The Evergreen State College Institutional Repository

The Science of Wetland Buffers and its Implication for the Management of Wetlands

Item

Title (dcterms:title)

Eng The Science of Wetland Buffers and its Implication for the Management of Wetlands

Date (dcterms:date)

2000

Creator (dcterms:creator)

Eng McMillan, Andrew

Subject (dcterms:subject)

Eng Environmental Studies

extracted text (extracttext:extracted_text)

THE SCIENCE OF WETLAND BUFFERS AND ITS IMPLICA nON FOR THE

MANAGEMENT OF WETLANDS


by
Andrew McMillan


A Thesis

Submitted in partial fulfillment

of the requirements for the degree

Master of Environmental Studies

The Evergreen State College

August 2000


This Thesis for the Master of Environmental Studies Degree

by


Andrew McMillan


has been approved for

The Evergreen State College

by


John Perkins

Member of the Faculty


David Milne
Member of the Faculty

y~~

Paula Ehlers
Department of Ecology

Date

ABSTRACT

The Science of Wetland Buffers and Its Implication for Wetland Management
Andrew McMillan

The protection of upland buffers around wetlands is a source of controversy for
wetland regulators. Despite considerable scientific evidence that buffers are
necessary to maintain wetland functions, the protection of buffers is frequently
challenged as being an unnecessary and overly burdensome requirement of
private property owners. Most local governments in Washington require the
protection of buffers around wetlands although the required widths vary greatly.
In 1995, the Growth Management Act was amended to require that local
governments must include the "best available science" when adopting regulations
to protect wetlands and other critical areas. Guidance adopted in spring, 2000 by
the state Department of Community, Trade and Economic Development defines
key characteristics of good scientific information and identifies and defines
sources of valid scientific information. With this information, local governments
are directed to either rely upon documents provided by state agencies or conduct
their own independent review of the scientific literature to determine the "best
available science." Where local governments deviate from the best available
science in adopting local policies and regulations, they must specify why they
deviated and what the possible environmental consequences might be.
The scientific literature on wetland buffers is substantial, and unequivocal in
establishing that protection of buffers is critical to maintaining a wetland's
functions and values. Numerous studies conducted across the United States and
elsewhere in the world document the ways that buffers protect wetlands from the
adverse impacts of adjacent development. The principal buffer functions that
protect wetlands are: removal of sediments, nutrients and toxic substances in
surface and shallow, subsurface runoff; reduction of noise, light and human and
pet intrusion into wetlands; and the provision of adjacent riparian and upland
habitat critical to numerous wildlife species that utilize wetlands. The scientific
literature also indicates that the buffer characteristics and widths necessary to
maintain wetland functions and values are dependent on site-specific conditions.
The primary factors that should dictate buffer character and width are: 1) the
quality, sensitivity and functions of the wetland; 2) the nature of adjacent land
uses and their potential to impact the wetland; and 3) the character of the existing
buffer area, including soils, slope and vegetation. While site-specific factors
should be evaluated to determine effective buffer widths, generally widths of 15 ­
30 meters are the minimum necessary to protect wetland water quality and widths
of 30 - 100 meters are necessary to protect wetland wildlife habitat.
According to the Washington State Growth Management Act, wetland buffer
protection and management programs must incorporate the best available science.

However, local regulatory programs also need to be predictable for landowners
and efficient for local staff to implement. Historically, most local buffer
regulations have addressed the need for efficiency and predictability by adopting
fixed buffer widths. However, given the need for site-specific consideration of
the three factors outlined above, reliance on standard buffer widths may not be
adequate to protect wetland functions in many cases and may require more than is
necessary in other situations. By establishing standard buffer widths based on the
type of wetland and the type of adjacent land use and including specific
provisions for making site-specific adjustments, local governments can address
the need for predictability and efficiency while incorporating the best available
SCIence.

Table of Contents


List of Figures

iv


List of Tables

iv


Acknowledgements

v


Introduction

1


Chapters


7


1

Best Available Science

2

The Science of Wetland Buffers

29


3

Wetland Buffer Protection and Management at the

Local Government Level

56


Buffer Protection Policies, Regulations and

Methods Based on Best Available Science

77


4

References Cited

99


Appendices

A. Summary of Rating System Criteria by Category
and Data Sources


109


B. Guidance on Determining the Buffer Score for the
Advanced Buffer Method


111


C. Method for Determining Soil Texture

116


iii

List of Figures

Figure
Figure 1 - Example of Applying the Advanced Buffer
Determination Method

90

List of Tables

Table 1 - Characteristics of a Valid Scientific Process

22

Table 2 - Sources and Typical Characteristics of Scientific Information

23

Table 3 - Characteristics of Effective Buffers

53

Table 4 - A Summary of Pollutant Removal Effectiveness and
Wildlife Habitat Value Based on Buffer Width

55

Table 5 - Advanced Buffer Width Determination Method

87

Table 6 - Buffer Score Method

90

Table 7 - Wetland Characteristics

93

Table 8 - Description of Potential Development Impacts

94

Table 9 - Buffer Characteristics

95

Table 10 - Buffer Functions

96

Acknowledgements

I would like to thank my thesis committee members, Dr. John Perkins, Dr. David
Milne and Paula Ehlers for their willingness to critique this document and provide
helpful suggestions for improvement. I would also like to thank my colleagues at
the Washington Department of Ecology for their encouragement and support.
Special thanks are due to my parents, Mort and Mary McMillan; they instilled in
me a love of learning from an early age and have supported me in following my
path for 41 years now.
Finally, my greatest appreciation and gratitude are given to my life partner,
Evonne Hedgepeth. She showed me through her own efforts that advanced
degrees can be obtained only through hard work and discipline and that the
rewards are worth the effort. In addition to all of the "normal" support that most
partners provide, Evonne also contributed greatly to the readability of this
document through her editing.

v

Introduction

Wetlands, otherwise known as marshes, bogs or swamps, are important
aquatic resources that humans have only recently begun to appreciate fully. Since
scientific studies in the 1960s and 1970s demonstrated the many valuable
functions that wetlands provide, these areas have become the subject of increased
governmental protection. In recent years, wetlands have been at the center of the
debate over private property rights, as more state and local governments have
begun to regulate land uses in and around wetlands.
One of the most controversial elements of wetlands regulation has been
the practice of requiring narrow upland areas around wetlands to be protected as a
way of buffering the wetland from the impacts of adjacent development. Despite
scientific evidence documenting the value of buffers, this practice has been
challenged by some as an unnecessary and overly burdensome requirement of
private property owners. In this controversy, most of the attention has been
focused on the width of buffer necessary to ensure that the wetland is protected.
In Washington State, the protection of buffers adjacent to wetlands and

streams has been a common practice for over a decade (Castelle et al., 1992).
However, the primary regulation of wetlands occurs at the local government level,
and the lack of statewide minimum requirements for wetland protection has
resulted in a wide range of wetland and buffer protection approaches. Recent
amendments to the state Growth Management Act have added a requirement that
local governments include the "best available science" in formulating their
wetland policies and regulations. This change has sparked an interest in
understanding exactly what constitutes "best available science" and what it has to
say about wetland buffers, among other issues.
In an attempt to provide some clarity and guidance on using best available

science to protect and manage wetland buffers, this paper addresses four primary
issues:

1

1) What is best available science and what does it mean to include it in policies

and regulations?

2) What does the best available science say about wetland buffers?

3) What are the primary concerns related to buffer protection and management?

4) How can best available science on buffers be incorporated into local

government wetland protection policies and regulations?

Each of these issues is addressed in a separate chapter. Before turning to a
discussion of these issues, this introduction briefly defines wetlands, describes
their ecological and social functions, describes wetland protection approaches, and
defines buffers.

Wetlands definition
Wetlands are areas in which water is at or near the surface of the land long
enough to cause distinguishable changes in the soil and vegetation (Lewis, 1995;
Mitsch and Gosselink, 1993). The source of water is usually one or more of the
following: flooding from streams or rivers, precipitation, surface runoff from a
surrounding catchment, and groundwater. Many wetlands are inundated or
saturated for only a portion of the year. Wetlands can occur at the edges of lakes,
streams or estuaries, on slopes where seeps or springs are found, or in depressions
on the land. Many different names are used to describe different wetland types
including marshes, swamps, bogs, mires, and wet meadows. When wet areas are
inundated with standing water deeper than 2 meters for most of the year, they are
called deepwater areas.
In Washington, the state regulatory definition of wetlands is the same as

the federal definition: "Wetlands means areas that are inundated or saturated by

surface or ground water at a frequency and duration sufficient to support, and
that under normal circumstances do support, a prevalence of vegetation adapted
for life in saturated soil conditions. Wetlands generally include swamps,
marshes, bogs and similar areas. [RCW 36.70A.030 (20)]

2

This definition describes three basic elements of a wetland: 1) inundation
or saturation; 2) vegetation adapted to wet conditions; and 3) saturated soils. The
need to identify wetland boundaries in the field has led to the development of a
field-based methodology for determining when these three factors (or parameters)
are present. Currently, the principal method used in Washington to identify
wetlands and delineate their boundaries is the Washington State Wetland
Identification and Delineation Manual (Ecology, 1996).

Wetland functions and values
"Wetlands functions and values" is a widely used and often confusing
term. Generally, wetland functions are considered to be the ecological processes
and benefits provided by wetlands such as nutrient cycling, aquifer recharge and
habitat for wildlife species. Wetland values are considered to be the social
activities that people conduct in wetlands and the benefits that people derive from
wetlands, such as recreation and aesthetic appreciation. However, many of the
ecological processes of wetlands also provide social benefits such as flood
damage reduction or water quality improvement. The imprecise use of these
terms and other related terms such as "wetland functional values" has led to some
confusion on the part of wetland scientists, managers, and the public.
Perhaps a better way of defining the many things that wetlands provide to
nature and society would be to refer to the ecological processes as ecological

functions and the social activities that people conduct in wetlands (e.g. duck
hunting) as social functions. Then, the term values would refer to how much
value society places on particular ecological and social functions. For example, a
given wetland may store and detain floodwaters from an adjacent stream. This
process of storing and detaining the flood water is an ecological function. The
performance of this ecological function may result in less flood damage to human
structures downstream. If so, this function may be highly "valued" by society.
However, if there are no human structures downstream, then this function may not
be valued highly by society.
3

However one defines and distinguishes the functions that wetlands
perform, current federal, state and local laws, policies and regulations affirm the
importance of wetlands. Over the past 30 years, wetland science has
demonstrated the many ecological and social benefits that are derived from the
protection of wetlands. This knowledge has led to the development of regulatory
and non-regulatory efforts, at all levels of government, to protect, enhance and
restore wetlands.

Wetland protection
The primary means of protecting wetlands is through regulation of land
uses including activities both in and around wetlands (Kusler, 1983). Adequate
protection of wetlands necessitates the regulation of direct impacts (such as
filling, draining, clearing, excavating and discharge of pollutants), as well as
indirect impacts (such as alterations to a wetland's water regime or microclimate,
disturbances to wildlife, and non-point pollution). Numerous federal, state and
local laws regulate land uses in and near wetlands. Most of these laws address
broader issues such as water pollution, wildlife habitat or shoreline management;
few of them provide comprehensive protection of wetlands. None of the federal
laws provide comprehensive protection of wetlands and few states have a specific
wetland protection statute.
In Washington State, the Shoreline Management Act, the Water Pollution

Control Act and the Growth Management Act (GMA) all provide for some degree
of protection for wetlands. However, none of these laws provide adequate
coverage of all wetland types and all land uses (see Wetland Regulations
Guidebook {Ecology, 1995} for more detail on laws covering wetlands in
Washington). The Growth Management Act specifically requires local
governments to designate and protect wetlands (as one of five types of "critical
areas"). However, it provides no standards for how to do so other than to state
that local governments must" ... include the best available science in developing

4

a.

L 5Mb pea s .

policies and development regulations to protect the functions and values of critical
areas." The result is a wide variety of approaches and little consistency in the
protection standards for wetlands across the state.

In addition to regulating land uses, several non-regulatory approaches can
be effective in protecting wetlands. These include public acquisition of wetlands,
public-funded restoration of wetlands, and the promotion of landowner
stewardship. Stewardship activities include: education of landowners to foster
voluntary protection of wetlands on their property; cash payments to landowners
for the protection of wetlands and/or buffers; cost-share programs to help fund
enhancement and restoration actions; and tax relief programs that reduce property
taxes in exchange for protection of wetlands and/or buffers. Unfortunately,
funding for non-regulatory approaches is limited and these programs are not
widely utilized.

Wetland buffers

Wetland buffers are an important tool for protecting wetlands and are
particularly critical for protecting wetlands from indirect impacts. A buffer is
broadly defined as "a barrier or treatment zone designed and maintained to protect
one area from the negative impacts of an adjoining area" (Desbonet et al., 1993).
They can range in size from the large buffer zones typically established around
military firing ranges to minimize noise impacts on neighboring residences, to a
fence or hedgerow placed between two suburban yards. A wetland buffer is
typically defined as an upland area of natural or planted vegetation that is
maintained and managed to protect a wetland from the adverse impacts of an
adjacent land use.
Although the term "buffer" is commonly used to describe a protected
upland fringe around an aquatic resource, other terms describe similar areas.
"Vegetated Filter Strips" (VFSs) are a specific type of constructed buffer usually
consisting of a narrow (5-15m) strip of planted grasses along the edge of an

agricultural field. VFSs are used as a Best Management Practice (BMP) in
agricultural settings and are primarily designed for sediment removal. "Riparian
buffers" are widely described in the forestry literature and are typically associated
with streams and rivers. While riparian buffers frequently include wetlands
within them, they are usually comprised of forested upland areas along a flowing
water course.
Whatever names are used to describe them, these areas are intended to
help protect the character and function of aquatic resources. In many cases,
establishing a buffer means simply protecting the existing vegetated area adjacent
to a wetland or stream. If the upland fringe is well-vegetated with trees, shrubs,
and herbaceous plants, all that may need to be done is to designate and protect a
certain width of area measured horizontally from the edge of the aquatic resource.
However, in many cases, the vegetation and/or the soil around the aquatic area has
been significantly disturbed. In these situations, some restoration actions must be
taken in order to create a properly functioning buffer.
Many factors should be considered in determining the appropriate
character and width of buffer necessary to protect a wetland. Considerable debate
and controversy surrounds the issue of determining appropriate buffers and most
buffer regulations adopted by local governments in Washington reflect an attempt
to achieve a balance between scientific understanding, administrative feasibility,
and economic impacts to landowners. However, the Growth Management Act
requirement to include the "best available science" in wetland protection policies
and regulations, compels state and local governments to understand what best
available science is, what it says about wetland buffers, and how to incorporate it
into local wetland protection programs.

6

Chapter 1 - Best Available Science
Introduction
The Washington State Growth Management Act (GMA) requires that local
governments include the best available science in developing policies and
regulations for the protection of wetlands and other "critical areas" (RCW
36.70A.172). The term "best available science" is not defined in the GMA, nor
does the law specify what it means to "include" it in policies and regulations.
Under the GMA, local governments have adopted a wide range of approaches to
protect wetlands, and some of these have been challenged as to whether they
"included" the best available science. Considerable energy and attention
continues to be devoted to the issue of just how best available science can and
should be incorporated into local (and state) regulations.
With the recent listing of several anadromous fish species as "threatened"
or "endangered" under the federal Endangered Species Act (ESA), this issue is
receiving additional scrutiny. The ESA uses a term similar to best available
science and requires that efforts to protect and recover species be based solely on
science.
This chapter examines the available literature on best available science,
and draws upon a draft rule proposed by the Washington State Department of
Community, Trade and Economic Development to provide a possible definition of
best available science and a framework for how to include it in policies and
regulations (Draft rule, WAC 365-195, DCTED, 1999). (NOTE: Where language
from WAC 365-195 appears in this chapter it is italicized.i

GMA Context

The Washington State Growth Management Act (GMA) was passed in
1990 in response to concerns that uncoordinated and unplanned growth posed a

7

threat to the environment, sustainable economic development, and the quality of
life in Washington. The GMA requires state and local governments to manage
Washington's growth by identifying and protecting critical areas and natural
resource lands, designating urban growth areas, preparing comprehensive plans,
and implementing the latter through capital investments and development
regulations.
Of particular concern to many citizens was the lack of protection for
environmentally sensitive areas such as wetlands, streams, and habitat for fish and
wildlife. To address this concern, the GMA required all cities and counties in the
state to "designate and protect critical areas" (RCW 36.70A.170) "Critical areas"
were defined to include wetlands, frequently flooded areas, critical aquifer
recharge areas, geologically hazardous areas, and fish and wildlife conservation
areas.
The GMA granted latitude to local governments in determining how best
to protect critical areas. The statute provided no minimum standards and little
guidance on how critical areas are to be protected. The result was a great variety
of locally developed programs with a wide range of standards and methods for
protecting critical areas.
In 1995, the GMA was amended to include a new requirement: "In

designating and protecting critical areas under this chapter, counties and cities
shall include the best available science in developing policies and development
regulations to protect the functions and values of critical areas" (RCW
36.70A.172(l). However, the legislature did not define the term "best available
science" nor did it clarify the meaning of the verb "include". The lack of clarity
about these two terms has led to continued confusion and debate regarding the
adequacy of local efforts to protect critical areas.
In an attempt to provide some clarity, the Washington State Department of

Community, Trade and Economic Development (CTED), the primary state agency
responsible for administering the GMA, has developed guidelines on how to
include best available science in local critical area policies and regulations. These

8

guidelines define the terms and provide direction on how to evaluate and
incorporate scientific information when developing policies and regulations.
Clarity on this issue was necessary to assist local governments, state
agencies, the regulated community, and the public in determining how best to
protect the functions and values of critical areas through the inclusion of the best
available science. This issue was particularly relevant after the listing in 1999 of
several anadromous fish species as Threatened or Endangered under the federal
Endangered Species Act (ESA). The National Marine Fisheries Service (NMFS)
pointed out that the ESA has a similar requirement to use the "best scientific and
commercial data available." Thus, clarification and guidance on how to identify
and include the best available science in local land use policies and regulations
may have implications beyond administration of the GMA.

Relevant Literature

The phrase "best available science" is not used in any other Washington
State or federal environmental statute. The federal Endangered Species Act
(ESA) contains the phrase "best scientific and commercial data available" but
does not define it. Likewise, the Marine Mammal Protection Act of 1972 requires
the use of "best available scientific data" but provides no definition. Federal
courts have issued conflicting opinions on the ESA phrase (these opinions are
reviewed below). The GMA phrase also has been the subject of several rulings
of the three Growth Management Hearings Boards (Growth Boards) but has not
been clearly defined in any of them. Additionally, the term "include" in this
context has been the subject of Growth Board decisions.

The role of the Growth Management Hearings Boards
In 1991, the GMA was amended to create three regional Growth

Management Hearings Boards to hear and determine allegations of non­
compliance with the GMA and to reflect regional diversity.

9

• The Central Puget Sound Growth Management Hearings Board (Central
Board) has jurisdiction over King, Kitsap, Pierce and Snohomish Counties
and cities within them.
• The Western Washington Growth Management Hearings Board (Western
Board) has jurisdiction over all cities and counties west of the crest of the
Cascade Mountains that are not within the Central Board's boundaries.
• The Eastern Washington Growth Management Hearings Board (Eastern
Board) has jurisdiction over all cities and counties east of the crest of the
Cascade Mountains.
These boards "hear and determine" allegations that a city, county or state
agency has failed to comply with the goals and requirements of the GMA. The
boards are quasi-judicial panels that review local actions when a petition (appeal)
is filed by a party with standing (there are several ways of obtaining "standing"
under the GMA. See RCW 36.70A.280).
Actions subject to review by the boards include adoption or amendments
of critical area regulations. A local government's action is presumed valid and
compliant with the GMA upon adoption; therefore, a petitioner has the burden to
overcome this presumption by demonstrating that the local action is clearly
erroneous in complying with the requirements of the GMA (RCW 36.70A.320).

Additionally, an appellant may request that a Growth Board invalidate the local
action if it is found to substantially interfere with the goals of the GMA. Since
many disputes center on conflicting views of the meaning of GMA terms or
provisions, a board may need to interpret the GMA to clarify ambiguities or
reconcile internal conflicts. This is particularly true in the case of appeals that
claim that local critical area regulations fail to include the best available science.

GMHB decisions on best available science

The three Growth Boards have ruled on at least eleven cases related to best
available science, expressing different opinions regarding the terms "best
available science" and "include." The Western and Eastern Boards reached similar

10

-

conclusions while the Central Board has taken a distinctly different approach.
The five cases that most clearly articulate the views of the three boards are
described below.
In HEAL v. City of Seattle (1996, No. 96-3-0012), the Central Board

deferred to local governments to determine what information constitutes best
available science and concluded that the term "include" was akin to "consider"
and, thus, did not require any particular substantive outcome. Rather, so long as
information that the local government considered to be best available science was
evaluated during the process of developing Critical Area Ordinance (CAO)
regulations, the local government was free to ignore it and adopt regulations based
on other factors. Further, in Tulalip Tribes of Washington v. Snohomish County
[Tulalip II] (1996, No. 96-3-0029), the Central Board ruled that, "As the Tribes
state and the record reveals, the County had the best available science before it
when it developed and adopted the CAO ..... Having this information before it
means that the County included it in developing its CAO." However, the HEAL
decision was appealed to Superior Court and was remanded back to the Central
Board in June, 1997 based on the Court's interpretation that the GMA term
"include" requires a substantive use of the best available science. This decision
has since been appealed to the State Court of Appeals.
Contrary to the Central Board, the Western Board has interpreted RCW
36.70A.172(1) to require a substantive outcome. In Clark County Natural
Resources Council v. Clark County (1996, No. 96-2-001), the Western Board
ruled that the term "include" is different from "consider," that local governments
must use a "reasoned process" to analyze scientific information, and that local
governments must "include best available science in a substantive way in both the
designation and protection components of critical areas." However, the Western
Board deferred to local discretion to determine what constitutes best available
science. They ruled that, "Local diversity has an impact in determining what is
the 'best' science. The goals of the Act, the practicality of the 'science' and the
fiscal impact, relating to the availability of information and to the ultimate

11

decision, must be balanced by a local government in determining how to designate
and how to protect critical areas." In other rulings on best available science, the
Western Board has either explicitly or implicitly relied upon its rationale in the
Clark County case.
The Eastern Board has agreed with the Western Board's conclusion that
the term "include" implies a substantive outcome but has not attempted to define
best available science. In two cases, Woodmansee v. Ferry County(96, No. 95-1­

0010) and Moore v. Whitman County (1997, No. 96-1-005), the Eastern Board
used the term "utilize" to describe how best available science should be addressed
and distinguished it from the term "consider." In another case, Easy and

Washington Environmental Council v. Spokane County (1997, No. 96-1-0016),
the Eastern Board rejected the Central Board's reasoning in HEAL and echoed the
Western Board's Clark County ruling in determining that the law requires a
substantive inclusion of best available science.
Thus, the three Growth Boards have devoted some attention to the issue of
how to include best available science but have failed to provide a clear definition
of the term and have not produced a consistent approach to how best available
science should be included in local policies and regulations.

The Endangered Species Act and best available science
As mentioned above, the ESA includes the requirement that implementing
agencies" ... shall use the best scientific and commercial data available." Neither
the statute nor its implementing regulations define this phrase and the legislative
history does not illuminate Congress's intentions. In a 1994 article in the Idaho
Law Review, Laurence Bogert explains: "As with much of the legislative process,
it can be assumed that Congress believed the language was self-explanatory... ,
But perhaps the omission of further illumination was purposeful." (Bogert, 1994).
Another commentator claims that "Congress intended the listing process (of
endangered species) to be an open door, the broadest possible net for species
threatened with risk to their survival," and that the" .. .legislative requirement for

12

listing remains simple and unexceptional; the decision need only be scientifically
sound" (Houck 1993).
Federal courts have issued numerous rulings on the Endangered Species
Act but few of them have addressed the issue of "best scientific and commercial
data available." A review of those cases that have addressed this phrase fails to
turn up a clear definition and shows conflicting opinions on a standard for best
scientific data available (Bogert, 1994). As an illustration, in Roosevelt

Campobello International Park Commission v, EPA (1982), the First Circuit
Court of Appeals ruled that agencies cannot rely only on scientific information
that is readily available. Agencies also must do "all that is practicable" to collect
relevant data or conduct additional studies. However, in Pyramid Lake Paiute

Tribe v. US Department of the Navy (1990), the Ninth Circuit Court ruled that
even "admittedly weak" scientific information is satisfactory if no plaintiff can
point to existing information that challenges the agencies' conclusions. Most
court cases that have addressed this issue have clearly deferred to the federal
agencies to judge the adequacy of scientific information, only requiring that they
make that information available for public review and scrutiny. It is not clear
whether state courts would grant this same level of deference to state agency
expertise, since the state Administrative Procedures Act (APA) gives less
deference to state agencies than the federal APA grants to federal agencies.
Thus, as with the GMA, the "best available science" language in the ESA
is susceptible to differing interpretations. However, under the ESA, no confusion
exists over how the best scientific data available should be used or "included."
The ESA contains no requirements to balance science with economics or any
other competing interests. The ESA requires federal agencies to base decisions
regarding the listing or delisting of species solely on the basis of the best scientific
and commercial data available [16 U.S.C. § 1533(b)(l)(A)].
Recently, the National Marine Fisheries Service has stated in public
discussions of the ESA that they expect best available science to be the foundation
for efforts to protect and recover threatened or endangered salmon species. They

13

recognize that the best available science may provide numerous options for
protection and recovery but they have stated that any efforts that ignore good
science are not going to "pass muster" (Grady, 1999).

Other Federal Statutes

Several other federal laws dealing with fish and wildlife protection have
included mandates for the use of best scientific information, but none have
defined the terms. Additionally, unlike the ESA, none of them require sole
reliance on science to make management decisions. The 1972 Marine Mammal
Protection Act requires the use of "best available scientific data" as a way to
counter what Congress at the time viewed as too much emotionalism in the debate
and decision-making about the protection and management of marine mammals
(Doremus, 1997). In the Magnuson Act (1976), Congress called for the use of the
"best science available" to assist in the setting of regional fishing quotas.
However, in this Act, Congress clearly intended that the scientific information
include economic and sociological information (Bogert, 1994; Doremus, 1997).

Defining Best Available Science
Legislative bodies commonly use terms in statutes that are not clearly
defined, but it is not always problematic. In some cases, an undefined term may
have a common usage, may have been defined in other statutes, or may be a
relatively unimportant term. However, in the case of best available science, none
of these criteria are true. Best available science is a critical term that has no
common usage; nor has it been defined in any other statute. Perhaps this
"oversight" was intentional since, without a definition, each local government is
able to define the term as it suits them. Or, perhaps the legislature believed best
available science to be such an unambiguous term that a definition was
unnecessary. More than likely, legislators were responding to two competing
interests: environmental interest groups that wanted more scientific objectivity
and less local politics dictating local critical area regulations, and development
14

interest groups that feared the imposition of state-mandated standards and
advocated local autonomy to develop local standards. By requiring the inclusion
of best available science but not defining what it meant, the legislature gave each
of the competing interest groups some of what they wanted.
At any rate, the need remains for local decision-makers to be able to
identify best available science and determine how to include it in local critical
area policies and regulations. The Growth Management Hearings Boards have
provided little guidance on how to identify best available science and
contradictory perspectives on how it should be included. Recently, the
Washington Department of Community, Trade and Economic Development
(CTED), the state agency responsible for administering the GMA at the state
level, has stepped into this void and begun developing guidance that it is adopting
into state regulations. It is a common practice for agencies responsible for the
administration of a statute to adopt rules that define ambiguous legislative terms
and fill in the gaps in statutes. CTED rules adopted under the GMA do not have
the same legal standing as other state regulations, in that they are guidelines that
local governments need only consider in developing local GMA policies and
regulations. Nevertheless, in the absence of any legislative clarification of these
terms, CTED guidelines likely will be considered as the state "standard."
Before describing the CTED guidelines, it may be useful to consider the
meaning of each of the three words in the phrase "best available science"
separately, starting with standard dictionary definitions. Additionally, while none
of the statutes that require best available science define any of the words in the
phrase, some judicial cases may shed light on possible meanings.

Defining "Best"
According to Webster's Encyclopedic Unabridged Dictionary of the
English Language (1989), "best" means "of the highest quality, excellence or
standing" or "most advantageous, suitable or desirable."

15

In the Clark County case, the Western Growth Management Hearings

Board wrote, "'Best' means that within the evidence contained in the record, a
local government must make choices based upon the scientific information
presented to it. The wider the dispute of the scientific evidence, the broader the
range of discretion allowed to local government." The federal judiciary has not
defined "best" but have indicated that the "best" science is relative. In several
cases they have upheld agency decisions based on weak or inconclusive scientific
information where no conflicting evidence was presented (Bogert, 1994;
Doremus, 1997).
In cases where the scientific evidence is conflicting, determining which

science is the "best" is more difficult. The CTED guidelines provides a good
framework for evaluating scientific information and determining which is
"sound", if not which is "best." However, under the GMA, local governments are
given latitude in choosing among conflicting evidence.

Defining "Available"

According to Webster's Encyclopedic Unabridged Dictionary of the
English Language (1989),

"available" means "suitable or ready for use,"

"readily attainable and accessible."
Again in the Clark County case, the Western Board wrote, '" Available'
means not only that the evidence must be contained within the record, but also
that the science must be practically and economically feasible." Federal court
decisions have given contradictory views on how available the best scientific
information must be. At times they have said that agencies are under no
obligation to develop new scientific information - only that they must evaluate all
information that comes to their attention (Doremus, 1997). In other cases, they
have ruled that agencies must conduct additional studies, if necessary, to collect
the best scientific information (Bogert, 1994).
It is possible that a Growth Board could require a local government to set

up and conduct additional scientific studies where information is lacking.

16

However, the emphasis has been (and likely will continue to be) on the
information that is provided in the public record through the lengthy process of
developing and adopting local policies and regulations. This public process
generally produces ample scientific information from agencies and interested
public and private organizations. It is likely that any future debates over the
"availability" of scientific information will center around the issue of how
practical it is to apply the information and what the economic consequences of
that application might be.

Defining "Science"

According to Webster's Encyclopedic Unabridged Dictionary of the
English Language (1989),

"science" means "systematic knowledge of the

physical or material world", or "a branch of knowledge or study dealing with a
body of facts or truths systematically arranged and showing the operation of
general laws", or "knowledge gained by systematic study."
None of the Growth Management Hearings Board cases or federal court
decisions have attempted to define "science," perhaps because none of the cases
involved a dispute over what constituted science. Alternatively, perhaps it has
been assumed that the nature of science is so obvious that no definition is needed.
However, in the context of critical areas protection, local governments
frequently are in the position of needing to evaluate a wide range of information
that includes scientific fact, economic data, personal opinion, and philosophical
perspective. Given the mandate to "include" the best available science, local
government decision-makers must be able to distinguish science from other types
of information and determine which scientific information is of highest quality
(best) and most accessible or practical (available).
What sets scientific information apart from other types of information is
its grounding in empirical observation and its independence from individual
preferences and beliefs. The scientific process is responsible for the production of
these characteristics and consists of five basic steps: a) formulation of

17

hypotheses, b) use of empirical data to test predictions of the hypotheses, c)
quantification of data, if possible, d) formal peer review, and e) a willingness to
reject a "proven" hypotheses in the light of new data judged to be reliable.
Philosophy of science in the last forty years has added many other complexities to
the debate about the nature of science and how it changes (Kuhn, 1962), but these
five characteristics are generally sufficient to distinguish "scientific" information
from non-scientific information.
Taken together, these five steps comprise an iterative process that
produces observations and findings that are repeatable and available for critique.
This tends to correct for an individual's subjective tendencies. Individually, a
couple of key elements of this process make the resulting information more
trustworthy than information that has not been similarly developed.
First, a scientist must describe the data collection methods used, to enable
others to undertake the same experiment or observations and determine whether
the resulting data are consistent. Second, a scientist presents the data and makes
inferences about what the data mean, which allows others to independently
examine the data and decide whether the inferences are reasonable. Third, the
methods, data, and conclusions are presented for critique through established
channels including journals and symposia, providing opportunity for critical peer
review by others with expertise in the field of study and a mechanism for
corroboration and dissent. The scientist and others interested in the subject are
then able to respond to this critique by revising or developing new hypotheses,
collecting additional data, and presenting new ideas and information for further
review and critique.
This iterative process of the scientific method is described by Doremus
(1997) as similar to building a staircase. "Data serve as the raw materials.
Scientists use those materials to create a step, reinforcing it until it can bear the
weight of the scientific community's skepticism. When the step is strong enough,
the community climbs onto it, and begins constructing the next step. Occasionally

18

a step collapses and must be rebuilt. Scientific knowledge thus evolves over
time."
Because every individual, even a prominent scientist, is subject to bias,
this process of developing scientific information serves to weed out those
hypotheses or theories that cannot be supported by repeated observation and
analyses of different scientists. In recent decades, the objectivity of science has
been called into question and scientists have had to admit that, like all humans,
they have biases. Biases may be financially or politically motivated, or the result
of adherence to a certain philosophy or "school of thought." Indeed, a whole field
of science may have a bias by subscribing to a certain "paradigm" about the way
the natural world operates. However, the regular upheavals and subsequent
"tossing-out" of once dominant paradigms demonstrates that the scientific process
ultimately provides new and better knowledge, albeit sometimes rather slowly.
Thus, information produced by a rigorous scientific process is generally
the most accepted type of knowledge. The more rigorous the process, the more
acceptable the information is likely to be to the community of scientists.
Reliability is another aspect of scientific information that is important
when dealing with biological systems. Natural systems are inherently complex
and it is difficult to study nature in a controlled environment. Studies of
biological systems produce results that vary widely and, thus, are more subject to
different interpretations than findings in other branches of science such as physics.
The wide variation in organisms, communities, climate, and other natural
phenomenon produces results that are difficult to repeat and can be difficult to
interpret. Reliability can be increased by conducting more expensive and time­
consuming experiments or by repetition of simpler, more practical ones.
Statistical tests of significance also help to establish reliability by assisting
scientists in discriminating between random and meaningful variation. Generally,
scientists accept that some underlying "cause" is at work, when data, which would
be expected to occur by random chance less than 5% of the time, are obtained.

19

The acceptability and reliability of scientific information are particularly
important when attempting to determine what scientific information is the "best."
In general, information developed through a rigorous scientific process is "better"

than information that was not. Likewise, information that is the result of multiple
studies of the same or similar phenomena is "better" than information provided by
a single study. For the most part, scientists regard new knowledge that has
withstood the scrutiny of peers as "best".
Based on the above discussion, a reasonable definition of best available
science is "the highest quality information developed through the scientific

process that is accessible and practical to use."
However, this definition does little to help local governments identify the
appropriate body of work that needs to be included in their decision-making.
How does one, especially a non-scientist, identify the "highest quality" science
and distinguish it from science of a lower quality? When confronted with
conflicting scientific information, how does a local decision-maker evaluate
which science is "better?" How accessible and practical must science be? How
much effort must a local government invest in trying to locate the best available
science?

A Proposed Model for Identifying Best Available Science
The CTED rule provides a good framework for answering these questions.
It outlines the responsibilities of local governments to identify and evaluate

scientific information and provides criteria for determining whether information is
scientific and for evaluating the quality of scientific information.

Identifying Best Available Science
The CTED rule clarifies that it is the responsibility of a local government's
elected decision-makers to ensure that the best available science is included in
their policies and regulations. Specifically, the local government executive
agencies must first identify and compile the best available science that is relevant
20

to the critical areas they are attempting to protect. Recognizing that most local
governments do not have the staff expertise or time to conduct a complete review
of the available scientific literature on all critical areas, the rules recommend that
local governments employ or consult with a qualified scientific expert (or team of
experts) to assist them and/or consult with state natural resource agencies to
provide the necessary expertise. While any local government is free to conduct its
own analysis, many will choose to use the information provided by agencies with
expertise, where it is available, to incorporate into their local policies and
regulations.
To assist in the identification and evaluation of relevant scientific
information, the CTED rule describes scientific information and provides criteria
for evaluating the quality of scientific information. It lists eight sources of
scientific information and specifies six different characteristics, one or more of
which must be present for each of the sources to be considered scientifically
objective and reliable. To determine whether information received during the
public participation process is reliable scientific information, a county or city must
determine whether the source of the information displays the characteristics of a
valid scientific process. The characteristics generally to be expected in a valid
scientific process are listed in Table 1.

21

Table 1 - Ch"'4racteristjps of a "V.q
. lid Scientifi c Process"

...

1. Peer review. The information has been critically reviewed by other
p erson s who are experts in that scientifi c disciplin e. The criticism of the peer
reviewers has been addressed by the propon ents of the information.
Publication in a refere ed scientifi c journal usually indic ates that the
information has been app rop riately peer-re viewed.
2. Methods. The methods that were used to obtain the information are
clearly stated and able to be repli cated. The meth ods are standardized in the
pertin ent scientific dis ciplin e or, if not, the methods hav e been appropriately
peer-r eviewed to assure their reliability and validity.
3. Logical conclusions and reasonable inferences. The conclusions
presented are based on reas onable assumptions supported by other studies
and consistent with the general theory underlying the assumptions. The
conclusions are logically and reasonably derivedfrom the assumptions and
supported by the data presented. Any gaps in information and inconsistencies
with other pertinent scientific information are adequately explained.
4. Quantitative analysis. The data have been analyzed using appropriate
statistical or quantitative methods.
5. Context . The information is pla ced in proper context. The assumption s,
analytical techniques, data, and conclusions are appropriately fram ed with
respect to the prevailing body of pertin ent scientific knowledge.
6. References. The assumptions, analytical techniques, and conclusions are
well-referenced with citations to relevant, credible literature and other
pertin ent existing information.

* from the CTED rule.
(Note: Language from the CTED rule is in italic s)
Som e sources of information routinely exhibit all or som e of the characteristics
listed in Table 1. Information deri ved from one of these sources may be
considered scientifi c information if the source posses ses the characteristics
necessary to ensure the information is scientifi cally valid and reliable. A county
or city may consider information to be scientifi cally valid if the sourc e poss esses
the characteristics listed in Table 1. Tabl e 2 provides a general indication of the
characteristics typically associated with common sources of scientific
information.

22

Table 2 - Sburcesof Sciiintific,f/nforlT)ation!~'

;,CHARACTE/flISTICS

(characteristics are from Table 1)
1 2
3
4
5
6
A. Research. Research data collected
and analyzed as part of a controlled experiment
x x x x x x
(or other appropriate methodology) to test a
specific hypothesis.
B. M onitoring. Monitoring data collected
periodically over time to determine a resource
x x y x x
trend or evaluate a manaqement proorem.
C. Inventory. Inventory data collected
from an entire population or population segment
(e.g., individuals in a plant or animal species) or
x x y x x
an entire ecosystem or ecosystem segment
(e.g ., the species in a particular wetland).
D. Survey. Survey data collected from a
x x y x x
statistical sample from a population or
ecosystem.
E. Modeling. Mathematical or symbolic
simulation or representation of a natural system.
Models generally are used to understand and
explain occurrences that cannot be directly
x x x x x x
observed.
F. Assessment. Inspection and
evaluation of site-specific information by a
x x
x x
qualified scientific expert. An assessment may
or may not involve collection of new data.
G. Synthesis. A comprehensive review
and explanation of pertinent literature and other
x x x
x x
relevant existing knowledge by a qualified
scientific expert.
H. Expert Opinion. * Statement of a
qualified scientific expert based on his or her
best professional judgment and experience in the
x
x x
pertinent scientific discipline. The opinion mayor
may not be based on site-specific information.
x = characteristic must be present for information derived to be
considered scientifically valid and reliable
y= presence of characteristic strengthens scientific validity and
reliability of information derived, but is not essential to ensure
scientific validitv and reliability

* Wheth er a person

is a qualifi ed scientific expert with expertise appropriate to the
relevant critical areas is determin ed by the person 's professional credentials and/o r
certification, any advan ced degre es earn ed in the pertin ent scientifi c disciplin e from a
recogni zed univ ersity, the number of years of expe rience in the pertin ent scientific
dis ciplin e, recognized leadership in the discipline of interest, f ormal training in the
spec ific area of expe rtise, and fie ld and/or laborat ory expe rience with evidence of the
ability to produ ce peer-reviewed publications or other prof essional literature. No one

23

factor is determinative in deciding whether a person is a qualified scientific expert.

(WAC 365-195-905).
The CTED guidance further specifies some common sources of
information that local governments may receive that do not constitute science:

Common sources of nonscientific information. Many sources of information
usually do not produce scientific information because they do not exhibit the
necessary characteristics for scientific validity and reliability. Information from
these sources may provide valuable information to supplement scientific
information, but should not be used as a substitute for valid and available
scientific information. Common sources of nonscientific information include the
following:
(i) Anecdotal information. One or more observations which are not part
of an organized scientific effort (for example, "I saw a grizzly bear in that area
while I was hiking").
(ii) Non-expert opinion. Opinion of a person who is not a qualified
scientific expert in a pertinent scientific discipline (for example, "I do not believe
there are grizzly bears in that area").
(iii) Hearsay. Information repeated from communication with others (for
example, "At a lecture last week, Dr. Smith said their were no grizzly bears in
that area (WAC 365-195-905).

The rule goes on to address the situation where valid scientific information
is unavailable or incomplete. It states,

Where there is an absence of valid scientific information or incomplete
scientific information relating to a county's or city's critical areas, leading to
uncertainty about which development and land uses could lead to harm of critical
areas or uncertainty about the risk to critical area function of permitting
development, counties and cities should use one of the following approaches:

24

(1) A "precautionary or a no risk approach, " in which development and
land use activities are strictly limited until the uncertainty is sufficiently resolved;
or
(2) As an interim approach, an effective adaptive management program
that relies on scientific methods to evaluate how well regulatory and non­
regulatory actions achieve their objectives. Management, policy, and regulatory
actions are treated as experiments that are purposefully monitored and evaluated
to determine whether they are effective and, if not, how they should be improved
to increase their effectiveness. An adaptive management program is a formal and
deliberate scientific approach to taking action and obtaining information in the
face of uncertainty. To effectively implement an adaptive management program,
counties and cities must be willing to (i) pay for a research program (ii) change
course based on the results and interpretation of new information that resolves
uncertainties, and (iii) commit to the appropriate timeframe and scale necessary
to reliably evaluate regulatory and non-regulatory actions affecting critical areas
protection and anadromous fisheries. (WAC 365-195-920).

The rule language outlined above provides useful guidance for identifying
and evaluating scientific information. It will also provide guidance to those
agencies or individuals interested in compiling scientific information for local
governments to consider. However, while the identification and evaluation of
scientific information is an important step, the process of "including" best
available science in policies and regulations is crucial.

Including the best available science in local policies and
regulations

RCW 36.70A.172 requires that local governments must "include" the best
available science in critical area policies and regulations. As described above, the
term is not defined in statute and has been the subject of several Growth

25

Management Hearings Board cases. In a law review journal article recently
submitted for publication, Alan Copsey, CTEDs lead Assistant Attorney General
for GMA, addresses this issue in some depth (Copsey, 1999). He analyzed the
legislative record and determined that RCW 36.70A.172 was derived from a
recommendation of the Governor's Task Force on Regulatory Reform which
stated in its final report, "The GMA requires all local governments to provide for
the protection of certain critical areas. Because of the state's interest in these
areas, the Legislature must establish clear direction of the state's goals and
policies for the protection of these areas. The direction should be given by
requiring local governments to use the best available science when designating
and protecting critical areas."(emphasis added) (Governor's Task Force on
Regulatory Reform, 1994).
Further, the Final Legislative Report on this amendment also characterized
the effect of the amendment as requiring counties and cities to use best available
science. Copsey finds this word choice to be significant and argues that, had the
Legislature not intended for local governments to substantively incorporate best
available science, they would have required that local governments simply
"consider" best available science, a common type of requirement in the GMA
(Copsey, 1999).
In Webster's Encyclopedic Unabridged Dictionary of the English

Language (1989) "include" is defined as "to contain, embrace or comprise" or "to
contain as a subordinate element" or "involve as a factor." These definitions are
consistent with the approach taken by the two Growth Boards, which defined
"include" to require a substantive outcome, and with Copsey's analysis.
Webster's definition is also consistent with the conclusion that best available
science is not the sole foundation for critical area policies and regulations but
must be balanced with other considerations or factors; best available science is
one element or factor that must be included in the policies and regulations.
The proposed CTED rules recognize the difficulty in specifying exactly
how to include best available science and the need to consider other relevant

26

factors. Thus, they do not provide a prescriptive approach. They emphasize that
local governments should explain what science was evaluated and how it was
"balanced" with other factors. This approach allows others to understand and
critique how best available science was "included" in local policies and
regulations.
The rules state:

(1) To demonstrate that the best available science has been included in the
development of critical areas policies and regulations, counties and cities should
address each of the following on the record:
(a) The specific policies and development regulations adopted to protect
the functions and values of the critical areas at issue.
(b) The relevant sources of best available scientific information included
in the decision-making.
(c) Nonscientific information-including legal, social, cultural, economic,

and political information-considered as a basis for departing from
recommendations derived from the best available science. A county or city
departing from science-based recommendations should: (i) identify the
information in the record that supports its decision to depart from science-based
recommendations; (ii) explain its rationale for departing from science-based
recommendations; and (iii) identify potential risks to the functions and values of
the critical area or areas at issue and any additional measures chosen to limit
such risks. State Environmental Policy Act (SEPA) review often provides an
opportunity to establish and publish the record of this assessment.
(2) Counties and cities must include the best available science in determining
whether to grant applications for administrative variances and exceptions from
generally applicable provisions in policies and development regulations adopted
to protect the functions and values of critical areas. Counties and cities should
adopt procedures and criteria to ensure that the best available science is included
in every review of an application for an administrative variance or exception
(WAC 365-195-915).

27

This guidance clearly leaves it to the local government to determine how
to include best available science in policies and regulations but requires that the
rationale be clearly articulated. This will help prevent the blatant disregard of
scientific information and will expose those decisions that are based solely on
politics or economics. This approach will require that local decision-makers have
some understanding of what the best available science says and require them to
weigh this information seriously in their deliberations. It will help ensure that
scientific information is, in fact, included in local policies and regulations.
Furthermore, this approach will provide more information for anyone wishing to
challenge a local decision and for the Boards and courts that must evaluate such
challenges. Ultimately, it will be up to the Growth Management Hearings Boards
(or the courts) to provide a "bright-line" definition or standard for how best
available science must be included in local policies and regulations.
Fortunately, for those needing to develop critical area policies and regulations,
the science of wetland buffers is extensive and easily identifiable. Unlike other
aspects of critical areas protection, the topic of buffers has been researched and
documented over the past twenty years. A summary of this information is
outlined in Chapter two.

28

Chapter 2 The science of wetland buffers: a review of the

literature
The science of wetland buffers has been the subject of much study and
analysis during the past twenty years. Scientific studies in the 1960s and 70s
documented the important ecological functions of wetlands and led to efforts to
protect them. Research and experience demonstrated that allowing development
up to the edge of wetlands, streams or lakes resulted in impairment of these
ecological functions and led to the practice of protecting vegetated upland zones
around them.
The protection and management of vegetated areas around wetlands,
streams, and lakes is now a widely used method for maintaining the various
ecological and social functions performed by these aquatic resources in the face of
adjacent development. While some disagreement occurs today over whether a
buffer area should even be maintained around a wetland or along a stream, most
debate focuses on the character and width of buffers necessary to protect aquatic
system functions. Much debate also continues over what kinds of activities can be
allowed within a buffer area without compromising its functions.
The determination of appropriate buffers, whether at a programmatic or
site-specific scale, has usually involved a blending of science, politics, economics,
and sociology. However, the Washington State Growth Management Act
requires that the determination of appropriate buffers be based upon a solid
scientific foundation (see Chapter 1). Fortunately, considerable scientific data
currently exist from which to determine appropriate buffers for aquatic resources.
What follows is a general overview of what the relevant scientific literature (i.e.
"best available science") has to say about the use of buffers to protect wetland
functions.

29

Identifying the Best Available Science on Wetland Buffers

The following scientific information on wetland buffers was derived from
a variety of sources. The majority comes from studies published in refereed, peer­
reviewed journals in the fields of environmental science, agriculture, forestry, and
wildlife management. Considerable information comes from government
publications on wetland or riparian buffers published in the past ten years. The
roles and functions of wetland and riparian buffers have been widely studied and
increased scientific attention has been devoted to the subject since buffers became
a widely used management tool in the 1980s. There is considerable agreement
among scientific researchers on the ways that buffers function to protect aquatic
resources and on the buffer characteristics necessary to adequately protect them.
There are, however, some gaps in our understanding of buffer functioning, with a
need for additional research. A summary at the end of this chapter provides an
overview of what is known and what remains to be understood.
The scientific information on buffers outlined below is divided into four
sections: Buffers and Water Quantity; Buffers and Water Quality; Buffers and
Wildlife Habitat; and Buffer Protection.

Buffers and Water Quantity

The role of buffers in protecting wetland hydrology
The primary hydrologic function that wetland buffers perform is
"hydroperiod maintenance" i.e., moderation of water level fluctuations in the
wetland. Wetland plant and animal species are adapted to the natural fluctuations
in water levels within a wetland. As the land around a wetland is developed, the
hydrologic regime in the wetland can change. When the impervious area within
the drainage basin of a wetland increases, less water infiltrates into the ground and
more water flows across the surface of the land. This means that the runoff from
rainfall and snowmelt moves more quickly downgradient rather than moving

30

slowly through the soil. Thus, the wetland's hydroperiod exhibits both higher
than normal water levels during rainy periods and lower than normal levels during
dry periods. This fluctuation has been shown to have an adverse effect on wetland
vegetation and wildlife, particularly amphibians (Azous and Homer, 1995).
Studies in King County, Washington have shown that wetland hydroperiods are
adversely altered in watersheds with as little as ten to fifteen percent impervious
surface (Azous and Homer, 1997). Hydroperiod alteration is particularly acute in
wetlands that have significant surface water input, as opposed to groundwater
input.
In addition to moderating water level fluctuations within a wetland,

buffers playa role in floodwater storage and flood damage reduction. In
particular, buffer areas adjacent to riverine wetlands that are subject to overbank
flooding help detain flood waters. Also, since the establishment of buffers results
in development being set back from the edge of wetlands, flood damage to
property is less likely to occur when high water levels extend beyond the wetland
boundary.

How buffers protect wetland hydrology
Wetland buffers may help moderate hydroperiod fluctuations by detaining
surface runoff and slowly releasing it into the wetland. This effect is primarily a
function of surface water detention and soil infiltration. In a 1982 study, Wong
and McCuen determined that the most influential factors in determining the extent
of buffer performance of this function were the following: vegetation cover, soil
infiltration capacity, rainfall intensity and antecedent soil moisture conditions.

Buffer characteristics that affect protection of wetland hydrology
In most cases, the effect of a buffer on moderating hydroperiod

fluctuations is minimal compared to the effects of large-scale watershed alteration.
In wetlands with large watersheds and a high percentage of impervious surface,

buffers play an insignificant role in moderating hydroperiod fluctuations.

31

However, in wetlands with small surface drainage areas, buffers can play an
important role in maintaining natural hydroperiods. Little research has been
conducted as to appropriate buffer widths to perform this function. It seems
reasonable to assume that, as buffer width increases, the ability of the buffer to
moderate wetland hydroperiod fluctuations also increases. However, with the
exception of wetlands with small surface drainage basins, the use of buffers to
protect a wetland's hydroperiod is not nearly as effective as other approaches,
such as controlling the amount of impervious surface and using Best Management
Practices for controlling stormwater (Herson-Jones et al., 1995).

Buffers and Water Quality

The role of buffers in protecting wetland water quality.
The most widely studied of the different buffer functions is the protection
of water quality of downgradient aquatic areas. Considerable research has been
devoted to a buffer's ability to remove potential pollutants from surface and
ground water. Much of the attention has been devoted to how buffers protect
streams and rivers, primarily from agricultural and silvicultural activities.
However, buffers around wetlands perform water quality functions similarly to
buffers along streams. They trap sediment, denitrify nitrates and sequester
phosphorous and toxic substances. The same buffer processes remove sediment
and nutrients, regardless of whether they are adjacent to a stream, a wetland or a
lake. What differs is not the way in which the buffer performs its functions, but
the way the aquatic resource functions and how a particular pollutant or
disturbance affects those functions.
Wetlands perform many of the same water quality related functions
attributed to upland buffers. However, wetlands have a limited capacity to
perform these functions before they begin to suffer adverse impacts. Excessive
sediment can fill in wetlands, smother vegetation and harm invertebrate habitat.

32

Added nutrients can spur excessive plant and algae growth. Toxic substances can
accumulate to the point where they kill aquatic organisms.
Some wetlands are more susceptible to these harmful effects than others.
Bogs and wetlands with open water are subject to the harmful effects of increased
nutrients. However, other wetlands may not be harmed by the input of small
amounts of nitrates or other pollutants. In general, however, it is wise to limit the
introduction of sediment, nutrients or toxic substances into any wetland or water
body in order to reduce the risk of ecological impairment within the wetland or to
downgradient surface or ground water.
Our knowledge of how buffers improve water quality comes from
extensive studies carried out over the past 25 years, including data collection at
field sites with natural buffer conditions and controlled experiments on a variety
of different buffer characteristics. The principal pollutants studied have been
sediment, nitrogen (particularly nitrates) and phosphorous, and, in a few instances,
bacteria and toxic substances. While most of these studies have been conducted
in the Mid-Atlantic and Midwestern states and only a few in the Pacific
Northwest, similar conditions exist in Washington as at the various sites that have
been studied in other regions. Some generalizations can be made from the
scientific literature; however, the nature and extent of pollutant removal by
buffers is highly variable. The primary factors that influence pollutant removal
are discussed below.

How buffers improve water quality
Buffers provide water quality benefits through a variety of mechanisms.
Primarily, they improve water quality in four basic ways: 1) they remove
sediment (and attached pollutants) from surface water flowing across the buffer;
2) they biologically "treat" surface and shallow groundwater through plant uptake
or by biological conversion of nutrients and bacteria into less harmful forms; 3)
they bind dissolved pollutants by adsorption onto clay and humus particles in the
soil; and 4) they help maintain the water temperatures in the wetland through

33

shading and wind blockage. These mechanisms are discussed in more detail
below.

How buffers remove sediment
The primary mechanisms that remove sediment in a buffer are the
dissipation and slowing of surface water flow and infiltration. As water flowing
across a buffer is slowed, sediments drop out and are held in place by plants and
organic debris. The most important factors controlling this process are sheet flow
and filtration (Desbonnet et al., 1993; Castelle et al., 1992; Phillips, 1989a). If
water moves across a buffer as channelized flow, most of the sediments will be
carried with the water. A broad, sheet flow of water across the buffer, on the
other hand, allows for more slowing and settling as well as increased water
filtration by plant stems and organic debris.
The most critical buffer variables that affect sedimentation are slope and
the type of vegetation (Dill aha et al., 1989; Phillips, 1989a). On steeper slopes,
water is more likely to move in channels, too quickly to allow for settling. Denser
vegetation and organic debris help to slow flows and to filter out sediments. The
most effective types of vegetation are grassy areas, or forests with a dense
understory and organic litter and woody debris (Phillips, 1989a).
In most vegetated buffers, larger sediment particles drop out readily but
smaller particles may remain in suspension. If enough slowing and filtration is
provided, then finer sediments are removed. This is especially important to water
quality because many pollutants, such as insoluble phosphorous and certain
metals, are bound to sediments, in particular the finer sediments. Deposition of
fine sediments requires extensive detention time to allow for settling (Karr &
Schlosser, 1977).

How buffers remove nutrients
While nutrients are essential for living organisms and are a critical
component of a healthy aquatic ecosystem, excessive nutrients can have an

34

adverse impact on aquatic systems. The primary nutrients of concern are
phosphorous and nitrogen. Phosphorous is a limiting nutrient in most freshwater
systems, and inputs to surface waters can cause excessive plant and algae growth.
This, in turn, leads to reduced dissolved oxygen, increased suspended solids and
blocking of sunlight in the water column. Nitrogen is a limiting nutrient in most
estuarine (and some riverine) systems, and nitrates are a concern for human health
if they get into drinking water supplies.
As much as 85% of phosphorous (P) and some forms of nitrogen (N) in
surface waters are bound to sediments, and thus can be removed by the
mechanisms described above (cite). However, soluble P and nitrate must be
removed by other means. The principle mechanisms for removing soluble
nutrients are through plant uptake and nitrification/denitrification (for nitrogen).
Plant uptake is limited to the growing season and varies widely among
different plant species. Nitrification and denitrification can occur year round and
are most effective in seasonally saturated areas. These processes occur in the
shallow sub-surface zone of the soil (i.e. where plant roots and microbes are
found) and require an extended detention time to provide much removal. While
nitrates are readily removed by these processes, several studies have shown that
reduction of P is very limited beyond that removed through sedimentation (Karr
and Schlosser, 1977).

How buffers remove pathogens and toxic substances
Bacteria (such as fecal coliform) and toxic substances (such as pesticides
and metals) are removed by buffers through mechanisms like those described
above. Microbial treatment of bacteria by buffers has been demonstrated in
studies of feedlot runoff (Dillaha et al., 1988; Young et al., 1980). Removal of
metals occurs primarily by trapping sediments with attached metals, by plant
uptake, and by adsorption of dissolved metals onto clay or humus particles in the
soil. Removal of pesticides occurs primarily through biochemical processes that
degrade the pesticide (Patty et aI., 1997).

35

How buffers control erosion
Buffers are also effective at reducing erosion and scouring of lands
adjacent to wetlands. The vegetation in buffers reduces the erosive effect of
rainfall, dissipates surface flows and helps bind the soil, which reduces
channelization and erosion of the buffer area itself (Shisler et al., 1987). Plant
species with fine and very fine roots are most effective at binding the soil and
preventing erosion (Kleinfelder et al., 1992). By limiting erosion, buffers reduce
the deposition of sediment into wetlands.

How buffers maintain water temperature and microclimate
Buffers with forest vegetation help moderate air and water temperature
through shading and blocking the wind. Adequate buffers can help reduce
summer temperatures and maintain higher winter temperatures. Maintaining
natural water temperatures is important for three reasons: 1) many aquatic
organisms, such as fish, are adapted to a particular temperature range and cannot
tolerate greater fluctuations; 2) warmer water contains less dissolved oxygen
(which is necessary for aquatic life); and 3) warmer water weakens the bond
between nutrients and sediment particles, thus increasing soluble nutrients in the
water (Karr and Schlosser, 1977).

Buffer Characteristics that Affect Water Quality

The scientific literature on buffers makes clear that determining
appropriate buffer widths and characteristics to achieve a desired water quality
objective is very site-specific. How wide a buffer needs to be to improve water
quality to a desired level depends on several factors, principally the loading rate of
the pollutant, slope, soil type and vegetation composition and structure. A buffer
with a steep slope or sparse vegetation will require greater width to achieve the
same amount of sediment or nutrient removal as a buffer with a flatter slope and
dense vegetation. The relative importance of each of these factors relates to the
types of pollutants expected and the nature of the waterbody to be protected.

36

However, it is seldom possible to alter the slope or soil type present in a
buffer and there is only so much one can do with vegetation. Loading rates can be
reduced by pretreatment of the polluted runoff in detention basins or grassy
swales. In most cases, buffer width is the easiest factor to control (Phillips,
1989a). As a general rule, the wider the buffer, the more effective it is in
improving water quality (Castelle et al., 1992; Desbonnet et aI., 1993).
Furthermore, many studies show that the relationship of width to water quality
improvement is not linear. Beyond a certain width, it takes a progressively wider
buffer to achieve incremental improvements in pollutant removal (Desbonnet et
al., 1993; Castelle and Johnson, in press).
Determining appropriate buffer widths for water quality protection
requires a decision regarding the level of potential harm to the wetland that is
acceptable, as well as an understanding of the factors that influence buffer
functions. Chapter Three examines management issues in more detail but the
discussion below sheds some light on what the Best Available Science says about
the effectiveness of varying buffer widths in removing pollutants and protecting
water quality.

Buffer effectiveness in removing sediment
The most important factors influencing how well a buffer filters out
sediment from surface waters include the slope of the buffer, the roughness of the
ground surface (based on vegetation and organic debris) and the way water flows
across the buffer. The scientific literature on this buffer function is abundant and
consistent. Studies conducted around the world have shown that if water travels
as sheet flow across a well-vegetated area with little slope, then the majority of the
coarse sediments will drop out within a few meters (Dillaha et al., 1989; Karr &
Schlosser, 1977). Filtering of finer sediment particles requires further slowing of
the water and thus usually requires additional buffer width.

In one of the earliest studies of this function, Wilson (1967) demonstrated
that sand-sized sediment was deposited within 3 meters whereas silt and clay

37

required 15 m and 122 m respectively. Numerous studies have shown that, with a
slope less than 5%, a grassy buffer of 5-15 meters will effectively remove all but
the fine particles from sheetflow (Desbonnet et al., 1993; Ghaffarzadeh et al.,
1992). Other studies have shown sediment reduction rates of 75-92% with buffers
ranging from 25-30 m (Lynch et al., 1985; Wong & McCuen, 1982; Young et al.,
1980).
However, once the slope exceeds 5%, surface roughness is reduced, or
flow becomes channelized, the efficiency of a buffer is significantly reduced. For
example, in studies where buffer conditions were not optimal, buffer widths of
60-100 m were necessary to achieve sediment reductions of 50% (Gilliam and
Skaggs, 1988; Broderson, 1973).
In a review of 19 studies, Desbonnet et al. (1993) concluded that, if

properly designed, a buffer as small as 2 m wide could remove up to 60% of
suspended sediment whereas a 25 m buffer could remove 80%. However, to
achieve even small increases above 80%, buffer widths would have to be
increased significantly. In a similar comparison, Wong & McCuen (1982) found
that, under similar conditions, a 30.5 m buffer removed 90% of sediments while a
61 m buffer was needed to remove 95%.

Buffer effectiveness in removing nutrients
Numerous studies have evaluated the effectiveness of vegetated buffers at
removing nitrogen and phosphorous (the primary nutrients of concern to water
quality). However, the characteristics that determine buffer effectiveness at
removing nitrogen are different from those that determine buffer effectiveness at
removing phosphorous, as noted below.

Nitrogen removal
Since most nitrogen in surface runoff occurs in the soluble form, buffer
effectiveness is dependent upon microbial action and plant uptake. These
processes require significant contact time between the water and the shallow,

38

biologically active zone in the soil. Thus, the factors that determine buffer
effectiveness at removing N are slope, soil composition, and width. The desired
characteristics are flat slopes, soils with high organic content, and soils that are
permeable, but not too much so. Highly permeable sandy soils will allow water to
infiltrate below the biologically active zone, and relatively impermeable clay soils
will not allow adequate infiltration. High organic content in the soil provides the
carbon necessary to fuel microbial activity.
Studies of nitrogen removal by buffers have produced variable results
likely due to the wide range of conditions that were evaluated. Using the 3-zone
system described below, Schultz et al. (1995) concluded that buffers 20-30 m
wide would "be effective" at removing nitrogen. Other studies of varying buffer
types have shown that buffers 6 to 20 m wide have resulted in N reductions of 47
to 99% (Patty et al., 1997; Daniels and Gilliam, 1996). Desbonnet et al. (1993)
developed a buffer width effectiveness curve for nitrogen based on a review of 26
studies. They concluded that buffer widths as small as 9 m could reduce nitrogen
as much as 60% whereas buffer widths of up to 60 m would be required to reduce
nitrogen by 80%.

Phosphorous removal

Since most phosphorous in surface water runoff is bound to fine sediment
particles, the effectiveness of a buffer in removing P is related to the same factors
that determine effective fine sediment removal (Karr & Schlosser, 1977). These
include flat slopes, sheet flow and high surface roughness. Some additional P can
be removed through plant uptake but it is minimal compared to removal rates for
sediment-bound P (Karr and Schlosser, 1977).
Studies have reported wide variations in P removal, ranging from
reductions of 62% with a 4 m buffer (Doyle et al., 1977), and 56-93% with a 9 m
buffer (Dillaha et al., 1989), to 50% with a 30 m buffer (Edwards et al., 1983).
Thompson et al. (1978) obtained reductions of 44% and 70% with 12 m and 36 m
buffers, respectively. Young et al. (1980) reported reductions of 67% and 88%

39

with buffers of 21m and 27m. Using a buffer width effectiveness curve,
Desbonnet et al. (1993) plotted 27 studies of P removal and determined that, on
average, a 12 m buffer would remove 60% whereas an 85 m buffer was necessary
to remove 80%.

Buffer effectiveness in removing bacteria and pathogens
Effective removal of bacteria and pathogens requires the settling of
suspended solids. In a study of feedlot runoff, Young et al. (1980) found that a 35
m grass buffer reduced microorganisms in surface water runoff to acceptable
levels for primary contact recreational use «l,OOO/lOOm1.). Grismer (1981)
determined that a 30 m grass strip reduced fecal coliform by 60%.

Buffer effectiveness in maintaining water temperature
Studies of the temperature moderation function of buffers have examined
the type and width of forested areas adjacent to open water bodies. Shade is the
critical factor and is relative to the slope, aspect, and height of vegetation. Swift
and Messer (1971) concluded that a 25 m width of mature forest is generally
sufficient to maintain natural water temperatures. Broderson (1973) found that
15 m forested buffers were adequate for small streams (less than 5
cubic/feet/second). Lynch et al. (1985) determined that a 30 m forested buffer
along a stream maintained water temperatures within 10 C of background.

Summary of Buffer Effectiveness for Water Quality Improvement
Numerous studies have demonstrated the effectiveness of buffers in
removing pollutants from surface and ground water. These investigations
encompass 30 years of study and a wide range of conditions. While the designs of
the various studies and the conditions assessed vary widely, a general consensus
emerges on several points. These are as follows:

40

1) Vegetated buffers are effective at removing many pollutants from
surface and ground water, and thus play an important role in protecting
downgradient receiving waters;
2) The primary processes and mechanisms that provide water quality
improvement in buffers are well understood;
3) Sheet flow and shallow ground water flow, rather than channelized
flow, are necessary for effective removal of pollutants;
4) Buffer effectiveness at removing pollutants is dependent upon a few
critical factors including slope, soil type, surface roughness, loading rates,
vegetation type and width;
5) Precise determination of appropriate buffer widths and characteristics is
dependent upon an evaluation of the above and other factors; and
6) In the absence of a site-specific evaluation of the above factors, buffer
widths in the IS -30 m range are the minimum necessary to provide an
effective buffer for water quality improvement (Castelle et al., 1992;
Johnson and Ryba, 1992; Desbonnet et al.,1993).

Several authors (Schultz et al., 1995; Lowrance, 1992; Welsch, 1991)
advocate the use of a Riparian Buffer System that includes three distinct zones:
Zone 1, a grassy strip at the outer edge of the buffer designed to maximize sheet
flow; Zone 2, a managed forested area designed to provide maximal surface
roughness and serve as a transition zone to the next zone; Zone 3, a natural
forested area adjacent to the waterbody of concern. This 3-zone system,
according to most authors, should provide adequate sediment removal as well as a
wider range of buffer functions if its total width is 20 - 50 meters.

41

Buffers and Wildlife Habitat
The role of wetland buffers in protecting wildlife habitat
Wildlife habitat is always included in any generic list of wetland functions.
This is because numerous studies have shown that wetlands are utilized by a large
percentage of wildlife (Thomas, 1979; Brown, 1985; Brown et al., 1990). While
some species depend on wetlands for a majority of their life requirements, other
species utilize wetlands for only a portion of their life cycle or for specific needs.
All wildlife need food, water, shelter from the elements and predators, and
places to breed and to rear their young. A "habitat" is defined as a place occupied
or utilized by a specific population of organisms to supply one or more of these
basic requirements for survival (Brown et aI., 1990). Each animal species is
adapted to certain habitats that meet its life needs. The health and success of any
species is directly related to the quality and quantity of habitat available to it.
As humans alter the natural landscape, wildlife are crowded into smaller
and increasingly isolated fragments of habitat. Roads, agricultural fields, houses,
and other developments eliminate habitat available for most wildlife species and
block their movement between suitable habitat areas. Furthermore, very few
species (for example, most aquatic insects and fish) utilize only aquatic habitats.
Most species that utilize wetlands (or other aquatic areas) require terrestrial
habitats as well in order to meet their life requirements. Birds, which can fly in
and out of wetland habitats, may be able to locate and utilize terrestrial habitats
that are some distance from wetlands. Some birds, mammals, and amphibians
need only a small area of terrestrial habitat adjacent to a wetland to meet their life
needs. Other species, including mammals, reptiles, and amphibians, need larger
terrestrial habitats and must travel over land to reach them, thus requiring
vegetated travel corridors within which to navigate through human-altered
landscapes. While the particular habitat needs of each species are unique,
providing diverse, connected habitats of certain sizes can provide for the needs of
many species.

42

Wetland buffer zones are essential to maintaining viable wildlife habitat
because they can perform several essential functions: 1) they provide an
ecologically rich and diverse transition zone between aquatic and terrestrial
habitats; 2) they provide the necessary terrestrial habitats for many species; 3)
they sometimes provide travel corridors between otherwise isolated habitat areas;
and 4) they screen wetland habitat from the disturbances of adjacent human
development.

How buffers protect wildlife habitat
Buffers protect wildlife habitat in two essential ways: 1) by providing
habitat essential to meeting certain life requirements of many species; and 2) by
ameliorating the adverse impacts of human activities adjacent to the wetland.

Providing essential habitat for wildlife
The ecological conditions of wetland and stream buffer zones are diverse,
dynamic and include components of both terrestrial and aquatic habitats (Brown et
al., 1990; Porter, 1981; Thomas et al., 1979). Called riparian zones, these
transitional areas between terrestrial and aquatic habitats provide important
habitat for a wide range of species. While these riparian zones may comprise a
small portion of a larger habitat area, they receive disproportionally higher use by
wildlife species (Thomas et al., 1979; Brown, 1985; Oakley et al., 1985) because
they provide a diversity of habitats in a small area.
First described by Leopold (1933) as the "edge effect," this phenomenon
of higher wildlife use of transition zones, particularly between aquatic and
terrestrial habitats, has been demonstrated in studies of birds (Beecher, 1942;
McElveen, 1977), mammals (Bider, 1968; Matthews and Strauss, 1981) and
amphibians (Bury, 1988). The same pattern has been demonstrated in the Pacific
Northwest in studies by Oakley et al. (1985), Knight (1988) and Cross (1988). As
much as 85% of the wildlife species found in Washington State utilize wetlands
and their adjacent riparian zones (Brown, 1985; Thomas, 1979).

43

Many wildlife that are identified as "wetland dependent" and considered
by the public to be "wetland species," require adjacent upland areas for many of
their critical life needs (Naiman, 1988; WDW in Castelle et al. 1992). For
example, many waterfowl need access to upland areas for nesting (Duebbert and
Kantrud, 1974; Foster et al., 1984; WDW in Castelle et al., 1992). Also, most
species of amphibians require upland areas for a portion of their life cycle (Bury,
1988).
As described above, buffer zones provide a transition area between aquatic
and terrestrial environments and provide a critical component of wildlife habitat.
The specific habitat functions provided by riparian buffer areas include: 1) sites
for foraging, breeding and nesting; 2) cover to escape predators or weather; and
3) corridors for dispersal and migration.

In addition, vegetated buffer zones protect habitat by maintaining the
microclimate through temperature moderation and by providing a source of
organic matter input to aquatic systems. This includes both large organic debris
(logs, root wads, limbs), which provide habitat structure in aquatic environments,
and particulate and dissolved organic matter, which provide a source of food for
invertebrates and thus help form the foundation of the food chain. Consequently,
buffer zones comprised of native vegetation with multi-canopy structure, snags
and down logs provide habitat for the greatest range of wildlife species (Brown,
1985; Groffman et al., 91).

Ameliorating the effects of adjacent human activities

In addition to providing essential habitat for wildlife, buffer zones also
"buffer" wildlife from the disturbance of adjacent human activities. The intrusion
of noise, light, domestic animal predators (cats, dogs, etc.) and direct human
disturbance (trampling, litter) can have a significant adverse impact on wildlife
use of wetlands. Many wildlife species in wetlands are scared off by unscreened
human activity within 200 feet (WDW in Castelle et al., 1992). Noise and light
can disrupt feeding, breeding, and sleeping habits of wildlife. Domestic pets scare

44

wildlife, causing them to flee and expend energy. Dogs and cats prey on some
wildlife species and are particularly damaging to ground nesting species
(Churcher & Lawton, 1989). Dense shrub and tree vegetation in a buffer adjacent
to a wetland can limit intrusion and screen out noise, light and movement from
adjacent human development (Castelle et aI., 1992).

Buffer Effectiveness in Providing & Protecting Wildlife Habitat
The scientific literature on buffers makes it clear that determining
appropriate buffer widths and characteristics to protect wildlife habitat requires a
site-specific evaluation. While most attention in wetland buffer management is
focused on width, the determination of how wide a buffer needs to be to meet the
habitat requirements of wildlife depends on several factors: 1) the type of land
uses adjacent to the wetland; 2) the specific type of wildlife that use the wetland
and surrounding areas; 3) the vegetative character of the buffer zone; and 4) the
presence of habitat features such as snags and dens. A general rule about the
value of vegetated buffers to wildlife, however, is "the bigger the better and some
is better than none" (Desbonnet et al., 1993).
With that noted, abundant scientific literature addresses the needs of a
wide variety of wildlife species. Many of the buffer studies focus on a particular
group of wildlife species such as amphibians, neotropical migratory songbirds, or
waterfowl. Some studies have investigated just one species of wildlife, such as
beaver or pileated woodpeckers. Additionally, a few studies have examined all of
the habitat-related functions of buffers. A sample of the relevant literature, with
an emphasis on Pacific Northwest sites and species, follows.

Buffers and general wildlife habitat

In addition to the numerous studies that have highlighted a particular
species or group of species, several reviews of the literature have focused on
buffer needs for wildlife in general and they generally agree about the appropriate
width of buffers to protect wildlife.

45

Castelle et al. (1992) examined the literature on buffers and concluded that
appropriate buffer widths for wetlands with important wildlife functions range
from 60 - 90 meters (200-300 feet) in western Washington and 30 to 60 meters
(100-200 feet) in eastern Washington. Desbonnet et al. (1993) reviewed twelve
wildlife buffer studies and concluded that buffer widths of 15-30 meters were
necessary for low intensity land uses and 30 - 100 meters for high intensity land
uses. Norman (1996) analyzed numerous wildlife studies and proposed a 50 m
baseline buffer to protect most wetland functions, but asserted that additional
buffer area might be needed to protect certain sensitive species. Chase et al.
(1995) concluded that 30 m would be adequate for certain habitat functions
(invertebrates, amphibian breeding habitat, and foraging [but not nesting] for birds
and some mammals) but asserted that buffers greater than 30 m would be needed
to meet other wildlife habitat needs. Other studies concluded that buffers of 60 m
(Howard & Allen, 1989) and 60-100 m (Groffman et al., 1991) would be
sufficient to meet most wildlife needs.

Buffers and bird habitat
Numerous studies have documented avian use of wetlands and their
buffers. In a study of bird use of freshwater wetlands in urban King County,
Washington, Milligan (1985) determined that bird species diversity was strongly
correlated with the percentage of the wetland boundary that was buffered by at
least 15 m of tree and shrub vegetation. Foster et al. (1984) found that waterfowl
breeding use of wetlands in the Columbia Basin of Washington was greatest in
smaller « 1 acre) wetlands. They also determined that 68 % of waterfowl nests
were in upland areas within 30 m of the wetland edge and 95% were found within
95 m. Castelle et al. (1992) reported that wood duck nesting in wetland buffers
occurred as far as 180 m from the wetland edge with an average distance of 80 m.
Short & Cooper (1985) found that buffers of 50 m (for foraging) and 100 m (for
nesting) were found effective at buffering great blue herons from human
disturbances. Schroeder (1983) found that pileated woodpeckers nested within 50

46

m of water. Groffman et al. (1991) determined that most neotropical migratory
species needed a 100m buffer around wetlands to provide adequate habitat.
However, in a study of wetlands and biodiversity in Ontario, Canada,
Findlay and Houlahan (1997) determined that species diversity of mammals,
birds, herptiles and plants were all negatively correlated with road density within
2 km of a wetland and were positively correlated with forest cover within 2 km.
They suggest that protecting buffers of less than a kilometer or two is not adequate
to maintain plant and wildlife diversity in wetlands.

Buffers and amphibian habitat
While no studies have evaluated the wetland buffer requirements
specifically for amphibians in the Pacific Northwest (PNW), a recent paper by
Richter (1997) documented amphibian use of buffers in the PNW. Richter
concurred with the conclusions from research that has been conducted elsewhere
regarding appropriate buffer widths, and suggests that buffer widths equal to two
to three tree heights would be optimum. Research conducted elsewhere in the
country recommended buffers of 164 m in humid climates (Semlitsch, 1998) and
buffers of 30 - 100 m in arid climates (Rudolph & Dickson, 1990).

Buffers and mammal habitat
Studies have shown that beaver utilize adjacent uplands within 30 m of
water for most of their foraging needs in eastern Washington, while they forage as
far as 100 m in western Washington (WDW in Castelle et al., 1992). Allen
(1982) concluded that mink use adjacent forested areas as far as 180 m, but that
most of their use is concentrated within 100 m of water.

Buffers and wildlife corridors
As described above, the maintenance of wildlife populations in wetlands
often requires a suitable wildlife travel corridor between a wetland and other
habitats in addition to an adequate buffer around the wetland. Amphibians and

47

mammals both need travel corridors comprised of shrub and tree species to
provide adequate cover and microclimate maintenance. Richter (1997)
recommends a minimum corridor width of 150 m to ensure that soil moisture is
maintained and suggests that wider corridors are required to maintain air
temperature and humidity.

Buffers and human disturbance
As discussed above, wetland buffers also protect wildlife habitat by
limiting intrusion by humans and pets, and by screening out the noise, light, and
motion of human activities. Several studies have examined the effectiveness of
buffers in limiting human disturbance.
Shisler et al. (1987) evaluated 100 sites in New Jersey and found the
degree of human disturbance was correlated with the width of a buffer and the
type of adjacent land use. They concluded that buffers 15 - 30m wide were
needed to protect wetlands from disturbance from low intensity land uses
(agriculture, recreation, and low density residential housing.) For high intensity
land uses (high density residential housing and commercial/industrial
development) they recommended 30-50m buffers. They also found that the most
effective buffers at screening human disturbances had steep slopes with dense
shrub understory vegetation.
Cooke (in Castelle et al., 1992) analyzed 21 wetland sites in western
Washington and concluded that buffers < 15m were generally ineffective in
screening out human disturbance. Josselyn et al. (1989) examined the effects of
human recreational activity on waterbirds in the San Francisco Bay area. They
concluded that unscreened human activity within 15 - 50 m was disturbing to
waterbirds. Groffman et al. (1991) determined that 32 m of dense forested buffer
was necessary to reduce noise from commercial areas to background levels.

48

Summary of Buffer Effectiveness in ProvidinglProtecting Wildlife Habitat

The determination of an appropriate buffer for protecting wildlife habitat
must take into account a number of factors. A site-specific determination based
on the species to be protected, the condition of the buffer and the type of adjacent
land use will be the most effective way to select an appropriate buffer width.
However, given the need for establishing general buffer widths for management
considerations, the scientific evidence on buffers for wildlife could be
summarized as, "An appropriate buffer to maintain wildlife habitat functions for
all but the most highly degraded wetlands, would be comprised of native tree and
shrub vegetation and range from 30 to 100 meters."

Buffer Protection
Buffers will only provide the necessary functions to protect wetlands for as
long as the buffers themselves remain intact. Buffer areas can be altered over
time in at least two primary ways: human disturbance and wind damage.

Human disturbance
Human activities are the most common mechanism for altering buffers
over time. If vegetation is cut or trampled, soils are compacted, or channels are
created, a buffer's ability to protect a wetland will be compromised. Cooke (in
Castelle et al., 1992) analyzed 21 wetland sites in western Washington and
concluded that buffers less than 15m wide were more susceptible to being reduced
over time by human disturbance. Nearly all of the buffers less than 15 m in width
were significantly reduced in a few years and some were eliminated by clearing of
vegetation. Of the buffers wider than 15m, most were intact and showed fewer
signs of human disturbance. In a study in the Monterey Bay area of California,
Dyste (1995) examined 15 wetlands with buffers and determined that all of the
buffers suffered from human alteration.

49

Wind damage
In the Pacific Northwest, long-term protection of buffers must take into

account high-velocity wind storms and the potential for trees in a buffer to blow
down. Maintaining a forest canopy is important to many buffer functions
including shading, screening of adjacent disturbance, and wildlife habitat. In a
summary of the literature on windfirmness of riparian buffers, Pollock and
Kennard (1998) concluded that trees in narrow buffers less than 23 meters wide
have a much higher probability of suffering significant mortality from windthrow
than trees in wider buffers. They conclude that buffers in the range of 23 - 35
meters constitute the minimum width which can be expected to incur minimal
windthrow losses in the long term.

Summary of what the best available science says about
buffers and wetland functions
The information outlined above draws upon a significant portion of the
available scientific information on wetland buffers. It represents studies spanning
several countries and many years of research. It is clear that much is known about
the ways buffers function to protect wetlands and other aquatic resources, and that
there is considerable agreement on the buffer characteristics necessary to ensure
adequate protection of these resources. Tables 3 and 4 below summarize much of
this information.
However, there are some gaps in the scientific information and a few
areas of dispute. Listed below are summary statements about what is certain,
what is uncertain, and what is unknown but researchable.

What is certain
• Buffers are critical to maintaining wetland and aquatic resource health and
functions.

50

• The characteristics and widths of buffers necessary to maintain aquatic
resource health and functions are dependent on site-specific conditions.
• Vegetation type and density, soil type, slope, and width are the key buffer
characteristics that determine the effectiveness of buffers in protecting the
water quality of aquatic resources.
• Vegetation type and density, width, and connectivity to other habitat areas are
the key buffer characteristics that determine the effectiveness of buffers in
protecting the wildlife habitat of aquatic resources.
• Buffers have a minimal effect on protecting a wetland's hydroperiod if the
wetland is in a basin with a high percentage (> 15%) of impervious surface.
• Buffer effectiveness generally increases with width, though beyond a certain
width (generally 30-50 m) the law of diminishing returns applies to
effectiveness at removing pollutants such as coarse sediments and nutrients.
•

In order to determine the appropriate width and character of buffer one must

consider four factors:
1) the quality, sensitivity and functions of the aquatic resource;
2) the nature of adjacent land use activity and its potential for
impacts on the aquatic resource;
3) the character of the buffer area (including soils, slope,
vegetation, etc.);
4) the intended buffer functions.

What is uncertain
• The specific width adequate to provide a specific buffer function in all
situations. Since buffer effectiveness is dependent on a variety of site-specific
characteristics, it is not possible to determine a single buffer width that is
adequate for all situations.
• Which studies conducted in other parts of the country and elsewhere in the
world are directly applicable to Washington state.

51

What is unknown but researchable
• How well buffers function over time. There is concern that buffers have a
finite carrying-capacity for filtering nutrients, beyond which they cease to
provide this function.
• Whether maintaining a buffer without providing sufficient corridors for
wildlife movement will adequately protect a wetland's wildlife species.
• Necessary buffer widths adequate to protect specific wetland dependent
wildlife species in Washington.
• Necessary buffer widths adequate to maintain water quality in wetlands for
different soil types and climatic conditions in different areas of Washington
state.

52

Primary.mechanism s
or otocesses
Sediment
" ~ !"4"7;., I .
remova '':L

Settling of sediments
via slowing surface
water flows
Infiltration
Phvsical filtration
Ni trification &
denitrification
Infiltration
Plant uptake
Settling of sediments
Plant uptake (minor)

L.:
t_,,!­

."

Nitrogen

removaf

. '':

'~"

),

-Phosphorous
removal
'"
"i':"

';",-,.

-;

Sheetflow of surface
water
Residence time
Surface roughness

Shallow slopes
Dense vegetation
Organic debris
Pervious soils

Seasonal saturation
Sheetflow of surface
water
Residence time
Same as for sediment
removal

Shallow slopes
Dense vegetation
Pervious soils
Seasonal saturated areas
S ame as for sediment
removal

by microbes
\ :-:

..

.....

Sediment removal
,. 1 Plant uptake
Adsorption

.

10-200 m

Karr & Schlosser 77, Dillaha
89, Castelle et al. 92, Desbonnet
et al. 93

Shallow slopes
Dense vegetation
Pervious soils

5 - 35 m

":'.

I Young et al. 80, Grismer 81

Groffman et al. 91

See above
Residence time
Binding soils

See above
See above
Clay or organic soils

unknown

Residence time

See above

18 - 35 m I 97

Lowrance et al. 97, Patty el al.

' ~

,T '·Pesticides
,

53


Phillips 89, Castelle el al. 92,
Desbonnet et al 93, Daniels &
Gilliam 96, Patty et al, 97

t\

-: , .

.. : Meta ls ,
- .;"

10-100 m

I~

Toxics removal
- .,.,;.Bacteria "'~ I Biological breakdown I Residence time
or,Jr';"

Dillaha 89, Gilliam & Skaggs
88, Phillips 89, Castelle et al,
92, Ghaffarzadeh el al 92,
Desbonnet et al 93 ,

Biochemical
dezradation

Critical fa ctors
Microclimate
~
\.
protectioii
~::;';Q'.

Shading
Wind blockage

r,

Blocking light
Absorbing noise
Blocking movement of
humans & pets
Depends of species:

WfIdlife1:habitat
- Screening..
noise, light, ,~
.intrusion, etc.
:Wildlife Habitat
:'
.,'

... .

- Nesting,
feeding,

b1?-~edilfg; ~t.c .
!lJ

Wildlife,habitat"
•

".

._ '.!

- Travel
cor.ridors
..
_"

54

-;;,. ~

Cover
Food sources
.. Specialized niches
(snags, logs, tree
canopy, etc.)

I

I'

I

Cover
Screens noise, light,
etc.
Maintains microclimate

Vegetation height
and density
Aspect
Slope
Vegetation height &
density
Slope

I Buff er characteristics I
Dense, forested
vegetation

Dense, multi-strata
vegetation
Steep slopes

I Depends on species.

I
Vegetation strata
Vegetation species &
other food sources
Presence of
specialized niches

Generally, multi-strata
vegetation with snags
and down logs will
provide best habitat
for the greatest
number of soecies.

I Vegetation height & I Dense, .multi-strata
density

vegetation

Range of
widths
15 - 100 m Swift & Messer 71,
Broderson 73, Lynch et al.
85, Richter 97, Pollock &
Kennard 98
15 - 50 m Milligan 85, Shisler 87,
Josselyn 89, Groffman et
al. 91, Castelle et al. 92

15 - 200 m

Foster et al. 84, Brown 85,
Bury 88, Naiman 88,
Groffman et al. 91,
Castelle et al. 92,
Desbonnet et al. 93,
Norman 96, Semlitsch 98

I 150+ m I Richter 97, Semlitsch 98

,~"

'15 ,
"

. .,. ,' 20

~.t

""

- '~

...

,,1.,

600 '

55


~,

' ,1

Pollutant . B~mov a l Effectiveness

Wildlife Habitat Value.

Approximately 50 % or greater sediment and
ollutant removal
Approximately 60 % or greater sediment and
ollutant removal
Greater than 60 % sediment and pollutant removal
Approximately 70 % or greater sediment and
ollutant removal
Approximately 70 % or greater sediment and
ollutant removal
Approximately 75 % or greater sediment and
ollutant removal
Approximately 80 % or greater sediment and
ollutant removal
Approximately 80 % or greater sediment and
ollutant removal
Approximately 90 % or greater sediment and
ollutant removal
Approximately 99% or greater sediment and
ollutant removal

Poor habitat value; useful for temporary activities of
wildlife
Minimally protects stream habitat; poor wetland
habitat; useful for temoorarv activities of wildlife
Minimal zeneral wildlife & avian habitat value
Minimal wildlife habitat value; some value as

avian habitat

May have use as a wildlife travel corridor for some

specie s as well as general avian habitat

Minimal general wildlife habitat value

Fair-to-good general wildlife and avian habitat value
Good general wildlife habitat value; may protect

siznificant wildlife habitat

Excellent general wildlife value; likely to support a

diverse communit

Excellent general wildlife value; supports a diverse
communi tv; orotection of siz nificant soecies

Chapter 3 - Wetland Buffer Protection and Management

at the Local Government Level
The protection and management of wetland buffers involves a mix of
science, law, sociology, politics and economics. Local governments are used to
meshing many different disciplines and balancing many different viewpoints in
developing local land use policies and regulations. Under the Growth
Management Act (GMA), local governments are required to balance many
competing interests and needs in the development of policies, programs and
regulations for managing for future growth. One of these competing interests is
the need to protect Critical Areas, including wetlands. As described in Chapter
One, the GMA specifies that local governments must include the best available
science in the development of policies and regulations aimed at protecting the
functions and values of Critical Areas. Chapter Two demonstrates that the best
available science is unequivocal that protection of buffer areas around wetlands is
a critical component of protecting wetland functions and values. It also shows
that there are many factors that need to be considered in protecting and managing
buffers.
This chapter outlines the many considerations that local governments
should take into account when developing policies and regulations for the
protection and management of buffers. In addition to the scientific information
about buffer effectiveness, there are many administrative and legal considerations
that must be addressed in the regulation of buffers. Most local governments in
Washington currently regulate wetlands and their buffers through local
ordinances. Most of these ordinances were developed in the 1980s and early
I990s. Local governments were not required to include best available science
prior to 1995 and thus, many of these ordinances were based more on political and
economic expediency than on scientific information. This chapter attempts to
incorporate the relevant scientific information about buffer management with the
author's experience with buffer regulation and management over the past 15 years.
Included in this is a discussion of the primary issues and a variety of approaches

56

to consider when developing buffer protection and management regulations.
First, however, it is helpful to understand the legal and historical context
surrounding the protection of wetlands and their buffers.

The legal context
In most cases, the protection of wetlands and their buffers is the result of
government regulation and thus must be based on the government's authority to
provide for the health, safety and welfare of its citizens (Platt, 1996). Protecting
buffer areas around wetlands is controversial because it usually requires a
landowner to forgo the use of that portion of hislher property for anything other
than aesthetic enjoyment. While some landowners decide to protect wetlands and
buffers because they value the ecological or aesthetic benefits provided by these
areas, many choose not to do so.
The legal authority to regulate wetlands and other natural resources
originates in the U.S. Constitution, which charges government to provide for "the
general welfare." This provision has been interpreted by the courts over the years
to include the regulation of activities that could affect the health, safety, or welfare
of a community. Often referred to as "police powers," this authority allows a city
or county to regulate the location of development through zoning laws and to
require landowners to protect natural resources such as streams, lakes and
wetlands (Platt, 1996). This power also provides the authority to restrict uses in
potentially hazardous areas such as floodplains and steep slopes.
Thus, a local government's authority to protect wetlands is based upon the
fact that wetlands playa role in protecting public health and safety (e.g. water
quality improvement, flood reduction, groundwater recharge, and other processes)
and providing for the general welfare (e.g. habitat and aesthetics). Any reasonable
actions undertaken to ensure that wetlands continue to provide these functions are
supportable under the government's police powers.
Establishing and implementing wetland or buffer regulations, however,
must be done in a manner that does not result in the denial of reasonable use of a

57


landowner's property. The Fifth Amendment to the Constitution states, " ... nor
shall private property be taken for public use without just compensation." This
passage has been interpreted differently by courts over the years but is generally
understood to mean that any government action that denies a landowner all
"reasonable" economic use of hislher property requires compensation (Platt,
1996). If the protection of a certain width of buffer results in a property owner
being unable to develop hislher property in a way otherwise allowed by law, then
a government agency runs the risk of being sued for a "takings"- i.e. the taking of
private property without just compensation. Most local governments avoid this
dilemma through the development of "variance" procedures that allow for case­
specific decisions in which buffer requirements are altered to allow reasonable
use. These procedures are described in more detail below.

The historical context
The modem controversy over wetlands protection is a product of
American culture's historical perspective on wetlands. While protection of lakes
and streams may engender debate and conflict over the level of private property
restrictions, few people argue over whether streams and lakes should be protected.
People generally understand the value of streams and lakes and the need for their
protection; not so with wetlands. Until very recently, wetlands have been viewed
as useless wastelands that should be "reclaimed" and put to productive use.
Historically, government agencies even paid landowners to clear and drain
swamps and marshes (Siry, 1984).
Only during the past 30 years has the public perception of wetlands begun
to change. A growing understanding that wetlands provide beneficial functions to
society has led to a shift in government policy and programs. In the 1970s, after
two hundred years of paying landowners to destroy wetlands, the federal
government began to protect wetlands. Soon after, state and local governments
began to follow suit. This relatively recent and sudden shift in attitude has
contributed significantly to the considerable conflict between the government's

58

need to protect the public interest and the desire of private property owners to use
their property as they see fit.
In the eyes of many property owners, protection of wetlands on their land

denies them use of acreage they believed would be developable (and that was
developable in the recent past). This perspective is compounded by the fact that
many people view wetlands as land that happens to be wet for part of the year, not
as a water resource. In addition, wetland boundaries appear to change seasonally
and are more difficult to identify than lake or stream boundaries. This leads to
many disagreements over the extent of wetland area that should be protected.
Furthermore, efforts to protect upland buffers around wetlands are viewed as an
even greater "land grab" by the government.
Conflicts between landowners and government agencies over wetland
protection increased throughout the 1980s, as more state and local governments
began to restrict land uses in and near wetlands. In 1988, the National Wetlands
Policy Forum, a coalition of government agencies and private interest groups,
developed the concept of "No Net Loss" (Conservation Foundation, 1988). This
concept holds that, since the United States already has lost as much as 60% of its
otiginal wetlands (Frayer et al., 1983), we must strive to avoid the loss of any
more wetlands. Recognizing that some loss of wetlands undoubtedly will
continue as a result of necessary development, the No Net Loss goal states that
wetland losses should be offset by the creation and restoration of wetlands. This
goal is directed at maintaining both wetland acreage and wetland functions.
Many federal, state and local government wetland protection programs
have adopted No Net Loss as their primary goal. The federal government and
many states (including Washington) have a further intention to achieve a net gain
in wetland acreage and function, primarily through non-regulatory restoration of
wetlands (Gardner, 1989).
In Washington state, the responsibility for protecting wetlands is shared by

the federal, state and local levels of government. No comprehensive federal or
state wetland protection laws currently exist but several laws provide some

59


protection for wetlands (see Wetland Regulations Guidebook {Ecology, 1994}).
While federal and state agencies playa significant role in protecting wetlands in
Washington, local governments are the principal agencies responsible for ensuring
the protection of wetlands, through local land-use regulation and provisions of the
state Growth Management Act (GMA).
Efforts to protect wetlands and their buffers will continue to be rife with
conflict as government agencies attempt to balance the public interest with private
property rights. By basing a wetland protection program on a foundation of sound
science and by providing flexibility to address site-specific situations, a
government agency can achieve an appropriate balance between these two
competing interests.

Buffer Management & Best Available Science

The best available science (see Chapter Two) makes clear that the
protection of buffers around wetlands is necessary to protect wetland functions.

,.I

The best available science also provides considerable guidance on buffer
characteristics, including widths, which are necessary to protect specific wetland
functions. The best available science does not provide clear direction on how to
structure buffer protection and management programs. However, in addition to
providing technical information on buffer effectiveness, the best available science
provides information that should help guide the development of buffer protection
policies and regulations. This information can be summarized as follows:
•

Four primary factors should be considered in determining the appropriate
width and character of buffers,:

I) the quality, sensitivity and functions of the aquatic resource;

2) the nature of adjacent land use activity and its potential for

impacts on the aquatic resource;

3) the character of the existing buffer area (including soils, slope,

vegetation, etc.);


60

4) the intended buffer functions.
• Site-specific information is needed to determine effective buffer character and
width;
• It is important to manage surface water discharges to wetland buffers to ensure

effective treatment of pollutants.
• Generally, buffer widths "shrink" over time due to infringement from adjacent
activities.

Ideally, this guidance should be incorporated into any local government
buffer regulations. There are, however, many different ways to incorporate this
information into a buffer protection program. The challenge for local governments
in Washington is to develop buffer protection and management approaches that
incorporate the best available science and which provide a reasonable and
defensible means of establishing and maintaining effective wetland buffers.

_,i

Developing local buffer policies and regulations
A local government's buffer protection strategy should include both
regulatory and non-regulatory components. While regulation is critical to protect
adequate buffers in the face of increasing development, a non-regulatory approach
can address some buffer issues that a regulatory approach cannot. In some cases,
providing incentives to landowners is more effective at protecting buffers than
regulation. In any case, the foundation of both regulatory and non-regulatory
approaches is a sound policy framework that spells out why buffer protection is
important and sets the tone and direction for how buffers are to be protected.

Buffer policy development
Buffer policy language should articulate that buffers are critical to the
protection of wetlands and their functions. Typically, this policy language is
contained in a local comprehensive plan and in development regulations. It should

61


state the goals of buffer protection efforts. Stated goals could include, for
example: 1) buffer protection should be based on sound science; 2) flexibility
should be provided to address site-specific situations; 3) buffer standards, and
criteria for varying from standards, should be predictable for landowners; 4) staff
implementing the buffer programs should be well-trained; 5) non-regulatory
incentives should be used to help protect buffers where regulation is impractical
or onerous; and 6) buffer protection should be balanced with allowing reasonable
use of private property.

Non-regulatory Incentives for Buffer Protection
Typically, buffers are formally established at the time that a new
development is proposed adjacent to a wetland. However, since buffer regulation
is a recent phenomenon, most existing development dating from 1985 or before
likely was constructed prior to the regulation of wetlands and their buffers. In
addition, agricultural activities adjacent to wetlands are largely unregulated and
without buffers. Therefore, many wetlands have minimal or no buffers and will
,\

remain in this condition unless and until a new development activity is proposed
adjacent to them.
In these situations, non-regulatory incentives are the primary means of
providing an adequate buffer area to protect wetland functions. By providing
financial incentives to landowners it is sometimes possible to restore and enhance
buffer areas for wetlands that otherwise would remain unprotected. Outlined
below are several programs available to local governments in Washington to
provide incentives to landowners to protect wetland buffers. For more
information on landowner incentive programs, see the Department of Ecology
guidebook, Exploring Wetlands Stewardship (Ecology, 1996b).
Washington State's Open Space Taxation Act (ReW 84.34) is unique in
the nation. It combines the strong incentive approach of "open space" property
tax valuation with the fund raising opportunities of a conservation levy. Few
other state's offer as strong a landowner incentive program to local governments.

62

I

Tax incentives - The Current Use Taxation Program allows counties to assess
property taxes based on the "current use" of a parcel rather than on its
development potential. This program establishes three categories for enrollment:
Agricultural; Timber; or Open Space. Wetlands and their buffers can be enrolled
under the "Open" category. Under the "Open" classification, property taxes are
reduced by a percentage, based on an evaluation system (called the Public Benefit
Rating System or PBRS) developed by the county. Once enrolled, the property
must remain in the program for at least 10 years or be subject to early withdrawal
penalties. The amount of tax reduction under the PBRS is based on the ecological
value of the property and the degree of protection afforded. Each county can
develop its own criteria for the type of resources that qualify for this category and
the degree of tax reduction offered. All counties have programs with an Open
Space category but only 14 of the 39 counties in Washington have implemented a
PBRS and some of these allow tax reductions for the protection of wetland or
riparian buffers.

Acquisition or Conservation Easement Programs - Another provision of RCW
84.34 is the Conservation Futures Levy. It allows counties to charge a fee of up to
6.25% per $1000.00 of assessed property value to raise funds for the purchase and
management of conservation land. Once enacted by the legislative body of the
county, this levy collects funds that may be used to purchase land outright, or to
pay landowners to adopt conservation easements on their property. These funds
can be used to pay for buffer protection and enhancement. Thus far, 11 counties
in Washington have enacted this levy.
Another program available to local governments in Washington is the Real
Estate Excise Tax. RCW 82.46.070 allows counties to impose a real estate excise
tax on transfers of property where the proceeds are used exclusively for the
acquisition of land or easements and maintenance of conservation areas. This tax
can be enacted by a resolution of the county legislative body or by public petition.
In either case, a majority of voters in the county must approve the tax, including a

63


specified maximum rate. San Juan County is the only county that has adopted this
program.
In addition to these local programs, there are several cost-share funding

programs available from the federal government to help pay for the protection,
restoration and/or enhancement of buffer areas. Most of these programs are
directed at agricultural lands and are administered by the Natural Resources
Conservation Service. Other states (Maryland, Virginia) have developed similar
cost-share programs for assisting landowners in protecting and restoring buffers
but Washington has no comparable program.

Wetland buffer regulations
Regulations for the protection of wetland buffers should address a number
of issues: 1) standards for buffer character and width; 2) criteria and procedures
for varying from a standard; 3) allowable uses within buffers; 4) best
management practices to enhance and ensure effective buffer function; and 5)
provisions for the delineation and demarcation of buffers and their maintenance
I

'I

over time.
In most cases, the primary concern will be "how wide does the buffer

need to be?" This issue dominates any discussion of buffer regulation and
generates the most conflict. However, before determining appropriate standards
for buffer widths, a local government needs to decide how best to balance the
need for a predictable and cost-effective approach with the desire for a flexible
approach that is responsive to site-specific situations.
The options for buffer regulatory approaches range from variable-width
buffers that are determined case-by-case based on multiple site-specific factors, to
fixed-width buffer standards. Between these two extremes, there are many
intermediate options that combine some elements of each. Each approach has its
advantages and disadvantages, and deciding which is most appropriate requires
careful consideration.

64


Variable-width Approach
The case-by-case variable-width approach is probably the most consistent
with what the best available science says about buffer effectiveness. This
approach usually requires the development of a detailed formula and methodology
for the consideration of site-specific factors such as wetland type, adjacent land­
use, vegetation, soils, and slope. By taking into consideration all relevant site­
specific factors prior to determining the appropriate buffer width, this approach
helps ensure that the buffer is adequate to protect wetland functions without being
any larger than is necessary.
However, the above approach is time-consuming, costly to implement and
provides a less predictable outcome. It requires either that the applicant hire a
consultant to conduct the necessary analysis, or that the government agency staff
conduct the analysis. In either event, the local government staff must have
appropriate training and expertise to conduct or review the analysis. In addition,
this approach requires considerable effort up-front to develop the formula and
methodology for site-specific evaluation. While methods exist for evaluating site­
specific buffer characteristics (Brown et al., 1990; Diamond and Nilson, 1988;
Groffman et al., 1993; Roman and Good, 1985), each was developed for unique
conditions that are not directly applicable to Washington. This approach also
does not provide any predictability for applicants. They have no idea how large of
a buffer may be required until considerable time and money are invested in the
analysis.
Using a case-by-case, variable-width approach also can result in attempts
to manipulate the site-specific data and frequent haggling with applicants.
However, if the local jurisdiction can afford the development and implementation
costs, this approach may be the most scientifically and legally defensible.

Fixed-width Approach - By contrast, a fixed-width approach provides
predictability and is inexpensive to administer. The downside of this "one-size­
fits-all" approach is that it results in some buffers being too small to adequately

65

protect a wetland's functions, and some buffers being larger than necessary to
protect a wetland's functions. Over time, this inequity may erode public and
political support for the buffer program. Frustrated landowners can point to the
"over-regulation" of those buffers that are larger than necessary and
environmentally-minded citizens can point to those buffers that are smaller than
needed to protect wetland functions. It also is difficult to determine an
appropriate standard width, because no one size buffer can be demonstrated to
protect all wetland types adequately in all situations unless that standard width is
very large. Furthermore, it is difficult to argue that a fixed-width approach
includes the "best available science" since the scientific literature clearly
recommends different buffer widths based on a variety of different factors. While
no local governments in Washington currently use a single, fixed-width approach,
there are several states (California, New Hampshire, New Jersey) that do.

Combining the Fixed-width Approach with Site-specific Variables - There are,

however, several ways to modify a standard, fixed-width approach to incorporate
some of the factors that contribute to buffer effectiveness. Some drawbacks of the
fixed-width approach can be rectified by developing a wetland rating system that
divides wetlands into different categories based on specific characteristics. Then,
different buffer width standards can be assigned to each category. This approach
provides predictable widths, yet allows some tailoring of buffer widths to wetland
functions. For example, the Washington State Wetland Rating System divides
wetlands into four categories based on the following wetland characteristics: 1)
rarity; 2) sensitivity to disturbance; 3) irreplaceability; and 4) habitat functions.
This hierarchical rating system allows one to establish larger standard buffer
widths for "more valuable" wetlands and smaller standard buffers for "less
valuable" ones. Most local governments in Washington currently designate buffer
widths based on the Washington State Wetland Rating System or a similar
approach.

66


Another way to tailor a fixed-width approach to address site-specific
factors is to have different standard widths based on the type of adjacent land use,
thus incorporating another of the four factors that are known to affect buffer
effectiveness. A buffer regulation could require a larger buffer width for high­
intensity adjacent land uses and a smaller buffer width if the adjacent land use is
low-intensity. This approach can be combined with a wetland rating system to
provide a more scientifically valid approach.
Other critical factors, such as the character of the buffer itself and the
desired buffer functions, can be addressed by establishing criteria and procedures
for varying from a fixed width. This approach allows for some site-specific
tailoring of the standard buffer width on a case-by-case basis without the need for
developing a standard formula or methodology for determining site-specific
widths. In this approach, criteria for increases or reductions from the standard
buffer width are developed and the applicant or any other interested party is given
the option of "making a case" as to why the standard buffer width should be
increased or decreased. Agency staff then evaluate the proposal for deviation
from the standard buffer width against the criteria, and decide if such a deviation
is warranted.
The criteria for allowing a deviation from the standard buffer width should
address the various site characteristics determined by best available science to be
the most important. These include buffer characteristics such as slope, soil type
and vegetative cover and/or the habitat needs of particular wildlife species. For
reducing standard buffer widths, an applicant should have to demonstrate that a
smaller buffer will protect the functions and values of the wetland. This will
generally require hiring a qualified expert and preparing a site-specific report for
the local administrator's review and approval. It is also important to have a
minimum buffer width below which the buffer cannot be reduced (see chapter 4
for recommended language).

67


Reasonable Use Criteria

Another situation in which standard buffer widths may need to be reduced
on a case-by-case basis is when protection of the buffer will result in a property
owner being denied reasonable use of his/her land. For example, if a landowner
has a one-acre parcel that was zoned for one single-family residence and a wetland
comprises 80% of the parcel, then protection of a buffer around the wetland might
mean that the parcel is undevelopable. In this case, the landowner would have a
strong case that protection of the wetland and buffer would deny himlher all
reasonable use of the property. However, if the buffer was reduced, it may be
possible to construct a single house on the property and avoid a "takings" claim.
(Another alternative would be for the government agency to purchase the lot at
fair-market value; however, seldom is this economically feasible for local
government agencies.) Thus, buffer regulations should include a provision
allowing for buffer reduction in situations where reasonable use would be denied.
Such a provision should include requirements that the applicant demonstrate that
there are no feasible alternatives to reducing the buffer such as revising the
development design, that critical wetland functions or public health and safety
will not be impaired, and that the inability to derive reasonable economic use of
the property is not the result of the applicant's own actions, such as dividing the
property in a way that created an unbuildable lot (see chapter 4 for recommended
language).

Buffer Averaging

Buffer averaging is a tool for balancing buffer protection with specific site
development needs. It allows a buffer to vary in width around a given wetland.
For example, if the standard width for a buffer around a wetland is 30 meters,
buffer averaging would allow the width to vary between a minimum and a
maximum width but require that the buffer area average 30 meters in width.
Typically this is done to allow development to occur closer than usual to the
wetland in order to fit a particular development "footprint" onto a given site.

68

However, it also can be used to protect a natural feature (such as a stand of trees
or snags) that otherwise would fall outside of the standard buffer width. Buffer
averaging can also be used to provide connectivity with adjacent habitat areas or
to address those situations where pre-existing development has reduced a buffer
area to a width less than the required standard. Criteria for buffer averaging
typically require a minimum buffer width (either a designated width or a
percentage of the standard buffer width) and documentation to ensure that the
averaging of the buffer will not impair overall buffer functions (see chapter 4 for
recommended language).

Uses within buffers
Another critical issue that buffer regulations need to address is the type of
uses that are allowed within the buffer. Most developers will want to make some
use of the buffer area to try to recoup some of their "lost" property. This usually
means they will want to place stormwater treatment facilities (e.g. detention ponds
and bioswales) in the buffer or construct trails or provide for some form of active
or passive recreational use. In addition, over time, residents adjacent to the buffer
often will want to use it for some activity. Thus, it is essential that buffer
regulations address which uses are allowed in a buffer.
Generally, any use that results in the creation of impervious areas, clearing
of vegetation or compaction of soils will be incompatible with buffer functions.
Typically, buffers need to be densely vegetated with trees and shrubs to perform
water quality and habitat related functions. In most cases, this requirement
precludes any human uses of the buffer. However, it may be necessary in some
situations to utilize the outer area of the buffer for initial treatment of surface
water runoff, via the construction of bio-filtration swales or water spreading
features to ensure sheet flow.
In other situations, it may be desirable to allow some focused use of the

buffer for educational and recreational activities, and to prevent wide-spread
disturbance of the buffer. If it appears inevitable that adjacent residents will use

69

the buffer to gain access to a wetland for aesthetic or recreational enjoyment, then
it may be preferable to concentrate that use in a smaller area and minimize
disturbance of the soil and vegetation by constructing trails, viewing platforms, or
similar facilities. Additionally, providing some educational or recreational
developments in buffers may enhance the general public's understanding and
appreciation of wetlands and their functions and values.
Many regulations include criteria for evaluating proposals for use of buffer
areas. These criteria typically include general language about prohibited uses but
allow for variances if certain conditions are met (see chapter 4 for recommended
language).

Enhancement/restoration
Frequently, upland areas adjacent to wetlands have been altered by
previous land use practices. In many cases, the vegetation has been cleared or
significantly degraded and the soil has been disturbed. Also, it is not uncommon
to find that the existing buffer area is comprised of non-native vegetation. In
these situations, simply "protecting" a set width of buffer area may fail to provide
the necessary characteristics to protect a wetland's functions. It is usually
desirable, therefore, to restore the buffer to a more naturally vegetated condition.
In other cases, a buffer area may be in relatively good condition but still be

sparsely vegetated with trees and shrubs. It may be desirable in this case to
improve the screening and habitat value of the buffer by planting additional trees
and shrubs.
Buffer regulations should be designed to ensure that buffer areas provide
the maximum possible protection of a wetland's functions. In cases where the
buffer is not well vegetated, it is helpful to have incentives for enhancement or
restoration of the buffer area. Buffer regulations can encourage buffer
enhancementlrestoration simply by requiring a greater width to be protected if the
buffer is not well-vegetated with native species. Landowners typically will prefer

70

to invest in buffer improvements such as planting vegetation or constructing a
fence, in exchange for a narrower width.

Best management practices to enhance or ensure effective buffer function

Water quality protection
It is clear from the best available science (see chapter 2) that a buffer's

effectiveness at removing pollutants is largely a factor of how water carrying
pollutants travels across and through the buffer. In addition, the scientific
literature is full of references to pre-treatment practices that enhance a buffer's
effectiveness at removing pollutants and reduce the width of buffer necessary
(Dillaha et al., 1989; Lowrance et al., 1997; Welsch, 1991).
In areas with agricultural or silviculturalland uses, the primary pollutants

of concern are sediments, nutrients, and pesticides. Narrow (5-10 m) grass filter
strips have been shown to be effective at removing coarse sediments and attached
pollutants as well as helping encourage sheetflow and infiltration of surface
runoff, thus enhancing a buffer's effectiveness at removing remaining pollutants
(Dillaha et al., 1989, Welsch, 1991, Wong and McCuen, 1982). Therefore,
requiring or encouraging the construction of a narrow grass filter strip between
agricultural or silvicultural areas and wetland buffers is strongly advised.
In urban areas, the pollutants of concern are primarily sediments and

metals from roads, parking lots and construction sites. Adequate treatment of
stormwater runoff is critical to remove most of the pollutants and to reduce peak
flows prior to discharge to a wetland or its buffer (see below for more discussion
of stormwater). To encourage sheetflow and infiltration, stormwater should be
dispersed through a shallow infiltration trench at the outer edge of the buffer.
In residential areas, the pollutants of concern include sediments, metals,

nutrients and pesticides (from lawns). A combination of appropriate stormwater
treatment and the use of a grass filter strip or grassy swale is recommended to
pretreat and disperse surface runoff prior to introduction into a buffer.

71

Stormwater management
In addition to the introduction of pollutants, development adjacent to or
upgradient from a wetland can alter the quantity and timing of surface and/or
ground water inputs to the wetland. Considerable research has been conducted by
the King County Stormwater Management Project that documents the adverse
impacts from alterations to a wetland's hydroperiod (see chapter 2). The best
available science also shows that upland buffers around wetlands do little to
ameliorate these impacts except in wetlands with small contributing basins.
Thus, it is imperative that adequate stormwater management practices be applied
to any project adjacent to, or upgradient from, a wetland. This includes such
practices as the construction of settling/detention facilities as well as treatment
with a grassy swale (Ecology, 1992). Inadequately detained and treated
stormwater will overwhelm a buffer's ability to filter and treat pollutants. Direct
surface discharges to buffers will usually result in channelized surface flow that
significantly reduces pollutant removal and can erode buffers.

Wildlife habitat
The two primary actions that can be taken to reduce impacts to wildlife
habitat are 1) to ensure that the wetland and its buffer are connected to other
habitat areas, and 2) to reduce the intrusion of noise, light, people and pets.
Ensuring connectivity is usually a matter of site design. Some wetlands
will already be isolated from other habitat areas and it will not be possible to
provide connectivity. On sites where wetlands are currently connected to other
habitat areas, it is important to maintain that connectivity through corridors.
While the scientific literature indicates that wildlife travel corridors should be as
wide as 150 m, it may be beneficial to provide a corridor of any size. Corridors of
less than 30 m will only provide the cover for small mammals and less sensitive
birds. Local wildlife experts should be consulted to determine the appropriate
corridor design for a given site. Buffer averaging may be a useful tool to help

72


ensure connectivity with adjacent habitat areas without unduly burdening the
landowner.
Reducing the intrusion of noise, light, people and pets can be
accomplished in many ways. As specified in chapter 2, buffers vegetated with
dense trees and shrubs are effective at reducing intrusion of noise and light.
Additionally, projects can be designed to reduce noise and light intrusion by
locating noisy areas like parking lots, playgrounds, and loading docks away from
the edge of the buffer. Lighting can be designed and located so it points away
from the wetland and its buffer. Fences and/or berms can be constructed to block
noise and light. Fences can also be used to limit human and pet intrusion. Dense
shrubs can be planted along the edge of a development to block noise and light
and limit intrusion. Shrubs with thorns are also a deterrent to human intrusion.
With forethought and careful planning, projects can be designed to reduce
impacts to wildlife habitat. When combined with adequately vegetated buffers of
sufficient width, these measures can help ensure that disturbance to wildlife use of
a wetland is minimized.

Buffer Management Issues
Many steps need to be considered to ensure that, once established, buffers
continue to provide the functions for which they were protected. These steps
frequently are overlooked or given scant attention by local governments and result
in the degradation of buffers over time (Cooke in Caste lIe et aI., 1992.)

Buffer ownership
The issue of who owns the area included in a buffer is an important one.
There are basically two options: the buffer area can be included in a separate tract
or lot and held in common ownership by a homeowners association, agency or
non-profit organization; or, it can be included into lots owned by adjacent
landowners.

73

The second option is often pursued by a developer who wants to divide the
buffer among individual lots in order to achieve a required minimum lot size.
However, a study by Cooke (in Castelle et al., 1992) of buffer areas in two
counties in western Washington showed that buffers that were owned by many
different lot owners were more likely to be degraded over time. Even with
easement language on each lot owner's deed specifying the buffer protection
provisions, owners tend to clear buffer vegetation over time to expand lawns,
build storage sheds or serve other uses. If the buffer area is not held in some kind
of common ownership, it is much more difficult to enforce against those
landowners who encroach upon its boundaries. Therefore, when feasible,
wetlands and their buffer areas should be placed in a separate, non-buildable tract
that is owned and maintained by an organization that is dedicated to protecting the
buffer.

Buffer delineation, recording & signage
Clearly delineating and marking a buffer area helps ensure that it is not
degraded over time. Following project approval, and prior to site construction,
the buffer should be measured, recorded on applicable legal documents, and
clearly marked on the ground. During the construction phase, constructing a
temporary sediment fence or "clearing limits" fence helps to ensure that the
boundary is seen by equipment operators and that the wetland and buffer are
protected from erosion during construction. Following construction, a fence may
still be desirable to demarcate the boundary and to limit human and pet access and
reduce the intrusion of noise and light.
Placement of signs along the buffer boundary is important for two reasons:
to help mark the boundary and to help educate landowners about the purpose and
value of protecting buffer areas. In areas with high potential for human intrusion
and degradation of the buffer, more extensive signage explaining the value of the
buffer may be necessary to develop support for protecting the buffer. In addition
to signs, brochures can be developed and distributed to adjacent landowners to

74

explain the reasons why buffers and wetlands are protected and what human
activities are allowed. Typically, applicants are responsible for developing and
constructing fences and signs and for distributing educational materials.
However, local jurisdictions can develop standards for fences, signs and
educational materials to ensure consistency and effectiveness. Maintenance of
fences and signs is typically the responsibility of the adjacent land owner or a
homeowners association, if applicable, or lies with the local jurisdiction.

Buffer maintenance

In cases where enhancement or restoration of a buffer is required,
monitoring and maintaining the buffer area is essential. A
monitoring/maintenance program should include evaluation of vegetation planting
success and provide for contingency measures if vegetation survival standards are
not met. Responsibility for this is usually born by the developer or landowner. It
is also important to monitor buffer areas when human use is allowed or expected.
Adverse effects of human access such as vegetation trampling, littering and soil
compaction or erosion should be evaluated periodically by a monitoring program
and corrected if found. Local jurisdictions can develop and implement a buffer
maintenance and monitoring program but few have done so. Alternatively,
applicants can be required to monitor and maintain buffers and submit regular
reports to the local jurisdiction.

Buffer enforcement
Simply designating and marking the boundaries of buffer areas is not
sufficient to protect buffers in all cases. Regular monitoring of buffer areas is
critical to determine whether vegetation and soils are being impacted and to
ensure that adjacent development does not encroach on the buffer over time.
Where illegal activities occur, enforcement actions to restore the buffer may be
necessary. Local jurisdictions should establish a buffer enforcement program
similar to enforcement programs for private stormwater or wastewater facilities.

75

This chapter has outlined the primary buffer regulation and management issues a
local government should consider. Chapter 4 presents model language for three
different approaches to determining appropriate buffers.

76


Chapter 4 - Buffer Protection Policies, Regulations and

Methods Based on Best Available Science


Some local governments in Washington have staff with the expertise to
evaluate scientific information on wetland buffers and to develop protection
programs that include the best available science. Most local governments,
however, lack staff with wetlands expertise and must rely on guidance or models
developed by others. This chapter integrates the best available scientific
information outlined in chapter 2 with the approaches outlined in chapter 3 to
provide recommended buffer protection and management language for local
policies and regulations. With minimal effort, a local government can take this
language and refine it to fit within their existing critical area policies and
regulations.
In addition to policy language and general standards that should be

included in any buffer regulations, this chapter provides three different options
for determining appropriate buffer widths to protect wetland functions and values.
A local government can select the buffer width determination method that best
meets its needs, taking into account the expertise of staff, the amount of time and
effort they want staff to devote to site-specific evaluations, and the degree of
predictability they want to provide to the regulated community.

Model Buffer Policies

Few local governments in Washington have adopted specific policies for
buffer protection for wetlands or other critical areas. Buffer policies can be
included in comprehensive plans and/or in development regulations. Examples of
buffer policy statements include the following:
1) buffer protection should be based on sound science;
2) flexibility should be provided to address site-specific situations;

77

3) buffer standards, and criteria for varying from standards, should be
predictable for landowners;

4) staff implementing the buffer programs should be well-trained;

5) non-regulatory incentives should be used to encourage landowners to

protect buffers where regulation is impractical or onerous; and

6) buffer protection should be balanced with allowing reasonable use of

private property.


Model Buffer Regulations

Wetland buffer regulations are generally located in a wetlands section of
critical area regulations. Many of the standard requirements for wetland buffers
will be applicable to other critical areas. Thus, much of the language in this
section can be applied to any type of buffer and could be included in any section
of local regulations that addresses buffers for critical areas.

Definition & Purpose Statement
Buffers are designated areas adjacent to a regulated wetland (or other
critical area) that protect it from impacts of adjacent human activities. Generally,
buffers are areas of native vegetation that are maintained in a natural state.
Buffers protect wetlands from adjacent development by filtering surface water
and shallow groundwater runoff, screening noise, light and activity, reducing
human and pet intrusion, and providing upland habitat critical to the survival of
wetland wildlife species.

General Buffer Standards
*Note: recommended widths in this chapter are expressed in feet rather than
meters because state and local regulatory agencies and the regulated community
in Washington calculate distances in English equivalents rather than metric.

78


a. Buffers shall be required for all regulated wetlands, including those created or
restored as compensation for approved wetland alterations.
b. Buffer width should be determined based on the method described in section
c. Buffer width shall be measured horizontally from the wetland boundary as
determined in section _.
d. A building setback zone of 15 feet is required from the outer edge of the
wetland buffer. Minor structural intrusions into the building setback zone may be
allowed by the (approval authority) based on a determination that such intrusion
will not adversely impact the wetland or its buffer.
e. Except as otherwise specified, wetland buffer areas shall be retained in their
natural condition. Where buffer disturbance has occurred, revegetation with
native species may be required.
f. Buffer areas shall be protected through a permanent legal instrument such as a
deed restriction or conservation easement.
g. The location of the outer edge of the buffer shall be marked in the field prior to
any construction activity adjacent to the buffer, in such a way as to ensure that no
unauthorized intrusion into the buffer will occur; and shall be maintained
throughout the duration of any construction activities. Permanent fencing may be
required on a site- specific basis.
h. A permanent physical demarcation of the outer edge of the buffer shall be
erected prior to occupation of the adjacent property and maintained in perpetuity.
Such demarcation may consist of fencing or signage as approved by the (approval
authority). Buffer identification signs must be posted at an interval of one per lot
or every 100 feet, whichever is less, and must be maintained in perpetuity. At a
minimum, signs must identify the area behind the sign as a protected wetland
buffer and state that disturbance of vegetation or soils is prohibited.

79

Permitted uses within buffers
The following activities shall be permitted within a wetland buffer to the
extent they are not prohibited by any other applicable law and provided they are
conducted in a manner as to minimize impacts to the buffer and adjacent wetland:

a. Conservation or restoration activities aimed at protecting the soil, water,
vegetation or wildlife;
b. Passive recreation, including walkways or trails located in the outer 25% of the
buffer area, wildlife viewing structures, and fishing access areas, provided these
are designed and approved as part of an overall site development plan;
c. Educational and scientific research activities provided prior approval is
obtained from the (approval authority);
d. Normal and routine maintenance and repair of any existing public or private
facilities provided appropriate measures are undertaken to minimize impacts to
the wetland and its buffer and that disturbed areas are restored immediately to a
natural condition.
The following activities may be permitted within a wetland buffer for
Category 3 or 4 wetlands (based on the Dept. of Ecology Wetland Rating Systems
(Ecology, 1991), provided they are not prohibited by any other applicable law,
they are conducted in a manner as to minimize impacts to the buffer and adjacent
wetland, and written approval is obtained from the (approval authority):

a. Stormwater management facilities, limited to stormwater dispersion outfalls
and bioswales, may be allowed within the outer 25% of the buffer of a Category 3
or 4 wetland, provided that a determination is made that no other location is
feasible, and the location of such facilities will not have an adverse impact on the
functions and values of the wetland.

80


Reasonable use criteria
If a property owner demonstrates that application of standard buffer

regulations would deny all reasonable economic use of the property, the buffer
width may be reduced by the (approval authority). The buffer width shall be
reduced as needed to allow reasonable economic use, only if all of the following
are demonstrated:

1) that no feasible on-site alternative design is possible that would allow for

reasonable economic use of the parcel without reducing the buffer; and
2) that buffer averaging and buffer enhancement including fencing where
appropriate, have been utilized to the full extent practicable to maintain the most
effective buffer possible; and
3) that the buffer reduction will not adversely affect threatened or endangered
plant or animal species; and
4) that the buffer reduction will not result in damage to nearby public or private
property nor threaten the health or safety of people on or off the property; and
5) that the inability to derive reasonable economic use of the property is not the
result of actions in segregating or dividing the property, thus creating the
undevelopable condition after the effective date of these regulations.

Methods of Establishing Buffer Widths

Following are three different methods of determining buffer widths for
individual wetlands. As described in chapter 3, a variety of approaches can be
utilized, ranging from a single, standard buffer width for all wetlands to
determining widths on a case-by-case basis. Most local jurisdictions will want to
select an method that lies somewhere between these two extremes. The three
methods presented below were developed to provide a range of options for local
governments to consider.

81

Basic Buffer Method
This method is very similar to the Department of Ecology's recommended
model that was developed in 1990 (Ecology, 1990). It bases standard buffer
widths on intensity of land use and wetland category as determined by a four-tier
wetland categorization system (see Appendix A for the criteria for each category).
These standard widths can be adjusted up or down based on site-specific criteria.
This method has been modified slightly from the Ecology model based on review
of other local government programs and discussions with other wetland
specialists. The advantages of this method are that: l ) it is relatively simple to
apply; 2) it provides predictable buffer widths as well as some flexibility to
address site-specific conditions; and 3) it is similar to many existing local
government buffer determination methods. The disadvantages are that: 1) it does
not take into account the condition of the buffer area and, thus, may prescribe a
buffer width that is greater or lesser than necessary; and 2) it divides wetlands into
categories based on an established rating system which was not designed
specifically for buffer width decisions. The latter means that some wetlands in
one category may need buffers as wide as a wetland in a higher category or as
narrow as a wetland in a lower category. These disadvantages result in the need to
apply variance procedures involving time consuming site-specific evaluations in
order to arrive at an appropriate buffer width. Nevertheless, this type of approach
is widely used in Washington, has been subjected to broad peer review, and has
been accepted thus far as incorporating the best available science. The widths
expressed below are generally consistent with the findings in chapter two
regarding the best available science.

Standard Buffer Widths
The width of wetland buffer zones shall be determined based on wetland
category and proposed land use as follows:

82


Category I wetland
High intensity land use

300 feet

Low intensity land use

200 feet

Category II wetland
High intensity land use

200 feet

Low intensity land use

100 feet

Category III wetland
High intensity land use

100 feet

Low intensity land use

50 feet

Category IV wetland
High intensity land use

50 feet

Low intensity land use

25 feet

Wetland categories are determined based on the Department of Ecology's
Wetland Rating Systems for Eastern (Dept. of Ecology, 1991) and Western
Washington (Dept. of Ecology, 1993).
High intensity land uses include those that are associated with moderate to
high levels of human disturbance including, but not limited to, residential
development at greater densities than 1 unit per 5 acres, including all multi-family
residential development, commercial and industrial development, and active
recreational development such as ball fields.
Low intensity land uses include those that are associated with low levels of
human disturbance including, but not limited to, residential development at
densities of 1 unit per 5 acres or less, agricultural or silvicultural activities,
passive recreational development, and open space.

83

Increasing standard buffer widths
Standard buffer widths may be increased on a case-by-case basis when it is
determined that a larger buffer is necessary to protect wetland functions and
values based on site-specific characteristics. This determination shall be
supported by documentation provided by the (approval authority) showing that an
increased buffer is necessary based on one or more of the following criteria:
1) a larger buffer is needed to maintain existing documented use by wildlife
species; or
2) the buffer or adjacent uplands are susceptible to severe erosion and standard
erosion-control measures will not prevent adverse impacts to the wetland; or
3) the buffer area has minimal vegetative cover and has a slope greater than 15%.

Decreasing standard buffer widths
The (approval authority) may decrease standard buffer widths on a case­
by-case basis when it is determined that a smaller area is adequate to protect
wetland functions and values based on site-specific characteristics. This
determination shall be supported by documentation provided by the applicant
showing that a reduced buffer is adequate based on one of the following criteria:

a. an enhancement plan by a qualified wetlands specialist demonstrates that an
enhanced buffer with native vegetation plantings will improve buffer functions to
the point where a reduced width will provide equal or better protection of wetland
functions and values than the standard width without enhancement. The
city/county may require long-term monitoring of the buffer and wetland with
appropriate contingency actions if adverse impacts to the wetland occur.; or

b. the existing buffer area is vegetated with greater than 90% areal cover of native
species and has a slope of less than 5% and a report by a qualified wetlands
specialist demonstrates that a smaller than standard buffer will provide all of the
buffer functions necessary to protect all functions and values of the wetland. The

84

city/county may require long-term monitoring of the buffer and wetland with
appropriate contingency actions if adverse impacts to the wetland occur.

In no case shall the standard buffer width be reduced by more than 50%, or the

buffer width be less than 25 feet.

Buffer Averaging
The (approval authority) may modify standard buffer widths on a case-by­
case basis by averaging buffer widths. Averaging of buffer widths may be
allowed where the applicant demonstrates through a report by a qualified wetlands
specialist that either: a) averaging is necessary to avoid an extraordinary hardship
to the applicant caused by circumstances peculiar to the property; or b) the
wetland contains variations in sensitivity due to existing physical characteristics,
and it would benefit from a wider buffer in places and would not be adversely
impacted by a narrower buffer in other places; or c) the character of the buffer
varies in slope, soils or vegetation and the wetland would benefit from a wider
buffer in places and not be adversely impacted by a narrower buffer in other
places
AND all of the following criteria are met:
i. that averaging the buffer width will not result in adverse impacts to the
functions and values of the wetland; and
ii. that the total area contained within the buffer after averaging is no less than that
which would be contained within the standard buffer; and
iii. in no instance shall the buffer width at any point be reduced by more than 50%
of the standard width, nor less than 25 feet.
The Basic Method is a straightforward way of determining standard buffer
widths and similar approaches are used widely by local governments in
Washington. However, although this method requires little staff time or expertise
to arrive at the standard buffer widths, local governments must be prepared for
frequent requests by applicants for variances from the standard widths.

85

Applicants will often request reduced buffers based on site-specific buffer
conditions. These requests can require considerable staff time and expertise to
review and make variance decisions. The next method described can help
alleviate some of this burden by incorporating buffer conditions into the initial
determination of buffer widths.

Advanced Buffer Determination Method
The Advanced Buffer Determination Method provides a practical
alternative to the Basic Method. It incorporates three primary factors that the
scientific literature says are important in deciding on appropriate buffers to protect
wetland functions: 1) wetland type; 2) type of adjacent land use; and 3) buffer
characteristics. The primary advantage of this method is that it prescribes a buffer
width that is more tailored to the specific characteristics of the site being
evaluated without the need for a special study by a wetlands specialist.
Use of the Advanced Method will result in a more site-specific and
scientifically supportable buffer width than the Basic Method, while still
providing a high level of predictability for landowners. It also removes much of
the subjectivity and debate that may accompany attempts to design site-specific
buffers using the Basic Method.
The disadvantages of the Advanced Method are that: 1) it requires an
evaluation of buffer characteristics prior to identifying an appropriate width; and
2) wetland types are divided differently than most existing wetland rating systems
in use in Washington.
The Advanced Method of determining buffer widths derives from the
practice of developing environmental decision-making models, also known as
"multiple criteria assessment" models (Hruby, 1999). These types of models are
based on the selection and scaling of key variables that are known to be related to
the system or process being modeled. The variables and their scaling are founded
on hypotheses about how the variables combine to determine an appropriate
buffer width, since specific, quantitative data about the relationships between the

86

variables are lacking. The variables in the Advanced Method (wetland type, land­
use intensity, and buffer slope, soils and vegetation) were selected and scaled by
the author following analysis of the scientific literature. The buffer widths were
selected based on the literature and the author's judgment that these widths would
ensure a low level ofrisk that a wetland's functions would be impaired. This
same method could be applied using greater or lesser buffer widths if one were
willing to assume a greater or lesser level of risk.
Applying the Advanced Method requires that one determine the wetland
type and land use intensity adjacent to the wetland using the descriptions below,
evaluate the buffer area using the buffer scoring model (Table 6), and determine
the buffer width using Table 5.
Table 5 illustrates the primary factors and recommended buffer widths of
this approach. The land uses, wetland types and buffer scoring method are
defined below.

: Buffe r
High intensity
Moderate"
Low intensity

. Score
(buffer
widths
in feet)

350
250
200

300
200
150

250 250
150 200
100 150

200
150
100

150 125 100
100 100 75
75 75 50

75
50
25

Land Use definitions
High intensity: High intensity land use includes those that are associated
with moderate to high levels of human disturbance, including but not limited to
residential development at greater den sities than 1 unit per 5 acres, including all
multi-family residential development, commercial and industrial development and
active recreational development such as ball fields.
Moderate intensity: Moderate intensity land use includes those that are
associated with moderate levels of human disturbance, including but not limited

87

to residential development at densities of 1 unit per 5 acres or less, and
agricultural activities.
Low intensity: Low intensity land use includes those that are associated
with low levels of human disturbance, including but not limitedto silvicultural
activities, passive recreational development, and open space.

Wetland Types
Wetland types are divided into three categories based on three primary
factors: 1) sensitivity to inputs of nutrients or toxic substances; 2) sensitivity to
human disturbances (noise, light, intrusion); and 3) likely presence of wetland­
dependent wildlife species needing adjacent upland habitat to meet critical life
needs. The criteria for placing a wetland in one of the three categories are based
on the Washington State Wetland Rating System (Ecology, 1993) and are found in
Appendix A. (These three categories differ from the four categories found in the
Ecology rating system because this approach is based solely on buffer needs
whereas the Ecology rating system addresses buffers, mitigation ratios and impact
avoidance.) For purposes of establishing buffer widths, this type of wetland
categorization scheme is more consistent with the best available science than the
Ecology rating systems because it groups wetlands based solely on their need for
buffering from adjacent land uses.

Wetland Type A
This category contains:
1. All Category 1 wetlands
2. Category 2 wetlands with open water*
3. Category 2 estuarine wetlands

Wetland Type B
This category contains:
1. Category 2 wetlands without open water*

88

2. Category 3 wetlands with open water*
3. Category 3 estuarine wetlands

Wetland Type C

This category contains:

1. Category 3 wetlands without open water*

2. Category 4 wetlands

* Open water means any area of standing water present for more than one month
at any time of the year without emergent, scrub-shrub or forested vegetation.
[This definition is consistent with the Washington State Wetland Rating System
(Ecology, 1993).J

Buffer Score
The buffer score takes into consideration three primary factors (slope,
soils, and vegetation) that determine how well a buffer removes sediment,
nutrients, and toxic substances, screens out adjacent human disturbances, and
provides shading, microclimate protection, and general wildlife habitat. The
buffer score is determined by adding scores from the three categories outlined in
Table 6 below. These criteria should be applied to the existing buffer area within
the maximum buffer width based on the type of wetland at issue (350 feet for
Type A, 250 feet for Type B, 125 feet for Type C; Table 5). One does not need to
apply these criteria to the buffer area around the entire perimeter of the wetland
unless the proposed project surrounds the entire wetland. However, one must
determine whether the slope, soils and plant community are uniform across the
buffer. (See Appendix B for definitions of terms and guidance on how to address
buffers that vary in slope, soils or plant community.)

89


Slope*
> 10% avg

5-10 % avg

<5% avg

* See

ts.
=1

=2

=3

Soils*

ts.

Sand, loamy sand,
clay or silty clay

Vegetation*

ts.

To tal
Score

Bare ground > 30 % or
Impervious surface> 20% or
Herb aceous vegetation with
=1
< 30 % shrub/tree cover
Conditions other than
described above or below = 2

=1

Sandy clay, sandy clay
loam, silty clay loam,
or clay loam
=2

Tree cover> 50 % with shrub
cover > 50 % or Tree cover
50% with herb cover > 80 %
or Shrub cover> 80%
=3

Loam, silt loam or
sandy loam
=3

Appendix B for definitions of term s and guidance and examples of how to

determine buffer scores.

Figure 1, below illustrates how the Advanced Buffer Determination
Method can be applied to a hypothetical site.

Figure 1. Example of Applying the Advanced Buffer Determination Method

•
Slope = 8%
(points = 2)

•

•
Reside nt ial Housing

2 homes/acre

(high-intensity land use)


••

•

_Soils = silt loam --:.
(points = 3)
\

Wetland
TypeB

,
,

\

-,

,

-- 250 feet

,
,

-­

Vegetation cover
trees - 60%
shrubs - 20%
herbs - 100%
(points = 3)

,

,

,

-'

,

,

,

,

,

,
,

Slope = 2 pts

Soils = 3 pts

Veg = 3 pts

Total = 8 pts


I Buffer width = 150 feet

90


Application of this method will result in a buffer width that is adequate to
protect a wetland's functions, based on site-specific characteristics. However,
local governments that choose to use this type of method may want to include the
language outlined under the Basic Method above for increasing or reducing buffer
widths to address those few instances in which an even more detailed, site­
specific approach is necessary. Additionally, buffer averaging and reasonable use
exception language above should be included with the Advanced Method.
While the Advanced Method requires more data collection than the Basic
Method to determine a buffer width, it should save local government staff time
because the extra data collection costs are typically born by the applicant, and
requests for variances will be less frequent, since the prescribed buffer widths are
based on more site-specific information. However, occasions will arise that
necessitate a more detailed, site-specific analysis and the method described below
is designed for such occasions.

Making site-specific determinations of buffer widths
Most local governments likely will utilize an approach similar to one of
the two options described above because these approaches provide predictability
for applicants and take less staff time and expertise to implement. However,
given the lack of precision involved in categorizing wetlands, land uses, and
buffer characteristics, it may be appropriate to make a site-specific determination
to arrive at an optimum buffer. From the landowner or project applicant
standpoint, an optimum buffer generally will be the smallest that is absolutely
necessary to protect the wetland's functions. From the resource protection
standpoint, an optimum buffer will be the one that ensures little or no risk to the
wetland and the functions it provides.
The buffer widths included in the two methods above are designed to
provide a buffer that ensures a low level of risk to the wetland based on a general
understanding of the wetland's functions. However, all wetlands, even those in
the same category, function differently. Likewise, similar land uses can have

91

distinctly different levels of impact on wetlands depending on site-specific
practices. Additionally, local government staff frequently need to evaluate land
owner requests to increase or decrease standard buffers based on site-specific
information.
A site-specific approach to determining buffers allows for consideration of
more detailed information. However, making a site-specific determination
requires collection and evaluation of considerably more data than applying a
standardized approach. The site-specific method described below provides a
standard format for collecting and evaluating site-specific information to help in
determining an appropriate buffer. With this format, the results can be quickly
reviewed for accuracy and adequacy. This method could be used as the primary
basis for determining buffers or to make decisions about increasing or decreasing
a standard buffer width as determined by one of the two methods described above.
However, use of this method requires that one exercise substantial judgment in
evaluating the data collected and arriving at a final decision regarding buffer
width.

Site Specific Buffer Determination Method
The method outlined below for making site-specific buffer determinations
follows a five-step data gathering and evaluation process. Each step requires that
site-specific data be collected and/or evaluated by a person or team with expertise
in wetland ecology. This will most typically be conducted by a consultant hired
by a project applicant. This information should be provided to the appropriate
decision-maker in the form of a report and the decision-maker should ensure that
someone with appropriate expertise reviews the report for accuracy and adequacy.

STEP 1: Describe the wetland's characteristics by filling out the table below.

The information in Table 7 will provide a general description of the
wetland including basic physical characteristics that contribute to a wetlands

92

functions as well as more specific information on wildlife species expected to use
the wetland. This information will hel p in determining the wetl and' s needs for
buffering from adjacent land uses.

Table 7 - Wetland Characteristics
Recor d the following information about the wetland under consideration.
Wetland area
(in acres)
-:
2 Wetland rating (class/category)i '
s and name of rating system
3'" Hydrogeomorphic Class
(riverine, depressional,slope,
",
lacustrine fringe, estuarine fringe)
4 Cowardin classes present

(forested, scrub/shrub, emergent,

open water, aquatic bed)

Area of permanent open water
5
6 Area of seasonal open water

1

,

(

.~ \'

7
8

Area of vegetated standing water
Source(es) of water inputto the
wetland

":

0,

Threatened, Endangered,
Sensitive or rare plant species

present

10 .Threatened/, Endangered,

Sensi ti ve or rare animal species

present

11 Known or expected bird species
utilizing the wetland as habitat
12 Known or expected mammal "

species utilizing the wetland as

habitat

9

.',


13 Known or expected fish species

utilizing the wetland as habitat


14

Known or expected herptile
species utilizing the wetland as
habitat

,:

93


STEP 2: Descr ibe the level of impact from adjacent development and
measures to be taken to minimize impacts

Table 8 - Description of Potential Development Impacts
Describe the type of
development
Describe how surface water
16 . . runoff will be addressed
in cluding plans for treatment
and release to wetlands or
streams.
Ii)
Describe how surface runoff
17 will affect the hydroperiod of
the wetland and what
• pollutants might be introduced
into the wetland.
Describe the potential for noise
18 and light to affect the wetland
and steps taken to reduce noise
and light impacts on the
wetland.
Describe the potential for .:
19 human and pet intrusion into
the wetland and steps taken to
minimize intrusion.
j

94


STEP 3: Describe the characteristics of the buffer

Table 9 - Buffer Characteristics
Evaluate the area within 300 feet of the wetland edge in the vicinity of the
proposed development and answer the questions below. Make a drawing to
answer Questions 21-22
~j

v.

20a

~

"

."

soms
.,.

.

_

Described the mapped
! soil type including ,
horizons, texture and
: drainage class.

Draw a typical
soil horizon
(0-20 ") for
the buffer soils

IP

,

20b

Do fieldobservatipns
• confirm the mapped soil
type?
20e If not, describe soH type

observed in the field

including horizons, "

texture and drainage

class.


21


SLOPE

On a drawing of the
buffer area, show area~ ·
where the slope is:
VEGETATION
On a drawing of the .
buffer area, indicate

approximate percent of

areal cover of each

vegetative strata as well

as bare areas and areas

.with buildings or

impervious surfaces

Describe measures that

could betaken to

improve the functioning

of the buffer area.


<5 %
5% -10 %
>10 %

Strata

Tree

Shrub

Herbaceous

Bare

Buildings/impervious

95


STEP 4: Determine the buffer functions and width needed to protect the
wetland

Table 10 . Buffer Functions
Based on the information.recorded in T~.bles 7, 8 and 9, ,a b ove, determme
.•
wh ich buffer functions a"~~.;needed to pr6t~~t.the wetla iiq ~ For each function
determined to be needed.idescribe the width necessary tojprotect the ~etland
and p rovide a rationale tor :the width selected. Include ~ descriptiorrbf
enhancement activiti ~,s, pr oposed to improve the bUff~16r otherwlsgiprotect
the wetland.
.t,~~
r. ;'
f'l;~

;.

Buffer Function
<%

ti

Needed?
YIN

_

r'

Needed Width & Rationale

Buffer or Site
,E.Ilhancement

Sediment removal

Nutrient removal

-Toxics removal . '
(specify type of
toxic substance)
Shading &
micr oclima te
protection
Screening noise,
light, intr usion
General wild life
habitat

Habitat for
particular species

96


STEP 5: Determine the appropriate width of buffer and enhancement
actions necessary to protect the wetland,

Summary
(Describe the
overall width
needed to protect
the wetland & a
summary of the
enhancement
actions,needed)

Currently, most site-specific buffer determinations are conducted by
consultants for project applicants. The consultants provide a short narrative
statement advocating a particular buffer width based on certain wetland or buffer
characteristics. Rarely do these reports contain the detailed information
necessary to adequately determine an appropriate buffer, and thus, it is difficult to
refute or concur with the recommendation provided by the report . The five-step
process outlined above provides a "transparent" method for determining site­
specific buffers. This process provides all of the relevant documentation and
rationale needed to make a site-specific buffer determination and displays it in a
manner that is easy to review.
A local government will need to allocate considerable staff time and
expertise if the Site-specific Method is used as the primary means of determining
buffer widths. Even if applicants provide all of the data required for this method,
local government staff will need to have the time and technical expertise to review
each buffer determination and corroborate the conclusions. Thus, this method
will be most helpful when used in conjunction with one of the other two methods
described above. Then , it would only be applied in those few cases when the
applicant or local government believes that the buffer prescribed by the Basic or
Advanced Methods is wider or narrower than is scientifically justified .

97

Conclusion
The best available scientific information unequivocally states that buffers
are necessary to protect and maintain the water quality, habitat, and hydrologic
functions of wetlands. The best available science also outlines four primary
factors to be considered in determining appropriate buffer widths: 1) the quality,
sensitivity and functions of the aquatic resource; 2) the nature of adjacent land
use activity and its potential for impacts on the aquatic resource; 3) the character
of the existing buffer area (including soils, slope, vegetation, etc.); and 4) the
intended buffer functions. Given the tremendous variability of wetland types,
land uses and buffer conditions across the landscape, developing a single buffer
width that is appropriate for all situations is not possible. Thus, methods are
needed that will take into account these primary factors and prescribe appropriate
buffer widths.
However, regulatory buffer methods must provide some level of
predictability for land owners and must be easy to apply. The three methods of
determining wetland buffers outlined above provide methods that incorporate the
best available science and are practical for regulatory programs. A local
government or any other entity can select the method that best fits its needs and
feel confident that the method will provide a scientifically sound approach to
determining wetland buffers.

98


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108


Appendix A
Summary of Rating System Criteria by

Category and Data Sources

Data Sources

Criteria for Each Category
Category I Wetlands are:
Those that have a documented occurrence in the
wetland of a federal or state listed endangered or
threatened plant,
.
animal, or fish species; or . . . . . . . . .. .
i)

DNR Natural Heritage Program
WA Department of Fish &
Wildlife

ii) High quality native wetland communities
which qualify for inclusion in the Natural
Heritage Information System; or .....

DNR Natural Heritage Program

iii) Documented as regionally significant
waterfowl or shorebird concentration areas;

WA Department of Fish &

Wildlife


or

iv) Wetlands with irreplaceable ecological
attributes; or
.

Field Data Form

v)

Local Government

Documented wetlands of local significance.

Category II Wetlands satisfy no

Category I Criteria and are:

i) Those that have a documented occurrence in the
wetland of a federal or state listed
sensitive plant,
.
animal, or fish species; or
ii) Those that contain priority species or
habitats recognized by state agencies; or

DNR - Natural Heritage Program
WA Department of Fish &
Wildlife
WA Department of Fish &
Wildlife

iii) Wetlands with significant functions which may
not be adequately replicated through creation or
restoration; or

Field Data Form

iv) Wetlands with significant habitat value of 22 or
more ooints: or

Field Data Form

109

Criteria for Each Category

Data Sources

Category III Wetlands satisfy no
Category I, II, or IV criteria and are:
i) Wetlands with significant habitat value of
21points or less; .. or

Field Data Form

ii) Documented wetlands of local significance.

Local Government

Criteria IV Wetlands satisfy no
Category I, II, or III criteria, and are:
i) Wetlands less than 1 acre and, hydrologically
isolated and, comprised of one vegetated class that is
dominated (> 80% areal cover) by any species from
the list in Table 4 (see Rating System document) .. or,

Field Data Form

ii) Wetlands less than two acres and

hydrologically isolated, with one vegetated class,
and> 90% of areal cover is any combination of
species from the list in Table 3 (see Rating System
or,
document) .....

Field Data Form

iii) Wetlands that are ponds excavated from
uplands and are smaller than 1 acre without a surface
water connection to streams, lakes, rivers, or other
wetlands throughout the year; and that have less than
1/10 acre of vegetation.

Source: Washington State Wetland Rating System, published by the
Washington State Department of Ecology, Publication No. 93-74.

110

Appendix B
Guidance on Determining the Buffer Score for the Advanced
Buffer Method
The following guidance is intended to help a user apply the Advanced Buffer
Method for determining wetland buffers. This method requires the collection and
evaluation of data on the wetland type, proposed land uses and existing or
enhanced buffer conditions. The criteria and methods for determining the wetland
type are found in the Washington State Wetland Rating System documents
published by the Washington Department of Ecology (Ecology, 1993). The
definitions of land uses are found in the body of Chapter 4. This appendix
provides definitions and guidance determine the appropriate buffer score based on
slope, soils and vegetation.

Buffer Score
Once the wetland type and adjacent land use are determined, the buffer score can
be calculated. To calculate the buffer score, evaluate the area adjacent to the
wetland within the maximum width required for the wetland type and land use in
Table 5. (e.g. for a Type B wetland and a high-intensity land use, the evaluation
area would be 250 feet.) It will help to draw a map of the area and sketch in the
vegetation, soil and slope characteristics as in the figures below.
Three characteristics of a buffer must be assessed in order to determine the buffer
score. The buffer scoring method requires that one examine the buffer's slope,
soils and vegetation and select the description from Table 6 that best fits the
situation.

Slope - This is determined based on the percent grade of the buffer area between a
flat surface (0%) and a vertical surface (100%). Many buffer areas will have a
relatively uniform slope while others will vary in slope across the buffer. It is not
necessary to determine the precise angle of the slope; rather, one must determine
whether the average slope falls in the category of < 5%,
5-10%, or > 10%.
If the slope is not uniform perpendicular to the wetland edge, one must calculate
the average slope across the buffer (see figure B-1). If the slope is not uniform
parallel to the wetland edge, one should divide the buffer into segments based on
the average slope perpendicular to the wetland edge and calculate a different slope
score for each buffer segment (see figure B-1).

111


Figure B-t: Calculating buffer slope score

VVet:l a nd

...

.

t-""­ - - - - """'"'"'---­ - - - ­ •

A v e r age slope == 7.5 0 /
S l o p e sco re = 2

0

,

,

Soils - The soil score is based on the texture of the soil in the buffer area. Soils
should be determined by consulting a soil survey document (such as a Soil
Conservation Service survey) and making a site investigation. Since soil surveys
are generally done at a very small scale, the mapped units are subject to
inaccuracies. It is always important to confirm the mapped unit for a soil type by
examining soil s in the field to corroborate that they match the description in a soil
survey. Soils should be examined to a depth of 3 feet.
Soil textures are determined based on the relative amounts of sand, silt, and clay
in the soil. This is typically determined by the texture-by-feel-analysis. This
involves wetting approximately 25 grams of soil and performing a serious of
squeezing tests in one's hand to determine the relative texture (see Appendix C
below). This test requires experience in analyzing different soil types and is best
performed by a soil scientist. However, with a bit of experience and a little
training from a soil scientist, anyone can learn to perform the test. Additionally,
lab tests can be conducted to measure the precise percentages of sand , silt, and
clay and determine the soil texture.

If soils are not uniform perpendicular to the wetland edge, one should base the
buffer soil score on the soil type that constitutes the greatest percentage of the
buffer area. If no soil type is dominant, use the soil type that scores lowest (see
figure B-2). If soils are not uniform parallel to the wetland edge, divide the buffer
into segments based on differences in the soil texture (see figure B-2).

112


Figure B-2: Calculating buffer soil score

...
...


150 feet
Soils = loam

Area A
Soils score = 3 ·

Wetland

..
..


125 feet
Soils = silt

.,

•

,

~ rcaB

...

I So ils s,:~re =
,
,

125 feet
Soils = loam

. i

2J

Vegetation - To determine the buffer vegetation score one must assess the entire
buffer area and calculate the percent areal cover of each category of vegetation as
follows:
• Impervious surface - pavement, asphalt, buildings or highly compacted
bare ground .
• Bare ground - unvegetated sailor gravel
• Herbaceous strata - Non-woody vegetation such as grasses, forbs and
mosses .
• Scrub-shrub strata - Woody vegetation less than 20 feet tall.
• Tree strata - Woody vegetation greater than 20 feet tall..
Once the areal cover is calculated, select the buffer vegetation description that
most closely matches the area. If the vegetation is not uniform perpendicular to
the wetland edge, calculate the buffer vegetation score based on an average for the
entire buffer area (see figure B-3). If the vegetation is not uniform parallel to the
wetland edge, divide the buffer area into segments based on differences in the
vegetation. Then, calculate a buffer vegetation score for each segment (see figure
B-3).

113

Figure B-3: Calculating buffer vegetation score
,

,

"1<+- - - - - . ',,"""0(- - - - - ----.
. ,
Vegetation

"

Trees = 90%
Shrubs = 40%
erbs = 60%

Vegetation

Herbs = 100%

"
,

Area A
Trees avg = 45%
" Sh r ub s avg = 20%
, Herbs avg = 80%
'. (Veg. Score = 2)

•
A

Wetland

•,
•

B

..
Vegetation

Shrubs = 40%
Herbs = 50%

:

Area B
Shrubs avg = 20%
Herbs avg = 75%
(Veg. Score = 1)

.:

When scores have been calculated for each of the three buffer characteristics, they
should be added together to produce the overall buffer score (see figure B-4).
When non-uniformity of one or more of the buffer characteristics has necessitated
dividing the buffer into segments, it will produce potentially different buffer
scores for each segment. This may result in a buffer width that varies for each
segment (see figure B-5).

114


Figure B-4: Calculating bu ffer score - general

,

,

,

Slope = 8%
(points = 2)

,

,,

~

,
,
,
,

,

+-- Soils= silt loam

Wetland
TypeB

~


(points = 3)

+-

,

,

,

-,

,

250 feet

Vegetation cover
trees - 60%
+- shrubs - 20%
,'
,
herbs - 100%
,
(points = 3)
,

--.

,

,

,

,

,

BufferScore

,
,
,
,
,

Slope = 2 pts
Soils = 3 pts
Veg = 3 pts
Total = 8 pts

,

Buffer width = 150 feet

Figure B-5: Calculating buffer score - complex

,

Vegetation cover
shrubs ­ 20%
herbs ­ 80%
(points = 1)

,

,

,

,,
,,

,

'----+.\
- -­

- - I
~

Wetland
TypeC

+--------1

Area A

Buffer Score

Slope=2

Soils =3

Veli: = 1

Total = 6 pts

,
,
,
,

Buffer width =;: tOO feet

Slope = 10% I
(points = 2L -,'­' - - - - + , ,
I

Area A
I
1 - - - - - - - - - - - 1 2 5 feet
Area B
Slope = <5%
(points = 3)
,.-----.~

,
,
,

,

Vegetation cover
trees ­ 20%
shrubs ­ 80%
herbs-100%
( oints = 2)

,

,
,

,
,
,
,
,
,

Area B
Buffer Score
Slope =3
Soils = 3
Veg =2
Total = 8 pts
I BuffefWidth ;= 7S feet

115


Appendix C

Method for Determining Soil Texture


Texture-By-Feel Analysis

Place app rox imately 2j grams o f soil in
palm. Add water dropwise and knead
the soi l to b reak down al l ag grega tes .
Soil is at the proper consistency when
plastic and mo ldable. like moist puny .

P lace ball o r soil be tween thumb and Iorefin ger genUy pusJ\ing the
soil with the thumb. squeez ing il upward into a ribbon. Form a

ribbon of unifonn

urckness

and width. Allow the ribbon

end ex tend over the forefi nger. breakin g from

its own

'0 em erge

weig ht,

116

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