Chapter 20.24


20.24.005    Purpose.

20.24.010    Identification and rating.

20.24.015    Regulated activities.

20.24.020    Exemptions and allowed uses in wetlands.

20.24.030    Wetland buffers.

20.24.040    Critical areas reports.

20.24.050    Compensatory mitigation.

20.24.005 Purpose.

(1) Recognize and protect the beneficial functions performed by many wetlands, which include, but are not limited to, providing food, breeding, nesting and/or rearing habitat for fish and wildlife; recharging and discharging ground water; contributing to stream flow during low flow periods; stabilizing stream banks and shorelines; storing storm and flood waters to reduce flooding and erosion; and improving water quality through biofiltration, absorption, and retention and transformation of sediments, nutrients, and toxicants.

(2) Regulate land use to avoid adverse effects on wetlands and maintain the functions and values of wetlands throughout the city of Oak Harbor.

(3) Establish review procedures for development proposals in and adjacent to wetlands.

(a) Compliance with the provisions of this chapter does not constitute compliance with other federal, state, and local regulations and permit requirements that may be required. (Ord. 1801 § 14, 2018).

20.24.010 Identification and rating.

(1) Identification and Delineation. Wetlands shall be identified and delineated by a qualified wetland professional in accordance with the currently approved federal manual and regional supplements, using the criteria in the definition of wetland in OHMC 20.02.020. Wetland delineations are valid for five years; after such date the city shall determine if a revision or additional assessment is necessary.

(2) Rating. Wetlands shall be rated according to the Washington Department of Ecology wetland rating system, as set forth in the Washington State Wetland Rating System for Western Washington: 2014 Update (Ecology Publication No. 14-06-029, or as revised and approved by Ecology), which contains the definitions and methods for determining if the criteria below are met.

(a) Category I wetlands include:

(i) Relatively undisturbed estuarine wetlands larger than one acre;

(ii) Wetlands of high conservation value that are identified by scientists of the Washington Department of Natural Resources Natural Heritage Program;

(iii) Mature and old-growth forested wetlands larger than one acre;

(iv) Wetlands in coastal lagoons; or

(v) Wetlands that perform many functions well (scoring 23 or more points). These wetlands:

(A) Represent unique or rare wetland types;

(B) Are more sensitive to disturbance than most wetlands;

(C) Are relatively undisturbed and contain ecological attributes that are impossible to replace within a human lifetime; or

(D) Provide a high level of functions.

(b) Category II wetlands include:

(i) Estuarine wetlands smaller than one acre, or disturbed estuarine wetlands larger than one acre;

(ii) Wetlands with a moderately high level of functions (scoring between 20 and 22 points);

(c) Category III wetlands:

(i) Are wetlands with a moderate level of functions (scoring between 16 and 19 points); and

(ii) Can often be adequately replaced with a well-planned mitigation project.

Wetlands scoring between 16 and 19 points generally have been disturbed in some ways and are often less diverse or more isolated from other natural resources in the landscape than Category II wetlands.

(d) Category IV wetlands have the lowest levels of functions (scoring fewer than 16 points) and are often heavily disturbed. These are wetlands that should be replaceable, or in some cases improvable. However, experience has shown that replacement cannot be guaranteed in any specific case. These wetlands may provide some important functions and should be protected to some degree.

(3) Illegal Modifications. Wetland rating categories shall not change due to illegal modifications made by the applicant or with the applicant’s knowledge. (Ord. 1801 § 15, 2018; Ord. 1440 § 3, 2005).

20.24.015 Regulated activities.

(1) For any regulated activity, a critical areas report, in accordance with OHMC 20.24.040, may be required to support the requested activity.

(2) The following activities are regulated if they occur in a regulated wetland or its buffer:

(a) The removal, excavation, grading, or dredging of soil, sand, gravel, minerals, organic matter, or material of any kind.

(b) The dumping of, discharging of, or filling with any material.

(c) The draining, flooding, or disturbing of the water level or water table.

(d) Pile driving.

(e) The placing of obstructions.

(f) The construction, reconstruction, demolition, or expansion of any structure.

(g) The destruction or alteration of wetland vegetation through clearing, harvesting, shading, intentional burning, or planting of vegetation that would alter the character of a regulated wetland.

(h) “Class IV – General Forest Practices” under the authority of the “1992 Washington State Forest Practices Act Rules and Regulations,” WAC 222-12-030, or as thereafter amended.

(i) Activities that result in a significant change of water temperature, a significant change of physical or chemical characteristics of the water entering the wetland, or respective buffer sources, including quantity and hydroperiod, or the introduction of pollutants, including pesticides and herbicides.

(3) Subdivisions. The subdivision and/or short subdivision of land in wetlands and associated buffers are subject to the following:

(a) Land that is located wholly within a wetland or its buffers may not be subdivided.

(b) Land that is located partially within a wetland or its buffer may be subdivided; provided, that an accessible and contiguous portion of each new lot:

(i) Is located outside of the wetland and its buffer, and

(ii) Meets the minimum lot size requirements of Chapter 19.20 OHMC. (Ord. 1801 § 16, 2018).

20.24.020 Exemptions and allowed uses in wetlands.

(1) The following wetlands may be exempt from the requirement to avoid impacts and they may be filled if the impacts are fully mitigated based on the remaining actions in OHMC 20.24.050. In order to verify the following conditions, a critical area report for wetlands, in accordance with OHMC 20.24.040 must be submitted. These exemptions are in addition to the exemptions established in OHMC 20.12.040.

(a) All isolated Category IV wetlands less than 4,000 square feet that:

(i) Are not associated with riparian areas or their buffers;

(ii) Are not associated with shorelines of the state or their associated buffers;

(iii) Are not part of a wetland mosaic;

(iv) Do not score six or more points for habitat function based on the Washington State Wetland Rating System for Western Washington: 2014 Update (Ecology Publication No. 14-06-029, or as revised and approved by Ecology);

(v) Do not contain a priority habitat or a priority area for a priority species identified by the Washington Department of Fish and Wildlife, do not contain federally listed species or their critical habitat, or species of local importance identified in Chapter 20.25 OHMC; and

(b) Wetlands less than 1,000 square feet that meet the above criteria and do not contain federally listed species or their critical habitat are exempt from the buffer provisions contained in this chapter.

(2) Activities Allowed in Wetlands. The activities listed below are allowed in wetlands. These activities do not require submission of a critical areas report, except where such activities result in a loss of the functions and values of a wetland or wetland buffer. These activities include:

(a) Those activities and uses conducted pursuant to the Washington State Forest Practices Act and its rules and regulations, WAC 222-12-030, where state law specifically exempts local authority, except those developments requiring local approval for Class 4 – General Forest Practice Permits (conversions) as defined in Chapter 76.09 RCW and Chapter 222-12 WAC.

(b) Conservation or preservation of soil, water, vegetation, fish, shellfish, and/or other wildlife that does not entail changing the structure or functions of the existing wetland.

(c) Drilling for utilities/utility corridors under a wetland, with entrance/exit portals located completely outside of the wetland buffer; provided, that the drilling does not interrupt the ground water connection to the wetland of percolation of surface water down through the soil column. Specific studies by a hydrologist are necessary to determine whether the ground water connection to the wetland or percolation of surface water down through the soil column will be disturbed.

(d) Enhancement of a wetland through the removal of nonnative invasive plant species. Removal of invasive plant species shall be restricted to hand removal unless permits from the appropriate regulatory agencies have been obtained for approved biological or chemical treatments.

(e) Storm water management facilities. A wetland or its buffer can be physically or hydrologically altered to meet the requirements of an LID, runoff treatment or flow control BMP if all of the following criteria are met:

(i) The wetland is classified as a Category IV or a Category III wetland with a habitat score of three to five points; and

(ii) There will be “no net loss” of functions and values of the wetland; and

(iii) The wetland does not contain a breeding population of any native amphibian species; and

(iv) The hydrologic functions of the wetland can be improved; and

(v) The wetland lies in the natural routing of the runoff, and the discharge follows the natural routing; and

(vi) All regulations regarding storm water and wetland management are followed, including, but not limited to, local and state wetland and storm water codes, manuals, and permits; and

(vii) Modifications that alter the structure of a wetland or its soils will require permits. Existing functions and values that are lost would have to be compensated/replaced.

(3) Storm water LID BMPs required as part of new and redevelopment projects can be considered within wetlands and their buffers. However, these areas may contain features that render LID BMPs infeasible. A site-specific characterization is required to determine if an LID BMP is feasible at the project site. (Ord. 1801 § 17, 2018; Ord. 1440 § 3, 2005).

20.24.030 Wetland buffers.

Wetland buffers shall be established to protect the integrity, functions and values of the wetland.

(1) Measurement of Wetland Buffers. All buffers shall be measured perpendicular from the wetland boundary as surveyed in the field.

(2) Buffer Standards. When a buffer lacks adequate vegetation to protect the wetland functions and values, the director may increase the standard buffer, require buffer planting or other enhancements, and/or deny a proposal for buffer reduction or buffer averaging. Buffers may not include areas that are functionally and effectively disconnected from the wetland by an existing public or private road as determined by the director. Functionally and effectively disconnected means that the road blocks the protective measures provided by a buffer or it disrupts the life cycle of wildlife documented to be using the area.

(3) The following buffer widths have been established in accordance with best available science. They are based on the category of wetland and the habitat score as determined by a qualified wetland professional using the Washington State Wetland Rating System for Western Washington: 2014 Update (Ecology Publication No. 14-06-029, or as revised and approved by Ecology). The adjacent land use intensity is assumed to be high.

(a) Standard buffer widths are identified in Table 20.24.030(a)(i).

(b) An applicant may be administratively allowed a 25 percent decrease in the width of buffers identified in Table 20.24.030(a)(i) if all impact minimizing measures identified in Table 20.24.030(a)(ii) are implemented, where applicable, to a specific proposal.

Table 20.24.030(a)(i) 

Wetland Category

Standard Buffer Width (in feet)

3 – 5

6 – 7

8 – 9

Category I:
Based on total score




Category I:
Wetlands of high conservation value



Category I:

(buffer width not based on habitat scores)

Category I:




Category I:
Estuarine and coastal lagoons

(buffer width not based on habitat scores)

Category II:
Based on score




Category II:
Interdunal wetlands

(buffer width not based on habitat scores)

Category II:
Estuarine and coastal lagoons

(buffer width not based on habitat scores)

Category III: (all)




Category IV: (all)



Table 20.24.030(a)(ii) 


Required Measures to Minimize Impacts


Direct lights away from wetland


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 feet heavily vegetated buffer strip immediately adjacent to the outer wetland buffer

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

Storm water runoff

Retrofit storm water detention and treatment for roads and existing adjacent development

Prevent channelized flow from lawns that directly enters the buffer

Use low impact development techniques to the greatest extent possible

Change in water regime

Infiltrate or treat, detain, and disperse into buffer new runoff from impervious surfaces and new lawns

Pets and human disturbance

Use privacy fencing or plant dense vegetation to delineate buffer edge and to discourage disturbance using vegetation native to western WA and appropriate for the local conditions

Place wetland and its buffer in a separate tract or protect with a conservation easement


Use best management practices to control dust

(4) Increased Buffer Widths. When a larger buffer is necessary to protect wetland or other critical area functions and values based on site-specific characteristics, the director shall have the authority to require increased buffer widths in accordance with the recommendations of a qualified professional. This documentation must include, but not be limited to, the following criteria:

(a) The wetland is used by a state or federally listed plant or animal species or has essential or outstanding habitat for those species, or has unusual nesting or resting sites such as heron rookeries or raptor nesting trees; or

(b) The adjacent land is susceptible to severe erosion, and erosion-control measures will not effectively prevent adverse wetland impacts; or

(c) The adjacent land has minimal vegetative cover or slopes greater than 30 percent.

(5) Modifications to Buffer Widths. Any modifications to the buffer width are to be based on the specific wetland functions, site-specific characteristics, location of the wetland within the watershed or sub-basin, and the proposed land use.

(a) Averaging Buffer Widths. The director shall have the authority to average wetland buffer widths on a case-by-case basis, where a qualified wetlands professional demonstrates to the director’s satisfaction that all of the following criteria are met:

(i) The total area contained in the buffer after averaging is no less than that contained within the buffer prior to averaging;

(ii) 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 area report from a qualified wetland professional.

(iii) The buffer at its narrowest point is never less than either 75 percent of the required width or 75 feet for a Category I and II, 50 feet for Category III, and 25 feet for Category IV, whichever is greater.

(iv) Disturbed portions of the buffer will be enhanced with native plantings.

(b) Averaging to allow reasonable use of a parcel may be permitted when all of the following are met:

(i) There are no feasible alternatives to the site design that could be accomplished without buffer averaging.

(ii) The averaged buffer will not result in degradation of the wetland’s functions and values as demonstrated by a critical area report from a qualified wetland professional.

(iii) The total buffer after averaging is equal to the area required without averaging.

(iv) The buffer at its narrowest point is not less than 75 percent of the required width; provided, that minimum buffer widths shall never be less than 75 feet for a Category I and II, 50 feet for Category III, and 25 for Category IV, whichever is greater.

(c) Regional Benefit. The director shall have the authority to reduce the width of the standard buffer on a case-by-case basis if all of the following criteria are met:

(i) The buffer is adjacent to a critical area that is being significantly restored through a city-approved mitigation plan that has regional benefit to critical area functions as determined by the director;

(ii) A critical area report has been submitted to the city that demonstrates the reduced buffer will protect the functions and value of the critical area being restored; and

(iii) The reduced buffer shall be clearly described in any applicable SEPA, MDNS or EIS document and shall be subject to review and comment by the public agencies with jurisdiction and affected tribes.

(6) Buffers on Wetland Mitigation Sites. All wetland 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. Or, the buffer can be determined on a case-by-case basis where it can be shown that the buffer is protective of the functions and values of the compensatory wetland.

(7) Buffer Maintenance. 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 mitigation bond.

(8) Impacts to Buffers. Requirements for the compensation for impacts to buffers are outlined in OHMC 20.24.050.

(9) Overlapping Critical Area Buffers. If buffers for two contiguous critical areas overlap (such as buffers for a stream and a wetland), the wider buffer applies.

(10) Allowed Uses. The following uses may be permitted within a wetland buffer, provided they are not prohibited by any other applicable law and they are conducted in a manner so as to minimize negative impacts to the buffer and adjacent wetland:

(a) Conservation or restoration activities aimed at protecting the soil, water, vegetation, or wildlife.

(b) Passive recreation facilities designed and in accordance with an approved critical areas report, including:

(i) Wildlife viewing structures; and

(ii) Walkways and trails, provided pathways are limited to minor crossings having no adverse impacts on water quality. They should generally be parallel to the perimeter of the wetland, located in the outer 25 percent of the wetland buffer area, and avoid removal of significant trees. They should be limited to pervious surfaces no more than five feet in width for pedestrian use only. Raised boardwalks utilizing nontreated pilings may be acceptable.

(c) Educational and scientific research activities.

(d) Normal and routine maintenance and repair of any existing public or private facilities within an existing right-of-way; provided, that the maintenance or repair does not increase the footprint or use of the facility or right-of-way.

(e) Drilling for utilities/utility corridors under a buffer, with entrance/exit portals located completely outside of the wetland buffer boundary; provided, that the drilling does not interrupt the ground water connection to the wetland or percolation of surface water down through the soil column. Specific studies by a hydrologist are necessary to determine whether the ground water connection to the wetland or percolation of surface water down through the soil column would be disturbed. If avoidance of an entrance/exit drilling portal is not feasible, buffer disturbance is permitted with a restoration plan from a qualified wetland professional.

(f) Repair and maintenance of nonconforming uses or structures, where legally established within the buffer, provided they do not increase the degree of nonconformity.

(g) Storm water management facilities, limited to storm water dispersion outfalls and bioswales, may be allowed within the outer 25 percent of the buffer of Category III or IV wetlands only; provided, that:

(i) No other location is feasible; and

(ii) Their location, with mitigation, will not degrade the functions or values of the wetland.

(h) Fencing is allowed in conformance with OHMC 20.12.140. (Ord. 1874 § 2, 2019; Ord. 1801 § 18, 2018; Ord. 1440 § 3, 2005).

20.24.040 Critical areas reports.

If required by the director in accordance with OHMC 20.12.070(2), a critical areas report shall be prepared by a qualified wetlands professional and shall include the following:

(1) A site plan for the project containing the following:

(a) Maps (to scale) depicting delineated and surveyed wetlands and required buffers on site, as well as buffers for off-site critical areas that extend onto the project site or that might be impacted by the proposed activity; the proposed development; other critical areas; grading and clearing limits; and areas of proposed impacts to wetlands and/or buffers (include square footage estimates).

(b) A depiction of the proposed storm water management facilities and outlets (to scale) for the development, including estimated areas of intrusion into the buffers of any critical areas. The written report shall contain a discussion of the potential impacts to the wetland(s) associated with anticipated hydroperiod alterations from the project.

(2) A written report for the project containing the following:

(a) The name and contact information of the applicant; the name, qualifications, and contact information for the primary author(s) of the wetland critical area report; a description of the proposal; identification of all the local, state, and/or federal wetland-related permit(s) required for the project.

(b) A vicinity map for the project.

(c) Documentation of any fieldwork performed on the site, including field data sheets for delineations, rating system forms, baseline hydrologic data, etc.

(d) A description of the methodologies used to conduct the wetland delineations, wetland ratings, or impact analyses, including references.

(e) Identification and characterization of all critical areas, wetlands, water bodies, shorelines, floodplains, and buffers on or adjacent to the proposed project area. For areas of the project site, estimate conditions within 300 feet of the project boundaries using the best available information.

(f) For all wetlands on the subject property and within 300 feet of the project boundary, provide the following: required buffers; wetland rating, including a description of and score for each function (OHMC 20.24.010); wetland buffer width (OHMC 20.24.030); hydrogeomorphic classification; wetland acreage based on a professional survey from the field delineation (acreages for on-site portion or estimate entire wetland area including off-site portions); Cowardin classification of vegetation communities; habitat elements; soil conditions based on site assessment and/or soil survey information; and to the extent possible, hydrologic information such as location and condition of inlets/outlets (if they can be legally accessed), estimated water depths within the wetland, and estimated hydroperiod patterns based on visual cues (e.g., algal mats, drift lines, flood debris, etc.). Provide acreage estimates, classifications, and ratings based on entire wetland complexes, not only the portion present on the proposed project site.

(g) A description of the proposed actions, including an estimation of acreages of impacts to the wetlands and buffers based on the field delineation and survey and an analysis of site development alternatives, including a no-development alternative.

(h) An assessment of cumulative impacts to wetlands and buffers from development of the site.

(i) Evaluation of the functions of the wetland and adjacent buffer. Include data sheets and references for the method used.

(j) A description of reasonable efforts made to apply mitigation sequencing pursuant to mitigation sequencing (OHMC 20.12.090) to avoid, minimize, and mitigate impacts to critical areas.

(k) A discussion of measures, including avoidance, minimization, and compensation, proposed to preserve existing wetlands and restore any wetlands that were degraded prior to the current proposed land use activity.

(l) A conservation strategy for habitat and native vegetation that addresses methods to protect and enhance on-site habitat and wetland functions.

(3) If compensatory mitigation is proposed, a mitigation plan is required that includes the information identified in OHMC 20.24.050(8).

(4) Unless otherwise provided, a critical areas report may be supplemented by or composed, in whole or in part, of any reports or studies required by other laws and regulations or previously prepared for and applicable to the development proposal site, as approved by the director. (Ord. 1801 § 19, 2018; Ord. 1440 § 3, 2005).

20.24.050 Compensatory mitigation.

(1) Requirements for Compensatory Mitigation.

(a) Compensatory mitigation for alterations to wetlands and buffers shall be used only for impacts that cannot be avoided or minimized and shall achieve equivalent or greater biologic functions. Compensatory mitigation plans shall be consistent with the standards in OHMC 20.12.090, 20.12.100 and this section, and with reference to the Wetland Mitigation in Washington State – Part 2: Developing Mitigation Plans – Version 1 (Ecology Publication No. 06-06-011b, Olympia, WA, March 2006, or as revised), and Selecting Wetland Mitigation Sites Using a Watershed Approach (Western Washington) (Publication No. 09-06-32, Olympia, WA, December 2009).

(b) Mitigation ratios shall be consistent with subsection (7) of this section.

(c) Mitigation requirements may also be determined using the credit/debit tool described in Calculating Credits and Debits for Compensatory Mitigation in Wetlands of Western Washington: Final Report (Ecology Publication No. 10-06-011, Olympia, WA, March 2012, or as revised) consistent with subsection (4) of this section.

(2) Types of Compensatory Mitigation. Mitigation for lost or diminished wetland and buffer functions shall rely on a type listed below in order of preference. A lower-preference form of mitigation shall be used only if the applicant’s qualified wetland professional demonstrates to the approval of the director that all higher-ranked types of mitigation are not viable, consistent with the criteria in this section.

(a) Restoration. Restoration (OHMC 20.02.020(85)) of wetlands is divided into re-establishment and rehabilitation.

(i) Reestablishment (OHMC 20.02.020(83)). Reestablishment results in a gain in wetland acres (and functions). Activities could include removing fill material, plugging ditches, or breaking drain tiles.

(ii) Rehabilitation (OHMC 20.02.020(84)). Rehabilitation results in a gain in wetland function but does not result in a gain in wetland acres. Activities could involve breaching dikes to reconnect wetlands to a floodplain or return tidal influence to a wetland.

(b) Establishment (Creation, OHMC 20.02.020(78)). Establishment results in a gain in wetland acres. Activities typically involve excavation of upland soils to elevations that will produce a wetland hydroperiod, create hydric soils, and support the growth of hydrophytic plant species.

(c) Enhancement (Enhancement, OHMC 20.02.020(79)) is undertaken for specified purposes such as water quality improvement, flood water retention, or wildlife habitat. Enhancement results in a change in some wetland functions and can lead to a decline in other wetland functions but does not result in a gain in wetland acres. Activities typically consist of planting vegetation, controlling nonnative or invasive species, modifying site elevations or the proportion of open water to influence hydroperiods, or some combination of these activities. Applicants proposing to enhance wetlands or associated buffers shall demonstrate how the proposed enhancement will increase the wetland’s/buffer’s functions, how this increase in function will adequately compensate for the impacts, and how existing wetland functions at the mitigation site will be protected.

(d) Protection/Maintenance (Preservation, OHMC 20.02.020(82)). Preservation includes the purchase of land or easements or repairing water control structures or fences. This term also includes activities commonly associated with the term preservation. Preservation does not result in a gain of wetland acres. Permanent protection of a Category I or II wetland and associated buffer at risk of degradation can be used only if:

(i) The city determines that the proposed preservation is the best mitigation option;

(ii) The proposed preservation site is under threat of undesirable ecological change due to permitted, planned, or likely actions that will not be adequately mitigated under existing regulations;

(iii) The area proposed for preservation is of high quality or critical for the health of the watershed or basin due to its location. Some of the other high quality features include:

(A) Rare wetland types such as bogs, mature forested wetlands, estuaries, or vital wildlife habitat;

(B) The presence of habitat for priority or locally important wildlife species;

(C) Priority sites in an adopted watershed plan;

(iv) The preserved wetland and buffer are protected in perpetuity through a conservation easement, deed restriction, or dedication as a separate tract;

(v) The city may approve other legal and administrative mechanisms in lieu of a conservation easement if it determines they are adequate to protect the site;

(vi) Creation, restoration, and enhancement opportunities have also been considered and preservation is the best mitigation option. To the extent appropriate and practicable, preservation should be done in conjunction with creation, restoration, and/or enhancement;

(vii) Some combination of mitigation where preservation may be an element is utilized based on an ecological evaluation employing the credit/debit tool described in Calculating Credits and Debits for Compensatory Mitigation in Wetlands of Western Washington: Final Report (Ecology Publication No. 10-06-011, Olympia, WA, March 2012, or as revised).

(3) Location of Compensatory Mitigation. Site selection for compensatory mitigation shall be based on a location that will provide the greatest ecological benefit and have the greatest likelihood of success. Where feasible, mitigation shall occur in the same sub-basin as the permitted wetland alteration. However, if it can be demonstrated that a mitigation site in an alternative sub-basin or watershed would provide a greater ecological benefit and offer a more successful replacement of wetland functions and values, compensatory mitigation may take place in an alternative sub-basin or watershed. If a mitigation bank or in-lieu-fee program is proposed for the required mitigation, documentation shall be provided that demonstrates there is an ecological benefit. The documentation shall also include how locating the mitigation out of the sub-basin or watershed will not impact other nearby critical areas.

(4) Wetland Mitigation Banks. Credits from a certified wetland mitigation bank may be used to compensate for impacts located within the service area specified in the mitigation bank instrument. Use of credits from a wetland mitigation bank certified under Chapter 173-700 WAC is allowed if:

(a) The approval authority determines that it would provide appropriate compensation for the proposed impacts; and

(b) The impact site is in the service area of the bank; and

(c) The proposed use of credits is consistent with the terms and conditions of the certified mitigation bank instrument; and

(d) Replacement ratios for projects using bank credits is consistent with replacement ratios specified in the certified mitigation bank instrument.

(5) In-Lieu-Fee (ILF) Mitigation. Credits from an approved in-lieu-fee program may be used when all the following apply:

(a) The approval authority determines that it would provide environmentally appropriate compensation for the proposed impacts; and

(b) The proposed use of credits is consistent with the terms and conditions of the approved in-lieu-fee program instrument; and

(c) Projects using in-lieu-fee credits shall have debits associated with the proposed impacts calculated by the applicant’s qualified wetland professional using the credit assessment method specified in the approved instrument for the in-lieu-fee program; and

(d) The impacts are located within the service area specified in the approved in-lieu-fee instrument.

(6) Timing of Compensatory Mitigation. It is preferred that compensatory mitigation projects be completed prior to activities that will disturb wetlands. If that is infeasible, compensatory mitigation shall be completed immediately following disturbance and prior to use or occupancy of the action or development. Construction of mitigation projects shall be timed to reduce impacts to existing fisheries, wildlife, and flora.

(7) Wetland Mitigation Ratios.

(a) When an applicant proposes to alter a wetland, the affected wetland acreage shall be replaced through wetland creation or reestablishment, rehabilitation, enhancement, or preservation according to the ratios established in the table below.

Category and Type of Wetland 

Creation or Reestablishment




Category I – Natural Heritage Site

Not considered possible




Category I – Mature Forested





Category I – Based on functions





Category II





Category III





Category IV





(8) Compensatory Mitigation Plan. When a project involves wetland and/or buffer impacts, a compensatory mitigation plan prepared by a qualified wetlands professional shall be required, meeting the following minimum standards:

(a) Wetland Critical Area Report. A critical area report for wetlands must accompany or be included in the compensatory mitigation plan and include the minimum parameters described in OHMC 20.24.040.

(b) Compensatory Mitigation Report. The report must include a written report and plan sheets that contain, at a minimum, the following elements:

(i) The written report must contain, at a minimum:

(A) Description of how the project design has been modified to avoid, minimize, or reduce adverse impacts to wetlands;

(B) Complete site characterization to include parcel size, soils, vegetation, hydrology, wildlife, and topography;

(C) Complete site characterization of the proposed mitigation site to include parcel size, soils, vegetation, hydrology, wildlife, and topography;

(D) Goals, objectives, and performance standards for the mitigation proposal;

(E) A description of the proposed mitigation construction activities and timing of activities;

(F) Performance standards for upland and wetland communities, a monitoring and a maintenance schedule and actions proposed by year for a minimum of five years.

(ii) The scaled plan sheets must contain, at a minimum:

(A) Surveyed edges of the existing wetland and buffers, proposed areas of wetland and/or buffer impacts, location of proposed wetland and/or buffer compensation actions.

(B) Conditions expected from the proposed actions on site, including future hydrogeomorphic types, vegetation community types by dominant species (wetland and upland), and future water regimes.

(C) A planting plan for the compensation area, including all species by proposed community type and water regime, size and type of plant material to be installed, spacing of plants, typical clustering patterns, total number of each species by community type, and timing of installation.

(9) Buffer Mitigation Ratios. Impacts to buffers shall be mitigated at a minimum 1:1 ratio. Compensatory buffer mitigation shall replace those buffer functions lost from development.

(10) Monitoring. Mitigation monitoring shall be required for a period necessary to establish that performance standards have been met, but not for a period less than five years. If a scrub-shrub or forested vegetation community is proposed, monitoring may be required for 10 years or more. The project mitigation plan shall include monitoring elements that ensure certainty of success for the project’s natural resource values and functions. (Ord. 1874 § 3, 2019; Ord. 1801 § 20, 2018; Ord. 1440 § 3, 2005).