HomeMy WebLinkAboutSpecial 2004-12-13 Item 5A - Ordinances - Sensitive Areas and Revisions to TMC r COUNCIL AGENDA SYNOPSIS
J� h/9`ry Initials ITEM No.
',1,,i y 4 1E1 Meeting Date Prepared by 1 Mayor's review 1 Council review
11 4 el 12/13/04 SL L, i
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1908 cA M
ITEM INFORMATION
CAS NUMBER: 04-130 I ORIGINAL AGENDA DATE: Apr 11 29, 2004
AGENDA ITEM TITLE Adopt new Sensitive Areas Ordinance and revisions to TMC 18.06, Definitions, TMC
18.50.110 and TMC 18.70.050.
CATEGORY Discussion Motion ''Resolution Ordinance Bid Award Public Hearing Other
Mtg Date Mtg Date Mtg Date Mtg Date Mtg Date Mtg Date Mtg Date
SPONSOR Council Mayor Adm Svcs DCD Finance Fire Legal Pe7R Police PW
SPONSOR'S Adopt a new chapter 18.45, Sensitive Area regulations and other regulations that support
SUMMARY the revisions made to the sensitive areas ordinance through Council and Planning
Commission review. The other affected regulations are TMC 18.06, Definitions, TMC
18.50.110, Supplemental Development Regulations and TMC 18.70.050, Nonconforming
Lots, Structures and Uses.
REVIEWED BY COW Mtg. CA &P Cmte F &S Cmte Transportation Cmte
Utilities Cmte Arts Comm. El Parks Comm. Planning Comm.
DATE: 4/29; 5/13; 5/20; 6/10; 6/24; 7/22; and 9/16/04
RECOMMENDATIONS:
SPONSOR /ADMIN.
COMMITTEE planning Commission
COST'IMPACT FUND SOURCE
EXPENDITURE REQUIRED AMOUNT BUDGETED APPROPRIATION REQUIRED
N/A N/A N/A
Fund Source:
Comments:
MTG. DA RECORD OF COUNCIL ACTION
9 -20 -04 1 Briefing on Natural Environment Chapter Sensitive Areas Ordinance revisions
10 -04 -04 1 Public Hearing on 2004 Amendments to Tukwila Comp Plan Regulations
10 -25 -04 Begin deliberations on Natural Environment Chapter regulations
11-01 11-23-04 continue deliberations conclude deliberations on SAO n
MTG. DATE ATTACHMENTS. v A -E
12 -13 -04 Memo, proposed ordinances: new SAO TMC 18.45 w/ attachmenand
amendments to TMC 18.06, 18.50.110 and 18.70.050.
City of Tukwila
Steven M. Mullet, Mayor
DepaJ. ~uient of CommunifJI Development
Steve Lancaster, Director
INFORMATION MEMO
To:
From:
Date:
Subject:
f Jr
Mayor Mullet, Members of the City Council \ .J~VJ y
Steve Lancaster, Director, Department of Commllp.i~evelopment
December 8, 2004 ./'
Adoption of new Sensitive Areas Ordinance and amendments to TMC 18.06,
TMC 18.50.110 and TMC 18.70.050
ISSUE
The City is required by the Growth Management Act to adopt Comprehensive Plan policies and
regulations that incorporate Best Available Science
BACKGROUND
The Council met on December 6, 2004 to review a revised draft of the Sensitive Areas
Ordinance that reflected the changes approved at the review sessions October 25, November I
and November 23, 2004. The Council also reviewed amendments to TMC l8.06, TMC
18.50.110 and TMC l8.70.050.
DISCUSSION
Attached to this memo are a new Sensitive Areas Ordinance, TMC 18.45, and ordinances
revising TMC l8.06, Definitions, TMC l8.50.ll0, Supplemental Development Standards, and
TMCl8.70.050, Nonconforming Lots, Structures and Uses. These ordinances reflect the
revisions made by the Council during its review of the Planning Commission recommended
sensitive areas regulations.
RECOMMENDATION
Adopt the attached ordinances.
Attachments: Sensitive Areas Ordinance
Amendments to TMC 18.06
Amendments to TMC l8.50.ll0
Amendments to TMC.70.050
q:\1-04 SAO Update\12-8 Council Memo.doc
6300 Southcenter Boulevard, Suite #100 · Tukwila, Washington 98188 · Phone: 206-431-3670 · Fax: 206-431-3665
City of Tukwila
Washington
Ordinance No.
AN ORDINANCE OF THE U,1 { COUNCIL OF THE CITY OF TUKWILA,
WASHINGTON, UPDATING REQUIREMENTS FOR REGULATING
DEVELOPMENT ON SENSITIVE AREAS AND Bt.Jl'.l'I::RS TO
INCORPORATE NEW STATE REQUIREMENTS; REPEALING ORDINANCE
NOS. 1758 (PART), 1770 ~25 AND ~26, 1796 ~3 (PART), AND 1834 ~5;
PROVIDING FOR SEVERABILITY; AND ESTABLISHING AN EFFELu vE
DATE. \
WHEREAS, the State Growth Management Act (GMA) requires the adoption of
development regulations that protect the functions and values of sensitive areas,
including wetlands, watercourses, fish and wildlife habitat conservation areas, and
areas of potential geological instability; and
WHEREAS, RCW 36.70A.172 requires local governments to include the best
available science (BAS) in developing policies and development regulations to protect
the functions and values of sensitive areas, and to give special consideration to
conservation or protection measures necessary to preserve or enhance anadromous
fisheries; and
WHEREAS, the City's efforts to acco~modate growth and to protect sensitive areas
are guided by Countywide Planning Policies and the Tukwila Comprehensive Plan as
recently updated by Ordinance No. 2069 adopted November 22, 2004; and
WHEREAS, the City uses a combination of regulatory and non-regulatory
approaches to protect the functions and values of sensitive areas, including S~UU'Lwater
controls and clearing and grading regulations, habitat restoration projects, and public
education activities; and
WHEREAS, the City participates in the Water Resource Inventory Area 9 planning
process for the Green-Duwamish River, which is expected to be completed in 2005, and
will identify specific priorities for habitat investments, monitoring and adaptive
management needs at a watershed scale, and will help guide future habitat protection
actions in the urban area; and
WHEREAS, the City contracted with professional experts at Adolfson Associates to
.I:"'t'are a review of best available science for wetlands and watercourses, which
resulted in two reports found in Attachment A and Attachment B to this ordinance; and
WHEREAS, the City contracted with professional experts at Landau Associates to
prepare a review of best available science for areas of potential geologic instability,
which resulted in a report found as Attachment C to this ordinance; and
WHEREAS, the Planning Commission and City Council reviewed the BAS studies
prepared by the professional experts along with other BAS material noted in
Attachment D; and.
WHEREAS, the Growth Management Act requires the balancing of economic
development, housing and sensitive area protection goals among others; and
WHEREAS, Attachment E describes departures from Best Available Science in the
following areas: 1) the use of a three-tiered wetland rating system, 2) a wetland
mitigation ratio of 1.5:1 for creation or restoration of wetlands in urban areas, 3) buffer
widths in urban areas, 4) exceptions for isolated 1,000 square foot wetlands in urban
areas, and 5) wetland buffer reduction of up to 50% with mitigation in urban areas; and
SAO Adoption 18.45 12/10104
Page 1 of 26
WHEREAS, the Planning Commission held an open house on May 12, 2004 and a
public hearing on May 20, 2004 to obtain public input, and reviewed the sensitive area
regulations at public meetings on April 29, June 10, June 24, July 22, September 16,2004;
and
WHEREAS, the City Council held a public open house on September 28, 2004 and
public hearing on October 4, 2004 to obtain public input on the sensitive area
regulations as recommended by the Planning Commission, and reviewed the sensitive
area regulations at public meetings on September 20, October 25, November 1,
November 8, November 23, and December 6, 2004; and
WHEREAS, State agencies, including the Department of Community, Trade and
Economic Development; Department of Ecology; and Department of Fish and Wildlife
received notification and copies of the draft regulations for review at least 60 days prior
to adoption;
WHEREAS, the City received comments from the Department of Community, Trade
and Economic Development, and the Department of Ecology and addressed these
comments in the ordinance or as departures;
NOW, THEREFORE, THE CITY COUNCIL OF J. rt.b CITY OF TUKWlLA,
WASHINGTON, DO ORDAIN AS FOLLOWS:
Section 1. Regulations established. Tukwila Municipal Code Chapter 18.45
(Environmentally Sensitive Areas), is hereby established to read as follows:
Chapter 18.45
ENVIRONMENTALLY SENSITIVE AREAS
Sections:
18.45.010 Purpose
18.45.020 Best Available Science
18.45.030 Sensitive Area Applicability, Maps and Inventories
18.45.040 Sensitive Area Special Studies
18.45.050 Interpretation
18.45.060 Procedures
18.45.070 Sensitive Area Permitted Uses
18.45.080 Wetland Designations, Ratings and Buffers
18.45.090 Wetland Uses, Alterations and Mitigation
18.45.100 Watercourse Designations, Ratings and Buffers
18.45.110 Watercourse Uses, Alterations and Mitigation
18.45.120 Areas of Potential Geologic Instability Designations, Ratings and Buffers
18.45.130 Areas of Potential Geologic Instability Uses ..Exemptions, Alterations, and
Mitigation
18.45.140 Abandoned Mine Areas
18.45.150 Fish and Wildlife Habitat Conservation Areas - Designation, Mapping, Uses
and Standards
18.45.160 Sensitive Area Master Plan Overlay
18.45~170 Sensitive Areas Tracts and Easements
18.45.180 Exceptions
18.45.190 Appeals
18.45.200 Recording Required
18.45.210 Assurance Device
18.45.220 Assessment Relief
18.45.010 Purpose
A. The purpose of TMC Chapter 18.45 is to protect the environment, human life and
property, designate and classify ecologically sensitive areas such as regulated wetlands
and watercourses and geologically p"7"rdous areas and to protect these areas and their
functions and values, while also allowing for reasonable use of public and private
property. These regulations are prepared to comply with the Growth Management Act,
SAO Adoption 18.45 12/10/04
Page 2 of 26
RCW 36.70A, to apply best available science according to WAC 365-195-900 to 925 and
to protect critical areas as defined by WAC 365-190-080.
B. Standards are hereby established to meet the following goals of protecting
environmentally sensitive areas:
1. Minimize developmental impacts on the natural functions and values of these
areas.
2. Protect quantity and quality of water resources.
3. Minimize turbidity and pollution of wetlands and fish-bearing waters and
maintain wildlife habitat.
4. Prevent erosion and the loss of slope and soil stability caused by the removal
of trees, shrubs, and root systems of vegetative cover.
5. Protect the public against avoidable losses, public emergency rescue and
relief operations cost, and subsidy cost of public mitigation from landslide, subsidence,
erosion and flooding.
6. ProtE!ct the community's aesthetic resources and distinctive features of
natural lands ~d wooded hillsides.
7. Balance the private rights of individual property owners with the
preservation of environmentally sensitive areas.
8. Prevent the loss of wetland and watercourse function and acreage, and strive
for a gain over present conditions.
9. Give special consideration to conservation or protection measures necessary
to protect or enhance anadromous fisheries.
10. Incorporate the use of best available science in the regulation and protection
of sensitive areas as required by the state Growth Management Act, according to WAC
365-195-900 through 365-195-925 and WAC 365-190-080.
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18.45.020 Best Available Science
A. Policies, regulations and decisions concerning sensitive areas shall rely on Best
Available Science to protect the functions and values of these areas and must give
'special consideration to conservation or protection measures necessary to preserve or
enhance anadromous fish and their habitats.
B. Nonscientific infonnation may supplement scientific infonnation, but is not an
adequate substitution for valid and available scientific infonnation.
C. Incomplete or unavailable scientific infonnation leading to uncertainty for
permitting sensitive area impacts may require application of effective adaptive
management on a case by case basis. Adaptive management relies on scientific
methods to evaluate how well regulatory or non-regulatory actions protect sensitive
areas or replace their functions.
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18.45.030 Sensitive Area Applicability, Maps, and Inventories
A. Applicability - The provisions of TMC Chapter 18.45 shall apply to all land uses
and an development activities in a sensitive area or a sensitive area buffer as defined in
the Definitions chapter of this title. The provisions of TMC Chapter 18.45 apply
whether or not a permit or authorization is required within the City of Tukwila. No
person, company, agency or applicant shall alter a sensitive area or buffer except as
consistent with the purposes and requirements of TMC Chapter 18.45. The following
are sensitive areas regulated by TMC Chapter 18.45:
1. Abandoned coal mines;
2. Areas of potential geologic instability: Oass 2, 3, 4 areas (as defined in the
Definitions chapter of this title and TMC 18.45.120.A);
3. Wetlands;
4. Watercourses;
5. Fish and Wildlife Habitat Conservation Areas.
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Page 3 of 26
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The Growth Management Act also identifies frequently flooded areas and areas
of seismic instability as critical areas. Regulations governing frequently flooded areas
are found in TMC 16.52, Flood Zone Management. Areas of seismic instability are
defined and regulated through the Washington State Building Code.
B. The City shall not approve any permit or .otherwise issue any authorization to
alter the condition of sensitive area land, water or vegetation or to construct or alter any
structure or improvement in, over, or on a sensitive area or its buffer, without first
ensuring compliance with the requirements of TMC Chapter 18.45.
C. Approval of a permit or development proposal pursuant to the provisions of
TMC Chapter 18.45 does not release the applicant from any obligation to comply with
the provisions of TMC Chapter 18.45.
D. When TMC Chapter 18.45 imposes greater restrictions or higher standards upon
the development or use of land than other laws, ordinances or restrictive covenants, the
provisions of TMC Chapter 18.45 shall prevail.
E. It is the obligation of the property owner to comply with all relevant provisions
of this Code. \
F. Sensitive Areas Maps and Inventories
1. The distribution of many sensitive areas in Tukwila is displayed on the
Sensitive Areas Maps, on file with the Department of Community Development (DCD).
These maps are based on site assessment of current conditions and review of the best
available scientific data and are hereby adopted by reference.
2. Studies, preliminary inventories and ratings of potential sensitive areas are on
file with DCD.
3. As new environmental information related to sensitive areas becomes
available, the Director is hereby designated to periodically add new information to the
Sensitive Areas Map. Removal of any information from the sensitive area maps must
be approved by the City Council.
4. Regardless of whether a sensitive area is shown on the sensitive areas map,
the actual presence or absence of the features defined in the code as sensitive areas shall
govern. The Director may require the applicant to submit technical information to
indicate whether sensitive areas actually exist on or adjacent to the applicant's site,
based on the definitions of sensitive areas in this code.
5. All revisions, updates and reprinting of sensitive areas maps, inventories,
ratings and buffers shall conform to TMC Chapter 18.45.
18.45.040 Sensitive Areas Special Studies
A. Required - An applicant for a development proposal that may include a
sensitive area and! or its buffer shall submit those studies as required by the City and
specified below to adequately identify and evaluate the sensitive area and its buffers.
1. A required sensitive areas study shall be prepared by a person with
experience and training in the scientific discipline appropriate for the relevant sensitive
area in accordance with WAC 365-195-905(4). A qualified professional must have
obtained a B.S. or B.A. or equivalent degree in ecology or related science, engineering,
environmental studies, fisheries, geotechnical or related field, and two years of related
work experience.
a. A qualified professional for Fish and Wildlife Habitat Conservation Areas
must have a degree in ecology or related sciences and professional experience related to
the subject species.
b. A qualified professional for wetland sensitive area studies must be a
certified Professional Wetland Scientist or a non-certified Professional Wetland Scientist
with at least two years of full-time work experience as a wetlands professional,
including delineating wetlands using the state or federal manuals, preparing wetland
reports, conducting function assessments, and developing and implementing mitigation
plans.
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SAO Adoption 18.45 12/10/04
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c. A qualified professional for a geological hazard study must be a
professional geotechnical engineer as defined in the Definitions chapter of this Title,
licensed in the state of Washington.
d. A qualified professional for watercourses means a hydologist, geologist,
engineer or other scientist with experience in preparing watercourse assessments.
2. The sensitive areas study shall use scientifically valid methods and studies in
the analysis of sensitive area data and shall use field reconnaissance and reference the
source of science used. The sensitive area study shall evaluate the proposal and all
probable impacts to sensitive areas in accordance with the provisions of TMC Chapter
18.45.
B. Wetland and Watercourse Sensitive Area Studies -- The sensitive area study shall
contain the following information, as applicable:
1. The name and contact information of the applicant, a description of the
proposal, and identification of the permit requested;
2. A copy of the site plan for the development proposal showing: sensitive
areas and buffers and the development proposal with dimensions; clearing limits;
proposed S~vuuwater management plan; and mitigation plan for impacts due to
drainage alterations;
3. The dates, names and qualifications of the persons preparing the study and
documentation of any fieldwork performed on the site;
4. Identification and characterization of all sensitive areas, water bodies, and
buffers adjacent to the proposed project area or potentially impacted by the proposed
project;
5. A statement specifying the accuracy of the study and assumptions used in the
study;
6. Determination of the degree of hazard and risk from the proposal both on the
site and on adjacent properties;
7. An assessment of the probable cumulative impacts to sensitive areas, their
buffers and other properties resulting from the proposal;
8. A description of reasonable efforts made to apply mitigation sequencing to
avoid, minimize and mitigate impacts to sensitive areas;
9. Plans for adequate mitigation to offset any impacts;
10. Recommendations for maintenance, short-term and long-term monitoring,
contingency plans and bonding measures; and
11. Any technical information required by the director to assist in determining
compliance with TMC Chapter 18.45.
C. Geotechnical Report
1. A geotechnical report appropriate both to the site conditions and the
proposed development shall be required for development in Class 2, Class 3, Class 4
areas, and any areas identified as Coal Mine Hazard Areas unless waived pursuant to
TMC 18.45.040.D.
2. Geotechnical" reports for Gass 2 areas shall include at a minimum a site
evaluation review of available information regarding the site and a surface
reconnaissance of the site and adjacent areas. Subsurface exploration of site conditions
is at the discretion of the geotechnical consultant.
3. Geotechnical reports for Class 3, Class 4 and Coal Mine Hazard Areas shall
include a site evaluation review of available information about the site, a surface
reconnaissance of the site and adjacent areas, a feasibility analysis for the use of
infiltration on-site and a subsurface exploration of soils and hydrology conditions.
Detailed slope stability analysis shall be done if the geotechnical engineer recommends
it in Class 3 or Coal Mine Hazard Areas, and must be done in Gass 4 areas.
4. Applicants shall retain a geotechnical engineer to prepare the reports and
evaluations required in this subsection. The geotechnical report and completed site
evaluation checklist shall be prepared in accordance with the generally accepted
SAO Adoption 18.45 12/1 0/04
Page 5 of 26
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geotechnical practices, under the supervision of and signed and stamped by the
geotechnical engineer. The report shall be prepared in consultation with the
appropriate City department. Where appropriate, a geologist must be included as part
of the geotechnical consulting team. The report shall make specific recommendations
concerning development of the site.
5. The opinions and recommendations contained in the report shall be
supported by field observations and, where appropriate or applicable, by literature
review conducted by the geotechnical engineer which shall include appropriate
explorations, such as borings or test pits, and an analysis of soil characteristics
conducted by or under the supervision of the engineer in accordance with standards of
the American SocietY of Testing and Materials or other applicable standards. If the
evaluation involves geologic evaluations or in~c~t'~etations, the report shall be reviewed
and approved by a geotechnical engineer.
D. Sensitive Area Study - Modifications to Requirements
1. The Director may limit the required geographic area of the sensitive area
study as appropriate if:
a. The applicant, with assistance from the city, cannot obtain permission to
access properties adjacent to the project area; or
b. The proposed activity will affect only a limited part of the site.
2. The Director may allow modifications to the required contents of the study
where, in the judgment of a qualified professional, more or less information is required
to adequately address the potential sensitive area impacts and required mitigation.
E. Waiver - If there is written agreement between the Director and the applicant
concerning the sensitive area classification and type, the Director may waive the
requirement for sensitive area studies provided that no adverse impacts to sensitive
areas or buffers will result. There must be substantial evidence that the sensitive areas
classification is correct, that there will be no detrimental impact to the sensitive areas or
buffers, and that the goals, purposes, objectives and requirements of TMC Chapter 18.45
will be followed.
F. Review of Studies - The Department of Community Development will review
the information submitted in the sensitive area studies to verify the information,
confirm the nature and type of the sensitive area, and ensure the study is consistent
with TMC Chapter 18.45. At the discretion of the Director, sensitive area studies may
undergo per review, at the expense of the applicant.
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18.45.050 Interpretation
The provisions of TMC Chapter 18.45 shall be held to'be minimum requirements in
their interpretation and application and shall be liberally construed to serve the
purposes of TMC Chapter 18.45.
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18.45.060 Procedures
When an applicant submits an application for any building permit, subdivision,
short subdivision or any other land use review which approves a use, development or
future construction, the location and dimensions of all sensitive areas and buffers on the
site shall be indicated on the plans submitted. When a sensitive area is identified, the
following procedures apply. The Director may waive item numbers 1, 2, 4 and 5 of the
following if the size and complexity of the project does not warrant that step in the
procedures and the Director grants a waiver pursuant to TMC 18.45.040 D.
1. Sensitive areas study and geotechnical report.
a. The applicant shall submit the relevant study as required in TMC
21.04.140 and TMC Chapter 18.45.
b. It is intended that sensitive areas studies and information be utilized by
applicants in preparation of their proposals and therefore shall be undertaken early in
the design stages of a project.
SAO Adoption 18.45 12/10/04
Page 6 of 26
2. Planned residential development permit - Any new residential subdivision
or multiple family residential proposal that includes a wetland or watercourse or its
buffer on the site may apply for a planned residential development permit and meet the
requirements of the Planned Residential Development District chapter of this title.
3. Denial of use or development - A use or development will be denied if the
Director determines that the applicant cannot ensure that potential dangers and costs to
future inhabitants of the development, adjacent properties, and Tukwila are minimized
and mitigated to an acceptable level.
4. Preconstruction meeting - The applicant, specialist(s) of record, contractor,
and department representatives will be required to attend pre-construction meetings
prior to any work on the site.
5. Construction monitoring - The specialist(s) of record shall be retained to
monitor the site during construction.
6. On-site Identification - The Director may require the boundary between a
sensitive area and its buffer and any development or use to be permanently identified
with fencing, or with a wood or metal sign with treated wood, concrete or metal posts.
Size will be determined at the time of permitting, and wording shall be as follows:
"Protection of this natural area is in your care. Alteration or disturbance is
prohibited pursuant to TMC Chapter 18.45. Please call the City of Tukwila for more
information."
18.45.070 Sensitive Area Permitted Uses
A. General Uses - The uses set forth in this entire section, including subsections A.
through D, and the following general uses, may be located within a sensitive area or
buffer, subject to the provisions of TMC 21.04 and of the mitigation requirements of
TMC Chapter 18.45:
1. Maintenance and repair of existing uses and facilities provided no alteration
or additional fill materials will be placed or heavy construction equipment used in the
sensitive area or buffer.
2. Nondestructive education and research.
3. Passive recreation and open space.
4. Maintenance and repair of essential streets, roads, rights-of-way, or utilities.
5. Actions to remedy the effects of emergencies that threaten the public health,
safety or welfare.
6. Maintenance activities of existing landscaping and gardens in a sensitive area
buffer including but not limited to mowing lawns, weeding, harvesting and replanting
of garden crops and pruning and planting of vegetation. The removal of established
native trees and shrubs is not permitted.
B. Permitted Uses Subject To Administrative Review - The following uses may be
permitted only after administrative review and approval by the Director:
1. Maintenance and repair of existing uses and facilities where alteration or
additional fill materials will be placed or heavy construction equipment used.
2. Construction of new essential streets and roads, rights-of-way and utilities.
3. New surface water discharges to sensitive areas or their buffers from
detention facilities, pre-settlement ponds or other surface water management structures
may be allowed provided that the discharge meets the clean water standards of RCW
90.48 and WAC 173.200 and 173.201 as amended, and does not adversely affect water
level fluctuations in the wetland or adversely affect watercourse habitat and
watercourse flow conditions relative to the existing rate.
4. Regional stormwater detention areas may be allowed in a Type 3 wetland,
Type 3 or 4 watercourse and/ or their buffers per the standards of 18.45.090 and
18.45.110. Design shall be subject to the standards of this section and other applicable
City standards, including mitigation. Type 1 wetlands and Type 1 and 2 watercourses
shall not be used for regional stormwater detention.
SAO Adoption 18.45 12/10/04
Page 7 of 26
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5. Enhancement or other mitigation including landscaping with native plants.
6. Essential Utilities
a. Essential utilities must be constructed to minimize, or where possible
avoid, disturbance of the sensitive area and its buffer.
b. All construction must be designed to protect the sensitive area and its
buffer against erosion, uncontrolled stormwater, restriction of groundwater movement,
slides, pollution, habitat disturbance, any loss of flood carrying capacity and storage
capacity, and excavation or fill detrimental to the envirorunent.
c. Upon completion of installation of essential utilities, sensitive areas and
their buffers must be restored to pre-project configuration, replanted as required and
provided with maintenance care until newly planted vegetation is established.
d. All crossings must be designed for shared facilities in order to minimize
adverse impacts and reduce the number of crossings.
7. Essential Streets, Roads and Rights-of-Way
a. E!1sential streets, roads and rights-of-way must be designed and
maintained to prevent erosion and avoid restricting the natural movement of
groundwater.
b. Essential streets, roads and rights-of-way must be located to COrhVUH to
the topography so that minimum alteration of natural conditions is necessary. The
number of crossings shall be limited to those necessary to provide essential access.
c. Essential streets, roads and rights-of-way must be constructed in a way
that does not adversely affect the hydrologic quality of the wetland, or watercourse
and! or its buffer. Where feasible, crossings must allow for combination with other
essential utilities.
d. Upon completion of construction, the area affected must be restored to an
appropriate grade, replanted according to a plan approved by the Director, and
provided with care until newly-planted vegetation is established.
8. Public Use and Access
a. Public access shall be limited to trails, boardwalks, covered or uncovered
viewing and seating areas and displays, and must be located in areas that have the
lowest sensitivity to human disturbance or alteration.
b. Public access must be specifically developed for interpretive, educational
or research purposes by, or in cooperation with, the City or as part of the adopted
Tukwila Parks and Open Space Plan.
c. No motorized vehicle is allowed within a sensitive area or its buffer
except as required for necessary maintenance, agricultural management or security.
d. Any public access or interpretive displays developed along a sensitive
area and its buffer must, to the C"~CHt possible, be connected with a park, recreation or
open-space area.
e. Vegetative edges, structural barriers, signs or other measures must be
provided wherever necessary to protect sensitive areas and their buffers by limiting
access to designated public use or interpretive areas.
f. Access trails must incorporate design features and materials that protect
water quality and allow adequate surface water and groundwater movement.
g. Access trails must be located where they do not disturb nesting, breeding
and rearing areas and must be designed so that sensitive plant and critical wildlife
species are protected.
9. Dredging, Digging or Filling
a. Dredging, digging or filling within a sensitive area or its buffer may occur
only with the permission of the Director and only for the following purposes:
(1) Uses permitted by TMC 18.45.080, 18.45.090, 18.45.110, 18.45.130;
(2) Maintenance of an existing watercourse;
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SAO Adoption 18.45 12/10/04
Page 8 of26
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(3) Enhancement or restoration of habitat in conformance with an
approved mitigation plan identified in a sensitive area study;
(4) Natural system interpretation, education or research when
undertaken by, or in cooperation with, the City; .
(5) Flood control or water quality enhancement by the City;
(6) Maintenance of existing water quality controls, for normal
maintenance needs and for any diversion, rerouting, piping or other alteration
permitted by TMC Chapter 18.45;
(7) Filling of abandoned mines.
b. Any dredging, digging or filling shall be performed in a manner that will
minimize sedimentation in the water. Every effort will be made to perform such work
at the time of year when the impact can be lessened.
c. Upon completion of construction, the area affected must be restored to an
appropriate grade, replanted according to a plan approved by the Director, and
provided with fare until newly-planted vegetation is established.
C. Permitted Uses Subject to Exception Approval - Other uses may be permitted
upon receiving a reasonable use exception pursuant to TMC 18.45.180. A use permitted
through a reasonable use exception shall conform to the procedures of TMC Chapter
18.45 and be consistent with the underlying zoning.
D. Uses allowed under a Sensitive Area Master Plan prepared and approved under
the provisions of TMC 18.45.160.
18.45.080 Wetlands Designations, Ratings and Buffers
A. Wetland Designations.
1. For the purposes of TMC Chapter 18.45, "wetlands" and "regulated
wetlands" are defined in the Definitions chapter of this title. A wetland boundary is the
line delineating the outer edge of a wetland established by using the Washington State
Wetland and Delineation Manual, as required by RCW 36.70A.175 (Ecology Publication
#96-94) and consistent with the 1987 Corps of Engineers Wetland Delineation Manual.
2. For the purposes of this section, the U.S. Fish and Wildlife Service's
"Oassification of Wetlands and Deepwater Habitats of the United States FWS/OBS-
79/31" (Cowardin et al., 1979), contains the descriptions of wetland classes and
subclasses.
3. Wetland areas within the City of Tukwila have certain characteristics,
functions and values and have been influenced by urbanization and related
disturbances. Wetland functions include, but are not limited to the following:
a. Improving water quality;
b. Maintaining hydrologic functions (reducing peak flows, decreasing
erosion, groundwater); and
c. Providing habitat for plants, mammals, fish, birds, and amphibians.
B. Wetland Ratings. Wetlands shall be designated Type 1, Type 2 or Type 3 as listed
below:
1. Type 1 wetlands are those wetlands that meet any of the following criteria:
a. The wetland is characterized by the presence of species listed by the
federal government or State as endangered or threatened, or the presence of critical or
outstanding habitat for those species;
b. The wetland has 40-60% permanent open water in dispersed patches with
two or more classes of vegetation;
c. The wetland is equal to or greater than five acres in size and has three or
more wetland classes, one of which may be substituted by permanent or open water; or
d. The wetland is documented as regionally significant waterfowl or
shorebird areas by the State Department of Fish and Wildlife.
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2. Type 2 wetlands are those wetlands that meet any of the following criteria:
a. The wetland is equal to or greater than one acre in size;
b. The wetland has three or more wetland classes and is less than 5 acres;
c. The wetland is characterized by the. presence of nesting sites for priority
species as listed by the Washington State Department of Fish and Wildlife; or
d. The wetland is hydrologically connected (non-isolated) to a Type 1 or
Type 2 watercourse.
3. Type 3 wetlands are those wetlands that are greater than 1,000 sq. ft. and less
than one acre in size with two or fewer wetland classes.
C. Wetland Buffers - A buffer area shall be established adjacent to designated
wetland areas. The purpose of the buffer area shall be to protect the integrity, functions
and values of the wetland area. Any land alteration must be located out of the buffer
areas as required by this section. Wetland buffers are intended in general to:
1. Minimize long-term impacts of development on properties containing
wetlands;
2. Protect wetlands from adverse impacts during development;
3. Preserve the edge of the wetland and its buffer for its critical habitat value;
4. Provide an area to stabilize banks, to absorb overflow during high water
events and to allow for slight variation of aquatic system boundaries over time due to
hydrologic or climatic effects;
5. Reduce erosion and increased surface water runoff;
6. Reduce loss of or damage to property; .
7. Intercept fine sediments from surface water runoff and serve to minimize
water quality impacts; and
8. Protect the sensitive area from human and domestic animal disturbances.
An undisturbed sensitive area or buffer may substitute for the yard setback and
landscape requirements of the TMC 18.50 and 18.52.
D. Special Buffer Studies - Applicants for a use or development within a wetland or
its buffer shall be required to conduct a sensitive area study to provide a buffer analysis
for the sensitive area. This study may be waived by the Director pursuant to TMC
18.45.040 D.
E. Wetland Buffer Widths - The following standard buffers shall be established
from the wetland edge:
1. Type 1 Wetland; 100 foot buffer.
2. Type 2 Wetland; 80-foot buffer.
3. Type 3 Wetland; 50-foot buffer.
F. Buffer Setbacks
1. All commercial and industrial buildings shall be set back 15 feet and all other
development shall be set back ten feet from the buffer's edge. The building setbacks
shall be measured from the foundation to the buffer's edge. Building plans shall also
identify a 20-foot area beyond the buffer setback within which the impacts of
development will be reviewed.
2. The Director may waive setback requirements when a site plan demonstrates
there will be no impacts to the buffer from construction or occasional maintenance
activities (see TMC Figure 18-2).
G. Variation of Standard Wetland Buffer Width
1. The Director may reduce the standard wetland buffers on a case-by-case
basis, provided the reduced buffer area does not contain slopes 15% or greater. The
approved buffer width shall not result in greater than a 50% reduction in width.
2. Buffer reduction with enhancement may be allowed by the Director as a Type
2 permit if:
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a. Additional protection to wetlands will be provided through the
implementation of a buffer enhancement plan;
b. The existing condition of the buffer is degraded;
c. Buffer enhancement includes, but is not limited to the following:
(1) Planting vegetation that would increase value for fish and wildlife
habitat or improve water quality;
(2) Enhancement of wildlife habitat by incorporating structures that are
likely to be used by wildlife, including wood duck boxes, bat boxes, snags,
rootwads/ stumps, birdhouses and heron nesting areas; or
(3) Removing non-native plat species and noxious weeds from the buffer
area and replanting the area subject to 2.c.(1) above.
3. Buffers for all types of wetlands will be increased when they are determined
to be particularly sensitive to disturbance or the proposed development will create
unusually adverse impacts. Any increase in the width of the buffer shall be required
only after completion of a wetland study by a qualified wetlands specialist or expert
that documentS the basis for such increased width. An increase in buffer width may be
appropriate when:
a. The development proposal has the demonstrated potential for significant
adverse impacts upon the wetland that can be mitigated by an increased buffer width;
or
b. The area serves as habitat for endangered, threatened, sensitive or monitor
species listed by the federal government or the State.
4. Every reasonable effort shall be made to maintain the existing viable native
plant life in the buffers. Vegetation may be removed from the buffer as part of an
enhancement plan approved by the Director. Enhancements will ensure that slope
stability and wetland quality will be maintained or improved. Any disturbance of the
buffers for wetlands shall be replanted with a diverse plant community of native
northwest species that are appropriate for the specific site as determined by the
Director. If the vegetation must be removed, or because of the alterations of the
landscape the vegetation becomes damaged or dies, then the applicant for a permit
must replace existing vegetation along wetlands with comparable specimens, approved
by the Director, which will restore buffer functions within five years.
5. The Director shall require subsequent corrective actions and long-term
monitoring of the project if adverse impacts to regulated wetlands or their buffers are
identified.
18.45.090 Wetlands Uses, Alterations and Mitigation
A. No use or development may occur in a Type 1, Type 2 or Type 3 wetland or its
buffer except as specifically allowed by TMC Chapter 18.45. Any use or development
allowed is subject to review and approval by the Director. Where required, a mitigation
or enhancement plan must be developed and must comply with the standards of
mitigation required in TMC Chapter 18.45.
B. Alterations
1. Alterations to wetlands are discouraged and are limited to the minimum
necessary for project feasibility. Requests for alterations must be accompanied by a
mitigation plan, are subject to Director approval, and may be approved only if the
following findings are made:
a. The alteration will not adversely affect water quality;
b. The alteration will not adversely affect fish, wildlife, or their habitat;
c. The alteration will not have an adverse effect on drainage and! or
stormwater detention capabilities;
d. The alteration will not lead to unstable earth conditions or create an
erosion hazard or contribute to scouring actions;
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e. The alteration will not be materially detrimental to any other property;
and
f. The alteration will not have adverse effects on any other sensitive areas.
2. Alterations are not permitted to Type 1 wetlands unless specifically exempted
under the provisions of TMC Chapter 18.45.
3. Alterations to Type 2 wetlands are prohibited except where the location or
configuration of the wetland provides practical difficulties that can be resolved by
modifying up to .10 (one-tenth) of an acre of wetland. Mitigation for any alteration to a
Type 2 wetland must be provided at a ratio of 1.5:1 for creation or restoration and 3:1
for enhancement and must be located contiguous to the altered wetland.
4. Isolated Type 3 wetlands may be altered or relocated only with the
permission of the Director. A mitigation or enhancement plan must be developed and
must comply with the standards of mitigation required in TMC Chapter 18.45.
5. Mitigation plans shall be completed for any proposals for dredging, filling,
alterations and,relocation of wetland habitat allowed in TMC Chapter 18.45.
6. Isolated wetlands formed on fill material in highly disturbed environmental
conditions and assessed as having low overall wetland functions may be altered and! or
relocated under TMC Chapter 18.45. These wetlands may include artificial hydrology
or wetlands unintentionally created as the result of construction activities. The
determination that a wetland is isolated is made through the Type 2 permit process. A
mitigation or enhancement plan must be developed and must comply with the
standards of mitigation required in TMC Chapter 18.45.
C. Mitigation Sequencing. Applicants shall, demonstrate that reasonable efforts
have been examined with the intent to avoid and minimize impacts to wetlands and
wetland buffers. When an alteration to a wetland or its required buffer is proposed,
such alteration shall be avoided, minimized or compensated for in the following order
of preference:
1. Avoidance of wetland and wetland buffer impacts, whether by finding
another site or changing the location of the proposed activity on-site;
2. Minimizing wetland and wetland buffer impacts by limiting the degree of
impact on site;
3. Mitigation actions that require compensation by replacing, enhancing, or
substitution shall occur in the following order of preference:
a. restoring wetlands on upland sites that were formerly wetlands;
b. enhancing significantly degraded wetlands;
c. creating wetlands on disturbed upland site~such as those with vegetative
cover consisting primarily of exotic introduced species or noxious weeds.
D. Mitigation Plans.
1. The mitigation plan shall be developed as part of a sensitive area study by a
specialist approved by the Director. Wetland and/or buffer alteration or relocation
may be allowed only when a mitigation plan clearly demonstrates that the changes
would be an improvement of wetland and buffer quantitative and qualitative functions.
The plan shall follow the performance standards of TMC Chapter 18.45 and show how
water quality, wildlife and fish habitat, and general wetland quality would be
improved.
2. In order to achieve the City's goal of no net loss of wetland functions and
acreage, alteration of wetlands will require the applicant to provide a restoration or
creation plan to compensate for the impacts to the wetland and will compensate at a
ratio of 1.5 to 1.
3. Impacts to wetlands may be mitigated by enhancement of existing
significantly degraded wetlands, however, in order to achieve the City's goal of no net
loss of wetland functions and acreage, mitigation through enhancement must be
compensated at a ratio of 3:1. Applicants proposing to enhance wetlands must produce
a sensitive area study that identifies how enhancement will increase the functions of the
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degraded wetland and how this increase will adequately mitigate for the loss of
wetland area and function at the impact site. An enhancement proposal must also show
whether existing wetland functions will be reduced by the enhancement actions.
E. Mitigation Location.
1. On-site mitigation shall be provided, except where the applicant can
demonstrate that:
(a) On-site mitigation is not scientifically feasible due to problems with
hydrology, soils, waves or other factors; or
(b) Mitigation is not practical due tq potentially adverse impact from
surrounding land uses; or
(c) Existing functional values created at the site of the proposed restoration
are significantly greater than lost wetland functional values; or
(d) That established regional goals for flood storage, flood conveyance,
habitat or other wetland functions have been established and strongly justify location of
mitigation at at;lother site.
2. Off-site mitigation shall occur within the same watershed where the wetland
loss occurred.
3. Mitigation sites located within the Tukwila city limits are preferred.
However, the Director may approve mitigation sites outside the city upon finding that:
(a) Adequate measures have been taken to ensure the non-development and
long-term viability of the mitigation site; and
(b) Adequate coordination with the other affected local jurisdiction has
occurred.
4. In selecting mitigation sites, applicants shall pursue siting in the following
order of preference:
(a) Upland sites that were formerly wetlands;
(b) Idled upland sites generally having bare ground or vegetative cover
consisting primarily of exotic introduced species, weeds or emergent vegetation;
(c) Other disturbed upland;
(d) Existing degraded wetland.
F. Mitigation Standards. The scope and content of a mitigation plan shall be
decided on a case-by-case basis. As the impacts to the sensitive area increase, the
mitigation measures to offset these impacts will increase in number and complexity.
The components of a complete wetlands mitigation plan are as follows:
1. Baseline information of quantitative data collection or a review and synthesis
of existing data for both the project impact zone and the proposed mitigation site;
2. Environmental goals and objectives that describe the purposes of the
mitigation measures. This should include a description of site-selection criteria,
identification of target evaluation species and resource functions;
3. Performance standards of the specific criteria for fulfilling environmental
goals! and for beginning remedial action or contingency measures. They may include
water quality standards, species richness and diversity targets, habitat diversity indices,
or other ecological, geological or hydrological criteria;
4. A detailed construction plan of the written specifications and descriptions of
mitigation techniques. This plan should include the proposed construction sequence
and construction management, and be accompanied by detailed site diagrams and
blueprints that are an integral requirement of any development proposal;
5. Monitoring and! or evaluation program that outlines the approach for
assessing a completed project. An outline shall be included that spells out how the
monitoring data will be evaluated by agencies that are tracking the mitigation project's
progress;
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6. Contingency plan identifying potential courses of action, and any corrective
measures to be taken when monitoring or evaluation indicates project performance
standards have not been met; and
7. Performance security or other assurance devices as described in TMC
18.45.210.
G. Mitigation Timing. Mitigation projects shall be completed prior to activities that
will permanently disturb wetlands and either prior to or immediately after activities
that will temporarily disturb wetlands. Construction of mitigation projects shall be
timed to reduce impacts to existing wildlife, flora and water quality, and shall be
completed prior to use or occupancy of the activity or development. The Director may
allow activities that permanently disturb wetlands prior to implementation of the
mitigation plan under the following circumstances:
1. To allow planting or re- vegation to occur during optimal weather conditions;
2. To avoid disturbance during critical wildlife periods; or
3. To account for unique site constraints that dictate construction timing or
"s phasing.
H. Permitted Uses Subject to Exception Approval. Other uses may be permitted
upon receiving a reasonable use exception pursuant to TMC 18.45.180. A use permitted
through a reasonable use exception shall conform to the procedures of TMC Chapter
18.45 and be consistent with the underlying zoning.
18.45.100 Watercourse Designations, Ratings and Buffers
A. Watercourse Ratings: Watercourse ratings are based on the existing habitat
functions and are rated as follows:
1. Type 1 Watercourse: Watercourses inventoried as Shorelines of the State,
under RCW 90.58. These watercourses shall be regulated under TMC 18.44, Shoreline
yj Overlay.
2. Type 2 Watercourse: Those watercourses that have perennial (year- round) or
intermittent flows and support salmonid fish use.
3. Type 3 Watercourse: Those watercourses that have perennial flows and are
not used by salmonid fish.
4. Type 4 Watercourse: Those watercourses that have intermittent flows and are
not used by salmonid fish.
B. Watercourse Buffers. Any land alteration must be located out of the buffer areas
as required by this section. Watercourse buffers are intended in general to:
1. Minimize long -term impacts of development on properties containing
watercourses;
2. Protect the watercourse from adverse impacts during development;
3. Preserve the edge of the watercourse and its buffer for its critical habitat
value;
4. Provide shading to maintain stable water temperatures and vegetative cover
for additional wildlife habitat;
5. Provide input of organic debris and uptake of nutrients;
6. Provide an area to stabilize banks, to absorb overflow during high water
events and to allow for slight variation of aquatic system boundaries over time due to
hydrologic or climatic effects;
=1r 7. Reduce erosion and increased surface water runoff;
8. Reduce loss of, or damage to, property;
9. Intercept fine sediments from surface water runoff and serve to minimize
water quality impacts; and
10. Protect the sensitive area from human and domestic animal disturbance.
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An undisturbed sensitive area or buffer may substitute for the yard setback and
landscape requirements of TMC 18.50 and 18.52.
C. Special Buffer Studies -- Applicants for a use or development within a
watercourse or its buffer shall be required to conduct a sensitive area study to provide a
buffer analysis for the sensitive area. This study may be waived by the Director
pursuant to TMC 18.45.040 E.
D. Watercourse Buffer Widths - The following buffer widths apply to each side of
a watercourses:
1. Type 1 Watercourse: Regulated under TMC 18.44, Shoreline Overlay.
2. Type 2 Watercourse: 100-foot-wide buffer.
3. Type 3 Watercourse: 80-foot-wide buffer.
4. Type 4 Watercourse: 50-foot-wide buffer.
E. Buffer Setbacks
1. All commercial and industrial buildings shall be setback 15 feet and all other
development shall be setback 10 feet. Building setbacks shall be measured from the
foundation to the buffer's edge. Building plans shall also identify a 20-foot area beyond
the buffer setback within which the impacts of development will be reviewed.
2. The Director may waive setback requirements when a site plan demonstrates
there will be no impacts to the buffer from construction or occasional maintenance
activities (see TMC Figure 18-2).
F. Variation of Standard Watercourse Buffer Width.
1. The Director may reduce the standard watercourse buffers on a case-by-case
basis, provided the buffer does not contain slopes 15% or greater. The approved buffer
width shall not result in greater than a 50% reduction in width. Any buffer reduction
proposal must demonstrate to the satisfaction of the Director that it will not result in
direct, indirect or long-term adverse impacts to watercourses, and that:
(a) The buffer is vegetated and includes an enhancement plan as may be
required to improve the buffer function and value; or
(b) If there is no significant vegetation in the buffer, a buffer may be reduced
only if an enhancement plan is provided. The plan must include using a variety of
native vegetation that improves the functional attributes of the buffer and provides
additional protection for the watercourse functions and values.
2. Buffers for all types of watercourses will be increased when they are deter-
mined to be particularly sensitive to disturbance or the proposed development will
create unusually adverse impacts. Any increase in the width of the buffer shall be
required only after completion of a watercourse study by_a qualified specialist or expert
that documents the basis for such increased width. An increase in buffer width may be
appropriate when:
(a) The development proposal has the demonstrated potential for significant
adverse impacts upon the watercourse that can be mitigated by an increased buffer
width; or
(b) The area serves as habitat for endangered, threatened, sensitive or monitor
species listed by the federal government or the State.
3. Every reasonable effort shall be made to maintain the existing viable plant life
in the buffers. Vegetation may be removed from the buffer as part of an enhancement
plan approved by the Director. Enhancements will ensure that slope stability and
watercourse quality will be maintained or improved. Any disturbance of the buffers for
watercourses shall be replanted with a diverse plant community of native northwest
species that are appropriate for the specific site as determined by the Director. If the
vegetation must be removed, or because of the alterations of the landscape the
vegetation becomes damaged or dies, then the applicant for a permit must replace
existing vegetation along watercourses with comparable specimens, approved by the
Director, that will restore buffer functions within five years.
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4. The Director shall require subsequent corrective actions and long-term
monitoring of the project if adverse impacts to regulated watercourses or their buffers
are identified.
18.45.110 Watercourse Uses, Alterations and Mitigation
A. General Permitted Uses
1. The uses set forth in this entire section, including subsections A through G.
and TMC 18.45.070, may be located within a watercourse or its buffer, subject to the
provisions of TMC 21.04 and of TMC Chapter 18.45.
2. No use or development may occur in a watercourse or its buffer except as
specifically allowed by TMC Chapter 18.45. Any use or development allowed is subject
to the standards of TMC Chapter 18.45.
B. Alterations.
1. Diverting or rerouting may only occur with the permission of the Director
and an approv~d mitigation plan.
2. Any watercourse that has critical wildlife habitat, or is necessary for the life
cycle or spawning of salmonids, shall not be rerouted unless it can be shown that the
habitat will be improved for the benefit of the species.
3. A watercourse may be rerouted or day lighted as a mitigation measure to
improve watercourse function.
C. Piping. Piping of any watercourse should be avoided. Relocation of a
watercourse is preferred to piping; if piping occurs in a watercourse sensitive area, it
shall be limited and shall require approval of the Director.
1. Piping of Type 1 watercourses shall not be permitted.
2. Piping may be allowed in Type 2, 3 or 4 watercourses if it is necessary for
access purposes.
3. Piping may be allowed in Type 4 watercourses if the watercourse has a
degraded buffer, is located in a highly developed area and does not provide shade,
temperature control etc. for habitat. The applicant must comply with the conditions of
this section, including:
a. Providing excess capacity to meet needs of the system during a 100-year
flood event; and
b. Providing flow restrictors, and complying with water quality and existing
habitat-enhancement procedures.
4. No process that requires maintenance on a regular basis will be acceptable
unless this maintenance process is part of the regular and normal facilities maintenance
process or unless the applicant can show funding for this maintenance is ensured for as
long as the use remains.
5. Piping projects shall be performed pursuant to the following applicable
standards:
a. The conveyance system shall be designed to comply with the standards in
current use and recommended by the Department of Public Works.
b. Where allowed, piping shall be limited to the shortest length possible as
dG~cuuined by the Director to allow access onto a property.
c. Where water is piped for an access point, those driveways or entrances
shall be consolidated to serve multiple properties where possible, and to minimize the
length of piping.
d. When required by the Director, watercourses under drivable surfaces shall
be contained in an arch culvert using oversize or superspan culverts for rebuilding of a
stream bed. These shall be provided with check dams to reduce flows, and shall be
replanted and enhanced according to a plan approved by the Director.
e. All watercourse crossing shall be designed to accommodate fish passage.
Watercourse crossings shall not block fish passage where the streams are fish bearing.
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f. Stormwater runoff shall be detained and infiltrated to preserve the
watercourse channel's dominant discharge.
g. All construction shall be designed to have the least adverse impact on the
watercourse, buffer and surrounding environment.
h. Piping shall be constructed during periods of low flow, or as specified by
the State Department of Fish and Wildlife.
i. Water quality must be as good or better for any water exiting the pipe as
for the water entering the pipe, and flow must be comparable.
D. Permitted Uses Subject to Exception Approval - Other uses may be permitted
upon receiving a reasonable use exception pursuant to TMC 18.45.180. A use permitted
through a reasonable use exception shall conform to the procedures of TMC Chapter
18.45 and be consistent with the underlying zoning.
E. Mitigation - All impacts to a watercourse that degrade the functions and values
of the watercourse shall be avoided. If alteration to the watercourse is unavoidable, all
adverse impacts to the watercourse and its buffer resulting from a development
proposal or alteration shall be mitigated in accordance with an approved mitigation
plan as described below.
1. Plans. Mitigation plans shall be completed for any proposals of dredging,
filling, diverting, piping and rerouting of watercourses.
2. Plan Contents - The mitigation plan shall be developed as part of a sensitive
area study by a specialist approved by the Director. The plan must show how water
quality, treatment, erosion control, pollution reduction, wildlife and fish habitat, and
general watercourse quality would be maintaine~ or improved. All such plans must be
approved by the Director.
3. Mitigation Standards - The scope and content of a mitigation plan shall be
decided on a case-by-case basis. As the impacts to the sensitive area increase, the
mitigation measures to offset these impacts will increase in number and complexity.
The components of a complete mitigation plan are as follows:
a. Baseline information of quantitative data collection or a review and
synthesis of existing data for both the project impact zone and the proposed mitigation
site.
b. Environmental goals and objectives that describe the purposes of the
mitigation measures. This should include a description of site-selection criteria,
identification of target evaluation species and resource functions.
c. Performance standards of the specific criteria for fulfilling environmental
goals, and for beginning remedial action or contingency measures. They may include
water quality standards, species richness and diversity targets, habitat diversity indices,
or other ecological, geological or hydrological criteria. The following shall be
considered the minimum performance standards for approved stream alterations:
(1) Maintenance or improvement of stream channel habitat and
dimensions such that the fisheries habitat functions of the compensatory stream reach
meet or exceed that of the original stream;
(2) Bank and buffer configuration should be restored to an equal or
enhanced state of the original stream;
(3) The channel, bank and buffer areas shall be replanted with native
vegetation which restores or improves the original in species, sizes and densities;
(4) The stream channel bed and the biofiltration systems shall be
equivalent to or better than in the original stream;
(5) The original fish and wildlife habitat shall be maintained or
enhanced; and
(6) Relocation of a watercourse shall not result in the new sensitive area
or buffer extending beyond the development site and onto adjacent property without
the agreement of the affected property owners.
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d. Detailed construction plan of the written specifications and descriptions of
mitigation techniques. This plan should include the proposed construction sequence
and construction management, and be accompanied by detailed site diagrams and
blueprints that are an integral requirement of any development proposal.
e. Monitoring and! or evaluation program that outlines the approach for
assessing a completed project. An outline shall be included that spells out how the
monitoring data will be evaluated by agencies that are tracking the mitigation project's
process.
f. Contingency plan identifying potential courses of action, and any
corrective measures to be taken when monitoring or evaluation indicates project
performance standards have not been met.
g. Performance security or other assurance devices as described in TMC
18.45.210.
F. Mitigation Timing - Department of Community Development-approved plans
must have the mitigation construction completed before the existing watercourse can be
modified. The Director may allow activities that permanently disturb a watercourse
prior to implementation of the mitigation plan under the following circumstances:
1. To allow planting or re-vegetation to occur during optimal weather
conditions; or
2. To avoid disturbance during critical wildlife periods; or
3. To account for unique site constraints that dictate construction timing or
phasing.
G. Permitted Uses Subject to Exception App~oval - Other uses may be permitted
upon receiving a reasonable use exception pursuant to TMC 18.45.180. A use permitted
through a reasonable use ex",<:,!,~:on shall conform to the procedures of TMC Chapter
18.45 and be consistent with the underlying zoning.
...
18.45.120 Areas of Potential Geologic Instability Designation, Rating and Buffers
A. Designation. Areas of potential geologic instability are classified as follows:
1. Class 1 areas, where landslide potential is low, and which slope is less than
15%;
2. Oass 2 areas, where landslide potential is moderate, which slope is between
15% and 40%, and which are underlain by relatively permeable soils;
3. Class 3 areas, where landslide potential is high, which include areas sloping
between 15% and 40%, and which are underlain by relatively impermeable soils or by
bedrock, and which also include all areas sloping more stgeply than 40%;
4. Oass 4 areas, where landslide potential is very high, which include sloping
areas with mappable zones of groundwater seepage, and which also include existing
mappable landslide deposits regardless of slope;
B. Buffers -- Buffers for areas of potential geologic instability are intended to:
1. Minimize long-term impacts of development on properties containing
sensitive areas;
2. Protect sensitive areas from adverse impacts during development;
3. Prevent loading of potentially unstable slope formations;
4. Protect slope stability;
5. Provide erosion control and attenuation of precipitation surface water and
stormwater runoff; and
6. Reduce loss of or damage to property.
An undisturbed sensitive area or buffer may substitute for the yard setback and
landscape requirements of TMC 18.50 and 18.52.
C. Each develv!,uLent proposal containing or threatened by an area of potential
geologic instability Oass 2 or higher shall be subject to a geotechnical report pursuant
to the requirements of TMC 18.45.040 B and 18.45.060. The geotechnical report shall
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analyze and make recommendations on the need for and width of any setbacks or
buffers necessary to achieve the goals and requirements of TMC Chapter 18.45.
Development proposals shall then include the buffer distances as defined within the
geotechnical report.
D. Buffers may be increased by the Director when an area is determined to be
particularly sensitive to the disturbance created by a development. Such a decision will
be based on a City review of the report as prepared by a qualified geotechnical engineer
and by a site visit.
18.45.130 Areas Of Potential Geologic Instability Uses, Exemptions, Alterations and
Mitigation.
A. General - The uses permitted in the underlying zoning district may be
undertaken on sites that contain areas of potential geologic instability subject to the
standards of this section and the recommendations of a geotechnical study.
B. Exemptions - The following areas are exempt from regulation as geologically
hazardous area\s:
1. Temporary stockpiles of topsoil, gravel, beauty bark or other similar
landscaping or construction materials;
2. Slopes related to materials used as an engineered pre-load for a building pad;
3. Any temporary slope that has been created through legal grading activities
under an approved permit may be regraded without application of TMC Chapter 18.45
under an approved permit;
4. Roadway embankments within right-of,.way or road easements; and
5. Slopes retained by approved engineered structures.
C. Alterations
1. Prior to permitting alteration of an area of potential geologic instability, the
applicant must demonstrate one of the following:
a. There is no evidence of past instability or earth movement in the vicinity
of the proposed development, and where appropriate, quantitative analysis of slope
stability indicates no significant risk to the proposed development or surrounding
properties; or
b. The area of potential geologic instability can be modified or the project can
be designed so that any potential impact to the project and surrounding properties is
eliminated, slope stability is not decreased, and the increase in surface water discharge
or sedimentation shall not decrease slope stability.
2. Where any portion of an area of potential geologic instability is cleared for
development, a landscaping plan for the site shall include tree replanting with an equal
mix of evergreen and deciduous trees, preferably native, and approved by the Director.
Replacement vegetation shall be sufficient to provide erosion and stabilization
protection.
D. Disclosures, Declarations and Covenants
1. It shall be the responsibility of the applicant to submit, consistent with the
findings of the geotechnical report, structural plans which were prepared and stamped
by a structural engineer. The plans and specifications shall be accompanied by a letter
from the geotechnical engineer who prepared the geotechnical report stating that in
his/her judgment, the plans and specifications conform to the recommendations in the
geotechnical report; the risk of damage to the proposed development site from soil
instability will be minimal subject to the conditions set forth in the report; and the
proposed development will not increase the potential for soil movement.
2. Further recommendations signed and sealed by the geotechnical engineer
shall be provided should there be additions or exceptions to the original
recommendations based on the plans, site conditions or other supporting data. If the
geotechnical engineer who reviews the plans and specifications is not the same engineer
who prepared the geotechnical report, the new engineer shall, in a letter to the City
SAO Adoption 18.45 12/10/04
Page 19 of26
accompanying the plans and specifications, express his or her agreement or
disagreement with the recommendations in the geotechnical report and state that the
plans and specifications conform to his or her recommendations.
3. The architect or structural engineer shall submit to the City, with the plans
and specifications, a lc~~c~ or notation on the design drawings at the time of permit
application stating that he or she has reviewed the geotechnical report, understands its
recommendations, has explained or has had explained to the owner the risks of loss due
to slides on the site, and has incorporated into the design the recommendations of the
report and established measures to reduce the potential risk of injury or damage that
might be caused by any earth movement predicted in the report.
4. The owner shall execute a Sensitive Areas Covenant and Hold Harmless
Agreement running with the land, on a form provided by the City. The City will file
the completed covenant with the King County Department of Records and Elections at
the expense of the applicant or owner. A copy of the recorded covenant will be
forwarded to the owner.
E. Assurani;:e Devices. Whenever the City d\:;~cu...ines that the public interest would
not be served by the issuance of a permit in an area of potential geologic instability
without assurance of a means of providing for restoration of areas disturbed by, and
repair of property damage caused by, slides arising out of or occurring during
construction, the Director may require assurance devices pursuant to TMC 18.45.210.
F. Construction Monitoring.
1. Where recommended by the geotechnical report, the applicant shall retain a
geotechnical engineer to monitor the site during construction. The applicant shall
preferably retain the geotechnical engineer who prepared the final geotechnical recom-
mendations and reviewed the plans and specifications. If a different geotechnical
engineer is retained by the owner, the new geotechnical engineer shall submit a letter to
the City stating whether or not he! she agrees with the opinions and recommendations
of the original geotechnical engineer. Further recommendations, signed and sealed by
the geotechnical engineer, and supporting data shall be provided should there be
exceptions to the original recommendations.
2. The geotechnical engineer shall monitor, during construction, compliance
with the recommendations in the geotechnical report, particularly site excavation,
shoring, soil support for foundations including piles, subdrainage installations, soil
compaction and any other geotechnical aspects of the construction. Unless otherwise
approved by the City, the specific recommendations contained in the soils report must
be implemented by the owner. The geotechnical engineer shall make written, dated
monitoring reports on the progress of the construction to the City at such timely
intervals as shall be specified. Omissions or deviations .from the approved plans and
specifications shall be immediately reported to the City. The final construction
monitoring report shall contain a statement from the geotechnical engineer that, based
upon his or her professional opinion, site observations and testing during the
monitoring of the construction, the completed development substantially complies with
the recommendations in the geotechnical report and with all geotechnical-related
permit requirements. Occupancy of the project will not be approved until the report
has been reviewed and accepted by the Director.
G. Conditioning and Denial of Use or Developments.
1. Substantial weight shall be given to ensuring continued slope stability and
the resulting public health, safety and welfare in determining whether a development
should be allowed.
2. The City may impose conditions that address site-work problems which
could include, but are not limited to, limiting all excavation and drainage installation to
the dryer season, or sequencing activities such as installing erosion control and
drainage systems well in advance of construction. A permit will be denied if it is
determined by the Director that the development will increase the potential of soil
movement that results in an unacceptable risk of damage to the proposed development,
its site or adjacent properties.
SAO Adoption 18.45 12/10/04
Page 20 of 26
18.45.140 Abandoned Mine Areas
A. Development of a site containing an abandoned mine area may be permitted
when a geotechnical report shows that significant risks associated with the abandoned
mine workings can be eliminated or mitigated so that the site is safe. Approval shall be
obtained from the Director before any building or land-altering permit processes begin.
B. Any building setback or land alteration shall be based on the geotechnical report.
C. The City may impose conditions that address site-work problems which could
include, but are not limited to, limiting all excavation and drainage installation to the
dryer season, or sequencing activities such as installing drainage systems or erosion
controls well in advance of construction. A permit will be denied if it is determined
that the development will increase the potential of soil movement or result in an
unacceptable risk of damage to the proposed development or adjacent properties.
D. The owner shall execute a Sensitive Areas Covenant and Hold Harmless
Agreement running with the land, on a form provided by the City. The City will file the
completed covenant with the King County Division of Records and Elections at the
expense of the applicant or owner. A copy of the recorded covenant will be forwarded
to the owner.
"
18.45.150 Fish and Wildlife Habitat Conservation Areas - Designation, Mapping,
Uses and Standards
A. Designation. Fish and wildlife habitat conservation areas include the habitats
listed below:
1. Areas with which endangered, threatened, and sensitive species have a
primary association;
2. Habitats and species of local importance, including but not limited to bald
eagle habitat, heron rookeries;
3. Commercial and recreational shellfish areas;
4. Kelp and eelgrass beds;
5. Mudflats and marshes;
6. Naturally occurring ponds under 20 acres and their submerged aquatic beds
that provide fish or wildlife habitat;
7. Waters of the State;
8. State natural area preserves and natural resource conservation areas; and
9. Areas critical for habitat connectivity.
B. Mapping.
1. The approximate location and extent of known fish and wildlife habitat
conservation areas are identified by the City's Sensitive Areas Maps, inventories, open
space zones, and Natural Environment Background Report. The City designates 1, 2, 5,
6, 7, and 9 above as known fish and wildlife habitats within its current limits.
2. Fish and wildlife habitat conservation areas correlate closely with the areas
identified as regulated watercourses and wetlands and their buffers in Tukwila. The
Green/Duwamish River is recognized as the most significant fish and wildlife habitat
corridor. In addition to the Sensitive Areas Maps, the following maps are to be used as
a guide for the City, but do not provide a final habitat area designation:
a. Washington State Department of Fish and Wildlife Priority Habitat
Species Maps;
b. Anadromous and resident salmonid distribution maps contained in the
Habitat Limiting Factors reports published by the Washington Conservation
Commission; and
c. Washington State Digital Coastal and Coastal Zone Management
Program.
SAO Adoption 18.45 12110/04
Page 21 of26
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C. Uses and Standards. Fish and wildlife habitat conservation areas will be
regulated through TMC 18.44, Shoreline Overlay District and the regulations in TMC
Chapter 18.45 related to wetlands and watercourses.
..
18.45.160 Sensitive Area Master Plan Overlay
A. The purpose of this Section is to provide an alternative to preservation of existing
individual wetlands, watercourses and their buffers in situations where an area-wide
plan for alteration and mitigation will result in improvements to water quality, fish and
wildlife habitat and hydrology beyond those that would occur through the strict
application of the provisions of TMC Chapter 18.45.
B. The City Council may designate certain areas as Sensitive Area Master Plan
Overlay districts for the purpose of allowing and encouraging a comprehensive
approach to sensitive area protection, restoration, enhancement and creation in
appropriate circumstances utilizing best available science. Designation of Sensitive
Area Master Plan Overlay districts shall occur through the Type 5 decision process
established by TMC 18.104. .
C. Criteria for designating a Sensitive Area Master Plan Overlay district shall be as
follows:
1. The overlay area shall be at least 10 acres.
2. The City Council shall find that preparation and implementation of a
Sensitive Area Master Plan is likely to result in net improvements in sensitive area
functions and values when compared to development under the general provisions of
TMC Chapter 18.45.
D. Within a Sensitive Area Master Plan Overlay district, only those uses permitted
under TMC 18.45.070, 18.45.090 and 18.45.110 shall be allowed within a Type 1 wetland,
a Type 1 watercourse, or their buffers.
E. Within a Sensitive Area Master Plan Overlay district, the uses permitted under
TMC 18.45.070, 18.45.090 and 18.45.110 and other uses as identified by an approved
Sensitive Area Master Plan shall be permitted within Type 2 and Type 3 wetlands and
their buffers; and within Type 2, 3 and 4 watercourses and their buffers, provided that
such uses are allowed by the underlying zoning designation.
F. A Sensitive Area Master Plan shall be prepared under the direction of the
Director of Community Develuy...ent. Consistent with subsection A, the Director may
approve development activity within a Sensitive Area Overlay District for the purpose
of allowing and encouraging a comprehensive approach to sensitive areas protection,
creation, and enhancement that results in environmental benefits that may not be
otherwise achieved through the application of the requirements of TMC Chapter 18.45.
G. The Director shall consider the following factors when determining whether a
proposed Sensitive Areas Overlay and Master Plan results in an overall net benefit to
the environment and is consistent with best available science:
1. Whether the Master Plan is consistent with the goals and policies of the
Natural Environment Element of the Tukwila Comprehensive Plan.
2. Whether the Master Plan is consistent with the purposes of TMC Chapter
18.45 as stated in TMC 18.45.010.
3. Whether the Master Plan includes a Mitigation Plan that incorporates stream
or wetland restoration, enhancement or creation meeting or exceeding the requirements
of TMC 18.45.090 D. and! or TMC 18.45.110 D., as appropriate.
4. Whether proposed alterations or modifications to sensitive areas and their
buffers and! or alternative mitigation results in an overall net benefit to the natural
environment and improves sensitive area functions and values.
5. Whether the Mitigation Plan gives special consideration to conservation and
protection measures necessary to preserve or enhance anadromous fisheries.
6. Mitigation shall occur on-site unless otherwise approved by the Director. The
Director may approve off-site mitigation only upon determining that greater protection,
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SAO Adoption 18.45 12/10/04
Page 22 of 26
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restoration or enhancement of sensitive areas could be achieved at an alternative
location within the same watershed.
7. Where feasible, mitigation shall occur prior to grading, filling or relocation of
wetlands or watercourses.
8. At the discretion of the Director, a proposed Master Plan may undergo peer
review, at the expense of the applicant. Peer review, if utilized, shall serve as one
source of input to be utilized by the Director in making a final decision on the proposed
action.
H. A Sensitive Area Master Plan shall be subject to approval by the Director of
Community Development. Such approval shall not be granted until the Master Plan
has been evaluated through preparation of an Environmental Impact Statement (EIS)
under the requirements of TMC 21.04. The EIS shall compare the environmental
impacts of development under the proposed Master Plan relative to the impacts of
development under the standard requirements of TMC Chapter 18.45. The Director
shall approve the Sensitive Area Master Plan only if the evaluation dearly demonstrates
overall enviropmental benefits, giving special consideration to conservation or
protection measures necessary to preserve or enhance anadromous fisheries.
18.45.170 Sensitive Areas Tracts and Easements
A. In development proposals for planned residential or mixed use developments,
short subdivisions or subdivisions, and boundary line adjustments and binding site
plans, applicants shall create sensitive areas tracts or easements, in lieu of an open space
tract, per the standards of the Planned Residential Development District chapter of this
title.
B. Applicants proposing development involving uses other than those listed in
TMC 18.45.170A, on parcels containing sensitive areas or their buffers, may elect to
establish a sensitive areas tract or easement which shall be:
1. If under one ownership, owned and maintained by the ownership;
2. If held in common ownership by multiple owners, maintained collectively; or
3. Dedicated for public use if acceptable to the City or other appropriate public
agency.
C. A notice shall be placed on the title or plat that sensitive area tracts or easements
shall remain undeveloped in perpetuity.
18.45.180 Exceptions
A. Wetlands 1,000 sq. ft. and less that do not me~.t any of the criteria of TMC
18.45.080.B are exempt from the requirements of TMC Chapter 18.45.
B. Reasonable Use Exceptions.
1. If application of TMC Chapter 18.45 would deny all reasonable use of the
property containing wetlands, watercourses or their buffers, the property owner or the
proponent of a development proposal may apply for a reasonable use exception.
2. Applications' for a reasonable use exception shall be a Type 4 decision and
shall be processed pursuant to TMC 18.104.
3. If the applicant demonstrates to the satisfaction of the Planning Commission
that application of the provisions of TMC Chapter 18.45 would deny all reasonable use
of the property, development may be allowed which is consistent with the general
purposes of TMC Chapter 18.45 and the public interest.
4. The Commission, in granting approval of the reasonable use exception, must
determine that:
a. There is no feasible on-site alternative to the proposed activities, including
reduction in size or density, modifications of setbacks, buffers or other land use
restrictions or requirements, phasing of project implementation, change in timing of
SAO Adoption 18.45 12/10/04
Page 23 of 26
'.
activities, revision of road and lot layout, and! or related site planning that would allow
a reasonable economic use with fewer adverse impacts to the sensitive area.
b. As a result of the proposed development there will be no unreasonable
threat to the public health, safety or welfare on or off the development proposal site.
c. Alterations permitted shall be the minimum necessary to allow for
reasonable use of the property.
d. The proposed development is compatible in design, scale and use with
other development with similar site constraints in the immediate vicinity of the subject
property if such similar sites exist.
e. Disturbance of sensitive areas has been minimized by locating any
necessary alterations in the buffers to the greatest extent possible.
f. The inability to derive reasonable use of the property is not the result of:
(1) a segregation or division of a larger parcel on which a reasonable use
was permittable after the effective date of the sensitive areas ordinance number 1599,
June 10, 1991; \
(2) actions by the owner of the property (or the owner's agents,
contractors or others under the owner's control) that occurred after the effective date of
the sensitive areas ordinance provisions that prevents or interferes with the reasonable
use of the property; or
(3) a violation of the sensitive areas ordinance;
g. The Commission, when approving a reasonable use exception, may
impose conditions, including but not limited to a requirement for submission and
implementation of an approved mitigation plan designed to assure that the
development:
(1) complies with the standards and policies of the sensitive areas
ordinance to the extent feasible; and
(2) does not create a risk of damage to other property or to the public
health, safety and welfare.
h. Approval of a reasonable use exception shall not eliminate the need for
any other permit or approval otherwise required for a project, including but not limited
to design review.
B. Emergencies - Alterations in response to an emergency that poses an immediate
threat to public health, safety or welfare, or that poses an immediate risk of damage to
private property. Any alteration undertaken as an emergency shall be reported within
one business day to the Department of Community DevelvYULent. The Director shall
confirm that an emergency exists and determine what, if ~y, mitigation and conditions
shall be required to protect the health, safety, welfare and environment and to repair
any damage to the sensitive area and its required buffers. Emergency work must be
approved by the City. If the Director determines that the action taken, or any part
thereof, was beyond the scope of an allowed emergency action, then the enforcement
provisions of TMC 8.45 shall apply.
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18.45.190 Appeals
A. Any appeal of a final decision of DCD made pursuant to TMC Chapter 18.45
shall be an appeal of the underlying permit or approval and shall be taken to the
Planning Commission. Any such appeal shall be processed pursuant to TMC 18.108.020
and TMC 18.116.
B. In considering appeals of decisions or conditions, the following shall be
considered:
1. The intent and purposes of the sensitive areas ordinance;
2. Technical information and reports considered by the DCD; and
3. Findings of the Director, which shall be given substantial weight.
SAO Adoption 18.45 12/10/04
Page 24 of 26
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18.45.200 Recording Required
The property owner receiving approval of a use or development pursuant to TMC
Chapter 18.45 shall record the City-approved site plan clearly delineating the wetland,
watercourse, areas of potential geologic instability or abandoned mine and their buffers
designated by TMC 18.45.080, 18.45.090, 18.45.100, 18.45.120 18.45.140 and 18.45.150
with the King County Division of Records and Elections. The face of the site plan must
include a statement that the provisions of TMC Chapter 18.45, as of the effective date of
the ordinance from which TMC Chapter 18.45 derives or thereafter amended, control
use and development of the subject property, and provide for any responsibility of the
property owner for the maintenance or correction of any latent defects or deficiencies.
18.45.210 Assurance Device
A. In appropriate circumstances, the Director may require a letter of credit or other
security device acceptable to the city, to guarantee performance and maintenance
requirements of TMC Chapter 18.45. All assurances shall be on a form approved by the
City Attorney. \
B. When alteration of a sensitive area is approved, the Director may require an
assurance device, on a form approved by the City Attorney, to cover the monitoring
costs and correction of possible deficiencies. Monitoring of buffer alterations shall be
. required for three to five years. All other alterations shall be monitored for five years.
C. The assurance device shall be released by the Director upon receipt of written
confirmation submitted to the Department from the applicant's qualified professional
that the mitigation or restoration has met its performance standards and is successfully
established. Should the mitigation or restoration meet performance standards and be
successfully established in the third or fourth year of monitoring, the City may release
the assurance device early. The assurance device may be held for a longer period, if at
the end of the monitoring period, the performance standards have not been met or the
mitigation has not been successfully established.
D. Release of the security does not absolve the property owner of responsibility for
maintenance or correcting latent defects or deficiencies or other duties under law.
18.45.220 Assessment Relief
A. Fair Market Value - The King County Assessor considers sensitive area
regulations in determining the fair market value of land under RCW 84.34.
B. Current Use Assessment. Established sensitive area tracts or easements, as
defined in the Definitions chapter of this title and provided for in TMC 18.45.170, may
be classified as open space and owners thereof may qualify for current use taxation
under RCW 18.34; provided, such landowners have not received density credits, or set-
back or lot size adjustments as provided in the Planned Residential Development
District chapter of this title.
C. Special Assessments. Landowners who qualify under TMC 18.45.220B shall also
be exempted from special assessments on the sensitive area tract or easement to defray
the cost of municipal improvements such as sanitary sewers, storm sewers and water
mains.
Section 2. Repealer. Ordinance Nos. 1758 (part), 1770 ~25 and ~26, 1796 ~3 (part),
and 1834 ~5; are hereby repealed.
Section 3. Severability. If any section, subsection, paragraph, sentence, clause or
phrase of this ordinance or its application to any person or situation should be held to
be invalid or unconstitutional for any reason by a court of competent jurisdiction, such
invalidity or unconstitutionality shall not affect the validity or constitutionality of the
remaining portions of this ordinance or its application to any other person or situation.
SAOAdoption 18.45 12/10/04
Page 25 of 26
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Section 4. Effective Date. This ordinance or a summary thereof shall be published
in the official newspaper of the City, and shall take effect and be in full force five days
after passage and publication as provided by law.
PASSED BY THE CITY COUNCIL OF THE CITY OF TUKWILA, WASHINGTON,
at a Special Meeting thereof this day of ,2004.
All~ll AUTHENTICATED:
Steven M. Mullet, Mayor
Jane E. Cantu, CMC, City Clerk
APPROVED AS TO FORM BY:
Filed with the City Clerk:
Passed by the City Council:
Published:
Effective Date:
Ordinance Number:
Office of the City Attorney
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SAO Adoption 18.45 12/10/04
Page 26 of 26
Al""lACHMENT A
JUNE 2003
BEST AVAILABLE SCIENCE ISSUE PAPER:
WETLANDS
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Prepared for:
City of Tukwila
Department of Community Development
6300 South center Boulevard
Tukwila, WA 98188
Prepared by:
Adolfson Associates, Inc.
5309 Shilshole Avenue NW, Suite 200
Seattle, Washington 98107
TABLE OF CONTENTS
1.0 INTRODUCTION ............................................................................................................. 1
1.1 Project Authorization.. ....... ..................................... ................ ............... ................. 1
1.2 State Growth Management Act Requirements......................................... 1
1.3 Overview of City Environment .................. ............................................................. 1
2.0 STATE OF THE SCIENCE FOR WETLANDS AND WETLAND BDf41f.l!;RS ......... 2
2.1 Importance of Wetlands and Buffers ......................................................................2
2. 2 Wetland Definition...... ........................................................................... ................. 2
2.3 Wetland Functions and Values................................................................................3
2.3.1 Flood Water Attenuation and Flood Peak Desynchronization..................... 4
2.3.2 Stream Base Flow Maintenance and Groundwater Support .......................4
2.3.3 Shoreline Protection .......... ............................ ....................................... ....... 5
2.3 .4 Water Quality lInprovement................ ........................................................ 5
2.3.5 Biological Support and Wildlife Habitat..................................................... 6
2.3.6 Recreation, Education, and Open Space ..................................................... 6
2.4 Wetland Functional Assessment Methods .............................................................. 7
2. 5 Wetland Rating System .................... ..................... ........... .................. ....... ...... ........ 7
2.6 Functions and Values of Wetland Buffers .............................................................. 8
2.7 Wetland Mitigation & Enhancement Strategies...................................................... 9
~ ... 2.7.1 Wetland and Buffer Mitigation Success...................................................... 9
~~~ 2.7.2 Mitigation Ratios....................................................................................... 11
3.0 FUNCTIONS AND VALVES OF WETLANDS AND WETLAND BUFFERS IN
TUKWILA ...... ............ ....... .............. ... ........ .............................. ............. ........ .................. 12
4.0 D AT A 'G APS ..................................................................................................................... 13
5.0 RECOMMENDATIONS.........................~.......ERROR! BOOKMARK NOT DEFINED.
5.1 Regulatory Framework of Wetlands Regulations. Error! Bookmark not defined.
6.0 REFEREN CES ................. ............................... .... .................................... ........................ 14
Adolfson Associates. Inc.
June 2003
Pagei
1.0 INTRODUCTION
1.1 Project Authorization
At the request of the City of Tukwila, Adolfson Associates, Inc. (Adolf son) has prepared this paper
to provide an overview of the "best available science" pertaining to management of wetlands and
its application to urban environments such as those found in the City of Tukwila (the City). The
preparation of this report was made possible by funds made available through the Washington State
Department of Community, Trade and Economic Development. This paper will provide guidance
to the City in development and revisioq. of the City's critical areas ordinance- Tukwila Municipal
Code (TMC) Chapter 18.45 Sensitive Areas Overlay.
This paper discusses the results of the best available science review for wetlands and evaluates the
applicability of the science to wetland regulations in the City. Adolfson has based our review of
the city environment on two days of field investigation, existing literature, and preliminary
information from the City regarding its update of the wetland and stream inventory.
1.2 State Growth Management Act Requirements
~.. ": -
}
In 1990, a new rule under Washington State's Growth Management Act (GMA)
(RCW 36.70A.060) required counties and cities to adopt development regulations that protect the
functions and values of critical areas, including wetlands. In 1995, the Washington State
legislature added a new section to the GMA. to ensure that counties and cities consider reliable
scientific information when adopting policies and development regulations to designate and protect
critical areas. As a result of this legislation, in 2000 the Growth Management Division of
Washington's Office of Community Development (OCD) adopted as a rule procedural criteria to
. guide cities and counties in identifying and including the best available science in their critical area
policies and regulations. In accordance with RCW 36.70A.172(1), communities "shall include the
best available science in developing policies and development regulations to protect the functions
and values of critical areas, including wetlands."
n addition, the Washington Department of Ecology is currently researching and preparing a best
available science paper for wetlands in the State of Washington. The paper is anticipated to be
completed in the Summer of 2003. Information on wetlands provided here does not include the
results of Ecology's more comprehensive review, which, is n9t currently publicly available.
1.3 Ove.rview of City Environment
The City of Tukwila is an urban city within the upper Duwamish/lower Green River valley.
Tukwila is at the convergence of the Lower Green River and the Upper Duwamish River forming
the greater GreenlDuwamish River Basin. Tukwila sits in the river valley bottom, with numerous
municipalities upstream and on the hilltops surrounding the city. There are three main sub-basins
within the Tukwila city limits: Riverton Creek, Southgate Creek, and Gilliam Creek drainage
Adolfson Associates. ./nc.
June 2003
Page 1
areas.. These three drainage sub-basins contain the majority of wetlands located within the City
limits. Land uses in Tukwila are characterized by a mosaic of commercial, industrial, and
residential developments. Many of the wetlands have been degraded as a result of urbanization. Of
the existing wetlands, there is wide variety of wetland types ranging from small, emergent systems
preserved between roadways, to larger forested diverse systems.
The City of Tukwila is currently preparing an update to the existing wetland and stream inventory.
This inventory will identify locations of aquatic areas and detennine their relative function and
value for regulatory purposes. Adolfson's analysis of the environmental setting in Tukwila was
conducted during two site visits undertaken with planning staff. Additional infonnation regarding
wetlands in Tukwila was provided by City staff. City staff are in the process of updating the
wetland inventory, and preliminary inventory and GIS infonnation was analyzed in the preparation
of this study. This review of Best Available Science will be updated with detailed inventory
infuuuation and GIS products at a later date. A review of the best available science in relation to
shorelines in the City of Tukwila was prepared by others but available for review (Pentec, 2002).
2.0 STATE OF THE SCIENCE FOR WETLANDS AND WETLAND
BUFFERS
This section summarizes the state of the science, or "best available science" for wetlands and
wetland buffers. Higher preference has been given to science and research conducted in the Pacific
_ Northwest versus research from other areas of the United States. This infonnation is a summary of
€;? existing literature and is not intended to be an ex~lusive list of all best available science currently
publ.ished on wetlands, but is intended to provide a brief overview of scientifically valid
infonnation useful for local planning. Adolfson has referenced findings from selected scientific
literature where applicable, including relevant studies from the Office of Community
Development's "Citations of Recommended Sources for Designating and Protecting Critical
Areas. "
2.1 Importance of Wetlands and Buffers
Wetlands provide important functions and values for both the human and biological environment-
these functions include flood control, water quality improvement, and nutrient production. This
paper builds on the wetland i entory (prepared by the City) by discussing in greater detail relevant
research pertaining to wetland functions and values, as well as the challenges of managing wetland
areas in urban settings and developed areas such as those found in Tukwila.
2.2 Wetland Definition
Wetlands are fonnally defined by the Corps of Engineers (Corps) (Federal Register, 1982), the
Environmental Protection Agency (EPA) (Federal Register, 1986), the Washington Shoreline
Management Act (SMA) (197l) and the Washington State Growth Management Act (GMA)
(1992) as "... those areas that are inundated or saturated by surface or groundwater at a frequency
and duration sufficient to support, and that under nonnal circumstances do support, a prevalence of
vegetation typically adapted for life in saturated soil conditions. Wetlands generally include
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swamps, marshes, bogs, and similar areas" (Federal Register, 1982, 1986). In addition, the SMA
and the GMA definitions add: "Wetlands do not include those artificial wetlands intentionally
created from non-wetland site, including, but not limited to, irrigation and drainage ditches, grass-
lined swales, canals, detention facilities, wastewater treatment facilities, farm ponds, and landscape
amp.nities, or those wetlands created after July 1, 1990 that were unintentionally created as a result
of the construction of a road, street, or highway. Wetlands may include those artificially created
wetlands intentionally created from non-wetland areas to mitigate the conversion of wetlands".
This same definition of wetland is used in the Washington State Wetlands Identification and
Delineation Manual (Ecology, 1997).
2.3 Wetland Functions and Values
Wetlands are integral parts of the natural landscape. Their "functions and values" to both the
environment and to the general public depend on several elements including their size and location
within a basin, as well as their diversity and quality. While each wetland provides various
beneficial functions, not all wetlands perform all functions, nor do they perform all functions
equally well (Novitski et aI., 1995).
.:'''':'''.
\~:~%!~
Several studies have found that wetland functions and values are compromised by urbanization
(Azous and Horner, 2001; Mitsch and Gosselink, 2000; Castelle et al., 1992a; May et al., 1997;
Booth, 2000; City of Portland, 2001). In urban settings individual functions of wetlands may not
be optimally functioning. However, the combined effect of functional processes of wetlands within
basins provides benefits to both natural and human environments. For example, wetlands can
provide significant stormwater control, even if they are degraded and comprise only a small
percentage of area within a basin. Also, wetlands are important elements of stream systems and
fish habitat. Within the urban environment, even degraded wetlands can provide rearing and refuge
habitat for fish and ot r wildlife, along with other benefits to keeping streams healthy.
The geographic location, topography, geology, and level of existing urbanization in the City of
Tukwila limit to what extent its wetlands can provide the functions described below. However,
even in urban settings where individual functions of wetlands are not optimal, the combined effect
of the functional conditions within the wetland systems may provide many of the functional
benefits to be expressed. Protection and restoration of wetlands will maintain and improve their
functional benefits to both natural and human environments.
The functions provided by wetlands and their assigned human-based values have been identified
and evaluated through several studies (Cowardin et aI., 1979; Adamus et aI., 1987; Mitsch and
Gosselink, 2000; Hruby, 1995; Reppert et aI., 1979; Cooke, 1995). These functions include:
. Rood water attenuation and flood peak desynchronization;
. Stream base flow maintenance and groundwater support;
. Shoreline protection;
. Water quality improvement;
. Biological support and wildlife habitat; and
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. Recreation, education, and open space.
2.3.1 Flood Water Attenuation and Flood Peak Desynchronization
Flood water attenuation and flood peak desynchronization can be controlled by wetlands ability to
control stormwater flow and slowly releasing it to adjacent water bodies and or groundwater
(Novitzki, 1979 and Verry and Boelter, 1979 in Mitsch and Gosselink, 2000). A wetlands
effectiveness in controlling runoff is based on factors such as the storage capacity and outlet
. discharge capacity of the wetland relative to the magnitude of stonnwater inflow (Marble, 1992;
Reinelt and Homer, 1991).
~~~
The loss of wetland systems in urban at\eas affects their function in attenuating stormwater runoff,
resulting in increased flood frequency and higher peak flood flows in drainage basins (Azous and
Homer, 2001; Mitsch and Gosselink, 2000; Booth, 2000). Human infrastructure and aquatic
habitats can be damaged by large and frequent flood events (City of Portland, 2001; Booth, 2000;
May et al., 1997; Mitsch and Gosselink, 2000; Cooke, 1995). Reduced flood storage capacity can
be partially replaced through wetland restoration, stonnwater control facilities, or potentially the
use of isolated, degraded, and low-value wetlands as stonnwater facilities. However, even in
basins where flood storage has been maintained, discharge volumes from detention facilities in
areas with moderate to high levels of impervious surface are still substantially higher than in less-
urbanized or natural environments because of reduced rainfall infiltration into pervious soils
(Booth, 2000). As a result, while wetlands can substantially contribute to flood control in basins,
reduction of total impervious surface is also necessary to reduce flood flows and peaks (Booth,
2000). Wetlands can also be. negatively affected by direct discharge of stonnwater and alteration of
the hydrologic cycle due to increases in impervious surface. Increased discharge to wetlands can
alter the hydrodynamics and hydroperiod (the pattern of fluctuating water levels) in a wetland,
resulting in substantial modifications to plant and animal communities adapted to pre-existing
hydrologic conditions (Azous and Homer, 2()Ol). Use of only degraded, low-quality wetlands that
are not associated with stream systems for stonnwater control can limit these impacts (Homer et
aI., 1996).
Wetlands providing erosion control functions are typically found in shallow, floodplain systems
where velocities are slow and vegetation is dense and woody (Carter, 1986; Greeson et al., 1979;
Sather and Smith; 1984; Brinson, 1993). They are found less frequently in groundwater slope
driven systems where water flow rates and levels are high enough to suspend and transport
sediments such as in urban environments. As little as 10 percent impervious surface in a watershed
can result in stream channel instability (Booth, 1991 and Booth and Reinelt, 1993 in Schueler,
1994). Increasingly higher storm flows can result in sediment loading of the stream and destruction
of habitat for fish and other aquatic organisms (Richter, 2001, Ludwa, 2001, Richter and Azous,
2001, Azous and Homer, 2001).
2.3.2 Stream Base Flow Maintenance and Groundwater Support
Stream baseflow and groundwater recharge are functions of wetlands performed by retaining large
quantities of water and slowly releasing it to streams or groundwater (Mitsch and Gosselink, 2000;
Erwin, 1990). In general, relevant studies on wetland deep aquifer recharge are lacking, while the
contribution of wetlands to near-surface (surficial) aquifers has been well documented. Available
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studies indieate that some wetland types provide greater recharge to groundwater systems than
others (Carter et aI., 1979; Novitzki, 1979; Carter and Novitzki, 1988). Maintaining stream flow is
an important function of wetlands to stream flow-sensitive salmonids in the Pacific Northwest.
Wetlands provide baseflow during the region's typically dry season (City of Portland, 2001; Booth,
2000; May et aI., 1997; Mitsch and Gosselink, 2000). Generally, large, permanently-flooded,
depressional wetlands that are the headwaters of or connected to salmonid streams and are located
in the .upper one-third of the watershed have the best ability to provide stream baseflow and
groundwater support (Brinson, 1993; Gwin et al., 1999; Cooke, 2000). Wetlands in the upper part
of the watershed affect flows downstream, whereas those wetlands lower in the watershed affect
less of the overall stream system. Several studies have noted the importance of wetlands, and many'
have found that wetland loss, reduction, and vegetation alteration reduce their capacity to provide
baseflow s.uPport to streams (Booth, 2000; Schueler, 2000; City of Portland, 200 l; Mitsch and
Gosselink, 2000; Brinson, 1993).
~
2.3.3 Shoreline Protection
Wetlands adjacent to waterbodies serve to provide protection for the shoreline of that stream, river.
or lake. Decreased water velocity, vegetative structure, soil root-binding properties, and substrate
type in wetlands influence the effects of water-related erosion in adjacent water bodies (Carter,
1986; Greeson et aI., 1979; Sather and Smith; 1984; Brinson, 1993). The erosion control function
is particularly effective in floodplain wetlands where velocities are slow and vegetation is dense
and woody. Wetlands in basins that have relatively undeveloped shorelines and stream banks that
contain dense woody vegetation along the Ordinary High Water Mark (OHWM) of a lake or stream
and extend more than 200 to 600 feet from the OHWM provide the highest level of shoreline
protection and erosion control (Hruby et aI., 1999; Cooke, 2000).
2.3.4 Water Quality Improvement
Removal of sediment and pollutants from storm water are important water quality functions of
wetlands (Mitsch and Gosselink, 2000; Cooke, 1995). A wetlands' ability to perform water quality
improvements can depend on a wetland's size, location within the basin, vegetation community
structure, and productivity (Washington Department of Ecology, 1996; Marble, 1992).
Wetland vegetation is important for nutrient cycling. The vegetative structure of wetlands slows
the flow of water, causing sediments, nutrients such as nitrogen and phosphorous, petroleum
products, heavy metals, pesticides, and herbiddes to settle out of the water column. Particulates
are removed through settling, and then stored in wetland sediments (Washington Department of
Ecology, 1996; Sather and Smith, 1984). Forested areas store greater amounts of nutrients for
longer periods but generally offer less frictional resistance to water flow, where dense emergent
vegetation creates frictional resistance to water flows, takes up nutrients rapidly, and releases it
seasonally (Washington Department of Ecology, 1996). However, wetlands have limits to the
amount of sediments, nutrients and toxicants they can assimilate, and these will be transported out
of the wetland once a wetland reaches capacity (Mitsch and Gosselink, 2000; Washington
Department of Ecology, 1996).
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Wetlands are affected by physical alteration in urban environments, such as changes in hydroperiod
and loss of wetland area. Alteration of wetlands eliminates or reduces their ability to process
sediment, nutrients, and chemicals. An increase or decrease sedimentation rates can result from
severe water fluctuations, and can limit denitrification and phosphorous retention (Washington
Department of Ecology, 1996). In urbanized watersheds, pollutant concentrations in wetlands are
generally higher than those in undeveloped watersheds (Homer et aI., 1996). Most studies have
focused on a wetland's ability to treat runoff, and few have directly address the impacts of urban
runoff on water quality in wetlands. In addition, sedimentation and pollutants are found to have a
negative effect on invertebrates, amphibians, and fish, particularly salmonids, in riparian wetlands,
urban streams, and lakes (City of Portland, 200l; Booth, 2000; May et aI., 1997; Mitsch and
Gosselink, 2000; Schueler, 1994).
2.3.5 Biological Support and Wildlife Habitat
Wetlands provide opportunities for grazing of living green plants by wildlife, and for organisms
that depend on detritus and/or organic debris for a food source (Erwin, 1990; Zedler et aI., 1990).
Both wetland vegetation and upland forest habitats are highly productive for food production
(Hruby et al., 1999), and can contribute up to 99 percent of the energy in aquatic food webs (Budd
et aI., 1987). These food sources are especially important for fish that feed on both terrestrial and
aquatic insects, which in turn feed on organic matter exported from adjacent riparian areas
(including wetlands) (Cummins, 1974 and Gregory et al., 1991 in City of Portland, 2001; Higgs
et al., 1995). Wetland habitats generally provide greater structural and plant diversity, more edge
habitat where two or more habitat types adjoin, more varied forage, and a predictable water source
~ which increases wildlife species abundance and diversity (Kauffman, et al., 2001; O'Connell et aI.,
2000). Many species of waterfowl, amphibians, insects, and some species of fish and mammals
(such as beaver) depend on wetlands for foraging, breeding, and refuge. It has been found that
wildlife species richness increases when wetlands are surrounded by natural undisturbed upland
habitat (WDFW, 1992; Richter and Azous, 200l; Azous and Horner, 2001; Hruby et aI., 1999).
Wetlands and surrounding uplands provide specialized habitat and wildlife linkages for special
status species such a endangered; threatened, proposed, candidate, sensitive, monitor, and species
of local importance (Mitsch and Gosselink, 2000; Hruby et al., 1999). Alterations in hydroperiod
can cause excess flooding or drying of wetlands, which can be harmful or lethal to amphibians
(Richter et al., 1991).
2.3.6 Recreation, Education, and Open Space
In urbanizing areas, aquatic resources and adjacent uplands provide opportunities for greenway.s
and open space. In Tukwila, wetlands and adjacent uplands provide important resources for
wildlife viewing, passive recreation, and education about natural wetland-upland ecosystems. The
Interurban Trail provides bicycle and pedestrian users a unique opportunity for residents to view a
variety of wetland-upland habitats along the trail. These areas can also be important for
commercial purposes because they attract tourists and local visitors.
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2.4 Wetland Functional Assessment Methods
As"described above, the functions provided by wetlands and their assigned human-based values
have been identified and evaluated through many scientific studies (Cowardin et al., 1979; Adamus
et al., 1987; Mitsch and Gosselink, 2000; Hruby, 1995; Reppert et al., 1979; Cooke, 1995). Several
functional assessment methods have been developed to identify functions performed in a wetland
and evaluate the effectiveness of the wetland in performing that function. Some methods are
quantitative, while others are qualitative. For example, the Reppert method is a qualitative
functional assessment based on vegetative and wetland habitat features, and uses the wetland
classification system adopted by the US Fish and Wildlife Service. Several modified methods have
since been developed from Reppert to create semi-quantitative assessment methods, such as the
Wetland and Buffer Functions Semi-quantitative Assessment Methodology by Sarah Cooke (1996).
Other assessment methods, including those developed by the US Anny Corps of Engineers, are
more quantitative. For example, the Hydrogeomorphic Method (HOM) is based on the concept that
wetland functions are driven primarily by the wetland's geomorphology (Le., position in the
landscape) and hydrologic characteristics (Brinson, 1993; Brinson, 1995). Other semi-quantitative
functional assessment methods include the Wetland Evaluation Technique (WET) developed by
Adamus et al. (1987) and the Indicator Value Assessment (IV A) by Hruby et al. (1995).
In 1996, Washington Department of Ecology (Ecology) began the Washington State Wetland
Function Assessment Method (WFAM) project. The new functional assessment method, which
was published in 1999, is a modified version of the HOM approach and is designed to provide a
~;:\ more scientific approach to assessing wetland functions (Hruby et aI, 1999). This method is based
\~~%~ on research using reference wetlands; to date, Ecology has developed methods based on reference
wetlands for riverine and depressional wetlands in the lowlands of western Washington only.
While ba science, this method requires additional field investigations and extensive training
and cannot be conducted rapidly.
In 2000, Washington Department of Transportation (WDOT) developed another method for rapid
wetland assessments for linear projects (Null et aI., 2000). This method is also cited in the OCD
citations for best available science. The WDOT method is considered a qualitative method.
2.5 Wetland Rating System
Wetlands are typically preserved or protected based upon size and habitat and their relative
functions and values~ Consequently, higher functioning wetlands or larger high quality wetlands
are considered a greater priority for protection than lower quality smaller wetlands with lesser
functions. Local governments strive to prioritize or rank wetlands from higher function and value
to lower function and value in order to determine development standards and protective measures
which are tailored to the relative importance of different wetlands.
In the State of Washington, the Department of Ecology (Ecology) has developed a wetland rating
system for ranking wetlands according relative importance. This rating system is outlined in the
Washington State Wetland Rating System for Western Washington (Publication No. 93-74, Ecology
1993). Wetlands in this system are rated into four distinct categories; from Category I wetlands of
highest value to Category IV wetlands of lowest value. Category I and IV wetlands are defined
specifically in the rating system. However, Category II and III wetlands are determined by the.
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summarized results of a rating form. The rating fonn uses semi-quantitative criteria such as size,
level of disturbance, habitat diversity, connectivity to streams or other habitats, and buffer quality
to Classify wetlands as Category II or III.
2.6 Functions and Values of Wetland Buffers
Wetland buffers are vegetated upland areas immediately adjacent to wetlands. These areas provide
beneficial functions that enhance and protect the many functions and values of wetlands described
above. Buffers areparticularly important for wildlife because many of the wildlife species also
require terrestrial habitats for their survival. Many of the functions associated with stream riparian
areas also apply to wetland buffers. Terrestrial habitats surrounding wetlands provide a buffer to
help mitigate the impacts of urbanization.
Buffer areas retain sediments, nutrients, pesticides, pathogens, and other pollutants that may be
present in runoff (Washington Department ofEcology~ 1996). Reduction of sediment and pollutant
discharge to wetlands prevents alterations to plant and animal communities and degradation of
water quality in wetlands. Buffers also increase the ability of wetlands to further provide sediment
and pollutant removal as a result. Terrestrial habitats infiltrate flood water, reducing the effect of
water level fluctuations within wetlands. Wetland buffers composed of forested and shrub
vegetation provide shade which in turn maintains water and wildlife habitat quality.
A scientific literature review points to required buffer width to protect a given habitat function or
group of functions depends on numerous site-specific factors. These factors include the plant
community (species, density, and age), aspect, slope, channel width, and soil type, as well as
adjacent land use. The body of science indicates that the appropriate buffer width for a given
wetland is specific to the environmental setting and functions to be achieved by that buffer.
Wildlife species that use wetlands for a portion of their life cycle also depend on terrestrial habitats
for food, cover, nesting, and/or travel corridors. A variety of wildlife species utilize the edge
habitat between wetlands and uplands habitat. Terrestrial habitat areas provide a source of large
woody debris used by wildlife for foraging, nesting, and cover (O'Connell, 2000). Buffers provide
separation between wetland habitat and human disturbance. This distance improves the quality of
wildlife habitat by lessening the effects of noise, light, and human motion/activity upon animal
species sensitive to these disturbances. Buffers also provide area over which sediment or pollutant
removal can occur, and for flood flow attenuation.
,Several literature reviews have been published summarizing the effectiveness of various buffer
widths, mainly for riparian areas, but also for wetlands (Castelle et aI., 1992a; Castelle and
Johnson, 2000; Desbonnet et aI., 1994; FEMAT, 1993). Generally, the riparian buffer literature
also applies to wetlands because very similar functions are provided by riparian buffers as those for
wetlands. However, the effects of buffers on streams and fish habitat differ from the effects on
wetlands. For example, large woody debris from riparian areas along streams primarily contributes
to instteam structure and fish habitat, while large woody debris in wetlands provides structure or
foraging habitat for a variety of wildlife species. McMillan (2000) provides the most recent
literature review specific to wetland buffers in western Washington.
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Studies of .buffers in forest practices and agriculture indicate that buffers ranging from 25 to
100 feet may be adequate to preserve many of the beneficial functions to wetlands. However,
urban wetlands have many different variables affecting wetland functions and applying these buffer
ranges may not be adequate to protect the wetland systems. Due to the type and degree of
cumulative impacts to urban wetlands (and streams) that have already occurred as a result of high
levels of total impervious area and past disturbance to wetlands, it may be necessary to develop.
new strategies to successfully address the issue of adequate buffers in the context of basin-wide
change (Booth, 2000; Azous and Horner, 2001; Booth and Reinelt, 1993).
Many studies indicate that buffers ranging from 100 to 150 feet wide provide most (on the order of
80 percent) of potential functions in most situations. In th~se studies, the relationship between
buffer width and effectiveness is logarithmic, so that after a certain width an incremental increase
in buffer width provides diminishing functional effectiveness. One study indicates that 90 percent
of sediment removal can be accomplished within the first 100 feet of a riparian buffer, but an
additional 80 feet of buffer is needed to remove just fiye percent more sediment (Wong and
McCuen, 1982).
2.7 Wetland Mitigation & Enhancement Strategies
The Clean Water Act Section 404(b)(I) Guidelines for wetland mitigation require "no net loss" of
wetlands by first avoiding, minimizing, rectifying, and reducing impacts to wetlands and their
functions. Where loss of wetland acreage and/or functions is necessary, replacement or
~ !~ compensatory mitigation should be required. Local jurisdictions in Washington implement these
guidelines through local critical area regulations. Most local jurisdictions require compensatory
mitigation for impacts to wetlands and/or their buffers resulting from development or associated
activities. Jurisdictions generally allow four types of mitigation: creation, restoration,
enhancement, and exchange (Gwin et al., 1999). The different types of mitigation are generally
considered to be in-kind (replacement of same functions and acreage as the impacted wetland) and
are typically constructed on the development site where the wetland impact occurred.
Off-site and out-of-kind wetland mitigation has also been allowed by agencies in certain cases. The
U.S. Army Corps of Engineers and other agencies have allowed off-site preservation of wetlands,
and there has been growing interest in mitigation banks in Washington. Mitigation banking may
give developers additional options for mitigation; banking also allows creation or preservation of
larger and higher quality wetlands than might have been established on anyone development site.
Use of a single site for" multiple mitigation efforts also facilitates adequate maintenance and
monitoring, which in turn, increase the success of the project. Ecology has written a draft
Mitigation Banking Rule to facilitate the use of this type of mitigation. The OCD Draft Model
Critical Areas Ordinance also includes mitigation banking as an allowed type of mitigation.
2.7.1 Wetland and Buffer Mitigation Success
Most wetland mitigation projects have not been successful for various reasons and have resulted in
lost acreage, wetland types, and wetland functions (Castelle et al., 1992b; Washington Department
of Ecology, 2001; Mockler et al., 1998). Castelle et aI., (1992b) reported that 50 percent or more of
the mitigation projects studied did not meet permit requirements. Common problems included:
......... - ..-.....
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. Inadequate design;
.. Failure to implement the design;
. Lack of proper maintenance, site infestation by exotic species;
. Grazing by geese or other animals;
. Destruction by floods, erosion, fires, or other catastrophic events;
. Failure to maintain water levels and failure to protect projects from on-site and off-site
impacts such as sediment and pollutant loading; and
. Off-road vehicles.
.
A predominant problem throughout wetland mitigation sites is the invasion of the site by non-
native plant species. Studies have found that at least 50 percent of species in mitigation sites were
non-native (Magee et al., 1999; Ecology, 2001). Mitigation areas that were not protected by upland
buffer had a larger percentage of non-natives, and long-term maintenance of sites resulted in lower
percentages of non-natives. Gwin et al., (1999) also found mitigation areas to be functionally
different from replaced wetlands,. resulting in net loss of function and, in some cases, net loss of
wetland area. The use of wetland exchange and enhancement of existing wetlands to replace lost
wetlands does not actually create new wetlands but improves or modifies the functions of existing
wetlands to compensate for those lost, therefore resulting in a "net loss" of wetland acreage and
possibly wetland functions (depending on how the enhancement was implemented) (Shaffer et al.,
1999; Gwin et al., 1999; Ecology, 200l).
~~~~~
~~:~~ ;
Ecology (2001) conducted a study of 24 mitigation sites in Washington and found that although
mitigation success has improved in the last 10 years, there is still much room for improvement.
The Ecology (2001) study had the following findings:
. Only 29 percent of the projects were achieving all their specified measures;
. Only 84 percent of the total acreage of mitigation was actually established;
. Only 65 percent of the total acreage of lost wetlands was replaced with new wetlands;
. 54 percent of the projects were found to be minimally successful or not successful;
. Wetland enhancement as a type of mitigation performed poorly, compared to creation
(50 percent of enhancement sites provided minimal or no contribution to overall wetland
. functions; 75 percent of sites provided minimal or no contribution to general habitat
function); and
. 60 percent of created wetlands were moderately or fully successful and provided signi ant
contribution to water quality and quantity functions.
Mitigation has been more successful for some wetland types, including emergent and open water
wetlands (Castelle et aI., 1992b). Other wetland types have been very difficult or impossible to
replicate, such as mature forested or bog systems, or wetlands that contain habitat for sensitive
wildlife species. Restoration of prior wetlands was often found to be easiest to achieve. The
likelihood of success of restoration is greater than other types of mitigation because the site will
benefit from restored hydrology, and seed sources from the original wetland may be prese~t and
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viable. However, some authors suggest that mitigation projects in urban settings may not be able to
recreate a historic wetland ecosystem due to changes in water regime and nutrient input (Ehrenfeld,
2000; Horner, 1997; Booth, 2000). .
Ecology (2001) concluded that although better site selection, design and perfomiance standards
will help to improve wetland mitigation, consistent follow-up [adaptive management], both to
correct problems with current projects and to provide feedback for decision-making on future
projects, will result in the greatest overall improvement. Most successful projects had long-term
monitoring of at least five years and applied adaptive management strategies. Many other studies
support long-term (at least five years) monitoring for mitigation projects (Kentula, 2002; Kusler
and Kentu1a, 1990).
The literature indicates that on-site, in-kind mitigation is desirable and can be most successful at
replacing lost wetland functions, but is dependent on site constraints, particularly hydrologic
conditions. The literature is conflicting on whether on-site mitigation or off-site mitigation can
adequately compensate for loss of wetlands and their functions (Erwin, 1990; Castelle et al., 1991a;
Kusler, 1992). However, Kusler (1992) suggests that in cases where there are many small isolated
wetlands and compensatory mitigation has been determined to necessary (after evaluating
mitigation sequencing), off-site mitigation may be more successful at replacing lost wetland
acreage and fu,nctions, because replacement of these small wetlands is difficult to achieve. More
functional benefit may be reached through a larger mitigation that is established within the context
of landscape level assessment to determine optimum location to meet the "needs" of the hydrologic
and ecological system (Kusler, 1992; Washington Department of Ecology, 2001; Bedford, 1996).
~
Buffer mitigation projects generally are affected by the same factors as wetland mitigation.
Success of plant growth in the buffer depends on water, nutrient and soil requirements for plants,
and controlling the invasion of non-native species (Gwin et al., 1999; Magee et al., 1999).
Success of buffer mitigation projects also depends on human disturbance in the
eas often include restoration or establishment of forest habitat, this can be
difficult to achieve based on experience from wetland systems. Buffers in some urban
environments, due to close proximity to development, have been altered through dumping of
debris, clearing, and other human disturbances (Desbonnet et al., 1994; Cooke, 1992, Castelle et al.,
1992a). Some buffers that were included in some residential lots in King County were eventually
converted to lawn. However, impacts to buffer areas were less likely in areas where residents had
been educated about the value of buffers (Gwin et al., 1999; Kentula, 2002).
2.7.2 Mitigation Ratios
Generally, wetland mitigation is implemented over a larger area than the wetland area adversely
affected by a proposed project. Mitigation ratios are typically greater than 1: 1 for several reasons.
Higher ratios act as disincentives to fill wetlands. They provide an opportunity to achieve certain
functions over a larger area, thus compensating for a temporal loss of function from the smaller but
presumably more mature impact site. In addition they compensate for the inability to achieve full
replacement acreage of lost wetlands (Washington Department of Ecology, 2001; Kusler and
Kentula, 1990).
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Several authors and agencies have recommended various replacement ratios (Castelle et aI.,
1992b). Most ratios are based on known failures of compensatory mitigation and designed to
compensate for historic loss of wetlands. Studies of the success of mitigation projects suggest that
replacement ratios based on mitigation success could be between 3: 1 ~nd 1.25: 1. Mitigation ratios
for wetlands in most local jurisdictions in western Washington currently range between 1: 1 and 4: 1.
However, more information is needed to understand whether lost wetland functions and acreage
can be entirely compensated for. The Draft OCD Model Critical Areas Ordinance (2002)
rec~mmends the following wetland mitigation ratios by classification of wetland:
Category I wetlands - 6: 1
Category II wetlands - 3: 1
Category III wetlands - 2: 1
Category N wetlands - 1.5: 1
3.0 FUNCTIONS AND VALUES OF WETLANDS AND WETLAND
BUFFERS IN TUKWILA
(:! .
The City of Tukwila is currently preparing a wetland inventory in the Urban Growth Area. This
inventory is anticipated to be complete in 2003. Our review is based upon two days of field
investigations and preliminary information on wetland habitats and functions provided by the City
(Schultz, 2001). The majority of wetlands identified in the City are classified as forested and
scrub-shrub wetlands and are largely isolated from stream and river systems. Other, more degraded
wetlands support emergent habitats. Most of these wetlands are supported by perennial hydrology.
In general, the City's wetlands lie within developed areas, and have degraded and narrow buffers.
Where wetlands have been protected along streams, surface water runoff has the potential to be
attenuated. In these areas, development has been limited within the natural floodway of the streams
and forested/scrub-shrub wetlands provide a high level of stormwater control. However, the use of
wetlands for stormwater facilities has substantially altered the structure and hydrodynamics of these
wetlands, and potentially lessened their ability for natural flood water attenuation and flood peak
desynchronization. Few wetlands in the City have been used formally for stormwater detention;
however, informal use of wetland in stormwater is a common practice.
Riparian wetlands, particularly those in the upper portions of drainage basins in Tukwila, provide
the highest level of stream base flow benefits. Groundwater discharge is the primary contributor to
base flow in wetlands and streams in Tukwila. Providing groundwater recharge and base flow for
streams is and important functions of wetlands in Tukwila due to the high levels of impervious
surface, which limit infiltration in upland areas. Base flow is particularly important for salmonid-
bearing streams that have low flows during the dry season. The size and vegetative structure of
many riparian wetlands in the upper portions of all basins have been reduced or altered,
compromising their ability to provide stream base flow and possibly groundwater support. Ground
water discharge provides a large perennial base flow to streams that supports aquatic and terrestrial
life.
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Larger and less disturbed wetland complexes, such as in the upper Riverton Creek sub-basin,
contain diverse vegetation which are most effective for improving water quality. Smaller disturbed
wetlands, such as in the lower portions of the Riverton Creek basin, have a more limited ability to
improve water quality due to their small size and less diverse vegetat~on cover. However, small
wetlands may be the only wetlands existing in these basins, such as in Southgate Creek, and
therefore, are important for providing water quality functions.
Wetlands and wetland buffer do support wildlife habitat within the City limits. Wildlife species in
Tukwila forage on riparian- and wetland-dependent species such as insects, stream dwelling
invertebrates, and fish. The presence of wetlands within and along wildlife linkages also provides
critical habitat for fish and wildlife, such as rearing areas for juvenile salmon and water sources for
all wildlife. Much of the remaining habitat structure in Tukwila for nest and roost sites and
productive areas for forage for species is present in riparian and wetland areas. Many wetlands
could be enhanced for wildlife by removing non-native plant species and replanting with natives.
These areas are highly valued, particularly within urb~n communities such as Tukwila;
Due to urbanization in the City, wetland buffers are typically degraded and narrow. Non-native
blackberry is a common shrub component in buffer areas. This is especially true in the lower parts
of the drainage sub-basins where most development has occurred. In steeper areas such as hillsides
and valley walls, wetland buffers are less degraded due to constraints on development from steep
slopes. Enhancement of degraded buffers has been an important goal for restoration of buffer
functions in the City.
-::;,.~'\:
~~~~~~;::~
~,;,"4.0 DATA GAPS
Two data gaps were discovered in the preparation of this study. The first is the lack of best
available science literature pertaining specifically to urbanizing watersheds and buffers needed to
protect wetlands in the Pacific Northwest.
The second data gap is the lack of detailed and current information on each of Tukwila' s wetlands
and riparian habitats. Preliminary wetland inventory information was provided by the City for this
study. However, updated information including habitat types, wetland functions and values, and
buffer quality is still in preparation by the City.
Adolfson Associates. Inc.
June 2003
Page 13
5.0' REFERENCES
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Bedford, B.L. 1996. The need to define hydrologic equivalence at the landscape scalefor
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Booth, D. B. 2000. Forest cover, impervious-surface area, and the mitigation of urbanization
impacts in King County, Washington. Prepared for King County Water and Land
Resources Division. Seattle, Washington.
Booth, D.B. and L. Reinelt. 1993. Consequences of Urbanization on Aquatic Systems: Measured
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Watershed '93 A National Conference on Watershed Management. March 21-24, 1993.
Alexandria, VA.
Budd, W.W., P.L. Cohen, P.R. Saunders, and F.R. Steiner. 1987. Stream Corridor Management in the
Pacific Northwest: I. Determination of Stream-Corridor Widths. Environmental Management
11 :587 -597.
~.'~~
'" ....;
Brinson. 1993. Changes in the Functioning of Wetlands Along Environmental Gradients.
WETLANDS, Vol. 13, No.2, June 1993, pp. ~5-74.
Carter, V, M.S. Bedinger, R.P.Novitski, and W. O. Wilen. 1979. Water resources and wetlands, in
Wetland Functions and Values: The State of Our Understanding, P.E. Greeson, J.R. Clark,
I.E. Clark, eds. American Water Resource Association, Minneapolis, MN, pp. 377-388.
Carter, V. 1986. An Overview of the Hydrologic Concerns Related to Wetlands in the United
States. US Geological Survey, Reston, V A.
Carter, V, and RP.Novitski. 1988. Some comments on the relation between ground water and
wetlands, in The Ecology and Management of Wetlands, D.D. Hooke et al, eds., vol. l:
Ecology of Wetlands, Timber Press, Portland, OR, pp. 68-86.
Castelle, AJ., C. Conolly, M. Emers, E.D. Metz, S. Meyer, M. Witter, S.S. Cooke, D. Sheldon, and
D. Dole. 1992a. Wetland Buffers: Use and Effectiveness. Adolfson Associates, Inc. for
Shorelands and Coastal Zone Management Program. Wash. Department of Ecology.,
Olympia, Wash.
Castelle, A.I., C. Conolly, M. Emers, E.D. Metz, S. Meyer, M. Witter, S. Mauermann, M. Bentley,
D. Sheldon, and D. Dole. 1992b. Wetland Mitigation Replacement Ratios: Defining
Equivalency. Adolfson Associates, Inc. Shorelands and Coastal Zone Management Program,
Washington Department of Ecology, Olympia, Publ. #92-08.
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Castelle, A.J., and A.W. Johnson. 2000. Riparian Vegetation Effectiveness. National Council for
Air and Stream Improvement Tech. Bull. No. 799.
City of Portland. 2001. Streamside Science and an Inventory of Significant Riparian and Wetland
Resources. Discussion Draft. City of Portland, Oregon Bureau of Planning.
Cooke Scientific Services, Inc. 1992. Wetland Buffers - A Field Evaluation of Buffer Effectiveness
. in Puget Sound. Prepared for Washington Department of Ecology.
Cooke Scientific Services, Inc. 1995. Wetland and Buffer Functions Semi-Quantitative
Assessment Methodology.
Cooke Scientific Services, Inc. 2000. Wetland and Buffer Functions Semi-Quantitative
Assessment Methodology (SAM) Final Working Draft User's Manual.
Cowardin, L.M., V. Carter, F.C. Golet, and E.T. LaRoe. 1979. Classification of Wetlands and
Deepwater Habitats of the United States. U.S. Fish and Wildlife Service. Pub!. #
FWS/OBS-79/31. 131 p.
Desbonnet, A., P. Pogue, V. Lee, and N. Wolff. 1994. Vegetated Buffers in the Coastal Zone.
Coastal Resources Center, Rhode Island Sea Grant, Univ. of Rhode Island.
Erhenfeld, J.G. 2000. Evaluating Wetlands within an Urban Context. Urban Ecosystems 4:69-85.
~.:~
Erwin, K.L. 1990. Wetland evaluationfor restoration and creation. In Kusler, J.A., and M.E.
Kentula, eds" Wetland Creation and Restoration: The Status of the Science. Island Press,
Washington, DC.
FEMAT. 1993. Forest Ecosystem Management: An Ecological, Economic and Social Assessment.
Report of the Forest Ecosystem Management Assessment Team, USDA Forest Service et
al., Washington, D.C.
Greeson, P.E., J.R Clark, J.E. Clark, eds. 1979. Wetland Functions and Values: The State of Our
Understanding. American Water Resource Association, Minneapolis, MN.
Gwin, S.E., M.E. Kentula, P.W. Shaffer and US Environmental Protection Agency. 1999.
Evaluating the Effects of Wetland Regulation Through Hydrogeomorphic Classification and
Landscape Profiles. WETLANDS, Vol. 19, No.3, pp. 477-489.
Higgs, D.A., J.S. McDonald, C.D. Levings, and B.S. Dosanjh. 1995. Nutrition and Feeding Habits
in Relation to Life History Stage. In Groot, C., L. Margolis, and W.C. Clarke, eds.
Physiological Ecology of Pacific Salmon. UBC Press, Vancouver, B.C.
Homer, RR 1997. Section 1:. Overview of the Puget Sound Wetlands and Stonnwater Manao'-'ment
Research Program. Pages 1-25 in Azous, A.L. and R.R. Horner, editors. Wetlands and
Urbanization, Implications for the Future. Washington Department of Ecology, Olympia,
W A, King Cou rces Division, Seattle, W A and University of
Washington., Seattle, W A.
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Horner, R.R, S.S. Cooke, K.O. Richter, A.L. Azous, L.E. Reinelt, B.L. Taylor, K.A. Ludwa, and
M. Valentine. 1996. Wetlands and Urbanization, Implications/or the Future. Puget Sound
Wetlands and Stormwater Management Research Program, Final Report, Engineering
Professional Programs, University of Washington, Seattle, 1996.
Hruby, T., W.E. Cesanek, and K.E. Miller. 1995. Estimating Relative Wetland Values/or
Regional Planning. WETLANDS, Vol. l5, pp. 93-107.
Hruby, T., T. Granger, K. Brunner, S. Cooke, K. Dublanica, R. Gersib, L. Reinelt, K. Richter, D.
Sheldon, E. Teachout, A. Wald, and F. Weinmann. 1999. Methods/or Assessing Wetland
Functions. Volume I: Riverine and Depressional Wetlands in the Lowlands o/Western
Washington. W A State DepartIhent of Ecology Publication #99-l15, July 1999.
Kauffman, J.B., M. Mahrt, L.A. Mahrt, and W.D. Edge. 2001. Wildlife 0/ Riparian Habitats.
Chapter 14 in Johnson, D.H. and T.A. O'Neil. 2001. Wildlife-Habitat Relationships in
Oregon and Washington. Oregon State University Press. Corvallis, Oregon.
Kentula, M.E. 2002. Tracking Changes in Wetlands and Urbanization: Sixteen Years 0/ Experience
in Portland, OR.. US EPA presentation at Urban Wetlands Sustaining Multiple Functions
Conference. May 20-21,2002. Portland State University, Portland, OR.
Kusler, J .A., and M.E. Kentula, eds. 1990. Wetland Creation and Restoration: The Status of the
Science. Island Press, Washington, DC.
~
Kusler, J. 1992. Mitigation Banks and the Replacemento/Wetland Functions and Values. In
Effective Mitigation: Mitigation Banks and Joint Projects In the Context of Wetland
Management Plans. Proceedings from National Wetland Symposium. June 24-27, 1992.
Palm Beach Gardens, FL.
Ludwa, K.A. 2001. Emergent Macroinvertebrate in Relation to Watershed Development. In
Wetlands and Urbanization: Implications for the Future., Azous and Horner, Lewis
Publishers, Boca Raton, Florida. 2001.
Magee, T.K., T.L. Ernst, M.E. Kentula, and K.A. Dwire. 1999. Floristic Comparison o/Freshwater
Wetlands in an Urbanizing Environment. WETLANDS, Vol. 19, No.3, pp. 517-534.
Marble, A.D. 1992. A Guide to Wetland Functional Design. Lewis Publishers, Boca Raton, Florida.
May, C.W., R.R. Homer, J.R. Karr, B.W. Mar, and E.B. Welsh. 1997. Effects of Urbanization on
Small Stream in the Puget Sound Lowland Ecoregion. Watershed Protection Techniques,
2:483-494.
May, C.W., E.B. Welch, R.R. Homer, J.R. Karr, and RW. Mar. 1997. Quality Indices for
Urbanization Effects in Puget Sound Lowland Streams. Wat. Res. Tech. Rep 154.
Washington Department of Ecology, Olympia W A.
McMillan, A. 2000. The science of wetland buffers and its cations for the management of
wetlands. Master's Thesis. The Evergreen State College.
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Mitsch, W. J. and J.G. Gosselink. 2000. Wetlands. 3rd ed. Van Nostrand Reinhold, New York.
Mockler, A., L. Casey, M. Bowles, N. Gillen, and J. Hansen. 1998. Results of Monitoring King
County Wetland and Stream Mitigations. King County Department of Environmental
Services, King County, W A. '
Novitski RP. 1979. Hydrologic characteristics of Wisconsin's wetland and their influence on
, floods, stream flow, and sediment, in Wetland Functions and Values: The State of Our
Understandin~, P.E. Greeson, J.R Clark, J.E. Clark, eds. American Water Resource
Association, Minneapolis, MN, pp. 377-388.
Novitski RP., D. Smith, and J.D. Fretwell. 1995. Restoration, Creation and Recovery of
Wetlands: Wetland Functions, Values and Assessment. United States Geological Survey
Water Supply Paper 2425. "
O'Connell, M.A. J.G. Hallett, S.D. West, K.A. Kelsey, D.A. Manuwal, and S.F. Pearson. 2000.
Effectiveness of Riparian Management Zones in Providing Habitatfor Wildlife. Submitted
to the LW AG, Timber Fish and Wildlife Program. Cheney, Washington.
( }!
Reinhelt, L.E. and R R. Horner. 1991. Urban Stormwater Impacts on Hydrology and Water
Quality of Palustrine Wetlands in the Puget Sound Region. pp. 33-42 in Proceedings Puget
Sound Water Quality Authority Research Meeting, Seattle, W A, January, 1991.
Reppert, RT., W. Sigles, E. Stakhiv, L. Messman, and C. Meyers. 1979. Wetlands Values:
Concepts and Methods for Wetlands Evaluation. lnst. for Water Resources, U.S. Army
Corps of Engineers, Fort Belvoir, VA. Res. rpt. 79-Rl.
Richter K. 0., A. Azous, S.S. Cooke, R Wisseman, and R. Homer. 1991. Effects of Stonnwater
Runoff on Wetland Zoology and Wetland Soils Characterization and Analysis, PSWSMRP,
Seattle, W A.
Richter and Azous. 2001. Amphibian Distribution, Abundance, and Habitat Use In Wetlands and
Urbanization: Implications for the Future., Azous and Homer, Lewis Publishers, Boca
Raton, Florida. 2001.
Richter. 2001. Macroinvertebrate Distribution, Abundance, and Habitat Use In Wetlands and
Urbanization: Implications 'for the Future., Azous and Homer, Lewis Publishers, Boca
R~ton, Florida. 200 I.
Sather, H.J. and D. Smith. 1984. An Overview of Major Wetland Functions and Values. Fish and
Wildlife Service, USDI. FWS.OBS-84-18.
Schueler T. 1994. The Importance of Imperviousness. Watershed Protection Techniques 1(3), pp.
100-111.
Schueler T. 2000. The Architecture of Urban Stream Buffers, Article 39 in The Practice of
Watershed Protection, Center for Water ed Protection, Ellicott City, MD, 2000.
Page 17
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Schultz, Gary. 2002. Memo to Jack Pace, Deputy Director City of Tukwila. Sensitive Areas:
Preliminary Habitat and Functions Characterization. October 28, 2001 [sic 2002].
Shaffer, P.W., M.E. Kentula, and S.E. Gwin. 1999. Characterization of wetland hydrology using
hydrogeomorphic classification. WETLANDS, Vol. 19, No.3, pp. 490-504.
Todd. 2000. Making Decisions about Riparian Buffer Width. 2000. International Conference on
Riparian Ecology and Management in Multi-Land Use Watersheds, American Water
Resources Association Conference Proceedings, August 28-3l, 2000, Portland, Oregon.
pp. 445-449. .
Washington Department of Ecology. 1\993. Washington State Wetlands Rating System - Western
Washington. Washington Department of Ecology, Olympia, Publ. #93-74.
~
Washington Department of Ecology. 1996. Water Quality Guidelinesfor Wetlands: Using the
Surface Water Quality Standards for Activities Involving Wetlands. Washington Department
of Ecology, Olympia, Publ. #96-06.
Washington State Department of Ecology . 1997. Washington State Wetlands Identification and
Delineation Manual. Washington State Department of Ecology, Publication No. 96-94.
~,
Washington Department of Ecology. 2001 Washington state wetland mitigation evaluation study
phase 2: Success. Publication 01-06-021.
WDFW.199Z. Buffer Needs of Wetland Wildlife. Final Draft, February 12, 1992. Olympia,
Washington.
Wong, S.L., and R.H. McCuen. 1982. The Design of Vegetative Buffer Strips for Runoff and
Sediment Control. A Technical Paper Developed as part of a Study of Stormwater
Management in Coastal Areas Funded by Maryland Coastal Zone Management Program.
23pp.
Zedler, 1.B., R. Langris, J. Cantilli, M. Zalejko, K. Swift, and S. Rutherford. 1988. Assessing the Function of
Mitigation Marshes in Southern California. pp. 323-330. In J.A. Kusler, S. Dalky, and G. Brooks,
eds. Proceedings of the national Wetlands Symposium: Urban Wetlands. Association of State
Wetland Managers. Byrne, NY.
Adolfson Associates, Inc.
June 2003
Page 18
Al"lACHMENT B
JUNE 2003
BEST AVAILABLE SCIENCE ISSUE PAPER:
WATERCOURSES
Prepared for:
City of Tukwila
Department of Community Development
6300 South center Boulevard
Tukwila, WA 98188
Prepared by:
Adolfson Associates, Inc.
5309 Shilshole Avenue NW, Suite 200
Seattle, Washington 98107
TABLE OF CONTENTS
1.0 INTR 0 D U CTI ON................... ........ .............. ........... ...... .......................... .... ....... .......................... 1
1.1 Project Authorization........................ ...... ............... .............. ..... ........... .................... ........... 1
1.2 Overview of Growth Management Act Requirements ....................................................... I
1.3 Overview of the City Environment .................................................................................... 2
2.0 STATE OF THE SCIENCE FOR WATERCOURSES AND RIPARIAN AREAS ................ 2
2.1 Importance of Watercourses and Riparian Areas ............................................................... 3
2.2 Functions and Values of Watercourses............. ............ ......... ......................... ......... ........... 3
2.2.1 Stream Flow..... ....................................... ............ ............... ..... ..... ........... .... ........... 3
2.2.2 Water Quality.. ,.... ...... ....... ........ ........ ......... ........ ............ ............................ ........... 4
2.2.3 In-stream StructUral Diversity....................... ............... ............... ................... ....... 5
2.2.4 Biotic Input...... .......... ........ ~.......... ....... ..... ..... ......... ........ ......... .............. ......... .... ... 7
3.0 FUNCTION AND VALUES OF RIPARIAN B~14'.tt'ERS .......................................................... 8
3.1 Application of Buffer Widths .... ..................... .... .......... ............... ............. ........ ....... ........... 9
3.2 Stream Management in Urban Environments................................................................... 10
3.3 Fisheries Habitat and Salmonid Use in the City of Tukwila ............................................ 11
3.3.1 GreenlDuwamish River ..... ........... ..... .... ............... ................... ............... ........ ..... 12
3.3.2 Black River...... .................. ........... ..... ..... ....... ..... ......................... .... ....... ............. 12
3.3.3 Gilliam Creek.. .......... ........ ..................... ...... ...... .................. ......... ................. ..... 13
3.3.4 Southgate Creek.... ......................................... ......................... ....... ......... ............. 13
3.3.5 Riverton Creek... ........................... ..... .... ....... ... ....... ........... ... ....... ........ ........... ..... 13
3.3.6 Other Watercourses ....... ........ ............ ....... ..... ....................... ....... ........ ................ 14
FUNl..uONS AND VALUES OF WATERCOURSES AND RIPARIAN AREAS IN
4.0
TUKWILA ............................... .................................................................................................... 14
5.0 DATA GAPS ......................................... .... ................................................................................... 15
6.0 RECOMMENDATIONS ............................................. ERROR! BOOKMARK NOT Dbt'lL"ffiD.
6.1 Regulatory Framework of Watercourse Regulations ........Error! Bookmark not dermed.
7.0 REFEREN CES ............................................................................................................................ 16
A.r.r .c.NDIX A: EJ!~J!ECTS OF ECOSYSTEM ALIJ!.RATIONS ON SALMONIDS....................... A-I
A.r.r .c.NDIX B: LITERATURE FINDINGS, RIPARIAN BUFFERS BY FUNCTION.................. B-1
LIST OF TABLE
Table 1. Riparian Habitat Area Buffer Recommendations: Washington Department of Fish
and Wildlife ................................................................................................................................... 8
Adolfson Associates. Inc.
June 2003
Pagei
1.0 INTRODUCTION
1.1 Project Authorization
At the request of the City of Tukwila, Adolfson Associates, Inc. (Adolfson) has prepared this
issue paper to provide an overview of the "best available science" pertaining to management of
streams found in the City of Tukwila (the City). The preparation of this report was made
possible by funds made available through the Washington State Department of Community,
Trade and Economic Development. This paper will provide guidance to the City in development
and revision of the City's critical area$ ordinance - Tukwila Municipal Code (TMC) Chapter
18.45 Sensitive Areas Overlay.
This paper discusses the results of the best available science review for streams and evaluates the
applicability of the science to stream regulations in the City. Adolfson has based our review of
the city environment on two days of field investigation, existing literature and prelimin'ary
information from the City regarding its update of the stream inventory. City staff are in the
process of updating the watercourse inventory, and this preliminary review of Best Available
Science will be updated with inventory information and GIS products at a iater date. A 'review of
the best available science in relation to shorelines in the City of Tukwila was prepared by others
but available for review (Pentec, 2002).
1.2
Overview of Growth Management Act Requirements
In 1995, Washington State's legislature added a new section to the state's Growth Management
Act (OMA) to ensure that cities and counties consider reliable scientific information whc;m
adopting policies and regulations to designate and manage critical areas. The new section, RCW
36.70A.172, requires all cities and counties to include "best available science" in developing .
policies and regulations to protect the functions and values of critical areas. One of the
objectives of GMA is to protect the functions and values of critical areas by (1) accurately
describing these functions and values; (2) understanding the likely adverse impacts associated
with proposed land use planni ives; and (3) making land use decisions that minimized
or eliminated those adverse impacts to the extent possible.
. .
The state's Office of Community Development (OCD) adopted procedural criteria in 2002, to
implement these changes to the GMA and to provide guidance for identifying best available
science. The rule makers concluded that identifying and describing functions and values and
estimating the types and likely magnitudes of adverse impacts were scientific activities. Thus,
RCW 36.70A.172(1) and implementing regulations require the substantive inclusion of best
available science in developing critical area policies and regulations. These policies and
regulations must also give "special consideration" to preserve or enhance anadromous fisheries,
including salmon.' Subsequently, local government adopting policies and development
regulations to protect critical areas needs to document that it has given special consideration to
conservation or protection measures necessary to preserve or enhance anadromous fisheries.
Local governments should document that these measures are grounded in the best available
Adolfson Associates, Inc.
June 2003
Page 1
science. The rule states that special consideration should be given to habitat protection measures
based on the best available science.
The purpose of this report is to summarize and discuss the best available science relating to the
functions and values of streams and riparian areas, particularly relating to the needs of
anadromous fisheries in the City of Tukwila (City). Thisreport is intended to accompany the
stream inventory currently being prepared by City staff (in progress).
1.3 Overview of the City Environment
The City of Tukwila is an incorporate~ city with a population of approximately l5,OOO located in
King County, Washington. Tukwila and its planned annexation areas occupy approximately
10 square miles, and are generally bounded by the cities of Seattle to the north, Renton to the
east, Kent to the south, and SeaTac to the southwest. . ..
The GreenlDuwamish River is the main water feature in the City, flowing south to north through
the planning area. Along with the river, there are seven major tributaries and several minor ones
that drain into the GreenlDuwamish River within Tukwila. A detailed stream inventory is being
prepared by the City. In the Tukwila Municipal Code (TMC), tributary streams are called
watercourses, which are defined in TMC l8.06.920 as:
~~ ~~
"...a course or route formed by nature or modified by man, generally consisting of a
channel with a bed and banks or sides substantially throughout its length along which
surface water flows naturally other than the GreenlDuwamish River. The channel or bed
need not contain water year-round. Watercourses do not include irrigation ditches,
stormwater runoff channels or devices, or other entirely artificial watercourses unless that
are used by salmonids or to conveyor pass through stream flows naturally occurring prior
to construction of such devices."
Tukwila is a largely urbanized city, and a substantial portion of the development that has
occurred in the City has been commercial and industrial in nature. The most heavily industrial
areas are located along the GreenlDuwamish River, and water-based commerce has been, and
continues to be, an important component of these commercial and industrial activities.
Developmentof the immediate shoreline of the Gree Duwamish River is constrained by a series
of levees. In general, most easily-developable areas within the City limits have been developed.
Some redevelopment is occurring, as is development on some hillsides.
2.0 STATE OF THE SCIENCE FOR WATERCOURSES AND
RIPARIAN AREAS
This section summarizes the state of the science, or "best available science" for streams and
stream buffers. Higher preference has been given to science and research conducted in the
Pacific Northwest versus research from other areas of the United States. This information is a
summary of existing literature and is not intended to be an exclusive list of all best available
science currently published on streams, but is intended to provide a brief overview of
Adolfson Associates. Inc.
June 2003
Page 2
scientifically valid information useful for local planning and regulatory review. Adolfson has
referenced findings from selected scientific literature where applicable, including relevant
st.udies from the Office of Community Development's "Citations of Recommended Sources for
Designating and Protecting Critical Areas."
2.1 Importance of Watercourses and Riparian Areas
Stream systems are one of the most productive natural systems. Riparian areas playa significant
role in the protection of the functions of adjacent aquatic habitats. Both provide important
habitats for aquatic species and other wildlife as well as contribute to recreation, water supply,
economic, cultural and historic values, Specific watercourse functions are discussed in the
following section.
2.2 Functions and Values of Watercourses
Elements necessary for healthy salmonid populations and for other aquatic organisms rely on
processes sustained by the dynamic interaction between the stream and the adjacent riparian area
(Naiman et al., 1992).
~:~.~,:,
:...... .."
~-:~;:{~;.~
. Maintaining stream baseflows;
. Maintaining water quality;
. Providing in-stream structural diversity; and
. Providing biotic input of insects and organic matter.
2.2.1 Stream Flow
Stream flow is the amount and velocity of water flowing in a stream. In urban systems,
discharge regimes are often substantially altered. Urbanization changes the volume, rate, and
timing of water flowing through stream systems, which can impact the physical characteristics of
the stream channel (Booth, 1991). Stream degradation has been associated with the quantity of
impervious surface in a basin (Booth, 2000; May et aI., 1997; Homer and May, 2000). Studies in
Puget Sound lowland streams show that alteration can occur in basins with as little as 10 percent
total impervious surface. However, dramatic effects can be seen relative to discharge in basins
where impervious surface exceeds 40 percent (May et aI., 1997). In addition, medium-sized
flood events in moderately urbanized watersheds are found to have peak-flow increases of two to
three times the amount of runoff than non-urbanized watersheds (Booth et aI., 2000). Increases
in peak flow are more apparent as smaller, more frequent floods relative to larger floods (Booth
et al., 2001).
Stream flow or discharg significant influence on salmonids during their various life
stages. The quantity of stream water available for use by fish and other aquatic species will
determine how habitats will be effectively used in a particular basin. Adult chinook and
steelhead, for example, require greater water depths to spawn as compared to other salmonids.
Adolfson Associates, Inc.
June 2003
Page 3
€
and thus, commonly spawn in larger streams. Smaller species, such as cutthroat trout and coho
salmon, can successfully spawn in smaller headwater streams (Wydoski and Whitney, 1979).
Reaches of streams that are dry or have low flows in summer may limit summer rearing habitat
for these species. While low flows may limit access to some streams or reaches, excessively
high flows can also affect both stream habitat and reproductive success. Riparian areas often
have shallow groundwater tables, as well as areas where groundwater and surface waters
interact. Groundwater flows out of riparian wetlands, seeps, and springs to support stream
baseflows. Surface water that flows into riparian areas during floods or as direct precipitation
can infiltrate into groundwater in riparian areas and be stored for later discharge to the stream
(Ecology, 200 I; City of Portland, 200 I). Stream baseflow is particularly important to stream-
flow sensitive salmonids in the Pacific Northwest, because riparian areas provide baseflow from
groundwater during the region's typically dry season (City of Portland, 2001; Booth, 2000; May
et al., 1997; Schueler, 2001).
2.2.2 Water Quality
Salmonid fish requires water that is both colder and has lower nutrient levels than many other
types of fish. High water quality is a crucial need of all native salmonid fish and is important to
other aquatic species adapted to living in Pacific Northwest streams as well. Parameters for
salmonids in particular are discussed below.
2.2.2.1 Water TemDerature
While no single temperature provides for all of the needs of all species or life stages of salmonid
fish, many authors have identified water temperature ranges suitable for the various species and
developmental stages of salmonids (EPA, 200l; City of Portland, 2001; Sullivan et aI., 1990).
The general range of temperatures required to support healthy salmonid populations is generally
considered to be between about 390 and 630 F (NMFS, 1996; USFWS, 1998). Cutthroat trout
have the highest range of temperature tolerances of native salmonids (Pauley et aI., 1989 in City
of Portland, 2001). Above 630 F, however, salmonids begin to exhibit stress that may cause
sublethal effects including reduced growth and overall survival. Stresses increase until
temperatures exceed lethal limits (Moyle and Cech, 1998; Thomas et a!., 1986). Lethallimits
vary widely by species and development stage; constant temperatures in excess of 780 F, as one
example, are within the lethal range for coho salmon (Thomas et al., 1986). Coho salmon are
less tolerant of high stream temperatures than other salmonids because they usually spend a full
year in freshwater. Riparian vegetation, particularly forested riparian areas, can affect water
temperature by providing shade to reduce solar exposure and regulate high ambient air
temperatures, ameliorating water temperature increases (Brazier and Brown, 1973; Corbett and
Lynch, 1985).
2.2.2.2 Dissolved Oxvaen
Dissolved oxygen is one of the most influential water quality parameters for stream biota,
including salmonid fish (Lamb, 1985). The most significant factor affecting dissolved oxygen
levels in most streams is temperature, with cooler waters maintaining higher levels of oxygen
than warmer waters (Lamb, 1985). Other factors that can contribute to oxygen levels includes
water turbulence (the amount of aeration) and biochemical oxygen demand created by organic
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Page 4
decomposition from natural organic materials, organic pollution (pet waste, sewage, etc.), and
aquatic algae respiration. Nutrients may originate from human-induced sources such as
fertilizers (both chemical and natural), pet waste, and leaking sewers, or from natural processes
such as decomposing algae or dead plant materials that fall into streams (Lamb, 1985).
2.2.2.3 Metals and Pollutants
Common pollutants in urban areas include nutrients such as phosphorus. and nitrogen, pesticides,
bacteria, and miscellaneous contaminants such as PCBs and heavy metals. Impervious surfaces
collect and concentrate pollutants from different sources and deliver these materials to streams
during rain storms. In general, concentrations of pollutants increase in direct proportion to total
impervious area (May, et aI., 1997). "I)"ndisturbed riparian areas can retain sediments, nutrients,
pesticides, pathogens, and other pollutants that may be present in runoff, protecting water quality
in streams (Ecology, 2001; City of Portland 2001).
Elevated nitrogen and phosphorus levels in runoff are. a typical problem in urban watersheds.
They can lead to increased in-stream plant growth, which results in excess decaying plant
material that consumes oxygen in streams and reduces aquatic habitat quality (Kerwin, 2001).
Metals and hydrocarbons are often transported with sediments. Heavy metals, Polychlorinated
Biphenyls (PCBs), and other contaminants may be toxic to fish and wildlife (Kerwin, 200l).
The primary sources of metals and hydrocarbons in urban areas appear to be industry and
automobiles (Lynch et aI., 1985). Gas and oil, toxins from rooftops, and industrial and
household chemicals (paint, cleaning products, etc.) are also pollution sources in streams.
~. The extent to which salmonids are exposed to toxic substances such as pesticides is largely
unknown (Washington Department of Agriculture et aI., 2001). Toxic substances can have an
acute and/or chronic effect on salmonids and other aquatic organisms, and the toxicity of many
elements depends on independent factors (Kerwin, 2001). The acute effects of toxic discharges
are easy to observe as they are often the result of an episodic event where large numbers of fish
are killed. However, chronic impacts such as effects on growth or reproduction, occur over time
and may not be readily connected to a single source or event.
2.2.3 In-stream Structural Diversity
Salmonid species ilize a wide variety of both fresh and saltwater habitats. However, there are
several general habitat elements that support many species of salmonid fish. The National
Marine Fisheries Service (NMFS, 1996) and U.S. Fish and Wildlife Service (USFWS, 1998)
have developed guidelines to address habitat physical elements necessary to support healthy
salmonid populations across this range of variability. These physical habitat elements are
discussed below.
2.2.3.1 Substrate
Under natural conditions, the redistribution of substrate through bank erosion and channel
movement is a natural occurrence and is necessary to maintain clean, sediment-free gravels. In
urban basins, increases in stormflow quantities and velocities can cause scouring that can
displace stream substrates, which in turn reduces the quality and quantity of spawning areas
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(May et al., 1997). Scouring can result from increased runoff from impervious surfaces and from
increases in velocities as a result of channelization (straightening) and the removal of streamside
vegetation. Increased runoff rates from impervious surfaces can also flush spawning gravel from
streams (Bledsoe and Watson, 2001).
To balance the displacement of gravel resulting from natural redistribution or scour, streams
must have a constant source of new material. However, when vegetated riparian corridors have
been developed with urban land uses and stream banks stabilized to protect development, there is
little gravel or woody debris that it allowed to move to the stream system (May et al., 1997). In
general, armoring of stream banks with riprap or revetments reduces the supply of gravel and
LWD (May et al., 1997).
A wide variety of substrate sizes within a stream may provide habitat for use by several different
salmonid species. Fine sediments such as sand and silts can fill spaces between gravel and
reduces the opportunities for spawning and reproduction (Murphy et al., 1981; Thornon et al.,
1997). .
2.2.3.2 !-arae Woodv Debris
Large woody debris serves many functions in the stream environment, which creates habitat
diversity (for example pool habitat for rearing and cover for refuge). Woody debris adds
roughness to the stream channel, which slows water velocities and traps sediment (Shirvell,
1990). Because coniferous logs are slower to decompose, they generally provide more benefit as
(~~~) large w09dy debris than deciduous species (May et al., 1997).
Sources of large woody debris are often limited in urban stream systems. Movement of the
stream channel, undercutting of banks, windthrow, and flood events are all methods of
recruitment of woody debris to the stream. However, when riparian areas have been cleared and
developed, and the stream bank stabilized for development, there is little large woody debris
. available for recruitment (May et al., 1997). This is frequently the situation in urban streams
where large conifers have been removed, during land clearing and development activities in or
adjacent to riparian corridors, or where large woody debris may be removed from streams to
reduce perceived hazards associated with flooding. Man-made features such as culverts or
bridges, which restrict the ability of the stream to pass woody debris downstream, also hinder
recruitment. Increased runoff rates from impervious surfaces can also flush large woody debris
from streams (Bledsoe and Watson, 2001).
Many authors have found that more than h~lf of all large woody debris recruitment is from
within 15 feet of streams, and about 90 percent comes from trees growing within about 50 feet of
streams (Murphy and Koski, 1989; McDade et al., 1990; Van Sickle and Gregory, 1990).
2.2.3.3 Pool Qualitv and Quantitv
Large, deep pools with cover provided by woody debris, overhanging vegetation, or other
features such as boulders, typically provide more habitat value than smaller, shallow pools (May
et aI., 1997). Adult salmonids of all species require pools with sufficient depth and cover to
protect them from predators during their spawning migration. Adult salmon often hold in pools
during daylight, moving upstream from pool to pool at night.
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Pools, although important for most species of salmonid fish, are just one type of habitat that
salnionid fish require. Multiple habitats allow niche separation to occur so multiple populations
of fish with similar habitat needs can be maintained. Other habitats, like riffles and glides, are
also needed to provide the full complement of habitats necessary to support the range of
salmonid species and development stages present. Riffles provide habitat for many of the
aquatic insects that rearing salmonids utilize as food. Riffles and cascades create turbulence that
contributes to increase stream dissolved oxygen levels. Some salmonids may prefer pools, but
can also successfully compete using other habitat types. Cutthroat trout are often found in faster
water habitats such as glides and riffles. One study of urbanizing basins found that, for multiple
reasons including competition, physiology, and food preferences, cutthroat trout densities may
actually increase in streams that have lower pool frequencies compared to more diverse pristine
systems (May et al., 1997).
2.2.3.4 . FloodDlain Connectivity and Off-Channel Refuaia
~~
Off-channel wetlands and side channels in riparian areas provide foraging habitat, over-wintering
habitat, and refuges for rearing fish (Swales and Levings, 1989; City of Portland, 2001). These
areas, which includes wetlands connected to the stream channel and side channel habitats, also
have high levels of productivity and provides areas for juvenile fish to forage and grow before
outmigrating to salt water. Previous studies have shown the importance of off channel and river
margin rearing habitat to juvenile chinook (Bjornn and Reiser, 1991). Juvenile coho salmon,
which are not strong swimmers compared to other juvenile salmonids, often spend the winter
rearing in quieter off-channel pools and wetlands with ample woody debris cover (Bisson, et al.,
1988). Studies in urban and urbanizing areas indicates that off-channel habitat and refugia may
be reduced by urban development (Kerwin, 200l). Causes of this loss includes channel
straightening and disconnection from adjacent wetland areas.
2.2.4 Biotic Input
Riparian areas provide food for salmonids, both directly and indirectly (Meehan et al., 1977).
Insects falling from overhanging vegetation provide food for fish, while leaves and other organic
matter falling into streams provide food and nutrients for many species of aquatic insects, which
in turn provide forage for fish. In Puget Sound lowland streams, leaf litter from adjacent forested
riparian areas is a primary source of organic carbon and nutrients (Horner and May, 1999).
Many species of aquatic invertebrates have become adapted to feed on dead and decomposing
organic material that has fallen or washed into the stream from adjacent uplands (Benfield and
Webster, 1985).
Salmonids consume a wide range of food sources throughout their life cycles. Most juvenile
salmonids that rear in streams prey on aquatic invertebrates and terrestrial insects that fall into
streams from overhanging vegetation (Horner and May, 1999; May et al., 1997). In some
streams during the summer, an estimated 50 percent of the diet of juvenile salmonids is
comprised of terrestrial insects (City of Portland, 200 1 ). Availability of stream invertebrates as a
prey source for salmonids depends on both habitat area and habitat quality; specifically, the
amount of stream that can produce prey organisms and the amount of habitat that provides
opportunity for fish to exploit the prey base.
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3.0 FUNCTION AND VALUES OF RIPARIAN BUFFERS
Riparian buffers along stream banks help mitigate the impacts of urbanization and disturbance on
adjacent lands (Finkenbine et al., 2000. in Bolton and Shellberg, 2001). Knutson and Naef
(1997) summarize many of the functions of riparian buffers for Washington. The Washington
Department of Fish and Wildlife's (WDFW) recommended standard buffer widths for the state's
five-tier stream typing system is based on this latter research (Table 1) (OCD, 2002).
Table 1. Riparian Habitat Area Buffer Recommendations:
Washington Department of Fish and Wildlife
Type 1 & 2, shorelines of statewide significance
Type 3 or other perennial or fish bearing streams, 5-20 feet wide
Type 3 or other perennial or fish bearing streams, less than
5 feet wide
Type 4 and 5 (low mass wasting potential)
Type 4 and 5 (high mass wasting potential)
250 feet
200 feet
150 feet
150 feet
225 feet
Source: OCD, 2002; For definitions of the stream types see the Washington Administrative Code Sections 222-16-
030 and 031.
~%~~
Buffer widths reported to be effective for riparian functions vary considerably; the literature is
not.definitive in identifying one buffer width for each function studied (Williams and Lavey,
1986; Johnson and Ryba, 1992). The wide range of reported effective buffer widths indicates
that site-specific factors are important in determining the outcome of each study. Buffer studies
have been conducted in a wide variety of locations (e.g., Puget Sound lowlands, montane forests
of the Cascade Crest), and land use settings (primarily agricultural and forestry) using a variety
of research methods. Moreover, studies have been conducted in a wide range of channel types
(e.g., stream order, channel size, channel morphology) and site characteristics (e.g., slope, aspect,
soil type, vegetative cover). Most of the available research has been conducted in forestry
settings where the focus has been to document the effects of timber harvest.
A general relationship between buffer width and buffer effectiveness is apparent in the research
findings (Appendix A). Studies indicate that buffers 100-to l50-feet (30 to 45 meters) wide
provide most (on the order of80 percent) of the potential functions. The literature also indicates
that the relationship between buffer width and effectiveness is logarithmic, so that after a certain
width an incremental increase in buffer width provides diminishing functional returns. However,
there is little r~search on effectiveness of riparian buffers in urban environments (Herson-Jones
et al., 1995). Buffer distances should be viewed mainly as guidelines, as the literature shows that
site-specific factors may impact buffer effectiveness just as much as buffer width (Naiman et al.,
1992; Castelle et al., 1994).
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3.1 Application of Buffer Widths
The geomorphic settings of streams influence their fluvial characteristics, which in turn influence
their channel migration zone, ability to absorb flood flows, and the ability buffers to provide
their various functions. An overall conclusion of the review of scientific literature is that buffer
widths required to protect a given habitat function or group of functions depends on numerous
site-specific factors. The importance of riparian functions can vary by stream size and channel
width. Small headwater tributary streams are strongly influenced by riparian vegetation, where
such vegetation provides shading of waters and contributes large amounts of organic materia1.
Temperatures in larger streams below headwaters benefit less from overhanging vegetation.
Diversity of a plant community (species, density, age) in a buffer may determine how well a
buffer will perform functions. Aspect, soil type and slope all playa role in buffer effectiveness.
In riparian areas located on steep slopes and/or highly erodible soils, larger buffers may be
appropriate to reduce risks of erosion and delivery of fine sediment to streams. In general, as
stream size increases, the importance of shading and terrestrial organic inputs decrease, with a
increasing significance of algal or rooted vascular plant production and organic transport from
upstream (Vannote, et al., 1980).
(~~~?-.
.,....~.:"...~..
\... .,:;:!,,/':;
'.~..' - ..-~
Studies of buffer widths for moderation of stream temperatures generally range from 35 to
150 feet (Appendix A; Knutson and Naef, 1997). Much of the variability in the literature is
related to the presence or absence of a mature tree canopy. For example, forested buffers of
75 to 100 feet were found to provide 60 to 80 percent of the shade of conditions in fully forested
watersheds (Brazier & Brown, 1973; Steinblums et a1., 1984).
Recommended buffer widths for sediment and pollutant retention vary from 15 to 860 feet
(Appendix A; URS, 2002; Knutson. and Naef, 1997). This wide variation is due in general to the
particular pollutant being evaluated. Buffers of 50 to 100 feet may provide substantial pollutant
removal'benefits, and can remove 75 to 80 percent of pollutants depending on site-specific
conditions and buffer type (Lynch et a1., 1985; Castelle & Johnson, 2000; Wong & McCuen,
1982; Castelle et al., 1992). Studies have concluded that buffers of 100 feet can achieve
sediment removal efficiencies of75 to 100 percent. Wong and McCuen (1982) indicate that
90 percent of sediment removal can be accomplished within the first 100 feet of a riparian buffer,
but an additional 80 feet of buffer is required to remove five percent more sediment
(Appendix A). Most papers also conclude that larger buffers are required on steeper slopes to
reach the same level of pollutant removal.
Riparian vegetation may contribute up to 90 percent of the biotic input in stream systems (Budd
et al., 1987). Recommended buffers for maintenance of benthic communities range from 33 feet
to greater than 100 feet. However, most studies found that buffers of 100 feet were necessary
maintain healthy benthic communities (Robyet a1., 1977; Newbold et a1., 1980; Castelle &
Johnson, 2000). Buffers exceeding 100 feet were found to maintain the benthic diversity of
unlogged forested basins (Erman et al., 1977; May et a1., 1997). Although vegetated buffers are
necessary for organic input, no studies have focused on effective buffer widths specifically for
biotic input functions.
Because riparian areas store and slowly release water, they provide a continuous flow of water to
streams. A standardization of buffer width for stream baseflow has not been studied thoroughly.
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The effectiveness of the buffer for this function is significantly influenced by site-specific
conditions such as soil type, subsoil penneability, and topography, including the morphology of
the streambed and floodplain area, among other factors. Riparian areas with perfectly
functioning conditions (PFC's) can reduce the effects of flood flows and desynchronize peak
crests and flow rates of floods (Novitzki, 1979). Upland and wetland areas can infiltrate
floodflows, which in turn, are released to the stream as baseflow. Vegetation in the riparian zone
slows floodwaters, allowing infiltration, and alleviates downstream flooding (Bolton &
Shellberg, 2001).
Riparian buffer widths for wildlife habitat vary greatly depending on individual wildlife species,
but are generally on the order of 100 to 600 feet. (Appendix B, Knutson and Naef, 1997).
Studies have found that a buffer of 100 feet is necessary to maintain macro-invertebrate diversity
(Gregory et al., 1980); buffers of 100 to l65 feet are required for most amphibian and reptile
species (Rudolph and Dickson, 1989). Larger riparian buffers of 300 to 650 feet are needed to .
provide adequate migration corridors for certain species of wildlife (such as birds and mammals).
Quality of the buffer can also be a significant factor in determining the quality of wildlife habitat.
For example, buffer zones comprised of native vegetation with multi-canopy structure, snags,
and down logs provide habitat for the greatest range of wildlife species (McMillan, 2000).
Presence of sensitive resources, such as areas inhabited by fish or wildlife species of special
concern, are areas where larger buffers may be appropriate. Such an approach may minimize
impacts to such species from impacts such as human intrusion, light and glare, and noise.
~
3.2 Stream Management in Urban Environments
Many recent studies have focused on the general effects of urbanization on streams in the
lowland Puget Sound region (Booth, 2000; Horner and May, 1999). In these studies, a g
a greater emphasis on evaluation of buffer effectiveness in the
context of other watershed processes and evaluation of landscape-level alterations to watersheds
(Roni et aI., 2002; Richards et aI., 1996).
The loss or disturbance of native riparian area is closely tied to urbanization in a watershed
(Homer and May, 1999; Leavitt, 1998). However, water quality and coverage of impervious
area have also been associated with stream degradation and impacts to native riparian areas. The
adverse impacts of impervious area and water quaIity functions are compounded by degradation
of riparian areas (Bledsoe and Watson, 2001; May et aI., 1997). Effectiveness of a riparian area
is limited where streams have been channeliied or drainage routed through stormwater detention
and treatment system~. Degraded riparian areas are less effective at removing sediments and
pollutants washed from parking lots and roads where stormwater is not able to interact with
streamside vegetation.
Land uses, such as high-density residential development or commercial development, located
adjacent to riparian areas can result in greater impacts than lower density single-family
residential uses (Pitt et aI., 1986). Impacts may differ due to factors such as disturbance from
light, noise, human intrusion, and edge effects on wildlife. Riparian areas, if intact, can separate
streams from uplands and surrounding development, protecting streams from human
encroachment, which can result in direct impacts to stream banks or channels, as well as aquatic
life from increased access by humans or pets, and increased light or noise (Leavitt, 1998).
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In most urban areas prescriptive buffers may not be adequate to restore streams because most of
the functions of buffers have been compromised by past land use actions. For example,
restoration of the natural woody debris recruitment function of riparian areas is difficult in areas
that lack mature forested streamside vegetation (Larson, 2000). New watershed-based strat~gies
may need to be implemented that would address hydrology, water quality, and riparian functions
to successfully address management of buffer width and quality, land use controls, and
stormwater management (Booth, 2000; Homer and May, 1999). When applied in the context of
a basin-wide change, these strategies may most effectively address protection, enhancement, and
restoration of stream systems.
3.3 Fisheries Habitat and Salmonid Use in the City of Tukwila
The City of Tukwila includes one river and four tributary watercourses that have documented
salmonid use, ~nd provide salmonid habitat (Adolfson, 1999). These include the Black River,
Gilliam Creek, Southgate Creek, and Riverton Creek. Other small watercourses are located in
the City, but are not known to provide opportunities for fish use due to significant habitat
modification and isolation (Adolfson, 1999).
~'" '.......
(~~~;?
The Washington Administrative Code (WAC) states that special consideration must be given to
"measures necessary to preserve or enhance anadromous fisheries." Consideration for
. "Anadromous" fish species refers to those species that reproduce in fresh water and migrate to
salt water for some portion of their life, returning to fresh water. Some anadromous fish species
repeat the cycle while others die after one cycle. The term "fisheries" commonly refers to stocks
of fish that are managed for commercial, recreational, cultural, or ceremonial uses (WDFW,
1997).
The use of stream habitats varies by species, by developmental phase, or even by individuals
within the larger population (Reiser and Bjornn, 1979). There are, however, many needs that are
common to all anadromous fish, as well as to the overall health of many other aquatic organisms
including benthic macroinvertebrates, which are an important food source for salmonids and
other animals. These elements includes clean and cold water, suitably-sized spawning gravels
and other in-stream diversity for use as habitat, food sources, rearing habitats in proximity to
food, refuges from predators and environmental conditions such as sufficiently high flows, and
unconstrained migration routes.
In urban settings where individual functions and elements of stream habitat are not optimal for
salmonids, the combined effect of conditions in a stream basin may allow salmonids to
successfully use its habitats (Appendix A). The combined effects of the individual processes that
form and support habitat, such as input of organic material and substrate types, are sufficient to
allow some salmon ids to live and reproduce. In addition, small changes in stream function
(e.g., improving habitat access by removing a fish-passage barrier), in combination with
watershed-based restoration strategies, may provide substantial benefits to salmonid populations
in urbanized basins. "
The geographic location, topography, geology, and level of existing urbanization in the City of .
Tukwila limit the extent to which its streams can provide the necessary biological requirements
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June 2003
Page 11
for salmonid species and other aquatic organisms. The species potentially present in Tukwila
waterbodies includes all Pacific salmon (except pink salmon), bull troutIDolly Varden, coastal
resident/sea-run cutthroat trout, rainbow trout/steel head, and long-fin smelt (WDFW, 1998 and
1994; Wydoski and Whitney, 1979).
3.3.1 Green/Duwamish River
The GreenlDuwamish River flows generally north through the City of Tukwila from
approximately River Mile (RM) 5 to RM 17. The Green River flows north to become the
Duwamish River in the vicinity of the confluence of the Black River. The GreenlDuwamish
River watershed is often referred to as Water Resources Inventory Area 9 (WRIA 9) (Kerwin,
2001). Both natural and man-made rrtodifications during the early 1900's reduced the drainage
basin to its present configuration, which is one quarter of its original extent (Wamer and Fritz
1995). Presently, the GreenlDuwamish River is completely constrained by dikes, limiting the
river to its present channel.
The extensive water regime and channel modifications have resulted in existing habitat
conditions that were not historically present in the GreenlDuwamish River system. Most of the
oxbows, side channels, sloughs, and associated wetlands historically present in the City have
been filled or otherwise isolated from the river channel. Modification of the channel has changed
the natural mixing action of the estuary, resulting in a distinct salt wedge and simplified mixing
zone (Dawson and Tilley 1972 in Warner and Fritz 1995). Despite these changes, the
(Williams et al., 1975). Williams states that the lower GreenlDuwamish River is "vital to
salmon as a transition area for adaptation of migrants to salinity changes."
A fisheries investigation by Warner and Fritz (1995) identified 33 species of fish in the lower
GreenlDuwamish River system. Anadromous salmonid species such as Chinook salmon
(Oncorhynchus tshawytscha), coho salmon (0. kisutch), cutthroat trout (Salmo clarki), and bull
trout (Salvelinus confluentus) were found in the lower river within City of Tukwila boundaries.
Other salmonid species including chum salmon (0. keta), pink salmon (0. gorbuscha),
smelt
(Spirinchus thaleichthys), sticklebacks (Gasterosteus aculeatus), and mountain whitefish
(Prosopium williamson i) were also found in the lower GreenlDuwamish River (Warner and
Fritz, 1995).
3.3.2 Black River
The Black River is a remnant of the outlet of Lake Washington prior to the opening of the
Montlake Cut and the Hiram Chittenden Locks in1916. At that time, the outlet was diverted
from the Black River at the south end of Lake Washington to the Montlake Cut. The Black
River now serves primarily as a stonnwater detention basin and its flow is controlled by a flood
control dam operated by the Corps of Engineers upstream of the City limits. Although only the
mouth of the Black River is within the City, the river provides unobstructed off-channel rearing
habitat and access to other watercourses beyond the City limits. Fish presence has been
documented in the Black River (Kerwin, 2001).
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Page 12
3.3.3 .Gilliam Creek
Gilliam Creek is the largest of the watercourses within the City, draining an area of
approximately 1,800 acres between South l44th Street, Pacific Highway South, Strander
Boulevard, and the GreenlDuwamish River. Virtually the entire drainage basin has been
developed, and the stream system has been fragmented throughout its entire length by long
culverts, road crossings, development within buffer areas, channelization, and bank armoring.
Anadromous salmonid presence in Gilliam Creek is limited by a hanging culvert, with a
108-inch-diameter flap gate, passes under the dike of the GreenlDuwamish River. Resident fish
may be present in Gilliam Creek. However, this culvert largely precludes upstream fish passage
except potentially during extremely high tides and/or high instream flow levels in the
GreenlDuwamish River. While Gilli~m Creek does not likely contain suitable substrate or other
habitats for use by spawning salmonids, approximately the lower 1,500 feet may provide
foraging and rearing habitat. Anadromous salmonids have been observed in the lower section of
Gilliam Creek (Adolfson, 1999).
3.3.4 Southgate Creek
The Southgate Creek basin is roughly delineated by 35th Avenue South, South 144th Street,
Interstate 5, and the GreenlDuwamish River. The area has been entirely developed, and like
Gilliam Creek, Southgate Creek is fragmented throughout its length by long culverts, road
crossings, buffer development, and channelization.
~..,~..
(~~~: Southgate Creek is known to be used by juvenile coho and cutthroat trout (Adolfson, 1999).
Anadromous salmonid species appear to have access to Southgate Creek from the
GreenlDuwamish River to Southgate Creek through a 72-inch culvert (with no flap gate). The
lower 1,000 feet of the stream is known support fish rearing and foraging. However, spawning
habitat is limited (Adolfson, 1999). Access to the upper areas of the drainage is precluded by
several long culverts (Adolfson, 1999).
3.3.5 Riverton Creek
Riverton Creek drains an area approximately delineated by Military Road/33rd Avenue South,
South 133rd Street, East Marginal Way, and the GreenlDuwamish River. Virtually the entire
drainage basin has been developed; and many long culverts, road crossings, urban development,
and channelization have fragmented the stream habitat.
Riverton Creek flows into the GreenlDuwamish River through a 6 inch culvert and a 48-inch
culvert, both with flap gates. The lower portion of Riverton Creek creates a "moat" around an
office complex that appears to be part of a remnant oxbow or side channel.of the
GreenlDuwamish River. Upstream, Riverton Creek is generally confined to a narrow, straight
engineered stream channel. Fish presence is documented up to large set of concrete steps in the
channel, which blocks fish access upstream of Pacific Highway South (Adolfson, 1999). The
lower portions of Riverton Creek are used by coho and cutthroat trout for foraging and rearing, .
but it is not known to contain suitable substrate or other habitats for spawning (Adolfson, 1999).
Adolfson Associates. Inc.
June 2003
Page 13
(
3.3.6 Other Watercourses
The City contains many small watercourses that are remnant portions of previously existing
natural drainage systems, but are not known to support fish use (Adolfson, 1999). One such
watercourse has limited open channel area and enters a pressurized drainage conveyance system
west of Southcenter before discharging into the GreenlDuwamish River near South l80th Street.
4.0 FUNCTIONS AND VALUES OF WATERCOURSES AND
RIPARIAN AREAS IN TUKWILA
The City of Tukwila is in the process ,of updating their stream inventory. In this inventory,
watercourses will be mapped and evaiuated as to their ability to perform basic stream functions
such as contributing to stream baseflow, water quality improvement, and providing in-stream
habitat and structure.
Watercourses. in Tukwilaare primarily groundwater discharge systems. Groundwater emerges at
the bottom of hillsides and on slopes as seeps, and either form watercourses or riparian wetlands.
Riverton Creek, Southgate Creek, and Gilliam Creek are all examples of groundwater discharge
systems. Precipitation and stormwater runoff are minor contributors to stream baseflow in
Tukwila.
Water quality in the City's watercourses is largely un-documented. However, there is extensive
scientific information available for the GreenlDuwamish River. In general, temperature ranges
for Tukwila watercourses are likely to fall within the upper levels of acceptable limits for healthy
salmonid populations (Kerwin, 2001, Adolfson, 1999). As with many urban stream systems, the
likely contributors to increased stream temperatures in Tukwila are lack of shade, low baseflows,
degraded channels (high width-to-depth ratios), and warm water inputs from stormwater. Water
temperatures likely exert some influence on dissolved oxygen levels in the City's streams,
meaning that factors affecting stream temperatures also could influence dissolved oxygen levels.
The steeper sections of streams in the City are likely to have high dissolved oxygen levels, while
the slower and shallow gradient sections of streams are likely to have low dissolved oxygen
levels that may not be healthy for fish. The GreenlDuwamish River has been listed on the state
303(d) list of impaired waters for temperature and dissolved oxygen levels (Kerwin, 2001). As
for pollutants and metals, little specific information is known about the presence of toxic
substances in Tukwila's watercourses. However, the GreenlDuwamish River is listed on
Washington state's 303(d) list for mercury, metals, pH, and fecal coliform (Kerwin, 2001).
In-stream habitat structure includes substrate, LWD, pool quality and frequency, and refugia.
All species of salmonids present in Tukwila streams require clean gravel to spawn, and under
natural conditions, bank erosion and channel movement replenish stream gravel, providing new
gravel for spawning. There has been limited documentation of substrate types in Tukwila's
watercourses. However, given the extent of impervious cover in the City's basins and the likely
associated high flows, it is probable that native substrate has been altered by erosion and
sedimentation (Kerwin, 2001). Off-channel wetlands and side channels are rare in the City of
Tukwila, as most of the wetlands are disconnected from streams, and many of the stream
channels have been modified and straightened.
Adolfson Associates, Inc.
June 2003
Page 14
There is little documentation related to specific pool quality or habitat frequency in Tukwila's
streams. Studies have shown, however, that stream habitat in urban and urbanizing streams
typically includes reduced pool frequency and reduced overall habitat quality (May, et aI., 1997).
As one"example, May, et al. (1997) found a dramatic decline in habitat functions as total basin
impervious area increased above the 5 to 10 percent range. Two significant factors limiting
stream habitat structure in urban areas include the lack of pool-forming large woody debris
recruitment from riparian areas and increased frequency and magnitude of peak discharge rates,
which may scour pools and woody debris from the channel.
Riparian stream buffers in the City of Tukwila are varied in width and condition depending on
location in the watershed. Typically, the headwater and upper portions of streams in Tukwila
have intact, forested buffers. However, in the lower sections of the streams, urbanization has
encroached on the riparian zone, and the ability of buffers to perform functions such as large
woody debris recruitment or water quality improvement have been compromised.
5.0 DATA GAPS
Two data gaps were discovered in the preparation of this study. The first is the lack of best
available science literature pertaining to urbanizing watersheds and buffers needed to protect
environmentally sensitive areas in the urban areas of the Pacific Northwest.
The second data gap is the lack of detailed and specific information on each of Tukwila's
(~ , watercourses and riparian habitat. In addition to the watercourse inventory currently being
,:!;:;~) prepared by the City, an assessment of fish and wildlife use in Tukwila's streams and riparian
corridors would prove useful in making policy decisions and modifications regarding sensitive
areas. In addition, documentation of water quality parameters and buffer quality could be
included as part of this background documentation.
Adolfson Associates, Inc.
June 2003
Page 15
6.0 REFERENCES
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Center for Streamside Studies, University of Washington, Seattle, W A.
~
Booth, D.B. 1991. Urbanization and the Natural Drainage System-Impacts, Solutions, and
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Booth, D. B. 2000. Forest cover, impervious-surface area, and the mitigation of urbanization
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Castelle, AJ., C. Conolly, M. Emers, E.D. Metz, S. Meyer, and M. Witter. 1992. Wetland
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and Coastal Zone Manage. Program, Washington Dept. of Ecology, Olympia, W A.
Castelle, AJ., C. Conolly, M'. Emers, E.D. Metz, S. Meyer, M. Witter, S. Mauennann, T.
Erickson, and S.S. Cooke. 1992. Wetland Buffers: Use and Effectiveness. Publ. 92-10.
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\
City of Tukwila. 2002. Tukwila Municipal Code (TMC). Chapter 18.06.920.
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(' ....
~~~:}} Doyle, R.C., D.C. Wolf, and D.F. Bezdicek. 1975. Effectiveness of Forest Buffer Strips in
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California Water Resources Center, University of California, Davis, CA.
Gilliam, J.W., and RW. Skaggs. 1986. Natural Buffer Areas and Drainage Control to Remove
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Gregory, S.V. 1980. Effects of Light, Nutrients, and Grazing on Periphyton Communities in
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of Riparian Zones: Focus on Links Between Land and Water. BioScience 41:540-551.
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Groffman, P.M., A.J. Gold, T.P. Husband, R.C. Simmons, and W.R. Eddleman. 1990. An
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. Horner, RR, and C.W. May. 1999. Regional Study Supports Natural Land Cover Protection as
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Puget Sound streams. Center for Urban Water Res. Management, University of
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Waters. J. Environ. Qual. 14:472-478.
<
Johnson, A.W., and D. Ryba. 1992. A Literature Review of Recommended Buffer Widths to
Maintain Various Functions of Stream Riparian Areas. King County Surface Water
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Recommendations. Bellevue, W A.
Kerwin. 2001. Salmon Habitat Limiting Factors Report: WRIA 9. Washington State
Conservation Commission, Olympia W A.
Knutson, K.C. and V.L. Naef. 1997. Management Recommendations for Washington's Priority
Habitats: Riparian. Washington Department of Fish and Wildlife, Olympia W A.
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U ni versity of Washington. Seattle, Washington.
Lynch, J.A., E.S. Corbett, and K. Mussallem. 1985. Best Management Practices for Controlling.
Nonpoint-Source Pollution on Forested Watersheds. J. Soil Wat. Conserv.40:164-167.
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Washington Department of Ecology, Olympia WA.
McDade, M.H., FJ. Swanson, W.A. McKee, J.P. Farnklin, and J. Van Sickle. 1990. Source
Distances for Coarse Woody Debris entering Small Streams in Western Oregon and
Washington. Can. J. For. Res. 20:326-330.
McMillan, A. 2000. The Science of Wetland Buffers and Its Implications for the Management of
Wetlands. Masters Thesis, The Evergreen State College and Washington Department of
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';
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Wilson, L.G. 1967. Sediment Removal from Flood Water by Grass Filtration. Transactions of the
ASAEpp.35-37.
~
Wong, S.L., and R.H. McCuen. 1982. The Design of Vegetative Buffer Strips for Runoff and
Sediment Control. A Technical Paper Developed as part of a Study of Stormwater
Management in Coastal Areas Funded by Maryland Coastal Zone Management
Program. 23 p.
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Washington Press. Seattle, Washington.
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in Controlling Pollution from Feedlot Runoff. J Environ. Qual. 9:483-497.
Adolfson Associates, Inc.
June 2003
Page 22
(
APPENDIX A: EFFECTS OF ECOSYSTEM ALTERATIONS ON
SALMONIDS
Adolfson Associates, Inc.
June 2003
Appendix A
.,:~~~~:~'pj~
Increased Temperature
Water Quality
Sediment/Substrate
Habitat Access
Channel Structure
Channel Structure
(contd.)
Adolfson Associates, Inc.
June 2003
Decreased Temperature
Dissolved Oxygen
Gas Supersaturation
Nutrient Loading
Surface Erosion
Mass Failures and
Landslides
Physical Barriers
Flood Plains
Side-Channels
Pools and Riffles
Large Wood
"4,,~J#;~~i,~,jI9i~~"~tfflt~b,~~~ii~~~RrH,i~!~.~~!~~'~m~n .
Altered adult migration patterns, accelerated
development of eggs and alevins, earlier fry emergence,
increased metabolism, behavioral avoidance at high
temperatures, increased primary and secondary
production, increased susceptibility of both juveniles and
adults to certain parasites and diseases, altered
competitive interactions between species, mortality at
sustained temperatures of >73-840 F, reduced
biodiversity.
Cessation of spawning, increased egg mortalities,
susceptibility to disease.
Reduced survival of eggs and alevins, smaller size at
emergence, increased physiological stress, reduced
growth.
Increased mortality of migrating salmon.
Increased primary and secondary production, possible
oxygen depletion during extreme algal blooms, lower
survival and productivity, increased eutrophication rate
of standing waters, certain nutrients (e.g., non ionized
ammonia, some metals) possibly toxic to eggs and
juveniles at high concentrations.
Reduced survival of eggs and alevins, reduced primary
and secondary productivity, interference with feedings,
behavioral avoidance and breakdown of social
organization, pool filling.
Reduced survival of eggs and alevins, reduced primary
and secondary productivity, behavioral avoidance,
formation of upstream migration barriers, pool filling,
addition of new large structure to channels.
Loss of spawning habitat for adults; inability of juveniles
to reach overwintering sites or thermal refugia, loss of
summer rearing habitat, increased vulnerability to
predation.
Loss of overwintering habitat, loss of refuge from high
flows, loss of inputs of organic matter and large wood,
loss of sediment removal capacity.
Loss of overwintering habitat, loss of refuge from high
flows.
Shift in the balance of species, loss of deep water cover
and adult holding areas, reduced rearing sites for
yearling and older juveniles.
Loss of cover from predators and high flows, reduced
sediment and organic matter storage, reduced pool-
forming structures, r:educed organic substrate for
macroinvertebrates, formation of new migration barriers,
reduced capacity to trap salmon carcasses.
Page A-I
..!..',;'~~,~~~n!~~~lt~t~f!~ :'.n~~~H~~njfijj~};~6':?i'.:~j1f~~l~.~~~!~iJim~~ .
Reduced survival of eggs and alevins, loss of inter-
gravel spaces used for refuge by fry, reduced
macroinvertebrate production, reduced biodiversity. .
Reduced exchange of nutrients between surface and
subsurface waters and between aquatic and terrestrial
ecosystems, reduced potential for recolonizing disturbed
substrates.
)~~~;(11'~~!~tJ; . ~fl~"
Substrate
Hyporheic Zone
(biologically active
groundwater area)
Discharge
Peak Flows
Hydrology
Low Flows
Rapid Fluctuations
::~~.,
Production of Large
Wood
Production of Food
Organisms and Organic
Matter
Riparian Forest Shading
. Vegetative Rooting
Systems and
Streambank Integrity
Nutrient Modification
Chemicals
Exogenous Material
Exotic Organisms/Plants
Source: httD://www.Dsmfc.org/efh/Jan99-sec3-2.htm
Adolfson Associates. Inc.
June 2003
Altered timing of discharge related life cycle cue (e.g.,
migrations), changes in availability of food organisms
related to timing of emergence and recovery after
disturbance, altered transport of sediment and fine
particulate organic matter, reduced prey diversity.
Scour-related mortality of eggs and alevins, reduced
primary and secondary productivity, long-term depletion
of large wood and organic matter, involuntary
downstream movement of juveniles during high water
flows, accelerated erosion of streambanks.
Crowding and increased competition for foraging sites,
reduced primary and secondary productivity, increased
vulnerability to predation, increased fine sediment
deposition.
Altered timing of discharge-related life cycle events
(e.g., migrations), stranding, redd dewatering,
intermittent connections between mainstream and
floodplain rearing habitats, reduced primary and
secondary productivity.
Loss of cover from predators and high flows, reduced
sediment and organic matter storage, reduced pool-
forming structures, reduced organic substrate for
macrohlvertebrates.
Reduced production and abundance of certain
macroinvertebrates, reduced surface-drifting food items,
reduced growth in some seasons.
Increased water temperature, increased primary and
secondary production, reduced overhead cover, altered
foraging efficiency.
Loss of cover along channel margins, decreased
channel stability, increased streambank erosion,
increased landslides.
Altered nutrient inputs from terrestrial ecosystems,
altered primary and secondary production.
Reduced survival of eggs and alevins, toxicity to
juveniles and adults, increased physiological stress,
altered primary and secondary production, reduced
biodiversity. .
Increased mortality through predation, increased
interspecific competition, introduction of diseases,
habitat structure alteration.
Page A-2
( ~
APPENDIX B: LITERATURE FINDINGS, RIPARIAN
BUFFERS BY FUNCTION
Adolfson Associates, Inc.
June 2003
Appendix B
100 Castelle & Johnson, Approaches 100% particulate
2000 oraanic matter production
100 I Lvnch et aI., 1985 175-80% removal
100 I Wong & McCuen, 1982 190% removal
200 I Wong & McCuen, 1982 195% removal
Sediment Removal 200 I Horner & Mar, 1982 180% removal in grassy swale
200 Broderson, 1973 Removal of most sediment on
slopes> 50%
290 1 Gilliam & Skaggs, 1986 150% deposition
295 - 400 I Wilson, 1967 I Clay
13 I Doyle et aI., 1975 I Grass buffers.
15 Madison et aI., 1992 90% removal of NH4-N, N03-
N, and P04-P
50 1 Castelle et aI., 1992 180% pollutant removal
53 I Jacobs & Gilliam, 1985 I Most sediment removal
100 I Lvnch et aI., 1985 175-80% pollutant removal
Pollutant Removal 100 Grismer, 1981 Reduced fecal coliforms by
60%
120 Young et aI., 1980 Minimum for nutrient
reduction
"':~.;'"
860 Vanderholm & Dickey, 80% removal on a 4% slope
1978
16 - 33 Castelle & Johnson, 40-60% LOD input
2000
33 McDade et al., 1990 <50% of naturally occurring
LOD
50 I McDade et aI., 1990 160-90% of all LOD
65 - 100 Castelle & Johnson, 80-100% LOD input
2000
65 1 Murphy & Koski, 1989 195% of LOD '
Large Woody Debris . 100 I McDade et aI., 1990 185% of nat. occurring LOD
Recruitment
100 I May et aI., 1997 I Recommended minimum
150 I Harmon et aI., 1986 I Supply mo~t LOD
150 Robison & Beschta, Supply most LOD
1990
165 Van Sickle & Gregory, Minimum for LOD input
1990
330 I May et aI., 1997 1 Sensitive streams
35-80 I Brazier & Brown, 1973 160-80% shade
Stream Water Temp.
Moderation 40 Corbett & Lynch, 1985 Control stream temperature
fluctuations
Adolfson Associates. Inc.
June 2003
Page B-1
50 Broderson, 1973 Buffer widths decrease as
tree heiQhts increase
55 Steinblums et aI., 1984 Maximum angular canopy
density
55 Moring, 1975 Maintain stream temperature
if forested conditions
75 - 90 Steinblums et aI., 1984 60-80% shade
100 Beschta et aI., 1987 Minimum shade to level of old
growth forest
100 Lynch et at, 1985 Maintain stream temperatures
that are within 1 C of areas
that artHfillt forested
33 Culp and Davies, 1983 Minimutfffor healthy
communities
100 Robyet aI., 1977 Maintain benthic communities
similar to streams in fully
forested areas
100 Newbold et al., 1980 Maintain healthy benthic
communities
Maintenance of Benthic 100 Castelle & Johnson, Minimum for healthy benthic
Communities 2000 communities
100 Erman et aI., 1977 Maintain macroinvert diversity
€~'
.:.~>'<:~ >100 May et at, 1997 Benthic integrity or B-181 -
...:!.;~~:":..~;,
high in stream with >70%
upstream buffer intact
>100 Erman et aI., 1977 Macroinverts similar to
prelogged condition
100 I Gregory et aI., 1980 I Macroinvertebrate diversity
100-300 Caste lie et al., 1992 Range for most wildlife
species
Wildlife Habitat 100 - 310 Rudolph & Dickson, Reptiles & amphibians
1990
105 Groffman et at, 1990 Forested buffer for minimizing
noise impacts to wildlife
(Ac1olfson, 2002)
Adolfson Associai~s, l~c:
. June 2003
Page B-2
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',,-.'.,
ATTACHMENT C
November 8, 2002
City ofTukwila
Dept. of C..........unity Development
6300 Southcenter Boulevard, Suite 100
Tukwila, Washington 98188
Attn: Ms. Nora Gierloff
RE: CITY OF TuKWILA
GEOLOGICALLY HAZARDOUS AREAS ORDINANCE REVIEW
TuKWILA, WASHINGTON
Dear Ms. Gierloff:
This letter accompanies Landau Associates' revised draft report on our review of Tukwila's
Geologically Hazardous Areas ordinance and related information. Our services were provided in
accordance with our February 22, 2002 proposal and the City's April 3, 2002 authorization.
Several of the references cited in the report were on back order. The last of these, a map from
USGS, was just received.
Please call after you have had a chance to review the revised. draft, to discuss comments or
questions.
~
LANDAU ASSOCIATES, INC.
Wit.iam D. Evans, P.G.
Associate
11/25102 1:IPROJECT\4S7IOOS.OI0lC.,1.Ir DfI Rptcloc
WDEljas
TABLE OF CONTENTS
Page
1.0 INTRODUCTION 1-1
2.0 EXISTING CITY POLICIES AND CODES 2-1
3.0 WHAT ARE GEOLOGICALLY HAZARDOUS AREAS 3-1
4.0 WHAT IS BEST AVAILABLE SCIENCE 4-1
5.0 USING BAS IN DEVELOPING qEOLOGICALL Y HAZARDOUS AREAS REGULATIONS 5-1
6.0 SOURCES OF BAS FOR THE CITY OF TUKWILA 6-1
6.1 LOCAL INFORMATION 6-1
6.2 FEDERAL, STATE, AND LOCAL INFORMATION . 6-1
6.3 RECOMMENDED SOURCES OF GEOLOGICALLY HAZARDOUS AREAS BAS
INFORMATION 6-1
7.0 POLICY AND REGULATORY CONSIDERA 1;IONS 7-1
7.1 POLICIES 7-1
7.2 REGULATIONS 7-2
7.3 ZONING 7-4
8.0 USE OF THE REPORT
8-1
-
BffiLIOGRAPHY
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1.0 INTRODUCTION
The Washington State Growth Management Act (GMA) (RCW 36.70A) requires cities to
designate and protect critical areas (RCW 36.70A.050; WAC 365 -190; and WAC 365 -195). According
to the GMA, critical areas include:
Wetlands
Critical aquifer recharge areas
Frequently flooded areas
Geologically hazardous areas
Fish and wildlife habitat conservation areas
In 1995 the Iegislature added a new section to the GMA [RCW 36.70A.172(1)] that requires
cities to consider best available science (BAS) when adopting policies and development regulations to
designate and protect critical areas. In addition, WAC 36.70A.172(1) requires cities to give special
consideration to conservation or protection measures necessary to preserve or enhance anadromous
fisheries.
The GMA also has a requirement whereby cities and counties must update their comprehensive
plans and development regulations (RCW 36.70A.130). For Tukwila this deadline was September 1,
2002. However, the 2002 Legislature amended the deadline date to December 1, 2004, and every seven
years thereafter.
This report addresses the GMA requirements for updating comprehensive plans and development
regulations as they pertain to geologically hazardous areas within the City of Tukwila (City).
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2.0 EXISTING CITY POLICIES AND CODES
The City's December 4, 1995 Comprehensive Land Use Plan (Comp Plan) sets the policies for
managing designated critical areas. Within the Natural Environment element of the Comp Plan, Goal 4.1,
Policy 4.1.1, provides the framework for protecting natural topography and geology, and preventing
significant erosion, sedimentation and degradation of hillsides. The Comp Plan provides this protection
through the Sensitive Areas, Land Altering and Tree Regulations. . Comp Plan Goal 4.3, Policies 4.3.1
through 4.3.4, identifies the steps to be followed to reduce potential impacts and liabilities associated with
development in geologically hazardous areas..
Tukwila Municipal Code (TMC) Chapter 18.45 establishes standards for the use and development
of environmentally sensitive areas within the City. According to this code, the following geologically
hazardous areas are to be regulated:
1. Abandoned coal mines.
2. Areas of geologic instability, including:
a) Class I Areas (low landslide potential) - Slopes less than 20%.
b) Class 2 Areas (moderate landslide potential) - Slopes between 20% and 40%, underlain
by relatively permeable soil.
c) Class 3 Areas (high landslide potential) - Slopes over 20%, underlain. by relatively ~ ;~}
impermeable soil or bedrock, and all areas sloping more than 40%.
d) Class 4 Areas (very high landslide potential) - Mapped landslide areas (regardless of
slope) and areas of groundwater discharge.
3. Areas of potential seismic instability.
TMC Chapter 16.54, Land Altering, was adopted to control accelerated erosion and
sedimentation, and to supplement Uniform Building Code (UBC) requirements for excavation and filling.
TMC Chapter 18.54,. Tree Regulations, was adopted, among other things, to maintain and
enhance certain benefits provided by vegetation and promote retention of native species in sensitive areas
and their buffers.
In addition to the above, the City has a handout describing geotechnical report guidelines, and
miscellaneous permit checklists for land altering activities and construction of retaining walls over 4 ft in
height. The City uses a peer review process for development applications within Class 3 and Class 4
potential landslide areas.
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3.0 WHAT ARE GEOLOGICALLY HAZARDOUS AREAS
WAC 365-190:.080(4) Minimum Guidance' to Classify Critical Areas, defines geologically
hazardous areas as areas susceptible to one or more of the following:
I. Erosion hazard
2. Landslide hazard
3. Seismic hazard, or
4. Areas subject to other g~ological events such as coal mine hazards and volcanic hazards.
According to WAC 365-190~080( 4), cities should classify geologically hazardous areas according
to known or suspected risk, no risk, or unknown risk. WAC 365-190-080(4) also provides clarification
for each of these geologically hazardous areas, as summarized below:
I) Erosion Hazard Areas: At least those areas identified by the USDA Soil Conservation
Service as having "severe'" rill and int~~~riller()~i()n haz;u-d.
2) Landslide Hazard Areas: Those areas potentially subject to landslides based on, but not
limited to, the following:
a) Areas of historic failures
b) Areas with all three of the following characteristics
Slopes steeper than 15%
Hillsides intersecting geologic contacts with a relatively permeable
sediment overlying a relatively impenneable sediment or bedrock; and
Springs or groundwater seepage
(".
"'-...-
c) Areas that have shown movement during the Holocene epoch (within last 10,000
years) or which are underlain or covered by mass wastage of that epoch
d) Slopes that are parallel or sub-parallel to plains of weakness in subsurface
materials
e)
Slopes having gradients steeper than 80% subject to rockfall during seismic
shaking
Area' potentially unstable as a result of rapid stream incision, stream bank
'erosion, and undercutting by wave action
Areas that show evidence of, or are at risk from snow avalanches
Areas located in a canyon or on an active alluvial fan, presenting or potentially
subject to inundation by debris flow or catastrophic flooding
Any areas' with a slope of 40% or steeper and with a vertical relief often or more
feet, except areas composed of consolidated rock. A slope is delineated by
establishing its toe and top and measuring by averaging the inclination over at
least ten feet of vertical relief.
f)
g)
h)
i)
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3) Seismic Hazard Areas: These areas subject to severe risk of damage as a result of
earthquake induced ground shaking, slope failure, settlement, soil liquefaction or surface
rupture.
4) Other Geologic Events: Within the City these include, but are not necessarily limited to:
a) Volcanic hazards associated with debris flows or mudflows (and/or related
flooding within the GreenlDuwamish River Valley).
b) Mine hazards associated with known and unknown underground workings.
c) Expansive soil associated with weathered bedrock.
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4.0 WHAT IS BEST AVAILABLE SCIENCE
\,~-
WAC 365-195-900 through 925 provides local governments with a procedure for acquiring and
evaluating scientific information to determine whether it constitutes best available science (BAS), and
with guidance for demonstrating they have included BAS in their critical areas ordinance. The guidance
notes that the "cbi;tral:teristics"of a valid sCientific proce'ss to meet BAS criteria include:, peer- r~view;
methods; ,logical conclusion~. and r~asonable i";~. ,",nces; . quantitative' analysis; 'context; and references.
.~ ~ . ." . . ,". ,. . ". . " .' '. .' - - - . .,.
The guidance also identifies "sources" of scientific information to meet BAS criteria, to include: research;
monitoring; inventory; survey; modeling; assessment; synthesis; and expert opinion. The relationships
between "characteristics" and "sources" are shown in Table I, WAC 365-195,.905(5)(b).
The guidance also notes that there are nonscientific sources of relevant information, but that these
should not be used as a substitute for (pre-existing) valid scientific information.
While the above guidelines may seem straight forward, in reality the scientific information local
governments must rely on to meet BAS requirements is often incomplete or dated. Accordingly, reliance
on an expert or team of experts familiar with the available information, and its limitations, is often
required.
To demonstrate that BAS has been included in policy and rule making, the City should have:
. Policies' and regulations adopted, to protectti1efunctions and values of geologicaUyhazardous
areas. This requirement is contained in RCW 36.70A.I72, where it is applied to all critical
areas.
~.
.,.
".
In an urban land use context, geologically hazardous areas ,typically. do nothav~ measurable
"functions and 'Values." They represent landforms which, whencombined~vvith,~~rta~n
geologic, anthropogenic and/or meterQlogic' events, can .be ,a threat to lifean4property,
especially in areas where inadequate/inapP.\o't'~:~te, developmenth~o~curred. For example,
the Duwamish River VaUey bottom is mapped as a seismic hazard area due to the presence of
loose, sandy soil and a shallow groundwater table. However, these conditions only become a
hazard during seismic events when ground shaking, liquefaction or surface rupture threaten
lives and property. Accordingly, policies and regulations adopted to protect the functions and
values of geologic haZardous areas should, in our opinion, be primarily directed at life safety
issues and the.protection of property.
. Copies of, or referen to, the BAS used during geologically hazardous areas decision
making. This is a relatively straight-forward requirement that must be met for any valid
scientific study.
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. . Copies '6f, or reference to, . any. nonscientific irifotmation. used' during. geologically. bw.ardous
areas decision making, and the rationale for using suchiI1foririation. This type of infonnation
is typically site specific and often quite useful. Accordingly, the source should be
documented and any qualifiers applied.
. Steps-takerilo'address risks attributed to geologically hazardous areas. This is most often
implemented through critical areas regulations, the UBC and zoning.
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\-.
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5.0 USING BAS IN DEVELOPING GEOLOGICALLY HAZARDOUS AREAS
REGULATIONS
RCW 36.70A.250 established three Growth Management Hearings Boards to hear matters within
their .respective jurisdictions. The City of Tukwila is within the jurisdictional boundary of the Central
Puget Sound Board. Based on an article by the Assistant Attorney Generals Office (Copsey 2002) the
three boards differ in their' interpretation of RCW 36.70A.172(1) [requirement to consider BAS], as
. follows:
Easter" Washington Board: BAS "must substantially control the standard established and must be
reflected in the record."
Western Washington Board: BAS mandates "substantive consideration" to ensure "scientifically
respectable conclusions." .
Cen.tral Washington Board: BAS decisions are deferred to the local jurisdiction to determine if the
critical areas regulation "was derived from a process where the evidence of the BAS was in the
record; and was it considered substantively - was it discussed, deliberated upon and balanced
with other factors." .
Based on direction provided by the Central Puget Sound Board, it is our opinion that to meet the
Board's requirements the City will first need to compilesourc;esofrel~vatlt scientific: and nonscientific
iq.f<;)I'II\~tionregardinggeologi<;ally hazardpusareas (key sources are cited later in this report). This
information should then be "substantively considered" when updating the geologically hazardous areas
section of the City's sensitive (critical) areas ordinance and associated zoning changes (if any), and used
during subsequent permitting actions. The adopted regulations which are derived from the prpcess should
be protective of the structure, functions and values of geologically hazardous areas as they pertain to life-
safety issues and the protection ,of property. These steps should not preclude development within
geologically hazardous areas, but should require a commensurate level of protection as risk increases.
RCW 36. 70A.172( I) imposes a duty on the City to give special consideration to the protection of
anadromous fisheries. This is most often accomplished through the regulation of fish and wildlife habitat
conservation areas and wetlands. As noted above, geologically hazardous 'areas are regulat~dprimarily to
prevent loss 'of life and property caused by inappropriate development. However, geologically hazardous
areas often overlap with other critical areas, (e.g. wildlife habitat conservation areas and landslide hazard
areas are often both steep wooded slopes). For the purposes of this study, we have assumed that
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~
protection of geologically hazardous -areas, as described herein and when used in. conjunction with other
code provisions (i.e. erosion control measures required in the CitY's Land Altering code section), will be
adequately protective of anadromous fisheries. Coml;arisQn:by thcCity,ofvari()ussetbacks ~n4 bu(fers
wilL likely be 'required to verify'. that the buffers and setbacks' for ge()logicanyhazardouslU'~as arc;.not
urmecessariJy,ov~r..or. '"nqerPro~e,cti'Veas . cOJnp~ed to; required ~etbacb'. 'arid' buffets:' for' other' critiCal
areas.
11113102 Q:\SAO\FINAL LANDAU REPOR1\TIJKWlLA GEOHAZ REV RPT.DOC
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6.0 SOURCES OF BAS FOR THE CITY OF TUKWILA
6.1 LOCAL INFORMATION
At the present time the City relies on seven primary information sources for identifying
geologically hazardous areas. These sources include:
1 Geologic Hazards Evaluation, Tukwila, Washington, includes a 17 sheet map folio,
GeoEngineers Inc., date not specified, but post 1990
Tukwila Topographic Base Map, 10 foot contours, dated mid summer 1999
3 Natural Resources Conservation Service, Soil Survey Division, King County Area, 1973
King County GIS- derived sensitive areas information for flood plain, seismic, landslide and
erosion hazard areas, dates not cited
Abandoned Underground Coal Mine Hazard Assessment, Hart Crowser, May 3, 1990
Private geotechnical reports numerous authors and dates
7 Personal experience of City staff.
With the exception of sources 6 and 7, the above referenced documents are listed in the attached
Bibliography, along with other information sources reviewed during this study. The reetiirin ended list of
BAS resource materials include§ 23 'Citations.
6.2 FEDERAL, STATE, AND LOCAL INFORMATION
Other sources of information potentially relevant to the identification of geologically hazardous
areas within the City are available and were evaluated during the course of this study. Many are listed in
the attached bibliography, but not necessarily included in the list of recommended BAS information
sources for the City.
6.3 RECOMMENDED SOURCES OF GEOLOGICALLY HAZARDOUS
AREAS BAS INFORMATION
Based on a review of the sources listed in the attached bibliography, it is our opinion that the
following documents and information sources best represent BAS for designating and protecting
geologically hazardous areas within the City of Tukwila. These sources are highlighted (bolded) in the
11/13/02 Q:1SAOIFINAL LANDAU REPORT\TUKWILA GEOHAZ REV RPT.DOC 6-1
attached Bibliography. The following list also indicates where the source can be found, or if a copy was
included with this report.
Soil Survey of King County Area, Washington 1973. U.S. Dept of Agriculture, National
Resource Conservation Service. (Qut of Print. available throuflh Kine! Countv)
Mullineaux, D.R., 1965, Geologic map of the Renton quadrangle, King County,
Washington: U.S. Geological Survey, Geologic Quadrangle Map GQ-40S, scale 1:24000.
(J<co1Jv'inclUlJedwlth: i'e.tibrtJ
Mullineaux, P.R., 1961, Qeology ~fthel~ento~, A\lbuni, and Black Diamond quadrangles, .
Washington: U.S. Geological Survey, Professional Paper 672, scale 1 :24000. fJ'ctJrfViifClUiJed.
with'YejjiJ,.t~ '
. .
Tubbs, D.W.~ 1974, Landslides arid associated damage during early 1972 in part of west-
central King County, Washington: U.S. Geological Survey, Miscellaneous Investigations Series
Map 1-852-B, scale 1 :48000. (JcoDviiiiHud~t1WM"feiOortj
Waldron, H.H., 1962, Geologic map of the Des Moines quadrangle, Washington: U.S.
Geological Survey, Geologic Quadrangle Map GQ-1S9, scale 1:24000. (JcoDv'includedwith .
C!QJort~
Yount, J.C., Minard, J.P., and Dembroff, G.R., 1993, Geologic map of surficial deposits in
the Seattle 30' by 60' quadrangle,Washin~on: U.S. Geological Survey, Open-File Report OF-93-
233, scale 1:100000. (J cOtJV'ifiCliidiif1'\tiiltr'evort) .'
Aerial Photos.,.. Public and Private Sources. (e. fl. Walker and Associates. Seattle. W A)
City ofTukwila., 1999. Tukwila Topographic Base Map, 10 ft. contours
City ofTukwila, Washington. fCitv Owned)
GeoEngineers, Inc., Post 1990. ,Geologic Hazards Evaluation, Tukwila, Washington.
City of Tukwila, Washington. fCitv Owned),
King County Department of Natural Resources, 1998. King County, Washington Surface Water
Design Manual. September. (Available throutzh Kine! Countv).
King County sensitive areas map folio, GIS-derived sensitive areas information, includes geologically
hazardous areas mapping information. King County, Washington. (Available throuflh Kin~
Countv)
Washington State Department of Natural Resources. 2002. Geologic Map of Washington -
Northwest Quadrant, Geologic Map GM-SO. (lcoDv included with report)
Washington State Office of Community Development. 2002., Citations of Recommended
Sources of Best Available Science for Designating and Protecting Critical Areas. March 2002.
(Available online at: www.oed. wa. .v:ov/info/lfld/flrowth/bas/BAS Citations Final.pdt)
Project specific reports submitted by applicant. Cite as nonscientific if information has not been
peer reviewed. (Citv Owned)
Local Inform including but not limited to, photographs, diary entries, written and verbal
11113102 Q:\SAO\FINAL LANDAU REPORT\TUKWILA GEOHAZ REV RYT.DOC
6-2
'statements, etc., provided the source is documented and information is not used in lieu of other
p f valid scientific data. C(L Owned).
Department of Ecology., 1993., Slope Stabilization and Erosion Control Using Vegetation
A Manual of Practice for Coastal Property Owners. Publication 93 -30. (Available online at:
hiln://www.ecv.wa.gov/programs/sea/pubs/93-30/index.html)
Department of Ecology. 1993. Vegetation Management: A Guide for Puget Sound Bluff
Property Owners. Publication 93 -31.
(Available online at: httn: //www.ecv.wa.gov/ programs /sea/nubs /93 -3 /intro.html)
Department of Ecology. 1995. Surface Water and Groundwater on Coastal Bluffs: A Guide
for Puget Sound Property Owners. Publication 95 -107.
(Available online at: httn: /www.ecv.wa.c-ov /programs /sea/pubs /95- 107 intro.html)
Palmer, S.P., Schasse, H.W., and Norman, D.K., 1994, Liquefaction susceptibility for the
Des Moines and Renton 7.5- minute quadrangles, Washington: Washington Division of Geology
and Earth Resources, Geologic Map GM -41, scale 1:24000. (1 copy included :with report)
Walsh, T.J., Pringle, P.T., 1993. Suggestions for Growth Management Planning for Seismic
Hazards. Division of Geology and Earth Resources, Washington Department of Natural
Resources.Washington Geology, vol. 22, no 2. (1 copy included with report)
Hart Crowser, 1990. Abandoned Underground Coal Mine Assessment, Tukwila,
Washington. City of Tukwila, Dept. of Comm. Development Planning Division. (City Owned)
Walsh, T. J. 1994. Growth management planning for abandoned coal mines. Washington
Geology, vol. 22, no. 2, pp. 33 -34. (1 comiricluded with report)
Uniform Building Code, 1997., International Conference of Building Officials Vol. 2,
Chapter 18 pp 43 -50. (Available through City of Tukwila. Planning Division)
The private geotechnical reports in City files and the personal experience of City staff can
continue to be used. However, as noted previously, the limitations associated with non -peer reviewed
and/or nonscientific data should be carefully evaluated and documented in conjunction with use on any
given project.
1
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"
Landslide Hazard Areas: The principal goals and policies for high landslide hazard areas
are essentially those currently stated in the Comp Plan.
Seismic Hazard Areas: The principal goals within high seismic hazard areas should
follow those outlined in the UBC to protect lives, with less emphasis on preservation; of
property. Policies which flow from these goals should focus on code sections dealing
with life safety issues and critical areas.
Other Geologically Hazardous Areas: The principal goals within high: volcanic "and mine
hazard areas, :to' °protect lives With less emphasis on preservation f property. The
principal goal within areas underlain by expansive soil/bedrock should be to minimize
damage tai, infraspucture. Policies which flow from these goals should focus fit;"•, life
safety, infrastructure l reserVatiOa critical areas.
7.2 REGULATIONS
Regulations that address geologically hazardous areas are currently contained in TMC Chapters
16.54 (erosion) and 18.45 (all others). Suggested changes and additions to the code, as related to
geologically hazardous areas, are summarized below:
1. Co nsideration should be given to addressing all geologically hazardous areas; within. one:
code This could be accomplished in Chap tt+ir 18:45, or by.cross reference'to the
erosion control requirements contained in Chapter 16:54. Since erosion control is closely
linked to sedimentation and protection of anadromous fisheries, we suggest that either or
both of these code sections note that consideration has been given to anadromous
fisheries and that the City's requirements are adequately protective.
2. Consideration should be given to substantially revising existing Chapter 18.45 to follow
the form outline in WAC 365 -190: Alternatively, using either the Office of Community
Developments' (OCD) Model Code Recommendations for Designating and Protecting
Critical Areas (chapters on General Provisions and Geologically Hazardous Areas)
(currently 2 draft, May 2002), or Critical: Areas fcir.Pieree County (chapters on General
Provisions, Use and Activity Regulations, Landslide Hazard Areas, Seismic Hazard
Areas, Mine Hazard Areas and Erosion Hazard Areas) (currently draft, March 2002)
could be used as a "template" for Tukwila's geologically hazardous areas. regulation.
Either would require modification to meet Tukwila's specific circumstances, but may
save time over revising the existing code.
The OCD model code is available to local jurisdictions as a "guide and provides
performance measures and references to BAS. The OCD model code lacks descriptive
figures, but is generally consistent with the Washington State Department of Ecology
(Ecology) Stormwater Management Manual for Western Washington (August 2001) and
other critical areas regulations that may overlap with those addressing geologically
hazardous areas.
To our knowledge, Pierce County is the only major county in the state with a draft critical
areas ordinance out for public review at this time (available on line at the Pierce County
web site). The draft Pierce County Ordinance is structured differently than OCD's model
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code, but has useful figures which help describe buffers, setbacks, etc. The Pierce
44
County draft also uses a phased approach "letter ",."verification" and "report") to address
proposed land uses within geologically hazardous areas. In our opinion, the phased
approach is desirable, as it allows for an increasing level of effort roughly proportional to
'risk: WAC 365 190- 080(4)(b) describes risk categories that should be addressed within
geologically hazardous areas. The draft Pierce County code also includes detailed
geotechnical report requirements and a plat/title notification form.
3. Consideration should be given to including Uniform Building Code (UBC) (1997 or
latest version) provisions for top and toe of slope setbacks. The Pierce County draft
ordinance incorporates UBC requirements.
4 Consideration should be given to revising the current 20 'percent slope threshold
downward to 15 percent. This would be consistent with the value cited in WAC 365-
190- 080(4).
:5. Overall, the post 1990 GeoEngineers, Inc. Geologic Hazards. Evaluation: still: appears; to
identify those areas of the City :subject. to the greatest landslide, erosion and seismic
hazards.. Accordingly, it is our opinion that the G eoEngineers study 'does not need to be
updated: at this time.
6. Consideration should be given to incorporating newly adopted ,geologist „licensing
t y provisions, into the City's geologically hazardous areas regulation. Laws relating to
AL Crir co geologists are covered in 18.220 RCW and WAC 308 -15, and include provisions for
licensing geologists, engineering geologists and hydrogeologists. After July 1, 2002,
geologists must be licensed to practice in the State of Washington. If the City adopts
such a provision, we suggest tailoring' the roles of the geologist and geotechnical engineer
to ,the•speeific :area of interest. For example, a geotechnical engineer could likely
complete a seismic evaluation in the Southcenter area without significant geologist input,
however, it would likely require a team of a qualified geologist and engineer to complete
the study of a complex landslide.
7. Assuming the existing code is modified to meet GMA requirements contained in RCW
36.70A.172, consideration should be given to incorporating- a -:phased :approach to the
investigation of geologically hazardous areas, as noted previously. In our opinion, this
allows focusing of resources where they are most needed, accommodates the risk
evaluation cited in WAC 365- 190- 080(4)(b), and takes into,consideration the inherent
inaccuracies of geologic and other maps. It is also our opinion that the use of outside
peer review for development applications within Class 3 and `Class 4 areas 'should be
continued, until such time as the City hires in -house geotechnical expertise. The peer
review process is one of the fundamentals for achieving BAS. The use of outside peer
review for applications within Class 2 areas could also be better evaluated using a phased
approach.
8. For the future subdivision of land, consideration should be given to placing geologically
hazardous areas, and their buffers, into separate tracts. This applies primarily to landslide
hazard and mine hazard areas. On existing parcels, consideration should be given to
including these areas in conservation easements. We suggest continuation of the City's
practice of plat and title notification within geologically hazardous areas.
9. Consideration should be given to including expansive soil/weathered bedrock to the
City's list of geologically hazardous areas, within the "other hazards" category. We are
t t
aware of one location, west of Interurban Avenue South between SR 405 and I -5, that
contains expansive soil /weathered bedrock. Further development is that area, or the use
11/13/02 ()MAMMAL LANDAU REPORTITUKWILA GEOHAZ REV RPT.DOC 7-3
of excavated material from that area for structural fill elsewhere in the City, would
represent a geologic hazard. This area could be noted on an overlay map, addressed in
the code text, or both.
10. Whenever nonscientific information is used in the study of geologically hazardous areas,
consideration should be given to the method(s) of data collection and evaluation. We
suggest use of a form that accompanies non scientific information to document the nature
and source.
7.3 ZONING
The use of zoning to address; geologically hazardous areas may be viable in some limited
locations. However, the dynamic nature of geologic processes and somewhat rigid rules imposed by
zoning may result in unintended consequences. For example, requiring large residential lots within steep
slope areas may appear desirable. However, low densities that go with large lots often preclude
installation of adequate storm and sanitary sewer facilities, which ultimately can lead to more frequent
slope stability problems.
Therefore, it is our opinion that accurate geologically hazardous areas overlay maps, combined
with a phased investigation/design approach, will be the best approach to meet the City's Comp Plan and
BAS goals. The maps and supporting information should be periodically updated. We also suggest that
the geologically hazardous areas mapping information be put into a GIS format for accuracy, ease of use,
and the ability to update as needed.
11/13/02 Q:\SAOIFINAL LANDAU REPORTITUKWILA GEOHAZ REV RPT.DOC 7-4
8.0 USE OF THE REPORT
This report was prepared for the exclusive use of the City of Tukwila for specific application to
the geologically hazardous areas ordinance review. Within the limitations of scope, schedule, and budget,
the analyses and findings presented in this report were prepared in accordance with generally accepted
geological and geotechnical engineering principles and practices in the King County area at the time this
report was prepared. We make no other warranty either express or implied.
We appreciate this opportunity to be of service to the City of Tukwila. Please contact us if you
have any questions or if we can be of further service.
LANDAU ASSOCIATES, INC.
William D. Evans, P.G.
Associate
Dennis R. Stealer, P.E.
Principal
WDE/DRS /jas
11/13/02 Q:1SAO\FINAL LANDAU REPORTITUKWILA GEOHAZ REV RPT.DOC 8 -1 D
BIBLIOGRAPHY
CITATIONS FOR GEOLOGICALLY HAZARDOUS AREAS
TUKWILA, WASHINGTON
FEDERAL MAPS/INFORMATION
EROSION HAZARD AREAS
USDA. 1973. Soil Survey of King County Area, Washington. U.S. Department of Agriculture, National
Resource Conservation Service.
LANDSLIDE HAZARD AREAS
Godt, J.W. 1997 Digital compilation of Landslide Overview Map of the Conterminous ,United States.
Scale 1:4,000,000. U.S. Geological Survey Open File Report 97 -289.
Miller, R.D. 1973. Map Showing Relative Slope Stability in Part of West- Central King County,
Washington. U.S. Geological Survey Miscellaneous Investigations Series Map I- 852 -A.
Mullineaux, D.R. 1965. Geologic Map of the Renton Quadrangle, King County, Washington. Scale
1:24,000. U.S. Geological Survey Geologic Quadrangle Map GQ -405.
Mullineaux, D.R. 1961. Geology of the Renton, Auburn, and Black Diamond Quadrangles,
Washington. Scale 1:24,000. U.S. Geological Survey Professional Paper 672.
Tubbs, D.W. 1974. Landslides and Associated Damage During Early 1972 in Part of West Central
King County, Washington. Scale 1:48,000. U.S. Geological Survey Miscellaneous Investigations
Series Map I- 852 -B.
USGS. 1995. Des Moines, Wash. 7.5 Minute Series (Topographic). Des Moines Quadrangle. N4722.5-
W12215/7.5. Scale 1:24,000. U.S. Geological Survey. Denver, Colorado.
USGS. 1994. Renton, Wash. 7.5 Minute Series (Topographic. Renton Quadrangle. N4722.5-
W 12207.5/7.5. Scale 1:24,000. U.S. Geological Survey. Denver, Colorado.
USGS. 1975. Slope Map of Part of West- Central King County, Washington. Scale 1:48,000. U.S.
Geological Survey Miscellaneous Investigations Series Map I- 852 -E.
Wold, R. L., Jr., and C. Jochim. 1989. Landslide Loss Reduction: A Guide for State and Local
Government Planning. Federal Emergency Management Agency. Washington, DC.
Waldron, H.H. 1962. Geologic Map of the Des Moines Quadrangle, Washington. Scale 1:24,000.
U.S. Geological Survey Geologic Quadrangle Map GQ -159.
Yount, J.C., J.P. Minard, and G.R. Dembroff. 1993. Geologic Map of Surficial Deposits in the
Seattle 30' by 60' Quadrangle, Washington. Scale 1:100,000. U.S. Geological Survey Open -File
Report 93 -233.
11/5/02 1: Project \457 \005.0I0\Bibliography Tukwila 1
Yount, J.C. and H.D. Gower. 1991. Bedrock Geologic Map of the Seattle 30' by 60'
gi P f y Quadrangle,
Washington. Scale 1 :100,000. U.S. Geological Survey Open -File Report 91 -147.
SEISMIC HAZARD AREAS
Chleborad, A. F. and R.L. Schuster. 1998. "Ground Failure Associated With the Puget Sound Region
Earthquakes of April 13, 1949, and April 29, 1965." In: Assessing Earthquake Hazards and Reducing
Risk in the Pacific Northwest. Rogers, A. M., T.J. Walsh., W.J. Kockelman, and G.R. Priest (eds.). U.S.
Geological Survey Professional Paper 1560, Vol. 2, pp. 373 -440.
Gower, H.D., J.C. Yount, and R.S. Crosson. 1985. Seismotectonic Map of the Puget Sound Region,
Washington. Scale 1:250,000. U.S. Geological Survey Miscellaneous Investigations Series Map I -1613.
Kockelman, W. J. 1998. "Techniques for Reducing Earthquake Hazards." In Assessing Earthquake
Hazards and Reducing Risk in the Pacific Northwest. Rogers, A.M., T.J. Walsh, W.J. Kockelman, and
G.R. Priest (eds.). U.S. Geological Survey Professional Paper 1560, Vol. 2, pp. 479 -496.
May, P. J. 1998. "Earthquake Risk Reduction Prospects for the Puget Sound and Portland, Oregon
Areas." In: Assessing Earthquake Hazards and Reducing Risk in the Pacific Northwest. Rogers, A.M.,
T.J. Walsh, W.J. Kockelman, and G.R. Priest (eds.). U.S. Geological Survey Professional Paper 1560,
Vol. 2, pp. 497 -515.
Perkins, J. B. and K.K. Moy. 1998. "Liability for Earthquake Hazards or Losses and its Impacts on the
Cities and Counties of Washington." In: Assessing Earthquake Hazards and Reducing Risk in the Pacific
( Northwest. Rogers, A.M., T.J. Walsh, W.J. Kockelman, and G.R. Priest (eds.). U.S. Geological Survey
Professional Paper 1560, Vol. 2, pp. 543 -545.
Rogers, A.M., T.J. Walsh, W.J. Kockelman, and G.R. Priest. 1996. "Map Showing Known or Suspected
Faults with Quaternary Displacement in the Pacific Northwest." In: Assessing Earthquake Hazards and
Reducing Risk in the Pacific Northwest. Rogers, A.M., T.J. Walsh, W.J. Kockelman, and G.R. Priest
(eds.). Scale 1:2,000,000. U.S. Geological Survey Professional Paper 1560, Plate 1.
Rogers, A.M., T.J. Walsh, W.J. Kockelman, and G.R. Priest (eds.). 1998. Assessing Earthquake Hazards
and Reducing Risk in the Pacific Northwest. U.S. Geological Survey Professional Paper 1560, Vol. 2,
545 pp., 6 plates.
MINE HAZARD AREAS
VOLCANIC HAZARD AREAS
Casadevall, T.J. (ed.). 1991. First International Symposium on Volcanic Ash and Aviation Safety
Programs and Abstracts. U.S. Geological Survey Circular 1065.
TSUNAMI HAZARD AREAS
Good, J. W. 1995. Tsunami Education Planning Workshop Findings and Recommendations. U.S.
National Oceanic and Atmospheric Administration Pacific Marine Environmental Laboratory. NOAA
Technical Memorandum ERL PMEL -106. 41 pp., Hazards, Vol. 14, No. 2, p. 79 -83.
11/5/02 I: Project457\005.o10\Bibliography Tukwila 2
STATE. /LOCAL MAPS AND INFORMATION
GENERAL
Aerial Photos Public and Private Sources
City of Tukwila. 1999. Tukwila Topographic Base Map. 10 ft contours. City of Tukwila,
Washington.
Copsey, Alan D. 2002. The Designation and Protection of Critical Areas Under the Growth
Management Act. May 9.
GeoEngineers, Inc. Post -1990. Geologic Hazards Evaluation, Tukwila, Washington. City of
Tukwila, Washington.
King County Department of Natural Resources. 1998. King County, Washington Surface Water
Design Manual. September.
King County. Sensitive Areas Map Folio, GIS- Derived Sensitive Areas Information. King County,
Washington.
DNR. 2002. Geologic Map of Washington Northwest Quadrant. Geologic Map GM -50.
Washington State Department of Natural Resources.
OCD. 2002. Citations of Recommended Sources of Best Available Science for Designating and
Protecting Critical Areas. Washington State Office of Community Development March.
Project specific reports submitted by applicant. Cite as nonscientific if information has not been
peer reviewed.
Local Information, including but not limited to, photographs, diary entries, written and verbal
statements, etc., provided the source is documented and information is not used in lieu of other
valid scientific data.
EROSION HAZARD AREAS
Ecology. 1993. Slope Stabilization and Erosion Control Using Vegetation: A Manual of Practice for
Coastal Property Owners. Washington State Department of Ecology. Publication 93 -30.
LANDSLIDE AREAS
Ecology. 1995. Surface Water and Groundwater on Coastal Bluffs: A Guide for Puget Sound
Property Owners. Washington State Department of Ecology. Publication 95 -107.
Ecology. 1993. Vegetation Management: A Guide for Puget Sound Bluff Property Owners.
Washington State Department of Ecology. Publication 93 -31.
Ecology. 1978 -1980. Slope Stability Maps and Coastal Zone Atlas. Vols. 1 -12, maps, scale 1:24,000.
Washington State Department of Ecology.
11 /5/02 1: Project \457 \005.010 \Bibliography Tukwila 3
Gerstel, W. J., M.J. Brunengo, W.S. Lingley, Jr., R.L. Logan, and T.J. Walsh. 1997. "Puget Sound
Bluffs: The Where, Why, and When of Landslides Following the Holiday 1996/97 Storms." Washington
Geology. Vol. 25, No. 1, pp. 17 -31.
Thorsen, G. W. 1989. "Landslide Provinces in Washington." In: Engineering Geology in Washington.
Washington State Department of Natural Resources, Division of Geology and Earth Resources. Bulletin
78, Vol. I, pp. 71 -89.
SEISMIC HAZARD AREAS
DNR. Digital Geology of Washington State. Scale 1:100,000. Washington State Department of Natural
Resources, Division of Geology and Earth Resources.
Miller, R.D. 1974. Map Showing Relative Compressibility in Part of West- Central King County,
Washington. U.S. Geological Survey Miscellaneous Investigations Series Map I- 852 -C.
Palmer, S. P. 1994. "Revision to the 1994 Uniform Building Code Seismic Zone Map for Washington
and Oregon." Washington Geology. Vol. 22, No. 2, p. 35.
Palmer, S.P., H.W. Schasse, and D.K. Norman. 1994. Liquefaction Susceptibility for the Des
Moines and Renton 7.5 Minute Quadrangles, Washington. Scale 1:24,000. Washington State
Department of Natural Resources, Division of Geology and Earth Resources. Geologic Map GM-
41.
Walsh,. T.J. and P.T. Pringle. 1993. Suggestions for Growth Management Planning for Seismic
Hazards. Washington State Department of Natural Resources, Division of Geology and Earth
Resources.
MINE HAZARD AREAS
Hart Crowser. 1990. Abandoned Underground Coal Mine Assessment, Tukwila,Washington.
Prepared for: City of Tukwila, Department of Community Development Planning Division.
LaSalata, F.V., M.C. Menard, and J.T. Walsh. 1985. Inventory of Abandoned Coal Mines in the State of
Washington. Washington State Department of Natural Resources, Division of Geology and Earth
Resources. Open File Report 84 -6.
Walsh, T.J. 1994. "Growth Management Planning for Abandoned Coal Mines." Washington
Geology. Vol. 22, No. 2, pp. 33 -34.
VOLCANIC HAZARD AREAS
Pringle, P. T. 1994. "Volcanic Hazards in Washington A Growth Management Perspective."
Washington Geology. Vol. 22, No. 2, pp. 25 -33.
Waldron, H. H. 1989. "Volcanic Hazards in Washington." In: Engineering Geology in Washington.
Washington State Department of Natural Resources, Division of Geology and Earth Resources. Bulletin
78, Vol. I, pp. 91 -96.
11/5/02 1: Project\457 \005.010\Bibliography Tukwila 4
TSUNAMI HAZARD AREAS
Manson, C.J. and L. Walkling. 1998. Tsunamis on the Pacific Coast of Washington State and Adjacent
Areas A Selected, Annotated Bibliography and Directory. Washington State Department of Natural
Resources, Division of Geology and Earth Resources. Open File Report 98-4.
OTHER RESOURCES
GENERAL
American Institute of Professional Geologists. 1993. The Citizens' Guide to Geologic Hazards, Part Ill.
pp. 116.
LANDSLIDE AREAS
Hollingsworth, R. A., and G.S. Kocs. 1981. "Soil Slumps and Debris Flows: Prediction and Protection."
Bull. Assoc: of Engrg. Geologists. Vol. 18, pp. 17 -28.
Kockelman, W.J. 1986. "Some Techniques for Reducing Landslide Hazards." Bull. Assoc. of Engrg.
Geologists. Vol. 23, pp. 29-49.
Schuster, R. L. 1989. "Long -Term Landslide Hazard Mitigation Programs: Structure and Experience
From Other Countries." Bull. Assoc. of Engrg. Geologists. Vol. 26, pp. 109 -133.
Schuster, R.L., and R.L. Krizek R. L. (eds.). 1978. Landslides, Analysis, and Control. National
Research Council, Transportation Research Board. Special Report 176, 234 pp.
International Conference of Building Officials. 1997. 1997 Uniform Building Code. Vol. 2, Chapter
18 pp. 2-43 2 -50.
Wieczorek, G.F. 1984. "Preparing a Detailed Landslide- Inventory Map for Evaluation and Reduction."
Bull. Assoc. of Engrg. Geologists. Vol. 24, pp 337 -342.
SEISMIC HAZARD AREAS
Berlin, G. L. 1980. Earthquakes and the Urban Environment. CRC Press, Boca Raton, Florida.
International Conference of Building Officials. 1997. 1997 Uniform Building Code. Vol. 2, Chapter 16
pp. 2 -1— 2 -38.
Note: Bolded sources used as Best Available Science for Tukwila.
11/5/02 I: Project \457 \005.010\Bibliography Tukwila 5
ATTACHMENT D
In addition to the Best Available Science Reports prepared by Adolfson Associates
(Attachments A and B) and Landau Associates, Inc. (Attachment C) the Planning
Commission and /or City Council was presented with the following information:
Washington State Department of Fish and Wildlife Inventory Data Memorandum from
Gary Schulz dated July 16, 2004 regarding Habitat and Species Mapping Data Products
May 20, 2004 Memorandum from Teresa Vanderburg, Adolfson Associates, regarding
Sensitive Areas Ordinance Update
Classification of Wetlands and Deepwater Habitats of the United States, Fish and
Wildlife Service, U.S. Department of the Interior, December, 1979, pages 1 -13, 19 -21.
Memorandum dated June 4, 2004 on Sensitive Area Buffer Analysis, prepared by Carol
Lumb.
Washington State Wetland Mitigation Evaluation Study, Phase 2: Evaluating Success,
January 2002, excerpts: Executive Summary, pages 74 -93.
A Literature Review of Recommended Buffer Widths to Maintain Various Functions of
Stream Riparian Areas, prepared by King County Surface Water Management Division,
February, 1992 by Alan Johnson and Diane Ryba.
Watercourse and Wetland Buffer Comparison Charts, November, 2004, prepared by
Adolfson Associates.
Memorandum dated November 18, 2004 from Gary Schulz to Carol Lumb regarding
Proposed Revision to Tukwila Watercourse Rating System.
Comments Received on the Planning Commission Recommended Draft Sensitive Areas
Ordinance:
John Song, property owner, City of Tukwila
Chad Armour, Wetland Consultant
Richard Robohm, Department of Ecology with Draft Appendix 8 -C, Guidance on
Widths of Buffers and Ratios for Compensatory Mitigation to be used with the
Western Washington Wetland Rating System; Draft Appendix 8 -E, Rationale for
Draft Guidance on Buffers and Other Protection for Wetlands; and Draft
Appendix 8 -F, Rationale for the Draft Guidance on Ratios for Compensatory
Mitigation to be Used with the Wetland Rating System
Lynn Kohn, Department of Community, Trade and Economic Development
Brooke Alford, City resident
q: \1 -04 SAO Update\Attachment D.doc
AIUIACHMENT E
City of Tukwila
Steven M. Mullet, Mayor
Department of CommunifJI Detlelopment
Steve Lancaster, Director
INFORMATION MEMO
Date:
Subject:
Mayor Mullet, Members of the City Council ~
Steve Lancaster, Director, Department of Community Development '
Teresa Vanderburg, Director of Natural Sciences, Adolfson Associat
December 9, 2004
DEPARTURES FROM BEST AVAILABLE SCIENCE
To:
From:
ISSUE
The City is required by the Growth Management Act to include "Best Available Science" in
adopting Comprehensive Plan policies and critical area (i.e. sensitive area) regulations.
BACKGROUND
As required by the 1990 Growth Management Act (GMA) and RCW 36.70A.l72(l), the City of Tukwila
is in the process of updating its Sensitive Areas Ordinance (SAO) to include "best available science" to
"protect the functions and values of critical areas." The best available science rule (WAC 365-195-900
through 365-195-925) states that cities and counties must include "best available science" when
developing policies and development regulations to protect the functions and values of critical areas and
must give "special consideration" to salmonids.
GMA requires consideration of and planning toward 13 goals, including as one of those goals -protection
of critical areas. As stated in the Washington Administrative Code (WAC), these 13 goals are not listed
in any order of priority. It is up to the local jurisdiction to tailor its approach to GMA and balance its
response to the 13 goals. It is recognized by CTED that these goals may conflict and difficult decisions
must be made in order to address each of the goals in a way that meets the needs of the local setting and
local government.
In 2002, the City retained Adolfson Associates Inc. (Adolf son) to assist in updating those regulations
using "best available science." This memorandum has been provided by Adolfson to assist the City
Council in its discussions of wetland regulations and document for the record the findings of fact.
Overview of City's Process
In 2002, Adolfson prepared draft reviews of the "best available science" related to streams and wetlands
in the City ofTukwila. Over 50 scientific references were evaluated to summarize the science of stream
and wetland protection and management. During this same period of time, the City of Tukwila undertook
a wetland and stream inventory and prepared GIS maps illustrating the approximate location of these
features. Adolfson reviewed this inventory of streams and wetlands, which included wetland ratings
based upon the City's existing wetland rating system.
.
6300 Southcenter Boulevard, Suite #100 · Tukwila, Washington 98188 · Phone: 206-431-3670 · Fax: 206-431-3665
Memorandum: Departures from Best Available Science
December 9, 2004
Major technical resources evaluated in 2002 and 2003 included:
City of Tukwila's Geographical Information System (GIS) maps and new wetland inventory
(2002 and 2003);
Citations of Recommended Sources for Designating and Protecting Critical Areas (OCD 2002);
Washington State Department of Community, Trade and Economic Development's (CTED)
Critical Areas Assistance Handbook (2003);
Draft Freshwater Wetlands in Washington State, Volume 1 A Synthesis of the Science (Ecology,
August 2003).
Adolfson provided two technical reports for the City of Tukwila outlining the "best available science
City of Tukwila Best Available'Science Issue Paper: Watercourses (Adolfson, June 2003)
City of Tukwila Best Available Science Issue Paper: Wetlands (Adolfson, June 2003).
During preparation of these reports, Adolfson reviewed red -lined code revisions made by City staff with
the assistance of their Urban Environmentalist. Adolfson provided guidance and engaged in discussions
with City staff regarding possible changes to wetland and stream regulations to better incorporate "best
available science." Adolfson recommended a number of code modifications, many of which were
incorporated into the draft SAO by Planning Staff.
DISCUSSION
Departures from the Washington State Department of Ecology's Recommendations
The City's proposed SAO has included "best available science" in its development of the Sensitive Areas
Ordinance as required by the rule. However, there are three areas within the wetland regulations
proposed by Tukwila, which may be considered departures from the recommendations of the Washington
State Department of Ecology (Ecology). These three areas were identified in a draft letter from Ecology
dated October 4, 2004 prepared by Mr. Richard Robohm, and include: 1) the City's wetland rating
system, 2) the wetland buffers proposed, and 3) mitigation ratios. The draft comments received on
October 4, 2004, were later finalized in a letter received from Ecology on November 12, 2004. The
following section of this memorandum describes both the scientific and non scientific information used as
a basis for departures from the recommendations described in Ecology's review letter.
Wetland Ratine System
In 2002, Adolfson began work with City of Tukwila staff to update its wetland regulations as required
under GMA. Adolfson provided our review of the "best available science" for the City of Tukwila based
upon scientific references available in 2002 and 2003 and the State of Washington Department of
Community, Trade and Economic Development (CTED) Critical Areas Assistance Handbook (2003).
The Example Ordinance provided in the Handbook recommends use of the state wetland rating system
published by the Washington State Department of Ecology (Ecology) in 1993. However, Ecology staff
were not recommending use of this older state rating system since the Department was in the process of
developing a new four- tiered rating system. Because the new Ecology rating system was not available
yet, and in order to meet the GMA deadline of December 1, 2004, the City chose to move forward with
revisions to its existing three tiered wetland rating system. This system has worked well for the City for
many years to rank wetlands according to high, moderate and low function and value.
2
q: \1 -04 SAO Update \Council Review \Departures.doc
Memorandum: Departures from Best Available Science
December 9, 2004
In addition to the requirement for use of "best available science" the WAC requires certain types of
protection for wetlands as critical areas. WAC 365-190-080 (l)(a) requires that a wetland rating system
be developed by local jurisdictions to rank wetlands according to their relative function, value and
uniqueness. As per this section of the WAC, the local jurisdiction should consider the following:
I) Washington State four-tier wetland rating system:
2) Wetland functions and values;
3) Degree of sensitivity to disturbance;
4) Rarity; and
5) Ability to compensate for destruction or degradation.
The City ofTukwila elected to revise it~ existing three-tiered wetland rating system in order to better rank
its wetlands. The wetland rating system is based upon diversity of habitats, wetland size, vegetation, and
the presence or absence of significant waterfowl or priority species. The revised system separates
wetlands according to habitat function and value, degree of sensitivity to disturbance (e.g., presence of
significant waterfowl or priority species) and ability to compensate for degradation (e.g., presence or
absence of habitat diversity). The rating system does not use rarity, such as the presence or absence of
bogs or fens, since no such systems are found in the City of Tukwila. Although this system does not use
a hydro-geomorphic approach to consider wetland functions such as flood control, water quality
improvement, etc., the City's three-tiered rating system is scientifically based, does rank wetlands from
higher to lower function and value, and therefore meets the requirements under WAC 365-190-180.
Wetland size is used as a proxy to rank the ability of the City's wetlands to provide area-related functions
such as stormwater storage, flood storage and water quality improvement. The City has developed a full
package of regulations and standards for wetlands that works interactively with the three-tiered wetland
rating system as revised.
In August 2004, Ecology revised and published final guidance on the state's new four-tiered wetland
rating system. This new rating system results in the same number of wetland categories (Category I
through IV) as the old state rating system, but uses a new scientific approach based upon the hydro-
geomorphic (water and landscape elements) or HGM functions ofthe wetland. This new system is
considerably more complicated to apply since it seeks to evaluate multiple functions and values of
wetlands related to its position in the landscape. Although the guidance arrived very late in the GMA
update process, Adolfson and City planning staff reviewed the new Ecology wetland rating system.
Adolfson staff and City staff met on site with Mr. Richard Robohm of Ecology on November 19,2004 to
review use of the new Ecology wetland rating system and its application to the City of Tukwila.
Adolfson recognizes that the new state rating system is more comprehensive in its evaluation of wetland
functions using the HGM methods. However, Adolfson and City staff determined, due to the higher level
of complexity in the rating form and increased opportunity for subjectivity between evaluators using the
form, to recommend continued use of the City's revised three-tiered system. While it is acknowledged
that the new 2004 Ecology wetland rating system may be appropriate for ranking wetlands at a state or
county level where there is a wide diversity of wetland types, highly urban areas such as Tukwila find that
a more simplistic system makes better practical and scientific sense given the lesser diversity of wetland
types. For example, using the new state wetland rating system, there are likely no Category I wetlands in
the City of Tukwila and possibly only a few Category II.
Adolfson and City staff believe that wetland functions and values will be protected, as mandated under
the GMA, with the City rating system as revised. The non-scientific information used to support this
decision is outlined above, and includes City staff's need for an easily and consistently applied rating
system that minimizes staff and developer misinterpretation. Adolfson and staff do not identify any
3
q:\l-04 SAO Update\Council Review\Departures.doc
Memorandum: Departures from Best Available Science
December 9, 2004
potential risks to the functions and values of wetlands by using the revised three-tiered rating system for
wetlands. This system adequately ranks wetlands found within the City limits. According to the City's
code, wetland functions must be assessed if a proposed project will impact wetlands. Baseline
information and quantitative data collection or synthesis of existing data is required from an applicant
proposing wetland impact and mitigation for wetlands in the City; this information is required for both the
project impact zone and the proposed mitigation site. The City chooses to rely on its requirements for
wetland function assessment in order to evaluate wetland impacts and proposed mitigation rather than
adopt the State's rating system to provide both a ranking of wetlands and a functional assessment method.
Wetland Buffer Widths
The wetland buffers in the City ofTuk'Yila's proposed SAG range from 50 to 100 feet, which are at the
low end of the range of buffer widths supported by the scientific literature. The science recommends
wetland buffers ranging from 25 to 300 feet or more, depending upon the functions being considered and
the particulars of the scientific studies cited. In fact, buffers as small as 10 feet were found to be effective
for some functions, such as water quality improvement (Ecology, 2003). In general, however, the
science alone says that bigger buffers are better. In a natural setting, the wider the buffer, the more
opportunity there is for the buffer to perform its functions.
As summarized in the Draft Freshwater Wetlands in Washington State, Volume I-A Synthesis of the
Science (Ecology, August 2003), effective wetland buffer widths range from 25 feet for minimal
protection to 350 feet for maximum protection. Typically, larger buffers 150 feet to 300 feet or more are
needed to protect wildlife habitat for all species, including sensitive wildlife species. However, it is also
recognized that in an urban setting, larger buffers may not be available or fully functioning due to existing
roads and infrastructure or degraded existing conditions.
It is clear from the literature that wetlands and buffers perform recognized functions to different degrees.
The differing levels of functional performance can be attributed to, among other things, the physical
condition of the wetland and/or buffer; the position ofthe system in the surrounding landscape; the
intensity of disturbance that the system experiences; and the level of disturbance the system has
experienced in the past (Ecology, 2003). Science further recognizes that the most effective way to protect
the functions of individual wetlands and their buffers is to evaluate each wetland/buffer complex on a
case-by-case basis using site-specific information. The scientific literature also supports the idea that if
case-by-case wetland regulation/protection is not used, a prescriptive approach (the approach where
standard buffers are applied to broad categories of wetlands) must protect the most vulnerable systems
and should therefore err on the side of protecting more rather than less in terms of both acreage and
function.
Clearly, it is not feasible for local governments to regulate wetlands on an individual basis. Governments
need to be fiscally responsible and need to offer some degree of certainty to citizens and developers in
terms of land use. Further, city planners normally do not have the expertise or time to analyze each
wetland individually. Therefore most local governments use a prescriptive approach to wetland
protection. The City of Tukwila has historically employed a prescriptive approach to assigning buffers to
wetlands and is proposing to modify that approach by increasing the prescribed standard buffer widths for
Class 2 and 3 wetlands, in order to increase wetland protection.
To determine appropriate buffer widths in the City of Tukwila, GIS mapping of inventoried wetlands was
evaluated along with the type, location and variety of wetlands known to exist within the City limits and
its urban growth area. The wetland inventory undertaken by the City's Urban Environmentalist
effectively tripled the number of identified wetlands from 21 identified in 1991 to 55 wetlands identified
in the 2003 wetland inventory. Detailed GIS maps were prepared for the City to designate these potential
wetland areas. Most of the wetlands are isolated in a highly urbanized setting and occur as isolated
4
q:\1-04 SAO Update\Council Review\Departures.doc
Memorandum: Departures trom Best Available Science
December 9, 2004
habitats in the urban landscape. Most of the wetlands are scrub-shrub or forested wetlands and have
disturbed buffers dominated by invasive species, such as Himalayan blackberry. Using the new state
wetland rating system, there are likely no Category I wetlands in the City of Tukwila and possibly only a
few Category II wetlands. The majority of wetlands in the City do not provide significant wildlife
habitat. They provide good habitat for birds and in some cases waterfowl (Le., Tukwila Pond) and small
mammals. The Priority Habitat and Species Maps for the City of Tukwila do not document the presence
of any sensitive species or priority habitats other than salmon ids that use the Green River.
Based upon a synthesis of the available scientific literature, Adolfson recommended that the buffer widths
for wetlands be increased in width from the current SAO to better protect wetland functions. The
proposed buffer widths in the draft SAO range from 50 feet to 100 feet. While lower than what is
recommended by Ecology, these buffers lie within the range provided by "best available science" for
minimal protection of wetland functions. The draft SAO also requires an increase in the buffer width
when the wetland is determined to be particularly sensitive to disturbance or the development creates
unusually severe impacts. In addition, the City's current stormwater management requirements are
anticipated to provide some of the buffer functions through use of stormwater detention, retention and
runoff flow control from urbanized development.
The City also included a buffer reduction policy in the new SAO. The scientific literature does not
provide a sharp quantitative distinction between the width of an effectively functioning buffer and the
width of an ineffective buffer. For example, the scientific literature supports the idea that a smaller, well-
vegetated buffer can outperform a degraded standard width buffer. Enhancement of a degraded buffer, if
successful, can result in improvement to buffer functions such as sediment retention and wildlife habitat.
On a case-by-case basis, where buffers are currently degraded, it may be possible to enhance buffer
conditions and reduce the proposed standard buffer widths for wetlands and still protect the integrity of
the wetland and its associated buffer. The City of Tukwila desires to provide an incentive to landowners
who have wetlands with degraded buffers and therefore has retained a buffer width reduction policy for
degraded buffers that can be improved through enhancement measures.
The City recognizes that its wetland buffer widths and buffer reduction policy may be considered a
departure from some of the best available science on the record and from the recommendations according
to Ecology. The potential risks to the functions and values of wetlands would be to wildlife habitat
functions provided in the wetland buffer (where the science says larger buffers are warranted) and to
pollutant removal functions of the buffer. Significant habitat for wildlife is not currently available in the
City of Tukwila. Citizens in the City have established a backyard wildlife program, which has received
national recognition by the National Wildlife Federation, that may help offset impacts to wildlife. In
addition, the City's steep slope regulations in its SAO, while focused primarily on protecting slope
stability, may protect some habitat, since habitat remaining is located on the steep valley walls. Pollutant
removal functions of the buffer indicate that between 60 to 70 percent sediment and pollutant removal
would be anticipated for a buffer range of 50 to 100 feet, respectively (Desbonnet et aI., 1994; Ecology,
2003). The City's storm water regulations require the installation of storm water management systems in
developments. These systems would provide the initial removal of pollutants and sediments before storm
water enters buffers or wetlands.
Wetland Mitilmtion Ratios
Wetland mitigation ratios supported by scientific research indicate that greater than I: I replacement of
wetland is necessary since many wetland mitigation projects have historically failed to meet all
performance criteria (Ecology 2003; National Academy of Sciences [NAS] 2001). The intent of
mitigation ratios greater than 1: I is to offset lost wetland functions over time, to compensate for the
failure of some mitigation projects, to offset the temporal loss in wetland functions between the impacted
5
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Memorandum: Departures from Best Available Science
December 9, 2004
wetland and the new mitigation wetland, and to address the fact that some wetland types are more
difficult to restore than others. Also, high mitigation ratios are often employed as a policy tool to
discourage impact by developers. The scientific record alone does not support mitigation ratios greater
than approximately 2:1 or 3:1. As a result, use of higher ratios becomes, in part, a policy decision.
Mitigation ratios studied nationwide by the NAS indicated that a 1.5: 1 ratio would be required to achieve
the lost wetland area using information on compliance from four states, as long as functional equivalency
is achieved (NAS, 2001). The NAS committee concluded that some types of wetlands can be
successfully restored or created (i.e., freshwater emergent marshes) and others are more difficult (Le.,
forested wetlands) or cannot be restored (i.e., bogs and fens). The scientific research indicates that the
main reasons that wetland mitigation projects often fail is: I) they were improperly installed, 2) the
design did not consider watershed issues relating to water flow, 3) subsequent follow-through by
regulatory agencies was lacking, and 4),mitigation projects were not monitored over a long enough period
oftime (5 years or longer) (Ecology, 2003; NAS 2001). The NAS committee recommended the
following important points: 1) impacts to wetlands that cannot be restored or created should be avoided,
2) installation of mitigation projects should occur prior to or concurrent with impacts, 3) use of a
mitigation ratios of more than 1:1,4) consideration of watershed issues and functional assessment in
developing the mitigation area, 5) long-term monitoring of the mitigation (over 5 years) and 6) long-term
stewardship of the site after monitoring is complete (NAS, 2001). The City's SAO is consistent with the
first four points of the NAS recommendations and provides for a five year monitoring period with the
ability to extend the period if the performance standards of the monitoring program have not been
achieved.
The City of Tukwila has chosen to strengthen requirements for mitigation and increase the mitigation
ratio for enhancement to ensure successful mitigation without requiring larger mitigation ratios.
Alterations are only permitted to the City's lowest rated wetlands (Type 3). Alterations are not permitted
to the City's highest rated wetlands (Type I) and only minimal alterations are permitted to Type 2
wetlands. The City has chosen to use mitigation ratios of 1.5: I for wetland creation and restoration and
3: 1 for wetland enhancement. While these ratios are less than those recommended by Ecology, they fall
within the range of the science and NAS recommendations. The City requires that an applicant avoid
impacts to a wetland first, minimize and then compensate according to mitigation ratios and requirements.
The monitoring period has been increased from three to five (5) years to track mitigation projects longer.
The City requires use of a functional assessment to look at the functions of the wetland being impacted
and the mitigation provided. Mitigation projects must be installed prior to or concurrent with
development impacts under most circumstances. Adolfson and City staff finds no risk associated with the
mitigation ratios proposed. However, the success of mitigation will be monitored and tracked by the
City's Urban Environmentalist and adaptive management strategies will be employed should the record
show that changes are warranted.
Small Wetlands
The SAO revises the exemption criteria for small wetlands. Currently, the Director may exempt
from compensatory mitigation isolated wetlands that are l,OOO square feet or smaller in area
which are low in value according to the rating methodology used in the 1991 Sensitive Areas
Ordinance (SAO). The revised SAO provides an exception for wetlands l,OOO square feet and
less that do not meet any of the criteria for Type 1 or 2 wetlands - the exception language has
been tightened to link the ability to alter a wetland to those that do not meet any of the Criteria
for Type 1 or 2 wetlands rather than retain the more nebulous language of wetlands that are "low
in value."
6
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Memorandum: Departures ftom Best Available Science
December 9, 2004
The purpose of the wetland exemption for small wetlands is to provide an appropriate balance
between protection of wetlands and the cost and burdens of code compliance and administration.
The goal is to focus staff review time and applicant mitigation effort on development proposals
affecting wetlands important to the City on a landscape-wide analysis level. The functions and
values of wetlands diminish as wetlands become smaller and more disturbed in the urban
environment. By definition, these wetlands have the lowest functions and values of all wetlands
identified in the City. Based on the City's experience in reviewing development applications
over the thirteen years since adoption of its original SAO, the small wetlands in Tukwila that fit
this size exception are typically low in habitat value and other wetland functions. Most of these
wetlands are isolated in the landscape due to man-made infrastructure (i.e. roads, buildings,
utility easements), are surrounded by highly disturbed land uses, and are often dominated by
invasive plants such as Himalayan blackberry, ivy, and/or lawn grasses.
The scientific record generally indicates that all wetlands regardless of size have some degree of
function and value. However, the best available science also recognizes that certain functions
such as floodwater retention, habitat for animals with large home ranges, and pollutant removal
are area-related and that larger wetlands have a greater capacity than smaller wetlands to perform
these functions (NAS, 200l). In some cases, small wetlands can provide important amphibian
habitat in King County, especially if these wetlands contain open water or seasonally ponded
water (Richter and Azous, 2001). However, it is also recognized that small habitats that are
fragmented in a landscape due to existing urban development become increasingly isolated and
ofless value to wildlife. Wetlands that are 1000 square feet or less and do not meet any of the
criteria for Class 1 or 2 wetlands, are not likely to provide important functions and values to the
City in the overall landscape context. The risk associated with the small wetland exception is
that some wetlands will be filled and no mitigation required. Given the compliance and staffing
costs involved in review and monitoring wetland mitigation projects, the risks must be balanced
against the cost for administration of the SAO.
Departures from the CrED Example Ordinance recommendations on Watercourse
Regulations
The City's proposed SAO has included "best available science" in its development of the watercourse
regulations as required by the rule. However, there is one area within the watercourse regulations
proposed by Tukwila, which may be considered a departure from the recommendations of the CTED
Example Ordinance related to buffers. As required by law, the draft ordinance was sent to the
Washington Department ofFish and Wildlife (WDFW) for state review and comment. The City received
no comment letter from WDFW on the watercourse regulations. This section ofthe memorandum
describes the proposed buffers on watercourses in the City as a departure from the state's guidance and
some of the best available science on the record.
Buffers on Watercourses
In the June 2003 Issue Paper, Adolfson summarized the best available science related to streams
(watercourses) and the functions and values of these waters in the City ofTukwila. This paper also
described the functions and values of riparian areas and buffers in protection of streams and fish habitat.
To meet the requirements for best available science and "special consideration for anadromous fisheries",
7
q:\1-04 SAO Update\Council Review\Departures.doc
Memorandum: Departures from Best Available Science
December 9,2004
the City has developed a new stream rating system based upon the presence or absence of salmon ids and
has increased stream buffer widths. The scientific literature on riparian buffer widths effective in
protecting watercourses is similar to that described in the wetland buffer section of this memo. In
general, the best available science states that riparian buffers of 100 to 200 feet wide provide most of the
potential functions to protect streams. For example, the Tri-County effort to protect federally-listed
salmon ids under the Endangered Species Act determined that 115 feet should be required on salmonid-
bearing streams in urban areas to protect stream functions. Riparian buffer widths necessary to protect
wildlife species using these areas vary greatly depending upon individual wildlife species and are
typically larger than 100 feet, up to 300 feet or more (Knutson and Naef, 1997).
Riparian buffer widths recommended by WDFW range from 250 feet on Type I and 2 streams to 150 feet
on Type 4 and 5 streams with low mass ,wasting potential (CTED, 2003). The City has proposed to
increase its riparian buffer widths to: 10'0 feet on Type 2 watercourses, 80 feet on Type 3 watercourses,
and 50 feet on Type 4 watercourses. Type I watercourses refer only to the Green River, which will be
protected under the City's Shoreline Management regulations. The City recognizes that its riparian buffer
widths are at the low end of the range of science and depart from the state's recommendations. The
reason for this decision relates to the urban character of the City, including existing development and
piping of streams in the valley floor. Most of the streams in the City do not provide habitat for
anadromous fish, other than the Green River. The ability to provide larger buffers is impaired by existing
development and infrastructure. The risk associated with the City's selection of lower stream buffer
widths is offset, in part, by storm water requirements, which serve to protect stream flow and water
quality. Further, the City continues to demonstrate its support for watershed-wide habitat improvement
and recovery of anadromous fisheries by its active participation in the Water Resource Inventory Area
(WRIA) 9 - Lower Green River watershed program sponsored by King County. Several significant
habitat restoration sites are located within the City and owned by the City.
Summary of Findings
In conclusion, Adolfson and City planners have worked together to develop and revise the SAO to
include the "best available science" and meet the GMA update goals. Our summarizing points are as
follows:
. The City has developed a revised SAO that includes "best available science" and balances the
City's need to meet all 13 goals ofGMA.
. The proposed SAO provides certainty to the City's residents and developers and ease of
implementation for City staff.
. The City recognizes that is a highly urbanized environment and has limited wildlife habitat.
. The City has implemented other programs to assist in the protection of wetlands and habitat
including its storm water management rules and the citizen initiated backyard wildlife habitat
program.
. The City continues to demonstrate its support for watershed-wide habitat improvement and
recovery of anadromous fish by its active participation in the Water Resource Inventory Area
(WRIA) 9 - Lower Green River watershed program sponsored by King County.
8
q:\I-04 SAO Update\Council Review\Departures.doc
."
City of Tukwila
Washington
Ordinance No.
AN ORDINANCE OF THE Lu f COUNCIL OF THE CITY OF TUKWILA,
WASffiNGTON, AMENDING ORDINANCE NO. 1758 AND .lU LE 18,
"ZONING," UPDATING THE DEFINmONS REGARDING SENSITIVE
AREAS; PROVIDING FOR SEVERABILITY; AND ESTABLISHING AN
b.t'.I:'J~Ln VB DATE.
WHEREAS, Ute state Growth Management Act (GMA) requires the adoption of
develvt'ment regulations that protect the functions and values of sensitive areas,
including wetlands, watercourses, fish and wildlife habitat conservation areas, and
areas of potential geological ins!abiIity; and
WHEREAS, RCW 36.70A.172 requires local governments to include the best
available science (BAS) in developing policies and development regulations to protect
the functions and values of sensitive areas, and to give special considerations to
conservation or protection measures necessary. to preserve or enhance anadromous
fisheries; and
WHEREAS, the City has revised its sensitive area regulations to address Best
Available Science, which has resulted in the need to revise certain of the definitions that
apply to environmentally sensitive areas to ensure consistency; and
WHEREAS, the Planning Commission held an open house on May 12, 2004 and a
public hearing on May 20, 2004 to obtain public input and reviewed the sensitive area
regulations at public meetings on April 29, June 10, June 24, July 22, and September 16,
2004; and
WHEREAS, the City Council held a public open house on C;;'t'~;;....ber 28, 2004 and
public hearing on October 4, 2004 to obtain public input on the sensitive area
regulations as recommended by the Plarming Commission and reviewed the sensitive
area regulations at public meetings on September 20, October 25, November 1,
November 8, November 23, and December 6, 2004; and
WHEREAS, state agencies, including the Department of Community, Trade and
Economic Devel:-'t'ment, Department of Ecology and Department of Fish and Wildlife
received notification and copies of the draft regulations for review at least 60 days prior
to adoption;
WHEREAS, the. City received comments from the Department of Community,
Trade and Economic Development, and the Department of Ecology and addressed
these comments in the ordinance or as departures;
NOW, THEREFORE, THE LU i COUNCIL OF THE CITY OF TUKWlLA,
WASHINGTON, DO ORDAIN AS FOLLOWS:
Section 1. Definitions Amended. Ordinance No. 1758, as codified at TMC Section
18.06, is hereby amended to read as follows:
~,:.;;., ....: ','
Definitions 18.06 12110/04
.J>age 1 of 31
~
Chapter 18.06
D~J:'lNITIONS
'-"
Sections:
18.06.005 General Definitions
18.06.010 Abandoned Mine Areas
18.06.015 Access Road
18.06.017 Adaptive Management
18.06.018 Adjacent
18.06.020 Adult Day Care
18.06.025 Adult Entertainment Practices
18.06.035 Alley
18.06.037 Amusement Device
18.06.045 Applicant
18.06.050 Area, Site
18.06.055 Areas of Potential Geologic Instability
18.06.060 Basetnent
18.06.065 Bed-and-Breakfast Lodging
18.06.069 Best Available Science
18.06.070 Best Management Practices
18.06.071 Binding Site Improvement Plan
18.06.072 Block
18.06.073 Boarding House
18.06.074 Brew Pub
18.06.075 Buffer
18.06.080 Building
18.06.085 Building, Accessory
18.06.090 Building Area
18.06.095 Building, Detached
18.06.097 Building FOv~t'.L;nt
18.06.100 Building Height
18.06.105 Building Line
18.06.110 Building, Nonconforming
18.06.115 Building Permit
18.06.118 Bulk Retail
18.06.120 Bus Station
18.06.125 Caliper
18.06.130 Canopy
18.06.135 Canopy Cover
18.06.137 Cargo Container
18.06.140 Certified Arborist
18.06.145 Oearing
18.06.150 Oinic
18.06.152 Oosed Record Appeal
18.06.155 Oub
18.06:165 Comprehensive Plan
18.06.173 Convalescent/Nursing Home
18.06.175 Cooperative Parking Facility
18.06.178 Correctional Institution
18.06.180 Coverage
18.06.183 Cul-De-Sac
18.06.185 Curb-Cut
18.06.190 Dangerous Waste
18.06.195 Day Care Center
18.06.196 Daylighting
18.06.198 Dedication
18.06.200 Density Transfer
18.06.202 Department
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18.06.203 Design Criteria
18.06.204 Design Guidelines
18.06.205 Designated Facility Zone
18.06.210 Development
18.06.215 Development Area
18.06.220 DiameterjDiameter-Breast-Height (D.B.H.)
18.06.225 Director
18.06.230 District
18.06.235 District, Overlay
18.06.237 Dormitory
18.06.240 Driveway
18.06.245 Dwelling, Manufactured or Mobile Home
18.06.250 Dwelling, Multi-Family
18.06.255 Dwelling, Single-Family
18.06.260 Dwelling Unit
18.06.264 Engineer, Geotechnical
18.06.266 Engirieer, Professional
18.06.268 Engineering, Geotechnical
18.06.270 Essential Public Facilities
18.06.275 Essential Root Zone
18.06.280 Essential Use
18.06.285 Essential Street, Road, Right-of-Way or Utility
18.06.290 Extremely Hazardous Waste
18.06.300 Family Child Care Home
18.06.310 Fence
18.06.315 Filling
18.06.318 Final Plat
18.06.320 Fire Lane
18.06.325 Floor Area
18.06.340 Fraternal Organization
18.06.345 Garage, Private
18.06.353 General Retail
18.06.355 Geologist
18.06.365 Grade
18.06.370 Grading
18.06.380 Groundcover
18.06.385 Hazardous Substance
18.06.390 Hazardous Substance Processing or Handling
18.06.395 Hazardous Tree
18.06.400 Hazardous Waste
18.06.405 Hazardous Waste Storage
18.06.410 Hazardous Waste Treatment
18.06.415 Hazardous Waste Treatment and Storage Facility, Off-Site
18.06.420 Hazardous Waste Treatment and [;~V~CLge Facility, On-Site
18.06.425 High Impact Environment
18.06:430 Home Occupation
18.06.435 Hospital
18.06.440 Hotel
18.06.445 Impervious Surface
18.06.450 Infrastructure
18.06.453 Integrated Site
18.06.454 Internet Data/Telecommunication Center
18.06.460 Junk Yard
18.06.465 Kennel
18.06.470 Laboratory, Medical And Dental
18.06.473 Land Surveyor
18.06.475 Land-Altering Activity
18.06.480 Land-Altering Permit
;'
Definitions 18.06 12/10/04
Page 3 of31
18.06.485 Landscape Architect
18.06.490 Landscaping or Landscaped Areas
18.06.493 Lease
18.06.495 Loading Space
18.06.500 Lot
18.06.505 Lot Area
18.06.510 Lot, Corner
18.06.515 Lot Coverage
18.06.520 Lot Depth
18.06.525 Lot Frontage
18.06.530 Lot Lines
18.06.535 Lot, Interior
18.06.540 Lot, Through
18.06.545 Lot Width
18.06.550 Low Impact Environment
18.06.555 Major Adjustment
18.06.560 Mall
18.06.565 Manufactured/Mobile Home Park
18.06.567 Manufacturing
18.06.568 Mass Transit Facilities
18.06.570 Mean High Water Mark
18.06.575 Mining And Quarrying
18.06.580 Minor Adjustment
18.06.581 Mitigation
18.06.583 Modular Home
18.06.585 Motel
18.06.590 Nonconforming Use
18.06.592 Office
18.06.593 Open Record Appeal
18.06.594 Open Record Hearing
18.06.595 Open Space
18.06.600 Open Space Tract
18.06.605 Ordinary High Water Mark
18.06.610 Parcel
18.06.611 Park and Ride
18.06.613 Parking, Commercial
P
18.06.615 Parking Space
18.06.617 Pawnbroker
18.06.618 Performance Bond or Guarantee
18.06.620 Performance Standards
18.06.625 Person
18.06.630 Plan
18.06.632 Planned Residential Development (PRD)
18.06.633 Planning Commission
18.06.635 Plat
18.06.636 Preliminary Plat
18.06.637 Principal Building
18.06.638 Private Access Road
18.06.640 Property Owner
18.06.645 Protected Tree/Protected Vegetation
18.06.650 Protection Measure
18.06.655 Protective Fencing
18.06.657 Public Meeting
18.06.660 Reach
18.06.665 Recreation Space
18.06.670 Recreation Space, Covered
18.06.675 Recreation Space, Uncovered
18.06.685 Residence
Definitions 18.06 12/10/04 Page 4 of 31
. .
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18.06.687 Restaurant
18.06.688 Restaurant, Fast Food
18.06.689 Right-of-Way
18.06.690 River Channel
18.06.695 River Environment
18.06.697 Roadway
18.06.700 Sanitarium
18.06.705 Screening
18.06.706 Secure Community Transitional Facility
18.06.707 Self Storage Facility
18.06.708 Senior Citizen Housing
18.06.710 Sensitive Area Buffer
18.06.715 Sensitive Area Regulated Activities
18.06.720 Sensitive Areas
18.06.725 Sensitive Areas Ordinance
18.06.730 Sensitive Area Tract or Easement
18.06.735 Servite Station
18.06.740 Setbacks
18.06.743 Shelter
18.06.745 Shelter Station
18.06.750 Shopping Center, Planned
18.06.760 Shoreline
18.06.765 Shoreline Zone
18.06.767 Short Plat
18.06.768 Short Subdivision
18.06.769 Short Subdivision Committee
18.06.770 Sign
18.06.775 Significant Tree
18.06.780 Site
18.06.785 Solid Planting
18.06.790 Story
18.06.795 Street
18.06.800 Structure
18.06.805 Structural Alteration
18.06.810 Studios
18.06.813 Subdivision
18.06.815 Substantial Construction
18.06.820 Surveyor
18.06.823 Theater
18.06.825 Tract
18.06.830 Trailer Court or Park
18.06.835 Trailer, Travel
18.06.840 Transit Center
18.06.845 Tree
18.06.850 Tree Gearing Permit
18.06~855 Turbidity
18.06.860 Understory Vegetation
18.06.863 Usable Floor Area
18.06.865 Use
18.06.870 Use, Accessory
18.06.875 Use, Conditional
18.06.880 Use, Permitted
18.06.885 Use, Primary or Principal
18.06.890 Use, Unclassified
18.06.895 Unlisted Use
18.06.900 Utilities
18.06.905 Variance
18.06.910 Vegetation
"~
.
Definitions \8.Q6 \2/\0/04
Page 5 of31
18.06.915 Vehicles
18.06.918 Warehouse
18.06.920 Watercourse
18.06.922 Wetland
18.06.924 Wetland edge
"'y 18.06.926 Wetland or Watercourse, Constructed
18.06.928 Wetland, Emergent
18.06.930 Wetland, Forested
18.06.932 Wetland, Isolated
18.06.933 Wetland, Regulated
18.06.934 Wetland, Scrub -Shrub
18.06.935 Yard
18.06.940 Yard, Front
18.06.945 Yard, Rear
18.06.950 Yard, Second Front
18.06.955 Yard, Side
S 18.06.005 General Definitions
Except where specifically defined in this chapter, all words used in this title shall
carry their customary meanings. Words used in the present tense include the future,
2/ and the plural includes the singular; the word "he" or "his" shall also refer to "she" or
"her," the word shall., is always mandatory, the word "may" denotes a use of
discretion in making a decision; the words "used" or "occupied" shall be considered as
though followed by the words "or intended, arranged or designed to be used or
j
occupied."
18.06.010 Abandoned Mine Areas
"Abandoned mine areas" means those areas directly underlain by, adjacent to, or
affected by mine workings such as adits, tunnels, drifts, or air shafts.
18.06.015 Access Road
"Access road" means that portion of a driveway which provides access to one or
more parking lot or area, provides access to more than one property or lot, or may
provide internal access from one street to another. This shall not include that portion of
-s% driveways whose primary function is to provide direct access to adjacent parking
spaces and which, as a secondary function, also provides circulation within parking
areas.
18.06.017 Adaptive Management
"Adaptive management" means the use of scientific methods to evaluate how well
regulatory and non regulatory actions protect a sensitive area.
18.06.018 Adjacent
"Adjacent" means lying near or close to; sometimes, contiguous; neighboring.
Adjacent implies that the two objects are not widely separated, though they may not
actually touch.
18.06.020 Adult Day Care
"Adult day care" means a facility which provides supervised daytime programs
where up to six frail and /or disabled adults can participate in social, educational, and
recreational activities led by paid staff and volunteers.
18.06.025 Adult Entertainment Establishments
A. "Adult entertainment establishments" means adult motion picture theaters,
adult drive -in theaters, adult bookstores, adult cabarets, adult video stores, adult retail
stores, adult massage parlors, adult sauna parlors or adult bathhouses, which are
defined as follows:
1. "Adult bathhouse" means a commercial bathhouse which excludes any
person by virtue of age from all or any portion of the premises.
Definitions 18.06 12/10/04 Page 6 of 31
2. "Adult bookstore" means a retail establishment in which:
a. 30% or more of the "stock -in- trade" consists of books, magazines,
posters, pictures, periodicals or other printed materials distinguished or characterized
by an emphasis on matter depicting, describing or relating to "specified sexual
activities" or "specified anatomical areas and /or
b. Any person is excluded by virtue of age from all or part of the
premises generally held open to the public where such material is displayed or sold.
3. "Adult cabaret" means a commercial establishment which presents go-
go dancers, strippers, male or female impersonators, or similar types of entertainment
and which excludes any person by virtue of age from all or any portion of the premises.
4. "Adult massage parlor" means a commercial establishment in which
massage or other touching of the human body is provided for a fee and which excludes
any person by virtue of age from all or any portion of the premises in which such
service is provided.
5. "Adult motion picture theater" means a building, enclosure, or portion
thereof, used for presenting material distinguished or characterized by an emphasis on
matter depicting, describing or relating to "specified sexual activities" or "specified
anatomical areas" for observation by patrons therein.
6. "Adult retail store" means retail establishment in which:
a. 30% or more of the "stock -in -trade" consists of items, products or
equipment distinguished or characterized by an emphasis on or simulation of "specified
sexual activities" or "specified anatomical areas and /or
b. Any person is excluded by virtue of age from all or part of the
premises generally held open to the public where such items, products or equipment
are displayed or sold.
7. "Adult sauna parlor" means a commercial sauna establishment which
excludes any person by virtue of age from all or any portion of the premises.
8. "Adult video store" means a retail establishment in which:
a. 30% or more of the "stock -in -trade" consists of prerecorded video
tapes, disks, or similar material distinguished or characterized by an emphasis on
matter depicting, describing or relating to "specified sexual activities" or "specified
anatomical areas and /or
b. Any person is excluded by virtue of age from all or any part of the
premises generally held open to the public where such prerecorded video tapes, disks
or similar material are displayed or sold.
13. "Specified anatomical areas" means:
1. Less than completely and /or opaquely covered human genitals, pubic
region, buttock, or female breast below a point immediately above the top of the areola;
2. Human male genitals in a discernibly turgid state even if completely or
opaquely covered.
C. "Specified sexual activities" means:
1. Acts of human masturbation, sexual intercourse or sodomy; or
2. Fondling or other erotic touching of human genitals, pubic region,
buttock or female breast; or
3. Human genitals in a state of sexual stimulation or arousal.
D. "Stock -in- trade" means:
1. The dollar value of all products, equipment, books, magazines, posters,
pictures, periodicals, prerecorded video tapes, discs, or similar material readily
available for purchase, rental, viewing or use by patrons of the establishment, excluding
material located in any storeroom or other portion of the premises not regularly open to
patrons; or
2. The number of titles of all products, equipment, books, magazines,
posters, pictures, periodicals, other printed materials, prerecorded video tapes, discs, or
similar material readily available for purchase, rental, viewing or use by patrons of the
i establishment, excluding material located in any storeroom or other portion of the
premises not regularly open to patrons.
Definitions 18.06 12/10/04 Page 7 of 31
18.06.035 Alley
.:4:::-. "Alley" means a public thoroughfare or way usually having a width of not more
than 20 feet which affords only a secondary means of access to abutting property and is
not intended for general traffic circulation.
18.06.037 Amusement Device
"Amusement device" means a structure such as a ferris wheel, roller coaster or
climbing wall.
18.06.045 Applicant
;:',V, "Applicant" means a property owner or a public agency or public or private utility
which owns a right -of -way or other easement, or has been adjudicated the right to an
;:4- easement pursuant to RCW 8.12.090, or any person or entity designated in writing by
the property or easement owner to be the applicant for a project permit, and who
requests approval for a project permit.
-.r:::; 18.06.050 Area, Site
r
"Site area" means the total two dimensional horizontal area within the property
lines excluding external streets.
jr'; 18.06.055 Areas of Potential Geologic Instability
"Areas of potential geologic instability" means those areas subject to potential
landslides and /or potential seismic instabilities.
18.06.060 Basement
s'% "Basement" means that portion of a building between floor and ceiling which is all
or partly below grade. If the finished floor level directly above a basement is more than
two feet above grade for more than 20% of the total perimeter or is twelve feet above
grade as defined at any point, such basement shall be considered as a story.
18.06.065 Bed and Breakfast Lodging
"Bed-and-breakfast" means an owner occupied dwelling unit that contains guest
rooms where lodging is provided for compensation.
::0- 18.06.069 Best Available Science
"Best Available Science" means that scientific information applicable to the
:y' sensitive area prepared by appropriate local, state or federal agencies, a qualified
"s'c,
scientist or team of qualified scientists, which will be consistent with the criteria
established in WAC 365- 195 -900 through WAC 365- 195 -925. Characteristics of a valid
scientific process will be considered to determine whether information received during
the permit review process is reliable scientific information. A valid scientific process
4.:
includes some or all of the following characteristics:
1. Peer reviewed research or background information.
2. Study methods clearly stated.
3. Conclusions based on logical assumptions.
4. Quantitative analysis.
f: 5. Proper context is established.
i :`:z 6. References are included that cite relevant, credible literature and other
pertinent information.
18.06.070 Best Management Practices
"Best management practices (BMPs)" means conservation practices and
management measures which serve to protect trees, including the following practices:
1. Avoiding physical damage to tree trunk, branches, foliage and roots;
f 2. Restricting the movement, operation, and location of construction materials
and equipment to avoid the area under a tree canopy;
3. Minimizing adverse changes in drainage conditions around tree roots;
1{;::".:'5?'":. Definitions 18.06 12/10/04 Page 8 of 31
j:;
4. Minimizing adverse changes to the chemical, physical, structural, and organic
characteristics of soil around tree roots;
5. Those conservation practices defined by the State of Washington Department
of Agriculture, Washington State Department of Ecology, and International Society of
Arborists as intended to protect trees.
'.,
18.06.071 Binding Site Improvement Plan
"Binding Site Improvement Plan" means an improvement plan processed in
accordance with Chapter 17.16, which is legally binding on the land owner, his heirs,
successors and assigns.
18.06.072 Block
"Block" means a group of lots, tracts or parcels, which have been subdivided, and
are entirely surrounded by highways or streets or in part by a well-defined or fixed
boundary .
18.06.073 Boarding House
"Boarding house" means a residential building or use which provides housing on
a short term commercial basis for tenants. The following uses are excluded: Bed and
breakfast facilities, hotels and motels, shelters, and facilities which provide short- or
long-term care for tenants suffering from physical, mental or other disabilities.
18.06.074 Brew Pub
"Brew pub" means
criteria:
1.
2.
3.
gallons);
4.
5.
6.
a restaurant-type establishment that meets the following
Sells beer for consumption on site and sale in sealed containers;
Restaurant portion can be no larger than 8,000 square feet;
Produces beer in batch sizes not less than seven U.S. barrels (thirty one
~
Produces no more than 2,000 barrels of beer per year;
The brew house is enclosed with an air treatment system;
Revenue from food sales must comprise at least 60%
of total business
revenues
18.06.075 Buffer
"Buffer" means an area separating two different types of uses or environments for
the purpose of reducing incompatibilities between them, or reducing the potential
adverse impacts of one use or environment upon the other.
18.06.080 Building
"Building" means a structure as defined in this definitions chapter. When a total
structure is separated by division walls without openings, each portion so separate shall
be considered a separate building.
18.06.085 Building, Accessory
" Accessory building" means a subordinate building, the use of which is incident to
the use of the main building on the same lot.
18.06.090 Building Area
"Building area" means the total ground coverage of a building or structure which
provides shelter, measured from the outside of its external walls or supporting
members or from a point four feet in from the outside edge of a cantilevered roof.
18.06.095 Building, Detached
"Detached building" means a building surrounded on all sides by open space.
Definitions 18.06 12110/04
Page 9 of31
"
18.06.097 Building FOv~t'~illt
"Building footprint" means the square footage contained within the foundation
perimeter of all structures located on a lot, plus overhangs projecting in excess of 18
inches, but excluding decks less than 18 inches above grade.
18.06.100 Building Height
"Building height" means the height of a building as calculated by the method in
the Washington State Building Code.
18.06.105 Building Line
"Building line" means the line of face or corner of part of a building nearest the
property line.
18.06.110 Building, Nonconforming
"Nonconforming building" means a building or structure which does not conform
in its construction, area, yard requirements or height to the regulations of the district in
which it is located.
18.06.115 Building Permit
"Building permit" means a permit for construction in accordance with specific
approved plans that are on file with the DCD.
18.06.118 Bulk Retail
"Bulk Retail" is a business or store that specializes in the sale of large goods,
requiring large on-site storage. Bulk retail is further distinguished by a lower trip
generation rate than other retail stores, as evidenced by a traffic study or other
appropriate analysis. Examples include furniture stores, appliance stores and other
uses as approved by the Director.
18.06.120 Bus Station
"Bus station" means a facility providing connections between buses serving
different inter-city routes.
,.'
,...... .
:-::"'.''':
::..
18.06.125 Caliper
"Caliper" means the American Association of Nurserymen standard for
measurement of trunk size of nursery stock. Caliper of the trunk shall be taken 6 inches
above the ground.
18.06.130 Canopy _
"Canopy" means an area encircling the base of a tree, the minimum extent of
which is delineated by a vertical line extending from the outer limit of a tree's branch
tips down to the ground.
18.06.135 Canopy Cover
"Canopy cover" means the cumulative areal ",,,~,,,ut of the canopy of all trees on the
site.
18.06.137 Cargo Container
"Cargo container" means a standardized, reusable vessel that was:
1. Originally, specifically or formerly designed for or used in the packing,
shipping, movement or transportation of freight, articles, goods or commodities;
and/ or,
2. Designed for or capable of being mounted or moved on a rail car; and/ or
3. Designed for or capable of being mounted on a chassis or bogie for
movement by truck trailer or loaded on a ship.
Definitions \8.06 \2/10/04
Page 10 of31
..
'<'"-.
18.06.140 Certified Arborist
"Certified arborist" means an arborist certified by the International Society of
Arboriculture or National Arborist Association.
18.06.145 Oearing
"Clearing" means removal or causing to be removed, through either direct or
indirect actions, any vegetation from a site. Actions considered to be clearing include,
but are not limited to, causing irreversible damage to roots or trunks; poisoning;
destroying the structural integrity; and/ or any filling, excavation, grading, or trenching
in the root area of a tree which has the potential to cause irreversible damage to the tree.
18.06.150 Oinic
"Oinic" means a building designed and used for the medical, dental and surgical
diagnosis and treatment of patients under the care of doctors and nurses and/ or
practitioners.
18.06.152 Oosed Record Appeal
"Oosed record appeal" means a quasi-judicial appeal to a hearing body
designated by this chapter from a decision regarding a project permit application that
was made after an open record hearing. Testimony and submission of relevant
evidence and information shall not be permitted at a hearing on such an appeal. The
hearing on such an appeal shall be limited to argument based on the testimony,
evidence and documents submitted at the open record hearing conducted on the project
permit application.
18.06.155 Oub
"Oub" means an incorporated or unincorporated association of persons organized
for a social, education, literary or charitable purpose.
18.06.165 Comprehensive Plan
"Comprehensive Plan" means the adopted City of Tukwila Comprehensive Plan.
18.06.173 Convalescent/Nursing Home
"Convalescent/nursing home" means a residential facility, such as a hospice,
offering 24-hour skilled nursing care for patients suffering from an illness, or receiving
care for chronic conditions, mental or physical disabilities or alcohol or drug
detoxification, excluding correctional facilities. Care may include in-patient
administration of special diets, bedside nursing care, and treatment by a physician or
psychiatrist.
18.06.175 Cooperative Parking Facility
"Cooperative parking facility" means an off-street parking facility shared by two
or more buildings or uses.
18.06.178 Correctional Institution
"Correctional institution" means public and private facilities providing for:
1. the confinement of adult offenders; or
2. the incarceration, confinement or detention of individuals arrested for or
convicted of crimes whose freedom is partially or completely restricted other than a jail
owned and operated by the City of Tukwila; or
3. the confinement of persons undergoing treatment for drug or alcohol
addictions whose freedom is partially or completely restricted; or
4. transitional housing, such as halfway houses, for offenders who are required
to live in such facilities as a condition of sentence or release from a correctional facility,
except secure community transitional facilities as defined under RCW 71.09.020.
....:
Definitions 18.06 12110/04
Page 11 of31
18.06.210 Development
"Development" means the construction, reconstruction, conversion, structural
alteration, relocation or enlargement of any structure that requires a building permit.
18.06.215 Development Area
`f "Development area" means the impervious surface area less the following
surfaces: the footprint of an exclusive recreational facility; a proportion of a recreational
facility footprint when contained within a general use building as follows: the portion
of the footprint area occupied by a recreational facility divided by the number of floors
in that portion of the building; vehicle circulation aisles between separate parking areas;
sidewalks; paths; and other pedestrian/recreation facilities clearly designed to enhance
the pedestrian environment.
18.06.220 Diameter /Diameter- Breast Height (d.b.h.)
"Diameter /diameter- breast height" (d.b.h.) means the diameter of any tree trunk,
measured at 4.5 feet above average grade.
18.06.225 Director
f> ass "Director" means the Director of the Department of Community Development.
`r 18.06.230 District
"District" means an area or district accurately defined as to boundaries and
location on the official zoning map (Figure 18 -10) and within which district only certain
types of land uses are permitted.
18.06.235 District, Overlay
"Overlay District" means a set of zoning requirements that is described in the title
text, mapped, and is imposed in addition to those of the underlying district
18.06.237 Dormitory
f "Dormitory" means a residential building or use which provides housing for
students attending an affiliated school or housing for members of a religious order.
Dormitories may include kitchens, cafeterias, meeting rooms, laundry rooms and other
accessory facilities to serve the residents of the facility.
18.06.240 Driveway
"Driveway" means a private road giving access from a public way to a building or
abutting grounds.
18.06.245 Dwelling, Manufactured Home or Mobile Home
"Manufactured home dwelling" or "mobile home dwelling" means a detached
residential dwelling unit fabricated in an off -site manufacturing facility for installation
or assembly at the building site, bearing an insignia issued by the State of Washington
certifying that it is built in compliance with the Federal Manufactured Housing
Construction and Safety Standards for manufactured homes.
18.06.250 Dwelling, Multi- Family
':;"f: "Multi- family dwelling" means a building designed to contain two or more
dwelling units. Duration of tenancy in multi- family dwellings is not less than one
month.
18.06.255 Dwelling, Single- Family
"Single- family dwelling" means a building or modular home, other than a mobile
or manufactured home, designed to contain no more than one dwelling unit plus one
accessory dwelling unit.
Definitions 18.06 12/10/04 Page 13 of 31
18.06.260 Dwelling Unit
"Dwelling unit" means the whole of a building or a portion thereof providing
complete housekeeping facilities for a group of individuals living together as a single
residential community, with common cooking, eating and bathroom facilities, other
than transitory housing or correctional facilities as defined in this code, which is
physically separated from any other dwelling units which may be in the same structure.
18.06.264 Engineer, Geotechnical
"Geotechnical Engineer" means a professional engineer who can document at least
four years of employment as a professional engineer in the field of geotechnical
engineering.
18.06.266 Engineer, Professional
"Professional Engineer" means an engineer licensed in the State of Washington.
18.06.268 Engineering, geotechnical
"Geotechrrlcal engineering" means the application of civil engineering technology
that combines the basic physical sciences, geology and pedology, with hydraulic,
structural, transportation, construction, and mining engineering as each relates to the
natural materials found at or near the earth's surface (soils and rock). Geotechnical
engineering includes:
Soils mechanics - kinematics, dynamics, fluid mechanics, and mechanics of
material applied to soils in order to build with or on soils.
Foundation engineering - applied geology, soil mechanics, rock mechanics,
structural engineering to design, and construction of civil engineering and other
structures. Evaluate foundation performance (static and dynamic loading), stability of
natural and excavated slopes, stability of permanent and temporary earth-retaining
structures, construction problems, control of water movement and soil pressures,
maintenance and rehabilitation of old buildings.
Rock engineering - buildings, dams, deep excavations, tunnels.
18.06.270 Essential Public Facility
"Essential public facility" means a facility which provides a basic public service,
provided in one of the following manners: directly by a government agency, by a
private entity substantially funded or contracted for by a government agency, or
provided by a private entity subject to public service obligations (Le., private utility
companies which have a franchise or other legal obligation to provide service within a
defined service area).
18.06.275 Essential Root Zone
"Essential root zone" means the area located on the ground between the tree trunk
and 10 feet beyond the canopy.
18.06.280 Essential Use
"Essential use" means that use for the preservation or promotion of which the use
district was created and to which all other permitted uses are subordinate.
18.06.285 Essential Street, Road, Right-of-Way or Utility
"Essential street, road, right-of-way or utility" means a utility facility, utility
system, street, road or right-of-way where no feasible alternative location exists based
on an analysis of technology and system efficiency.
18.06.290 Extremely Hazardous Waste
"Extremely hazardous waste" means those solid wastes designated in WAC 173-
303-070 through 173-303-103 as L,~.,.u,ely hazardous waste.
Definitions 18.06 12/10/04
Page14of31
.,
18.06.300 Family Child Care Home
"Family child care home" means a "family day-care provider" as defined in RCW
74.15.020: a state-licensed facility in the family residence of the licensee providing
regularly scheduled care for 12 or fewer children, including children who reside at the
home, within an age range of birth through 11 years, exclusively for periods less that 24
hours per day. An off-street parking space shall be made available for any non-resident
employee.
18.06.310 Fence
"Fence" means a wall or barrier for the purpose of enclosing space, separating
parcels of land or acting as a screen or protective barrier.
18.06.315 Filling
"Filling" means the act of transporting or placing (by any manner or mechanism)
fill material from, to, or on any soil surface, natural vegetative covering of soil surface,
or fill material (including temporary stockpiling of fill material).
18.06.318 Final Plat
"Final Plat" means the final drawing of the subdivision and dedication prepared
for filing for record with the Department of Records and Elections, and containing all
elements and requirements set forth in the subdivision code.
18.06.320 Fire Lane
"Fire lane" means an aisle, lane or roadway on an improved site which is
designed, constructed and required for emergency access of fire and aid unit vehicles.
18.06.325 Floor Area
"Floor area" means the sum of the gross horizontal areas of the floors of a building
or buildings, measured from the exterior walls and from the centerline of divisions
walls. Floor area includes basement space, elevator shafts and stairwells at each floor,
mechanical equipment rooms or attic spaces with headroom of 7 feet 6 inches or more,
penthouse floors, interior balconies and mezzanines, enclosed porches, and malls. Floor
area shall not include accessory water tanks and cooling towers, mechanical equipment
or attic spaces with headroom of less than 7 feet 6 inches, exterior steps or stairs,
terraces, breezeways and open spaces.
18.06.340 Fraternal Organization
"Fraternal organization" means a group of people formally organized for a
common interest, usually cultural, religious or entert~ent, with regular meetings,
rituals and formal written membership requirements.
18.06.345 Garage, Private
"Private garage" means sheltered or enclosed space designed and used for the
storage of motor vehicles or boats of the residents of the premises.
..
18.06.353 General Retail
"General Retail" is a business or a store which engages in the sale of goods and/ or
services to the general public. Examples include department stores and personal
service shops.
18.06.355 Geologist
"Geologist" means a person licensed to practice as a geologist in the State of
Washington who has earned a degree in geology, engineering geology, hydrogeology
or one of the related geological sciences from an accredited college or university, or a
person who has equivalent educational training and has experience as a practicing
geologist.
Definitions 18.06 12110/04
Page 15 of31
18.06.365 Grade
"Grade" (adjacent ground elevation) means the lowest point of elevation of the
finished surface of the ground between the exterior wall of a building and a point five
feet distant from said wall, or the lowest point of elevation of the finished surface of the
ground between the exterior wall of a building and the property line, if it is less than
five feet distant from said wall. In case walls are parallel to and within five feet of a
public sidewalk, alley, or other public way, the grade shall be the elevation of the
sidewalk, alley or public way.
18.06.370 Grading
"Grading" means any excavating, filling, clearing, or the creation of impervious
surface, or any combination thereof, which alters the existing surface of the earth.
18.06.380 Groundcover
Groundcover" means trees, shrubs and any other plants or natural vegetation
which covers or shades in whole or in part the earth's surface.
18.06.385 Hazardous Substance
"Hazardous substance" means any liquid, solid, gas or sludge, including any
material, substance, product, commodity or waste, regardless of quantity, that exhibits
any of the characteristics or criteria of hazardous waste as defined by WAC 173 -303.
18.06.390 Hazardous Substance Processing or Handling
"Hazardous substance processing or handling" means the use, storage,
manufacture, production, or other land use activity involving hazardous substances.
Hazardous substances processing and handling activities do not include individually
packaged household consumer products or quantities of hazardous substances of less
than five gallons in volume per container.
z
18.06.395 Hazardous Tree
"Hazardous tree" means a tree with a structural defect or disease, or which
impedes safe vision or traffic flow, or otherwise currently poses a threat to life or
property.
fig 18.06.400 Hazardous Waste
"Hazardous waste" means and includes all waste as defined in this definitions
chapter and all extremely hazardous waste as defined in this definitions chapter.
18.06.405 Hazardous Waste Storage
"Hazardous waste storage" means the holding of hazardous waste for a temporary
period. Accumulation of waste on the site of generation is not storage as long p g g as the
4;.
storage complies with applicable requirements of WAC 173 -303.
18.06.410 Hazardous Waste Treatment
"Hazardous waste treatment" means the physical, chemical, or biological
processing of dangerous waste to make such wastes nondangerous or less dangerous,
safer for transport, or amenable for energy or material resource recovery.
r 18.06.415 Hazardous Waste Treatment and Storage Facility, Off -Site
"Off -site hazardous waste treatment and storage facility" means the treatment and
storage of hazardous wastes from generators on properties other than that on which the
off -site facility is located.
18.06.420 Hazardous Waste Treatment and Storage Facility, On -Site
"On -site hazardous waste treatment and storage facility" means the treatment and
storage of hazardous wastes generated on the same site.
Definitions 18.06 12/10/04 Page 16 of 31
+r4i�
18.06.425 High Impact Enviromnent
"High impact enviromnent" means the area between the low-impact enviromnent
and a point 200 feet landward from the mean high water mark.
18.06.430 Home Occupation
"Home occupation" means an occupation or profession which is customarily
incident to or carried on in a dwelling place, and not one in which the use of the
premises as a dwelling place is largely incidental to the occupation carried on by a
resident of the dwelling place; provided, that:
1. There shall be no change in the outside appearance of the surrounding
residential develvt'ment;
2. No home occupation shall be conducted in any accessory building;
3. Traffic generated by such home occupations shall not create a nuisance;
4. No equipment or process shall be used in such home occupation which
creates noise, vibration, glare, fumes, odor, or electrical interference detectable to the
normal senses off the lot;
5. The business involves no more than one person who is not a resident of the
dwelling; and
6. An off-street parking space shall be made available for any non-resident
employee.
18.06.435 Hospital
"Hospital" means a building designed and used for the medical and surgical
diagnosis, treatment and housing of persons under the care of doctors and nurses. Rest
homes, nursing homes, convalescent homes and clinics are not included.
18.06.440 Hotel
"Hotel" means a building or portion thereof designed or used for the transient
rental of five or more units for sleeping purposes. A central kitchen and dining room
and accessory shops and services catering to the general public can be provided. Not
included are institutions housing persons under legal restraint or requiring medical
attention or care.
18.06.445 Impervious Surface
"Impervious surface" means those hard surfaces which prevent or retard the entry
of water into the soil in the manner that such water entered the soils under natural
conditions prior to development; or a hard surface area which causes water to run off
the surface in greater quantities or at an increased rate of flow from the flow present
under natural conditions prior to develvt'ment. Such surfaces include, but are not
limited to, rooftops, asphalt or concrete paving, compacted surfaces or other surfaces
which similarly affect the natural infiltration or runoff patterns existing prior to
develv t'ULent.
18.06.450 Infrastructure
"Infrastructure" means the basic installations and facilities on which the
contii1.uance and growth of a community depend, such as roads, public buildings,
schools, parks, transportation, water, sewer, surface water and communication systems.
18.06.453 Integrated Site
"Integrated site" means a commercial or industrial zoned property for which a
Binding Site Improvement Plan is being or has been approved and recorded. The site
typically contains within it multiple tracts of land under separate leasehold or
ownership, but functions as a single center. Characteristics of an integrated site
includes commonly shared access, parking, utilities, signage and landscaping; the site is
not bisected by a public or private street; and zoning and sign regulations are applied to
the entire site, as if there were no interior property lines.
Definitions 18.06 12/10/04
Page 17 of31
18.06.454 Internet Data /Telecommunication Center
"Internet data /telecommunication center" means a secure, climate controlled
facility with emergency backup power that contains internet data transmission and
switching equipment and /or telecommunication transmission and switching
equipment. This equipment may include computer network routers, switches and
servers for one or more companies.
18.06.460 Junk Yard
"Junk yard" means a lot, land or structure, or part thereof, used for the collection,
storage and sale of waste paper, rags, scrap metal or discarded material; or for the
collecting, dismantling, storage, salvaging and sale of parts of machinery or vehicles not
in running condition.
18.06.465 Kennel
"Kennel" means a place where four or more dogs or cats or any combination
i thereof are kept.
18.06.470 Laboratory, Medical and Dental
"Medical or dental laboratory" means premises devoted to sample testing or
product development in any branch of medicine or dentistry, including the application
of scientific principles in testing, analysis, or preparation of drugs, chemicals or other
products or substances but specifically excluding the commercial manufacturing or
storage and distribution operations in excess of 20,000 square feet of floor area.
18.06.473 Land Surveyor
"Land surveyor" means an individual registered in accordance with the provisions
of RCW 18.43 and licensed to perform land surveys in the State of Washington.
18.06.475 Land-Altering Activity
"Land- altering activity" means any activity that results in change of the natural
cover or topography, as defined in TMC 16.54, Land Altering.
18.06.480 Land Altering Permit
"Land- altering permit" means a permit for land altering activity issued by the City
of Tukwila pursuant to TMC 16.54, Land Altering.
18.06.485 Landscape Architect
"Landscape architect" means a person licensed by the State of Washington to
engage in the practice of landscape architecture as defined by RCW 18.96.030.
18.06.490 Landscaping or Landscaped Areas
"Landscaping or landscaped areas" means natural vegetation such as trees, shrubs,
groundcover, and other landscape materials arranged in a manner to produce an
aesthetic effect appropriate for the use to which the land is put.
18.06.493 Lease
"Lease" means a contract or agreement whereby one party grants to another party
general or limited rights, title or interest in real property. This definition is intended to
apply to those agreements which are ordinarily considered "ground leases and shall
not apply to those which are ordinarily considered "space leases."
18.06.495 Loading Space
"Loading space" means a space which is on the same site with the principal use
served and which provides for the temporary parking of a vehicle while loading or
unloading merchandise, materials or passengers.
Definitions 18.06 12/10/04 Page 18 of 31
18.06.500 Lot
"Lot" means a physically separate and distinct parcel of property which has been
created by plat, short plat or binding site plan, or which by reason of its ownership
history, was used as a separate legal building site prior to the requirement that lots be
created by plat, short plat or binding site plan.
18.06.505 Lot Area
"Lot area" means the total horizontal area within the boundary lines of a lot and
exclusive of street right -of -way, street easement, or private access roads serving more
than one lot authorized pursuant to the subdivision ordinance.
18.06.510 Lot, Corner
"Corner lot" means a lot abutting two or more streets or parts of the same street
forming an interior angle of less than 135 degrees within the lot lines.
18.06.515 Lot Coverage
"Lot coverage" means the surface of the subject property covered with impervious
surface, other than outdoor pools.
18.06.520 Lot Depth
"Lot depth" means the mean dimension of the lot from the front street line to the
rear line.
18.06.525 Lot Frontage
's "Lot frontage" means that front portion of. a lot nearest the street, except on a
corner lot in which case the front yard shall be considered the narrowest part of the lot
that abuts a street.
s. 18.06.530 Lot Lines
"Lot lines" means the property lines bounding the lot; except that in MDR and
HDR zones, lot lines shall also include the curbline or edge or easement, whichever
provides a greater width, of any adjacent 'access roads'.
r; 18.06.535 Lot, Interior
"Interior lot" means a lot other than a corner lot with only one frontage on a street.
18.06.540 Lot, Through
"Through lot" means a lot fronting on two streets that do not intersect on the
parcel's lot lines.
18.06.545 Lot Width
"Lot width" means the mean horizontal distance between lot side lines.
18.06.550 Low Impact Environment
"Low impact environment" means the area between the River Environment and a
point 100 feet landward from the mean high water mark having environmentally
protective land use regulations as established in the Shoreline Overlay District chapter
of this title.
18.06.555 Major Adjustment
"Major adjustment" means an adjustment determined by the Director as a major
change in a final development plan which changes the basic design, density, open space
or other substantive requirements or provisions.
18.06.560 Mall
"Mall" means an enclosed public area, typically a concourse, designed as a
pedestrian walkway along rows of shops and often set with landscaping and /or
seating.
Definitions 18.06 12/10/04 Page 19 of 31
18.06.565 Manufactured /Mobile Home Park
"Manufactured /mobile home park" means a master planned development
consisting of a grouping of manufactured or mobile home dwellings, and may include
park management offices and accessory community facilities for the exclusive use of
park residents, such as recreation, laundry or storage facilities.
18.06.567 Manufacturing
"Manufacturing" is a building or group of buildings which specializes in the
manufacturing of products or in the research and testing of products. Examples include
factories, testing laboratories, creameries, bottling establishments, bakeries, canneries,
printing and engraving shops.
18.06.568 Mass Transit Facilities
"Mass transit facilities" shall include structures and infrastructure for public or
private transportation systems having established routes and schedules such as transit
centers, committer and light rail facilities, both rail lines and stations, monorails, people
movers and other similar mass transit facilities but not including incidental
improvements such as bus stops.
18.06.570 Mean High Water Mark
"Mean high water mark" means the elevation of the surface of Green River and
Duwamish River waters when the discharge rate at the U. S. Geological Survey Stream
Gauging Station, Green River near Auburn (121130), is 9,000 cfs and as determined by
maps on file with the City Clerk.
'f t'' 18.06.575 Mining and Quarrying
"Mining and quarrying" means removal and processing of sand, gravel, rock, peat,
:•-;.•.74:: black soil, and other natural deposits, greater than 50,000 cubic yards cumulative.
18.06.580 Minor Adjustment
"Minor adjustment" means any change which is not determined by the Director to
be a major change.
r
18.06.581 Mitigation
"Mitigation" means replacing project induced sensitive area and buffer losses or
impacts, and includes but is not limited to the following:
1. Restoration: Actions performed to reestablish sensitive area and its buffer
functional characteristics and processes which have been lost by alterations, activities or
catastrophic events within an area which no longer meets the definition of a sensitive
area;
2. Creation: Actions performed to intentionally establish a sensitive area and its
buffer at a site where it did not formerly exist;
3. Enhancement: Actions performed to improve the condition of an existing
degraded sensitive area or its buffer so that the functions it provides are of higher
quality.
18.06.583 Modular Home
"Modular home" means a factory -built residential structure, transportable in one
or more sections, which meets the requirements of the Uniform Building Code.
18.06.585 Motel
"Motel" includes tourist cabins, tourist court, motor lodge, auto court, cabin court,
motor inn and similar names. A motel is a building or buildings, detached or in
connected units or designed as a single structure, the units of which are used as
individual sleeping or dwelling units having their own private toilet facilities, and may
or may not have their own kitchen facilities, and are designed primarily for the
Definitions 18.06 12/10/04 Page 20 of 31
accommodation of transient automobile travelers. Accommodations for travel trailers
are not included.
18.06.590 Nonconforming Use
%'s: "Nonconforming use" means the use of land which does not conform to the use
regulations of the district in which the use exists.
18.06.592 Office
"Office" is a building or a group of buildings dedicated to non manufacturing
types of work that are for the use of employees but may or may not be for use by the
general public. Examples include services such as accounting, advertising,
architectural /engineering, consulting, information processing, legal, medical and /or
dental.
18.06.593 Open Record Appeal
"Open record appeal" means a quasi-judicial appeal to a hearing body designated
by this chapter from a decision regarding a project permit application that was made
without an open record hearing. Testimony and submission of relevant evidence and
information shall be permitted at the hearing on such an appeal.
;:q 18.06.594 Open Record Hearing
"Open record hearing" means a quasi-judicial hearing conducted by a hearing
body which creates the official record regarding a permit application. Oral testimony
and submission of relevant evidence and documents shall be permitted at such a
hearing.
18.06.595 Open Space
ace P P
"Open space" means that area of a site which is free and clear of building and
P structures and is open and unobstructed from the ground to the sky.
18.06.600 Open Space Tract
"Open space tract" means a tract that is established to preserve open space, and
which is recorded on all documents of title of record for all affected lots and subsequent
owners.
18.06.605 Ordinary High Water Mark
"Ordinary high water mark (OHWM)" means the mark that will be found by
ss:< examining the bed and banks of a stream and ascertaining where the presence and
s action of waters are so common and usual as to distinctly mark the soil from that of the
sj:; abutting upland, in respect to vegetation.
0-4. 18.06.610 Parcel
'j "Parcel" means a tract or plat of land of any size which may or may not be
;:f subdivided or improved.
18.06.611 Park and Ride
"Park and Ride" means a facility for temporarily parking automobiles, the
`i =s%%" occupants of which transfer to public transit to continue their trips.
18.06.613 Parking, Commercial
"Commercial parking" is a use of land or structure for the parking of motor
vehicles as a commercial enterprise for which hourly, daily or weekly fees are charged.
18.06.615 Parking Space
"Parking space" means an off -street parking space which is maintained and used
for the sole purpose of accommodating a temporarily parked motor vehicle and which
has access to a street or alley.
Definitions 18.06 12/10/04 Page 21 of 31
:ids
18.06.617 Pawnbroker
"Pawnbroker" is an establishment engaged in the buying or selling of new or
secondhand merchandise and offering loans in exchange for personal property.
18.06.618 Performance Bond or Guarantee
"Performance bond or guarantee" means that security to ensure installation of
certain required improvements which may be accepted to defer those improvements
when such a deferment is warranted and acceptable to the City.
18.06.620 Performance Standards
"Performance standards" means specific criteria for fulfilling environmental goals,
and for beginning remedial action, mitigation or contingency measures, which may
include water quality standards or other hydrological, geological or ecological criteria.
18.06.625 Person
"Person" means any legal entity recognized by the State of Washington for the
purpose of assigning legal responsibility, to include but not limited to individuals,
partnerships, corporations, associations, commissions, boards, utilities, institutions, and
estates.
18.06.630 Plan
"Plan" means a sketch, survey or other drawing, photograph or similar document
which may be a part of the set of permit drawings or construction documents, sufficient
for the Director to make a final permit decision.
18.06.632 Planned Residential Development (PRD)
"Planned residential development (PRD)" means a form of residential
development characterized by a unified site design for a number of dwelling units,
clustered buildings, common open space, and a mix of building types. The PRD is an
overlay district which is superimposed over the underlying district as an exception to
such district regulations, as processed through procedures specified in the Planned
Residential Development District chapter of this title.
18.06.633 Planning Commission
"Planning Commission" means that body as defined under Title 2.36 of the
Tukwila Municipal Code.
18.06.635 Plat
"Plat" means a map or representation of a subdivision, showing thereon the
division of a tract or parcel of land into lots, blocks, streets, and alleys or other divisions
and dedications.
18.06.636 Preliminary Plat
"Preliminary plat" means a neat and approximate drawing of a proposed
subdivision or short plat, showing the general layout of streets and alleys, lots, blocks,
utilities, and restrictive covenants to be applicable to the proposal, and other elements
of a plat which shall furnish a basis for the approval or disapproval of the application.
18.06.637 Principal Building
"Principal building" means the principal structure on a lot or building site
designed or used to accommodate the primary use to which the premises are devoted.
18.06.638 Private Access Road
"Private access road" means a minor, privately owned and maintained road which
serves to provide access to lots as authorized pursuant to TMC 17.24.030 and 17.28.050.
Definitions 18.06 12/10/04 Page 22 of 31
18.06.640 Property Owner
"Property owner" means the owner of record for a site, or his or her authorized
representative.
18.06.645 Protected Tree /Protected Vegetation
"Protected tree /protected vegetation" means tree or area of understory vegetation
identified on an approved landscape plan to be retained and protected during
construction.
18.06.650 Protection Measure
"Protection measure" means the practice or combination of practices (e.g.
construction barriers, protective fencing, tree wells, etc.) used to control construction or
development activity, where such activity may impact vegetation which is approved for
retention in a Tree Clearing Permit.
18.06.655 Protective Fencing
"Protective fencing" means the temporary fence or other structural barrier
installed to prevent permitted clearing or construction activity from adversely affecting
vegetation that is approved for retention in a Tree Clearing Permit.
r:: 18.06.657 Public Meeting
"Public meeting" means an informal meeting or workshop to provide public
information regarding a project permit application and to obtain comments about the
application from the public. The information gathered at such a meeting does not
%.t::` constitute part of the official record regarding a project permit application.
18.06.660 Reach
"Reach" means a segment of a watercourse with uniform characteristics.
18.06.665 Recreation Space
"Recreation space" means covered and uncovered space designed and intended
for active and /or passive recreational activity including but not limited to tennis courts,
swimming pools, cabanas, playgrounds, playfields, or wooded areas, and specifically
excluding any parking area, driveway, or rockery.
18.06.670 Recreation Space, Covered
"Covered recreation space" means an area of ground covered or overlaid by an
artificial or manmade surface, such as rooftops or pavement.
18.06.675 Recreation Space, Uncovered
"Uncovered recreation space" means an area of ground characterized by a natural
surface, such as lawn, forests, or sandboxes (for children's play).
18.06.685 Residence
"Residence" means a building or structure, or portion thereof, which is designed
for and used to provide a place of abode for human beings.
r' 18.06.687 Restaurant
"Restaurant" is an establishment whose principal business is the sale of foods to be
eaten on the premises, including either indoor or outdoor seating, which may also
include an area reserved for the sale of alcoholic beverages.
18.06.688 Restaurant, Fast Food
"Fast Food Restaurant" means an establishment whose principal business is the
sale of foods, frozen desserts, or beverages served in or on disposable containers for
consumption while seated within the building or in a vehicle or incidentally within a
designated outdoor area, or for takeout with consumption off the premises.
::r: Definitions 18.06 12/10/04 Page 23 of 31
18.06.689 Right-of-Way
"Right-of-way" means a right belonging to a party to pass over land of another.
18.06.690 River Channel
"River channel" means that area of the river environment lying riverward of the
mean high water mark.
18.06.695 River Environment
"River environment" means the area between the mean high water mark and a
point 40 feet landward from the mean high water mark, having the most
environmentally protective land use regulations as established in the Shoreline Overlay
District chapter of this title.
18.06.697 Roadway
%1: "Roadway" means that improved portion of a street intended for the
accommodation of vehicular traffic, generally within curb lines.
18.06.700 Sanitarium
"Sanitarium" means a facility designed and used for the care, treatment and
housing of persons with specific chronic diseases. Convalescent homes are not
included.
18.06.705 Screening
"Screening" means a continuous fence and/or evergreen landscaped planting that
effectively conceals the property it encloses.
18.06.706 Secure Community Transitional Facility
"Secure community transitional facility" means a secure community transitional
facility as defined under RCW 71.09.020, which defines it as "a residential facility for
persons civilly committed and conditionally released to a less restrictive alternative
L''' under this chapter. A secure community transition facility has supervision and security,
and either provides or ensures the provision of sex offender treatment services. Secure
community transition facilities include but are not limited to the facilities established
pursuant to RCW 71.09.250 and any community-based facilities established under this
chapter and operated by the DSHS secretary or under contract with the secretary."
18.06.707 Self Storage Facility
"Self- Storage Facility" means a building designed and used for the purpose of
renting or leasing individual indoor storage space to customers who are to have access
to the space for the purpose of storing or removing personal property on a self service
basis.
18.06.708 Senior Citizen Housing
"Senior Citizen Housing" is housing in a building or group of buildings with two
or more dwelling and /or sleeping units, restricted to occupancy by at least one senior
citizen per unit, and may include Food Preparation and Dining activities, Group
Activity areas, Medical Supervision or other similar activities. Such housing is further
distinguished by the use of funding restrictions, covenants between the developer,
tenants, operators and/or the City or other agreements that restrict the development to
those individuals over 60 years of age. Senior Citizen Housing strategies may include
provisions for units dedicated to persons under 60 years of age that have medical
conditions consistent with definitions in the Americans with Disabilities Act; however,
the population of disabled individuals may not exceed 20% of the residents. These
s' y facilities may not include populations requiring convalescent or chronic care, as defined
%r under RCW 18.51.
Definitions 18.06 12/10/04 Page 24 of 31
18.06.710 Sensitive Area Buffer
"Sensitive area buffer" means an area lying adjacent to but outside a sensitive area
as defined by this Title, whose function is to protect sensitive areas from the potential
adverse impacts of development, land use, or other activities. A wetland or
watercourse sensitive area buffer also provides critical habitat value, bank stabilization,
or water overflow area functions.
18.06.715 Sensitive Area Regulated Activities
"Sensitive area regulated activities" means any of the following activities that are
directly undertaken or originate in a regulated wetland or watercourse or their buffers:
1. Removal, excavation, grading or dredging of soil, sand, gravel, minerals,
organic matter or material of any kind;
2. Dumping, discharging or filling with any material;
3. Draining, flooding or disturbing the water level or water table;
4. Driving of pilings;
5. Placing of obstructions;
6. Construction, reconstruction, demolition or expansion of any structure;
7. Destruction or alteration of wetlands, watercourses or their buffers through
clearing, harvesting, shading, intentional burning or planting of vegetation that would
alter the character of a regulated wetland, watercourse or buffer, provided that these
activities are not part of a forest practice governed under RCW 76.09 and its rules; or
8. Activities that result in a significant change to the water sources of wetlands
or watercourses. These alterations include a significant change in water temperature;
physical or chemical characteristics, including quantity; and the introduction of pollu-
tants.
18.06.720 Sensitive Areas
"Sensitive areas" means wetlands, watercourses, areas of potential geologic
instability (other than Class I areas), abandoned coal mine areas, and fish and wildlife
habitat conservation areas.
18.06.725 Sensitive Areas Ordinance
"Sensitive Areas Ordinance" means the Environmentally Sensitive Areas chapter
of this title or as amended hereafter which establishes standards for land development
on lots with sensitive areas (e.g. steep slopes, wetlands, watercourses, etc.).
::*/:-0 18.06.730 Sensitive Area Tract or Easement
"Sensitive area tract or easement" means a tract or portion of a parcel that is
;.1
created to protect the sensitive area and its buffer, whose maintenance is assured, and
,1
which is recorded on all documents of title of record for all affected lots and subsequent
owners.
18.06.735 Service Station
"Service station" means any area of land, including structures thereon, that is used
for the sale of gasoline or other motor fuels, oils, lubricants, and auto accessories which
f may or may not include washing, lubricating, tune -ups, and other minor servicing
rr incidental to this use, but no painting or major repair operations.
18.06.740 Setbacks
"Setbacks" means the distances that buildings or uses must be removed from their
lot lines except that roof eaves may intrude a maximum of 18 inches into this area.
18.06.743 Shelter
"Shelter" means a building or use providing residential housing on a short -term
basis for victims of abuse and their dependents, or a residential facility for runaway
minors (children under the age of 18).
;'i -n. Definitions 18.06 12/I0/04 Page 25 of 31
18.06.745 Shelter station
"Shelter station" means a shelter for protection from the elements for the waiting
customers of a public transportation system.
18.06.750 Shopping Center, Planned
"Planned shopping center" means a group of architecturally unified commercial
establishments built on a site which is planned, developed, owned, and managed as an
operating unit related in its location, size, and type of shops to the trade area that the
unit serves. The unit provides on -site parking in definite relationship to the types and
total size of the stores.
18.06.760 Shoreline
j "Shoreline" means the line at mean high water surrounding any body of water of
20 acres or larger or where the mean flow is 20 cubic feet per second or greater.
18.06.765 Shoreline zone
"Shoreline zone" means a 200 -foot area surrounding any shoreline in Tukwila
composed of three zones: (1) river environment, (2) low impact environment, and (3)
high impact environment.
18.06.767 Short plat
"Short plat" means the map or representation of a short subdivision.
s;- 18.06.768 Short Subdivision
"Short subdivision" means the division of land into nine or less lots, tracts, parcels,
sites or divisions.
18.06.769 Short Subdivision Committee
The Short Subdivision Committee (SSC) shall consist of the Director of the
Department of Community Development who shall be the chair, the Public Works
Director, and the Fire Chief, or their designated representatives.
18.06.770 Sign
"Sign" means any medium, including paint on walls, merchandise, or visual
communication device, its structure and component parts, which is used or intended to
be used to attract attention to the subject matter for advertising or identification
purposes. Bulletin boards and readerboards are considered to be signs.
18.06.775 Significant Tree
is
A "significant tree" means a tree (Cottonwood excluded) which is 4 inches or more
in diameter as measured 4.5 feet above grade.
%¢ss
18.06.780 Site
"Site" means any legally defined section of real property, whose boundaries are
recorded for purposes of assessing taxes with the County Assessor's Office.
s <r:. 18.06.785 Solid Planting
"Solid planting" means a planting of evergreen trees and or shrubs which will
prevent a through and unobscured penetration light.
of sight or li
P g P g g
18.06.790 Story
"Story" means story as defined in the Washington State Building Code.
18.06.795 Street
"Street" means a public thoroughfare which affords the principal means of access
to abutting properties.
Definitions 18.06 12/10/04 Page 26 of 31
rs,:
18.06.800 Structure
"Structure" means a combination of materials constructed and erected
permanently on the ground or attached to something having a permanent location on
the ground, but excluding all forms of vehicles even though immobilized. Not included
are residential fences, retaining walls less than three feet in height, rockeries and similar
improvements of minor character.
18.06.805 Structural Alteration
"Structural alteration" means any change in load or stress of the loaded or stressed
members of a building or structure.
18.06.810 Studios
"Studios" means a building or portion of a building used as a place of work by an
artist, photographer, or artisan, or used for dance instruction.
18.06.813 Subdivision
"Subdivision" means the division or redivision of land into ten or more lots, tracts,
parcels, sites or divisions.
18.06.815 Substantial Construction
"Substantial construction" means completion of more than 50% of the cost of work
described in specified and approved plans.
18.06.820 Surveyor
"Surveyor" means a person licensed by the State of Washington to engage in the
practice of land surveying, as defined by RCW 18.43.020.
18.06.823 Theater
"Theater" is a building or part of a building devoted to showing motion pictures
or for dramatic, dance, musical or other live performances.
18.06.825 Tract
"Tract" means a parcel of land proposed for subdivision or a distinct parcel
designated for a specific use.
4 18.06.830 Trailer Court Or Park
"Trailer court or park" means any area of land occupied or designed for the
occupancy of two or more travel trailers or mobile homes.
18.06.835 Trailer, Travel
"Travel trailer" means a vehicular portable structure built on a chassis, designed to
be used as a temporary dwelling for travel and recreational purposes.
18.06.840 Transit Center
"Transit center" means a location where groups of buses or other public
transportation vehicles can be brought together at the same time, allowing patrons to
transfer between the routes.
18.06.845 Tree
"Tree" means any self supporting woody plant, which at maturity is usually 20
feet or more in height and generally has one main trunk, with a potential diameter-
breast-height of 2 inches or more.
18.06.850 Tree Clearing Permit
"Tree clearing permit" means a permit issued by the Director authorizing tree
clearing activities, pursuant to the general permit provisions of this title.
Definitions 18.06 12/10/04 Page 27 of 31
I
18.06.855 Turbidity
"Turbidity" means a cloudy condition in water due to the suspension of silt, finely
divided organic matter, or other pollutants.
18.06.860 Understory Vegetation
"Understory vegetation" means small trees, shrubs, and groundcover plants,
growing beneath and shaded by the canopy of a significant tree, which affect and are
affected by the soil and hydrology of the area surrounding the significant tree roots.
f` 18.06.863 Usable Floor Area
"Usable Floor area" means that part of the floor area of any structure which is
>s actually used from time to time for any commercial purposes, such as a sales area,
display la area, walkways or storage area. Parking calculation shall not include common
P Y Y g g
corridors designed for the circulation of people at non retail establishments, restrooms,
elevator shafts and stairwells at each floor, mechanical equipment rooms or attic spaces
and exterior covered loading docks.
18.06.865 Use
"Use" means the nature of the occupancy, the type of activity, or the character and
form of improvements to which land is devoted or may be devoted.
18.06.870 Use, Accessory
"Accessory use" means a use incidental and subordinate to the principal use and
located on the same lot or in the same building as the principal use.
18.06.875 Use, Conditional
"Conditional use" means an unusual and /or unique type of land use which, due
to its nature, requires special consideration of its impacts on the neighborhood and land
uses in the vicinity.
18.06.880 Use, Permitted
"Permitted use" means any use authorized or permitted alone or in conjunction
with any other use in a specified district and subject to the limitation of the regulations
of such use district.
18.06.885 Use, Primary or Principal
"Primary or principal permitted use" means the use for which a lot, structure or
building, or the major portion thereof, is designed or actually employed.
18.06.890 Use, Unclassified
"Unclassified fr Unclassified use means an unusual, large-scale, unique and/or special type of
c, land use which, due to its nature, requires special review of its impacts on the
community and land uses in the vicinity.
18.06.895 Unlisted Use
"Unlisted use" means uses which are not specifically named as permitted in any
use classification contained within this title.
18.06.900 Utilities
"Utilities" means all lines and facilities related to the provision, distribution,
collection, transmission or disposal of water, storm and sanitary sewage, oil, gas,
power, information, telecommunication and telephone cable, or refuse, and includes
facilities for the generation of electricity.
18.06.905 Variance
"Variance" means an adjustment in the specific regulation of this title regarding a
particular piece of property as provided in the Variance chapter of this title.
Definitions 18.06 12/10/04 Page 28 of 31
18.06.910 Vegetation
"Vegetation" means living trees, shrubs or groundcover plants.
18.06.915 Vehicles
"Vehicles" means mechanical devices capable of movement by means of wheels,
skids or runners of any kind, specifically including, but not limited to, all forms of
trailers, recreational vehicles or mobile homes of any size whether capable of supplying
their own motive power or not, without regard to whether the primary purpose of
which device is or is not the conveyance of persons or objects, and specifically including
all such automobiles, buses, trucks, cars, vans, recreational vehicles, trailers and mobile
homes even though they may be at any time immobilized in any way and for any
period of time of whatever duration.
18.06.918 Warehouse
"Warehouse" is a building or group of buildings that are primarily for the storage
of goods.
18.06.920 Watercourse
"Watercourse" means a course or route formed by nature or modified by man,
generally consisting of a channel with a bed and banks or sides substantially
%s 9:' throughout its length along which surface water flows naturally including the
Green /Duwamish River. The channel or bed need not contain water year- round.
Watercourses do not include irrigation ditches, stormwater runoff channels or devices,
or other entirely artificial watercourses unless they are used by salmonids or to convey
or pass through stream flows naturally occurring prior to construction of such devices.
18.06.922 Wetland
"Wetland" means those areas that are inundated or saturated by groundwater or
=scar;:
surface water at a frequency and duration sufficient to support, and that under normal
circumstances do support, a prevalence of vegetation typically adapted for life in
saturated soil conditions. Wetlands generally include bogs, swamps, marshes, ponds,
lakes and similar areas. Wetlands do not include those artificial wetlands intentionally
created from non wetland sites, including but not limited to irrigation and drainage
ditches, grass -lined swales, canals, detention facilities, wastewater treatment facilities,
farm ponds, landscape amenities or those wetlands created after July 1, 1990 that were
unintentionally created as a result of the construction of a road, street or highway.
However, those artificial wetlands intentionally created from nonwetland areas to
mitigate conversion of wetlands as permitted by the City shall be considered wetlands.
18.06.924 Wetland Edge
"Wetland edge” means the boundary of a wetland as delineated based on the 1987
manual in use January 1, 1995 by the U.S. Environmental Protection Agency and the
U.S. Army Corps of Engineers.
18.06.926 Wetlands or Watercourses, Constructed
"Constructed wetlands" or "constructed watercourses" means those wetlands or
watercourses which an applicant can demonstrate were intentionally created from
nonwetland or nonwatercourse sites, including, but not limited to, irrigation and
drainage ditches, grass -lined swales, canals, detention facilities, wastewater treatment
facilities, farm ponds and landscape amenities; and does not mean those wetlands and
watercourses created through compensatory mitigation.
18.06.928 Wetland, Emergent
"Emergent wetland" means a regulated wetland with at least 30% of the surface
area covered by erect, rooted, herbaceous vegetation as the uppermost vegetative
stratum.
Definitions 18.06 12/10/04 Page 29 of 31
18.06.930 Wetlands, Forested
"Forested wetland" means a regulated wetland with at least 30% percent of the
surface area covered by woody vegetation 20 feet or greater in height that is at least
partially rooted within the wetland.
18.06.932 Wetland, Isolated
"Isolated wetlands" means those wetlands that:
Are not hydrologically connected to, and not contiguous to any 100 year floodplain of a
lake, river or stream, in accordance with current State and federal regulations; and have
no contiguous hydric soil and hydrophytic vegetation between the wetland and any
regulated surface water.
18.06.933 Wetlands, Regulated
"Regulated wetland" means ponds or lakes 30 acres or less and those lands subject
to the "wetland" definition contained in this chapter. Wetlands 1,000 sq. ft. and less that
do not meet any of the criteria of TMC 18.45.080B are not regulated.
18.06.934 Wetland, Scrub -Shrub
"Scrub -Shrub Wetland" means a wetland with at least 30% of its surface area
covered by woody vegetation less than 20 feet in height as the uppermost strata.
18.06.935 Yard
"Yard" means a required open space unoccupied and unobstructed by any
structure or portion of a structure from 30 inches above the general ground level of the
graded lot upward.
18.06.940 Yard, Front
"Front yard" means a yard extending between side lot lines across the front of a
lot. In MDR and HDR zones, this shall also include areas adjacent to 'access roads'.
18.06.945 Yard, Rear
"Rear yard" means a yard extending across the rear of the lot between inner side
yard lines.
18.06.950 Yard, Second Front
"Second front yard" means any yard adjacent to a public street that is not a front
yard as defined in the Definitions chapter of this title. (See also the Supplemental
Development Regulations chapter of this title and Figure 18-4.)
18.06.955 Yard, Side
"Side yard" means a yard extending from the rear line of the required front yard
to the rear lot line, or in the absence of any dearly defined rear lot line to the point on
the lot farthest from the intersection of the lot line involved with the public street.
j, Section 2. Severability. If any section, subsection, paragraph, sentence, clause or
phrase of this ordinance or its application to any person or situation should be held to
be invalid or unconstitutional for any reason by a court of competent jurisdiction, such
g4 invalidity or unconstitutionality shall not affect the validity or constitutionality of the
remaining portions of this ordinance or its application to any other person or situation.
Definitions 18.06 12/10/04 Page 30 of 31
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i pcfinitloos 18.0 12��0/04
44
1908
C lt
Y of Tukwila
Washington
Ordinance No.
AN ORDINANCE OF THE CITY COUNCIL OF THE CITY OF TUKWILA,
WASHINGTON, AMENDING TMC SECTION 18.50.110 TO EXPAND THE
PROTECTION OF ARCHAEOLOGICAL AND PALEONTOLOGICAL
SITES TO ALL ZONES OF THE CITY; REPEALING ORDINANCE
NO. 1853 §5; PROVIDING FOR SEVERABILITY; AND ESTABLISHING AN
11! EFFECTIVE DATE.
WHEREAS, archaeological and paleontological artifacts are important historical
and cultural resources which should be documented; and
WHEREAS, the location of these resources is not restricted to any particular
zoning district in the City; and
WHEREAS, the City desires that development activity is consistent with the
protection of archaeological and paleontological resources;
NOW, THEREFORE, THE CITY COUNCIL OF THE CITY OF TUKWILA,
WASHINGTON, DO ORDAIN AS FOLLOWS:
Section 1. Protection Expanded. TMC 18.50.110 is hereby amended to read as
follows:
18.50.110 Archaeological,/Paleontological Information Preservation Requirements
The following provisions shall apply in all zones:
1. If there is reason to believe that archaeological resources will be disturbed,
a cultural resources assessment shall be conducted and, if warranted, an
archaeological response plan and provisions for excavation monitoring by a
professional archaeologist shall be made prior to beginning construction. The
assessment should address the existence and significance of archaeological remains,
buildings and structures on the State or Federal historic registers, observable
paleontological deposits and may include review by the State Archaeologist.
2. It is recommended that the applicant coordinate a predetermination study
by a professional archaeologist during the geotechnical investigation phase, to
determine site archaeological potential and the likelihood of disturbing
archaeological resources.
3. Excavations into historically native soil, when in an area of archaeological
potential, shall have a professional archaeologist on site to ensure that all State
statutes regarding archaeological conservation/ preservation are implemented. The
applicant shall provide a written commitment to stop work immediately upon
discovery of archaeological remains and to consult with the State Office of
Archaeology and Historic Preservation (OAHP) to assess the remains and develop
appropriate treatment measures. These may include refilling the excavation with no
further responsibility.
Supplemental Development Regulations 18.50 12/10/04 Page 1 of 2
4. An applicant who encounters Indian burials shall not disturb them and
shall consult with OAHP and affected tribal organizations pursuant to State statutes.
5. The Director is authorized to:
a. conduct studies to generally identify areas of archaeological/
paleontological potential;
b. make determinations to implement these provisions; and
c. waive any and all of the above requirements, except for TMC 18.50.110-
4 (reporting of discovered Indian burials), if the proposed action will have no
probable significant impact on archaeological or historical resources that are eligible
for listing in the National Register of Historic Places, or on observable
paleontological resources. Examples of such actions include excavation of fill
materials, disturbance of less than 10,000 square feet of native soils to a depth of 12
inches, penetration of native soils with pilings over a maximum 8% of the building
footprint, and 'paving over native soils in a manner that does not damage cultural
resources. The above examples are illustrative and not determinative. A case -by-
case evaluation of archaeological /paleontological potential value and proposed
disturbance must be made.
Section 2. Repealer. Ordinance No. 1853, Section 5, is hereby repealed.
Section 3. Severability. If any section, subsection, paragraph, sentence, clause or
phrase of this ordinance or its application to any person or situation should be held to
be invalid or unconstitutional for any reason by a court of competent jurisdiction, such
p invalidity or unconstitutionality shall not affect the validity or constitutionality of the
remaining portions of this ordinance or its application to any other person or situation.
is Section 4. Effective Date. This ordinance or a summary thereof shall be published
in the official newspaper of the City, ty, and shall take effect and be in full force five days
after passage and publication as provided by law.
PASSED BY THE CITY COUNCIL OF THE CITY OF TUKWILA, WASHINGTON,
at a Special Meeting thereof this day of 2004.
ATTEST /AUTHENTICATED:
Steven M. Mullet, Mayor
Jane E. Cantu, CMC, City Clerk
Filed with the City Clerk:
APPROVED AS TO FORM BY: Passed by the City Council:
Published:
z Effective Date:
Office of the City Attorney Ordinance Number:
,Y e l..:•,
Supplemental Development Regulations 18.50 12/10/04 Page 2 of 2
A N I, y s.
It 1E..
1908
City u of T kwii Washington
Ordinance No.
AN ORDINANCE OF THE CITY COUNCIL OF THE CITY OF TUKWILA,
WASHINGTON, AMENDING ORDINANCE NO. 1819 §1 (PART),
PROVIDING EXEMPTIONS FOR SOME STRUCTURES AS THEY RELATE
TO SENSITIVE AREA BUFFERS; PROVIDING FOR SEVERABILITY; AND
•,..';'3'.;:q.::-..z...: ESTABLISHING AN EFFECTIVE DATE.
WHEREAS, the City has established limitations on the expansion and extension of
nonconforming uses and structures; and
WHEREAS, single family development may be affected by adoption of the new
r, sensitive area regulations; and
WHEREAS, TMC Section 18.70.050 contains an exemption under certain
circumstances for structures that have nonconforming yard setbacks; and
'-;r;'%. WHEREAS, it is appropriate to apply the same exemption found in Section
18.70.050 to nonconforming structures as they relate to sensitive area buffers;
"4'''' NOW, THEREFORE, THE CITY COUNCIL OF THE CITY OF TUKWILA,
4 WASHINGTON DO ORDAIN AS FOLLOWS:
Section 1. Regulations Amended. Ordinance No. 1819, Section 1 (part), as codified
at TMC Section 18.70.050, is hereby amended to read as follows:
Chapter 18.70
'....'i: NONCONFORMING LOTS, STRUCTURES AND USES
18.70.050 Nonconforming Structures
Where a lawful structure exists at the effective date of adoption of this title that
could not be built under the terms of this title by reason of restrictions on area, lot
i coverage, height,. y y
g ands or other characteristics of the structure, it may be continued so
long as the structure remains otherwise lawful subject to the following provisions:
`r; •r.,: 1. No such structure may be enlarged or altered in such a way that increases its
=;ri<: degree of nonconformity. Ordinary maintenance of a nonconforming structure is
:'.s permitted, pursuant to TMC Section 18.70.060, including but not limited to painting,
'':?::1"::•:-. roof repair and replacement, plumbing, wiring, mechanical equipment
repair /replacement and weatherization. These and other alterations, additions or
:.%;;x; enlargements may be allowed as long as the work done does not extend further into
any required yard or violate any other portion of this title. Complete plans shall be
required of all work contemplated under this section.
2. Should such structure be destroyed by any means to an extent of more than
50% of its replacement cost at time of destruction, in the judgment of the City's Building
:1;:- Official, it shall not be reconstructed except in conformity with provisions of this title,
except that in the LDR zone, structures that are nonconforming in regard to yard
setbacks or sensitive area buffers, but were in conformance at the time of construction
may be reconstructed to their original dimensions and location on the lot.
3. Should such structure be moved for any reason or any distance whatsoever, it
%:`t shall thereafter conform to the regulations for the zone in which it is located after it is
moved.
4. When a nonconforming structure, or structure and premises in combination, is
vacated or abandoned for 24 consecutive months, the structure, or structure and
premises in combination, shall thereafter be required to be in conformance with the
Nonconforming Lots, Structures and Uses 18.70 12/10/04 Page 1 of 2
regulations of the zone in which it is located. Upon request of the owner, the City
Council may grant an extension of time beyond the 24 consecutive months.
5. Residential structures and uses located in any single family or multiple family
residential zoning district and in existence at the time of adoption of this title shall not
be deemed nonconforming in terms of bulk, use, or density provisions of this title. Such
buildings may be rebuilt after a fire or other natural disaster to their original
dimensions and bulk, but may not be changed except as provided in the non-
conforming uses section of this chapter.
6. Single family structures in single- or multiple family residential zone districts,
which have legally nonconforming building setbacks, shall be allowed to expand along
the existing building line(s) if the existing distance from the nearest point of the
structure to the property line is not reduced.
7. In wetlands, watercourses and their buffers, existing structures that do not
meet the requirements of the Sensitive Areas Overlay District chapter of this title may
`ss be remodeled,: or replaced, provided that
r.. a. The new construction does not further intrude into or adversely impact an
undeveloped sensitive area or the required buffer;
b. The new construction does not threaten the public health, safety or welfare;
`?z and
c. The structure otherwise meets the requirements of this chapter.
8. In areas of potential geologic instability, coal mine hazard areas, and buffers, as
defined in the Sensitive Areas Overlay District chapter of this title, existing structures
may be remodeled, reconstructed or replaced, provided that
a. The new construction is subject to the geotechnical report requirements
and standards of Section 18.45.080E and 080F;
b. The new construction does not threaten the public health, safety or welfare;
c. The new construction does not increase the potential for soil erosion or
result in unacceptable risk or damage to existing or potential development or to
neighboring properties; and
d. The structure otherwise meets the requirements of this chapter.
9. A nonconforming use, within a nonconforming structure, shall not be allowed
to expand into any other portion of the nonconforming structure.
Section 2. Severability. If any section, subsection, .paragraph, sentence, clause or
phrase of this ordinance or its application to any person or situation should be held to
be invalid or unconstitutional for any reason by a court of competent jurisdiction, such
invalidity or unconstitutionality shall not affect the validity or constitutionality of the
remaining portions of this ordinance or its application to any other person or situation.
Section 3. Effective Date. This ordinance or a summary thereof shall be published
in the official newspaper of the City, and shall take effect and be in full force five days
after passage and publication as provided by law.
PASSED BY THE CITY COUNCIL OF THE CITY OF TUKWILA, WASHINGTON,
at a Special Meeting thereof this day of 2004.
ATTEST /AUTHENTICATED:
Steven M. Mullet, Mayor
Jane E. Cantu, CMC, City Clerk
Filed with the City Clerk
APPROVED AS TO FORM BY: Passed by the City Council:
Published:
Effective Date:
Office of the City Attorney Ordinance Number:
Nonconforming Lots, Structures and Uses 18.70 12/10/04 Page 2 of 2