t basins, grass
filters, deep ponds and polishing areas
designed primarily to remove contami-
nants from storm water. When practical,
natural landscape features that provide
water quality improvement functions
may be incorporated into the system.
The selection, combination and order of
the AWSMS components overcome limi-
tations often encountered by single com-
ponent practices.
Advantages of AWSMS include
(Schueler, 1992):
Reliable pollutant removal
Dampening of flood flows and
peaks
Creation of wildlife habitat and aes-
thetic potential
However, AWSMS may not be appro-
priate for every situation.
Disadvantages include:
A relatively high land requirement
Significant management demands
during and after establishment
Time required for vegetation to
mature and achieve optimum per-
formance
Potential for adverse impacts such
as increased water temperature
within sensitive watersheds
AWSMS are constructed systems that
mimic the complicated, interdependent
contaminant removal mechanisms of
natural wetlands. It is important to
remember that these artificial systems
are designed primarily to treat storm
water runoff. Although they may be
enhanced to provide some of the other
functional values of natural wetlands,
these considerations are secondary to
the systems pollutant removal potential
and should not be included if they com-
promise the pollution control function.
These artificial systems are not intended
to mitigate the historic loss of natural
wetland habitat. As such, artificial
storm water treatment systems are not
to be considered either restored or miti-
gation wetlands.
Conversely, natural wetlands, as well as
mitigation and restored wetlands
created to replace the full range of
wetland functions, should not be used
to treat storm water runoff. Although
natural wetlands provide water quality
benefits, discharging storm water
directly to natural wetlands can have
adverse impacts.
According to the U.S. Environmental
Protection Agency (US-EPA, 1993),
water level fluctuations affect wetlands
and wetland functions adversely. When
hydrologic changes or pollutants exceed
the assimilative capacity of natural wet-
lands, wetlands become stressed and
may be degraded or destroyed.
The Wisconsin Department of Natural
Resources (WDNR) strongly discour-
ages the use of natural wetlands for
storm water treatment. In fact, new
storm water discharges to wetlands
under WDNR regulatory authority
(Wisc. Admin. Code NR 103) are pro-
hibited if an alternative to the discharge
is available. Even where no reasonable
alternatives exist, such discharges are
not allowed if they will lead to signifi-
cant degradation of wetland function. 2
W I S C O N S I N S T O R M W A T E R M A N U A L _______________________________________________________________________________
Artificial wetland storm water treat-
ment systems have been successfully
constructed and operated in
Midwestern states, including Wisconsin
and Minnesota. Two Wisconsin projects
include the Lake View project and the
Delavan Lake project.
The Lake View Industrial Park project
near Kenosha created a 600-acre
wetland complex along the Des Plaines
River. The complex includes a storm
water management function and pro-
vides water quality benefits. At Delavan
Lake, an 85-acre wetland was con-
structed on a 145-acre site. The drainage
basin is 16.8 square miles. The wetland,
immediately upstream from Delavan
Lake, is designed to provide natural
water treatment by removing sediments
and nutrients before they reach the lake.
The wetland system includes three sedi-
mentation basins, a shallow marsh, a
sedge meadow and wet prairie areas.
Extensive sampling of the wetland will
continue into the future and should
provide data on the capabilities of a
Wisconsin AWSMS.
When properly designed, constructed
and operated, AWSMS remove pollu-
tants from storm water and reduce peak
flows reliably for many years. In addi-
tion, AWSMS provide wildlife habitat,
aesthetic appeal and educational and
passive recreational opportunities. To
minimize adverse water quality impacts
from storm water, all systems should
incorporate practices that promote
watershed conservation and pollution
prevention.
To function effectively, AWSMS need to
be properly designed, correctly installed
and diligently maintained. The guide-
lines in this chapter should assist with
these endeavors. Although free water
surface and subsurface flow wet-
lands have been constructed to provide
water quality improvements, subsurface
flow AWSMS usually are not appro-
priate in Wisconsin due to wide fluctua-
tions in storm water flow and seasonal
variations. Therefore, this publication
will discuss only free water surface
AWSMS.
The guidelines have been drawn from
an extensive review of national and
state research, as well as the practical
experience and insights of state storm
water experts. It is important to realize,
however, that research into AWSMS is
an ongoing process and further changes
in design can be expected.
Principles
Efficient pollutant removal
The principal pollutants found in urban
runoff include sediment, oxygen-
demanding substances (organic matter),
nutrients (mainly phosphorus and
nitrogen), metals (copper, lead and
zinc), pesticides, hydrocarbons and
trash or debris (US-EPA, 1993). The
form and fate of each contaminant will
be influenced by the design and geo-
graphic location of the AWSMS, the
time of year, hydrologic conditions and
other factors.
Studies investigating the effectiveness
of wetlands to treat storm water runoff
have been limited. Table 1 summarizes
reported pollutant removal efficiencies
for a variety of Midwestern natural and
constructed wetland systems. The range
of values illustrates the variability of
the results and the complexity of the
relationships between wetlands and
water quality. In general, AWSMS are
effective at removing suspended solids
and pollutants that adsorb to solids, but
are not as effective at removing dis-
solved pollutants (US-EPA, 1993). T
able 1.
A
verage removal ef
ficiencies for Midwestern storm water wetlands (adapted from Strecker et al., 1992)
Study &
Org.
NH
3
NO
3
TP
Ortho.
Dis.
COD
PB
ZN
CU
CD
location
System name
System type
TSS
VSS
TN
TK N
N
P
P
Brown 1985,
Fish Lake
natural
95
78
-20
36
0
3
7
2
8
Minnesota
wetland & pond
Lake Elmo
natural
88
80
38
-36
50
27
25
wetlands
Lake Riley
-20
20
20
7
2
5
-43
-30
Spring Lake
constructed
-300
-20
-14
1
1
-86
-7
-10
wetland
W
otzka &
McCarrons
constructed
94
94
83
85
63
78
53
93
90
Obert 1988,
W
etland
wetland
Minnesota
T
reatment
& pond
System
Hickok et al.
W
ayzata
natural
94
-44
78
94
82
80
67
1977
W
etland
wetland
Minnesota
Scherger &
Swift Run
natural
76
20
49
83
Davis 1982
wetland
Michigan
Barten 1987
Clear Lake
constructed
76
25
55
54
52
40
Minnesota
wetland
Oberts et al.
Lake Ridge
constructed
85
67
24
28
17
37
-5
8
5
2
1989
wetland
Minnesota
Carver constructed
20
1
-
6
-10
9
1
-3
1
6
Ravine
wetland
& pond
Hey & Barrett
W
etland 3
constructed
72
70
59
1991, Illinois
W
etland 4
wetlands
76
42
55
(Des Plaines
W
etland 5
8
9
7
0
6
9
River Project)
W
etland 6
9
8
9
5
9
7 4
W I S C O N S I N S T O R M W A T E R M A N U A L _______________________________________________________________________________
Pollutant removal
mechanisms
In general, AWSMS remove pollutants
through physical, chemical and biolog-
ical processes including absorption,
adsorption, filtration, microbial trans-
formation (biodegradation), precipita-
tion, sedimentation, uptake by vegeta-
tion and volatilization. These are sum-
marized in table 2.
Planning guidelines
D
esigning and constructing an effec-
tive AWSMS is a challenging task,
requiring a sophisticated under-
standing of hydrology, soils and
wetland plant ecology. The design of an
AWSMS must be based on a careful
analysis of many complex relationships
and characteristics within the watershed
and on-site. These include future land
uses in the watershed, velocity and
magnitude of flow, water depth and
fluctuation, circulation, seasonal and cli-
matic influences, groundwater condi-
tions, soil permeability and the long
term contribution of all systems in the
watershed.
An AWSMS should be a component of
larger landscape plans for watersheds
and proposed developments. Upland
prairie or forest buffers and grassed
swale systems will enhance the quality
and reduce the quantity of water
reaching AWSMS. A comprehensive
landscape approach also will increase
the sites marketability. Aesthetically,
the natural appearance of an AWSMS
can provide an excellent amenity to a
community or place of work. Local resi-
dents or property owners need to recog-
Table 2.
Contaminant removal mechanisms in AWSMS (adapted from Watson et al., 1989 and Horner, 1992)
Mechanism
Description
Contaminant affected
Enhancement techniques
Absorption
Assimilation of gas,
phosphorus
long residence times
liquid, or dissolved
synthetic organics
low flow velocities
substance into
oil
another substance
Adsorption
Adhesion of dissolved pollutants
phosphorus
shallow water depth
to suspended solids, sediments or
heavy metals
long residence times
vegetation. (Electrical attraction
synthetic organics
sheet flow
between positively charged pollutant
Al and