19.70.330 Specific standards for riparian management zones

19.70.330 Specific standards for riparian management zones.

A. A riparian management zone (RMZ) is a critical area; specifically, it is a type of fish and wildlife habitat conservation area. A project site’s RMZ is associated with each aquatic species upstream and downstream from the project site.

1. The RMZ consists of a watercourse and the area adjacent to the watercourse that has the potential to provide full riparian ecosystem functions for bank stability, shade, pollution removal, contributions of detrital nutrients, recruitment of large woody debris, and wildlife habitat. The width of the RMZ is the height of the tallest 200-year-old site-potential tree (SPTH₂₀₀) or 100 feet, whichever is greater, measured horizontally. The RMZ is measured from whichever of the following features is furthest from the center of the watercourse: (a) the ordinary high-water mark, (b) the top of bank, or (c) the outer edge of the channel migration zone (if one exists). In watercourses with braided channels or alluvial fans, the ordinary high-water mark will include the entire stream feature. The RMZ may exceed the 200-year-old site-potential tree height based on subsection (A)(3) of this section.

2. When a pipe or culvert that has known or potential fish habitat downstream and upstream from the pipe or culvert is daylighted, the watercourse formerly in the pipe or culvert will be regulated as a riparian watercourse, and the area adjacent to that watercourse will be regulated as a riparian management zone, as defined in subsection (A)(1) of this section. This section does not apply when the pipe or culvert is removed to provide a publicly owned facility designed primarily for water quality treatment, flow control, or stormwater conveyance.

3. Activities that may impact an RMZ must provide a critical areas report prepared by a qualified professional describing the functions and values of the RMZ. The report must include the 200-year-old site-potential tree height (SPTH₂₀₀) as determined by WDFW at https://gispublic.dfw.wa.gov/arcgis/rest/services/SPTH/SitePotentialTreeHeightPublic/MapServer.

If SPTH₂₀₀ was also calculated using site-scale data, that information must also be included. The report must describe the inner measurement point (e.g, ordinary high-water mark) and the extent of the RMZ with sufficient detail to allow field delineation. The report must demonstrate that the project will result in no net loss of the ecosystem functions for the RMZ and associated species.

a. The provisions of this section apply to all development on parcels containing an RMZ as defined in subsection (A)(1) of this section.

b. It is the long-term goal of the city to restore the city’s RMZs and to protect fish passage where scientifically justified. The city has determined that best available science supports protecting these RMZs as described in this section.

2. Watercourse. Development is prohibited within or over the riparian watercourse, except as provided in this subsection. The Director may approve access over the riparian watercourse, if the applicant demonstrates all of the following:

a. No other access is available.

b. The access is provided by a freestanding structure that maintains the natural channel and floodway of the watercourse.

c. The coverage of the watercourse and disturbance of the RMZ and any other adjacent environmentally critical area or buffer are kept to a minimum.

d. The material used to construct the access is durable and nontoxic to the maximum extent feasible. If using untreated wood is infeasible, wood treated with pentachlorophenol, creosote, chromate copper arsenate, or comparably toxic compounds is prohibited. Treated wood and other material shall be the least toxic and shall be applied and used according to National Oceanic and Atmospheric Administration Fisheries guidelines for using treated wood in or over aquatic environments.

e. In the watercourse, any action detrimental to habitat or actions affecting trees and vegetation, including but not limited to clearing or removal, is prohibited, except as provided in this subsection (B)(2).

3. Riparian Management Zone. The RMZ is defined in subsection (A)(1) of this section. Existing improved areas of public or private streets/driveways are excluded from the regulations for the RMZ. Development is prohibited in the RMZ, except as follows:

a. To provide the minimum necessary access if no other access is available to development approved under subsection (B)(2)(a) of this section.

b. On existing developed lots and platted lots existing prior to adoption of Ordinance 4025 that satisfies one or more of the provisions within Table 19.70.040(A), Exempt Activities, or Table 19.70.045, Permitted Alterations, if the applicant demonstrates that:

i. None of the development occurs within or over the watercourse except as provided in subsection (B)(2) of this section.

ii. The development complies with stormwater flow control and water quality requirements, regardless of whether the project would trigger the requirements based on the thresholds for area of land disturbing activity, size of the addition, or replacement of impervious surfaces provided in the Stormwater Management Manual adopted in AMC Chapter 19.76, Stormwater.

iii. Any development, including but not limited to coverage by impervious surface, does not exceed 35 percent of the total lot area, and provided further, that the maximum lot coverage does not exceed that allowed under AMC Chapter 19.42, Form and Intensity Standards.

iv. When compliance with stormwater flow control and water quality requirements is required solely based on subsection (B)(3)(b)(ii) of this section, the Director may approve a restoration plan in lieu of compliance with subsection (B)(3)(b)(ii) if the applicant demonstrates that the plan meets the following criteria:

(A) The watercourse and/or RMZ ecological function will be restored so that it prevents harmful erosion, protects water quality, and provides diverse habitat; and

(B) The restoration results in greater protection of the watercourse and RMZ than compliance with subsection (B)(3)(b)(ii) of this section.

c. In the RMZ any action detrimental to habitat and any action affecting trees and vegetation, including but not limited to clearing or removal, are prohibited, except as provided in subsection (B)(3)(a) or (b) of this section.

d. If the RMZ is degraded due to the lack of trees and vegetation, the presence of invasive or nonnative species, and/or the presence of impervious surface or other development, the applicant shall prepare and carry out a restoration plan that restores the ecological function of the RMZ to the extent commensurate with the impact of the development on the RMZ and according to mitigation standards pursuant to AMC 19.70.125, Mitigation requirements, and AMC 19.70.130, Mitigation plan requirements.

e. If the development is authorized pursuant to AMC 19.49.040, Nonconforming uses and structures, or Table 19.70.040(A), Exemptions, or Table 19.70.045, Permitted Alterations, the Director must require that the degraded portion of the RMZ be restored by removing existing nonnative and invasive plant species, and replanting with native trees and vegetation, and providing a five-year monitoring and maintenance plan consistent with the requirements of AMC 19.70.130, Mitigation plan requirements, based on a critical area restoration plan.

f. Small Project Waiver. The Director may approve fences, rockeries, or similar features or temporary disturbance for installation of utility lines in a RMZ if no construction occurs over, in, or within 15 feet of a watercourse or water body, and if the applicant demonstrates that the proposal meets the following criteria:

i. The feature is constructed on a lot that has been in existence as a legal building site consistent with AMC 19.49.040, Nonconforming structures.

ii. The feature:

(A) Does not contain floor area;

(B) Does not remove trees or native vegetation;

(D) Mitigates impacts to ecological functions.

iii. The Director’s decision must require:

(A) The use of fencing with a highly durable protective barrier during the construction to protect the RMZ.

(B) Mitigation pursuant to AMC 19.70.125 and 19.70.130 to offset the area of both temporary and permanent development.

C. Functionally Separated and Isolated Riparian Management Zones. Consistent with the definition of “riparian management zone” in this chapter, RMZs are places that potentially provide riparian ecosystem functions. Portions of the RMZ that are functionally isolated and physically separated from a watercourse due to existing, legally established public 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 watercourse may be excluded from the RMZ. If such an area provides any of the five primary RMZ functions (bank stability, shade, pollution removal, contributions of detrital nutrients, or recruitment of large woody debris) it will be retained within the RMZ; if it provides none of these functions it may be excluded. After an RMZ is determined by the decision-maker, based on a submitted critical area report, to be physically separated and functionally isolated, the area is no longer considered an RMZ critical area.

D. Piped Watercourses and Roadside Ditches. It is recognized that within the urban environment many historical streams have been substantially modified to accommodate development. Many of the regulated and mapped watercourses within the city of Anacortes pass through natural reaches, modified reaches, piped reaches, and sometimes along manmade roadside ditches.

1. Development along piped watercourses and ditches that do not meet the definition of a watercourse are subject to a 10-foot setback from the centerline of the piped watercourse or ditch and are subject to the recording of a utility easement granted to the city for access and maintenance of the watercourse infrastructure.

2. The voluntary opening and restoration or rehabilitation of a previously channelized, culverted, or piped watercourse is highly encouraged and may be approved by the decision-maker, when the following is demonstrated within a critical area report:

a. The restoration will result in a net gain in FWHCA functions, including an improvement in water quality and ecological functioning;

b. Opened channels must be designed to support fish and wildlife habitat and uninhibited fish access, unless demonstrated to be infeasible;

c. A reduction to the standard riparian management zone is allowed to a minimum of 25 feet, or as recommended by a qualified professional in the critical area report. Measured from the ordinary high water mark (OHWM) and which includes habitat improvements, and measures to prevent erosion, landslide and water quality impacts;

d. The proposal will not significantly increase the threat of erosion, flooding, slope stability or other hazards on the site or on adjacent properties;

e. The proposal must demonstrate that the conveyance will maintain the flow capacity and not create flooding elsewhere in the drainage basin.

E. Riparian Management Zone Enhancement Measures. Only those enhancement measures deemed most applicable and/or appropriate for RMZ enhancement projects will be considered in a RMZ modification proposal, and must be supported by best available science and a critical area report. These include, but are not limited to:

1. Removal of fish barriers to restore accessibility to fish;

2. Enhancement of fish habitat using log structures incorporated as part of a fish habitat enhancement plan;

3. Enhancement of fish and wildlife habitat structures that are likely to be used by wildlife, including wood duck houses, bat boxes, nesting platforms, snags, rootwads/stumps, birdhouses, and heron nesting areas;

4. Planting native vegetation within the buffer area, especially vegetation that would increase value for fish and wildlife, increase stream bank or slope stability, improve water quality, or provide aesthetic/recreational value; or

5. Creation of a surface channel where a watercourse was previously underground, in a culvert or pipe. Surface channels which are “daylighted” must be located within a riparian management zone and must be designed with energy dissipating functions or channel roughness features such as meanders and rootwads to reduce future bank failures or nearby flooding;

6. Removal or modification of existing stream culverts (such as road crossings) to improve fish passage, stream habitat, and flow capacities; or

7. Upgrading of retention/detention facilities or other stormwater management facilities beyond required levels. (Ord. 4025 § 2 (Att. A), 2022; Ord. 4015 § 2 (Att. A), 2022; Ord. 3064 § 2 (Att. A), 2021)