatum) was planted upslope from the shrubs. Controls consisted of existing pasture
grasses. Most trees are being grown on a 6- to 8-year rotation depending on species, and black
walnut is being grown on a 45- to 55-year rotation.
The plants for this MSRBS were selected to serve multiple purposes. Those purposes
included rapid growth, dense rooting habits, coppice regeneration ability for the trees and shrubs,
stiff stems for the grass, cover and food for wildlife, and a potential for being used as biomass for
energy. The desire was to develop an effective buffer in as short a time as possible to effectively
trap sediment and process chemicals and to demonstrate to landowners that a buffer strip with
woody plants could be grown rapidly.
In the study area, an existing field drain tile was providing subsurface drainage for one of
the fields and was discharging untreated water into Bear Creek. An approximately 0.12-acre
(500-m2) wetland was constructed to process field drainage tile water from a 12.11-acre
(4.9-hectare) cropped field. The wetland is 1.64 to 3.28 ft (0.5 to 1 m) deep and is surrounded by a
low berm. The bottom of the wetland was sealed with clay because of the presence of an
underlying substrate of alluvial sand. Organic soil was then placed as the top layer. The
agricultural drainage tile was excavated and rerouted to enter the wetland at the point farthest
from the creek, forcing the water to travel through the wetland before entering the creek. A gated
water level control structure at the wetland outlet provides complete control of the level
maintained within the wetland. Cattail (Tyfha glauca) rhizomes were collected from a nearby
wetland during the early spring when the shoots had just begun to elongate. The wetland was
planted in early June at a spacing of approximately 1.97 ft (0.6 m) on center. Willow cuttings
were planted on the stream side of the berm, and native grasses and forbs were planted on the
constructed berm for stabilization and to provide vegetation diversity.
Two soil bioengineering structures 262.48- to 328.1-ft (80- to 100-m)-long have been
developed as part of the MSRBS system. These structures used live staking and dead tree fascines
to stabilize severely eroding banks on the outside stream banks. In the spring of 1992 and 1993,
cuttings of dormant willow (Salix spp.) 3.28-ft (l-m)-long and 16.41- to 24.61-ft (5- to 7.5-cm) in
diameter were pounded into the creek bottom along the toe of the bank and into the stream bank.
A dead fascine system using bundles of harvested silver maple was wired together and staked into
the bank to provide protection for the cuttings. Most of the cuttings took root and grew. Record
floods occurred in the watershed in 1993, and the plantings withstood a record 500-year flood.
The resulting plant material reduces the speed of channel flow on the outside of the bend, causes
sediment to be deposited in the plant material, and stabilizes the bank against further collapse.
Results
Survival of the trees, shrubs, and switchgrass in the MSRBS has generally been very good.
Survival of the three fastest growing tree species was above 87 percent. Black walnut survival was
adversely influenced in the second year of growth because of intense grass competition. Ninebark
has grown very well, with heights of 6.56 ft (2 m) at the end of 1993. The red osier dogwood has
shown mixed growth and has been replaced in spots with nanking cherry (Pmnus tomentosa). The
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Case Studies
switchgrass is well established and has produced twice as much biomass as that of the pasture
grasses.
The MSRBS was evaluated for root biomass production, and preliminary data indicate very
high root production (Figure 3-11). This is important because plant roots increase soil stability by
mechanically reinforcing soil, and they increase the soil microbial activity that aids in the
processing of nutrients and agricultural chemicals. The mixture of trees, shrubs, and grasses
provides a dense matrix of roots throughout the soil column, providing greater stability than
single-species filter strips.
Water movement through the MSRBS reach of Bear Creek is sampled in the vadose zone (the
unsaturated zone of the soil above the water table including the rooting zone), the unconfined
shallow aquifer (located in the alluvium and glacial till), the bedrock aquifers, the drainage tiles,
and the stream channel. Various kinds of sampling equipment, including piezometers and
tensiometers, have been installed to access these different sources of water. Water samples were
analyzed for nitrate nitrogen and atrazine. The present protocol calls for monthly sample
collections between growing seasons and twice-monthly collections during the growing season.
Although early results do not accurately reflect the full remediation capability of the system
when it is mature, the preliminary results demonstrate that a developing MSRBS system can be
effective in reducing NFS pollutants. Results for nitrate nitrogen (NO3-N) and atrazirie are
shown in Figures 3-12 and 3-13. As can be seen, the NO3-N' concentrations in the MSRBS never
exceeded 2 ppm (2 mg/L) even though background levels of NO3-N exceeded 12 ppm (12 mg/L) in
the field. The buffer strip also showed adequate removal rates for atrazine. Data from
minipiezometers located at a depth of 9.84 ft (3 m) below the MSRBS confirm that these
chemicals are not moving below the buffer strip.
Preliminary data from the first 4 months of operation of the field drainage tile wetland
indicate that microbial degradation of NO3-N is taking place. Measurements are greater than 15
ppm (15 mg/L) at the inflow while measurements are less than 3 ppm (3 mg/L) at the outflow.
Under stormflow conditions when residence times are reduced, NO3-N levels are not as
effectively reduced. Based on this initial research, constructed wetland systems can be used to
protect existing natural wetlands in agricultural settings. Wetland plant species that can tolerate
excessive nutrient loading can be used in the constructed wetland to protect the more susceptible
species that occur in natural wetlands.
Visual observations of sediment movement suggest that no significant sediment has moved
through the buffer strip since the switchgrass, shrubs, and trees have become established.
Recommendations
The Iowa State University Agroforestry Research Team has developed preliminary
recommendations for Multi-Species Riparian Buffer Strips for Iowa based on their research at
Bear Creek General design recommendations include:
The general layout should consist of three zones, starting at the stream bank edge; the
first zone should include a strip of trees (four to five rows) 29.53- to 32.81-ft (9- to 10-m)
wide, the second zone should include a strip of shrubs (one to two rows) 9.84- to 13.16-ft
(3- to 4-m)-wide, and the third zone should include a strip of native warm-season grasses
22.97 to 26.25 ft (7 to 8 m) wide.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Soybeans Com Grass Swttctigrass Nlnebark Silver Maple Poplar Willow
110
7.700
330 990 2.340 15.300 5,130 9.920
Total Root Weight (kg/ha)
Schultz et al., 1995.
Figure 3-11. Root distribution of buffer strip vegetation by depth and arrangement.
19.300
15-
-12-
O b1
WITHIN FIELD
j~| FIELD BORDER
H SHRUB BORDER
TREE BORDER
if NO DATA
L *
i
I
tD
£
CN
>' a>'
CB
CM
N>
CM
DATE (1993)
Schultz etal., 1995.
Figure 3-12. Mean nitrate-nitrogen concentrations in the buffer strip.
DATE (1993)
Schultz et al.. 1995.
Figure 3-13. Mean atrazine concentrations in the buffer strip.
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Case Studies
Fast-growing trees are needed to develop a functioning MSRBS in the shortest possible
time.
Rows 1 through 3 in the tree zone should include fast-growing, riparian species such as
willow, cottonwood, silver maple, hybrid poplars, green ash, and box elder. Other
moderate-growth species include black ash, river birch, hackberry, shellbark hickory,
swamp white oak, pin oak, Ohio buckeye, and sycamore. The key to tree and shrub
species selection is to observe native species growing along existing natural riparian
zones and select the faster-growing species.
Shrubs should be included in the design to increase biodiversity and wildlife habitat.
Possible species include ninebark, red osier and gray dogwood, chokecherry, Nanking
cherry, nannyberry, sandbar willow, Bebb willow, peachleaf willow, pin cherry, wild
plum, and blackhaw.
Switchgrass is recommended because it produces a uniform cover and has dense, stiff
stems that provide a high frictional surface to intercept surface runoff. Other permanent
warm season grass, such as Indian grass, big bluestem, and little bluestem, can be included
as long as switchgrass is the dominant species.
Native perennial forbs may also be part of the mix, especially if they are seeded in clumps.
If wildlife habitat is an important component of the buffer strip, widths of 98.43 to
295.29 ft (30 to 90 m) would provide a more suitable wildlife corridor or transition zone
between the upland agricultural land and wetland/aquatic ecosystem.
Recommendations for tile wetland construction include:
A small wetland can be constructed at the end of the field tiles by constructing a basin
at the ratio of 1:100 (1 acre of wetland for 100-acre drainage). The bottom of the wetland
should be sealed with day if the soil texture is sandy.
Clay tile and perforated plastic tile used to drain fields might become plugged by tree and
shrub roots in the buffers. Two possible solutions to this problem exist: (1) replace the
tile passing through the buffer strip with solid tile or (2) plant a strip of warm season
grass above the tile line at a width of 65.62 to 98.43 ft (20 to 30 m) depending on the
woody plants that are planted.
Costs for establishment of the MSRBS system have been estimated at $358 to $396 per acre,
and annual maintenance costs are estimated at $20 per acre. The establishment and maintenance
costs do not include any existing governmental cost-share or other subsidy. Currently, there are
several cost-share programs available that will cover up to 75 percent of the expenses. A good
contact for information on potential cost-share programs is the local office of the USDA Natural
" Resources Conservation Service. Overall the MSRBS system seems to function quite well. In
addition to protecting riparian wetlands, the MSRBS system offers farmers a way to intercept
eroding soil, trap and transform NFS pollution, provide wildlife habitat, produce biomass for on-
farm use, produce high-quality hardwood in the future, and enhance the aesthetics of the
agroecosystem. As a streamside BMP, the MSRBS system complements upland BMPs and provides
many valuable benefits.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
References/Additional Information:
Schultz, R.C: 1994. Design and establishment of a multi-species riparian buffer strip. Leopold Center for
Sustainable Agriculture, Ames, IA.
Schultz, R.C. 1994. Multiple benefits from constructed multi-species riparian buffer strips. Leopold Center for
Sustainable Agriculture, Ames, IA.
Schultz, R.C., J.P. Colletti, T.M. Isenhart, W.W Simpkins, C.W Mize, and M.L Thompson. 1995. Design
and placement of a multi-species riparian buffer strip system. Agroforestry Systems Journal (29):201-226.
EPA Region 8 '
Watershed Approach to Municipal Stormwater Management, Fort Collins,
Colorado
Introduction
Fort Collins, a city of 92,000 people, is located in a quickly developing area of Colorado
known as the Front Range. The city, situated at 5,000 ft (1,524 m), has a semi-arid climate with
14 in (35.56 cm) of annual precipitation and an average of 300 days of sunshine. Due to the
pleasant climate, natural areas, and other factors, Fort Collins is experiencing significant growth.
This increase in development led the city to create a Stormwater Utility. Within the municipal
boundaries, three types of wetland communities can be found. The dominant community is
seasonally flooded riparian wetlands consisting of willow (Salix spp.), narrowleaf cottonwood
(Populus angustifolia), plains cottonwood (Populus sargentii), golden current (Ribes aurem), and
chokecherry (Prunus virginiana). The other two wetland communities are seasonally flooded
emergent marshes dominated by broad-leafed cattails (Typka latifolia) and bulrush (Serif us spp.);
and seasonally saturated wet meadows consisting of sedges (Carex spp.) and rushes Quncus spp.).
The Stormwater Utility's original mission was to create a drainage system that protects
citizens from flooding. The Utility typically manages the Stormwater system by drainage basin,
which is the land contributing Stormwater runoff to a particular point, usually a stream. The size
of a basin, anticipated rainfall amounts, and the type of land use (i.e., industrial, residential, or
natural) are factors used to calculate the need for flood control improvements. With the
implementation of the National Pollutant Discharge Elimination System (NPDES) permit
program and other programs, water quality became a critical component of Stormwater
management and required the Utility to take a new look at how drainage systems are designed
and managed.
Approach
It became apparent to the city that a drainage system designed to convey flood waters can
be planned to meet objectives other than the control of water quantity. For example, drainage
systems are typically along riparian wetland corridors, which provide a multitude of functions
and values such as wildlife habitat and recreation. Consequently, it became critical to look at the
protection and enhancement of these important wetland areas. The city revised the mission
statement for the Stormwater Utility to state the "purpose for the utility is to provide Stormwater
facilities for the drainage and control of surface and floodwaters in order that... pollution may
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be reduced and the environment should be protected and enhanced." Based on this new mandate,
the city developed primary and secondary objectives for the Stormwater Utility.
Primary stormwater objectives include:
Protect Fort Collins from flood waters.
Protect and enhance water quality in creeks, lakes, and wetlands.
Protect and restore creeks, lakes, and wetlands as critical wildlife habitat areas.
Protect water table aquifers from stormwater contamination.
Secondary stormwater objectives include:
Enhance a sense of community by including citizen participation in protecting local
natural areas.
Create trails to support the use of alternative transportation.
Promote recreational opportunities associated with trails and natural areas.
To accomplish these objectives, the Stormwater Utility decided to use a watershed
management approach as a holistic method to manage stormwater and drainage basins. A hplistic
approach requires looking at all factors that influence stormwater management, including those
factors not typically associated with stormwater management. For example, the Utility realized
that alternative transportation has a direct correlation to stormwater quality. A reduction in
automobile use improves air quality and reduces the amount of pollutants that can be
redistributed with precipitation. A reduction in automobile use also reduces the pollutants left on
pavement, which can enter the stormwater system through runoff. Carried to its fullest potential,
a greater reliance on alternative transportation can lead to a reduction in the amount of
impervious surface associated with roads and parking lots, thereby reducing the overall amount of
storm runoff contributed to the system.
Another example of looking at the system holistically is addressing the protection of
riparian wetland corridors along drainage systems. The riparian corridors provide important
benefits such as natural filters of storm runoff, wildlife habitat, and bank stabilization. In
addition, stormwater systems along riparian corridors can be considered as potential
greenway parks. In times when municipal budgets are limited, integrating park facilities and
stormwater systems can be an efficient way of using capital improvement resources.
A final example of how stormwater management and other issues are interrelated is
enhancing a sense of community by encouraging citizen participation in protecting local natural
areas. By raising the public's awareness of the natural areas along the stormwater system,
educational efforts to encourage people not to pollute (for example, encouraging them not to pour
chemicals down storm drains) become more effective because people realize the ultimate effects
of their actions (for example, they understand where those storm drains discharge). Furthermore,
an awareness of why BMPs are used can decrease the likelihood that they will be vandalized.
To begin applying the watershed approach, the Utility divided the urban watershed into
three primary and interactive components: land, tributaries, and receiving waters. The urban
landscape comprises industrial, commercial, and residential land uses and open space. Tributaries
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
are the minor components of the onsite stormwater system and can include features such as curbs
and gutters, as well as BMPs like grass swales and infiltration basins. The receiving waters are the
major components of the stormwater system and include streams and lakes. To organize its
watershed planning efforts, the city created four levels of service or grades that can be used to
evaluate the three primary components (Figure 3-14). These levels take into account the existing
conditions of the area as well as the restoration potential based on future better management.
This grading scheme will help staff and the City Council understand the interrelatedness of the
Figure 3-14. Conceptural master plan grades of Spring Creek.
components, make appropriate cost and benefit analysis, and prioritize projects. Methods to
objectively measure and grade sections of the stormwater system are being developed.
The "A" Service Level
A system at the "A" level is considered the ideal system. At the landscape level, introduction
of human-caused pollutants would be greatly minimized by a multitude of methods such as
natural landscaping, proper materials handling at all businesses, environmental education, and
alternative transportation. Minimization of impervious cover to reduce runoff would also be
addressed through development guidelines. The tributary system would be designed for water
quality protection and would rely on natural control and treatment methods such as buffer areas,
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grassed swales, infiltration basins, and constructed wetlands. The receiving waters would be
protected from stormwater impacts and would be maintained as diverse aquatic, wetland, and
riparian habitat.
The "B" Service Level
The "B" level indicates a good system that could be improved. At the landscape level,
pollution prevention would still be practiced on public and private property. This area might
already be developed, and therefore minimization of impervious area might not be realistic. The
tributary system relies on minimal use of concrete although it is not really designed to optimize
water quality treatment; however, the tributary system could be easily retrofitted with BMPs that
improve water quality and protect wetlands. The receiving waters are experiencing habitat
degradation such as lack of shade, little riparian buffer, or poor channel habitat, resulting in a "B"
rating.
The "C" Service Level
A "C" rating indicates a degraded system whose restoration could require significant
resources. At the landscape level, only the minimum standards of environmental regulations are
being followed, but there are opportunities to implement pollution prevention measures. The
tributary system provides efficient drainage through concrete channels and pipes but does not
provide any water quality benefit and might be difficult to retrofit. The receiving waters are
usually degraded and might be channelized. Usually, there is still some aquatic and wetland
habitat component, which could be enhanced through ecological restoration.
The "D" Service Level
The "D" level indicates a severely degraded system that will be difficult to improve. At the
landscape level, poor use and handling of chemicals, such as the excessive use of lawn chemicals
and leaking automotive fluids, are common. Consequently, the most significant area of
improvement would be to reduce the pollution inputs. The tributary system is similar to that of
the "C" service level. The receiving waters are typically channelized, or the channel is
experiencing severe erosion.
The adoption of a watershed management approach to stormwater and the related grading
scheme (service levels A through D) will help staff and the City Council make cost and benefit
trade-offs as the program matures. For example, in master planning there might be little increased
cost for a specific section of a creek to be upgraded to an "A" level. In a more developed part of
town, level "B" might be cost-prohibitive. In the example scheme provided in Figure 3-14, there
are no existing or proposed "D" ratings for any watershed sections.
Decisions about the practicality of various options will be reviewed at the time a basin
master plan or drainage criteria are revised and adopted. The City Council will also have an
opportunity to evaluate the costs and benefits as specific capital improvement projects or
education/enforcement programs are approved in the annual budget process. Tangible and
intangible benefits will be considered when making these decisions. Table 3-2 provides a
conceptual cost comparison of issues associated with watershed grades A through D.
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Protecting Natural Wetlands: A Guide' to Stormwater Best Management Practices
Table 3-2. Concept Cost Comparison of issues
Associated with Watershed! Cradles
Issue
Land Costs
Construction Cost
Opens Space Provided
Development Potential
(along drainages)
Maintenance Cost
Cratle A
Highest
Lowest
Highest
Lowest
Lowest
Graae B
Intermediate
Intermediate
Intermediate
Intermediate
Intermediate
crwie e
Intermediate
Intermediate
intermediate
Intermediate
Intermediate
GratSe o
Lowest
Highest
Lowest
Highest
Highest
As
Next Steps
For the Stormwater Utility to fully implement a watershed approach, the following steps
will need to be taken:
Develop an integrated approach between the various municipal departments
(Stormwater, Natural Resources, Parks and Recreation). Clarify implementation roles
between departments and eliminate cross purposes and redundancies. The city must
realize that the drainage system can play an important role in meeting a variety of city
goals, but the city must also understand and agree on a balance between competing
objectives. Some of these are:
- Aesthetics, groomed vs. natural appearance
- Efficient Stormwater flows vs. water and habitat quality
- Regulation vs. private property rights
- Service levels vs. cost
Refine the watershed rating system and develop methods to objectively measure
and rank sections of the- Stormwater system.
Adopt individual watershed master plans where the master planning of Stormwater
facilities and natural resource areas, including wetlands, is cooperatively completed
through the use of geographic information system (GIS) technology.
Modify storm drainage design criteria to include a variety of BMPs that protect water
quality and wetlands. Include components of the Natural Areas Mitigation Manual in the
City's storm drainage design criteria.
Formalize Stormwater education efforts and integrate them with other existing
municipal and county environmental education programs.
The Stormwater Utility is just beginning to create the framework for an integrated
watershed approach to Stormwater management. At the municipal level, a successful watershed
approach relies on communication and coordination between all departments to provide for a
cohesive program. It also requires close communication and input from the local citizens. By
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preventing pollution on the land, addressing the ecological effects of providing drainage services,
and preparing sound hydrologic analysis, objectives related to water quality, public safety, and
natural area protection can all be achieved.
References/Additional Information:
McBride, K. 1995. Stormwater quality: A watershed approach. City of Fort Collins, Colorado.
Lemna Nonpoint Source Treatment System, Chatfield Reservoir, Colorado
Chatfield Reservoir, located 15 mi (24 km) southwest of Denver, Colorado, impounds water
from the South Platte River drainage, a 2,969 mi2 (7,719.4 km2) watershed. The reservoir is a
flood control structure built and operated by the U.S. Army Corps of Engineers, and it has become
an important recreational facility for the metropolitan region. The developed lower portion of
this watershed system is the Plum Creek subwatershed, which is a 438-mi2 (1,338.8-km2) drainage
area in Douglas County. Plum Creek and Chatfield Reservoir in the Plum Creek subwatershed are
identified in the Denver Regional Council of Governments' (DRCOG) regional Clean Water Plan
as being affected by nonpoint source (NPS) pollution, primarily high phosphorus loading.
The magnitude of the problem is reflected by the total pounds of phosphorus that reach the
reservoir each year. The phosphorus loading of the reservoir is about 53,100 pounds (Ib)
(24,086 kg) per year from developed land and about 50,513 Ibs (22,912.67 kg) per year from
undeveloped land. The total maximum allowable load that will not exceed the in-reservoir
standard is 59,000 Ib (26,762.4 kg). Under normal conditions, about 48,300 Ib (21,908.88 kg) of
nonpoint-source-derived total phosphorus will need to be removed from the watershed.
In addition to degrading water quality, the high phosphorus loads are negatively impacting
the fringe wetlands associated with the reservoir and the riparian wetlands along Plum Creek. The
fringe wetlands are seasonally and permanently flooded lacustrine wetland communities with a
mixture of broad-leafed cattails (Typha latifolia), hard-stem bulrushes, (Serif us acutus), sedges
(Carex spp.), and rushes (Juncus spp.). The riparian wetlands are seasonally flooded palustrine
wetland communities with cottonwoods (Populus sargentif), sandbar willows (Salix exigua), and
chokecherries (Primus virginiana). Excessive phosphorus loads are allowing pollution-tolerant and
invasive species to take over and decrease plant biodiversity. Eutrophication of the reservoir is
promoting algal blooms, which are shading out submergent wetland species.
The Chatfield Basin Authority management program has identified many potentially usable
BMPs that could reduce phosphorus loading and offer ancillary benefits such as protection of
existing natural wetlands. The problem facing the Authority is predicting the effectiveness of
these BMPs. The Authority wants highly effective, low-cost, and easily maintained BMPs for the
watershed nonpoint source control program. The placement of small BMP structures at every site
of urban development that generates nonpoint source pollution appears to be a very costly
option. Therefore, a pilot project was selected to evaluate the effectiveness of a low-cost,
biologically based system.
Lemna System
A private corporation has developed a natural biological treatment process that uses aquatic
plants (duckweed) to assimilate nutrients and reduce pollutants in a pond environment.
Duckweed (Lemna sp.) is a small floating plant commonly found in many lakes, ponds, and slow-
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
moving streams. It consists of one or more leaves (called fronds) but has no visible stem. Over 35
species of duckweed grow worldwide in a variety of climates. Duckweed is an extremely fast-
growing plant that reproduces primarily by vegetative processes. The biomass can double in less
than 18 hours under optimal conditions. In Colorado conditions, the biomass is anticipated to
double in about 72 hours. Seasonal changes in weather and sunlight affect pond temperature and
thus the growth of duckweed. Optimum growth is achieved at 68 °F (20 °C) to 86 °F (30 °C).
Lemna is semi-tolerant of cold temperatures and will continue to grow slowly at temperatures
near 44 °F (7 °C). Nitrogen, phosphorus, and trace metals are needed to support the growth of
duckweed, with optimum growth possible when there is a balance of available nutrients. Low
levels of either nitrogen or phosphorus result in starved plants.
The use of Lemna has proven effective as a wastewater treatment nutrient removal system,
with the added benefit of reducing metals, biological oxygen demand, and total suspended solids
along with its constituents. The resultant effluents have low phosphorus concentrations (below
1 ppm (mg/L)). The by-product of the Lemna process is plant tissue, which has been used as a food
supplement for feedlots and as a compost product. The Chatfield Basin Authority has
implemented a pilot system usmgLemna to determine the system's effectiveness in removing
nutrients from Plum Creek before it enters Chatfield Reservoir. The pilot system is under
evaluation for 1 year to assess water quality benefits; it will then be monitored longer to assess
the effectiveness under various hydrologic loading conditions naturally encountered in the Plum
Creek subwatershed.
The main pollutant removal pathways are a combination of plant mat uptake and
precipitation. Management of the duckweed system for phosphorus removal maximizes growth
of the plant mat. The primary method for maximizing growth is mat density management. Mat
density management uses harvesting of the biomass to optimize the uptake of phosphorus. A
young duckweed plant population tends to have higher phosphorus uptake rates and grows faster
than an older plant population. Additionally, the water column can contain sufficient
concentrations of ions, which promote precipitation of insoluble salts. Some of the phosphorus,
for example, will precipitate and settle as calcium phosphates. The duckweed also reduces algae
growth by not allowing light into the water. Algae can contribute to increased total suspended
solids within the water and subsequent effluent discharge.
The treatment system consists of three primary components:
A patented floating-cell system that can be adapted to a wide variety of pond
configurations. This allows the system to be adapted to existing pond structures (e.g.,
gravel operation ponds). The floating cells are designed to contain and control locally
available Lemna plants.
An on-shore control unit and automatic sensing probes provide nutrient circulation and
assess chemical balance within the pond structure.
An aquatic harvester is used to inoculate, distribute, and hatvestLemna plants from the
pond surface. A single harvester can be used on many ponds to improve the cost
effectiveness of the system.
The advantages of the Lemna system over other more conventional biologically based
BMPs include:
Marginal, poor-quality lands can be selected for a site.
The system can be designed to accommodate the available site.
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The system hardware is simple and durable, which reduces future maintenance costs.
The by-product can be used as a high-protein food supplement for feedlots.
. The by-product can be composted and land-applied for beneficial reuse.
The disadvantages of the Lemna system over other more conventional biologically based
BMPs include:
An energy source is required for the various pieces of hardware, including the pump and
aquatic harvester.
Personnel are required to maintain and operate the system.
Pilot Scale Description
The Chatfield pilot system is located off-channel of Plum Creek with protective banks to
keep the system from being impacted by floods. The system is designed as a S-shaped pond or
lagoon. The final pond is about 45 ft (13.72 m) wide and 600 ft (182.88 m) long, with an average
depth of 5 ft (1.52 m) and maximum surface acreage of 6.2 acres (2.5 hectares) (Figure 3-15). A
small stilling basin was created near the outflow by placing a sandbag barrier across the pond with
a flow-through pipe and float release valve. Discharge into the system and outflow from the
system pass through similarly designed concrete boxes. These boxes have built-in flow weirs for
measuring flow.
Lemna System Site Plan
Barrier Wall
Stilling
Basin
Anchor and
Cable System
Outflow
Pond Bottom
Waterline
Influent Structure
Barrier Grid
System
DRCOG, 1994.
Figure 3-15. Lemna nonpoint source treatment system.
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The pond system is lined with a 20-mil PVC liner. A set of barriers was installed as shown in
Figure 3-15. This barrier system was anchored to the sides of the pond with a cable system and
was designed to keep the duckweed plants evenly distributed across the pond's surface. A
diversion structure was installed in Plum Creek. The system inflow sump tank and the return
outflow line were installed immediately above and below the diversion structure, thereby
preventing any drying of the stream as a result of this diversion. A small pump with a timer lifts
the water from the sump tank to the pond. Return flow relies on gravity, and the water is
discharged directly into Plum Creek below the point of diversion.
The final cost for the pilot project was $210,510, which was $42,510 more than the original
estimate for the project. The Chatfield Basin Authority anticipates spending an additional $7,500
over the next year to complete its evaluation of the system as a BMP.
Operation and Results
Inoculation with native duckweed is the primary operation necessaiy for successful start-up
of the system. Sources of duckweed included backwaters of streams and small ponds near
Chatfield Reservoir. The Chatfield system start-up in April 1994 did not produce the desired plant
densities, and additional plant material was collected and added to the system in April and May
1994. It appears that a low-nutrient duckweed system is much harder to inoculate and will require
a longer start-up period. Consequently, additional duckweed plants were added to the system and
undesirable algae were harvested.
Low or unbalanced concentrations of nitrogen or phosphorus can limit growth of
duckweed. Typically, this is not a problem for duckweed systems that rely on wastewater but
seems to be a problem with NPS pollution systems. Plum Creek was experiencing unusually low
nitrogen loading rates during the start-up period, which was resulting in poor duckweed growth.
Nitrogen was applied by spraying fertilizer onto the duckweed mat to compensate for nitrogen
deficiency.
Hand harvesting was used on the pilot system, although large systems usually use a
mechanical harvester. An investigation was made of local markets and disposal options. The plant
tissue is not classified as a biosolid, and the Chatfield Basin Authority has identified no apparent
disposal problems. The biomass can be composted onsite by mixing it with a carbon supplement
such as sawdust or wood chips.
Flow rates through the pilot duckweed system were designed at 23 days. The low stream
flows in Plum Creek and low nutrient loads required changes to the flow rate through the system.
The flow rate was shifted to a 10-day retention time. Based on a 10- day retention time and a
typical growing season extending from April to November, the duckweed system can process
about 24 pond volumes per year. Monitoring data at the end of the first growing season suggest
that the flow rate could be reduced to 5 days. Flow rate evaluation studies will be done by the
Chatfield Basin Authority during the 1994-1995 monitoring program.
The preliminary data from the 1994 growing season monitoring program show that the
system is reducing total phosphorus on the average of 71 percent per pond volume with an average
influent concentration of 0.1 ppm (0.1 mg/L) and a discharge concentration of 0.02 ppm (0.02
mg/L). The range of total phosphorus removal varied from 50 to 98 percent as shown in Figure
3-16. The preliminary water quality data suggest that a duckweed system used as a BMP could
achieve consistent 50 percent removal of nonpoint source phosphorus as required in the Chatfield
Basin Control Regulation.
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Percent Total Phosphorus Reduction
100-
July 12-20 July 21-27 July28-Aug2 Aug3-11 Aug 12-26 Aug27-Sept1
Summer Growing Season
DRCOG, 1994.
Figure 3-16. Range of total phosphorus removed by the Lemna system.
Conclusion
Although results of this project are preliminary, it appears that a scaled-up Lemna system
could function as a regional water quality enhancement and wetland protection system by
processing stream flows directly from Plum Creek or the South Platte River. The next steps the
Chatfield Basin Authority will take with the Lemna project include detailed water and biological
quality monitoring, cost-effectiveness evaluation of the system, a study ,of harvest material
disposal options, other research applications, and implementation of a full-scale nonpoint source
management system. When completed, the study will be submitted to the Urban and
Construction Subcommittee of the Colorado Nonpoint Source Task Force for consideration as a
Colorado Best Management Practice.
References/Additional Information:
DRCOG. 1994. Lemna nonpoint source treatment system: Final report and operation and maintenance manual.
Denver Regional Council of Governments, Denver, CO.
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EPA Region 9
Lincoln-Alvarado Project, Union City, California
A piece of property in Union City, California, consisting of 69 acres (28 hectares) of upland
habitat and approximately 12 acres (4.8 hectares) of wetland habitat, was proposed for a
multiphase warehouse/distribution complex. A section 404 permit was required from the Corps of
Engineers, San Francisco District, because 12.5 acres (5 hectares) fell within section 404
jurisdiction. The landowners proposed that 9 acres (3.6 hectares) would be developed and the
remaining 3 acres (1.2 hectares) would be incorporated into a 5-acre (2-hectare) onsite mitigation
area consisting of one-third marsh, one-third seasonal wetland, and one-third upland. After
extensive review by the Corps and other federal agencies and negotiation with the applicant, the
project was approved with the following requirements that included pretreatment of runoff: (1)
rainwater flow from the roofs of major buildings would be directed to grease/sediment traps and
then to wetlands, (2) 12 acres (4.8 hectares) of jurisdictional wetland would be preserved, (3) a
1.18-acre (0.47-hectare) buffer would be established, and (4) funding for the permanent
maintenance would be provided by assessments on a "benefits district" of all properties in the
subdivision (Association of Bay Area Governments, 1991).
References/Additional Information:
Association of Bay Governments. 1991. San Francisco Estuary Project. Status and trends report on wetlands and
related habitats in the San Francisco Bay Estuary. Third draft. Prepared under cooperative agreement with U.S.
Environmental Protection Agency. Agreement No. 815406-01-0. Association of Bay Area Governments,
Oakland, CA.
EPA Region 10
Riparian Area Wetland Restoration Project, Sawmill Creek, Idaho
Sawmill Creek is located in the Bureau of Land Management's (BLM) Big Butte Resource
Area, 37 mi (59.2 km) northwest of Howe, Idaho. Sawmill Creek resides within a 200,000-acre
(81,000-hectare) watershed that drains a high-elevation (6,400 ft (1,950 m)) desert valley
surrounded by mountains. Soils are derived from alluvial deposits consisting of limestone and
volcanic debris. The climate is semiarid, with hot summers and cold winters. Annual precipitation
averages 100 to 114 in (254 to 289.56 cm); 66 percent occurs as snow. Cattle grazing is the
primary land use activity along the creek, and fishing and camping activities are steadily
increasing.
Prior to 1986, the combined effects of flooding, wildfires, channelization, and fall grazing
had degraded the riparian area along Sawmill Creek, causing bank instability, lateral degradation
of the stream channel, and reduced fish habitat. In response, the BLM and the Idaho Department
of Fish and Game (IDFG) initiated the Sawmill Creek Project to restore the riparian zone and
improve channel morphology. Specific project objectives included (1) improved growth, vigor,
and regeneration of the riparian zone; (2) increased bank stability; (3) increased fish populations;
and (4) improved channel morphology.
Pretreatment surveys conducted by the BLM and the IDFG enabled these agencies to
identify critical areas and develop a riparian restoration plan. Approximately 8 mi (12.8 km) of
Sawmill Creek were treated by implementing the following BMPs.
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Installation of 8 mi (12.8 km) of fencing along the creek, creating an upstream and a
downstream riparian pasture. The upper 5 mi (8 km) of riparian pasture has been fenced-
off and allotted for spring grazing only, while the lower 3 mi (4.8 km) has been excluded
from grazing for up to 15 years. The previous grazing plan allowed season-long grazing
throughout the riparian zone.
Establishment of upland troughs for off-site livestock water. Planting of willow and
cottonwood cuttings in the lower half of the riparian pasture.
Photodocumentation was effectively used to monitor habitat improvement in the
treatment area. Project monitoring and evaluation included (1) established photo points, (2)
reconnaissance inventories every 3 years, (3) a willow survivability inventory, (4) infrared aerial
photographs of the site to be repeated every 10 years, and (5) water quality sampling. The BMP
implementation resulted in increased bank stability in both riparian pastures and expanded
natural riparian vegetation, especially onto gravel bars. However, survival of willow and
cottonwood plantings has been poor. Beavers have moved back into the area, and fish habitat
appears to have improved. Posttreatment response has been slower on the lower pasture
(compared to the upstream pasture) due to greater channel instability and pretreatment
degradation.
Funding for the restoration came from mitigation money from the Little Lost River
Diversion Project supplied by the BLM, USDA Soil Conservation Service, and Butte Soil and
Water Conservation District. Total project costs amounted to $90,000.
References/Additional Information:
Connin, S. 1991. Characteristics of successful riparian restoration projects in the Pacific Northwest. EPA 910/9-91-
033. U.S. Environmental Protection Agency, Region 10, Seattle, WA.
Sublet* Creek Restoration Project, Idaho
Sublett Creek is located within the Burley Ranger District on the Sublett Cattle
Allotment in Sawtooth National Forest, approximately 55 mi (88 km) southwest of Burley, Idaho.
The Sublett drainage encompasses approximately 917 acres (371 hectares) of high desert habitat
and is intercepted at its base by an irrigation reservoir. Local topography consists of moderately
dissected mountains; soils are derived from limestone. The local climate is frigid with 17 in (43.18
cm) of precipitation annually; 80 percent occurs as snow. Sublett Creek drains U.S. Forest Service
(USFS) land except for the lower half mile (0.8 km) above Sublett Reservoir, which is on private
land. Because Sublett Creek maintains a popular cold-water fishery, recreational use is heavy.
By 1979, impacts from cattle and camping along Sublett Creek had changed the natural
composition of streamside vegetation from desirable riparian species to Kentucky bluegrass,
^thistle, and other undesirable weeds. The creek had widened, becoming more shallow. Willows
were absent along several sections of the creek. Stream bank stability had decreased, increasing
instream sediment loads and reducing gravel beds available for spawning trout. In addition, cattle
were dying (from bloating) after grazing on watercress growing along Sublett Creek. In response
to these disturbances, the USFS and the Idaho Department of Fish and Game (IDFG) surveyed the
stream to inventory fish habitat and developed measures to protect and restore the riparian zone;
the USFS conducted a riparian habitat survey. Both surveys indicated that the drainage had been
severely damaged. To protect and enhance the creek, the USFS initiated the Sublett Creek
Restoration Project. Specific project objectives included (1) reducing cattle losses, (2) reducing
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the impact on canyon bottoms and riparian areas from cattle grazing, (3) stabilizing the stream
channel, (4) reducing siltation, and (5) improving fish habitat.
A new grazing allotment management plan (AMP) was developed in 1983 in conjunction
with the grazing permittee. The old allotment plan consisted of a rest rotation system in which
cattle were allowed to remain in a unit season long. The new AMP consists of a modified four-
unit rest rotation system with a 5-year rotation. Each of the units is rested 1 year out of 5 except
along the north fork of Sublett Creek, which is rested 2 years out of 5. Grazing on this section is
now permitted only in the spring. Other BMPs included, (1) establishment of stream bank
protection structures along unstable portions of the creek (willows were planted, but survival has
been poor), (2) construction of several drift fences, (3) installation of log dams to create
downstream pools, (4) installation of two cattle troughs on upland sites, and (5) improvement of
permittee herding and salting practices.
Posttreatment monitoring (since 1987) by the Sawtooth National Forest Riparian Team
includes (1) sampling to obtain cross section measurements, (2) green line measurement, and
(3) measurement of woody-species regeneration within the watershed. Photo points were
established prior to treatment and have been monitored since.
»
Since implementation of the new AMP, water quality and habitat in Sublett Creek have
improved and the area also looks better. Posttreatment improvements include (1) improved
quality and quantity of spawning gravel, (2) increased stream bank stability, (3) increased
productivity of riparian meadows and forage, (4) improved flow duration, (5) narrower and
deeper stream channels, and (6) decreased cattle losses. Monitoring from 1987 to 1990 indicates
that improvements are not continuous throughout all portions of the creek (Chard, 1991).
Drought conditions over the past 5 years might have contributed to the slow recovery on portions
of Sublett Creek during the last few years.
Funding for the project was provided by the USFS and the Sublett Cattle Allotment Grazing
Association. Project costs were split equally between these organizations; total costs amounted to
approximately $70,000, $10,000 of which was invested in the riparian zone.
References/Additional Information:
Chard, Jim. U.S. Forest Service, Burley, ID. Personal communication. July 1991.
Connin, S. 1991. Characteristics of successful riparian restoration projects in the Pacific Northwest. EPA 910/9-91-
033. U.S. Environmental Protection Agency, Region 10, Seattle, WA.
Bear Creek Restoration Project, Crook County, Oregon
The Bear Creek watershed is located southeast of Prineville, Oregon, in Crook County. The
watershed drains to the west from its origin in the Maury Mountains in the Ochoco National
Forest. The Bear Creek watershed drains approximately 55,500 acres (22,478 hectares) of
rangeland habitat; elevations range from 3,400 to 5,532 ft (1,036 to 1,686 m). Local topography
consists of rolling hills and valleys intersected by steep basaltic ridges and Incised drainages. Soils
are derived from Columbia River basalt and volcanic ash. The climate is semiarid with 12 in
(30.48 cm) of precipitation annually; 40 to 60 percent occurs as snow. Approximately 75 percent
of the watershed occupies public lands managed by the BLM, and the remaining 25 percent is
owned by cattle ranchers. The primary land use activity is cattle grazing.
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Case Studies
Since the 1860s intensive cattle grazing in the Bear Creek watershed had degraded riparian
areas along Bear Creek, reducing woody riparian species, lowering the water table, destabilizing
stream banks, and increasing instream sedimentation. Fire suppressions upland sites, coupled
with lowered water table levels permitted juniper to invade the watershed and replace native
herbaceous species, resulting in large areas of bare, erosive ground and reducing available forage.
Subsequent to these changes, heavy flooding and overland storm flow within the watershed
accelerated erosion and resulted in heavy sediment deposition in Prineville Reservoir and the
Crooked River. To control and reduce these impacts, the BLM initiated the Bear Creek
Restoration Project. Project objectives included (1) reducing juniper populations and replacing
them with herbaceous species, (2) increasing infiltration of precipitation into the soil, (3)
stabilizing stream banks, and (4) increasing native riparian vegetation and raising the stream-
bottom.
The Bear Creek Project involved 55,490 acres (22,473 hectares), of which 41,260 acres
(16,710 hectares) were administered by the BLM and funded from 1972 to 1978. Juniper trees
were cut on upland sites (approximately 14,000 acres (5,670 hectares)). Then prescribed burns
were used to inhibit further juniper invasion and to aid establishment of herbaceous species.
Thirty mi (48 km) of pasture and enclosure fencing was installed on both upland and riparian
sites, enclosing approximately 2.25 mi (3.6 km) of riparian area. In addition, 16 mi (25.6 km) of
juniper riprap was placed along banks on Bear Creek and several of its tributaries, sediment
catchment dams were installed in the creek to raise the creek bottom, springs were developed on
upland sites for livestock watering, and a new allotment management plan (AMP) was developed
to reduce the impacts of grazing on riparian areas. The old plan allowed season-long grazing on a
rest rotation basis. Under the new plan, allotments were divided into a greater number of
pastures and a deferred grazing system (20-day rotation period) was used. Grazing permittees and
local landowners constructed the pasture fencing and also installed some riprap.
Monitoring activities included (1) photo points on riparian and upland sites, (2) soil surface
factor transects to rate erosive potential, (3) macroinvertebrate analysis, (4) cross section stream
channel measurement, (5) riparian habitat inventories, (6) stream channel evaluation, and
(7) water quality sampling.
Project successes resulted from the watershed approach adopted by the BLM to reduce
sedimentation and restore the health of the entire drainage. Upland juniper populations have
been effectively reduced, and herbaceous species are more prevalent. As a result, less bare ground
now exists, erosion rates have declined, and water absorption has improved, as evidenced by the
appearance of new springs. Seventeen mi (27.2 km) of stream now support vigorous riparian
growth, bank erosion has declined, and sediment deposition behind the catchments has
controlled stream incision by elevating the stream bottom. The new AMP has provided sufficient
protection of the riparian areas to allow their regrowth. In addition, forage productivity has
increased from 70 to 340 animal unit months (AUMs). An AUM is defined as the amount of
forage required to maintain a mature 1,000-lb (453.6-kg) cow or the equivalent for a 1-month
period (USEPA, 1993).
The BLM funded the project with $650,000. Additional costs were borne by private
landowners and livestock grazers in the watershed.
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References/Additional Information:
Connin, S. 1991. Characteristics of successful riparian restoration projects in the Pacific Northwest. EPA 910/9-91-
033. U.S. Environmental Protection Agency, Region 10, Seattle, WA.
USEPA, 1993. Guidance specifying management measures for sources of nonpoint pollution in coastal waters.. EPA
840-D-92-002. U.S. Environmental Protection Agency, Office of Water, Washington, DC.
Camp Creek Restoration, Crook County, Oregon
Camp Creek is located 40 mi (64 km) southeast of Prineville in Crook County, Oregon. It
originates in the Maury Mountains of the Ochoco National Forest and drains to the east. The
Camp Creek watershed drains approximately 110,710 acres (44,838 hectares) of rangeland
consisting of sagebrush, juniper, and bunchgrass. This also includes coniferous forest habitat with
elevations ranging between 3,665 and 6,121 ft (111 and 1865 m). The drainage basin consists of
fluvial valleys surrounded by more resistant basalt buttes and hills. Soils consist of highly erodible
bentonitic and montmorillanitic clays. The climate is semiarid with 12 to 14 in (30.48 to 35.56
cm) of precipitation annually; 20 percent occurs as snow. Approximately 59,000 acres
(23,895 hectares) of the watershed are public land, and the remainder is held by private
landowners. Land use within the basin includes livestock and hay production.
Overgrazing, mismanagement of livestock, fire control, and intensive road/logging
development since the late 1800s have accelerated stream bank and upland erosion, channel
incision, dendritic gully spread, and riparian degradation, resulting in a drop in the local water
table. As a result, sagebrush and juniper have since invaded the area, replacing native grasses and
reducing available forage. In response to these disturbances, the BLM initiated the Camp Creek
Restoration Project in 1965. Project objectives included (1) stabilizing the steam channel and the
raising the water table on 31.6 river miles (50.844 km) and 383 acres (155 hectares) of riparian
habitat, (2) improving stream water quality and reducing sediment discharge, (3) restoring the
Camp Creek channel to 60 percent of its potential condition, and (4) increasing the forage
resource base for wildlife and livestock.
In 1964, the BLM developed an initial Camp Creek watershed plan. Plan implementation
included the following: (1) several detention dams were constructed, (2) 2.7 mi (4.34 km) of
Camp Creek were fenced off, (3) 1,000 Russian olive seedlings and willow cuttings were planted
along the upper portion of the creek, (4) severely disturbed areas were reseeded with tall
wheatgrass and sweetclover, (5) stream banks were riprapped with juniper trees, (6) juniper and
sagebrush were removed from several upland sites by cutting, chaining, and burning, and (7) low-
rock structures and gabions were installed in the creek to trap sediment and raise the water table.
In 1978 an intensive water quality and macroinvertebrate sampling survey was initiated.
Following continued watershed surveys, a revised watershed plan was drafted in 1985, which
initiated a new rest-rotation grazing plan. (Prior to this, grazing was year-round on open range.)
Private landowners have also removed juniper and placed riprap along the creek on their property.
Monitoring of the Camp Creek restoration project included (1) establishment of permanent
photo points on riparian and upland sites; (2) stream channel studies initiated in 1978 which
included water quality and macroinvertebrate surveys; (3) permanent range condition transects;
(4) upland erosion study plots; and (5) an intensive riparian zone hydrology study, which was
initiated in 1985.
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Case Studies
Success of the riparian restoration varied. Two to eight ft (0.51 to 2.44 m) of sediment was
deposited behind instream structures. One livestock crossing effectively acted as a check dam.
Beaver activity increased sediment deposition. Collectively, these treatments have elevated the
stream bottom and raised the water table within the floodplain. Juniper removal and prescribed
burning enabled grasses to reestablish on upland sites, increasing available forage and augmenting
infiltration of precipitation into the soil. Juniper riprapping stabilized stream banks and
increased sediment deposition, allowing reestablishment of riparian plant species. Gabions were
damaged by heavy flooding, however, a year after installation, and Russian olive and willow
plantings were drowned out by the rising water table. Fenced enclosures have been only partially
successful in limiting access of livestock to the creek. Several grazing permittees have failed to
prevent their cattle from damaging fencing and grazing within the enclosures.
Juniper removal and reintroduction of fire into the ecosystem have been essential to the
natural reestablishment of herbaceous plant species. Posttreatment structural maintenance has
been necessary to achieve project objectives. A shift from year-round grazing to spring and late
fall grazing adjacent to the riparian zone will protect fencing from damage incurred as cattle seek
shade and water during the summer months. Greater supervision of the site by the BLM and
grazing permittees will be necessary to keep cattle out of the riparian enclosures. Periodic surveys
and monitoring have revealed unexpected changes in the riparian habitat, allowing the BLM to
adopt new BMPs in response to these changes.
Financial support was appropriated from congressional funds, the Oregon Department of
Fish and Wildlife, Oregon State University, range improvement funds returned from grazing
permits, and local landowners.
References/Additional Information:
Connin, S. 1991. Characteristics of successful riparian restoration projects in the Pacific Northwest. EPA 910/9-91-
033. U.S. Environmental Protection Agency, Region 10, Seattle, WA.
The Chewaucan River Project, Lake County, Oregon
The Chewaucan River is located in Lake County, Oregon, approximately 10 mi (16 km)
southwest of Paisley, Oregon. The Chewaucan River Watershed drains approximately 30 mi2
(78 km2) of grassland/forest habitat with an average elevation of 6,000 ft. The upper portion of
the watershed is a grassland meadow where Dairy Creek and Elder Creek join to form Chewaucan
River. Downstream, the river drains several steep-sided canyons separated by open meadows. Soils
consist of alluvial material derived from adjacent highlands. The climate is semiarid with 20 in
(50.8 cm) of precipitation annually; 50 percent occurs as snow. The river basin is used for cattle
grazing, and several instream irrigation structures are present in the upper meadow (Schrader,
1991).
Overgrazing throughout the drainage basin degraded riparian habitat and reduced stream
bank stability. The confluence of Dairy Creek and Elder Creek was very unstable and highly
eroded. Spring flooding accelerated bank erosion throughout much of the upper basin. In 1964, a
flood event deposited flow out of the main stream channel, causing bank blowouts. A new
landowner recognized these problems and enlisted the help of the SoU Conservation Service
(now the Natural Resources Conservation Service) to obtain funding and expertise to rehabilitate
the area. The two groups initiated the Chewaucan River Project. Project goals included
(1) stabilizing stream banks, (2) enhancing riparian vegetation, (3) improving fish habitat, and
(4) eliminating erosion caused by dead shags lodged in the lower portion of the river.
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In 1988, approximately 2 mi (3.2 km) of riparian area in the upper meadow, including
portions of Dairy Creek and Elder Creek, and 1 mi (1.6 km) in a downstream canyon were treated.
Best management practices (BMPs) that were implemented included (1) riprapping stream banks
with juniper; (2) riprapping the confluence of Dairy Creek and Elder Creek with stone material;
(3) placing boulders in the river to enhance fish habitat; (4) removing snags from the lower
portion of the river; (5) treating one highly disturbed stream corner with, a geotextile mat, which
was then seeded and watered; (6) fencing 0.25 mi (0.4 km) of riparian pasture in the upper
meadow; (7) planting willows throughout the basin, and 8) excluding the lower pasture from
cattle grazing for 3 years.
Project monitoring was designed to include the establishment of five photo points along the
river to be monitored annually for a period of 10 years. Willow growth is also to be monitored for
10 years.
Project results included increased sediment deposition in back eddies caused by juniper
riprap, with riparian vegetation continuing to colonize the newly deposited sediment. Stream
bank stability increased throughout the treated portions of the river. Stream banks that had
sloughed onto riprapped sections were more sloped than previously. The geotextile mat worked
very well to stabilize the adjacent stream bank; however, it probably will not be used again
because of its expense. Removal of snags in the downstream reach oriented the river back into the
main thalweg, reducing bank erosion. Willow plantings were not as successful as other
treatments. Survivorship in the upper meadow was approximately 10 percent due to beaver
cutting and 40 percent in the lower meadow (Schrader, 1991). No immediate benefits to the
fishery from habitat enhancement have been recorded (Schrader, 1991).
The Chewaucan River Project cost in excess of $50,000, which was provided primarily by
the Governor's Watershed Enhancement Board with additional help from the Oregon Department
of Fish and Wildlife, Soil Conservation Service, U.S. Forest Service, and owners of the J-Spear
Ranch.
References/Additional Information:
Connin, S. 1991. Characteristics of successful riparian restoration projects in the Pacific Northwest. EPA 910/9-91-
033. U.S. Environmental Protection Agency, Region 10. Seattle, WA.
Schrader, Bill. Soil Conservation Service, Lakeview, OR. Personal communication. July 1991.
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Best Management Practices
Section 4
Best Management
Introduction
his section describes some of the best management practices (BMPs) that might be useful
in protecting natural wetlands from the effects of stormwater runoff or useful as part of a
stormwater runoff treatment system that includes a natural wetland. The BMPs are
grouped as follows:
NonstructuralBMPs
- Pollution Prevention
- Watershed Management Plans
- Preventive Construction Techniques
- Outreach and Educational Programs
- Riparian Areas
Structural BMPs
- Infiltration Basins
- Infiltration Trenches
- Sand Filters
- Grassed Swales
-Vegetative Filter Strips
- Vegetated Natural Buffers
- Open Spaces
- Extended Detention Dry Basins
-Wet Ponds
- Constructed Wetlands
- Porous Pavement and Concrete Grid Pavement
- Oil/Grit Separators or Water Quality Inlets
Level Spreaders
- French Drains
- Dry Wells or Roof Downspout Systems
- Exfiltration Trenches
BMPs in Series
Each BMP is described in a fact sheet that includes specific information about the BMP. The
fact sheet for each nonstructural BMP includes a description of the practice and sources of
additional information. The fact sheets for the structural BMPs, unconventional BMPs, and BMPs
in series are more detailed and include a definition and purpose, the scope and applicability of the
BMP, considerations for design criteria, potential impacts to wetlands, maintenance require-
ments, and sources of additional information, as applicable.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
The fact sheets are intended to provide information about different BMPs for evaluation
purposes. With information such as where a BMP is most applicable or what the potential impacts
on wetlands might be, a planner or watershed manager can develop a stormwater management
program that is as effective in protecting a wetland-and all of its functions as it is effective in
treating stormwater runoff.
It is important to note that the fact sheets are intended to be used as a planning tool and are
not meant to be used in the design of any of the BMPs. Other sources of information, such as
those listed at the end of each fact sheet, should be consulted for design, construction, and
operation and maintenance of the BMPs. It should also be noted that the BMPs included in this
document were selected because they have the potential, in a variety of situations, for reducing
impacts from stormwater runoff to wetlands. There are other BMPs that are not addressed here,
primarily because they might offer only one or two specialized applications to wetlands.
Remember to look at the site-specific conditions and develop a stormwater management
program to protect an individual wetland based on those site-specific needs. Use the information
provided in the first section of this document to help in identifying the particular conditions that
are unique to the site and to choose one or more BMPs accordingly.
Nonstructural BMPs - Pollution Prevention
Definition/Purpose
Pollution prevention is defined as the reduction or elimination of pollutant discharges to
the air, water, or land. Pollution prevention approaches to environmental protection include:
Elimination of pollutants by substituting nonpolluting chemicals or products (e.g.,
material substitution, changes in product specification), or altering product use.
Reducing the quantity and/or toxicity of pollutants generated by production processes
through source reduction, waste minimization, and process modifications.
Recycling of waste materials (e.g., reuse, reclamation).
Pollution prevention measures are used to reduce pollutant discharges and can be imple-
mented to reduce nonpoint source pollutants generated from the following activities:
The improper storage, use, and disposal of household hazardous chemicals, including
automobile fluids, pesticides, paints, solvents, etc.
Lawn and garden activities, including the application and disposal of lawn and garden
care products and the improper disposal of leaves and yard trimmings.
Turf management on golf courses, parks, and recreational areas.
Improper operation and maintenance of onsite disposal systems.
Discharge of pollutants into storm drains, including floatables, waste oil, and litter.
Commercial activities such as parking lots, gas stations, etc.
Improper disposal of pet excrement.
Industrial wastewater disposal in septic systems.
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Best Management Practices
Scope/Applicability
Pollution prevention practices can be applied to reduce the generation of nonpoint source
pollution in all areas and for numerous activities (e.g., residential, commercial, industrial,
institutional, transportation, public and private facilities). Pollution prevention is implemented
through various educational, volunteer, and incentive programs and through federal, state, and
local policies and regulations. Pollution prevention practices include the following:
Promoting public education programs regarding proper use and disposal of household
hazardous materials and chemicals.
Establishing programs such as Amnesty Days to encourage proper disposal of household
hazardous chemicals.
Developing used oil, used antifreeze, and hazardous chemical recycling programs and site
collection centers in convenient locations.
Encouraging proper lawn management and landscaping that includes proper pesticide
and herbicide use, reduced fertilizer applications and proper application timing, limit-
ing lawn watering, xeriscaping, reduced runoff potential, and training, certification,
and licensing programs for landscaping and lawn care professionals.
Encouraging proper onsite recycling of yard trimmings.
Encouraging the use of biodegradable cleaners and other alternatives to hazardous
chemicals.
Managing pet excrement to minimize runoff into surface waters.
Using storm drain stenciling in appropriate areas.
Encouraging alternative designs and maintenance strategies for impervious parking lots.
Controlling commercial sources of NPS pollutants by promoting pollution prevention
assessments and developing NPS pollution reduction strategies and training materials
for the workplace.
Promoting water conservation.
Discouraging the use of septic system additives.
Encouraging litter control.
Promoting programs such as Adopt-a-Stream to assist in keeping waterways free of
litter and other debris.
Promoting proper operation and maintenance of onsite sewage disposal systems (OSDS)
through public education and outreach programs.
Encouraging closure of floor drains or shallow disposal wells that dkect pollutants to
groundwater.
Potential impacts to wetlands
Benefits
Reduces pollutants at their source, thereby reducing pollutant loads in stormwater and
downstream wetlands.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Because discharges are prevented, reduces the need for structural BMPs and stormwater
controls designed to remove pollutants from stormwater.
Limitations
High participation crucial to success.
Difficult to monitor results.
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Delaware Department of Natural Resources and Environmental Control. 1989. Household hazardous waste.
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Agency, Region 5, Water Division, Wetlands and Watershed Section, Watershed Management Unit, Chicago,
IL.
U.S. General Accounting Office. 1990. Water pollution: Greater EPA leadership needed to reduce nonpoint source
pollution. GAO/ RCED-91-10.
Virginia Cooperative Extension Service. 1990. Report of the Virginia Cooperative Extension Service of Virginia
Polytechnic Institute and State University on pesticides and fertilizers in the urban environment. House document
no. 14. Commonwealth of Virginia, Richmond, VA.
Virginia Department of Conservation and Recreation. 1979. Best management practices handbook: Urban.
Virginia Department of Conservation and Recreation, Division of Soil and Water Conservation, Richmond,
VA.
Voorhees, P.H. 1989. Generation and flow of used oil in the United States in 1988. Presented at Government
Institutes/NORA Conference on Used Oil: Management & Compliance, Prepared for U.S. Environmental
Protection Agency, Office of Solid Waste, Economic Analysis Staff, Washington, DC, November 28, 1989.
Washington State Department of Ecology. 1991. Water quality guide: Recommended pollution control practices for
homeowners and small farm operators. #87-30. Washington State Department of Ecology, Olympia, WA.
Whalen, J. 1989. Pest management around your home. Water quality: It's not just a drop in the bucket - You can
make difference. University of Delaware, fact Sheet NPS 6.
World Wildlife Fund, The Conservation Foundation. 1991. Getting at the source: Strategies for reducing
municipal solid waste. World Wildlife Fund, Baltimore, MD.
Young, K., and D.L Danner. March 31, 1982. Urban planning criteria for non-point source water pollution
control. Department of Civil Engineering, Catholic University.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
NonstructuralBMPs - Watershed Management Plans
Definition/Purpose
Watershed planning is a process for determining future activities within a watershed and
should be a first step in implementing an effective stormwater/wetlands management program.
Watershed planning usually involves the development of a watershed management plan that
describes existing patterns of community life in a watershedincluding demographic trends,
housing, economic activity, natural resources, and infrastructure. In addition, watershed manage-
ment plans should recommend goals and policies (including control of land use) to manage future
development that should, in turn, minimize impacts on water resources, including wetlands.
A watershed management plan is based on a series of maps of the watershed and its re-
sources. The watershed management plan also contains text that explicitly addresses conflicts and
trade-offs among development, environmental protection, social issues (such as affordable
housing), transportation, and many other factors. Special-purpose planning (including wellhead
protection, underground injection control, and wetlands management planning) is one compo-
nent of a watershed plan. A generalized watershed is shown in Figure 4-1.
Figure 4-1. A generalized watershed showing natural and anthropogenic features.
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Best Management Practices
Scope/Applicability
Watershed management plans can be developed for any geographic area and are usually
applied through the use of watershed overlay maps or a geographic information system. Most
watershed management plans are implemented at the state and local government levels.
Figures 4-2 and 4-3 indicate varieties of watershed management planning map resources.
Potential impacts to wetlands
Benefits
Allows for resource inventory, including identifying wetland resources on a watershed
scale.
Allows for information analysis, including locating individual wetlands with respect to
other wetlands, adjacent land uses, and adjacent water bodies.
Allows wetland managers to assess wetland protection needs, develop wetland protec-
tion and restoration goals, plan mitigation strategies, and determine impacts from land
use changes to wetland resources.
Serves as a modeling mechanism to be used for testing various land use/stormwater
control scenarios within the watershed to determine options to best preserve overall
wetland function or improve the health of a degraded wetland system.
LARGE WATERSHED
SMALL WATERSHED
SITE
Adapted from MWCOG, 1993.
Figure 4-2. Watersheds nest within each other. The site indicated lies within both a small watershed
and larger watershed.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
LIMITS OF THE
BUFFER OVERLAY ZONE
STREAM VALLEY
CORRIDOR
LIMITS OF THE
WATERSHED CATCHMENT
R-3, C-1. R-1
INDICATE EXISTING
ZONING CLASSIFICATIONS
Adapted from MWCOG, 1993. *
Figure 4-3. Overlay zoning adds another measure of protection to critical resources.
Limitations
Watershed boundaries frequently overlap political boundaries.
Sources of Additional information
Aldrich, J.A., K.A. Cave, J.E. Swanson, and J.P. Hartigan. 1988. Stormwater master planning in urban coastal
areas: The Virginia Beach master plan. In Proceedings of the Symposium on Coastal Water Resources, American
Water Resources Association.
Alexandria Department of Transportation and Environmental Services. 1992. Alexandria supplement to the
Northern Virginia BMP handbook. Alexandria Department of Transportation and Environmental Services,
Alexandria, VA.
Coffey, S., W Berryhill, M. Smolen, and D. Miller. 1989. Watershed screening for nonpoint source impacts and
controls. Document No. 87-EXCA-3-8030. North Carolina State University and U.S. Environmental Protec-
tion Agency.
Franklin County, Florida. 1987. Chapter 28-22.100, 22.201, Land planning regulations for the Appalachicola
Bay Area Critical State Concern. Franklin County Administration Commission, Appalachicola, FL
Howard-Strobel, M.M., T.G. Simpson, and T.P. Dillingham. 1987. The Narrow River special area management
plan. Rhode Island Coastal Resources Management Council.
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Best Management Practices
Livingston, E.H. 1989. Florida nonpoint source Management flan. Vol. II. Nonpoint Source Pollution Management
Programs. Florida Department of Environmental Regulation. Chapter 8.
Marsalek, J., and H.Y.F. Ng. 1989. Evaluation of pollution loadings from urban nonpoint sources: Methodol-
ogy and applications. Journal of the Great Lakes Reservoir 15(3).
Martin, S.R. 1988. An urban stormwater retrofit assessment and planning method. In Symposium on Coastal
Water Resources, American Water Resources Association.
Metropolitan Washington Council of Governments, Washington Metropolitan Water Resources Planning
Board. 1983. Urban runoff in the Washington metropolitan area; Final report. Washington D.C. Urban Runoff
Project, EPA Nationwide Urban Runoff Program. Metropolitan Washington Council of Governments,
Washington, DC.
Myers, J.C. 1988. Governance of nonpoint source inputs to Narragansett Bay: A plan for coordinated action. The
Narragansett Bay Project, Rhode Island Department of Environmental Management and U.S. Environmental
Protection Agency, Providence, RI.
New York-New Jersey Harbor Estuaries Program. 1989. Nonpoint source pollution action plan.
Northern Virginia Planning District Commission. 1990. Evaluation of regional BMPs in the Occoauan Watershed.
Northern Virginia Planning District Commission. Annandale, VA.
Oregon Land Conservation and Development Commission. 1989. Chapter 660, Oregon Administrative Rules.
Puget Sound Water Quality Authority. 1989. Managing nonpoint pollution: An action plan handbook for Puget
Sound watersheds. Puget Sound Water Quality Authority.
Schueler, T.R., J. Gaffi, L Herson, P. Kumble, and D, Shepp. 1991. Developing effective BMP systems for urban
watersheds. Anacostia Watershed Restoration Team. Metropolitan Washington Council of Governments,
Washington, DC.
South Florida Water Management District. April 1989. Surface water improvement and management (SWIM)
plan for Biscayne Bay. South Florida Water Management District, West Palm Beach, FL
South Florida Water Management District. 1989. Technical document in support of chapter 40E-64, works of the
district within the Lake Okeechobee Basin.
USEPA. 1990. The lake and reservoir restoration guidance manual. 2nd ed. EPA-440/4-90-006.
USEPA. 1991. Nonpoints Source Watershed Workshop: Seminar Publication. EPA/625/4-91/027. Prepared by
Eastern Research Group for the U.S. Environmental Protection Agency, Office of Research and Development,
Center for Environmental Research Information, Cincinnati, OH.
Wisconsin Department of Natural Resources and Wisconsin Department of Agriculture, Trade, and Consumer
Protection. 1990. A nonpoint source control plan for the Milwaukee River South Priority Watershed Project.
Document no. WR-24590. Ozaukee County Land Conservation District and the Milwaukee River South
Advisory Subcommittee.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
NonstructwalBMPs - Preventive Construction Techniques
Definition/Purpose
Preventive construction techniques are practices applied to construction sites to control
pollution at the source. Pollution source controls are implemented through good management and
housekeeping techniques designed to minimize nonpoint source pollution from the sites. Typi-
cally, preventive construction techniques are developed to control runoff volumes and sediment,
but they can also be designed to control other NPS pollutants such as nutrients, oil and grease, and
pesticides.
An overall management plan for the control of nonpoint source pollution on a construction
site that addresses specific control measures to be implemented in an effective manner can be
applied as a preventive construction technique. The construction site pollution control plan
should address specific categories including erosion and sediment controls, equipment mainte-
nance and repairs, waste collection and disposal, storm sewer inlet protection, dust controls,
storage of construction materials, washing areas, demolition areas, sanitary facilities, and pest
controls. Some management and housekeeping techniques applied to these categories should
include the development and implementation of an effective erosion and sediment control plan;
the proper location of activities that can act as a source of pollutants to wetlands, streams, or
Stormwater conveyance systems in areas that are not subject to surface water runoff; the place-
ment of filtering devices to protect conveyance systems from settleable pollutants during
construction; the proper use and storage of chemicals; proper collection and disposal of wastes on
a site with adequate and properly located receptacles; and the maintenance of a site in a neat and
orderly condition.
Preventive construction techniques are used to minimize the contamination of Stormwater
on a site by reducing the availability of construction-related pollutants that might contaminate
runoff. Where the contamination of runoff water cannot be avoided, pollutants and polluted
water are controlled on site.
Scope/Applicability
Preventive construction techniques can be applied to all construction projects. The plan-
ning and management techniques applied to a location should be adapted to the site- specific
characteristics of a project. The
degree of planning and manage-
ment necessary to prevent or
minimize nonpoint source
pollution on a site will depend,
primarily, on the size and com-
plexity of the project.
See Figure 4-4.
Figure 4-4. Preventive construction
techniques.
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Best Management Practices
Design Criteria Considerations
Develop an overall plan for the control of nonpoint source pollution that addresses
specific measures that can be described and implemented in an effective manner.
Develop a plan that is specific to the characteristics of a site.
Potential impacts to wetlands
Benefits
Reduction in the amount of stormwater-associated pollutants entering adjacent or
downstream wetlands.
Reduction of construction site erosion resulting in a reduction of stormwater sediment
loads to downstream wetlands.
Reduction in the potential for downstream wetland degradation resulting from erosion
associated with peak stormwater flows.
Limitations
Possible reduction in the amount of surface water supplied to adjacent or downstream
wetlands as a result of rerouting.
Sources of Additional Information
Livingston, E., E. McCarron, C. Cox, and P. Sanzone. 1993. The Florida development manual: A guide to sound
land and water management. Stormwater/Nonpoint Source Management Section Florida Department of
Environmental Regulation, Tallahassee, FL.
USEPA. 1993. Guidance for specifying management measures for sources of nonpoint pollution in coastal waters.
EPA 840-B-92-002 . U.S. Environmental Protection Agency, Office of Water, Washington, DC.
Washington State Department of Ecology. 1992. Stormwater management manual for the Puget Sound Basin.
Publication no. 91-75. Washington State Department of Ecology, Olympia, WA.
Nonstructural BMPs - Outreach and Educational Programs
Definition/Purpose
Educational programs should improve wetlands protection program implementation by
maintenance personnel and government officials and should reduce individual contributions to
stormwater problems. Training programs and educational materials for public officials, contrac-
tors, and the public are crucial to implementing effective stormwater management programs.
Educational programs for public officials, contractors, and the public are also necessary to teach
the value of natural wetlands and the potential impacts of stormwater runoff. Contractor
certification and inspector training are important educational programs that add to the success of
stormwater management programs and their continued effectiveness. Programs for the public can
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
educate and encourage participation and support for pollution prevention efforts such as storm
drain stenciling, used oil and hazardous chemical recycling, litter control, street sweeping, lawn
management and landscaping, safe use and disposal of household hazardous materials and chemi-
cals, correct operation of onsite disposal systems, proper pet excrement disposal, water conserva-
tion, and closure of shallow disposal systems that direct pollutants to groundwater.
Scope/Applicability
Educational programs can be implemented in homes, residential communities, and at the
workplace. Training and certification programs can be implemented at all levels of government
and through numerous private and public institutions involved in wetland and stormwater
management including developers, contractors, scientists, engineers, and professional associa-
tions. The states of New Jersey, Virginia, Maryland, Washington, and Delaware, and the city of
Alexandria, Virginia, are examples of governments whose agencies have developed manuals and
training materials to assist in the implementation of urban runoff requirements and regulations
(USEPA, 1993).
Numerous public and private institutions are involved in or sponsor public education
programs, such as environmental organizations; neighborhood, business, civic, and professional
associations; school systems; churches; Boy Scouts and Girl Scouts of America; and 4-H Clubs. A
common program is storm drain stenciling to enhance public awareness (see Figure 4-5). Educa-
tional programs can be achieved through various public outreach media, including newsletters,
magazines, newspaper, audiovisuals, public meetings, or workshops.
Figure 4-5. Stencil spray painting to enhance public awareness.
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Best Management Practices
Potential impacts to Wetlands
Benefits
Teaches the public the value of natural wetlands and the positive and negative impacts
of stormwater.
Teaches the public how pollutants can impact wetlands via stormwater runoff and how
to prevent pollution from entering surface waters and groundwaters.
Provides opportunities for the public to participate in decision-making activities, to
observe wetlands and other aquatic ecosystems, and to gain "hands on" experience in the
field.
Prepares government officials and personnel to implement their stormwater and wetland
programs effectively and consistently, to make educated decisions regarding stormwater
controls, and to communicate the goals and objectives of stormwater/wetland policies to
the public.
Limitations
High participation crucial to the success of many public education programs
Difficult to monitor results.
Program results might not be realized for some time.
Programs require continuous funding and demands on personal time.
Sources of Additional information
Barton, S.S. 1989. Landscape management. Water quality: It's not just a drop in the bucket - You can make a
difference Fact sheet NFS 10. University of Delaware.
Barton, S.S. 1989. Lawn management for conservation. Water quality: It's not just a drop in the bucket - You can
make a difference Fact sheet NFS 11. University of Delaware.
Chesapeake Bay Foundation. 1989. Homeowner series: Septic systems and the Bay. Chesapeake Bay Foundation.
Citizen's Clearinghouse for Hazardous Wastes. Household hazardous wastes fact pack.
Citizens Program for the Chesapeake Bay. 1986. Baybook: A guide to reducing water pollution at home.
Baltimore, MD.
Delaware Department of Natural Resources and Environmental Control. 1989. Detergents and phosphorus.
Clean water series. Delaware Department of Natural Resources and Environmental Control, Dover, DE.
Delaware Department of Natural Resources and Environmental Control. 1989. Household hazardous waste.
Clean water series. Delaware Department of Natural Resources and Environmental Control, Dover, DE.
Delaware Department of Natural Resources and Environmental Control. 1989. Oil recycling. Clean water
series. Delaware Department of Natural Resources and Environmental Control, Dover, DE.
Delaware Department of Natural Resources and Environmental Control. 1989. Septic systems. Clean water
series. Delaware Department of Natural Resources and Environmental Control; Dover, DE.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
District of Columbia Department of Consumer and Regulatory Affairs. 1989. Homeowners urban guide on
ground maintenance. District of Columbia Department of Consumer and Regulatory Affairs, Washington, DC.
Firehock, K. 1991. Virginia's Erosion and Sediment Control Law: A citizen's action guide. Virginia Save Our
Streams Program, Izaak Walton League of America.
Hansen, R.C., and K.M. Mancl. 1989. Modern composting: A natural way to recycle wastes. Bulletin no. 792.
Ohio State University.
Himelick, K. 1989. Landscape design for water conservation. Water quality: It's not just a drop in the bucket - You
can make a difference. Fact sheet NPS 8. University of Delaware, Newark, DE.
Himelick, K. 1989. Plant selection for conservation. Water quality: It's not just a drop in the bucket - You can make
a difference. Fact Sheet NPS 9. University of Delaware, Newark, DE.
Land Management Project. 1990. Biological mosquito control, The Land Management Project - Land use and
water quality series. Fact sheet #7. Land Management Project, Providence, RI.
Land Management Project. 1990. Stormwater and wetlands, The Land Management Project - Land Use and
Water Quality Series. Fact sheet #6. Land Management Project, Providence, RI.
Land Management Project. Undated. The Land Management Project completion report: IMP publications
appendix. Rhode Island Department of Environmental Management and U.S. Environmental Protection
Agency, Providence, RI.
Livingston, E.H. 1989. Florida Nonpoint Source Management Plan. Vol. II Nonpoint Source Pollution Manage-
ment Programs. Florida Department of Environmental Regulation. Chapter 8.
Livingston, E.H., and E. McCarron. 1992. Stormwater management: A guide for Floridians. Florida Department
of Environmental Regulation, Stormwater/Nonpoint Source Management, Tallahassee, FL.
Maine State Planning Office, Maine Coastal Program. 1991. The estuary book: A guide to promoting understand-
ing and regional management of Maine's estuaries and embayments. Maine State Planning Office, Augusta, ME.
Mancl, K.M. 1985. Mound system for wastewater treatment. Agricultural engineering fact sheet. Document
No. SW-43. Pennsylvania State University, College of Agriculture, Cooperative Extension Service.
Mancl, K.M. 1985. Septic system failure. Agricultural engineering fact sheet. Document No. SW-41. Pennsylvania
State University, College of Agriculture, Cooperative Extension Service.
Mancl, K., and WL Magette. 1991. Correcting septic system problems. Water Resources Information, Maryland
Water Resources Research Center.
Mancl, K., and WL Magette. 1991. Maintaining your septic tank. Water Resources Information, Maryland
Water Resources Research Center.
Mancl, K., and WL Magette. 1991. Using septic tank-soil absorption systems in Maryland. Water Resources
Information, Maryland Water Resources Research Center.
Nebraska Department of Natural Resources. Undated. National Resources Districts, unique, progressive
leadership in conservation.
New Jersey Department of Environmental Protection, Division of Water Resources. Pamphlets promoting
solutions and suggestions for citizens concerned about clean water in New Jersey: The clean water book; Clean
ocean information about: litter, plastics, animal waste, and motor oil; New Jersey Water Watch; and others.
Page 4-16
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Best Management Practices
Northern Virginia Soil and Water Conservation District. 1980. You and your land: A homeowner's guide for
Fairfax County. Northern Virginia Soil and Water Conservation District, Fairfax, VA.
Northern Virginia Soil and Water Conservation District (NVSWCD). 1991. Please don't feed our streams.
Northern Virginia Soil and Water Conservation District, Fairfax, VA.
Oregon Department of Land Conservation and Development. Undated. Oregon Coastal Management Program:
A citizen's guide. Funded by the Office of Ocean and Coastal Resource Management, National Oceanic
Atmospheric Administration.
Ohio Environmental Protection Agency, Division of Water Quality Planning and Assessment. 1991. Nonpoint
Source Education/Demonstration Project evaluation report, nonpoint source pollution abatement in Ohio JI98'I-'I987.
Pitt, D.G., W Gould, Jr., and L LaSota. 1990. Landscape design to reduce surface water pollution in residential
areas. Water Resources 32. Water Resources Information, University of Maryland System, Cooperative
Extension Service.
Puget Sound Water Quality Authority. 1989. Managing nonpoint pollution: An action plan handbook for Puget
Sound watersheds. Puget Sound Water Quality Authority.
Salt Institute. 1983. Deicing salt facts (A quick reference.).
Shaver, H.E., and F.M. Piorko. Undated. The role of education and training in the development of the Delaware
Sediment and Stormwater Management Program. Delaware Department of Natural Resources and Environmen-
tal Control, Dover, DE.
South Florida Water Management District. April 1989. Surface water improvement and management (SWIM)
plan for Biscayne Bay. South Florida Water Management District, West Palm Beach, FL.
Southwest Florida Water Management District. Undated. A citizens guide to the S.W.IM. Priority List.
University of Maryland. 1983. Lawn care in Maryland. University of Maryland, Cooperative Extension
Service, College Park, MD. Bulletin 171.
U.S. Department of the Interior. Undated. Pollution prevention handbook. Pollution Prevention Series. U.S.
Department of the Interior, Washington, DC.
USEPA. 1988. Used oil recycling. EPA/530-SW-89-006. U.S. Environmental Protection Agency, Office of Solid
Waste, Municipal Solid Waste Task Force, Washington, DC.
USEPA. 1989. How to set up a local program to recycle used oil. U.S. Environmental Protection Agency, Office
of Solid Waste and Emergency Response, Washington, DC.
USEPA. 1991. Nonpoint Source Watershed Workshop: Seminar publication. EPA/625/4-91/027. Prepared by
Eastern Research Group for the U.S. Environmental Protection Agency, Office of Research and Development,
Center for Environmental Research Information, Cincinnati, Ohio.
USEPA. 1993. Urban runoff management information/education products. U.S. Environmental Protection
Agency, Region 5, Water Division, Wetlands and Watershed Section, Watershed Management Unit, Chicago,
IL.
Washington State Department of Ecology. 1991. Water quality guide: Recommended pollution control practices for
homeowners and small farm operators. No. 87-30. Washington State Department of Ecology, Olympia, WA.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Westchester County, New York 1981. Water quality management program: Best management practices manual on
highway deicing storage and application methods. Westchester County, White Plains, NY.
Whalen, J. 1989. Pest management around your home. Water quality: It's not just a drop in the bucket - You can
make a difference. Fact Sheet NFS 6. University of Delaware.
Wisconsin Legislative Council. 1991. Wisconsin legislation on nonpoint source pollution. Report no. 9. Wisconsin
Legislative Council.
Younger, L.K., and K. Hodge. 1992. 1991 International Coastal Cleanup results. Center for Marine Conserva-
tion, Washington, DC.
Nonstructural BMPs - Riparian Areas
Definition/Purpose
Riparian areas are vegetated ecosystems along a water body through which energy, material,
and water pass. These areas characteristically have a high water table and are subject to periodic
flooding and influence from the adjacent water body. Riparian areas encompass wetlands,
uplands, or combinations of these areas, and environmental conditions in the zone at times
resemble both wetland and upland. The complex organizations of biotic and abiotic elements that
make up riparian areas can be effective in removing suspended solids, nutrients, and other
contaminants from stormwater runoff.
Maintaining natural riparian areas helps to slow stormwater runoff, trap sediment, and
reduce the volume of runoff by allowing some infiltration to occur. Reducing the velocity of
stormwater runoff attenuates soil erosion processes and increases runoff contact time with soil
and vegetative surfaces. Increased contact of stormwater runoff with the soils and vegetation in a
riparian area can result in the infiltration of runoff and the filtration or uptake of stormwater-
associated pollutants.
Riparian areas are important to both the wetland and the upland as habitat for aquatic and
wetland-dependent wildlife species, as refuges for wildlife species during high-water events, as
seed reservoirs, and as buffers against extreme environmental conditions. Other functions of
riparian areas that contribute to water quality include shading, flood attenuation, and shoreline
stabilization. A typical riparian area is shown in Figure 4-6.
Scope/Applicability
Where natural riparian areas are present, they should be maintained around all wetlands
that might be impacted by stormwater flows. The removal of trees and other vegetation in the
riparian zone should be limited and heavy use should be minimized to reduce the potential for soil
compaction, which could result in decreased infiltration rates.
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Best Management Practices
WETLAND
GROUNDWATER
Figure 4-6. A typical riparian area.
Riparian areas should be a part of a series of BMPs for treating stormwater in densely
developed areas where there are high percentages of impervious surfaces or where discharge rates
are high and flow is concentrated.
Riparian areas should be maintained, when possible, in all areas where they exist and can be
combined with other structural or nonstructural BMPs as part of a stormwater treatment system.
They are useful in separating incompatible land uses, and can be effective in protecting sensitive
habitats such as wetlands, streams, lakes, and shorelines from adjacent land uses.
Design Criteria considerations
Maintain natural vegetation.
Avoid compaction of the soils.
Consider slope, vegetation, soils, depth to impermeable layers, runoff sediment character-
istics, type and quantity of stormwater pollutants, and annual rainfall when determining
widths.
Increase riparian area width with increased slope, where possible.
Combine natural riparian areas with other structural or nonstructural BMPs as
pretreatment where discharge rates are high or flows are concentrated.
Potential impacts to Wetlands
Benefits
Reduce the amount of stormwater-associated pollutants entering adjacent or down-
stream wetlands.
Reduce stormwater sediment loads to downstream wetlands.
Reduce the potential for downstream wetland degradation resulting from erosion
associated with peak stormwater flows.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Might result in recharge of groundwater from infiltration, benefiting adjacent baseflow-
dependent wetlands.
Maintain slope stability adjacent to wetlands and streams.
Provide a buffer between wetlands and adjacent land uses.
Provide critical habitat adjacent to wetlands and streams.
Protect aquatic life by preventing and reducing thermal warming impacts.
Limitations
« Might not adequately attenuate concentrated peak stormwater flows to adjacent or
downstream wetlands.
Sources of Additional information
Brown, M. 1991. Vegetative buffer zones. Prepared for the Southwest Florida Water Management District
Surface Water Improvement and Management Program. Henigar & Ray Engineering Associates, Inc., Crystal
River, FL.
Heraty, M. 1993. Guidance report I: Riparian buffer programs. Prepared for the U.S. Environmental Protection
Agency, Office of Wetlands, Oceans and Watersheds. Metropolitan Washington Council of Governments,
Washington, DC.
Livingston, E., E. McCarron, C. Cox, and P. Sanzone. 1993. The Florida development manual: A guide to sound
land and water management. Stormwater/Nonpoint Source Management Section Florida Department of
Environmental Regulation, Tallahassee, FL.
USEPA. 1993. Guidance for specifying management measures for sources of nonpoint pollution in coastal waters.
EPA 840-B-92-002. U.S. Environmental Protection Agency, Office of Water, Washington, DC.
Washington State Department of Ecology. 1992. Stormwater management manual for the Puget Sound Basin.
Publication no. 91-75. Washington State Department of Ecology, Olympia, WA.
Structural BMPs - Infiltration Basins
Definition/Purpose
Infiltration basins are stormwater impoundments that detain stormwater runoff and return
it to the ground by allowing runoff to infiltrate gradually through the soils of the bed and sides of
the basin. Infiltration basins are flat-bottomed, have no outlet, and are usually located to collect
stormwater runoff from adjacent drainage areas. Infiltration basins can be designed to control
peak discharges from relatively large design storms.
Infiltration basins can be designed as an off-line system for treating the first flush of
stormwater flows or to treat the peak discharges of the 2-year storm event. They remove both
soluble and fine particulate pollutants, provide groundwater recharge, and preserve the natural
water balance of a site by diverting a signifcant fraction of the annual runoff volume back into
the soil. Infiltration basins can maintain flow levels in small headwater streams during critical
dry-weather periods. They do not produce thermal or low dissolved oxygen impacts to down-
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Best Management Practices
stream waters as do wet ponds, infiltration basins can be used as sediment basins during the
construction phase of a site as long as the sediment is removed prior to final grading of the basin.
Scope/Applicability
Infiltration basins are effective at removing both soluble and fine particulates found in
stormwater runoff. (Coarse-grained pollutants should generally be removed before they enter an
infiltration basin.) Unlike other infiltration devices (e.g., trenches), basins can be adapted to
provide full control of peak discharges for large design storms. Infiltration basins can also be
adapted to relatively large drainage areas (up to 50 acres). Depending on the degree of storage/
exfiltration achieved in the basin, significant groundwater recharge, low flow augmentation, and
localized stream bank erosion control can be achieved (Schueler, 1987).
Infiltration basins can be used at locations with sufficient open space and proper topogra-
phy to allow gravity flow of stormwater to the basin. They are usually used in commercial and
large residential developments. Infiltration basins can serve drainage areas of 2 to 50 acres,
depending on local conditions. An infiltration basin must be located in permeable soils with
infiltration rates greater than 0.5 inches per hour. Soil and water table conditions should be such
that the system can provide for a new volume of storage through percolation or evapotranspira-
tion within a maximum of 72 hours following a stormwater event.
The use of infiltration basins is not recommended in the following situations: ultra-urban
areas, watersheds with risk of chronic oil spills or other contaminant spills, regions with cold
winters and snowmelt/f reeze and thaw conditions, arid regions where a dense vegetative cover
cannot be reliably maintained, regions with sole-source aquifers, and areas with predominantly
day or silt soils. Soils with a combined silt/clay percentage of over 40 percent by weight are
susceptible to frost heave and are not good candidates for infiltration basin applications. Basins
are also unsuitable if the site is located over fill soils that form an unstable upgrade and are prone
to slope failure.
It should be noted that infiltration basins have a high failure rate due to the tendency of the
basin soils to become clogged with sediments. Failure rates for infiltration basins in the mid-
Atlantic region range form 60 to 100 percent in the first 5 years, according to studies conducted in
Maryland (Schueler, 1992). Once a basin has become clogged, it is very difficult to restore its
original function; thus, many infiltration basins have been converted to retention basins or
constructed wetlands.
Design Criteria Consideration
Detention of the 2-year, 6-hour minimum storm to 72-hour maximum drawdown time.
Recommended size of contributing drainage area based on site-specific conditions (e.g.,
soil infiltration capacity or rainfall).
Pretreatment sediment forebay to dissipate the velocity of incoming runoff, spread the
flow, and trap the sediment.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Offsets to waterwells, onsite disposal systems, and fundations are based on hydrologic,
soil, ecologic, and topographic characteristics of the site or existing state or local require-
ments.
Flat-bottomed basin floor vegetated with dense turf grass, such as reed canary grass or tall
fescue.
« Shallow/Basin depth with inlet level with basin floor.
Riprap apron at inlet to prevent incoming runoff from reaching erosive energy levels and
scouring the pipe outfalls and to spread incoming runoff more evenly.
Emergency spillway.
Maximum side slopes of 3:1 (h:v) to allow vegetative stabilization, easier mowing, and
public safety.
Riprap level spreaders.
Uniform ponding depth across entire surface of basin; low spots should be leveled.
8 Contributing watershed slope less than 20 percent; 5 percent optimal.
Minimum 4-ft clearance between basin floor and bedrock level.
Minimum 4-ft clearance to seasonally high groundwater table.
Minimum 100 ft from drinking water wells.
Minimum 10 ft downgradient and 100 ft upgradient of foundations.
25-ft vegetated buffer around the basin perimeter; low-maintenance, water-tolerant
native plant species that provide food and cover for wildlife and act as a screen.
Initial and periodic tilling of basin floor.
Use of lightweight equipment in basin.
Maximum depth low enough to ensure complete drainage of basin within 72 hours;
depends on soil types present.
Design Considerations to improve Longevity
Stone trenches.
Sand surface layer.
Underdrains below basin floor.
Shorter dewatering rate (24 hr rather than 72 hr). v
Pretreatment forebays to control sediment inputs.
Small contributing watershed areas.
Shallow basin depths (standing water appears to promote soil compaction).
Off-line designs that bypass large storms and sediment inputs.
More efficient dewatering mechanisms in basins (e.g., stone trenches rather than soil).
Careful geotechnical investigation of soil conditions prior to excavation.
Page 4-22
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Best Management Practices
Potential impacts to Wetlands
Benefits
Recharge of groundwater from infiltration basins, benefiting baseflow-dependent
wetlands.
Reduction of stormwater sediment loads to downstream wetlands.
Reduction in the potential for downstream wetland degradation resulting from erosion
and hydroperiod changes associated with stormwater flows.
Reduction in the amount of stormwater-associated pollutants entering downstream
wetlands.
Limitations
Reduction in the amount of surface water supplied to adjacent or downstream wet-
lands as the result of rerouting and detention.
Short life span (5 years or less).
Might not be applicable in cold or arid climates, areas with impermeable soils, or areas
overlying sole source aquifers.
Filtering effect of the topsoil can be lost by distributing runoff directly into the subsoil
horizon.
Maintenance Requirements
Infiltration basins require relatively frequent inspection and maintenance. Infiltration
basins require inspection, sediment removal, tilling, erosion control, and debris and litter re-
moval. The frequency of sediment removal will depend on whether the basin is vegetated or
nonvegetated, its storage capacity, its recharge characteristics, the volume of inflow, and the
sediment load.
Infiltration basins require more frequent inspections after construction (see Figure 4-7),
with inspections tapering off to twice a year once performance has been verified. Once the basin
is put to use, it should be inspected after every major storm or at least once a month if no major
storm occurs. Inspections include monitoring of water levels for drainage and checking for
accumulation of sediment or signs of erosion or contamination.
Sediment removal from infiltration basins without vegetation should be performed annu-
ally or semiannually followed by tilling to maintain infiltration rates. Sediment removal should
be performed when the basin is dry to prevent compaction of the soils and clogging of infiltrative
surfaces. Care should be taken to avoid compaction of the basin floor by using light equipment or
possibly hand raking to remove sediments. After the sediment is removed, the basin should be
tilled. Rotary tillers or disk harrows are normally used, but deep plowing might be necessary if
heavy equipment has compacted the soil. Removal of sediments from vegetated basins might not
need to be performed as frequently because vegetative growth helps to prevent the formation of
impermeable layers on the surface of the soil. Dense vegetative growth on side slopes and buffer
strips will also help to prevent erosion from occurring.
Page 4-23
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Top View
Riprap
Outfall \
Protection
Flat Basin Floor with
Dense Grass Turf
Side View
Back-up Underdraln Pipe In Case of Standing Water Problems
Schuster, 1987.
Figure 4-7. Two views of an infiltration basin.
The basin should be checked annually for structural stability including the erosion of side
slopes, differential settlement, cracking, leakage, or tree growth on the embankments. Erosion
control is very important because the associated sediments can clog the infiltration basin. The
erosion of side slopes can be prevented by the maintenance of a dense turf having extensive root
growth that promotes infiltration through the basin sides, promotes bed stability, and inhibits
weed growth.
Sources of Additional information
Austin City Council. 1991. Environmental criteria manual. City Council, Austin, TX.
Gibb, A., B. Bennett, and A. Birkbeck. 1991. Urban runoff quality and treatment: A comprehensive review.
Prepared for the Greater Vancouver Regional District. File no. 2-51-246(242). March 15.
Land Management Project. 1990. Artificial wetlands. BMP fact sheet #6. U.S. Environmental Protection
Agency and Rhode Island Department of Environmental Management, Land Management Project, Provi-
dence, RI.
Livingston, E., E. McCarron, C. Cox, and P. Sanzone. 1993. The Florida development manual: A guide to sound
land and water management. Stormwater/Nonpoint Source Management Section Florida Department of
Environmental Regulation, Tallahassee, FL.
Maryland Department of Natural Resources. 1984. Maryland standards and specifications for stormwater
infiltration practices. Stormwater Management Division, Water Resource Division, Maryland Department of
Natural Resources, Annapolis, MD.
Page 4-24
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.Best Management Practices
Milone & MacBroom, Inc. 1991. Urban stormwater quality management for public water supply watersheds.
Prepared for South Central Connecticut Regional Water Authority, New Haven, CT.
Northern Virginia Planning District Commission. 1987. BMP handbook for the Occoquan watershed. Prepared
for the Occoquan Basin Nonpoint Pollution Management Program. Northern Virginia Planning District
Commission, Annandale, VA.
Schueler, T.R. 1987. Controlling urban runoff: A practical manual for planning and designing urban BMPs.
Metropolitan Washington Council of Governments, Washington, DC.
Schueler, TR., P.A. Rumble, and M-A. Heraty. 1992. A current assessment of urban best management practices:
Techniques for reducing non-point source pollution in the coastal zone. Prepared for the Metropolitan Washington
Council of Governments, Washington, DC.
Tahoe Regional Planning Agency, 1988. Water quality management plan for the Lake Tahoe Region, Handbook of
best management practices. Vol 2. November 30.
Virginia Department of Conservation and Recreation, USDA Soil Conservation Service, Virginia Department
of Transportation, Virginia Polytechnic Institute and State University College of Urban Design and Depart-
ment of Civil Engineering, Occoquan Monitoring Laboratory, and the Virginia Water Control Board. 1990.
Best management practices handbook: Urban.
Washington State Department of Ecology. 1992. Stormwater management manual for the Puget Sound Basin.
Publication no. 91-71 . Washington State Department of Ecology, Olympia, WA.
Structural BMPs - Infiltration Trenches
Definition/Purpose
An infiltration trench is an excavated trench backfilled with clean, coarse aggregate to
allow for the temporary storage of runoff. Runoff stored in the trench is allowed to infiltrate into
the soil in the trench bottom or is conveyed from the trench by an outflow pipe to downstream
stormwater detention or retention systems. Infiltration trenches are designed to provide tempo-
rary storage and infiltration for increased stormwater runoff associated with development.
Infiltration trenches can attenuate peak discharges associated with the design storm and may
replicate predevelopment hydrologic conditions.
Infiltration trenches remove fine particulates and soluble pollutants from runoff by
temporary storage and infiltration into the underlying soil. Pollutant removal from runoff in
infiltration trenches results from adsorption, filtration, and microbial decomposition in the soil.
Temporary storage and partial or complete infiltration of runoff in an infiltration basin can also
reduce downstream bankfull flooding and resultant stream bank erosion and can help to maintain
baseflow conditions. A typical infiltration trench is shown in Figure,4-8.
scope/Applicability
Infiltration trenches can be used on small individual sites or can be incorporated into
multiuse sites where open area is restricted. Pretreatment devices such as grassed swales or filter
Page 4-25
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Wellctp Observation Wol!
Emergency Overflow Berm
unoff Filters throug
20 Foot Wide Grass Buffer Strip
Sand Filter (6-12 Feet Deep)
or Fabric Equivalent
J! Runoff Exfiltrates
'through Undisturbed Subsoils
with a Minimum Final Infiltration Rate of 0.5 Inches/Hour
Schuster, 1987.
Figure 4-8. Typical infiltration trench.
strips should be incorporated with infiltration trenches to remove coarse participates from runoff
prior to its entering the trench.
Infiltration trenches should not be located in areas with shallow groundwater or adjacent to
groundwater-maintained wetlands because of the potential for adverse impacts resulting from
pollutants in the stormwater. Potential impacts to the natural hydroperiod of existing surface
water-maintained wetlands resulting from the rerouting of water through infiltration trenches
and away from these systems should also be considered.
Contributing areas should be less than 10 acres in size, and slopes should be less than 5
percent. Infiltration trenches cannot be installed in fill and should not be used in areas with low-
permeability soils. Their use may also be limited in areas where the ground remains frozen at
depth for extended periods of time or in arid areas with sparse vegetative cover.
Design criteria Considerations
Location in suitable soils with sufficient infiltration rates, preferably greater than 0.5
inches per hour.
Water table offset of at least 3 ft from the bottom of the trench.
Contributing area of less than 10 acres.
Contributing slopes of less than 5 percent.
Detention time of 48 to 72 hours to allow adequate pollutant removal.
Complete drainage of trench within 72 hours of a storm event to maintain aerobic
conditions
Pretreatment of stormwater inflow to remove coarse sediments.
Page 4-26
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Best Management Practices
Sizing of trench dependent on the volume of runoff to be controlled.
Use of observation wells to monitor performance.
Level trench bottom.
Offsets to waterwells, onsite disposal systems, foundations, etc. based on hydrologic, soil,
ecologic, and topographic characteristics of the site or existing state or local require-
ments.
Design Considerations to improve Longevity
Field verification of soil infiltration rates and water table location.
Use of pretreatment systems that provide some degree of storage (e.g., sump pits,
swales with check dams, plunge pools).
A layer of filter fabric 1 ft below surface of trench.
Use of a sand layer rather than filter fabric at the bottom of the trench.
Avoiding construction until all contributing watershed disturbances and construction
activities are completed.
Rototilling of trench bottom to preserve infiltration rates.
Potential impacts to wetlands
Benefits
Reduction of stormwater sediment loads to downstream wetlands.
Reduction in the potential for downstream wetland degradation resulting from
erosion associated with peak stormwater flows.
Reduction in the amount of stormwater-associated pollutants entering downstream
wetlands.
Limitations
Reduction in the amount of surface water supplied to adjacent or downstream
wetlands as the result of rerouting.
Embedding of downstream wetland substrates as the result of the removal of coarse
sediments.
Might not be applicable in cold or arid climates, areas with impermeable soils, or areas
overlying sole source aquifers.
Filtering effect of the topsoil can be lost by distributing runoff directly into the subsoil
horizon.
Page 4-27
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Maintenance Requirements
Infiltration trenches require periodic low-level maintenance. Because trenches are typically
smaller than other BMPs and are buried underground, they might receive little attention from
homeowners or might be relatively inaccessible. Infiltration trenches require continued monitor-
ing and maintenance according to a well-defined schedule that outlines responsibilities and
enforcement. Routine maintenance activities include inspection, buffer maintenance and
mowing, sediment removal, and tree pruning.
Inspections for drainage are typically performed frequently upon completion of construc-
tion and annually thereafter. Water level monitoring should be conducted several times within
the first few months of operation. The surface of the infiltration trench should be checked for
standing water after a rainstorm, and water levels in the observation well should be recorded over
several days to check drainage rates. If there is no observation well, a small hole can be dug down
to the first layer of filter fabric to observe the water level in the trench. The monitoring schedule
is reduced to an annual frequency once performance of the device has been verified.
The accumulation of sediments in the top foot of stone aggregate or the surface inlet should
be monitored on the same schedule as the observation well to check for surface clogging. When
infiltrative capacity is significantly reduced, sediment should be removed from the top of the
infiltration trench by removing the stone, replacing the filter fabric, and washing or replacing the
stone. Removal of sediment from the top of the infiltration trench should be required less
frequently if the trench is designed with a pretreatment inlet. Sediment should be cleaned out of
the pretreatment inlet, sediment trap, or grease trap on a regular basis.
Grass buffer strips adjacent to and growing over the infiltration trench should be inspected
annually for lush, vigorous growth. Bare spots should be reseeded or resodded, and eroded areas
should be repaired. Trees adjacent to the trench should be trimmed so that their leaves will not
dog the trench. Pioneer trees that start to grow near the trench should be removed to prevent
puncturing of the trench by their roots.
Sources of Additional information
Page 4-28
Gibb, A., B. Bennett, and A. Birkbeck. 1991. Urban runoff quality and treatment: A comprehensive review.
Prepared for the Greater Vancouver Regional District. File no. 2-51-246(242). March 15.
Livingston, E., E. McCarron, C. Cox, and P. Sanzone. 1993. The Florida development manual: A guide to sound
land and water management. Stormwater/Nonpoint Source Management Section Florida Department of
Environmental Regulation, Tallahassee, FL
Maryland Department of Natural Resources. 1984. Maryland standards and specifications for Stormwater
infiltration practices. Stormwater Management Division, Water Resource Division, Maryland Department of
Natural Resources, Annapolis, MD.
Northern Virginia Planning District Commission. 1987. BMP handbook for the Occoauan Watershed. Prepared
for Occoquan Basin Nonpoint Pollution Management Program. Northern Virginia Planning District Commis-
sion, Annandale, VA
Schueler, T.R., P.A. Rumble, and M.A. Heraty. 1992. A current assessment of urban best management practices,
techniques for reducing non-point source pollution in the coastal zone. Prepared for the Metropolitan Washington
Council of Governments, Washington, DC.
Westchester County Department of Planning. 1984. Best management practices manual for Stormwater runoff
control. Westchester County Environmental Management Council, White Plains, NY.
-------
Best Management Practices
Structural BMPs - Sand Fitters
Definition/Purpose
Sand filters are systems of underground pipes beneath a self-contained bed of sand designed
to treat urban stormwater. Runoff from a developed site is routed to the filters, infiltrated
through the sand, then collected in underground pipes and returned back to the stream or channel.
Sand filters are enhanced with the use of peat, limestone, gravel, and/or topsoil layers and may
have a grass cover. Sand filters remove sediment, trace metals, nutrients^ BOD, and fecal coliform
from the initial pulse of stormwater from a development site. They provide significant pollutant
removal and are useful for groundwater protection.
Scope/Applicability
Sand filters are adaptable for urban areas. They can be used to treat stormwater from small,
intensely developed sites (e.g., gas stations, convenience stores, small parking lots). Sand filters
have been used to retrofit existing stormwater management systems by locating them at the end
of existing stormwater outlet pipes. Sand filters are an off-line system (i.e., they should be located
outside the stream channel or drainage path). Sand filters are more costly to construct than
infiltration trenches by a factor of 2 or 3, but they have lower regular maintenance costs.
Sand filters are designed to treat stormwater quality, not quantity. They have a limited
ability to reduce peak discharges and do not provide detention for downstream areas such as
wetlands. Average removal rates of 85 percent for sediment, 35 percent for nitrogen, 40 percent
for dissolved phosphorus, 40 percent for fecal coliform, and 50 to 70 percent for metals have
been reported for sand filters. Two views of a sand filter design developed by the City of Austin,
Texas, are presented in Figure 4-9.
Design Criteria considerations
Sand filters can be used in areas with thin soils, high evaporation rates, low soil infiltra-
tion rates, and limited space.
Drainage areas can be as great as 50 acres; however, most sand filters will function well
with contributing watersheds ranging from 0.5 to 10 acres.
Two to 4 ft of head are needed for proper operation.
Using a peat or limestone layer in the filter bed and a grass cover can increase the pollut-
ant removal efficiency.
Minimum design depth of the filter should be 18 inches.
Filters designed with a long drawdown time (24 to 40 hours) can increase the pollutant
removal efficiency.
Page 4-29
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
TO STORMWATER
DETENTION BASIN
SEDIMENT CHAMBER
PLAN VIEW
FILTRATION BASIN
li |i H H H H H H
II H H H H II II H
H it II H II II II II
n ~ r TI~I~ ~ r n ~ r 7r
n M n n n
n n n n n n M n
n n ii n n n n n
FILTRATED OUTFLOW
FILTRATED OUTFLOW
UNDERDRAW PIPING SYSTEM
City of Austin, Texas, 1991.
Figure 4-9. Two views of a sand filter design.
Design Considerations to improve Longevity
Quarterly maintenance of the sand filter to maintain porosity aids in keeping the filter
operating efficiently.
Designs that include a flow splitter can help to prevent clogging.
Pretreatment to remove sediment will help to prevent clogging.
Designs that allow for access to the filter aid in maintenance and inspection of the
filter.
Regular removal of surface sediment increases the longevity of the filter.
Potential impacts to Wetlands
Benefits
Reduction in the amount of stormwater-associated pollutants entering downstream
wetlands.
Limitations
Primarily function as a water quality BMP and might not adequately attenuate concen-
trated peak stormwater flows to adjacent or downstream wetlands.
Might adversely affect downstream sediment or nutrient-depleted wetlands.
Page 4-30
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Best Management Practices
Maintenance Requirements
Sand filters require relatively frequent yet simple inspection and maintenance to maintain
performance. When a predetermined headloss is reached, the top layer of sand is removed and
replaced to restore the filtration capacity of the filter. The frequency of sediment removal
depends on the solids content of the water being filtered. To extend the life of the filter, system
designs incorporate a wet pool that is used to trap the coarse sediments before they reach the
filter. Sand filters require raking, surface sediment removal, and the removal of trash, debris, and
leaf litter. Peat-sand filters that have vegetation growing on their surface require vegetation
maintenance including periodic mowing. Mowing the grass short removes nutrients absorbed by
the plants and maintains a neat filter appearance.
Sand filters requke monitoring for hydraulic conductivity. Routine inspections are also
needed for sediment accumulation in the wet pool, health of the vegetative cover, and the removal
of trash deposited in the wet pond. The vegetative cover can be damaged by salt if the system is
not shut down over the winter season. Managers should select hardy vegetation that is resistant
to damage by salt, disease, and flooding.
Sources of Additional information
City of Austin, Texas. 1991. Design guidelines for water quality control basins, Public Works Department,
Austin, TX.
%
Galli, J. 1990. Peat-sand filters: A proposed stormwater management practice for urbanization areas. Prepared for
the Coordinated Anacostia Retrofit Program and the Office of Policy and Planning, DC Department of Public
Works, Washington, DC.
Gibb, A., B. Bennett, and A. Birkbeck. 1991. Urban runoff quality and treatment: A comprehensive review.
Prepared for the Greater Vancouver Regional District. File No. 2-51-246(242).
Land Management Project. 1990. Artificial wetlands. BMP fact sheet #5. U.S. Environmental Protection
Agency and Rhode Island Department of Environmental Management, Land Management Project, Provi-
dence, RI.
Metcalf & Eddy, Inc. 1979. Wastewater engineering: Treatment disposal reuse. 2nd ed. McGraw-Hill Book
Company, New York, NY.
Milone & MacBroom, Inc. 1991. Urban stormwater quality management for public water supply watersheds.
Prepared for South Central Connecticut Regional Water Authority, New Haven, CT.
Northern Virginia Planning District Commission. 1992. Northern Virginia BMP handbook: A guide to planning
and designing best management pratices in Northern Virginia. Northern Virginia Planning District Commission,
Annandale, VA.
Northern Virginia Planning District Commission. 1987. BMP handbook for the Occoquan Watershed. Prepared
for Occoquan Basin Nonpoint Pollution Management Program. Northern Virginia Planning District Commis-
sion, Annandale, VA.
Schueler, T.R., P.A. Rumble, and M.A. Heraty. 1992. A current assessment of urban best management practices,
techniques for reducing non-point source pollution in the coastal zone. Prepared for the Metropolitan Washington
Council of Governments, Washington, DC.
Page 4-31
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I
Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Schueler, T.R. 1987. Controlling urban runoff: A practical manual for planning and designing urban BMPs.
Metropolitan Washington Council of Governments, Washington, DC.
Washington State Department of Ecology. 1992. Stormwater management manual for the Puget Sound Basin.
Publication no. 91-75. Washington State Department of Ecology, Olympia, WA.
Structural BMPs - Grassed Swales
Definition/Purpose
Grassed swales are channels lined with grass or erosion-resistant plant species that are
constructed for the stable conveyance of stormwater runoff. They use the ability of vegetation to
reduce the flow velocities associated with concentrated runoff. Grassed swales are not usually
designed to control peak runoff loads independently and are often used in combination with
other best management practices. Where slopes are excessive, grassed swales can include exca-
vated depressions or check dams to enhance runoff storage or to decrease flow rates.
Grassed swales are primarily stormwater conveyance systems designed to channel and
transport stormwater without the resultant erosion associated with high-velocity runoff. The
reduction in flow velocities resulting from the conveyance of surface runoff through dense
vegetative cover can result in a reduction of peak discharges. Pollutants can be removed from
stormwater by filtration through the vegetation, by deposition, or in some cases by the infiltra-
tion of soluble nutrients into the soil. The degree of pollutant removal in a swale depends
primarily on the residence time of water in the swale and the extent of its contact with vegeta-
tion and the soil surface. The incorporation of excavated depressions or check dams into grassed
swales can enhance pollutant removal by increasing detention/retention times. An example of a
grassed swale is shown in Figure 4-10.
Scope/Applicability
Grassed swales can be used in large-lot single-family subdivisions and on campus-type office
or industrial sites in place of curbs and gutters. They are useful for runoff conveyance in highway
medians and are often combined with other best management practices. They can be used in all
areas of the country where the climate and soils allow for the establishment of dense vegetative
covers. Grassed swales have a limited ability to control runoff from large storms and should not
be used in areas where flow rates exceed 1.5 ft per second.
Design criteria considerations
Longitudinal swale slope of less than 2 percent or use of check dams or excavated depres-
sions where slopes exceed 4 percent.
Wide and shallow parabolic shape with side slopes of less than 3:1.
Development and maintenance of dense vegetation.
Greater than a 2-ft offset to the water table.
Page 4-32
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Best Management Practices
Side-slopes
3:1 or Less
Swale Slopes
as Close to
Zero as Drainage
Will Permit
Railroad Tie
Check-dam
(Increases infiltration)
Dense Growth
of Grass (Reed
Canary or KY-31
Tall Fescue)
Stone Prevents
Downstream Scour
Schueler, 1987.
Figure4-'IO. Grassed swale.
Use of underdrains if well-drained conditions are requked.
Discharge of runoff to wetlands or adjacent BMPs at nonerosive velocities.
Potential impacts to wetlands
Benefits
Potential creation of wetlands and wetland habitat in low-slope areas.
Potential for groundwater recharge in low-flow storm events, benefiting adjacent
baseflow-dependent wetlands.
Limitations
Reduction in the amount of surface water supplied to adjacent or downstream wetlands
as a result of the rerouting of surface water.
Potential for the introduction of pollutants to downstream wetlands during peak storm
events if conveyance is to the wetlands.
Maintenance Requirements
Maintenance requirements for grassed swales are relatively minimaLThese include
cleanout of sediment trapped behind check dams, mowing, litter removal, and spot vegetation
repair. The most important objective in the maintenance of grassed swales is the maintaining of a
Page 4-33
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
dense and vigorous growth of turf. Usually in residential subdivisions, homeowners adjacent to
the swales maintain the grass and remove litter. Education of homeowners is recommended
because the type of maintenance sought to maximize pollutant removal is somewhat different
from that used to maintain the average homeowner's lawn. For example, grass should not be cut
too short, excessive fertilizers should not be used so that contamination of receiving waters or
groundwater is avoided, and ditches should be kept free of lawn debris.
Periodic cleaning of vegetation and soil buildup in curb cuts is required so that water flow
into the swale is unobstructed. Sediments should be removed when they accumulate to 6 inches or
more at any spot or when they interfere with the grassed swale operation. During the growing
season, swale grass should be cut no shorter than the level of the design flow. Cuttings should be
removed promptly. Swale maintenance at the end of the growing season depends on whether the
objective is to remove nutrients or particulates. Grasses and wetland plants are mowed or cut to a
low height at the end of the growing season to promote nutrient removal; for other pollution
control objectives, such as sediment removal, plants are allowed to stand at a height exceeding the
design water depth by at least 2 inches at the end of the growing season. These plants will act as a
filter to screen out particles by slowing the velocity of water so that particles can settle.
Sources of Additional information
Gibb, A., B. Bennett, and A. Birbeck. 1991. Urban runoff quality and treatment: A comprehensive review.
Prepared for the Greater Vancouver Regional District. File no. 2-51-246(242).
Khan, Z., C. Thrush, P. Cohen, L Kulzer, R. Franklin, D. Field, J. Koon, R. Homer. 1992. Biofiltration swale
performance, recommendations, and design considerations. Municipality of Metropolitan Seattle Water Pollution
Control Department, Seattle, WA
Land Management Project. 1990. Artificial wetlands. BMP fact sheet #2. U.S. Environmental Protection
Agency and Rhode Island Department of Environmental Management, Land Management Project, Provi-
dence, RI.
Livingston, E., E. McCarron, C. Cox, and P. Sanzone. 1993. The Florida development manual: A guide to sound
land and water management. Stormwater/Nonpoint Source Management Section, Florida Department of
Environmental Regulation, Tallahassee, FL
Long Island Regional Planning Board. 1984. Nonpoint source management handbook. Long Island Regional
Planning Board, Hauppauge, NY.
Maryland Department of Natural Resources. 1984. Maryland standards and specifications for stormwater
infiltration practices. Stormwater Management Division, Water Resource Division, Maryland Department of
Natural Resources, Annapolis, MD.
Northern Virginia Planning District Commission. 1992. Northern Virginia BMP handbook: A guide to planning
and designing best management pratices in Northern Virginia. Northern Virginia Planning District Commission,
Annandale, VA.
Northern Virginia Planning District Commission. 1987. BMP handbook for the Occoquan Watershed. Prepared
for Occoquan Basin Nonpoint Pollution Management Program. Northern Virginia Planning District Commis-
sion, Annandale, VA
Schueler, TR., PA Kumble, and M.A. Heraty. 1992. A current assessment of urban best management practices,
techniques for reducing non-point source pollution in the coastal zone. Prepared for the Metropolitan Washington
Council of Governments.
Schueler, T.R. 1987. Controlling urban runoff: A practical manual for planning and designing urban BMPs.
Metropolitan Washington Council of Governments.
Page 4-34
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Best Management Practices
Structural BMPs - Vegetative filter Strips
Definition/Purpose
Vegetative filter strips are densely vegetated sections of land designed to convey runoff in
the form of sheet flow from adjacent developed sites. Level spreaders can be incorporated into the
design of vegetated filter strips to increase their effectiveness by distributing runoff over the full
length of the strip. Vegetative filter strips primarily function as water quality BMPs and do not
provide adequate detention or infiltration to reduce peak discharges to predevelopment levels.
Vegetative filter strips direct runoff in the form of sheet flow across grassed or forested
surfaces (see Figure 4-11). Reduction in flow velocities resulting from the conveyance of surface
runoff through dense vegetated cover results in the removal of particulate contaminants through
sedimentation, enhanced infiltration into the soil, and a reduction in the potential for down-
stream channel degradation. Vegetative filter strips may also reduce runoff volumes and contrib-
ute to groundwater recharge. Maximum water quality benefits of vegetative filter strips can be
obtained if the strips include the use of native vegetation (preferably undisturbed or conserved
natural areas).
A recent variation of vegetative filter strips is a technology referred to as bioretention. This
approach can be suitable for managing runoff from small drainage areas using a mixture of upland
plant materials and enriched soil composition. Bioretention can maximize nutrient uptake,
evapo-transpiration, infiltration, microbial degradation of metals and carbon-based pollutants,
and storage to help reduce peak flows from the drainage area served to predevelopment levels. It
should be noted, however, that bioretention methods require modification of existing site grading
practices to provide sheet flow as a runoff conveyance rather than traditional pipe inlet systems.
Barms Placed
Perpendicular
to Top of Strip Prevent
Concentrated Flows
Top Elevation of Strips
On Same Contour; '
Directly Abuts Trench
Stone Trench
Acts as
Level Spreader
Schueler,1987.
Figure 4-4'i. Vegatative filter strip between developed area, and sensitive aquatic habitat.
Page 4-35
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Scope/Applicability
Vegetative filter strips can be used on low- and medium-density residential and campus-type
office or industrial sites where the percentage of pervious area is sufficient to promote infiltra-
tion and filtering. They are often used to convey sheet flow runoff to other conveyance or
detention systems. Contributing drainage areas should be less than 10 acres in size with gentle
slopes so that runoff arrives at the site in the form of overland sheet flow.
Vegetative filter strips are useful as buffers between developed areas and sensitive aquatic
habitats such as wetlands, streams, and lakes and can be useful in stabilizing stream banks.
Vegetative filter strips are adaptable to most climates and are effective where dense vegetation
can be sustained on a year-round basis. They are not feasible in densely developed urban areas,
where there are high percentages of impervious surfaces, or where discharge rates are high and
flow is concentrated. A vegetative filter strip used for protecting a natural waterway in a com-
mercial construction setting is shown in Figure 4-12.
Design Criteria considerations
Contributing areas of less than 10 acres.
Uniform, even contributing slope of less than 5 percent.
Length of no less than 50 to 75 ft with an additional 4 ft for every increase in slope of 1
percent.
Width of no less than 20 ft.
Development and maintenance of dense erosion-resistant vegetation species.
Use of a level spreader at the top of the filter strip to distribute flow easily.
Layout of the top" edge of the filter strip on contour.
Use of native vegetation.
Diversion
Natural
Vegetative
Pilfer Strip
Exposed
Construction
Area
Existing Waterway
Adapted from Washington State Department Ecology, 1992.
Bgure4-'l2.. Vegatative filter strip.
Temporary
Sediment
Trap
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Best Management Practices
Potential impacts to Wetlands
Benefits
Reduction of stormwater sediment and pollutant loads to adjacent and downstream
wetlands.
Potential recharge of groundwater, benefiting adjacent baseflow-dependent wetlands.
Provide a buffer between wetlands and adjacent development.
Limitations
Primarily function as a water quality BMP and might not adequately attenuate concen-
trated peak stormwater flows to adjacent or downstream wetlands.
Maintenance Requirements
Frequent inspections and maintenance are required in the first few years after filter strip
construction while vegetation becomes established. Watering, fertilizing, and reseeding might be
required during the initial establishment of the strip to maintain a dense vegetative cover.
Established filter strips should be inspected on an annual basis for foot or vehicular damage.
Inspectors should note encroachment, gully erosion, density of vegetation, and evidence of
concentrated flows through or around the strip. A filter strip and its associated level spreader,
when used, should be inspected periodically during storms to ensure that flow is not concentrat-
ing and short circuiting through the strip. ,
Vegetated filter strips require periodic repair, regrading, and sediment removal to prevent
channelization. Sediments accumulating near the top of the strip should be removed to maintain
the original grade. Longer buffer strips present the option of management as a lawn, or as a .
succession of vegetation types from grass, to meadow, to second-growth forest. "Natural" filter
strips require less maintenance than grass lawns; however, corrective maintenance is still required
to prevent the formation of concentrated flows. Shorter strips are managed as a lawn or as a short
grass meadow and are mowed two or three times a year to suppress weeds and woody growth.
Sources of Additional information
Gibb, A., B. Bennett, and A. Birkbeck. 1991. Urban runoff quality and treatment: A comprehensive review.
Prepared for the Greater Vancouver Regional District. File no. 2-51-246(242).
Maine Department of Environmental Protection. 1992. Environmental management: A guide for town officials,
best management practices to control itonpoint source pollution. Maine Department of Environmental Protection,
Augusta, ME.
Maryland Department of Natural Resources. 1984. Maryland standards and specifications for stormwater
infiltration practices. Stormwater Management Division, Water Resource Division, Maryland Department of
Natural Resources, Annapolis, MD.
Milone & MacBroom, Inc. 1991. Urban stormwater quality management for public water supply watersheds.
Prepared for South Central Connecticut Regional Water Authority, New Haven, CT.
Page 4-37
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Northern Virginia Planning District Commission. 1987. BMP handbook for the Occoauan Watershed. Prepared
for Occoquan Basin Nonpoint Pollution Management Program. Northern Virginia Planning District Commis-
sion, Annandale, VA
Northern Virginia Planning District Commission. 1992. Northern Virginia BMP handbook: A guide to planning
designing best management pratices in Northern Virginia. Northern Virginia Planning District Commission,
Annandale, VA
Prince George's County. 1993. Design manual for use of bioretention in stormwater management. Prepared for
Prince George's County Government, Watershed Protection Branch, Landover, MD, by Engineering Technolo-
gies Associates, Inc., and Biohabitats, Inc.
Schueler, T.R. 1987. Controlling urban runoff: A practical manual for planning and designing urban BMPs.
Metropolitan Washington Council of Governments, Washington, DC.
Schueler, T.R., PA. Kumble, and MA. Heraty. 1992. A current assessment of urban best management practices,
techniques for reducing non-point source pollution in the coastal zone. Prepared for the Metropolitan Washington
Council of Governments, Washington, DC.
USEPA 1993. Guidance for specifying management measures for sources of nonpoint pollution in coastal waters.
EPA 840-B-92-002. U.S. Environmental Protection Agency, Office of Water, Washington, DC.
Virginia Cooperative Extension Program. 1994. £asy reference to sustainable landscape management and water
quality protection. Publication 426-612. Virginia Cooperative Extension Program, Blacksburg, VA
Washington State Department of Ecology. 1992. Stormwater management manual for the Puget Sound Basin.
Publication no. 91-75. Washington State Department of Ecology, Olympia, WA.
Structural BMPs - Vegetated Natural Buffers
Definition/Purpose
Vegetated buffer areas are barriers of natural or established perennial vegetation managed to
reduce the impact of development on the water quality of adjacent areas. They are effective in
separating incompatible land uses and in displacing activities that represent potential sources of
nonpoint source pollution from adjacent wetlands or water bodies. Vegetated buffer areas can be
spatially arranged in linear strips or as free forms depending on site characteristics.
Vegetated buffer areas function primarily as water quality BMPs and usually do not provide
adequate detention to reduce peak discharges to predevelopment levels. They reduce the velocity
of surface runoff from adjacent developed sites and provide area for infiltration of runoff into the
soil. Reduced flow velocities result in the removal of particulate contaminants through sedimen-
tation and reduce the potential for channel erosion or degradation. Vegetated buffer areas can also
reduce runoff velocities and contribute to groundwater recharge.
Scope/Applicability
Vegetated buffer areas can be used in large-lot, medium- to low-density single-family
subdivisions or campus-type office or industrial sites where the percentage of pervious area is
sufficient to promote infiltration. Vegetated buffer areas should be located in areas with gentle
Page 4-38
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Best Management Practices
slopes where runoff is conveyed in the form of sheet flow. They are useful in separating incom-
patible land uses, and they can be effective in protecting sensitive habitats such as wetlands,
streams, lakes, and shorelines from the impacts of adjacent development. Vegetated buffer areas
are also useful in combination with other structural BMPs. An example of a vegated buffer is
shown in Figure 4-13.
Design criteria Considerations:
Avoid compaction of the soils.
Consider slope, vegetation, soils, depth to impermeable layers, runoff sediment character-
istics, type and quantity of stormwater pollutants, and annual rainfall when determining
buffer widths.
Combine vegetated buffer areas with other structural or nonstructural BMPs as pretreat-
ment where discharge rates are high or flows are concentrated.
Slope of less than 5 percent.
Increased buffer width as slope increases.
Intermixed zones of vegetation (particularly, native vegetation) including grasses,
deciduous and evergreen shrubs, and understory and overstory trees.
Potential impacts to wetlands
Benefits
Reduction of stormwater sediment and pollutant loads to adjacent and downstream
wetlands.
Potential recharge of groundwater, benefiting adjacent baseflow-dependent wetlands.
Provide a buffer between wetlands and adjacent land uses.
Provide critical habitat adjacent to wetlands.
Adapted from State of Maine, DEP, 1992.
Figure 4-43. Vegetated natural buffer.
Page 4-39
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Limitations
Primarily function as a water quality BMP and typically do not adequately attenuate
concentrated peak stormwater flows to adjacent or downstream wetlands.
Maintenance Requirements
The inspection and maintenance of vegetated buffer areas are most important during the
period of initial establishment. Maintenance requirements during the first few years of establish-
ment include weed suppression and rodent protection in forested areas. Extra watering, fertiliz-
ing, and grass reseeding or tree replacement might also be necessary. Trees might need to be staked
to increase their survival rates. The condition of vegetated buffer areas should be inspected
periodically, especially after heavy runoff events, during the first few years after buffer area
creation to ensure that vegetation is healthy and that channelized flows are not developing.
Maintenance requirements are relatively minimal once a vegetated buffer area is estab-
lished. Routine maintenance is designed to promote the growth of dense, vigorous vegetation and
includes mowing, litter removal, repair of eroded areas, and spot vegetation repair. Sediments that
accumulate more than 6 inches at any spot should be removed. Watering and possible fertilization
might also be required periodically.
Established buffer areas should be inspected on an annual basis for foot or vehicular damage.
Inspectors should note encroachment, gully erosion, density of vegetation, and evidence of
concentrated flows through or around the vegetated buffer area. A plan view of the use of natural
vegatated buffers to protect riparian wetland areas is shown below in Figure 4-14.
Sources of Additional information
Brown, M. 1991. Vegetative buffer zones. Prepared for the Southwest Florida Water Management District
Surface Water Improvement and Management Program. Henigar & Ray Engineering Associates, Inc., Crystal
River, FL.
Chesapeake Bay Local Assistance Department. 1989. Local assistance manual. Chesapeake Bay Local Assitance
Department, Richmond, VA.
Heraty, M. 1993. Guidance report I: Riparian buffer programs. Prepared for the U.S. Environmental Protection
Agency, Office of Wetlands, Oceans and Watersheds. Metropolitan Washington Council of Governments,
Washington, DC.
Maine Department of Enviromental Protection. 1992. Environmental management: A guide for town officials,
best management practices to control nonpoint source pollution. Maine Department of Environmental Protection,
Augusta, ME.
Schueler, T.R., PA. Kumble, and M.A. Heraty. 1992. A current assessment of urban best management practices,
techniques for reducing non-point source pollution in the coastal zone. Prepared for the Metropolitan Washington
Council of Governments, Washington, DC.
Virginia Cooperative Extension Program. 1994. Easy reference to sustainable landscape management and water
quality protection. Publication 426-612. Virginia Cooperative Extension Program, Blacksburg, VA.
Washington State Department of Ecology. 1992. Stormwater management manual for the Puget Sound Basin.
Publication no. 91-75. Washington State Department of Ecology, Olympia, WA.
Page 4-40
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Best Management Practices
Schueler, 1987.
Figure 4-14. A plan view of natural vegatated buffer use.
Structural EMPs - Open Spaces
Definition/Purpose
Open spaces are grassed or wooded areas located within development sites to increase
pervious area. Open spaces function primarily as water quality BMPs and usually do not provide
adequate detention to reduce peak discharges to predevelopment levels.
Open areas reduce the velocity of surface runoff, resulting in an increased contact time of
sheet flow with the soil and vegetative surfaces. Reduced flow rates result in the removal of
particulate contaminants through sedimentation and reduce the potential of channel erosion or
degradation. Reduced flow velocities can improve water quality by increasing infiltration,
filtration, and adsorption of stormwater runoff on a site. Groundwater recharge can also occur as
the result of increased infiltration in open areas.
Scope/Applicability
Open areas can be used in locations with gently sloping topography where runoff is con-
veyed in the form of sheet flow. They should be located in well-drained or moderately well-
drained soils where offsets to the water table or bedrock exceed 4 ft. Open areas can be incorpo-
rated into lightly used recreational areas, or they can be maintained as meadows or wooded areas.
Open areas should not be located in heavily used areas because of the potential for soil compac-
tion, which could result in decreased infiltration rates on the site. An example of the use of open
space to maximize the preservation and protection of wetlands and other aquatic resources is
shown in Figure 4-15.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Design criteria considerations:
Contributing slopes of less than 5 percent.
Conveyance of runoff in the form of sheet flow.
Locate in well-drained or moderately well-drained soils.
Minimum water table and/or bedrock offset of 4 ft.
Adequate size of open area to provide sufficient levels of treatment.
Potential impacts to wetlands
Benefits
Reduction of stormwater sediment and pollutant loads to adjacent and downstream
wetlands.
Potential recharge of ground water, benefiting adjacent baseflow-dependent wetlands.
Provide a buffer between wetlands and adjacent development.
limitations
Primarily function as a water quality BMP and might not adequately attenuate concen-
trated peak stormwater flows to adjacent or downstream wetlands.
CLUSTER
DEVELOPMENT
OPEN SPACE
sn
mm
Figure 4-15. A plan view for maximizing the preservation and protection of wetlands.
Page 442
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Best Management Practices
Maintenance Requirements
The maintenance of open spaces is minimal once the vegetation is established. Frequent
inspections are required during the first few years to ensure a healthy, dense growth of the desired
forms of vegetation. Extra watering, fertilization, and reseeding might be required. Forested areas
might require weed suppression, rodent protection, watering, or staking to increase the survival of
trees and shrubs during the first few years after establishment. Cutting and spraying with ap-
proved herbicides might also be necessary to remove unwanted vegetation.
Open spaces should be inspected on an annual basis for damage by foot or vehicular traffic,
encroachment, gully erosion, and vegetation density. The effectiveness of the open space will
decrease over time as sediments accumulate. Inspectors should look for accumulated sediments so
that they can be removed before they damage vegetation. Routine maintenance includes removal
of trash and debris, repair of eroded areas, spot repair of vegetation, and mowing of the grass.
Sources of Additional information
Chesapeake Bay Local Assistance Department. 1989. Local assistance manual. CBLAD, Richmond, VA.
Northern Virginia Planning District Commission. 1987. BMP handbook for the Occoauan Watershed. Prepared for
Occoquan Basin Nonpoint Pollution Management Program. Northern Virginia Planning District Commission,
Annandale, VA.
Northern Virginia Planning District CommissiorL 1992. Northern Virginia BMP handbook A guide to planning designing
best management pratices in Northern Virginia. Northern Virginia Planning District Commission, Annandale, VA
Structural BMPs - Extended Detention Dry Basins
Definition/Purpose
Extended detention diy basins temporarily store stormwater runoff from a site and release it at
a controlled rate by use of a fixed outlet. They are designed not to have permanent standing water
and are usually dry between storm events. Extended detention dry basins control water quantity by
temporarily detaining stormwater, and they reduce downstream channel erosion by reducing the
frequency of bankfull and subbankfull flooding events. Extended detention dry basins provide some
water quality benefits by removing pollutants primarily through the settling of suspended solids.
They are designed and located to collect stormwater runoff from drainage areas and to control peak
discharges for one or more design storm frequencies.
Scope/Applicability
Extended detention dry basins can be used in locations with sufficient open space and
proper topography to allow gravity flow of stormwater to the basin and sufficient storage
without backup into surrounding areas. They can be used in combination with permanent pools,
or they can incorporate shallow marsh habitat in the normally inundated areas near their outlet
pipes to enhance pollutant removal. Extended detention dry basins are best suited for contribut-
ing drainage areas of over 30 acres and are not usually practical for areas less than 10 acres in size.
The natural hydrologic conditions and characteristics of adjacent or downstream wetlands should
Page 4-43
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
be considered in the design and placement of extended detention dry basins so that impacts to
these existing systems can be minimized. See Figure 4-16.
Design Criteria Considerations
Detention of the 2-year, 24-hour design storm for at least 40 hours with release at a rate
no greater than 50 percent of the predevelopment peak rate.
Sufficient storage for sedimentation to be effective before water leaves the basin.
Length-to-width ratio of 3:1 if possible.
Sufficient pond depth and cross-sectional area to establish low flow velocities.
Minimum slope of 2 percent on basin floors.
Minimum resuspension by reducing inflow velocities.
Native plants.
Potential Impacts to Wetlands
Benefits
Potential recharge of groundwater from extended detention ponds, benefiting baseflow-
dependent wetlands.
Reduction of stormwater sediment loads to downstream wetlands.
Potential reduction in the amount of stormwater associated pollutants entering down-
stream wetlands.
Reduction in the first-flush impact of stormwater runoff to downstream wetlands.
Maximum Elevation
vof Safety Storm
Maximum
Elevation
of Extended
Detention Pool
Aquatic Bench
Emergency Spillway
Safety
Bench
Adapted from MWCOG, 1992.
Figure 4-4 6. Schematic of an enhanced dry extended detention pond system designed to
accommodate protection of existing wetlands.
Page 4-44
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Best Management Practices
Elimination of the need for a permanent pool with habitat destruction potential.
Potential for the creation of high marsh or wet meadow wetlands within the extended
detention ponds through the incorporation of micropools.
Potential for the incorporation of complex boundaries and microtopography in the
pond design to enhance diverse vegetation and habitat. ,
Reduction in the potential for downstream wetland degradation resulting from erosion
associated with peak stormwater flows.
limitations
Reduction in the amount of surface water supplied to adjacent or downstream wet-
lands as the result of rerouting and detention.
Embedding of downstream wetland substrates as the result of the removal of coarse
sediments.
Changes to adjacent natural wetland hydroperiods.
Smothering of wetlands incorporated into extended detention ponds as a result of
increased sedimentation.
Thermal impacts to downstream wetlands resulting from the discharge of water from
extended detention ponds.
Low habitat diversity and limited structure of wetlands created in extended detention
ponds.
Maintenance Requirements
Extended detention dry basins can have relatively high maintenance burdens and costs.
Extended detention dry basins will not achieve their intended purpose unless routine and non-
routine maintenance tasks are performed on schedule. Responsibilities for maintenance need to
be clearly defined, maintenance schedules enforced, and regular inspections performed. Routine
maintenance includes mowing, debris and litter removal, erosion control, and the control of
nuisances.
Extended detention dry basins should be inspected on an annual basis to ensure that they
continue to operate as designed. The inspector should measure and record the drainage rate of
water after a storm to check that the design detention times are met. The flow control device
should be inspected regularly for evidence of clogging or too rapid release. In general, the ex-
tended detention dry pond should be inspected for structural soundness, sediment accumulation,
broken or missing parts, and trash and debris accumulation. The side slopes should be inspected
for rodent holes, tree growth, subsidence, erosion, and cracking. The spillway should be inspected
for clogging or missing rocks. The pilot channel to the upper stage, the flow path to the lower
stage, and the channel upstream and downstream of the basin should be checked for erosion
damage. The forebay/riser should be checked for sediment accumulation. Figure 4-17 indicates
typical locations for necessary maintenance access.
Trash and debris should be removed from the site. Trash should be removed from the debris
barriers when greater than 20 percent of the openings in the barrier are plugged, and it is espe-
cially important to remove floatable debris to prevent clogging of the control device or riser.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
The grass/ground cover of basins located in nonresidential areas should be moved at least
twice a year to control weeds and to discourage the growth of woody vegetation. Extended
detention dry basins located in residential areas require more frequent mowing. Dense vigorous
growth should be maintained on the bottom as well as on the sides of the extended detention dry
pond. The side slopes, emergency spillway, and embankment might also require periodic stabiliza-
tion from erosion damage.
Nonroutine maintenance includes the removal of accumulated sediments from the basin.
Accumulated sediments reduce the performance of an extended detention dry basin by gradually
reducing its capacity to treat stormwater, and by clogging the orifice or filter medium. After
sediments are removed, the area should be stabilized immediately with vegetation to prevent
sediments from clogging the control device. Other nonroutine maintenance activities include the
eventual replacement of the inlet, outlet, and riser works.
Sources of Additional information
Gibb, A., B. Bennett, and A. Birkbeck. 1991. Urban runoff quality and treatment: A comprehensive review.
Prepared for the Greater Vancouver Regional District. File No. 2-51-246(242).
Land Management Project. 1990. Artificial wetlands. BMP fact sheet #5. U.S. Environmental Protection
Agency and Rhode Island Department of Environmental Management, Land Management Project, Provi-
dence, RI.
Livingston, E., E. McCarron, C Cox, and P. Sanzone. 1993. The Florida development manual: A guide to sound
land and water management. Stormwater/Nonpoint Source Management Section Florida Department of
Environmental Regulation, Tallahassee, FL.
Milone & MacBroom, Inc. 1991. Urban stormwater quality management for public water supply watersheds.
Prepared for South Central Connecticut Regional Water Authority, New Haven, CT.
Northern Virginia Planning District Commission. 1987. BMP handbook for the Occoauan watershed. Prepared
for Occoquan Basin Nonpoint Pollution Management Program. Northern Virginia Planning District Commis-
sion, Annandale, VA
MAINTENANCE
-ACCESS
25'LANDSCAPED BUFFER
RIPRAP APRON Q,
STILLING BASIN
0
SHALLOW MARSH
(OPTIONAL)
PLAN
AUXILIARY SPILLWAYv
OUTLET RISER ,\.
FLOOD CONTROL ZONE\J\
FREaJENTLYINUNDATEDZONE\\ \
-X \ \\ >
ANTI-SEEP
COLLARS
SHALLOW MARSH
6"-12'DEEP (optional)
OUTLET
RISER
OUTFALL PROTECTION
PROFILE
Adapted from Milone & MacBroom, Inc., 1991.
Figure4-i7- Schematic ofdrypondshowingmaintenance features.
Page 4-46
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Best Management Practices
Schueler, T.R., P.A. Rumble, and M.A. Heraty. 1992, A current assessment of urban best management practices,
techniques for reducing non-point source pollution in the coastal zone. Prepared for the Metropolitan Washington
Council of Governments, Washington, DC.
Washington State Department of Ecology. 1992. Stormwater Management Manual for the Puget Sound Basin.
Publication no. 91-75. Washington State Department of Ecology, Olympia, WA.
Structural BMPs - Wet Ponds
Definition/Purpose
Wet ponds are depressions constructed by excavation and embankment procedures to store
excess runoff temporarily on a site. After a runoff event, overflow from the pond is released at a
controlled rate by an outlet device designed to release flows at various peak rates and elevations
until the design elevation of the pool is reached. Wet ponds maintain a permanent pool of water
between storm events. Wet ponds are located to collect stormwater inflows from adjacent
drainage areas and are usually designed to control peak discharges from relatively large design
storms.
Wet ponds regulate stormwater runoff from a given rainfall event by the temporary storage
of peak flows in order to mitigate quantity and quality impacts to downstream systems. Pollutant
removal in wet ponds results from the gravity settling of sediments/pollutants, the chemical
transformation and biological uptake of nutrients while water is detained in the pond, and the
infiltration of soluble nutrients through the soil profile. Extended detention time in the perma-
nent pool of wet ponds allows for increased sedimentation, transformation, and flocculation of
pollutants in the system. Decreased runoff rates from wet ponds reduce downstream channel
erosion and resultant sediment pollution. Wet ponds have been shown to be the most efficient
means of water quality protection when compared with other conventional BMPs.
Scope/Applicability
Wet ponds can be located in areas that have topographic conditions that allow for the .
gravity flow of stormwater and enough open space to allow sufficient sizing of the structure so
that it can adequately treat expected flows. Wet ponds can be used in low- and high-visibility
locations where contributing watersheds are greater than 10 acres in size or where continuous
baseflows exist to ensure dry-weather flow. They are not useful in arid regions where evapotrans-
piration exceeds rainfall, and their use is limited in areas where space is a constraint such as
densely developed urban localities. Wet ponds have been used in combination with wetlands and
other extended detention treatment methods. An extended detention wet pond is shown in
Figure 4-18.
Design criteria considerations
Extended detention of a 1-inch storm for 24 to 40 hours.
Permanent pool volume of at least 2.5 times the runoff volume generated by the mean
storm.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Sufficient volume in the permanent pool to allow for low-energy settling of sediments
between storms.
Use of pond liners in high-permeability soils.
Length-to-width ratio of 3:1 with a wedge shape.
Watershed area greater than or equal to 10 acres.
Access for maintenance equipment.
Enhanced conditions for biological treatment between storms (i.e., native vegetation in
shallow ponds).
Inlet and outlet pipes set to discharge at or below the permanent pool surface.
Stone riprap lining, plunge pools, energy dissipators, or other acceptable means should be
used below the pond outlet to prevent scouring.
Potential impacts to Wetlands
Benefits
Potential for the creation of emergent and high marsh wetlands within the wet pond.
Reduction of Stormwater sediment loads to downstream wetlands.
Potential for the incorporation of designs to enhance diverse vegetation and habitat.
Reduction in the potential for downstream wetland degradation resulting from erosion
associated with peak Stormwater flows.
Limitations
Changes to the natural hydroperiod of adjacent natural wetlands.
Reduction in the amount of surface water supplied to adjacent or downstream wetlands
as the result of rerouting and detention.
Emergency Spillway
Variable Extended
Detention Storage
uu
Reverse Extended
Detention Pipe
Adapted from Schueler, 1992.
Figure 4-18. Conceptual cross section view of an extended detention wet pond.
Page 4-48
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Best Management Practices
Potential for the introduction of pollutants to downstream wetlands during peak storm
events.
Embedding of downstream wetland substrates as the result of the removal of coarse
sediments.
Strong shifts in the trophic status of downstream communities.
Thermal impacts to downstream wetlands resulting from the discharge of water from
wet ponds.
Low habitat diversity and limited structure of wetlands created in wet ponds.
Maintenance Requirements
Maintenance requirements for wet ponds are relatively modest. Long-term performance
will be degraded, however, by the buildup of sediments. Therefore, a firmly established mainte-
nance and inspection program is required. Routine maintenance includes inspections, mowing of
the embayment and buffers, and the removal of trash and debris from the forebay.
Wet ponds should be inspected on an annual basis to ensure that they continue to operate as
designed. The inspector should monitor the water level after a storm to compare pond perfor-
mance against the design detention time. Other factors that contribute to the performance of the
pond that should be inspected are related to structural soundness, sediment accumulation,
appearance, security, and the ease of maintenance. The side slopes should be inspected for rodent
holes, tree growth, subsidence, erosion, and cracking. The barrel, spillway, and drain should be
inspected for clogging, and the forebay/riser should be checked for sediment accumulation. The
adequacy of the erosion protection measures for the channel upstream and downstream of the
basin should be noted, as well as any modifications that have occurred to the contributing
watershed or pond structure.
Trash and debris should be removed from the site as part of the periodic mowing regimen.
Maintaining a neat appearance at the site helps to discourage vandalism and illicit dumping. All
floatable debris around the riser should be removed, and the outlet should be checked for possible
clogging.
Mowing of the upper stage, side slopes, embankment, and emergency spillway is required at
least twice a year to prevent woody growth and the excessive growth of weeds. More frequent
mowing is required if the wet pond is located in a residential neighborhood. A dense vigorous
growth of grass or ground cover should be maintained around the wet pond. The side slopes,
emergency spillway and embankment might also require periodic stabilization from slumping and
erosion damage.
Nuisances associated with problem wet ponds include insects, weeds, odors, and algae. Algae
and mosquitoes can be controlled by the introduction of fathead minnows and other fish. This
practice is preferred over chemical application, especially in the case of ponds that discharge to
wetlands. Excessive growth of emergent, floating, and submerged vegetation can be mechanically
harvested or controlled with herbicides.
Nonroutine maintenance includes the removal of accumulated sediments from the basin.
Accumulated sediments reduce the performance of a wet pond basin by gradually reducing its
capacity to treat stormwater. Wet ponds require sediment removal when the storage capacity of
the permanent pool is significantly reduced.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Actual sedimentation rates depend on the size, degree of construction, and land use in the
watershed. Other nonroutine maintenance includes structural repairs and the replacement of
various inlet/outlet and riser works.
Sources of Additional information
Gibb, A., B. Bennett, and A. Birkbeck. 1991. Urban runoff quality and treatment: A comprehensive review.
Prepared for the Greater Vancouver Regional District. File No. 2-51-246(242).
Livingston, E., E. McCarron, C. Cox, and P. Sanzone. 1993. The Florida development manual: A guide to sound
land and water management. Stormwater/Nonpoint Source Management Section Florida Department of
Environmental Regulation, Tallahassee, FL.
Long Island Regional Planning Board. 1984. Nonpoint source management handbook. Long Island Regional
Planning Board, Hauppauge, NY.
Schueler, T.R. 1987. Controlling urban runoff: A practical manual for planning and designing urban BMPs.
Metropolitan Washington Council of Governments, Washington, DC.
Schueler, T.R., P.A. Kumble, and M.A. Heraty. 1992. A current assessment of urban best management practices,
techniques for reducing non-point source pollution in the coastal zone. Prepared for the Metropolitan Washington
Council of Governments, Washington, DC.
Washington State Department of Ecology. 1992. Stormwater management manual for the Puget Sound Basin.
Publication no. 91-735. Washington State Department of Ecology, Olympia, WA.
Westchester County Department of Planning. 1984. Best management practices manual for Stormwater runoff
control. Westchester County Environmental Management Council, White Plains, NY.
Structural BMPs - Constructed Wetlands
Definition/Purpose
Constructed wetlands are shallow pools constructed on nonwetland sites as part of the
Stormwater collection and treatment system. They provide growing conditions suitable for the
growth of emergent marsh plants. These systems are designed primarily for the purpose of
Stormwater management and pollutant removal from surface water flows. They are essentially a
type of wet pond with greater emphasis placed on vegetation and depth/area considerations.
Constructed wetlands are often used in sequence with a sediment basin, a forebay, or some type
of Stormwater pond.
Constructed wetlands are designed to maximize removal of pollutants from Stormwater
through physical, chemical, and biological mechanisms. They can be designed to store Stormwater
runoff temporarily, thereby lowering Stormwater quantity and quality impacts on receiving
systems including lakes, water supply reservoirs, streams, wetlands, and recharge aquifers for
water supply wells. Physical mechanisms of pollutant removal include sedimentation, filtration,
and volatilization. Chemical mechanisms include precipitation, adsorption to sediments, floccula-
tion, and transformations such as reduction. Biological mechanisms include plant and bacterial
nutrient uptake. Constructed wetlands can also be designed to allow for a wide diversity of plant
species and improved wildlife habitat.
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Best Management Practices
Scope/Applicability
Constructed wetlands can be used in locations with sufficient open space and appropriate
topography to allow gravity flow of stormwater and sufficient sizing of the structure to ad-
equately treat expected flows. They can be applied to most sites, including those with large
pollution and runoff loads, provided sufficient baseflow is available to maintain proper hydrology
to support wetland vegetation. Constructed wetlands might be useful as a retrofit for older dry
stormwater basins. It is important to remember that the hydrology of the watershed draining to
the constructed wetland must be capable of supporting the wetland. A schematic of a constructed
wetlands pond is shown in Figure 4-19.
Design Criteria Considerations
Volume should accommodate at least a 6-month, 24-hour storm for the watershed's
developed condition.
Wetland area should be greater than or equal to 2 percent of the watershed area.
Watershed of 5 acres or more.
Length-to-width ratio of 3:1 or greater; if this is not feasible, use baffles.
Vary water depth, with approximately 50 percent of the area about 0.5 ft deep and with
some open water, to provide diverse habitat.
Dry season baseflow must be adequate for vegetation maintenance, with evapotranspira-
tion considered.
Minimize short circuiting by using baffles, islands, and peninsulas to ensure a long
distance from inlet to outlet.
Incorporate islands to provide habitat and refuge for bkds.
Plant and soil pollutant removal effectiveness may vary with season.
Consider soil permeability and groundwater conditions. Lining may be necessary.
Organic soils provide best nutrient retention and plant substrate.
Vegetation should be selected for hydroperiod, climate, resistance to contaminants, stem
density (to promote sedimentation), and habitat value. Consider native vegetation.
Consider plant uptake/release of nutrients and contaminants, and possible plant harvest-
ing.
Use of forebay or other controls in "treatment train" design to pretreat runoff.
Erosion control should be employed in the forebay and at the outlet, preferably with
vegetation.
Design for easy maintenance.
Provide access for maintenance equipment.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
25% of Pond
Perimeter
Open Grass.
Safely Bench
33-Foot Wetbed Buffer /
Landscaped with Native
Trees/Shrubs lor Habitat
Schueler, 1992.
Figure 4-49. Schematic design oft
marsh system.
Gate \felves to Provide
Flexibility In Depth
Control
Use of Wetland Mulch
to Create Diversity
Constructed wetland for stormwater control with an enhanced shallow
Potential impacts to wetlands
Benefits
Reduction of flooding and erosive volocities and stormwater sediment loads to adjacent
and downstream wetlands.
Potential for the incorporation of designs to enhance diverse vegetation and wildlife
habitat in urban areas.
Reduction in the potential for downstream wetland degradation resulting from erosion
associated with peak stormwater flows.
Limitations
Changes to the natural hydroperiod of adjacent natural wetlands.
Reduction in the amount of surface water supplied to adjacent or downstream wetlands
as the result of rerouting and detention.
Smothering of vegetation in constructed wetlands resulting from sedimentation.
Potential for the introduction of pollutants to downstream wetlands during peak storm
events.
Embedding of downstream wetland substrates as the result of the removal of coarse
sediments.
Thermal impacts to downstream wetlands resulting from the discharge of water from
constructed wetlands.
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Best Management Practices
Potential takeover of vegetation by invasive aquatic nuisance plants.
Potential for blocking fish passage if constructed in stream channel.
Maintenance Requirements
Maintenance requirements for constructed wetlands receiving stormwater are high during
the first several years while vegetation is being established. Reinforcement planting and erosion
control BMPs might be necessary. Maintenance during the establishment phase involves frequent
inspection for erosion damage or subsidence on the embankment or spillway. Rills formed
through erosion should be filled and thoroughly compacted. It is important that the vegetated
cover on the embankment and spillway be dense and healthy. Mowing and fertilizing help
promote vigorous growth of plant roots that resist erosion. Mowing also prevents the growth of
unwanted woody vegetation.
Another type of maintenance that might be necessary during the initial growing season is
protection of the first year wetland vegetation growing at the water's edge and on the side slopes
from birds. Birds often feed on the carbohydrate-rich shoots of the young vegetation, a problem
referred to as "eat-out." The problem can be addressed by surrounding the open water area of the
constructed wetland with wire to limit access to the vegetation from the water, which is how the
birds get to the vegetation. The wire should be maintained until the wetland vegetation is well
established, which is usually by the second growing season.
Periodic inspections are necessary to ensure that the constructed wetland is operating as
designed. Constructed wetlands should be inspected after major storms during the first year of
establishment for the stability of banks and for flow channelization. For example, debris on
plants or dead vegetation that has fallen over should be removed to minimize damage to other
wetlands vegetation. Excessive accumulation of sediments in any part of the system should be
noted as well as any changes to the contributing watershed. The inspector should pay special
attention to the proper operation of pumps and water control structures, sealing, water level,
flow distribution, and density of vegetation during the first years of operation. Water level is the
most critical aspect of wetland plant survival within the first year after planting. Too much water
is often a greater problem than too little because the roots of plants do not receive enough oxygen.
Routine maintenance of constructed wetlands includes repair of fences, mowing of sod/
ground cover on embankments, and removal of trash accumulated in trash racks, outlet structures,
and valves. Burrowing animals may damage embankments and spillways. They can be discouraged
by including a thick layer of sand or gravel on the fill or by installing a wire screen to inhibit
burrowing. Organic matter accumulating in the wetland will eventually limit storage capacity
and the capacity to treat runoff. Accumulation of organic matter can be reduced by harvesting of
vegetation or seasonal drawdown to allow organic material to oxidize. Periodic sediment removal
from the forebay is necessary.
Mosquito problems are one of the more frequently cited drawbacks of constructed wet-
lands. Mosquitoes can be more of a problem in wetlands with tall cattails and bulrushes than
those with lower-growing vegetative forms due to the protection from predators afforded by the
taller plants. Cattails can be controlled by flooding for several weeks during the growing season
after the stems have been cut (stems need to be cut below the water level). Biological control of
mosquitoes can be enhanced by stocking the wetland with fish that are tolerant of low dissolved
oxygen conditions. Mosquitoes can also be controlled through judicious application of mosquito
larvicide using the optimum dosage level and applying only when larval density is high.
Page 4-53
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Sources of Additional information
Davis, L. 1995. A handbook of constructed wetlands, A guide to creating wetlands for: Agricultural wastewater,
domestic wastewater. Coal mine drainage, and Stormwater in the Mid Atlantic region. 5 vols. U.S. Department of
Agriculture, U.S. Environmental Protection Agency, and Pennsylvania Department of Environmental Resources.
Gibb, A., B. Bennett, and A. Birkbeck. 1991. Urban runoff quality and treatment: A comprehensive review.
Prepared for the Greater Vancouver Regional District. File no. 2-51-246(242).
Hammer, D. A. 1992. Creating freshwater wetlands. Lewis Publishers, Boca Raton, EL.
Kadlec, R. and R. Knight. 1996. Treatment wetlands. Lewis Publishers, Boca Raton, EL.
Land Management Project. 1990. Artificial wetlands. BMP fact sheet #3. U.S. Environmental Protection
Agency and Rhode Island Department of Environmental Management, Land Management Project,
Providence, RI.
Schueler, T.R. 1987. Controlling urban runoff: A practical manual for planning and designing urban BMPs.
Metropolitan Washington Council of Governments, Washington, DC.
Washington State Department of Ecology. 1992. Stormwater management manual for the Puget Sound Basin.
Publication no. 91-75. Washington State Department of Ecology, Olympia, WA.
Structural BMPs - Porous Pavement and Concrete Grid
Pavement
Definition/Purpose
Porous pavement is an alternative to conventional pavement designed to minimize surface
runoff. It may be constructed of asphalt or concrete and is similar to regular paving material
except that a larger-sized aggregate is used in the asphalt or concrete mixture to provide a high-
void course. Porous pavement is composed of four layers: the pavement course, the upper filter
course, a stone reservoir, and a lower filter course and filter fabric lining over the underlying soil
(see Figure 4-20).
A similar practice is concrete grid pavement, where modular, interlocking concrete blocks
having openings are used (see Figure 4-21). Runoff that permeates the porous pavement surface
enters an underground stone reservoir and gradually exfiltrates from the reservoir into the
surrounding subsoil.
Porous pavement can help to restore or maintain predevelopment hydrology by reducing the
volume of Stormwater runoff produced after development relative to runoff volumes generated
from roads and parking lots paved with conventional surfaces. By increasing the amount of
infiltration, porous pavement can provide groundwater recharge, low flow augmentation, and
stream bank erosion control through reduction of peak discharges. Pollutants are removed by
absorption, straining, and microbial decomposition as Stormwater seeps through the subsoil.
Sediments and particulate-associated pollutants are removed in the underground stone reservoir.
The use of porous pavement has added advantages in that it reduces land consumption, reduces or
eliminates the need for curb and gutters and conveyance systems, and reduces the tendency of
vehicles to hydroplane and skid. Other benefits can include storm detention and preservation of
water supplies to the vegetation around parking areas.
Page 4-54
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Best Management Practices
Scope/Applicability
The use of porous pavement is constrained to sites having deep and permeable soils, slopes
less than 5 percent, restricted truck traffic, and suitable adjacent land uses. The use of porous
pavement can also be restricted in regions with colder climates, arid regions or regions with high
wind erosion rates, and areas having sole-source aquifers. It is generally used only for parking lots
(between 0.25 acre and 10 acres in size) and lightly used access roads. Porous pavement is used
when the size of the development, or the lack of available space, limits the use of other BMPs. It
has limited retrofit capability because most soils in urbanized areas have been previously modified
to the extent that they are not capable of providing adequate infiltration rates. Porous pavement,
designed with an underdrain, can be used in areas where underlying soils, groundwater depth, or
bedrock restrict the ability of runoff to be disposed of by infiltration. Porous pavement reservoirs
with underdrains serve as underground detention facilities.
Reverse Perforated Pipe Only Discharges^ SsSi
Stone Reservoir Drains in 48-72 Hours or
352
Bern) Keeps Off-site
Runoff and Sediment
Out, Provides
Temporary Storage
Gravel
Course or
6-Inch
Sand Layer
Schueler, 1992.
Detail of cross section.
UndMurbod Soils with a Final Infiltration Rate Greater Than O27 Inches/Hour,
Preferably 0.50 Inches/Hour or More
Porous Pavement Course
(2.5-4.0 Inches Thick)
Filter Course
(0.5 Inch Diameter Gravel,
1.0 Inch Thick)
Stone Reservoir
(1.5-3.0 Inch
Diameter Stone)
Depth Variable Depending
on the Storage Volume
Needed, Storage Provided
by the Void Space Between
Stones
i «a»-» yor fs>f-.-
,'' ."Y :. * "-'- f «> Filter Course (Gravel, 2Hnch.es Deep)
' "- '^ Filter Fabric Layer
} Undisturbed Soli
Schueler, 1992.
Figure 4-20. Schematic cross section of a porous pavement system with storage reservoir.
Page 4-55
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Design Criteria Considerations
Field-verified infiltration rates greater than or equal to 0.5 inch per hour.
Site area of less than 10 acres with minimal contributions of runoff from the surrounding
watershed.
Slopes less than 5 percent.
Minimum clearance of 3 ft from the bottom of the system to the groundwater table.
Filter fabric lining to prevent the upward piping of underlying clays.
Reservoir of variable depth containing clean, washed, 1- to 2-inch-diameter stone.
Overlying filter course of 0.5- to 1-inch gravel.
Use of underdrains if well-drained conditions are lacking at a site.
20-ft-wide grass buffer around the pavement to filter pollutants from runoff contributed
by adjacent areas, if applicable.
Castellated Unit
Poured-in-Place Slab
Modular Unit
Lattice Unit
State of Washington. 1992.
Figure 4-21. Variations of concrete grid pavement.
Page 4-56
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Best Management Practices
Maintenance
Porous pavement requires quarterly vacuum sweeping and/or jet hosing to maintain poros-
ity and prevent clogging. Sediments will accumulate Where water is concentrated. These can be
removed by a vacuum cleaning street sweeper equipped with a brush followed by jet hosing.
Porous asphalt and concrete require no more additional maintenance than conventional paving
materials. Buffer strips surrounding the pavement will need mowing. Surfaces paved with
modular concrete blocks with open lattice might require mowing of grass growing up between the
lattice. Mowing is seldom required in areas of frequent traffic. Poured-in-place concrete grid
pavements can be plowed as long as the plow blade is set high enough to prevent damage to grass.
Fertilizers and deicing chemicals should not be used on concrete grid pavement because these
chemicals can damage the concrete. The application of abrasive material, such as sand or ash, in
times of heavy snowfall should be avoided due to the potential for clogging of the surface.
Cleaning techniques are effective only in restoring porous pavement that has reductions in
permeability of less than about 25 percent. Clogging may also be alleviated by drilling 0.5-inch
holes through the pavement every few feet. If severe clogging should occur, complete replacement
is required. Potholes and cracks can be repaired using conventional nonporous patching com-
pounds as long as the cumulative area being patched is minimal.
Porous pavement should be inspected several times in the first few months after construc-
tion and annually thereafter. Inspections of the pavement should be scheduled after major storms
so that areas of standing water can be identified. Water standing on the pavement might indicate
local or widespread clogging. The condition of the buffer strips adjacent to the pavement should
also be checked at the time of inspection.
potential impacts to wetlands
Benefits
Reduction in the amount of stormwater-associated pollutants entering adjacent wet-
lands.
Reduction of stormwater sediment loads to adjacent wetlands.
Reduction in the potential for adjacent wetland degradation resulting from erosion
associated with peak stormwater flows.
Potential recharge of groundwater from infiltration, benefiting adjacent basefiow-
dependent wetlands.
limitations
Might not adequately attenuate concentrated peak stormwater flows to adjacent
wetlands.
Possible reduction in the amount of surface water supplied to adjacent surface-flow-
dependant wetlands as a result of rerouting.
Not appropriate for high traffic areas or surfaces receiving frequent heavy vehicle traffic.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Sources of Additional information
Commonwealth of Virginia 1990. Best management practices handbook - Urban. Published by the Virginia
Department of Conservation and Recreation, Division of Soil and Water Conservation. Richmond, VA.
Livingston, E., E. McCarron, C. Cox, and P. Sanzone. 1993. The Florida development manual: A guide to sound
land and water management. Stormwater/Nonpoint Source Management Section Florida Department of
Environmental Regulation, Tallahassee, FL.
Schueler, T.R. 1987. Controlling urban runoff: A practical manual for planning and designing urban BMPs.
Metropolitan Washington Council of Governments, Washington, DC.
Schueler, T.R., PA. Rumble, and MA. Harity. 1992. A current assessment of urban best management practices:
Techniques for reducing non-point source pollution in the coastal zone. Technical guidance to implement section
6217(g) of the Coastal Zone Management Act. Prepared for the U.S. Environmental Protection Agency,
Office of Wetlands, Oceans, and Watersheds, Washington, DC.
Urbonas, B., and P. Stahre, 1993. Stormwater: Best management practices and detention for water quality,
drainage, and CSO management. PTR Prentice Hall, Englewood Cliffs, NJ.
Washington State Department of Ecology. 1992. Stormwater management manual for the Puget Sound Basin.
Publication no. 91-75. Washington State Department of Ecology, Olympia, WA.
Structural EMPs - Oil/Grit Separators or Water Quality Inlets.
Definition/Purpose
An oil/grit separator or water quality inlet is an underground concrete vault that can have
from one to three chambers. These structures are designed to remove sediments and hydrocarbons
from Stormwater runoff associated with roads and parking lots before it is discharged into the
storm sewer system or an infiltration BMP. Several different designs, which vary in their purpose,
removal mechanisms, space requirements, and Stormwater retention capacities, are used. Some
are designed simply for spill control and have limited capacity to treat the dispersed oil found in
Stormwater runoff from parking lots. Spill control oil/water separators consist of a chamber with
a submerged orifice that allows the oil to float at the top of the chamber, where it can be removed.
Other separator designs have multiple chambers and use sophisticated equipment to remove
oil from the surface and particles settled at the bottom. The American Petroleum Institute (API)
oil-water separator and the Coalescing Plate Separator (CPS) are two designs used in the State of
Washington. The hydraulic conditions for oil removal by the API separator are promoted by
baffles. The CPI separator contains a series of fiberglass or polypropylene plates that promote the
process of oil separation. Three-chambered oil/grit separators typically contain permanent pools
of water and are designed to remove oils by providing long contact times with particles so that
sorption onto particles will take place and the subsequent removal by gravity settling will occur.
A recently developed design in Canada includes a built-in diversion (bypass) structure. This
feature allows 80 to 90 percent of all rain hours (typically considered to capture most "first flush"
events) to enter the treatment chamber. The larger, problem-causing (flushing) storms (10 to 20
percent of all rain hours) are diverted around the treatment chamber.
Page 4-58
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Best Management Practices
Oil/grit separators are used to remove oil, grease, trash, and debris from runoff originating
from heavily trafficked areas such as gas stations, public works, transportation maintenance
facilities, industrial yards, loading areas, or other areas where hydrocarbon pollutant loads are
expected to be significant. Water quality inlets are frequently used to pretreat runoff before it is
conveyed through the storm drain network, or before treatment by a local infiltration BMP such
as an infiltration trench. Oil/grit separators provide minimal groundwater recharge, low flow
augmentation, peak runoff attenuation, or stream bank erosion control benefits. Figure 4-22
shows two views of a typical oil/grit separator.
Scope/Applicability
Oil/grit separators, when used alone, are restricted to highly impervious catchments of small
size (less than or equal to 2 acres) such as service stations, parking lots, convenience stores', and
fast food outlets. Oil/grit separators are adaptable for use in all regions of the country and are
frequently used as part of a series of BMPs. They are commonly used as pretreatment devices for
infiltration BMPs. Oil/grit separators can also be used as a pretreatment device for pond-type
BMP systems, to prevent oily sheens from developing on pond surfaces, and to remove trash.
Design Criteria considerations
Typically serve an area of less than 1 acre.
Horizontal velocity less than 3 ft per minute or 15 times the rise rate, whichever is
smaller.
Depth 3 to 8 ft.
Width 6 to 16 ft.
Use of baffles to prevent resuspension.
Removal covers that allow access for observation and maintenance.
Maximum pool volume in three chambered separators in the first and second chamber.
Chambers should be sized to provide at least 400 ft of wet storage per contributing acre.
Use of trash racks welded to the end plates between the first and second chambers in
multiple-chambered separators.
Upstream flow control to prevent the flushing of accumulated pollutants during major
storms.
Maintenance
Although the structural failure rate of water quality inlets is very low relative to other
stormwater treatment devices, regular removal of accumulated sediments' and debris is critical to
achieving any degree of pollutant removal effectiveness. Material that accumulates in the oil/grit
separator must be removed promptly or it might be flushed from the device during the next storm,
resulting in a pulse of highly concentrated contaminants to receiving waters. Cleanouts should be
performed at least twice a year, and weekly inspections are recommended. Separators should be
cleaned in time for the rainy season and after the first storm of the season.
Page 4-59
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Top View Overflow
Pipe
Manhole* f**\
tor Clean-out
Stormdmln
Met
*
/*«« \
d Jl'b^
I
h
r
, ^
V
Perforated Pipe Intel
Three-dumber Water Quality toilet
Underground Trench
Sid* View
Overflow Pipe
Impermeable Filter doth T«»tWelI
a-lncti Inverted
Orifices Elbow
e-ktchSind Liver
Schueler. 1987.
Figure 4-22. Two views of an oil/grit separator.
Limitations
Primarily function as a water quality BMP and might not adequately attenuate concen-
trated peak Stormwater flows to adjacent wetlands.
Possible reduction in the amount of surface water supplied to adjacent surface-flow-
dependent wetlands as a result of rerouting.
Potential negative impacts to adjacent or downstream wetlands from pollutants
associated with improperly maintained separators.
Sources of Additional Information
Gibb, A, B. Bennett, and A. Birkbeck. 1991. Urban runoff quality and treatment: A comprehensive review.
Prepared for the Greater Vancouver Regional District, the Municipality of Surrey, British Columbia Ministry
of Transportation and Highways, and British Columbia Ministry of Advanced Education and Training
Document no. 2-51-246 (242).
Romano, E 1990. Oil and water don't mix: The application of oil-water separation technologies in Stormwa-
ter quality management. Published by the Office of Water Quality, Municipality of Metropolitan Seattle
Seattle, WA. '
Schueler, T.R., PA. Kumble, and MA. Harity. 1992. A current assessment of urban best management
practices: Techniques for reducing non-point source pollution in the coastal zone. Technical guidance to implement
section 6217(g) of the Coastal Zone Management Act. Prepared for the U.S. Environmental Protection
Agency, Office of Wetlands, Oceans, and Watersheds, Washington, DC.
Page 4-0
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Best Management Practices
Schueler, T.R. 1987. Controlling urban runoff: A practical manual for planning and designing urban BMPs.
Metropolitan Washington Council of Governments, Washington, DC.
Ontario Ministry of Transportation and National Watef Research Institute, Environment Canada. 1994.
Stormwater management facilities inventory study. Burlington, Ontario.
Washington State Department of Ecology. 1992. Stormwater management manual for the Puget Sound Basin.
Publication no.91-75. Washington State Department of Ecology, Olympia, WA.
Structural BMPs - Level Spreaders
Definition/Purpose
A level spreader is a hydraulic device used to convert channelized flows from an outlet pipe or
culvert to sheet flow by causing the stormwater to spread out through a rock-lined trench before
discharging over a berm, thereby dissipating energy that could cause erosion of downstream areas.
The trench or channel is lined with filter fabric and covered with riprap, gabions, or a slope mattress
to retard flow and provide turbulence. Energy is dissipated as stormwater spreads out over the rocks
and then over the top of the berm. The berm is usually covered with riprap. Higher runoff velocities
may be treated by placing gabions in the trench instead of riprap.
Level spreaders are located at the outlet of channels or culverts and are used to protect a
receiving channel or downstream area from erosion by dissipating fluid energy. Level spreaders
can be used to attenuate erosive flow velocities in stormwater discharges before they reach a
vegetated BMP. They provide a moderate amount of coarse sediment removal and infiltration, but
they are primarily a flow control device rather than a stormwater treatment system. A level
spreader is shown in Figure 4-23.
Scope/Applicability
Level spreaders are used for moderate flows in small drainage areas. One of their primary
applications is to convert channelized flows from culverts to sheet flows upstream of a vegetated
filter strip or grassed swale. They should be constructed in undisturbed soils and discharge to
stabilized areas.
Design Criteria considerations
Grass-lined trench used for flows up to 5 ft per second (ft/s).
Riprap used for flows between 5 and 12 ft/s (median stone size of 8 inches, minimum
thickness of 1 ft used for 5- to 8-ft/s flows; median stone size of 16 inches, minimum
thickness 2 ft used for 8- to 12-ft/s flows).
Riprap-lined channel not suitable for velocities greater than 12 ft/s or pipe diameters
greater than 3 ft.
Gabion rock mattress or slope mattress required to transmit flows of very high energy
(between 12 and 20 ft/s).
Adjust dimensions for varying pipe sizes, flows, and velocities.
Page 4-61
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Maintenance
Level spreaders require inspection and possible repair after large storms.
Potential impacts to wetlands
Benefits
Reduction in the potential for adjacent wetland degradation resulting from erosion
associated with peak stormwater flows.
Possible reduction of stormwater sediment loads to adjacent wetlands.
Possible reduction in the amount of stormwater-associated pollutants entering adj acent
wetlands.
Limitations
Primarily a flow control device and might not adequately improve the water quality of
stormwater flows to adjacent wetlands.
Might not adequately attenuate concentrated peak stormwater flows to adjacent
wetlands.
DIRECTION OF FLOW
ENDWALL
MODIFIED RIPRAP
TOP OF BERM
TO BE LEVEL
EXISTING GRADE
OUTLET PIPE
(DIAMETER-D)
ENERGY DISSIPATOR AS NEEDED
ENDWALL
OUTLET PIPE
TIE INTO GRADE
Adapted from Milone & MacBroom, Inc., 1991.
Figure 4-23. Two views of a level spreader.
TOP OF BERM
MODIFIED RIPRAP
PLAN
Page 4-62
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Best Management Practices
Sources of Additional information:
Chow, V.T, 1978. Open channel hydraulics. Bureau of Reclamation. Hydraulic design of stilling basins and energy
dissipators. Document No. EM 25.
Livingston, E., E. McCarron, C. Cox, and P. Sanzone. 1993. The Florida development manual: A guide to sound
land and water management. Stormwater/Nonpoint Source Management Section Florida Department of
Environmental Regulation, Tallahassee, EL.
Milone & MacBroom, Inc. 1991. Urban stormwater quality management for public water supply watersheds: A
guide to nonpoint source pollution and mitigation. Prepared for the South Central Connecticut Regional Water
Authority, New Haven, CT.
U.S. Army Corps of Engineers. 1970. Hydraulic design offload control channels. Document no. EM 1110-2-
1601.
U.S. Department of Transportation, Federal Highway Administration. 1983. Hydraulic design of energy
dissipators for culverts and channels. Hydraulic Engineering Circular no. 14.
Washington State Department of Ecology. 1992. Stormwater management manual for the Puget Sound Basin.
Publication no. 91-75. Washington State Department of Ecology, Olympia, WA.
Structural BMPs - French Drains
Definition/Purpose
A French drain is a type of exfiltration system that consists of a perforated pipe drain placed
in a deep pit or trench that is filled with coarse open-grade rock. The trench is lined with filter
fabric and can be extended out laterally from the roadway to increase its water holding capacity.
Water exfiltrates from the trench and into the surrounding soil. Dutch drains are similar to French
drains except that water enters the Dutch drain through a cast iron grate at the trench surface
instead of from a perforated pipe. Both French drains and Dutch drains are used to store runoff
until it can percolate into the ground.
Scope/Applicability
French drains require permeable, well-drained soils. Soil permeability should be sufficient to
provide a reasonable rate of infiltration, and the offset of the water table from the base of the
trench facility should be enough to prevent pollution of the groundwater. Like other infiltration
practices, installation of a catch basin ahead of the drain will help prevent clogging by coarse
sediment and debris.
French drains are typically used in areas where space is restricted. They are normally used to
catch runoff from parking lots, roadways, and roof drains. They are not recommended where
runoff contains a high volume of suspended materials. Presettling, filtering, and oil and grease
separators are recommended for use with French drains if high volumes of suspended materials are
present in the runoff.
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Design criteria Considerations
Location in suitable soils with infiltration rates of at least 0.5 inch per hour.
Clearance of 6 to 10 inches between the trench bottom and the seasonal high groundwa-
ter level.
Overflow pipe capable of handling at least a 25-year storm event.
Sediment traps located at least every 150 ft for a French drain.
Complete drainage within 3 days after a storm to maintain aerobic conditions in the
trench.
Presettling or filtering of stormwater to remove coarse sediments.
Sizing of the trench based on volume of runoff to be controlled.
Use of observation wells to monitor performance.
Maintenance
Newly constructed French drains should be inspected quarterly after initial installation and
after large rainstorms. The frequency of inspections may be decreased after the performance of
the drain is verified, but inspections should be conducted on at least a yearly basis. Observation
wells should be monitored to observe the functioning of the drain. If a filter strip precedes the
drain, it should be inspected for patchy vegetation and erosion or signs of channelized flows.
Sediment that accumulates in the top foot of stone or at the inlet should be checked at the
time of inspection and removed if infiltration rates have been reduced. Sediment that has col-
lected in the sediment trap or pretreatment inlet should be removed periodically.
Potential impacts to Wetlands
Benefits
Reduction in the amount of stormwater-associated pollutants entering adjacent wet-
lands.
Reduction of stormwater sediment loads to adjacent wetlands.
Reduction in the potential for adjacent wetland degradation resulting from erosion
associated with peak stormwater flows.
Potential recharge of groundwater from infiltration, benefiting adjacent baseflow-
dependent wetlands.
Limitations
Might not adequately attenuate concentrated peak stormwater flows to adjacent
wetlands.
Possible reduction in the amount of surface water supplied to adj acent surface-flow-
dependant wetlands as a result of rerouting.
Page 4-64
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Best Management Practices
Sources of Additional information
Commonwealth of Virginia 1990. Best management practices handbook - Urban. Published by the Virginia
Department of Conservation and Recreation, Division of Soil and Water Conservation.
Dennis, J., J. Noel, D. Miller, C. Eliot. 1989. Phosphorus control in lake watersheds: A technical guide to
evaluating new development. Maine Department of Environmental Protection, Augusta, ME.
Livingston, E., E. McCarron, C. Cox, and P. Sanzone. 1993. The Florida development manual: A guide to sound
land and water management. Stormwater/Nonpoint Source Management Section Florida Department of
Environmental Regulation, Tallahassee, FL
Tahoe Regional Planning Agency. 1988. Water quality management plan for the Lake Tahoe Region: Handbook of
best management practices. Vol. 2.
Washington State Department of Ecology. 1992. Stormwater management manual for the Puget Sound Basin.
Publication no. 91-75. Washington State Department of Ecology, Olympia, WA.
Structural BMPs - Dry Wells or Roof Downspout Systems
Definition/Purpose
Dry wells are infiltration pits used primarily to collect rooftop runoff from residential or
commercial buildings, although they can be used to drain small parking lots. Dry wells may be
constructed similar to infiltration trenches, using a filter fabric-lined pit filled with gravel, or
they can consist of an underground perforated concrete tank lined with gravel. The interior of the
perforated concrete structure can be filled with coarse gravel to provide structural stability. Some
dry well designs incorporate an outlet pipe leading to a drain field.
Dry wells can be used to reduce the amount of runoff collected at storm sewers and storm-
water treatment facilities, especially when runoff from roofs is expected to be relatively clean.
Dry wells increase infiltration and therefore help to recharge groundwater, provide base flow in
streams, and reduce peak runoff volumes and stream bank erosion.
scope/Applicability
Dry wells are suitable for use in areas where the subsoils are sufficiently permeable to
provide reasonable infiltration rates and where there is sufficient offset to the groundwater. Their
use is restricted to small sources of runoff such as from roof drains, small parking lots, and tennis
courts. Roof downspout systems may be used to replace direct connections to sanitary sewers or
storm sewers. They are adaptable to retrofitting in subdivisions because they are small, inexpen-
sive, and relatively simple to install. Because dry wells provide minimal treatment of roof runoff,
they should not be used in areas where air deposition of pollutants constitutes a major portion of
the nonpoint source pollutant loads. A typical dry well/infiltratrion pit is shown in Figure 4-24.
In areas where runoff contains high concentrations of suspended materials, a method of settling
or pretreating runoff that filters out particles should be provided. Dry wells may be installed
under pavement if they are equipped with a small yard drain or grate-covered catch basin to
channel any overflow away from the overlying pavement.
Page 4-65
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Design criteria Considerations
Location in suitable soils having sufficient infiltration rates, preferably greater than 0.5
inch per hour.
Water table offset of at least 3 ft from the bottom of the well.
Detention time between 48 to 72 hours to allow for adequate pollutant removal.
Complete drainage of well within 3 days to maintain aerobic conditions.
Use of an observation well to monitor performance.
Filter fabric wrapped completely around the aggregate rock.
Length not to exceed 100 ft from the inlet sump.
Line pits for precast concrete dry wells with a minimum of 1 ft of 0.75-inch stone.
Avoid placement under pavement whenever possible.
Overflow drain for wells that are located beneath the pavement.
Maintenance
Dry wells and infiltration pits should be inspected frequently for proper drainage upon
completion of construction and annually thereafter once performance of the device has been
verified. Maintenance and inspection practices differ between dry wells and infiltration pits. Dry
wells require periodic maintenance and inspection to prevent clogging and eventual failure.
Filtering the stormwater through a fine mesh geotextile material will remove sediments and
prevent premature clogging. The cap on a perforated concrete dry well can be removed for water
level inspection and sediment removal. If the dry well becomes clogged, the rocks inside the
concrete well will need to be removed. Sediments blocking the openings in the perforated lining
should also be removed. After the rocks are removed, the well should be tested for drainage. If
drainage rates are unsatisfactory, the pre-cast concrete well might have to be removed. The pit
itself might need to be enlarged if the soil adjacent to the well has become clogged. The dry well
should then be rebuilt using dean rocks.
The maintenance of dry wells and infiltration pits is similar to that for an infiltration
trench. An observation well installed in an infiltration pit will facilitate the inspection of water
levels after storms. Frequent inspections are required during the rainy season. The accumulation
of sediments in the top foot of stone aggregate or the surface inlet should also be monitored on
the same schedule as the observation well to check for surface clogging. Clogging of the device is
usually due to the accumulation of sediments between the upper layer of stone and the protective
layer of filter fabric. When infiltrative capacity is significantly reduced, sediment should be
removed from the top of the infiltration pit by removing the stone, replacing the filter fabric, and
washing or replacing the stone.
Potential impacts to Wetlands
Benefits
Reduction in the potential for adjacent wetland degradation resulting from erosion
associated with peak stormwater flows.
Page 4-66
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Best Management Practices
Side View
Splaih Block Cap with Lock
VOK
12 Inches to Dry wall
Dry Well
Inlet Pipe
Filler Fabric
Lines Top.
Bottom end
Sides of Dry
Well
_ .|9_S ° ° 2_p;°
O O O O O Oln n
12 Inches to
Perforation
Building
Foundation
Test Well
ol Perforated
PVC Pipe.
Anchored with
Rebar
10 Foot
Minimum
Setback
Adapted from Milone & MacBroom, Inc., 1991.
figure. 4-24. Dry well/infiltration pit.
Possible reduction in sediment transport to adjacent wetlands resulting from reduced
overland flow.
Potential recharge of groundwater from infiltration, benefiting adjacent baseflow-
dependent wetlands.
Limitations
Might not adequately attenuate concentrated peak stormwater flows to adjacent wetlands.
Possible reduction in the amount of surface water supplied to adjacent surface-flow-
dependent wetlands as a result of rerouting.
May not adequately improve the water quality of stormwater flows to adjacent wetlands.
Sources of Additional information
Commonwealth of Virginia 1990. Best management practices handbook - Urban. Published by the Virginia
Department of Conservation and Recreation, Division of Soil and Water Conservation.
Page 4-67
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
Livingston, K, E. McCarron, C. Cox, and P. Sanzone. 1993. The Florida development manual: A guide to sound
land and water management. Stormwater/Nonpoint Source Management Section Florida Department of
Environmental Regulation, Tallahassee, FL.
Schueler, T.R. 1987. Controlling urban runoff: A practical manual for planning and designing urban BMPs.
Metropolitan Washington Council of Governments, Washington, DC.
Urbonas, B., and P. Stahre, 1993. Stormwater: Best management practices and detention for water quality,
drainage, and CSO management. PTR Prentice Hall, Englewood Cliffs, NJ.
Washington State Department of Ecology. 1992. Stormwater management manual for the Puget Sound Basin.
Publication no. 91-75. Washington State Department of Ecology, Olympia, WA.
Structural BMPs - Exfiltration Trenches
Definition/Purpose
Exfiltration trenches are a series of underground slotted pipe sections that temporarily store
Stormwater while it exfiltrates into the underlying soil through perforations or slots in the pipe. A
restrictor plate is placed at the end of the exfiltration pipe that controls the flow of water out of
the pipe by using a high-level overflow device or a restrictive orifice. Exfiltration trenches require
pretreatment of runoff to remove large particles of sediment and debris that may clog the pipes.
Scope/Applicability
Exfiltration trenches are used to provide groundwater recharge and a modest amount of
temporary runoff storage. They are frequently used under parking lots to save space and have the
advantage over infiltration basins of being hidden from sight. They can be used in situations where
basins are visually unacceptable. Exfiltration trenches provide some reduction in peak flows espe-
cially if they are oversized to store runoff. Pollutants are filtered out as water passes through the soil
under the system. Exfiltration trenches may be applied in moderately and well drained soils on low
to moderate slopes. Two views of an exfilteration system are shown in Figure 4-25.
_J
1
PIPE
SIZE
k
~1
-S---B -B----S---H--
---<= t=> ca.__
SLOTTED PIPE SECTION
Adapted from Milone & MacBroom, Inc., 1991.
Figure 4-2$. Two views of an exfiltration system.
RESTRICTOR PLATE with High Level
Overflow or Restrictive Orifice
-EXFILTRATIVE PERFORATIONS
OR SLOTS
END SECTION
Page 4-68
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Best Management Practices
Design criteria Considerations
Two-to 4-ft offset from the pipe invert to groundwater.
Two- to 4-ft offset to bedrock.
Settle or filter runoff to remove solids.
Level placement of pipes with no slope.
Size for 0.5-inch runoff minimum before overflow.
Use in combination with a stone bed to increase storage capacity.
Maintenance
Exfiltration trenches require preventive maintenance to function effectively. Frequent
cleanout of sediment traps and the maintenance or replacement of settling or filtering measures
might be necessary. If clogging of the facility occurs, replacement of the exfiltration trench might be
required.
Potential impacts to wetlands
Benefits
Reduction in the amount of stormwater-associated pollutants entering adjacent wetlands.
Reduction of stormwater sediment loads to adjacent wetlands.
Reduction in the potential for adjacent wetland degradation resulting from erosion
associated with peak stormwater flows.
Potential recharge of groundwater from infiltration, benefiting adjacent baseflow depen-
dent wetlands.
Limitations
Might not adequately attenuate concentrated peak stormwater flows to adjacent wetlands.
Possible reduction in the amount of surface water supplied to adjacent surface-flow-
dependent wetlands as a result of rerouting.
Sources off Additional information
Livingston, E., E. McCarton, C. Cox, and P. Sanzone. 1993. The Florida development manual: A guide to sound
land and water management. Stormwater/Nonpoint Source Management Section Florida Department of
Environmental Regulation, Tallahassee, FL
Milone & MacBroom, Inc. 1991. Urban stormwater quality management for public water supply watersheds: A guide
to nonpoint source pollution and mitigation. Prepared for the South Central Connecticut Regional Water Authority,
New Haven, CT
Page 4-69
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Protecting Natural Wetlands: A Guide to Stormwater Best Management Practices
EMPs in Series
Definition/Purpose
BMPs in series incorporate several stormwater treatment mechanisms in a sequence to
enhance the treatment of runoff. Some examples of serial BMPs include the use of multiple pond
systems, the combination of vegetated filter strips with grassed swales and detention ponds, and
the combination of grassed swales or vegetated filter strips with infiltration trenches.
By combining structural and/or nonstructural treatment mechanisms in series rather than
using a single method of treatment for stormwater runoff, the levels and reliability of pollutant
removal can be improved. By using serial BMPs, a single desired facility that might not provide the
necessary level of stormwater treatment without sequencing can be used. The effective lifetime
of a BMP can be increased by combining it with a pretreatment device, such as a grassed swale, to
remove suspended particulates prior to treatment in the downstream unit. Sequencing of BMPs
can also reduce the potential for resuspension of deposited sediments by reducing flow energy
levels or by providing longer flow paths for runoff. An example of using BMPs in series is shown
in Figure 4-26.
Scope/Applicability
The feasibility of using serial BMPs on a site depends on the characteristics of the individual
components in the sequence.
Top View
Side View
Dripline of Tree Should
Not Extend Over Trench
Berm (Grassed)
Slope of
Parking Lot
~\
Cars
Slotted Curb Spacers
Slotted Curbs Act
as a Level Spreader
Filter Strip
Directly Abuts
Pavement
Storm Drain
(If Partial Exfiltration)
Protective Filter
Cloth Layer
Sand Filter
Adapted from Schuster, 1991.
Figure 4-26. Example of BMPs in series.
Page 4-70
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Best Management Fractices
Design Criteria considerations
Design criteria considerations depend on the requirements of the individual BMPs. The
least expensive and most easily maintained component should be placed at the most upstream
position in the series.
Maintenance Requirements
The maintenance requirements for serial BMPs depend on the requirements of the indi-
vidual components of the system. (Refer to the individual BMP fact sheets.) A firmly established
maintenance and inspection program that addresses both routine and nonroutine tasks is neces-
sary to ensure that the system functions as designed.
The placement of the least costly and most easily maintained BMP at the most upstream
position in the series can reduce the maintenance requirements for the downstream components
in the system. If the overall system is designed properly, the cost for maintenance of the indi-
vidual components of the system can be reduced.
Potential impacts to wetlands
The potential impacts resulting from the placement of serial BMPs above, adjacent to, or
within wetlands will depend on the components of the system. The potential positive or negative
impacts of the individual components should be considered. The potential impacts of the indi-
vidual components of the serial BMP should then be evaluated as a whole to determine their
possible impact to adjacent or downstream wetlands.
Sources of Additional information
Northern Virginia Planning District Commission. 1987. BMP handbook for the Occoquan Watershed. Prepared
for Occoquan Basin Nonpoint Pollution Management Program. Northern Virginia Planning District Commis-
sion, Annandale, VA.
Northern Virginia Planning District Commission. 1992. Northern Virginia BMP handbook: A guide to planning
designing best management pratices in Northern Virginia. Northern Virginia Planning District Commission,
Annandale, VA.
Schueler, T.R., P.A. Kumble, and M.A. Heraty. 1992. A current assessment of urban best management practices,
techniques for reducing non-point source pollution in the coastal zone. Prepared for the Metropolitan Washington
Council of Governments, Washington, DC.
Page 4-71
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