A. Standard Wetland Buffer Width. The standard buffer widths in Table 20.80.420(A)(1) have been established in accordance with the best available science. The buffer widths shall be determined based on the category of wetland and the habitat score as assigned by a qualified wetland professional using the Washington State Wetland Rating System for Western Washington.
1. All buffers shall be measured perpendicular from the wetland boundary as surveyed in the field. The buffer for a wetland created, restored, or enhanced as compensation for approved wetland alterations shall be the same as the buffer required for the category of the created, restored, or enhanced wetland.
2. The standard buffer widths assume that the buffer is a relatively intact native plant community in the buffer zone adequate to protect the wetland functions and values at the time of the proposed activity. If the existing buffer is bare ground, sparsely vegetated, or vegetated with nonnative or invasive species that do not perform needed functions, then the applicant must either develop and implement a wetland buffer restoration or enhancement plan to maintain the standard width to create the appropriate plant community or the buffer must be widened to ensure that adequate functions of the buffer are provided.
3. The use of the standard buffer widths requires the implementation of the mitigation measures in Table 20.80.420(A)(2), where applicable to the development type, to minimize the impacts of the adjacent land uses.
4. If an applicant chooses not to apply the appropriate mitigation measures in Table 20.80.420(A)(2), then a 33 percent increase in the width of all buffers is required. For example, a 75-foot buffer with the mitigation measures would be a 100-foot buffer without them.
Table 20.80.420(A)(1) Wetland Buffer Requirements |
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Wetland Category | Buffer Width According to Habitat Score |
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Habitat Score of 3 – 4 | Habitat Score of 5 | Habitat Score of 6 – 7 | Habitat Score of 8 – 9 |
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Category I: Based on total score or Forested | 75 ft | 105 ft | 165 ft | 225 ft |
Category I: Estuarine | 150 ft (no change based on habitat scores) |
Category II: Based on total score | 75 ft | 105 ft | 165 ft | 225 ft |
Category III (all) | 60 ft | 105 ft | 165 ft | 225 ft |
Category IV (all) | 40 ft (no change based on habitat scores) |
Table 20.80.420(A)(2) Required Measures to Minimize Impacts to Wetlands (Measures are required, where applicable to a specific proposal) |
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Disturbance | Activities and Uses That Cause Disturbances | Required Measures to Minimize Impacts |
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Lights | • Parking lots • Warehouses • Manufacturing • Residential | • Direct lights away from wetland. |
Noise | • Manufacturing • Residential | • 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 ft heavily vegetated buffer strip immediately adjacent to the outer wetland buffer. |
Toxic runoff* | • Parking lots • Roads • Manufacturing • Residential areas • Application of agricultural pesticides • Landscaping | • Route all new, untreated runoff away from wetland while ensuring wetland is not dewatered. • Establish covenants limiting use of pesticides and fertilizers within 150 ft of wetland. • Apply integrated pest management. |
Stormwater runoff | • Parking lots • Roads • Manufacturing • Residential areas • Commercial • Landscaping | • 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 (per PSAT publication on LID techniques). |
Change in water regime | • Impermeable surfaces • Lawns • Tilling | • Infiltrate or treat, detain, and disperse into buffer new runoff from impervious surfaces and new lawns. |
Pets and human disturbance | • Residential areas | • 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. |
Dust | • Tilled fields | • Use best management practices to control dust. |
Disruption of corridors or connections | | • Maintain connections to off-site areas that are undisturbed. • Restore corridors. |
Notes: |
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* These examples are not necessarily adequate for minimizing toxic runoff if threatened or endangered species are present at the site. Additional mitigation measures may be required based on recommendation of a qualified professional, third party review, or State agency recommendations. |
B. Increased Wetland Buffer Width. Buffer widths shall be increased, on a case-by-case basis as determined by the Director, when a larger buffer is necessary to protect wetland functions and values. This determination shall be supported by a critical area report, prepared by a qualified professional at the applicant’s expense, showing that it is reasonably related to protection of the functions and values of the wetland. The critical area report must include, but not be limited to, the following criteria:
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. 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 SMC §
20.80.435 may be substituted.
C. Reduced or Averaged Wetland Buffer Width. A reduced or averaged standard wetland buffer width may be allowed under the following circumstances:
1. Buffer averaging to improve wetland protection may be permitted when all of the following conditions are met:
a. The wetland has significant differences in characteristics that affect its habitat functions, such as a wetland with a forested component adjacent to a degraded emergent component or is a “dual-rated” wetland with a Category I area adjacent to a lower rated area;
b. The buffer is increased adjacent to the higher functioning area of habitat or more sensitive portion of the wetland and decreased adjacent to the lower functioning or less sensitive portion as demonstrated by a critical areas report from a qualified wetland professional;
c. The total area of the buffer after averaging is equal to the area required without averaging; and
d. The buffer at its narrowest point is never less than either three-fourths of the required width or 75 feet for Category I and II, 50 feet for Category III, and 25 feet for Category IV, whichever is greater.
2. Averaging, through a critical area reasonable use permit consistent with SMC §
20.30.333 or critical area special use permit consistent with SMC §
20.30.336 or a shoreline variance consistent with 20.220.040, may be permitted when all of the following are met:
a. There are no feasible alternatives to the site design that could be accomplished without buffer averaging;
b. The averaged buffer will not result in degradation of the wetland’s functions and values as demonstrated by a critical areas report from a qualified wetland professional;
c. The total buffer area after averaging is equal to the area required without averaging; and
d. The buffer at its narrowest point is never less than either three-fourths of the required width or 75 feet for Category I and II, 50 feet for Category III, and 25 feet for Category IV, whichever is greater.
3. When the voluntary creation or expansion of a wetland that is not required as mitigation for a development proposal and would increase the area of the wetland and/or wetland buffer a buffer that is no less than 75 percent of the standard width shall be established. Further reductions in standard buffer width may be granted if the following are demonstrated:
a. A wetland buffer 75 percent of standard width would significantly limit the use of the property for existing or permitted uses, thus making the wetland creation or expansion project infeasible;
b. The proposed width reduction is the minimum necessary to achieve the restoration project;
c. There will be a net environmental benefit from the restoration project with the reduced riparian management zone width;
d. Granting the proposed relief is consistent with the objectives of the wetland creation or expansion project and consistent with the purposes of the City’s critical area regulations.
D. Buffers on Mitigation Sites. All mitigation sites shall have buffers consistent with the buffer requirements of this chapter. Buffers shall be based on the expected or target category of the proposed wetland mitigation site.
E. Buffer Maintenance. Except as otherwise specified or allowed in accordance with this chapter, wetland buffers shall 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 required monitoring period.
F. Overlapping Critical Area Buffers. If buffers for two contiguous critical areas overlap (such as riparian management zone for a stream and a wetland buffer), the wider area applies.
G. Physically Separated and Functionally Isolated Wetland Buffers. Consistent with the definition of “buffers” (SMC §
20.20.012), areas that are functionally isolated and physically separated from 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 shall be considered physically isolated and functionally separated wetland buffers and shall not be subject to the standards of this chapter. The obstruction causing the physical isolation or functional separation shall be significant enough in size that the wetland buffer cannot reasonably perform any of the ecological functions of a buffer including water quality, stormwater and floodwater conveyance, groundwater recharge and wildlife habitat. A critical areas assessment prepared by a qualified professional determining whether the area is functionally isolated is required unless deemed unnecessary by the Director.
(Formerly 20.80.330. Ord. 238 Ch. VIII § 5(C), 2000; Ord. 398 § 1, 2006; Ord. 469 § 1, 2007; Ord. 695 § 1 (Exh. A), 2014; Ord. 723 § 1 (Exh. A), 2015; Ord. 1045 § 1 (Exh. A), 2025)