AH
iOW OF CONSTRU
LANDS
a guide to creating wetlands for:
GRICULTURAL WASTEWATER
DOMESTIC WASTEWATER
COAL MINE DRAINAGE
STORMWATER
in the Mid-Atlantic Region
OLUME5: STORMWATER
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ACKNOWLEDGMENTS
Many people contributed to this Handbook. An Interagency Core Group provided the initial impetus for the Handbook, and later provided
guidance and technical input during its preparation. The Core Group comprised:
Carl DuPoldt, USDA - NRCS, Chester, PA
Robert Edwards, Susquehanna River Basin Commission,
Harrisburg, PA
Lamonte Garber, Chesapeake Bay Foundation, Harrisburg, PA
Barry Isaacs, USDA - NRCS, Harrisburg, PA
Jeffrey Lapp, EPA, Philadelphia, PA
Timothy Murphy, USDA - NRCS, Harrisburg, PA
Glenn Rider, Pennsylvania Department of Environmental
Resources, Harrisburg, PA
Melanie Sayers, Pennsylvania Department of Agriculture, Harrisburg, PA
Fred Suffian, USDA - NRCS, Philadelphia, PA
Charles Takita, Susquehanna River Basin Commission, Harrisburg, PA
Harold Webster, Penn State University, DuBois, PA.
Many experts on constructed wetlands contributed by providing information and by reviewing and commenting on the Handbook. These
individuals included:
Robert Bastian, EPA .Washington, DC
William Boyd, USDA - NRCS, Lincoln, NE
Robert Brooks, Penn State University,
University Park, PA
Donald Brown, EPA, Cincinnati, OH
Dana Chapman, USDA - NRCS, Auburn, NY
Tracy Davenport, USDA - NRCS, Annapolis,
MD
Paul DuBowy, Texas A & M University,
College Station, TX
Michelle Girts, CH2M HILL, Portland, OR
Robert Hedin, Hedin Environmental,
Sewickley, PA
William Hellier, Pennsylvania Department of
Environmental Resources, Hawk Run, PA
Robert Kadlec, Wetland Management
Services, Chelsea, MI
Douglas Kepler, Damariscotta, Clarion, PA
Robert Kleinmann, US Bureau of Mines,
Pittsburgh, PA
Robert Knight, CH2M HILL, Gainesville, FL
Fran Koch, Pennsylvania Department of
Environmental Resources, Harrisburg, PA
Eric McCleary, Damariscotta, Clarion, PA
Gerald Moshiri, Center for Wetlands and
Eco-Technology Application, Gulf Breeze,
FL
John Murtha, Pennsylvania Department of
Environmental Resources, Harrisburg, PA
Robert Myers, USDA - NRCS, Syracuse, NY
Kurt Neumiller, EPA, Annapolis, MD
Richard Reaves, Purdue University, West
Lafayette, IN
William Sanville, EPA, Cincinnati, OH
Dennis Sievers, University of Missouri,
Columbia, MO
Earl Shaver, Delaware Department of
Natural Resources and Environmental
Control, Dover, DE
Daniel Seibert, USDA - NRCS, Somerset, PA
Jeffrey Skousen, West Virginia University,
Morgantown, WV
Peter Slack, Pennsylvania Department of
Environmental Resources, Harrisburg, PA
Dennis Verdi, USDA - NRCS, Amherst, MA
Thomas Walski, Wilkes University, Wilkes-
Barre, PA
Robert Wengryznek, USDA - NRCS, Orono,
ME
Alfred Whitehouse, Office of Surface
Mining, Pittsburgh, PA
Christopher Zabawa, EPA, Washington, DC.
This document was prepared by Luise Davis for the USDA-Natural Resources Conservation Service and the US Environmental Protection
Agency-Region III, in cooperation with the Pennsylvania Department of Environmental Resources. Partial funding has been provided with
nonpoint source management program funds under Section 319 of the Federal Clean Water Act.
The findings, conclusions, and recommendations contained in the Handbook do not necessarily represent the policy of the USDA - NRCS,
EPA - Region III, the Commonwealth of Pennsylvania, or any other state in the northeastern United States concerning the use of constructed
wetlands for the treatment and control of nonpoint sources of pollutants. Each state agency should be consulted to determine specific
programs and restrictions in this regard.
PS5384RSEZ
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A HANDBOOK OF CONSTRUCTED WETLANDS
a guide to creating wetlands for:
AGRICULTURAL WASTEWATER
DOMESTIC WASTEWATER
COAL MINE DRAINAGE
STORMWATER
in the Mid-Atlantic Region
LJ.S. EPA Region III
Rd.^ Center for Km-ironm,,,,,,! iH,,rmi,t,Oi, Regional Center for Environmental
us,!r! Information
Philadelphia,' i9io3 1650 Arch Street (3PM52)
Philadelphia, PA 19103
VOLUMES: STORMWATER
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VOLUME 5
TABLE OF CONTENTS
CHAPTER 1. INTRODUCTION 3
CHAPTER 2. USING CONSTRUCTED WETLANDS TO TREAT STORMWATER RUNOFF 5
Introduction 5
System Description , 5
Advantages and Limitations of Constructed Wetlands 6
Characteristics of Stormwater 7
Contaminant Removal Processes 8
Biochemical Oxygen Demand and Suspended Solids 9
Nitrogen 9
Phosphorus 10
Metals and Other Toxic Materials 10
Pathogens 10
Performance of Stormwater Wetlands 11
CHAPTER 3. DESIGNING STORMWATER WETLANDS 13
Introduction 13
Siting 13
Hydrology 15
Configuration 16
Wetland 19
Transition Zone 19
Sediment Forebay 20
Micropool 20
Sizing 21
Treatment Volume 21
Wetland to Watershed Area Ratio 22
Depth/Surface Area Allocation 23
Treatment Area/ Volume Allocation 24
Length of Flow Path 24
Vegetation 24
Wildlife Habitat and Aesthetics 30
Safety 31
Education 31
CHAPTER 4. OPERATION AND MAINTENANCE 33
REFERENCES 35
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LIST OF TABLES
Table 1. Advantages and limitations of stormwater wetlands 6
Table 2. Characteristics of stormwater runoff 7
Table 3. Removal mechanisms in constructed wetlands 8
Table 4. Performance of stormwater wetlands 11
Table 5. Design guidelines 14
Table 6. Suggested depth/surface area allocations 23
Table 7. Suggested depth/surface area allocations for three wetland systems 23
Table 8. Suggested treatment area/volume allocation 24
Table 9. Landscaping guide 26
LIST OF FIGURES
Figure 1. Stormwater wetland system 5
Figure 2. Nitrogen transformations 9
Figure 3. Siting of wetlands within a watershed 15
Figure 4. Shallow marsh system 17
Figure 5. Pond-wetland system 18
Figure 6. Extended detention wetland 18
Figure 7. Transition zone 19
Figure 8. Schematic of sediment forebay 20
Figure 9. Cross-section of micropool 21
Figure 10. Removal rate vs. detention time for selected pollutants 22
Figure 11. Use of high marsh wedges to increase the length of the flow path 25
Figure 12. Landscaping zones 29
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CHAPTER 1
INTRODUCTION
This volume focuses on the use of constructed
wetlands to treat stormwater runoff. It is to be
used in conjunction with Volume 1: General
Considerations, which provides general informa-
tion on wetland hydrology, soils, and vegetation,
and on the design, construction, operation, and
maintenance of wetland systems.
The use of constructed wetlands to improve
the quality of stormwater runoff is a relatively new
concept that has been prompted by the effective-
ness of natural wetlands in controlling storm flows
and improving the quality of stormwater runoff.
Well-designed constructed wetlands can provide a
flexible and effective means of removing pollutants
from stormwater runoff and of reducing down-
stream flooding and erosion. Constructed wetland
treatment has thus been a valuable addition to the
list of urban Best Management Practice (BMP)
options.
Interest in using constructed wetlands for
stormwater has led to the publication of a number
of handbooks and manuals, among them several
that are specific to the Northeast and the mid-
Atlantic region:
Shaver, E., and J. Maxted. 1994. Construction of
Wetlands for Stormwater Treatment, pp 53-90 in
Proceedings, Symposium on Stormwater Runoff
and Quality Management, C. Y. Kuo (ed.). Penn
State University, University Park, PA.
Schueler, T. R. 1992. Design of Stormwater
Wetland Systems: Guidelines for Creating
Diverse and Effective Stormwater Wetlands in
the Mid-Atlantic Region. Metropolitan Washing-
ton Council of Governments, Washington, DC.
134 pp.
Strecker, E. W., J. M. Kersner, E. P. Driscoll, and R.
R. Homer. 1992. The Use of Wetlands for
Controlling Stormwater Pollution. EPA/600, The
Terrene Institute, Washington, DC. 66 pp.
Carlson, L. 1989. Artificial Wetlands for
Stormwater Treatment: Processes and Designs.
Rhode Island Department of Environmental
Management. 64 pp.
Much of the material in this volume has been
summarized from these publications.
VOLUME 5: STORMWATER
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CHAPTER 2
CONSTRUCTED WETLANDS TO TREAT STORMWATER RUNOFF
INTRODUCTION
Uncontrolled stormwater is a major contributor
to the nonpoint source (NFS) pollution of the
Nation's waters. Stormwater runoff originates from
a wide range of sources: from parking lots, road-
ways, roofs, and other impervious surfaces; from
exposed soils, such as construction sites and
denuded landscapes; and from vegetated surfaces,
such as lawns and golf courses. Uncontrolled
stormwater runoff accelerates erosion and down-
stream flooding, and transports large amounts of
contaminants to rivers, lakes, streams, and wet-
lands. Contaminants carried by runoff include
sediments, nutrients, oxygen-demanding sub-
stances, road salts, heavy metals, petroleum
hydrocarbons, pathogenic bacteria, and viruses.
Increasing urbanization has been accompanied
by large increases in the pollutant loads delivered
to receiving waters. Small volumes of stormwater
often carry large amounts of pollutants. For
example, while local stormwater runoff is respon-
sible for only a small percentage of the total flow
to San Francisco Bay, this runoff contributes more
than a third of all of the heavy metal pollution that
enters the Bay (Silverman 1989).
The objectives of stormwater runoff control are
to reduce the force of the flowing water, to reduce
the concentrations of pollutants carried by runoff,
and to provide aesthetics and wildlife habitat
(Livingston 1989).
SYSTEM DESCRIPTION
A constructed wetland for stormwater is a
shallow surface flow (SF) wetland (figure 1), also
called a marsh. Runoff enters the wetland system
during storms and temporarily raises the water
levels in the wetland. The water increases the
,-Pond Inflow
-Forebay
Illustration of stormwater constructed
wetland, with elevations
Transition Zom
Normal Pool Elevation
Cross-section of stormwater
constructed wetland
Figure 1: Stormwater wetland system (from Shaver and Maxted 1994).
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height of the permanent pool and may spread into
a transitional shore zone that is designed for
temporary storage of water. Water from the latest
storm displaces water that has been retained in
the wetland from previous storms. The dense
vegetation and almost level gradients of the
wetland slow the stormwater, dampening peak
flows and releasing the water gradually to a
downstream water body. As the water finds its
complex path through the wetland, a number of
physical, chemical, and biological mechanisms
remove contaminants in the stormwater or
convert them to more innocuous compounds.
Areas of deeper water can be included in the
wetland to increase residence times and to
provide fish and wildlife habitat. A sediment
forebay is usually placed before the wetland to
slow the influent stormwater and reduce sedi-
ment loads before the stormwater enters the
wetland. Trash, oil, and grease can be skimmed
in the forebay. A polishing pond is often placed
between the wetland outlet and the final dis-
charge structure. The deeper water of the pond
allows water to be discharged from the middle of
the water column surface, thereby avoiding the
release of organic-rich bottom sediments or any
floating plant debris.
ADVANTAGES AND
LIMITATIONS OF STORMWATER
WETLANDS
When properly designed, a constructed
wetland for stormwater runoff offers many ben-
efits as an urban BMP, including low cost, sim-
plicity of operation, reliable pollutant removal,
and the potential for wildlife habitat (table 1).
A constructed wetland also has a number of
limitations, including relatively large land re-
quirements and a degree of uncertainty not found
in more conventional approaches. And, since the
use of constructed wetlands for stormwater
management is fairly recent development, there is
little information on the long term capacity of
constructed wetlands to remove some persistent
pollutants or on the effects that such pollutants
may have on the wetlands.
Table 1. Advantages and limitations of constructed wetlands for stormwater.
Advantages
excellent removal of sediment
good removal of BOD and TSS
high tolerance of fluctuations in flow and water
quality
low maintenance
simplicity of operation
creation of wildlife habitat
aesthetic enhancement
possible increase in quantity and quality of
Nation's wetland resource if located in upland
areas or degraded wetlands
Limitations
large land requirements
susceptibility to shock loading due to the
"first flush"
possible flushing of stored pollutants during
high flows
seasonal variability in treatment effective-
ness
uncertainty as to treatment effectiveness
under all conditions
uncertainty as to long-term effects of pollut-
ants on wetland biota
6
VOLUME 5: STORMWATER
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CHARACTERISTICS OF
STORMWATER
Stormwater flows are episodic, with large,
rapid changes in volume, duration, and inten-
sity. A stormwater wetland is dominated by
surface runoff from rain and snowmelt, and
thus experiences wide fluctuations in the
amount and frequency of flow. This results in a
erratic pattern of inundation and subsequent
drawdown. The frequency and intensity of flow
depends on precipitation patterns and on the
amount of impervious surface in the watershed.
Large variability in the frequency and intensity
of rain and snow fall can be expected.
Stormwater can carry a wide variety of
urban NFS pollutants. Runoff from impervious
surfaces, such as parking lots and roadways, can
contain trash, suspended particulate matter,
nutrients (especially nitrogen and phosphorus)
from both vehicle exhaust and atmospheric
deposition, trace metals from metal corrosion,
material from worn brake linings and tires, salts
(especially deicing salts), and a wide array of
complex hydrocarbons (such as motor additives,
pesticides, rubber, oil, and grease). Runoff from
exposed soils, such as construction sites, can
carry large amount of sediment and organic
matter. Runoff from vegetated areas can contain
sediment, nutrients, pesticides, fertilizer, and
organic debris such as leaves. The types and
amounts of pollutants in stormwater vary widely
with the land uses in the contributing watershed,
with higher pollutant concentrations associated
with more intensive development and with
greater surface imperviousness (table 2)(Lakatos
and McNemar 1988).
The water quality of runoff also varies with
the frequency and intensity of rainfall. It has
been suggested that many water quality effects
result from the "first flush": in the early stages of
a storm, the pollutants that have accumulated on
surfaces such as streets and parking lots are
flushed by rainfall and runoff. The longer the
time between rainfalls, the greater the amount of
accumulated pollutants.
The more intense the storm, the greater the
force of the water and the more quickly the
Table 2. Characteristics of stormwater runoff (from Lakatos and McNemar 1988).
Pollutant Concentration (mg/Ll
Land Use
Forest
Agriculture
Construction sites
Medium density residential
High density residential
Commercial
tourist
general
Total-N
0.2
2.58
4.0
2.5
2.5
1.3
1.7
Industrial Variable; highly
Recreation
Open space/natural
Urban runoff
Total-N: total nitrogen
Total-P: total phosphorus, except
TSS: total suspended solids
*: data available for phosphate-P
0.6
1.35
0.1-12
Total-P
0.1
0.4
*0.5
0.35
0.4
*0.8
2.4
specific
*0.4
0.06
0.2-16
for commercial-tourist,
only
TSS
66
989
8,630
489
249
4,020
733
for type of industry;
48
8.7
29-11,280
Zinc
0
0
0
0.12
0.17
0
0.3
comparable
0
0
Lead
0
0
0
0.15
0.15
0.5
0.4
to commercial
0
0
Iron
0.4
1.9
2.3
0.4
1.4
4.2
1.1
0.5
0
construction, and recreation
VOLUME 5: STORMWATER
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pollutants are flushed. The flushing action and
inflow of the first inch of stormwater has been
estimated to carry about 90% of the pollution load
from a storm event (Livingston 1989, Hammer
1989), resulting in shock loading of the receiving
water. Wetland treatment of the first inch or so of
runoff can therefore have a significant effect on the
water quality consequences of the storm.
CONTAMINANT REMOVAL
PROCESSES
Wetlands remove contaminants through a
series of interacting physical, chemical, and
biological processes, including filtration, sedimen-
tation, adsorption, precipitation and dissolution,
volatilization, and biochemical interactions (table
3). Because of the large variations in location, size,
hydrology, and biology among stormwater wet-
lands, the dominant mechanisms vary from wet-
land to wetland.
Sedimentation and filtration are the predomi-
nant mechanisms for the removal of suspended
particulate matter and floating trash. These purely
physical processes also remove a significant
portion of other contaminants, such as biochemical
oxygen demand (BOD), nutrients, and pathogens,
that are associated with solids.
Adsorption is the principal removal mecha-
nism for dissolved pollutants such as phosphorus
Table 3. Removal mechanisms in constructed wetlands (after Brix 1993).
Wastewater Constituent
Biochemical Oxygen Demand (BOD)
Suspended solids
Organics
Nitrogen
Phosphorus
Metals
Pathogens
Floating debris
Removal Mechanisms
Microbial degradation (aerobic and anaerobic)
Sedimentation (accumulations of organic matter on sediment surfaces)
Sedimentation/filtration
Adsorption
Microbial degradation
Chemical ammonification followed by microbial nitrification
and denitrification
Plant uptake
Volatilization of ammonia
Soil sorption (adsorption-precipitation reactions with aluminum, iron,
calcium, and clay minerals in the soil)
Plant uptake
Adsorption
Microbial transformation and precipitation
Sedimentation/filtration
Natural die-off
Attack by antibiotics excreted from the roots of wetland plants
Predation by invertebrates and other microbes
Filtration
8
VOLUME 5: STORMWATER
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and dissolved metals. Adsorption is promoted by
the large amount of surface area provided by
suspended particulates, sediments, vegetation,
soils, and litter.
Soluble organic compounds are, for the most
part, degraded aerobically by microbes, especially
bacteria that grow on the surfaces of the plants,
litter, and the substrate. The oxygen needed to
support the aerobic processes is supplied by
diffusion from the atmosphere, by photosynthetic
oxygen production within the water column, and,
to some extent, by leakage of oxygen from the
roots of the vegetation. Some anaerobic degrada-
tion also occurs.
The low dissolved oxygen levels and reduc-
ing environment in wetlands convert some
dissolved metals, such as cadmium, lead, mer-
cury, and zinc, into less soluble sulfides, oxides,
and hydroxides (Strecker et al. 1992).
BIOCHEMICAL OXYGEN DEMAND AND
SUSPENDED SOLIDS
Wetlands provide a number of mechanisms
for removing BOD and total suspended solids
(TSS), and constructed wetlands are extremely
efficient at assimilating these contaminants. In a
survey of 324 municipal, industrial, stormwater,
and other constructed wetlands, Knight et al.
(1993) found that mass removal efficiencies for 5-
day biochemical oxygen demand (BOD5) were
generally 70% or more. TSS is removed prima-
rily by sedimentation and filtration, and removal
is enhanced as the complexity of surfaces within
the wetland increases. Cooper et al. (1993) found
that TSS removals increased as the amount of
plant litter accumulated.
The growth of plants (particularly under-
ground tissues) and the accumulation of plant
litter contribute to the removal of BOD and TSS
since plants and plant litter provide organic
carbon and attachment sites for microbial growth,
and promote filtration and sedimentation.
Longer detention times in the wetland increase
the amount of sedimentation that can occur.
NITROGEN
In wetlands, nitrogen occurs in a number of
forms, the most important of which are nitrogen
gas (N ), nitrite (NO ), nitrate (NO -), ammonia
Ģi Z* O
(NH ), and ammonium (NH +). The nitrogen
forms of concern are ammonia and total nitrogen.
Un-ionized ammonia can be toxic to fish and other
aquatic life while excess nitrogen contributes to
the over-enrichment of natural waters. Both
ammonia and nitrogen can add to the oxygen
demand in the receiving waters.
In contrast to the simplicity of BOD and TSS
removal, the chemistry of nitrogen removal is
complex (figure 2). Decomposition and mineral-
ization processes in the wetland convert a signifi-
cant part of organic nitrogen to ammonia. Ammo-
nia is oxidized to nitrate by nitrifying bacteria in
aerobic zones (nitrification) and nitrates are
converted to nitrogen gas by denitrifying bacteria
in anoxic zones (denitrification); the gas is re-
leased to the atmosphere.
The controlling step is usually the conversion
of ammonia to nitrate. Since nitrification is an
aerobic process, rates are affected by the availabil-
ity of oxygen for the nitrifying bacteria. Denitrifi-
cation is typically very rapid (Knight et al. 1993)
Ammonia
Nitrogen Gas
Nitrous Oxide Gas
Ozvgen
Upward '
Diffusion
.Ammonia Downward
Fixation. *?* Diffusion
Organic N Mineralization I
Nitrogen Gas
Nitrous Oxide Gas
Denitrification
Nitrate
Leaching
Figure 2. Nitrogen transformations
(after Gambrel and Patrick 1978, cited in Mitsch and
Gosselink 1986).
VOLUME 5: STORMWATER
9
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and the loss of nitrogen gas to the atmosphere
represents a limitless sink. To increase nitrogen
and ammonia removal, some municipal and
agricultural constructed wetland systems include
an open-water area to increase the oxygen avail-
able to the nitrifying bacteria. Hammer (1992)
suggests a marsh-pond-marsh sequence to improve
nitrogen removal. The water passes through a
wetland area to convert organic nitrogen to ammo-
nia, then through a pond (a deeper, open water
area) for the nitrification of ammonia to nitrate and
denitrification to nitrogen gas, then through
another wetland area to complete the denitrifica-
tion of nitrate.
Some nitrogen is taken up by plants and
incorporated into tissue, but this removal path-
way is of limited importance in wetlands in the
northeastern United States because the above-
ground parts of most emergent plants die back
yearly and below-ground tissue increases only
slowly (Brix 1993).
PHOSPHORUS
In the short term, phosphorus is a highly
mobile element in wetlands and is involved in
many biological and soil/water interchanges.
Dissolved phosphorus may be present in organic
or inorganic form and is readily transferred
between the two forms. Microbes and algae
control the seasonal uptake of phosphorus
(Richardson and Craft 1993). While the seasonal
uptake of phosphorus by vascular plants can be
significant, the phosphorus is mainly recycled
on an annual basis when the plants die back in
the fall.
The long-term removal of phosphorus by
wetlands is limited. The major sink for phos-
phorus in most wetlands is in the soil. Phospho-
rus may be buried in organic form in peats or
chemically adsorbed in complexed forms with
aluminum, iron, or calcium (Faulkner and
Richardson 1989). Soil adsorption can result in
significant removal of dissolved phosphorus for
a while after system startup, but removal then
decreases as adsorption sites become filled. The
length of the removal period depends on the
chemical adsorption capacity of the sediments.
Wetland soils have markedly different phospho-
rus adsorption capacities.
METALS AND OTHER Toxic MATERIALS
Toxic compounds are of concern because of
their potential effects on the biota of the wetland,
of the receiving waters, and on the birds and other
wildlife that may visit the wetland. Metals and
other toxics are captured in constructed wetlands
through a number of mechanisms, including
cation exchange with soils, oxidation in the
water column followed by precipitation, and
complexing with organic material in the sedi-
ments. The capacity of a wetland to assimilate
toxics depends on the chemical composition of the
toxic substance.
PATHOGENS
Pathogens are of concern because of possible
human contact and also because of possible
contamination of other species. For instance,
fecal coliform bacteria (an indicator of human
waste) are a concern along the Atlantic coastline
because of the need to protect shellfish beds.
Pathogens are removed by die-off and by
adsorption on solids. In general, pathogenic
microorganisms are highly host-specific and do
not survive long apart from the host. Some wet-
land plants excrete antibiotics which further aid in
the removal of pathogens. Constructed wetlands
can provide high percentage removals of patho-
gens and have been shown to remove bacteria and
viruses from domestic wastewaters at efficiencies
of 90% to 99% at residence times as short as 3 to 6
days. (Ives 1988). Removal of bacteria and viruses
is promoted by dense vegetation and long reten-
tion times. However, despite the high removal
rates, some stormwaters may still contain enough
organisms after wetland treatment to make the
water unsuitable for human or animal contact. If
10
VOLUME 5: STORMWATER
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pathogens are a concern, the water should be
passed through a vegetated filter strip after
leaving the wetland.
PERFORMANCE OF
STORMWATER WETLANDS
Detailed water quality monitoring data on
natural or constructed wetlands that receive
stormwater is limited. As yet, there is no way to
predict what level of treatment a given wetland
will provide, other than for suspended solids.
Differences in hydrology, detention time, and
runoff rates among constructed wetlands plus the
fact that treatment cycles often span several storm
cycles make pollutant removal efficiencies
difficult to assess (Strecker et al. 1992). However,
the systems that have been monitored have
shown moderate to excellent pollutant removals
despite widely varying designs and treatment
volumes. Two recent studies (Shaver and Maxted
1994, Schueler 1992) have shown similar removal
rates for the major pollutants in stormwater.
Shaver and Maxted (1994) summarized the
performance of 26 stormwater wetland systems
across the country and found that most sites were
sinks for total suspended solids, total nitrogen,
and total phosphorus, and that all sites were sinks
for total lead (negative numbers indicate net
exports) (Table 4).
Other metals (zinc, copper, cadmium, nickel,
and chromium) were also retained. The median
percent retention was highest for suspended solids
and lead, and lowest for total nitrogen. However,
performance varied widely for all parameters.
Schueler (1992) examined the performance of
nearly 60 stormwater pond and wetland systems
and projected the long-term removal rates for
stormwater wetlands in the mid-Atlantic region as:
total suspended solids 75%
total nitrogen 25%
total phosphorus 45%
organic carbon 15%
lead 75%
50%
zinc
bacteria
2 log reduction.
Schueler (1992) summarized his findings as:
removal rates for stormwater wetlands were
similar to conventional pond systems, such as
wet and dry detention ponds. In many cases,
wetlands provided better removal of suspended
solids than ponds, but lower and more variable
removal of phosphorus. The better solids re-
moval was thought to be due to the better settling
conditions provided by wetlands. The variable
phosphorus removal may be due to complex
patterns of phosphorus cycling in wetlands.
the most reliable overall performance was
achieved by sediment pond-wetland systems,
because the permanent pool of the pond reduced
incoming velocities and settled out solids before
the water entered the wetland. Pond-wetland
total suspended solids
total nitrogen
total phosphorus
total lead
Table 4. Performance of Stormwater Wetlands
(from Shaver and Maxted 1994)
Number of sites
Total
26
11
28
8
Sink
24
7
22
8
Source
2
4
6
0
Net retention f%)
Range Media
-300 to 96 76
-20 to 83 24
-120 to 97 46
6 to 94 83
VOLUME 5: STORMWATER
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systems also consistently provided better colder weather. Ice cover and snowmelt also
removal of phosphorus and nitrogen than did reduced removals.
other stormwater designs. . performance improved during the first several
performance declined somewhat during the fall years as wetlands matured. How long the im-
and winter, probably because of the nutrients provement could be expected to continue was
released when plants die back in the fall, and unknown.
because of lowered biological activity during
12 VOLUMES: STORMWATER
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CHAPTER 3
DESIGNING STORMWATER WETLANDS
INTRODUCTION
While there is a great flexibility in the ways
that a stormwater constructed wetland can be
fitted to a particular site, all constructed wet-
lands share an underlying design principle: to
catch and hold stormwater runoff long enough
for peak storm flows to be dampened, for
sediment to drop out, and for physical and
biochemical processes to reduce other contami-
nants before the water is discharged. The goal
should be to create a system that will be largely
self-maintaining. Also, it should be recognized
that the wetland will change as its hydrology
adjusts to changes in the watershed and as the
vegetative community evolves.
Because the use of constructed wetlands for
stormwater is a recent development, design
information is still limited, as are data on the
long-term performance of stormwater wetlands
under various conditions. However, for any
given site, there may be a number of possible
designs, any of which may adequately control
stormflows and improve water quality. The
design of a constructed wetland is based on the
size of the contributing watershed, the amount
of space available for the wetland, the topogra-
phy of the site, and the desired function(s) of
the wetland system (see Volume 1). The effec-
tiveness of a stormwater wetland in reducing
peak stormflows and improving water quality
can be enhanced by incorporating design ele-
ments such as shoals, islands, micropools, and
complex wetland microtopography. Encourag-
ing the growth of a diverse assortment of wet-
land plants, including emergent, shrub, and tree
species, also increases the effectiveness of
stormwater wetlands. Guidelines for design are
summarized in table 5.
SITING
Before the location for the constructed
wetland is chosen, the site should be carefully
assessed to determine:
the relation of the site to the existing land-
scape
potential locations for stormwater wetlands,
based on topography and available space
proposed or existing connections with up-
lands and existing land use
present and proposed surface drainage pat-
terns
the location and status of all natural wetlands,
including the source and quantity of baseflow
existing and proposed land use
existing and proposed structures
any site features, such as steep slopes, that
must be avoided (Schueler 1992).
Because hydrology is so important to the
functioning of wetlands, stormwater wetlands
should be located where the site hydrology will
support the long-term functioning of the wet-
land. The wetland should be located to take
advantage of the existing topography of the site
to collect and retain stormwater. Highway
construction offers excellent opportunities for
stormwater wetlands, particularly where large
tracts of land intersect with urban streams
(Linker 1989). Constructed wetlands are fea-
sible for almost any drainage area if the soils are
impermeable enough to allow for ponding with
little exfiltration. While there is generally no
technical lower size limit for sites, other con-
siderations (parking, etc.) may limit suitable
sites to those larger than an acre.
A stormwater wetland must not be placed in
a stream unless such a location has been dis-
cussed with the regulatory authority and a
VOLUME 5: STORMWATER
13
-------
permit has been obtained. A stormwater wetland
must not be placed in an existing natural wet-
land. However, when possible, a constructed
wetland should be located near existing wet-
lands. First, such areas are likely to provide
suitable hydrologic conditions. Second, existing
wetlands provide a source of seeds of wetland
plants. Third, the wildlife value of a wetland
increases as the total area of wetland habitat in
the vicinity increases. The constructed wetland
must be separated from natural wetlands by a
physical barrier so that pollutants in the
stormwater do not enter the natural wetland.
Depending on the size of the watershed, the
planner may have the option of constructing one
large wetland or several small wetlands. There
are two advantages to creating several small
wetlands at strategic locations in the watershed
rather than one larger wetland at the bottom of
the watershed: first, it may be easier to avoid
existing natural wetlands by siting a number of
smaller constructed wetlands in upland areas,
and second, using several small systems may
provide a greater level of control and affect a
larger number of streams than one large system
of similar total size (figure 3). Water quality
and quantity functions within a watershed are
cumulative, and even very small systems
provide important functions that benefit the
system as a whole. On the other hand, creating
one larger wetland rather than several small
ones may increase the wildlife habitat value of
the resulting wetland.
Siting
Gradient
Hydroperiod
Inlets and outlets
Pre treatment
Discharge
Internal configuration
Upland/wetland edge
Islands
Vegetation
Vegetation canopy
Human disturbance
Table 5. Design guidelines (after Shaver and Maxted 1994).
Locate near streams, lakes, or other wetlands
Avoid isolating the wetland
Low gradients promote deposition
A mixture of hydrologic conditions enhances diversity
A mixture of permanently and temporarily flooded areas expands functions
Multiple channels or outlets promote water storage
Braided channels promote water storage
A sediment forebay dissipates the energy of stormwater inflows
A sediment forebay reduces particulate loading of the wetland
A micropool at the outlet reduces the release of sediments and floating matter
Interspersion of vegetation and open water promotes diversity
Long flow paths increase hydraulic residence time
Complex surfaces increase surface area within wetland
Irregular shape increases perimeter length, diversifies habitat
Increase flow travel time
Provide safe habitat for waterfowl
Dense vegetation slows water flow, promotes sedimentation, reduces
resuspension of sediments
Dense vegetation promotes sheet flow
Shading reduces thermal impacts
Restricted public access protects functions
14
VOLUME 5: STORMWATER
-------
All the water leaving the watershed passes
through one large wetland placed at the
bottom of the watershed
Placing a wetland at the lower reaches of
each sub-watershed reduces the overall
movement of water and contaminants within
the watershed
Figure 3.
Siting of wetlands within a watershed
(after van der Valk and Jolly 1992).
If there are downstream wet systems -
wetlands, streams, lakes, or estuaries - that
receive stormwater runoff, the design of the
constructed wetland should maintain the
direction of flow to the downstream systems.
Otherwise, downstream wet ecosystems could
be altered by the change in hydrology. The
characteristics of the original hydroperiod should
be maintained to support the vegetation of the
downstream wet systems. The stormwater
wetland should not divert stormflows around or
away from areas that received surface runoff
before the wetland was built.
HYDROLOGY
The relationships between hydrology and the
characteristics of the wetland ecosystem must be
understood and included in the design to ensure
the long-term effectiveness of the wetland. Factors
to be evaluated include:
the total volume of water entering the system,
including stormwater runoff, direct precipitation,
streams, and groundwater infiltration
the total volume of water leaving the system,
including outflow, evapotranspiration, and
exfiltration
frequency and duration of stormflow
depth, frequency, and duration of inundation
water velocity and flow rate
seasonal and climatic influences (temperature, ice
cover)
the size of the contributing watershed and the
land use/cover types in the watershed.
Establishing hydroperiod (see Volume 1) is of
primary importance because this determines the
form, nature, and functions of the wetland. Ac-
ceptable high and low water elevations will deter-
mine the stormwater treatment volume capacity of
the wetland, the discharge structure, and bleed-
down orifice elevations (Livingston 1989). In
contrast to natural wetlands which are often
supported by groundwater, stormwater wetlands
are largely fed by surface water flows, which are
much more variable than groundwater flows. In
the Northeast and along the mid-Atlantic, precipi-
tation is distributed throughout the year, and
precipitation and stormwater runoff are often
sufficient to maintain stormwater wetlands. As
long as the soil stays moist, most wetland plants
can usually withstand periods in which there is no
standing water, although periods of drawdown may
alter the species composition of the vegetation
within the wetland.
VOLUME 5: STORMWATER
15
-------
The hydrology of stormwater wetlands is
strongly affected by the hydrology of the watershed
upstream of the wetland since the quantity, quality,
and location of surface and subsurface flows to the
wetland depend on upstream conditions. One of
the most important factors is the degree of urbaniza-
tion and therefore the percentage of surfaces, such
as rooftops and paved surfaces, that have been made
impervious. As the percentage of impervious
surfaces in the watershed increases, runoff volumes
and peak flow rates increase while infiltration and
base stream flow decrease. Removing trees and
other vegetation, and installing pipes or channels
for stormflow conveyance magnify these hydrologic
changes. Increasing urbanization in the future will
increase the magnitude of the changes in the hydrol-
ogy of the watershed and thus of the stormwater
wetland, and should be taken into consideration in
the wetland design.
The length of time the stormwater should be
retained in the wetland will depend on the require-
ments of the regulating authority. Determining the
desired hydraulic residence time requires balancing
removal efficiencies with the area available for the
wetland systems and the costs estimated for long-
term maintenance. Ferlow (1993) found that
heavily vegetated, flat-gradient (ą 1/2%) shallow
marsh and seasonally saturated scrub-shrub systems
in small contributing watersheds (5 to 20 ac, 2 to 50
ha) have the physical characteristics to pool water
at shallow depths for extended periods (18 to 24
hours or more) with simple outlet control.
CONFIGURATION
Designing the configuration of the stormwater
treatment system involves fitting the components of
the system to the site. A considerable degree of
flexibility in designing stormwater wetlands is
possible. The design should incorporate the follow-
ing (Schueler 1992):
providing adequate treatment volume by building
a large enough wetland basin to catch and retain
the stormwater long enough for treatment to occur.
maximizing surface area in relation to volume.
High surface area to volume (SA/V) ratios in-
crease sedimentation, adsorption, microbial
activity, and uptake of pollutants by algae. SA/V
ratios can be increased in two ways: by increas-
ing the surface area of the wetland, or by increas-
ing the number of surfaces within the wetland. A
complex internal structure of microtopography -
flats, shoals, islands, and pools - increases the
amount of surface in the wetland. Whatever the
microtopography of the wetland, as much area as
possible should be allocated to very shallow
depths (1 to 6 inches, 2.5 to 15 cm) to promote
sheetflow.
providing long flow paths at shallow depths to
maximize the contact of the stormwater with the
surfaces within the wetland. The effective length
of flow paths can be increased by adding baffles
and berms to create serpentine flow patterns, or
by building multiple cells.
providing a sediment forebay to absorb the force
of the inflowing water and provide space for
heavier particles to drop out.
providing treatment redundancy. The number of
removal pathways can be increased by creating
both deep and shallow areas, complex flow
paths, and a dense and diverse plant community.
Schueler (1992) found that systems that incorpo-
rated extended detention zones, permanent
pools, and wetlands of varying depths provided
higher and more reliable levels of pollutant
removal than did less complex systems.
providing an emergency spillway to bypass flows
that are greater than the design volume. Bypass-
ing extreme storm events protects the wetland
from scour and resuspension of settled material.
Hammer (1989) suggests a system comprising a
pond, a temporary stormwater storage area, a
shallow SF wetland, and a wet meadow to polish
the wetland effluent. Schueler suggests a number
of designs to accommodate various site constraints.
In a marsh system (figure 4), the majority of the
16
VOLUME 5: STORMWATER
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25% of pond perimeter open grass
Maintenance
Bench
gate valves provide
flexibility in depth control
25 loot wetland butler landscaped
with native trees/shrubs lor habitat
use of wetland mulch
to create diversity
Figure 4. Shallow marsh system
(after Schueler 1992).
system is a shallow SF wetland up to 18 inches
(0.5m) deep, which creates favorable conditions
for the growth of emergent plants. A sediment
forebay is placed before the wetland and a polish-
ing pond (micropool) is placed near the outlet. A
pond-wetland system (figure 5) consists of two
separate cells: a deep pond leading to a shallow
marsh. The pond provides vertical stormwater
storage, removes some pollutants, and reduces the
space needed for the system. An extended deten-
tion (ED) wetland (figure 6) provides extended
detention around the periphery of the wetland.
The shoreline of an ED wetland has a steep slope
to create a basin for stormwater detention. The
water level in an ED wetland system can increase
as much a 3 ft (1 m) after a storm, and then return
to normal levels within 24 hours. As much as
50% of the total treatment volume can be provided
as ED storage, which helps to protect downstream
channels from erosion and reduces the space
required for the wetland.
VOLUME 5: STORMWATER
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aquatic bencn
Figure 5. Pond-wetland system (after Schueler 1992).
\ pond buflvr 10 mctirs minimum
Figure 6. Extended detention wetland (after Schueler 1992).
18
VOLUME 5: STORMWATER
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WETLAND
The wetland is a shallow SF wetland [see
Volume 1). The wetland may encircle deeper
pools, in which case the wetland will form a
shallow underwater bench around the deeper
water. The bench should be at least 10 feet (3 m)
wide to provide for the abundant plant growth
that will effect water quality improvement. A
wide, shallow bench is also a safety feature if
public access will be allowed.
TRANSITION ZONE
The transition zone is the zone between the
water-covered portion of the wetland and sur-
rounding upland. The transition zone area can be
an important component of the system because it
temporarily stores stormwater runoff from large
storms. Shaver and Maxted (1994) recommend
that this zone should be no steeper than about a
10% slope (10 horizontal to 1 vertical) and should
be at least 20 ft (6 m) wide (as measured from
design normal pool)(figure 7) to provide adequate
stormwater storage. Hammer (1989) recommends
that the transition zone be sized to store 85% of
the anticipated runoff during the 10 year - 24 hour
storm and that a spillway sized for the 100 year -
24 hour storm should discharge to a grassed
waterway that bypasses the wetland system.
The transition zone will support a diverse
group of plants than can thrive in damp soil.
These plants can tolerate periods of inundation
but cannot live under constant inundation. Trees
can be planted in this zone. Trees will enhance
nutrient uptake, provide shade and moderate
temperatures, increase habitat diversity for wild-
life, and minimize mowing and maintenance.
A reverse slope, or swale, (figure 7) will
control erosion rills that can develop on longer
slopes and intercept particulates traveling down
the slope. The swale should direct overland flow
to the inlet of the wetland system.
The transition zone is an open space that can
be used during dry weather for casual recreation,
such as walking or bird watching.
Transition zone from wetland to upland
minimum 20' length
Reverse slope
above water level
minimum 10' length
Figure 7. Transition zone (from Shaver and Maxted 1994).
VOLUME 5: STORMWATER
19
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Inflow Pipe
24"-36"
I
Maximum 4'
Stone
Sized for Basin
2:1 slope
Figure 8. Schematic of sediment forebay
(from Shaver and Maxted 1994).
SEDIMENT FOREBAY
A sediment forebay (pond) placed before the
wetland is critical to the long-term performance
of the wetland system. The forebay will:
slow the incoming stormwater and absorb
much of its force
reduce peak stormflow volumes and equalize
flow to the wetland
capture coarse sediment loads so they do not
enter the wetland
provide sheetflow delivery of the stormflow to
the wetland.
The forebay protects the wetland by absorb-
ing much of the force of the inflowing
stormwater. The forebay also traps the larger,
heavier sediments (sands and gravels) while the
finer particles are carried into the wetland.
Since sands and gravels constitute a large per-
centage by volume of the pollutants, removing
them in a forebay rather than in the wetland
reduces the buildup of sediment in the wetland
and extends its life.
The forebay can be 4 to 6 feet (1.3 - 2 m)
deep. Shaver and Maxted (1994) and Schueler
(1992) recommend that the forebay comprise at
least 10% of the wetland volume with a mini-
mum of 0.1 watershed-inches. Gabions, stone
riprap, or an earthen dike can be used to sepa-
rate the forebay from the wetland (figure 8). At
some sites, it may be advantageous to use sev-
eral forebays at strategic locations to feed
stormwater to the wetland. If the stormwater is
expected to carry oil and grease, an oil and
grease trap should be installed in the forebay.
Since the forebay functions as a sediment
pond, access for heavy equipment must be pro-
vided. A concrete bottom simplifies cleanout.
MlCROPOOL
A micropool at the outlet is recommended.
The micropool acts as a polishing pond and
provides space for a reverse slope pipe (figure 9).
The reverse slope pipe design releases water from
the middle of the water column, thereby prevent-
ing the release of bottom sediments or floating
debris. The pipe inlet is usually about 1 ft (0.3 m)
below normal pool. Debris and plant wrack float
above the pipe inlet while sediments accumulate
below it.
Schueler (1992) suggests that this pond, like
the sediment forebay at the inlet, comprise about
20
VOLUME 5: STORMWATER
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IV
emergency spillway
bankfuil flooc1 storage (2yr.)
anti-seep collars
fig
/ / / / // /
The micropool is 4 to 6 ft deep and helps to protect the orifice of the reverse slope pipe extending
from the riser. The pipe withdraws water within 1 ft of normal pool and is equipped with a gate
valve to adjust detention times. The pond drain pipe is also equipped with a gate valve and is used
to drain the entire wetland for planting or sediment cleanout.
Figure 9. Cross-section of micropool
(from Schueler 1992).
10% of the treatment volume and be 4 to 6 ft
(1.3 to 2 m) deep.
A drain should be provided in case the
wetland needs to be drained so that the sedi-
ment forebay can be cleaned out. Schueler
(1992] suggests that the drain inlet should be
an upward-facing inverted elbow that will
extend above the bottom sediments (figure 9).
The pond drain should be equipped with a
lockable and adjustable gate valve. An anti-
seep collar prevents seepage from the barrel.
SIZING
TREATMENT VOLUME
Several guidelines for sizing stormwater
wetlands have been suggested. Shaver and
Maxted (1994) recommend that stormwater
wetlands should be sized to control the first inch
of runoff and release it over a 24 hour period. A
24-hour detention for the first inch of runoff will
provide approximately 80% reduction in TSS
(figurelO). This target is offered as a level that
can be achieved readily with available technol-
ogy. Water quantity considerations require peak
discharge control of the 2 and 10 year storms
(Shaver and Maxted 1994). Storage volume
requirements must agree with local ordinances
for stormwater.
Schueler (1992) recommends that stormwater
wetlands should be sized to capture and treat
90% of all runoff-producing storms. The 90%
criterion is offered by Schueler as a reasonable
and achievable goal. Schueler's approach factors
in the area of the watershed, the percent of the
site that is covered by impervious surfaces, and
the amount of stormwater that the watershed can
be expected to receive.
VOLUME 5: STORMWATER
21
-------
TSS
Pŧ
Zn
COO
TP
TN
12 19 24 30 31
Detention Tim* (hour*)
42
Figure 10. Removal rate vs. detention time for selected pollutants
(Schueler 1987).
The volume that meets the 90% criterion can
be determined from the regional rainfall frequency
spectrum (RFS). RFS hourly data are generally
available from the National Weather Service. The
RFS data are edited to remove minor storms that
do not produce measurable surface runoff. Treat-
ment volume (Vt) is derived from the maximum
volume that meets the 90% criterion, the percent
of the site covered by impervious surfaces (I), the
site runoff coefficient (Rv), and the area (A) con-
tributing stormwater to the wetland:
Vt = (90% rainfall x Rv x A /12) x 43,560
where Vt = treatment volume (cubic feet)
Rv = 0.05 + 0.009 (I)
I = percent site imperviousness
A = contributing area (acres)
WETLAND TO WATERSHED AREA RATIO
Strecker et al. (1992) found that treatment
performance increased and variability in treatment
performance decreased as the wetland area in-
creased in relation to watershed area.
Schueler (1992) indicates that the pollutant
removal capability of a stormwater wetland gener-
ally becomes more consistent when the wetland to
watershed area ratio (WWAR) is greater than 2%
and recommends a minimum WWAR of 2%. If the
wetland design incorporates a pond before the
wetland, or provides extended detention benches,
the WWAR can be reduced to 1%.
22
VOLUME 5: STORMWATER
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DEPTH/SURFACE AREA ALLOCATION
Creating areas of different depths in the wetland increases the surface area/volume ratio, encourages
sheetflow, and increases the internal structural complexity of the wetland. Depth/surface area allocations
shown in Table 6.
Table 6. Suggested depth/surface area allocations
(after Shaver and Maxted 1994)
depth
shallow marsh (0 to 1 ft below normal pool)
deep marsh (1 to 2 ft below normal pool)
deep water (2 to 4 ft below normal pool)
allocation of surface area f %1
50
30
20
Schueler (1992) suggests the following guidelines for allocating depths for three types of systems (see
figures 4-6):
Table 7. Suggested depth/surface area allocations for three wetland systems
(after Schueler 1992)
depth
shallow marsh (0 to 6 inches below normal pool)
deep marsh (6 to 18 inches below normal pool)
transition zone (0 to 2 ft above normal pool)
deep water (1 to 6 ft below normal pool)
sediment forebay
micropool
deepwater pool
allocation of surface
pond-
marsh wetland
40 25
40 25
5 5
5 0
5 5
5 40
area (%1
ED
wetland
40
40
10
5
5
0
VOLUME 5: STORMWATER
23
-------
TREATMENT AREA/ VOLUME ALLOCATION
Schueler (1992) suggests that the volume be allocated among the various depths, depending on site and
design constraints, as shown in Table 8:
Table 8. Suggested treatment area/volume allocation
(after Schueler
1992)
allocation of treatment volume f%)
depth
shallow marsh (0 to 6 inches below normal pool)
deep marsh (6 to 18 inches below normal pool)
transition zone (0 to 2 ft above normal pool)
deep water (1 to 6 ft below normal pool)
forebay
polishing pond
deepwater ponds
pond-
marsh wetland
25 10
45 20
0 0
10 0
10 10
10 60
ED
wetland
10
20
50
10
10
LENGTH OF FLOW PATH
The longest possible flow path should be
created to maximize the contact of the stormwater
with the surfaces in the wetland. Although the
flow path during high stormflow runoff may be
determined by the distance from the inlet to the
outlet, if wedges of shallow marsh are used to
create serpentine flow paths, the effective flow
path during dry weather can be much longer
(figure 11). For adequate treatment, Schueler
(1992) recommends that the length-to-width ratio
of the stormwater flow path be at least 1:1 and that
the dry weather flow path be at least 2:1. (The
length-to-width ratio is computed by dividing the
straight line distance from the inlet to the outlet by
the average width of the wetland.)
VEGETATION
The goal of planting stormwater wetlands is to
generate a dense, diverse vegetation that mimics
nearby natural wetlands (see Volume 1). Dense
growth facilitates sedimentation and provides
growth sites for microorganisms. A highly diverse
community of plants is less susceptible than low
diversity stands to damage by disease or animals,
and is pleasing to the eye. Planting plans for
stormwater wetlands should concentrate encourag-
ing desirable species.
If wildlife habitat is a goal, certain plants have
greater value than others (table 9). If flowering
wetland plants are desired, they must generally be
planted. The landscaping plan should include
trees. Trees provide shade and reduce temperature
increases, reduce wind and wave action in the
wetland, provide a more diverse habitat for wild-
life, and enhance nutrient removal. Shrubs and
trees along the shores of ponds and islands provide
nesting and perching sites for birds and cover for a
variety of other wildlife.
The two key factors in maintaining a healthy
and diverse plant community are to keep water
depths shallow and to ensure that wetland soils
stays moist between rainfalls. Most wetland
24
VOLUME 5: STORMWATER
-------
Direction of plow
^-
Sitormuafer
A. NORMAL, FLOW FATH
hi marsh
0. PRY
PATH
.iwrmal pool elevation
C. CROSS-sec-no* FROM
TO OUTFALL
ouffell ,
? micro poo I
Figure 11. Use of marsh wedges to increase the length of the flow path
(from Schueler 1992).
VOLUME 5: STORM WATER
25
-------
Table 9. Landscaping guide (from Schueler 1992).
Zone - the zone in the stormwater area the plant is suitable for. Refer to Figure 12.
Form the shape and the size of the plant at maturity.
Tolerance for periodic inundation - the plant's ability to survive flooded conditions.
Value to wildlife - the types of wildlife benefits provided by the plant.
Plant name, common
(Latin)
TREES AND SHRUBS
Smooth Alder
(Alnus serrulata)
American Beech
(Fagus grandifolia)
American Holly
(Ilex opaca)
Blackgum, Sourgum
(Nyssa sylvatica)
Black Willow
(Salix nigra)
Buttonbush
(Cephaianthus occidentalis)
Chokecherry
(Prunus virginiana)
Elderberry
(Sambucus canadensis)
Fringe Tree
(Chionanlhus virginicus)
Green Ash, Red Ash
(Fraxinus pennsylvanica)
Honey Locust
(Gledilsia triacanthos)
Highbush Cranberry
(Viburnum trilobum)
Larch, Tamarack
(Larix laricina)
Mountain Laurel
(Kalmia latHolia)
Persimmon
(Diospyros virginiana)
Red Chokeberry
(Pyrus arbutifolia)
Zone
4,5
5,6
5,6
4,5,6
3,4,5
2,3,
4,5
5,6
4,5,6
3,4,5
4,5
4.5,6
4,5,6
3,4
6
4,5,6
3,4,5
Form
Decid. shrub
6-12 feet
Decid. tree
60-80 feet
Decid. shrub
to 40-50 leet
Decid. tree
30-60 feet
Decid. tree
30-50 feel
Decid. shrub
6-9 feet
Decid. shrub
6-20 feet
Decid. shrub
3-1 2 feet
Decid. tree
10-20 feet
Decid. tree
30-80 feet
Decid. tree
70-80 feet
Decid. shrub
10 feet
Conif. tree
20-40 feet
Conif. shrub
5-10 feet
Decid. tree
30 feet
Decid. shrub
2-8 leet
Tolerance
for periodic
Inundation
Some
No
No
Yes
Yes
Yes
No
Yes
Probably
Yes
No
Yes
Yes
No
No
Yes
Value to
wildlife
Food, cover
Mast
Food, cover
Fruit
Cover,
cavities
Seeds, nectar
Fruit, cover
Fruit, cover
Cover
Cover, seeds
Cover
Fruit, cover
Nest tree,
seeds
Cover, nectar
Fruit, cover
Fruit, cover
Special
requirements
Prefers shade, rich,
well-drained soils
Prefers shade,
tolerates periodic
drought
Prefers sun
Full sun
Full sun to
partial shade
Well-drained
to moist soils
Full sun to
partial shade
Full sun to
partial shade
Full sun
Full sun
Full sun
Full sun, acidic
boggy soils
Partial shade,
acidic soils
Well-drained
soils
Partial sun
Notes
High wildlife value
Ornamental, high
wildlife value
Ornamental, high
wildlife value
Rapid growth,
stabilizes streambanks
Used by ducks,
shorebirds, butterflies
High wildlife value
Extremely high
wildlife value
Ornamental
Rapid growth.
stabilizes streambanks
Acidic soils only.
Emergency winter food
Rapid initial growth
Ornamental, attracts
hummingbirds
Not shade tolerant,
high wildlife value
26
VOLUME 5: STORMWATER
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Table 9. (continued)
Plant name, common
(Latin)
Red Maple
(Acer rubrum)
Red-osier Dogwood
(Cornus stolonifera)
Rhododendron spp
River Birch
(Betula ngra)
Shadbush,
Common Servlceberry
(Ame/anchier arborea)
Silky Dogwood
(Cornus amomum)
Silver Maple
(Acer saccarinum)
Southern Arrowwood
(Viburnum dentatum)
Spice Bush
(Lindera benzoin)
Zone
4,5,6
3,4,5
4,5,6
3,4
5,6
5.6
4,5,6
4,5
5.6
Swamp Magnolia, Sweet bay 3, 4
(Magnolia virgin/ana)
Swamp Oak
(Ouercus bicolor)
Sweetgum
(Liquidambar styraciflua)
Sycamore
(Platanus occidentalis)
Tulip-tree
(Liriodendron tulipifera)
Tupelo
(Nyssa sylvalica van biflora)
Willow Oak, Pin Oak
(Quercus phello&rpaluslris)
Winterberry
(Ilex laevigata)
Witch Hazel
(Hamamelis virginiana)
4,5
4,5,6
4,5,6
5
3,4,5
4,5,6
4,5
4,5
Form
Decid. tree
40-70 feet
Decid. shrub
4-8 feet
Conifer, shrub
5-1 2 feet
Decid. tree
20-40, to 90 feet
Decid. shrub
15-20 feet
Decid. shrub
4-10 feet
Decid. tree
60-80 feet
Decid. shrub
to 1 0 feet
Decid. shrub
12-25 feet
Conifer, tree
20 feet
Decid. tree
60 feel
Decid tree
50-70 feet
Decid. tree
80 feet
Decid tree
70 feet
Decid. tree
35 feet
Decid. tree
50-90 feet
Decid. shrub
8-10 feet
Decid. shrub
10 feet
Tolerance
tor periodic
Inundation
Yes
Yes
Only R.
viscosum
Yes
Yes
Yes
Yes
No
No
Yes
Yes
Yes
Yes
No
Yes
No-pte/tos
Yes-pa/usfr/s
No
No
Value to Special
wildlife requirements
Seeds, browse,
nest sites
Fruit, cover Shade
tolerant
Cover, nectar Acid soil,
shade
Cavities,
cover
Fruit, cover Prefers shade
Fruit, cover Shade, drought
tolerant
Seeds,
nest sites
Fruit, cover Partial sun
Fruit, cover Shade,
rich soils
Cover Shade
Mast
Seeds,
nest sites
Cavities
Seeds,
nest sites
Seeds,
cavities
Mast
Cover, fruit
Nest sites Shade
Notes
Rapid growth,
high wildlife value
Stabilizes streambanks,
high wildlife value
Ornamental, attracts
hummingbirds
Bank erosion control
High wildlife value
Ornamental
Ornamental
High wildlife value
Tolerates acid or
clay soils
Rapid growth
Rapid growth
Ornamental
High wildlife value
Ornamental
VOLUME 5: STORMWATER
27
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Table 9. (continued)
Plant name, common
(Latin) Zone
WETLAND PLANTS
Arrow Arum, Duck Corn 2
(Peltandra virginica)
Arrowhead, Duck Potato 2
(Saggitaria latifolia)
Broomsedge 2,3
(Andropogon virginianus)
Cattail 2.3
(Typha sppj
Coontail 1
(Ceratophyllum Vemersum)
Common Three-Square 2
(Scirpus americanus)
Soft-stem Bulrush 2,3
(Scirpus validus)
Lizard's Tail 2
(Saururus cernuus)
Pickerelweed 2,3
(Pontederia cordata)
Pondweed 2,3
(Potamogeton)
Rice Cutgrass 2,3
(Leersia oryzoides)
Sedges 2,3
(Carex sppj
Smartweed 2
(Polygonum spp;
Spatterdock 2
(Nuphar luteum)
Swltchgrass 2,3,4
(Panicum virgatum) 5,6
Sweet Flag 2,3
(Acorus ca/umus)
Water Iris 2,3
(Iris pseudoacorus)
Form
Emergent
Emergent
Grass
Emergent
Submergent
Emergent
Emergent
Emergent
Emergent
Submergent
Emergent
Emergent
Emergent
Emergent
Grass
Emergent
Wild Flower
Tolerance
for periodic
inundation
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Value to
wildlife
Berries
Tubers, seeds
Seeds, grass
Nest sites
Low
Seeds, cover
Seeds, cover
Low
Low
Seeds
Seeds, roots
Seeds, cover
Seeds, cover
Food, cover
Seed, cover
Low
Low
Special
requirements Notes
Stow colonizer, berries
eaten by Wood Ducks
Aggressive colonizer.
used by ducks
Tolerates tluctuating
water levels, used by
songbirds, browsers
Volunteer.
aggressive colonizer
Fast colonizer, tolerates
fluctuating water levels.
excellent wildlife value
Aggressive colonizer.
moderate wildlife value
Rapid growth.
shade tolerant
High value to waterfowl,
marsh and shorebirds
Shade tolerant, high
value to ducks, songbirds
High wildlife value
Fast colonizer, high
wildlife value
Fast colonizer, tolerates
fluctuating water levels
Tolerates wet/dry
conditions
Slow colonizer, tolerates
drying, eaten by muskrat,
beaver
Ornamental
28
VOLUME 5: STORMWATER
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plants do well in 6 inches of water or less.
The densest and most diverse plant growth
in wetlands is often found in very shallow
water. Shallow water zones also provide excel-
lent pollutant removal. For these reasons, as
much area as possible should be allocated to
shallow water.
The type of vegetation that can be established
depends on the depth of the water and on how
frequently the area will be under water. For
landscaping purposes, Schueler (1992) has
delineated six zones that differ in the amount of
soil moisture and the types of vegetation that will
grow well there. The six zones are shown in
figure 12 and the types of vegetation are listed in
table 9. The six zones are:
Zone 1: Deep water areas. Zone 1 includes
areas that are always under water. Water depths
range from 1 to 8 ft. These areas are too deep
for emergent wetland plants but will support
submerged plants, such as sago pondweed, and
floating plants, such as duckweed.
Zone 2: Shallow water areas. This zone is
permanently wet, with an average water depth of
less than 1 ft. These areas support a wide
variety of emergent wetland plants. Recom-
mended species include softstem bulrush,
common three-square, pickerelweed, sedges,
rushes, and arrow arum (see Volume 1).
Zone 3: Shoreline. Plants in this zone must be
able to withstand being inundated during storms
and drying during drier periods. Appropriate
species include emergents such as softstem
bulrush, sedges, switchgrass, and rice cutgrass;
shrubs such as buttonbush and chokecherry; and
trees such as black willow and river birch. To
attract wildlife, parts of this zone can be kept
free of vegetation and maintained as mudflats or
sandbars.
Zone 4: Riparian fringe. Plants in this zone
must be able to tolerate both wet and dry soil as
well as periodic inundation. Suitable species
include willows, river birch, highbush cranberry,
buttonbush, sweetgum, and red-osier dogwood.
ZONE 6:
Upland Slopn
ZONE 5: I
I Flooclrilaln Terrace |
ZONE
Deep Water ARM
Note: the width of the landscaping zone is related to the side-slope angle
(the steeper the slope, the narrower the zone)
Figure 12. Landscaping zones (from Schueler 1992).
VOLUME 5: STORMWATER
29
-------
Zone 5: Floodplain terrace. This zone includes
most of the embankment. Plants for this zone
prefer moist soil but can tolerate infrequent
inundation. Plants include spicebush, elder-
berry, persimmon, tulip tree, and silky dog-
wood. Trees and shrubs should not be planted
on the embankment or along the dam because
their roots can destabilize slopes. Generally,
only about half of the floodplain terrace is
planted with trees and shrubs.
Zone 6: Upland slopes. This area is seldom
inundated. Species that can be planted here
include dogwood, chokecherry, and elderberry.
For the wetland, Schueler (1992) recommends
planting five to seven species of emergent plants,
of which three should be arrowhead, common
three-square, and softstem bulrush. These three
species establish readily and spread, but are not
so aggressive as to become nuisances. The addi-
tional species can be chosen to enhance the
wildlife and aesthetic value the wetland.
Schueler (1992) recommends that the initial
planting cover about 30% of the shallow zone,
with particular attention given to areas next to the
shore.
A more natural appearance and, perhaps,
better plant survival may result when each species
is planted in groups or clumps, rather than evenly
distributed. Planting each species in a number of
clumps reduces competition among the species.
In contrast to the highly diverse array of
plants found in natural wetlands, stormwater
wetlands typically contain a limited number of
species. These species may include exotic and
invasive species, such a cattails and common
reed, that can thrive in the stressful conditions
found in stormwater wetlands. Ehrenfeld and
Schneider (cited in Schueler 1992) observed that
65% or more of the species in stormwater-influ-
enced wetlands were invasive or exotic species
whereas such species made up less than 1% of the
plants in natural wetlands. Livingston (1989)
notes that polluted stormwater represents in-
creased nutrients, which may lead to changes in
the dominant plants in the wetland. Since the
new dominants may be able to make more efficient
use of the added nutrients or to tolerate the pollut-
ants, the shift in species composition may benefit
pollutant removal.
The large fluctuations in flow that occur in
stormwater wetlands will affect the vegetative
community in the wetland. Large water level
fluctuations have been shown to decrease species
diversity. Indeed, the biota in stormwater wet-
lands may be determined more by their ability to
tolerate extremely variable conditions than to
make optimal use of the energy sources in the
water (Silverman 1989).
WILDLIFE HABITAT AND
AESTHETICS
While stormwater wetlands are primarily
treatment systems, the other benefits provided by
stormwater wetlands, such as wildlife habitat and
aesthetics, are also important. Piers, walkways,
and overlooks encourage the enjoyment of con-
structed wetlands by the public and can add an
educational component to the benefits provided by
a stormwater wetland. It may helpful to consult a
wildlife biologist during the design of the project.
Stormwater wetlands can provide habitat for a
large variety of wildlife, especially birds (for
instance, ducks, bitterns, songbirds, kingfisher,
and herons), turtles, salamanders, and frogs.
Stormwater wetlands should be designed to attract
wildlife only if the accumulated contaminants will
not be harmful to wildlife. Contaminants in
stormwater from some sites, for example, indus-
trial sites that produce hydrocarbons or heavy
metals, could become toxic to wildlife over time.
Shallow wetlands with gently sloping sides
maximize both pollutant removal and wildlife
habitat. A slope of about 10:1 along the shore
creates a shallow water habitat for tadpoles, small
fish, and aquatic insects, such as dragonflies and
mayflies, which in turn will provide food for
waterfowl such as ducks, wading birds such as
great blue herons, and other wildlife. The
shoreline can be an extremely productive habitat
30
VOLUME 5: STORMWATER
-------
for prey species (insects, frogs and turtles) which
will attract birds and mammals. The length of the
shoreline can be increased by building an irregu-
lar shoreline and, if the wetland is large enough,
by creating coves for nesting birds. For many
species, the number of nesting pairs that will
breed increases when birds can nest in coves
where they cannot be seen by other nesting pairs
(Brittingham n.d.). Creating an irregular shore-
line can easily increase the length of the shoreline
by 10 or 20%.
To keep the number of Canada geese in check,
the shoreline should not contain large areas of
mowed grass since geese are attracted to areas
that provide long glide paths. Geese generally
avoid ponds surrounded by shrubs or dense
vegetation, or areas where shrubs break up open
spaces and make it difficult to watch for predators
(Brittingham n.d.). Letting the grasses grow and
interspersing grassy and shrubby areas will limit
the attractiveness of the shoreline to flocks of
Canada geese.
Exposed mudflats and sandbars offer feeding
and loafing areas for shorebirds, wading birds,
and waterfowl. Mudflats and sandbars are cre-
ated and maintained by fluctuating water levels
that deposit nutrients onto the soil and keep
permanent vegetation from becoming established.
Mudflats and sandbars will develop naturally in
shallow ponds with gradual slopes, since the
slopes will be submerged during and after heavy
rains but will be exposed during drier periods.
If the wetland is large enough, a pond can be
included. The design of the pond will depend on
the specifics of the site, but as a general guide
25% to 50% of the pond should be between 2 ft
and 3 ft (0.3 to 1 m) deep to provide an area of
open water. If one objective of the pond is to
maintain fish, a deep water pool (at least 8 ft
deep, or almost 3 m) should be included.
Islands within the center of the pond can
provide a place for waterfowl to nest where they
will be protected from predators such as raccoons
or local dogs and cats. This is particularly impor-
tant in suburban and urban areas where popula-
tions of these predators are high. Even very small
ponds can contain an island. An island as small
as 6 ft x 6 ft (2 m x 2 m) will provide a nest site
for ducks. To be suitable for nesting, islands
should contain areas that are higher than the
anticipated high water level and should have
sloping sides so that water will drain off.
Grasses and shrubs can be planted to prevent
erosion and to provide nesting cover.
Nest boxes along the edge of the wetland and
nesting platforms within the pond will attract
wildlife. Eastern bluebirds, tree swallows, and
purple martins, and perhaps wood ducks, will
use the nest boxes while Canada geese and
mallards will nest on platforms. Loafing plat-
forms will attract turtles and ducks.
SAFETY
Wetlands, like any body of water, pose a
potential risk of drowning or injury, particularly
to young children. Designing shallow wetlands
with gently sloping sides, and eliminating any
holes or steep drop-offs will reduce hazards.
Warning signs can be placed at access points,
and lifesaving devices, such as ring buoys, ropes,
or long poles, can be placed near the shore.
Wetlands can be fenced, although this lowers the
aesthetic and recreational value of the wetland.
One major benefit of the dense vegetation of
wetlands is that it discourages people from
getting into wetlands. Any areas of the wetland
that might be accessible to the public should be
kept shallow and densely vegetated.
EDUCATION
Boardwalks, piers, and overlooks can be
provided for public access. Signs explaining the
components of the wetland and their functions can
be used to inform the public about why the wet-
land has been built, how it works, and the benefits
it provides.
VOLUME 5: STORMWATER
-------
32 VOLUME 5: STORMWATER
-------
CHAPTER 4
OPERATION AND MAINTENANCE
Well-designed stormwater wetlands should
require only minimal maintenance. However,
stormwater wetlands will require some periodic
maintenance and monitoring, especially during
the first several years while the wetland is
becoming established. During the first three
years, water levels must be checked and adjusted
occasionally until they become stabilized at
optimum levels. Water levels that are too high
by several inches can drown desirable plant
species and levels that are too low will cause a
shift to a drier, upland ecosystem. Undesirable
plants, such as common reed or purple loose-
strife, must be removed until desired vegetation
has become dense enough to compete with
aggressive species. Hand removal is the best
means of removing undesirable plants.
At a minimum, stormwater wetlands should
be inspected at least twice a year for the first two
years and once each year thereafter. The inspec-
tion should determine the amount of sediment
that has accumulated (particularly in the sedi-
ment forebay and micropool), check to make
sure that structures are in good condition, and
check for signs of plant stress or disease.
The use of pesticides, herbicides, and fertil-
izers should be restricted. For wetlands that
receive stormwater from roads or parking lots,
the use of sodium-free deicing salts will help to
maintain a diverse microbial community and
healthy vegetation.
Sediments should be cleaned out of the
sediment forebay periodically. Access areas and
embankments should be mowed twice a year to
prevent woody plants from becoming estab-
lished. Other areas can be allowed to develop
naturally.
VOLUME 5: STORMWATER
33
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REFERENCES
Brittingham, M. C. n.d. Providing Wetlands for
Wildlife while Controlling Stormwater. Penn
State Extension Circular 384, University Park,
PA. 19pp.
Brix, H. 1993. Wastewater treatment in con-
structed wetlands: system design, removal
processes, and treatment performance, pp 9-22
in Constructed Wetlands for Water Quality
Improvement, G. A. Moshiri (ed.). CRC Press,
Boca Raton, FL. 632 pp.
Carlson, L. 1989. Artificial Wetlands for
Stormwater Treatment: Processes and Designs.
Rhode Island Department of Environmental
Management, Kingston, RI. 64 pp.
Cooper, C. M., S. Testa, III, and S. S. Knight. 1993.
Evaluation of ARS and SCS Constructed Wet-
land/Animal Waste Treatment Project at
Hernando, Mississippi. National Sedimentation
Laboratory Research Report No. 2, Oxford, MS.
55 pp.
Faulkner, S. P., and C. J. Richardson. 1989. Physi-
cal and chemical characteristics of freshwater
wetland soils, pp 41-72 in Constructed Wetlands
for Wastewater Treatment: Municipal, Industrial
and Agricultural, D. A. Hammer (ed.). Lewis
Publishers, Chelsea, MI. 831 pp.
Ferlow, D. L. 1993. Stormwater runoff retention
and renovation: a back lot function or integral
part of the landscape? pp 373-379 in Con-
structed Wetlands for Water Quality Improve-
ment, G. A. Moshiri (ed.). Lewis Publishers,
Boca Raton, FL. 632 pp.
Hammer, D. A. 1989. Constructed wetlands for
treatment of agricultural waste and urban
Stormwater. pp 333-348 in Wetlands Ecology and
Conservation: Emphasis in Pennsylvania,
S. K. Majumdar, R. P. Brooks, F. J. Brenner, and R.
W. Tiner, Jr. (eds.). The Pennsylvania Academy
of Science, Philadelphia, PA. 395 pp.
Hammer, D. A. 1992. Designing constructed
wetland systems to treat agricultural nonpoint
source pollution. Ecological Engineering 1:49-82.
Knight, R. L., R. W. Rible, R. H. Kadlec, and S.
Reed. 1993. Wetlands for wastewater treatment:
performance database, pp 35-58 in Constructed
Wetlands for Water Quality Improvement, G. A.
Moshiri (ed.). Lewis Publishers, Boca Raton, FL.
632 pp.
Lakatos, D. F., and L. J McNemar. 1988. Wetlands
and Stormwater pollution management, pp 214-
223 in Proceedings National Wetland Sympo-
sium: Wetland Hydrology, J. A. Kusler and G.
Brooks (eds.). Association of State Wetland
Managers, Berne, NY.
Linker, L. C. 1989. Creation of wetlands for the
improvement of water quality: a proposal for the
joint use of highway right-of-way, pp 695-701 in
Constructed Wetlands for Wastewater Treatment:
Municipal, Industrial and Agricultural, D. A.
Hammer (ed.). Lewis Publishers, Chelsea, MI.
831 pp.
Livingston, E. H. 1989. Use of wetlands for urban
Stormwater management, pp 253-262 in Con-
structed Wetlands for Wastewater Treatment:
Municipal, Industrial and Agricultural, D. A.
Hammer (ed.). Lewis Publishers, Chelsea, MI.
831 pp.
Mitsch, W. J., and J. G. Gosselink. 1986. Wetlands.
Van Nostrand Reinhold, New York, NY. 539 pp.
Moshiri, G. A. 1993. Constructed Wetlands for
Water Quality Improvement. CRC Press, Boca
Raton, FL. 632 pp.
Richardson, C. J., and C. B. Craft. 1993. Effective
phosphorus retention in wetlands: fact or fiction?
pp 271-282 in Constructed Wetlands for Water
Quality Improvement, G. A. Moshiri (ed.). Lewis
Publishers, Boca Raton, FL. 632 pp.
VOLUME 5: STORMWATER
35
-------
Shaver, E., and J. Maxted. 1994. Construction of
wetlands for stormwater treatment, pp 53-90 in
Proceedings, Symposium on Stormwater Runoff
and Quality Management, C. Y. Kuo (ed.). Penn
State University, University Park, PA.
Schueler, T. R. 1987. Controlling Urban Runoff: a
Practical Manual for Planning and Designing
Best Urban Management Practices. Metropolitan
Council of Governments, Washington, DC. 213
pp + app.
Schueler, T. R. 1992. Design of Stormwater
Wetland Systems: Guidelines for Creating
Diverse and Effective Stormwater Wetlands in
the Mid-Atlantic Region. Metropolitan Council
of Governments, Washington, DC. 134 pp.
Silverman, G. S. 1989. Development of an urban
runoff treatment wetlands in Fremont, California.
pp 669-676 in Constructed Wetlands for Wastewater
Treatment: Municipal, Industrial and Agricultural,
D. A. Hammer (ed.). Lewis Publishers, Chelsea, MI.
831 pp.
Strecker, E. W., J. M. Kersner, E. D. Driscoll, and
R. R. Horner. 1992. The Use of Wetlands for
Controlling Stormwater Pollution. EPA/600, The
Terrene Institute, Washington, DC. 66 pp.
van der Valk, A. G., and R. W. Jolly. 1992. Recom-
mendations for research to develop guidelines for
the use of wetlands to control rural nonpoint source
pollution. Ecological Engineering 1:115-134.
36
VOLUME 5: STORMWATER
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GLOSSARY
abiotic not involving biological processes
aerobic requiring free oxygen
algae primitive green plants that live in wet environments
ALD anoxic limestone drain
AMD acidic mine drainage
AML abandoned mine lands
anaerobic a situation in which molecular oxygen is absent; lacking oxygen
anoxic without free oxygen
aquifer a permeable material through which groundwater moves
aspect the ratio of length to width
AWMS animal waste management system
baseflow the portion of surface flow arising from groundwater; the between-storm flow
biomass the mass comprising the biological components of a system
biotic the living parts of a system; biological
BMP Best Management Practice
BOD biochemical oxygen demand, often measured as 5-day biochemical oxygen demand (BOD5); the consump-
tion of oxygen by biological and chemical reactions
CEC cation exchange capacity
community (plant) the assemblage of plants that occurs in an area at the same time
denitrification the conversion of nitrate to nitrogen gas through the removal of oxygen
detritus loose, dead material; in wetlands, largely the leaves and stems of plants
emergent wetland a wetland dominated by emergent plants, also called a marsh
EC electrical conductivity
effluent the surface water flowing out of a system
emergent plant a non-woody plant rooted in shallow water with most of the plant above the water surface
ET evapotranspiration
evapotranspiration loss of water to the atmosphere by evaporation from the water surface and by transpiration by plants
exfiltration the movement of water from a surface water body to the ground
exotic species not native; introduced
HLR hydraulic loading rate; loading on a unit area basis
HRT hydraulic residence time; average time that moving water remains in a system
hydric soil a soil that is saturated, flooded, or ponded long enough during the growing season to develop anaerobic
conditions in the upper part of the soil
hydrolysis chemical decomposition by which a compound is resolved into other compounds by taking up the ele-
ments of water
hydroperiod the conversion of ammonia to nitrate through the addition of oxygen
infiltration the movement of water from the ground into a surface water body
influent the surface water flowing into a system
karst irregular, pitted topography characterized by caves, sinkholes, and disappearing streams and springs, and
caused by dissolution of underlying limestone, dolomite, and marble
marsh an emergent wetland
microbe microscopic organism; includes protozoa, bacteria, yeasts, molds, and viruses
-------
microorganism term often used interchangeably with microbe
native species one found naturally in an area; an indigenous species
nitrification the conversion of ammonia to nitrate through the addition of oxygen
non-persistent plant... a plant that breaks down readily after the growing season
non-vascular plant a plant without differentiated tissue for the transport of fluids; for instance, algae
NFS nonpoint source
organic matter matter containing carbon
oxidation the process of changing an element from a lower to a higher oxidation state by the removal of an
electron(s) or the addition of oxygen
pathogen a disease-producing microorganism
peat partially decomposed plant material, chiefly mosses
perennial plant a plant that lives for many years
permeability the capacity of a porous medium to conduct fluid
persistent plant a plant whose stems remain standing from one growing season to the beginning of the next
redox reduction/oxidation
reduction the process of changing an element from a higher to a lower oxidation state, by the addition of an
electron(s)
rhizome a root-like stem that produces roots from the lower surface and leaves, and stems from the upper surface
riparian pertaining to the bank of a stream, river, or wetland
SAPS successive alkalinity-producing system
SF surface flow
SSF subsurface flow
stolon a runner that roots at the nodes
scarification abrasion of the seed coat
stratification treatment of seed by exposure to cold temperatures
succession the orderly and predictable progression of plant communities as they mature
transpiration the process by in which plants lose water
tussock a hummock bound together by plant roots, especially those of grasses and sedges
tuber a short thickened underground stem having numerous buds or "eyes"
TSS total suspended solids
vascular plant a plant that possesses a well-developed system of conducting tissue to transport water, mineral salts, and
foods within the plant
wrack plant debris carried by water
-------
ABBREVIATIONS AND CONVERSION FACTORS
MULTIPLY
ac, acre
cfs, cubic foot per second
cfs, cubic foot per second
cm, centimeter
cm/sec, centimeter per second
°F, degree Fahrenheit
ft, foot
ft2, square foot
ft3, cubic foot
ft/mi, foot per mile
fps, foot per second
g/m2/day, gram per square meter per day
gal, gallon
gal, gallon
gpm, gallon per minute
ha, hectare
inch
kg, kilogram
kg/ha/day, kilogram per hectare per day
kg/m2, kilogram per square meter
L, liter
L, liter
Ib, pound
Ib/ac, pound per acre
m, meter
m2, square meter
m3, cubic meter
m3, cubic meter
m3/ha/day, cubic meter per hectare per day
mm, millimeter
mi, mile
BY
0.4047
448.831
2.8317 x 10"2
0.3937
3.28x 10'2
5/9 (°F- 32)
0.305
9.29xlO-2
2.83 x 10"2
0.1895
18.29
8.92
3.785
3.785 x 10'3
6.308 x lO"2
2.47
2.54
2.205
0.892
0.2
3. 531 x 10~2
0.2642
0.4536
1.121
3.28
10.76
1.31
264.2
106.9
3.94 x 10"2
1.609
To OBTAIN
ha, hectare
gpm, gallon per minute
m3/s, cubic meter per second
inch
fps, foot per second
°C, degree Celsius
m, meter
mz> square meter
m3, cubic meter
m/km, meter per kilometer
m/min, meter per minute
Ib/ac/day, pound per acre per day
L, liter
m3, cubic meter
L/s, liter per second
ac, acre
cm, centimeter
Ib, pound
Ib/ac/day, pound per acre per day
lb/ft2, pound per square foot
ft3, cubic foot
gal, gallon
kg, kilogram
kg/ha, kilogram per hectare
ft, foot
ft2, square foot
yd3, cubic yard
gallon, gal
gallon per day per acre, gpd/ac
inch
kilometer, km
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