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Ord 2074 - Sensitive Areas and Buffers (Repealed by Ord 2301)
0 C f la ity 0 1 Tu Washington Cover page to Ordinance 2074 The full text of the ordinance follows this cover page. AN ORDINANCE OF THE CFIY COUNCIL OF T14F CITY OF TUKWILA, WAS_ H_IN GTON, UPDATING REQUIREMENTS FOR REGULATING DEVELOPMENT ON SENSITIVE AREAS AND BUFFERS TO INCORPORATE NEW STATE REQUIREMENTS; REPEALING ORDINANCE NOS. 1758 (PAWI-), 1,770 §Z5 AND §26,1796 §3 (PART), AND 1834 §5; PROVIDING FOR SFVERA,BILI1rY,' AND ESTABLISHING AN EFFECTIVE DATE. Ordinance 2074 was amended or repealed by the following ordinances. 2174 §1 (part) 1 2301 0 19o8 City o f Tukwila Washington Ordinance No. 2074 AN ORDINANCE OF THE CITY COUNCIL OF THE CITY OF TUKWILA, WASHINGTON, UPDATING REQUIREMENTS FOR REGULATING DEVELOPMENT ON SENSITIVE AREAS AND BUFFERS 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 EFFECTIVE 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 accommodate 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 stormwater 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 prepare 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 12/10/04 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 THE CITY OF TUKWILA, 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 hazardous 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 12/14/04 Page 2 of 26 RCW 36.7OA, 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. Protect the community's aesthetic resources and distinctive features of natural lands and 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. 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 information may supplement scientific information, but is not an adequate substitution for valid and available scientific information. C. Incomplete or unavailable scientific information 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. 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 all 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: Class 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. SAO Adoption 18.45 12/14/04 Page 3 of 26 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. SAO Adoption 18.45 12/14/04 Page 4 of 26 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 hydrologist, 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 storm water 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.O4O.E. 2. Geotechnical reports for Class 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 Class 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 12/14/04 Page 5 of 26 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 interpretations, 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 peer review, at the expense of the applicant. 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. 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 E. 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 12/14/04 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 storm water 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 storm water detention. SAO Adoption 18.45 12/14/04 Page 7 of 26 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 storm water, restriction of groundwater movement, slides, pollution, habitat disturbance, any loss of flood carrying capacity and storage capacity, and excavation or fill detrimental to the environment. 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. Essential 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 conform 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 extent 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; SAO Adoption 18.45 12/14/04 Page 8 of 26 (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) (6) Flood control or water quality enhancement by the City; 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 care 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 "Classification 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. SAO Adoption 18.45 12/14/04 Page 9 of 26 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: SAO Adoption 18.45 12/14/04 Page 10 of 26 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, root wads/ 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 storm water detention capabilities; d. The alteration will not lead to unstable earth conditions or create an erosion hazard or contribute to scouring actions; SAO Adoption 18.45 12/14/04 Page 11 of 26 and e. The alteration will not be materially detrimental to any other property; 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 sites 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 SAO Adoption 18.45 12/14/04 Page 12 of 26 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 to 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 another 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; SAO Adoption 18.45 12/14/04 Page 13 of 26 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- vegetation 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 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 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; 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. SAO Adoption 18.45 12/14/04 Page 14 of 26 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. SAO Adoption 18.45 12/14/04 Page 15 of 26 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 approved 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 determined 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 super span culverts for rebuilding of a streambed. 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. SAO Adoption 18.45 12/14/04 Page 16 of 26 f. Storm water 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 maintained 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. SAO Adoption 18.45 12/14/04 Page 17 of 26 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 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. 18.45.120 Areas of Potential Geologic Instability Designation, Rating and Buffers A. Designation. Areas of potential geologic instability are classified as follows: 1. Class 1 area, where landslide potential is low, and which slope is less than 15 2. Class 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 steeply than 40 4. Class 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 storm water 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 development proposal containing or threatened by an area of potential geologic instability Class 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 SAO Adoption 18.45 12/14/04 Page 18 of 26 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 areas: 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 12/14/04 Page 19 of 26 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 letter 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. Assurance Devices. Whenever the City determines 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 12/14/04 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 12/14/04 Page 21 of 26 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. S. 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 Development. 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, SAO Adoption 18.45 12/14/04 Page 22 of 26 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 clearly demonstrates overall environmental 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 meet 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 12/14/04 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 Development. The Director shall confirm that an emergency exists and determine what, if any, 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. 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 .4 12/14/04 Page 24 of 26 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. SAO Adoption 18.45 12/14/04 Page 25 of 26 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 ATTEST/ AUTHENTICATED: (C t /cid (4 1 Jane E. Cantu, CMC, City Clerk APPROVED AS T• i M BY: Office of th ney SAO adoption 18.45 12/10/04 Page 26 of 26 Steven M. Mullet, Mayor Filed with the City Clerk: Passed by the City Council: Published: Effective Date: Ordinance Number: 2004. /2 -Q$ J2- /3 12- i'7- DL/ Z. 22- 041- SUMMARY OF ORDINANCE No. 2074 City of Tukwila, Washington On December 13, 2004, the City Council of the City of Tukwila, Washington, adopted Ordinance No. 2074, the main points of which are summarized by its title as follows: An ordinance of the City Council of the City of Tukwila, Washington, updating requirements for regulating development on sensitive areas and buffers 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 effective date. The full text of this ordinance will be mailed upon request. Approved by the City Council at a Special Meeting of December 13, 2004. /sD Jane E. Cantu CM Cit Y Clerk Published Seattle Times: December 17, 2004 ATTACHMENT A JUNE 2003 BEST AVAILABLE SCIENCE ISSUE PAPER: WETLANDS Prepared for: City of Tukwila Department of Community Development 6300 Southcenter 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 BUFFERS 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 Improvement 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 VALUES OF WETLANDS AND WETLAND BUFFERS IN TUKWILA 12 4.0 DATA GAPS 13 5.0 RECOMMENDATIONS ERROR! BOOKMARK NOT DEFINED. 5.1 Regulatory Framework of Wetlands Regulations Error! Bookmark not defined. 6.0 REFERENCES 14 Adolfson Associates, Inc. Page i June 2003 1.0 INTRODUCTION 1.1 Project Authorization At the request of the City of Tukwila, Adolfson Associates, Inc. (Adolfson) 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 revision 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." In 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 not currently publicly available. 1.3 Overview 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 Green/Duwamish 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, Inc. Page 1 June 2003 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 res 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 determine 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 information 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 information was analyzed in the preparation of this study. This review of Best Available Science will be updated with detailed inventory information 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 information is a summary of existing literature and is not intended to be an exclusive list of all best available science currently published on wetlands, but is intended to provide a brief overview of scientifically valid information 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 inventory (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 formally defined by the Corps of Engineers (Corps) (Federal Register, 1982), the Environmental Protection Agency (EPA) (Federal Register, 1986), the Washington Shoreline Management Act (SMA) (1971) 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 normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include Adolfson Associates, Inc. Page 2 June 2003 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 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. 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 al., 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 other 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 al., 1979; Adamus et al., 1987; Mitsch and Gosselink, 2000; Hruby, 1995; Reppert et al., 1979; Cooke, 1995). These functions include: Flood water attenuation and flood peak desynchronization; Stream base flow maintenance and groundwater support; Shoreline protection; Water quality improvement; Biological support and wildlife habitat; and Adolfson Associates, Inc. June 2003 Page 3 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 stormwater inflow (Marble, 1992; Reinelt and Horner, 1991). The loss of wetland systems in urban areas affects their function in attenuating stormwater runoff, resulting in increased flood frequency and higher peak flood flows in drainage basins (Azous and Horner, 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, stormwater control facilities, or potentially the use of isolated, degraded, and low -value wetlands as stormwater 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 stormwater 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 Horner, 2001). Use of only degraded, low quality wetlands that are not associated with stream systems for stormwater control can limit these impacts (Horner et al., 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 Horner, 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 Adolfson Associates, Inc. Page 4 June 2003 studies indicate that some wetland types provide greater recharge to groundwater systems than others (Carter et al., 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 al., 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 support to streams (Booth, 2000; Schueler, 2000; City of Portland, 2001; 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 al., 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 al., 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 herbicides 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). Adolfson Associates, Inc. Page 5 June 2003 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 (Horner 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, 2001; Booth, 2000; May et al., 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; Zedier et al., 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 al., 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 al., 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, 2001; Azous and Horner, 2001; Hruby et al., 1999). Wetlands and surrounding uplands provide specialized habitat and wildlife linkages for special status species such as 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 greenways 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. Adolfson Associates, Inc. Page 6 June 2003 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 Army Corps of Engineers, are more quantitative. For example, the Hydrogeomorphic Method (HGM) is based on the concept that wetland functions are driven primarily by the wetland's geomorphology (i.e., 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 (TVA) 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 HGM approach and is designed to provide a more scientific approach to assessing wetland functions Hruby et al, 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 based on 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 al., 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 Adolfson Associates, Inc. Page 7 June 2003 summarized results of a rating form. The rating form 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 are particularly 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 of Ecology; 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 al., 1992a; Castelle and Johnson, 2000; Desbonnet et al., 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. Adolfson Associates, Inc. Page 8 June 2003 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 these 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 five percent more sediment (Wong and McCuen, 1982). 2.7 Wetland Mitigation Enhancement Strategies The Clean Water Act Section 404(b)(1) 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 any one 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 al., (1992b) reported that 50 percent or more of the mitigation projects studied did not meet permit requifements. Common problems included: Adolfson Associates, Inc. Page 9 June 2003 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, 2001). 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 significant contribution to water quality and quantity functions. Mitigation has been more successful for some wetland types, including emergent and open water wetlands (Castelle et al., 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 present and Adolfson Associates, Inc. Page 10 June 2003 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 performance 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 Kentula, 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., 1992a; 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 functions, 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 p1aAt 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 buffer. Since buffer mitigation areas 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). Adolfson Associates, Inc. Page 11 June 2003 Several authors and agencies have recommended various replacement ratios (Castelle et al., 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 and 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) recommends 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 IV 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. Adolfson Associates, Inc. Page 12 June 2003 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 vegetation 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 urban 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 Adamus, P.R., Clairan, E.J., Smith, R.D., and Young R.E. 1987. 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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 -31, 2000, Portland, Oregon. pp. 445 -449. Washington Department of Ecology. 1993. Washington State Wetlands Rating System Western Washington. Washington Department of Ecology, Olympia, Publ. #93 -74. Washington Department of Ecology. 1996. Water Quality Guidelines for 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. 1992. 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. 23 pp. Zedler, J.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. Page 18 June 2003 ATTACHMENT B JUNE 2003 BEST AVAILABLE SCIENCE ISSUE PAPER: WATERCOURSES Prepared for: City of Tukwila Department of Community Development 6300 Southcenter 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 Overview of Growth Management Act Requirements 1 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 1 4 2.2.3 In- stream Structural Diversity 5 2.2.4 Biotic Input 7 3.0 FUNCTION AND VALUES OF RIPARIAN BUFFERS 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 Green/Duwamish 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 4.0 FUNCTIONS AND VALUES OF WATERCOURSES AND RIPARIAN AREAS IN TUKWILA 14 5.0 DATA GAPS 15 6.0 RECOMMENDATIONS ERROR! BOOKMARK NOT DEFINED. 6.1 Regulatory Framework of Watercourse Regulations Error! Bookmark not defined. 7.0 REFERENCES 16 APPENDIX A: EFFECTS OF ECOSYSTEM ALTERATIONS ON SALMONIDS A4 APPENDIX 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. Page i June 2003 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 preliminary 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 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). 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 (GMA) to ensure that cities and counties consider reliable scientific information when 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 planning alternatives; 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. Page 1 June 2003 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). This report 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 incorporated city with a population of approximately 15,000 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 Green/Duwamish 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 Green/Duwamish 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 18.06.920 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 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 that are used by salmonids or to convey or pass through stream flows naturally occurring prior to construction of such devices." Tukwila is a Iargely 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 Green/Duwamish River, and water -based commerce has been, and continues to be, an important component of these commercial and industrial activities. Development of the immediate shoreline of the Green/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. Page 2 June 2003 scientifically valid information useful for local planning and regulatory review. 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 Watercourses and Riparian Areas Stream systems are one of the most productive natural systems. Riparian areas play a 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 al., 1997; Horner 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 al., 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 al., 2000). Increases in peak flow are more apparent as smaller, more frequent floods relative to larger floods (Booth et al., 2001). Stream flow or discharge has a 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. Page 3 June 2003 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, 2001; City of Portland, 2001). 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 Iower 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 Temperature 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, 2001; City of Portland, 2001; Sullivan et al., 1990). The general range of temperatures required to support healthy salmonid populations is generally considered to be between about 39 and 63 F (NMFS, 1996; USFWS, 1998). Cutthroat trout have the highest range of temperature tolerances of native salmonids (Pauley et al., 1989 in City of Portland, 2001). Above 63 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 al., 1986). Lethal limits vary widely by species and development stage; constant temperatures in excess of 78 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 Oxygen 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 Adolfson Associates, Inc. Page 4 June 2003 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 al., 1997). Undisturbed 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, 2001). The primary sources of metals and hydrocarbons in urban areas appear to be industry and automobiles (Lynch et al., 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 al., 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 utilize 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 Adolfson Associates, Inc. Page 5 June 2003 (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 Larae Woody 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 woody 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 half 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 Quality and Quantity 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 al., 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. Adolfson Associates, Inc. Page 6 June 2003 Pools, although important for most species of salmonid fish, are just one type of habitat that salmonid 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 Floodolain 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, 2001). 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 failing 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, 2001). 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. Adolfson Associates, Inc. Page 7 June 2003 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 at, 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). 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, Tess than 5 feet wide Type 4 and 5 (low mass wasting potential) Type 4 and 5 (high mass wasting potential) 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 150 -feet (30 to 45 meters) wide provide most (on the order of 80 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 research 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). Adolfson Associates, Inc. June 2003 Table 1. Riparian Habitat Area Buffer Recommendations: Washington Department of Fish and Wildlife 250 feet 200 feet 150 feet 150 feet 225 feet Page 8 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 material. 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 play a 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 al., 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 al., 1985; Castelle Johnson, 2000; Wong McCuen, 1982; Castelle et al., 1992). Studies have concluded that buffers of 100 feet can achieve sediment removal efficiencies of 75 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 (Roby et al., 1977; Newbold et al., 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 al., 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. Adolfson Associates, Inc. Page 9 June 2003 The effectiveness of the buffer for this function is significantly influenced by site specific conditions such as soil type, subsoil permeability, 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 165 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 general trend has emerged that places 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 al., 2002; Richards et al., 1996). The loss or disturbance of native riparian area is closely tied to urbanization in a watershed (Horner 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 quality functions are compounded by degradation of riparian areas (Bledsoe and Watson, 2001; May et al., 1997). Effectiveness of a riparian area is limited where streams have been channelized or drainage routed through stormwater detention and treatment systems. 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 al., 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). Adolfson Associates, Inc. Page 10 June 2003 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 strategies 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; Horner 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, and 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 salmonids 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 Adolfson Associates, Inc. Page 11 June 2003 for salmonid species and other aquatic organisms. The species potentially present in Tukwila waterbodies includes all Pacific salmon (except pink salmon), bull trout/Dolly Varden, coastal resident/sea -run cutthroat trout, rainbow trout/steelhead, and long -fin smelt (WDFW, 1998 and 1994; Wydoski and Whitney, 1979). 3.3.1 Green /Duwamish River The Green/Duwamish 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 Green/Duwamish River watershed is often referred to as Water Resources Inventory Area 9 (WRIA 9) (Kerwin, 2001). Both natural and man made modifications during the early 1900's reduced the drainage basin to its present configuration, which is one quarter of its original extent (Warner and Fritz 1995). Presently, the Green/Duwamish 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 Green/Duwamish 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 Green/Duwarnish River serves as an important salmonid transportation and rearing area (Williams et al., 1975). Williams states that the lower Green/Duwamish 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 Green/Duwamish 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), steelhead trout (0. mykiss), and other anadromous fish species such as lamprey (Lampetra sp.), smelt (Spirinchus thaleichthys), sticklebacks (Gasterosteus aculeatus), and mountain whitefish (Prosopium williamsoni) were also found in the lower Green/Duwamish 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 stormwater 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). Adolfson Associates, Inc. Page 12 June 2003 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 144th Street, Pacific Highway South, Strander Boulevard, and the Green/Duwamish 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 Green/Duwamish 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 Green/Duwamish River. While Gilliam 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 Green/Duwamish 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 Green/Duwamish 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 Green/Duwamish 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 Green/Duwamish River through a 60 -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 Green/Duwamish 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 Green/Duwamish River near South 180th 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 evaluated 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 Tukwila are 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 Green/Duwamish 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 Green/Duwamish 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 Green/Duwamish 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. Page 14 June 2003 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 al., 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. Page 15 June 2003 6.0 REFERENCES Adolfson Associates, Inc. 1999. Draft City of Tukwila Endangered Species Act Screening Project. Seattle, Washington. Benfield, E. F. and J. R. Webster. 1985. 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National Council for Air and Stream Improvement Tech. Bull. No. 799. Adolfson Associates, Inc. Page 16 June 2003 Castelle, A.J., C. Conolly, M. Emers, E.D. Metz, S. Meyer, and M. Witter. 1992. Wetland Buffers: An Annotated Bibliography. Publ. 92 -11. Adolfson Assoc., for Shorelands and Coastal Zone Manage. Program, Washington Dept. of Ecology, Olympia, WA. Castelle, A.J., C. Conolly, M. Emers, E.D. Metz, S. Meyer, M. Witter, S. Mauermann, T. Erickson, and S.S. Cooke. 1992. Wetland Buffers: Use and Effectiveness. Publ. 92 -10. Adolfson Assoc., for Shorelands and Coastal Zone Manage. Program, Washington Dept. of Ecology, Olympia, WA. City of Portland. 2001. Streamside Science and an Inventory of Significant Riparian and Wetland Resources. Discussion Draft. City of Portland, Oregon Bureau of Planning. City of Tukwila. 2002. Tukwila Municipal Code (TMC). Chapter 18.06.920. Corbett, E.S. and J.A. Lynch. 1985. Management of Streamside Zones on Municipal Watersheds. pp. 187 -190. In R. R. 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Center for Urban Water Resources Management. Leavitt, J. 1998. The functions of riparian buffers in urban watersheds. Masters Thesis. University 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. Adolfson Associates, Inc. Page 18 June 2003 Madison,. C.E., R.L. Blevins, W.W. Frye, and B.J. Barfield. 1992. Tillage and Grass Filter Strip Effects upon Sediment and Chemical Losses. In Agronomy Abstracts. ASA, Madison, WI. May, C.W., R.R. Horner, 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. Horner, J.R. Karr, and B.W. Mar. 1997. Quality Indices for Urbanization Effects in Puget Sound Lowland Streams. Wat. Res. Tech. Rep 154. Washington Department of Ecology, Olympia WA. McDade, M.H., F.J. Swanson, W.A. McKee, J.F. Farnklin, and J. Van Sickle. 1990. Source Distances for Coarse Woody Debris entering Small Streams in Westem 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 Ecology, Olympia, WA. Meehan, W.R., F.J. Swanson, and J.R. Sedell. 1977. Influences of Riparian Vegetation on Aquatic Ecosystems with Particular Reference to Salmonid Fishes and Their Food Supply. USDA Forest Service General Technical Report MR -43. Contributed paper, Symposium on the Importance, Preservation and Management of the Riparian Habitat, July 9, 1977, Tucson Arizona. Moyle, P. B. and J. J. Cech, Jr. 1998. Fishes, An introduction to Ichthyology. Second Edition. Prentice Hall. Englewood, California. Murphy, M.L. and K V. Koski. 1989. 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Springer Verlag. New York, New York. 542 p. Adolfson Associates, Inc. Page 19 June 2003 National Marine Fisheries Service. 1996. Making Endangered Species Act Determinations of Effect for Individual or Grouped Actions at the Watershed Scale. NMFS Environmental and Technical Services Division. Newbold, J.D., D.C. Erman, and K.B. Roby. 1980. Effects of Logging on Macroinvertebrates in Streams With and Without Buffer Strips. Can. J. Fish Aquat. Sci. 37:1076 -1085. Pentec Environmental. 2002. Use of Best Available Science in City of Tukwila Shoreline Buffer Regulations Draft Final Report. Pitt, D.G., W.G. Gould, and L. LaSota. 1986. Landscape Design to Reduce Surface Water Pollution in Residential Areas.. Resources Information Bulletin No. 5. Univ. of Maryland. Cooperative Extension Service. 10 p. Reiser, D.W. and T.C. Bjornn. 1.979. Habitat Requirements of Anadromous Salmonids. USDA Forest Service. Pacific Northwest Forest and Range Experiment Station. General Technical Report PNW -96. 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A Framework to Assist in the Making of Endangered Species Act Determinations of Effect for Individual or Grouped Actions at the Bull Trout Subpopulations Watershed Scale (Draft).USFWS, Washington, DC. Van Sickle, J and S.V. Gregory. 1990. Modeling Inputs of Large Woody Debris to Streams from Falling Trees. Can. J. For. Res. 20:1593 -1601. Vanderholm, D.H., and E.C. Dickey. 1978. ASAE Paper No. 78 -2570. ASAE Winter Meeting, Chicago, IL. Vannote, R.L., G.W. Minshall, K.W. Cummins, J.R. Sedell, and C.E. Cushing. 1980. The River Continuum Concept. Canadian Journal of Fisheries and Aquatic Science 37:130 -137. Warner, E.J., and R.L. Fritz. 1995. The Distribution and Growth of Green River Chinook Salmon (Oncorhynchus tshawytscha) and Chum Salmon Oncorhynchus keta) Outmigrants in the Duwamish Estuary as. a Function of Water Quality and Substrate. Muckleshoot Indian Tribe Fisheries Department. Auburn, Washington. 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A Process for Evaluating Pesticides in Washington State Surface Waters for Potential Impacts to Salmonids. WSDA Publication No. 057, Olympia, WA. Williams, R.D., and E.D. Lavey. 1986. Selected Buffer References. Water Quality and Watershed Research Laboratory, Durant, OK. Williams, R.W., R.M. Laramie, and J.J. James. 1975. A Catalog of Washington Streams and Salmon Utilization: Volume 1, Puget Sound Region. Washington State Department of Fisheries. Olympia, Washington. Wilson, L.G. 1967. Sediment Removal from Flood Water by Grass Filtration. Transactions of the ASAE pp. 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. Wydoski, R.S. and R.R. Whitney. 1979. Inland Fishes of Washington. University of Washington Press. Seattle, Washington. Young, R.A., T. Huntrods, and W. Anderson. 1980. Effectiveness of Vegetated Buffer Strips in Controlling Pollution from Feedlot Runoff. JEnviron. Qual. 9:483497. Adolfson Associates, Inc. June 2003 Page 22 APPENDIX A: EFFECTS OF ECOSYSTEM ALTERATIONS ON SALMONIDS Adolfson Associates, Inc. June 2003 Appendix A Sediment/Substrate Adolfson Associates, Inc. June 2003 Attee& Increased Temperature Dissolved Oxygen s o i oI ofshes e` cirTheir' Ecos ',stems 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. Decreased Temperature Cessation of spawning, increased egg mortalities, Water Quality susceptibility to disease. Reduced survival of eggs and alevins, smaller size at emergence, increased physiological stress, reduced growth. Gas Supersaturation Increased mortality of migrating salmon. Nutrient Loading Increased primary and secondary production, possible oxygen depletion during extreme algal blooms, tower survival and productivity, increased eutrophication rate of standing waters, certain nutrients (e.g., nonionized ammonia, some metals) possibly toxic to eggs and juveniles at high concentrations. Surface Erosion Reduced survival of eggs and alevins, reduced primary and secondary productivity, interference with feedings, behavioral avoidance and breakdown of social organization, pool filling. Mass Failures and Reduced survival of eggs and alevins, reduced primary Landslides and secondary productivity, behavioral avoidance, formation of upstream migration barriers, pool filling, addition of new large structure to channels. Physical Barriers Loss of spawning habitat for adults; inability of juveniles Habitat Access to reach overwintering sites or thermal refugia, loss of summer rearing habitat, increased vulnerability to predation. Channel Structure Flood Plains Loss of overwintering habitat, loss of refuge from high flows, loss of inputs of organic matter and large wood, loss of sediment removal capacity. Side Channels Loss of overwintering habitat, loss of refuge from high flows. Pools and Riffles Shift in the balance of species, loss of deep water cover Channel Structure and adult holding areas, reduced rearing sites for (contd.) yearling and older juveniles. Large Wood Loss of cover from predators and high flows, reduced sediment and organic matter storage, reduced pool forming structures, reduced organic substrate for macroinvertebrates, formation of new migration barriers, reduced capacity to trap salmon carcasses. Page A -1 Hydrology Exogenous Material Substrate Hyporheic Zone (biologically active groundwater area) Discharge Peak Flows 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 Exotic Organisms /Plants Source: htto:// www .osmic.oro /efh/Jan99- sec3 -2.htm Adolfson Associates, Inc. June 2003 �E ±�c. arS�liiio�;i s es�t�li�d'rT�'elraEca$ .stems` Reduced survival of eggs and alevins, Toss 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. 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 macroinvertebrates. 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 Adolfson Associates, Inc. June 2003 APPENDIX B: LITERATURE FINDINGS, RIPARIAN BUFFERS BY FUNCTION Appendix B Sediment Removal Pollutant Removal Large Woody Debris Recruitment Stream Water Temp. Moderation Adolfson Associates, Inc. June 2003 100 100 100 200 200 200 290 295 400 13 15 50 53 100 100 120 300 860 16 -33 33 50 65 -100 65 100 100 150 150 165 330 35 80 40 Castelle Johnson, 2000 I Lynch et al, 1985 Wong McCuen, 1982 Wong McCuen, 1982 Homer Mar, 1982 Broderson, 1973 'Gilliam Skaggs, 1986 'Wilson, 1967 Doyle et al., 1975 Madison et al., 1992 1 Castelle et al., 1992 (Jacobs Gilliam, 1985 Lynch et al., 1985 Grismer, 1981 Young et al., 1980 Vanderholm Dickey, 1978 Vanderholm Dickey, 1978 Castelle Johnson, 2000 McDade et al., 1990 'McDade et al, 1990 Castelle Johnson, 2000 'Murphy Koski, 1989 'McDade et al., 1990 I May et al., 1997 I Harmon et al., 1986 Robison Beschta, 1990 Van Sickle Gregory, 1990 1 May et al., 1997 I Brazier Brown, 1973 Corbett Lynch, 1985 Approaches 100% particulate organic matter production 175 -80% removal 190% removal 95% removal 180% removal in grassy swale Removal of most sediment on slopes 50% 150% deposition Clay Grass buffers 90% removal of NH4 -N, NO3- N, and PO4 -P 180% pollutant removal Most sediment removal 175 -80% pollutant removal Reduced fecal coliforms by 60% Minimum for nutrient reduction 80% removal on a 0.5% slope 80% removal on a 4% slope 40 -60% LOD input <50% of naturally occurring LOD 160-90% of all LOD 80- 100% LOD input 195% of LOD 185% of nat. occurring LOD I Recommended minimum Supply most LOD Supply most LOD Minimum for LOD input 'Sensitive streams 60 -80% shade Control stream temperature fluctuations Page B -1 Maintenance of Benthic Communities Wildlife Habitat Wolfson, 2002) AdoIfson Associates, Inc. June 2003 50 55 55 75 -90 100 100 33 100 100 100 100 >100 >100 100 100 -300 100 310 105 B rode rson,1973 Steinblums et al., 1984 Moring, 1975 I Steinblums et al., 1984 Beschta et al., 1987 Lynch et al, 1985 Culp and Davies, 1983 Roby et al., 1977 Newbold et al., 1980 Castelle Johnson, 2000 Erman et al., 1977 May et al., 1997 Erman et al., 1977 Gregory et al., 1980 Castelle et al., 1992 Rudolph Dickson, 1990 Groffman et al., 1990 Buffer widths decrease as tree heights Increase Maximum angular canopy density Maintain stream temperature if forested conditions 160 -80% shade Minimum shade to level of old growth forest Maintain stream temperatures that are within 1C of areas that are;fElt%r forested Minimurr for healthy communities Maintain benthic communities similar to streams in fully forested areas Maintain healthy benthic communities Minimum for healthy benthic communities (Maintain macroinvert diversity Benthic integrity or B IBI high in stream with >70% upstream buffer intact Macroinverts similar to prelogged condition 1 Macroinvertebrate diversity Range for most wildlife species Reptiles amphibians Forested buffer for minimizing noise impacts to wildlife Page B -2 November 8, 2002 City of Tukwila Dept. of Community Development 6300 Southcenter Boulevard, Suite 100 Tukwila, Washington 98188 Attn: Ms. Nora Gierloff RE: CITY OF TUKWILA GEOLOGICALLY HAZARDOUS AREAS ORDINANCE REVIEW TUKWILA, WASHINGTON ATTACHMENT C 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. William D. Evans, P.G. Associate 11/23102 1:1TROJEC'M31 1 .005.0101Crr Ltr DR Rpt.doc WDE/jas 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 QEOLOGICALLY 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 CONSIDERATIONS 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 BIBLIOGRAPHY 11/13/02 QASAO\FINAL LANDAU REPORTTUKWfLA GEOHAZ REV RPT•DOC 11 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 area Fish and wildlife habitat conservation areas In 1995 the Iegislature added a new section to the GMA [RCW 36.70A.172(1)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 thereaft.r. 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). 11/13/02 Q:1SA01F1NAL LANDAU REPORTITUKW1LA GEOHAZ REV RPT.DOC 1 -1 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 geologicali 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 1 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. 11/13/02 Q:\SAO \FINAL LANDAU REPORI\TUKWILA GEOHAZ REV RPT.DOC 2 -1 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: 1. Erosion hazard 2. Landslide hazard 3. Seismic hazard, or 4. Areas subject to other geological 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: 1) Erosion Hazard Areas: At least those areas identified by the USDA Soil Conservation Service as having "severer rill and inter-rill .erosion hazard. 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 impermeable 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 f) 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 i) Any areas with a slope of 40% or steeper and with a vertical relief of ten 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. g) h) 11 /13/02 QASAOWINAL LANDAU REPOR7ITUKWILA GEOHAZ REV RPT.DOC 3 -1 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 Green/Duwamish River Valley). b) Mine hazards associated with known and unknown underground workings. c) Expansive soil associated with weathered bedrock. 11/13/02 Q:1SAOWINAL LANDAU REPOR1ITUKWn.A GEOHAZ REV RPT.DOC 3 -2 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 "characteristics" of a valid scientific process to meet BAS criteria include:. peer review; methods; _logical conciusions.. and reasonable inferences; 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 1, WAC 365 195- 905(5)(h). 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 protect the functions and values of geologically: hazardous areas. This requirement is contained in RCW 36.70A.172, where it is applied to all critical areas. In an urban land use context, geologically hazardous areas typically do not have measurable "functions and values." They represent landforms which, when coinbined.._with certain geologic, anthropogenic and /or meterologic events, can be a threat to life and property, especially in areas where inadequate /inappropriate, development,has occurred. For example, the Duwamish River Valley 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 reference 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. 1!/13/02 Q:ISAO\ETNAL LANDAU REPORT\TUKWILA GEOHAZ REV RPT.DOC 4 -1 Copies of, or reference to, any nonscientific information used during geologically hazardous areas decision making, and the rationale for using such infuriation. This type of information is typically site specific and often quite useful. Accordingly, the source should be documented and any qualifiers applied. Steps te address risks attributedto geologically hazardous areas. This is most often implemented through critical areas regulations, the UBC and zoning. 11/13102 Qf SAOIFINAL LANDAU REPORT\TUKWILA GEOHAZ REV RPT.DOC 4 -2 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: Eastern 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." Central 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 compile sources of relevant scientific and nonscientific information regarding geologically hazardous areas (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 process 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(1) 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 regulated primarily 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 11/13/02 Q:ISAO\FINAL LANDAU REPORTITUKWILA GEOHAZ REV RPT.DOC 5 -1 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. Comtarison :by the Cityof various,:setbacks and buffers will.•likely be .requiredl to verify -that :the buffers and setbacks for geologically. hazardous areas are not unneccssarily over-or under protective as comp to required setbacks` and buffers' for other' critical areas. 1I /13/02 Q:iSAO1FINAL LANDAU REPORTITUKWILA OEOHAZ REV RPT.DOC 5 -2 3' 7. 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 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 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 reeommended.list of BAS resource materials includes 2 '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 Q1SAO1FINAL LANDAU REPOR7\TUKWILA GEONAZ 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. (Out of Print. available through King County) Mullineaux, D.R., 1965, Geologic map of the Renton quadrangle, King County, Washington: U.S. Geological Survey, Geologic Quadrangle Map GQ -405, scale 1:24000. 0:00py=included with rtbort) Mullineaux, D.R., 1961, Geology of the Renton, Auburn, and Black Diamond quadrangles, Washington: U.S. Geological Survey, Professional Paper 672, scale 1:24000. iv included witlr`keport) Tubbs, D.W., 1974, Landslides and associated damage during early 1972 in part of west central King County, Washington: U.S. Geological Survey, Miscellaneous Investigations Series Map I- 852 -B, scale 1:48000. (l eeiy iritludei'ii►th ieborl) Waldron, H.H., 1962, Geologic map of the Des Moines quadrangle, Washington: U.S. Geological Survey, Geologic Quadrangle Map GQ -159, scale 1:24000. (1 comrincluded with report) Yount, J.C., Minard, J.P., and Dembroff, G.R., 1993, Geologic map of surficial deposits in the Seattle 30' by 60' quadrangle, Washington: U.S. Geological Survey, Open -File Report OF -93- 233, scale 1:100000. fl eoptritihlude`d' "W ih'i i or t Aerial Photos`— Public and Private Sources. Walker and Associates. Seattle. WA) City of Tukwila., 1999. Tukwila Topographic Base Map, 10 ft. contours City of Tukwila, Washington. Lty Owned) GeoEngineers, Inc., Post 1990. Geologic Hazards Evaluation, Tukwila, Washington. City of Tukwila, Washington. (City Owned) King County Department of Natural Resources, 1998. King County, Washington Surface Water Design Manual. September. (Available through King Countvl King County sensitive areas map folio, GIS- derived sensitive areas information, includes geologically hazardous areas mapping information. King County, Washington. (Available through King County, Washington State Department of Natural Resources. 2002. Geologic Map of Washington Northwest Quadrant, Geologic Map GM -50. (1 copy 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. ocd.wa. /info/IQd/Qrowth/bas /BAS Citations Final pdf) Project specific reports submitted by applicant. Cite as nonscientific if information has not been peer reviewed. Owned). Local Information, including but not limited to, photographs, diary entries, written and verbal 11113/02 Q:ISAOIFINAL LANDAU REPORTTUKWILA GEOHAZ REV RPT.DOC 6 -2 'statements, etc., provided the source is documented and information is not used in lieu of other valid scientific data. MO Ownedt 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: httn://www.ecv.wa.gov/programs/sea/nubs/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. nov/ nrogra rms /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.eov /programs /sea/aubs/95- 107 /intro.himl) 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. (I copu.ifalt?ded ;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 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 co..r rcluded.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 1/13/02 Q :\SAOWINAL LANDAU REPORMUKWILA GEOHAZ REV RPT.DOC 6 -3 7.1 POLICIES The City's 1995 Comp Plan Natural Environment element is based on Tukwila's 1991 Sensitive Areas Ordinance. Due to the number of GMA changes that have occurred during the past 7 years, it is our opinion that the Comp Plan should be updated during the next amendment cycle. Amendments should conform with GMA requirements, and for clarity, should use the terms and general regulatory approach outlined in RCW 36.70A; WAC 365 -190 and WAC 365 -195. Specific suggested changes to the Comp Plan are summarized below: 1 The GMA uses the terms "c'ltieal:; to include wetlands, frequently flooded areas, critical aquifer recharge areas, geologically hazardous areas, and fish and wildlife habitat conservation areas. We suggest that these 'or sit iilar`terrris: be: used.throughout. the Cotrip Plan. At the current time, the Natural Environment section of the Comp Plan includes a discussion on Natural Resource Lands (forest, mineral and agricultural lands [WAC 365- 195- 400(1)]. Historically, such lands have been managed on a for profit basis. Therefore, we suggest .moving this brief section to the Economic Development element of the Comp Plan. 3. The fifth paragraph of the Natural Environment element describes how land use and economic development practices are balanced to provide the direction for management of critical areas. By adopting RCW 36.70A:172 in 1995, the Legislature apparently sought to elevate the importance of science with respect to critical areas management. Accordingly, we of the Comp Plan language to reflect the legislative,intent (e.g. emphasize protection of critical areas over economics and/or political factors). 4. Goal 4 -3 and related policies deal specifically with the topic of geologically hazardous areas. We suggest expanding this section to address specific issues associated with geologically hazardous areas as summarized below. Erosion Hazard Areas: The principal goals within high erosion hazard areas should be: 1) protect anadromous fisheries, and 2) prevent excessive migration of soil/weathered bedrock via wind and water. Policies which flow from these goals 'should focus on code sections dealing with critical areas, land altering and tree preservation. 7.0 POLICY AND REGULATORY CONSIDERATIONS 11/I3/02 Q:1SAO\FINAL LANDAU REPORTTUKWILA GEOHAZ REV RPT.DOC 7 -1 Landslide Hazard Areas: The principal goals and policies for high landslide hazard areas are essentially those currently stated in the Comp Plan. Seismic lard Arms: 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, >are .t0 protect lives, With less emphasis' on preservation of property. The principal goal within areas underlain by expansive soil/bedrock should be to minimize_, damage toAnfrastructure. Policies which flow from these goals should focusi- OM,life safety;. infrastrttctirre PreserVitiOn; and critical °areas. 7.2 REGTJLATIONS 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. Consideration should be given to addressing :allgetSloidatl3i lia'r`dotis areas witlii�% lie code: section. This could be accomplished irrliast4fr'l 845, or by'cro,"sa= referece'to the erosion control requirements contained in Chapter' 16.541 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 4V.WAC 36.5, -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_Ateas forPietce'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 11/13/02 Q :LSAO`FINAL LANDAU REPORT TUKW1LA GEOI1AZ REV RPT.DOC 7 -2 5. code, but has useful figures which help describe buffers, setbacks, etc. The Pierce County draft also uses a. phased approach letter'",- `:`verit,cation "...arid "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 roughlyproportional risk: WAC 365- 190- 080(4Xb) 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) previsions, for top _and. toe of slope setbacks. The Pierce County draft ordinance incorporates UBC requirements. Consideration should be given to revising the curearie 20'15066a :'slifpe: threshold ,downWard'fd "1'S'peicerit. This would be consistent with the value cited in WAC 365- 190 -080(4). Overall, the post 1990 GeoEngineers, Inc. Geologic Hazards ;Evaluati©n stiil: appears to identify those, areas of the City:subjeeti to ;the .greatest landslide, erosion and seismic hazards Accordingly, it is our.opinion: that the GeoEngineers study' does not need to be updated:.at.this. time. 6. Consideration should be given to incorporating newly adopted:. :geologist licensing provisionOnto the. City's •geologically:hazardous areas,_ regulation. Laws relating to 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. ofthe geologist• aiid'gieitechiiicaLengineer to. the, :area: of hiterest. 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.:consiideratiomthe inherent inaccuracies of geologic and Other maps. It is also our opinion .that the use of "outside peer review for development' applications within Class 3lind 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 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 Q:1SAO\FINA1. 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. 1113/02 Q:\SAO1FfNAL LANDAU REPOR'I1TUKWILA GEOHAZ REV RPT.DOC 7-4 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, ENC. William D. Evans, P.G. Associate Dennis R. Stettler, P.E. Principal WDE/DRS /jas 8.0 USE OF THE REPORT 1 I /I3/02 Q:1SAO\FINAL LANDAU REPORTTUKWILA GEOHAZ REV RPr.DOC 8 -1 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, T.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 1- 852 -8. 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- W12207.5/7.5. 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. Joohim. 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. Millard, 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 I: Projcct1457 \005.010\Bibliography Tukwila 1 Yount, J.C. and H.D. Gower. 1991. Bedrock Geologic Map of the Seattle 30' by 60' 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 1: Project14571005.o101sibliography 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. G 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 Properly 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 I: Projectl457 \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. 1, 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 l: Project14571005.0101Bibliography 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 171. pp. 116. LANDSLIDE AREAS SEISMIC HAZARD AREAS Note: Bolded sources used as Best Available Science for Tukwila. 11/5/02 I: Projact1457\005.010\Bibliography Tukwila 5 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. 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. 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 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 To: Mayor Mullet, Members of the City Council From: Steve Lancaster, Director, Department of Community Development Teresa Vanderburg, Director of Natural Sciences, Adolfson Associat Date: December 9, 2004 Subject: DEPARTURES FROM BEST AVAILABLE SCIENCE ISSUE BACKGROUND City of Tukwila Department of Community Development INFORMATION MEMO ATTACHMENT E Steven M. Mullet, Mayor Steve Lancaster, Director 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. As required by the 1990 Growth Management Act (GMA) and RCW 36.70A.172(1), 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. (Adolfson) 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 of Tukwila. 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 Rating 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. q: \1 -04 SAO Update \Council Review\Departures.doc 2 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 (1)(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: 1) 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 of Tukwila elected to revise its 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 of the 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 q: \1 -04 SAO Update \Council Review \Departures.doc 3 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 of Tukwila's proposed SAO 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 1 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 of the 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 q: \1 -04 SAO Update \Council Review \Departures.doc 4 Memorandum: Departures from 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 (i.e., 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 salmonids 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 al., 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 Mitigation Ratios Wetland mitigation ratios supported by scientific research indicate that greater than 1:1 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 1:1 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 q: \1 -04 SAO Update \Council Review \Departures.doc 5 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 (i.e., 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: 1) 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 of time (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 1) and only minimal alterations are permitted to Type 2 wetlands. The City has chosen to use mitigation ratios of 1.5:1 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 1,000 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 1,000 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." q: \1 -04 SAO Update \Council Review \Departures.doc 6 Memorandum: Departures from 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 bx 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, 2001). 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 of less 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 CTED 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 of Fish and Wildlife (WDFW) for state review and comment. The City received no comment letter from WDFW on the watercourse regulations. This section of the 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 of Tukwila. 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 q: \1 -04 SAO Update \Council Review \Departures.doc 7 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 salmonids 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 salmonids 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 1 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: 100 feet on Type 2 watercourses, 80 feet on Type 3 watercourses, and 50 feet on Type 4 watercourses. Type 1 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 of GMA. 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. q: \1 -04 SAO Update \Council Review\Departures.doc 8