19.70.235 Required buffer areas.
A. Buffer Requirements. Wetland buffers must be established to protect the integrity, functions and values of the wetland. The standard buffer widths in Tables 19.70.235(B), 19.70.235(C) and 19.70.235(D) have been established in accordance with the best available science. The buffer widths must be determined based on the category of wetland, surrounding land use intensity, and the habitat score as assigned by a qualified wetland professional using the most up-to-date version of the Washington State Wetland Rating System for Western Washington.
1. Measurement of Wetland Buffers. All buffers must be measured horizontally from the edge of the wetland boundary as surveyed in the field. The width of the wetland buffer must be determined according to Tables 19.70.235(B), 19.70.235(C) and 19.70.235(D).
2. Buffer Standards. The buffer standards required by this chapter presume the existence of a dense vegetation community in the buffer adequate to protect the wetland functions and values. When a buffer lacks adequate vegetation, the decision-maker may increase the standard buffer, require buffer planting or other enhancements, and/or deny a proposal for buffer reduction or buffer averaging.
B. For the purposes of buffer determination below, land use intensity rating is as follows:
|
High Land Use Intensity |
Land use that includes the following uses or activities: commercial, industrial, institutional, retail sales, nonresidential use in zones where the primary intent is residential, residential, high-intensity recreation (such as golf courses, ball fields), and hobby farms. |
|
Moderate Land Use Intensity |
Land use that includes the following uses or activities: moderate-intensity open space (parks, paved trails, and logging roads). |
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Low Land Use Intensity |
Land use that includes the following uses or activities: forestry (cutting of trees only), low-intensity open space (such as outdoor recreation activities and natural resources preservation), unpaved trails. |
C. There are three sets of buffer standards, based on these parameters:
1. Buffer widths for wetlands that have a high level of function for wildlife habitat as indicated by a habitat function score of eight or nine points on the wetland rating form:
2. Buffer widths for wetlands that have a moderate level of function for wildlife habitat as indicated by a habitat function score of six or seven points on the wetland rating form:
3. Buffer widths for wetlands that have a low level of function for wildlife habitat as indicated by a habitat function score of three to five points on the wetland rating form:
D. Reducing Buffer Widths.
1. For wetlands that score six points or more for habitat function, buffer widths for high intensity may be reduced to moderate intensity if both of the following criteria are met:
a. A relatively undisturbed, vegetated corridor at least 100 feet wide is protected between the wetland and any other relatively undisturbed area, as defined in the 2014 Wetland Rating System, or any other priority habitat as defined by the Washington State Department of Fish and Wildlife. The latest definitions of priority habitats and their locations are available on the WDFW web site at: https://wdfw.wa.gov/species-habitats/at-risk/phs/list.
b. The corridor must be protected for the entire distance between the wetland and the relatively undisturbed area or priority habitat by some type of legal protection such as a conservation easement. Presence or absence of a nearby habitat must be confirmed by a qualified biologist.
2. The measures in Table 19.70.235(E) are implemented, where applicable, to minimize the impacts of the adjacent land uses.
3. For wetlands that score three to five habitat points, only the measures in Table 19.70.250(E) are required for the use of moderate intensity buffer widths.
4. If an applicant chooses not to apply the mitigation measures in Table 19.70.250(E), or is unable to provide a protected corridor where available, then high intensity buffer widths must be used.
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Disturbance |
Required Measures to Minimize Impacts |
|---|---|
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Lights |
• Direct lights away from wetland |
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Noise |
• Locate activity that generates noise away from wetland • If warranted, enhance existing buffer with native vegetation plantings adjacent to noise source • For activities that generate relatively continuous, potentially disruptive noise, such as certain heavy industry or mining, establish an additional 10-foot heavily vegetated buffer strip immediately adjacent to the outer wetland buffer |
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Toxic runoff |
• Route all new, untreated runoff away from wetland while ensuring wetland is not dewatered • Establish covenants limiting use of pesticides within 150 feet of wetland • Apply integrated pest management |
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Stormwater runoff |
• Retrofit stormwater detention and treatment for roads and existing adjacent development • Prevent channelized flow from lawns that directly enters the buffer • Use low intensity development techniques (for more information refer to the stormwater manual) |
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Change in water regime (increase or decrease in the frequency, duration, timing, extent, depth or variability of water in a wetland) |
• Infiltrate or treat, detain, and disperse into buffer new runoff from impervious surfaces and new lawns |
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Pets and human disturbance |
• Use privacy fencing OR plant dense vegetation to delineate buffer edge and to discourage disturbance using vegetation appropriate for the ecoregion • Place wetland and its buffer in a separate tract or protect with a conservation easement |
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Dust |
• Use best management practices to control dust |
E. Increasing Buffer Widths. Buffer widths may be increased, on a case-by-case basis, as determined by the decision-maker. This determination must be supported by appropriate documentation showing that it is necessary to protect wetland functions and values. Documentation must include, but is not limited to, any of the following:
1. The wetland is used by a plant or animal species listed by the federal government or the state as endangered, threatened, candidate, sensitive, monitored, or documented priority species or habitats, or the wetland is essential or outstanding habitat for those species or has unusual nesting or resting sites such as heron rookeries or raptor nesting trees; or
2. The adjacent land has slopes greater than 15 percent and is susceptible to severe erosion, and erosion-control measures will not effectively prevent adverse wetland impacts; or
3. The adjacent land has minimal vegetative cover on slopes greater than 30 percent. In lieu of increasing the buffer width where existing buffer vegetation is inadequate to protect the wetland functions and values, development and implementation of a wetland buffer restoration/enhancement plan in accordance with AMC 19.70.245, Compensatory mitigation performance standards and requirements, may be substituted.
F. Averaging Buffer Widths. The decision-maker may allow averaging of wetland buffer widths on a case-by-case basis when the critical area report demonstrates that the following criteria are met:
1. There is not a feasible alternative to the site design that could be accomplished without buffer averaging;
2. The buffer averaging improves the functions or values of the wetland, either through preservation of total buffer area or enhancement of buffer areas including the creation of connectivity and corridors;
3. The total area contained in the buffer area after averaging is no less than that which would be contained within the standard buffer;
4. The wetland contains variation in sensitivity due to existing physical characteristics or the character of the buffer varies in slope, soils, or vegetation, and the wetland would benefit from a wider buffer in places and would not be adversely impacted by a narrow buffer in other places;
5. The buffer width at its narrowest point is not reduced to less than 75 percent of the standard width.
G. Measurement of Wetland Buffers. All buffers must be measured perpendicular from the wetland boundary as surveyed in the field. The buffer for a wetland created, restored, or enhanced as a compensation for approved wetland alterations must be the same as the buffer required for the category of the created, restored, or enhanced wetland.
H. Buffers on Mitigation Sites. Buffer widths must be applied to mitigation sites consistent with the wetland ratings and buffer requirements of this chapter for subsequent development proposals based on expected category of the wetland once the mitigation actions are taken. Only fully vegetated buffers with predominantly native plants will be included in the new buffer area. Lawns, walkways, driveways, and other mowed or paved areas will not count towards the required buffer calculations.
I. Buffer Maintenance. Except as otherwise specified or allowed in accordance with this chapter, wetland buffers must be retained in an undisturbed or enhanced condition. In the case of compensatory mitigation sites, removal of invasive nonnative weeds is required for the duration of the mitigation bond.
J. Buffer Impacts. When buffer impacts occur, compensatory mitigation must be provided at a minimum ratio of one-to-one for the area impacted. The mitigation must occur on the same site when feasible or within the same wetland system preferably. The mitigation must ensure that the wetland functions and values are not diminished due to the buffer impacts.
K. Stormwater Management Facilities. Stormwater management facilities may be allowed in Category III and IV wetland buffers if they meet all of the criteria identified below:
1. The wetland is classified as a Category III or a Category IV wetland with a habitat score of three to five points or less; and
2. There will be “no net loss” of functions and values of the wetlands; and
3. The wetland does not contain a breeding population of any native amphibian species; and
4. The hydrologic functions of the wetland can be improved as outlined in questions 3, 4, and 5 of Chart 4 and questions 2, 3, and 4 of Chart 5 in the “Guide for Selecting Mitigation Sites Using a Watershed Approach” (available here: https://apps.ecology.wa.gov/publications/documents/0906032.pdf); or the wetland is part of a priority restoration plan that achieves restoration goals identified in a Shoreline Master Program or other local or regional watershed plan; and
5. The wetland lies in the natural routing of the runoff, and the discharge follows the natural routing; and
6. All regulations regarding stormwater and wetland management are followed, including but not limited to local and state wetland and stormwater codes, manuals, and permits; and
7. Modifications will require permits. Existing functions and values that are lost would have to be compensated/replaced through an approved mitigation plan.
L. Setbacks From Buffers. Buildings, structures, paving, and other hard surfacing must be set back a minimum distance of 10 feet from the edge of the wetland buffer, or edge of the wetland if no buffer is required, unless otherwise determined by the decision-maker that a smaller distance would meet the intent of this subsection. This setback is to avoid conflicts with tree branches and/or critical root zones of trees that are in the buffer or will be planted in the buffer. The following may be allowed in the building setback from the buffer if they do not cause damage to the critical root zone of trees in the buffer:
1. Landscaping;
2. Uncovered decks, roof eaves and overhangs, unroofed stairways and steps;
3. Pervious ground surfaces, such as driveways, patios, and parking may be allowed; provided, that it is engineered as a permeable pavement system as defined in this chapter. Such improvements may be subject to the requirements in AMC Chapter 19.76, Stormwater.
M. Functionally Separated and Isolated Buffers. Consistent with the definition of “buffer” in this chapter, areas that are functionally isolated and physically separated from a wetland due to existing, legally established roadways, railroads or other legally established structures or paved areas eight feet or more in width that occur between the area in question and the wetland must be considered physically isolated and functionally separated buffer. Once determined by the Director, based on a submitted critical area report, to be a physically separated and functionally isolated wetland buffer, development proposals are allowed in these areas. (Ord. 4025 § 2 (Att. A), 2022; Ord. 4015 § 2 (Att. A), 2022; Ord. 3064 § 2 (Att. A), 2021)