21.68.080 Shoreline Protective Structures.
A. Purpose. The purpose of this chapter is to provide standards and guidelines for the location and design of bulkheads, levees, and other shoreline protective structures that have the potential to adversely impact the shoreline natural environment. New development, however, should be located and designed to avoid the need for future shoreline stabilization to the extent feasible.
B. Permitted Shoreline Protective Structures.
1. New and replacement shoreline protective structures shall be allowed under the following circumstances only:
a. A geotechnical analysis prepared by a licensed professional engineer demonstrates that shoreline stabilization is necessary to prevent damage to or loss of the following facilities, due to wave action, and no practicable alternative exists. The geotechnical analysis shall evaluate on-site drainage problems away from the shoreline edge before considering structural shoreline stabilization.
i. Existing structures, where the structure is a single-family residence or where the fair market value of the structure to be protected equals or exceeds the construction cost of the shoreline protective structure;
ii. Existing private roads and bridges;
iii. Public roads and bridges, and regional light rail transit facilities; or
b. Shoreline structures are necessary to protect or enhance water quality or aquatic habitat; or
c. Shoreline structures are necessary to remedy an emergency situation; and
d. Shoreline structures, except temporary emergency construction, comply with the requirements of subsections B.2 through B.3 below, and RZC 21.68.080.C, Design Requirements for Shoreline Protective Structures.
e. Erosion is not being caused by upland conditions, such as the loss of vegetation and drainage.
f. Nonstructural measures, planting vegetation, or installing on-site drainage improvements are not feasible or not sufficient.
2. Shoreline protective structures, including replacement structures, shall not be located in salmon and steelhead spawning areas or freshwater clam beds, except under the following circumstances:
a. A hydraulic analysis demonstrates that the protective structure will have no adverse impacts on long-term stream or lake hydraulics affecting salmon and steelhead spawning areas or freshwater clam beds;
b. A biological inventory and analysis demonstrates that impacts to salmonids and freshwater clams are negligible; and
c. For nonstructural solutions, the proposed measures are necessary to protect or rehabilitate eroding shorelines, and are designed to protect or restore water quality and aquatic habitat.
3. Shoreline protective structures shall not be allowed where they will result in any of the following:
a. Increased or expanded residential development in undeveloped areas of the floodplain or upland of ecologically intact shorelines;
b. Creation of dry land waterward of the ordinary high water mark of a lake, stream, or wetland;
c. Loss of significant flood storage capacity in the floodplain;
d. Deflection or constriction of flood flows to a degree which will result in significantly increased flood heights on unprotected properties; or
e. Loss of shoreline ecological functions.
4. An existing shoreline stabilization structure may be replaced with a similar structure if there is a demonstrated need to protect principal uses or structures from erosion caused by currents or waves, provided the following is met:
a. The replacement structure shall be designed, located, sized, and constructed to assure no net loss of ecological functions;
b. Replacement walls or bulkheads shall not encroach waterward of the ordinary high water mark or existing structure unless the residence was occupied prior to January 1, 1992, and there are overriding safety or environmental concerns. In such cases, the replacement structure shall abut the existing shoreline stabilization structure.
c. Soft shoreline stabilization measures that provide restoration of shoreline ecological functions may be permitted waterward of the ordinary high water mark.
d. For the purposes of this section standards on shoreline stabilization measures, ”replacement” means the construction of a new structure to perform a shoreline stabilization function of an existing structure which can no longer adequately serve the purpose. Additions to or increases in size of existing shoreline stabilization measures shall be considered new structures.
5. Breakwaters and jetties are prohibited.
C. Design Requirements for Shoreline Protective Structures.
1. All proposals for new and replacement shoreline protective structures, except those necessary to remedy an emergency situation, shall include all of the following:
a. An evaluation by a licensed professional engineer or qualified geologist who has professional expertise about the region and local shoreline geology, and processes of the hazard to be addressed, the need for the shoreline protective structure by estimating time frames and rates of erosion, and the feasibility of nonstructural alternatives, such as the relocation of structures or biotechnical solutions, to address the particular hazard.
b. A hydraulic analysis prepared by a licensed professional engineer that sufficiently describes the proposal's effects on stream or lake hydraulics, including potential increases in base flood elevation, changes in stream or wave velocity, changes in groundwater movement, the potential for redirection of the normal flow or currents of the stream or lake, and potential for resultant erosion at other properties adjacent to the stream or lake.
c. A biological inventory and analysis prepared by a professional biologist that sufficiently describes the proposal's effects on fisheries, aquatic life, and wildlife. This shall include an evaluation of shoreline ecological functions that describe how the project will achieve no net loss of shoreline ecological functions.
d. Where mitigation is required, a monitoring program pursuant to RZC 21.64.010.P, Monitoring Program and Contingency Plan.
2. Structural solutions to stabilize or reinforce shorelines shall not be allowed, unless it is demonstrated that planting of vegetation, biotechnical measures, relocation or redesign of affected structures, or other nonstructural solutions are infeasible or ineffective in preventing or correcting significant erosion. This shall apply to new, replacement, repair, and emergency protective structures. Replacement or repair of bulkheads shall not be allowed, except where it can be demonstrated that replacement with a nonstructural solution is ineffective or infeasible. In general, hard armoring solutions are not permitted unless a geotechnical report pursuant to this section confirms that there is a significant possibility that such a structure will be damaged within three years as a result of shoreline erosion in the absence of such hard armoring measures, or where waiting until the need is that immediate, would foreclose the opportunity to use measures that avoid impacts of ecological functions.
3. Structures shall have no long-term detrimental effects on stream or lake hydraulics, including increased wave energy or erosion at other properties, or on fisheries, aquatic life, and wildlife.
4. Shoreline protective structures shall be designed to the minimum size, height, bulk, and extent necessary to remedy the identified hazard. Flood control dikes and levees shall be limited to the minimum height required to protect existing development in the floodplain from the design flood, as identified in the King County Flood Hazard Reduction Plan.
5. Methods selected for shoreline protection shall be appropriate for the length and configuration of the existing shoreline, erosional conditions at the site, the natural condition and habitat functions of the shoreline, and adjacent land uses, particularly single-family residences and public access.
6. Where structural solutions to shoreline protection are allowed, structures shall meet the following standards:
a. Structures shall be located landward of the ordinary high water mark, except as provided below:
i. Where a bulkhead exists, the toe of a replacement bulkhead shall not be located waterward of the toe of the existing bulkhead.
ii. To the extent necessary to protect the toe of a slope with a gradient of 40 percent or greater, a bulkhead may extend waterward of the ordinary high water mark up to a maximum of six feet beyond the ordinary high water mark.
iii. Flood control structures may extend waterward of the ordinary high water mark, but shall be located landward of the floodway and any wetlands associated with Class I streams or Lake Sammamish.
b. Filling behind bulkheads shall be the minimum amount and extent necessary to install the protective structure. Fill material must be nondissolving and nondecomposing, and shall be free of materials that would be detrimental to water quality. The elevation of the existing shoreline in the vicinity of the protective structure shall not be raised more than four feet, except where necessary for an approved flood control structure such as a levee or dike.
c. The existing contour of the natural shoreline shall be generally followed. Levees and dikes shall, where adjacent lands are within the same ownership or undeveloped, be set back from the ordinary high water mark to maintain natural bank gradients.
d. Vertical wall or solid slab bulkheads shall not be allowed, unless it is demonstrated that riprap bulkheading or an open structure is infeasible and ineffective. This shall apply to new, replacement, repaired, and emergency protective structures. Structures shall be designed with a tiered or sloping face, or similar design measure to minimize the impact of wave action.
e. Riprap faces shall be constructed to a stable slope and shall be of a material of sufficient size to be stable. All riprap areas shall be interplanted with native shrubs and groundcover of native species or erosion-control grasses.
f. Rock used for shoreline protective structures shall be composed of clean, angular material of a sufficient size to prevent its being washed away. Rock used for toe protection shall be smooth, well-rounded gravel material suitable for use by spawning salmon and steelhead. Alternatively, spawning gravel could be added on top of toe rock if toe protection needs to be more sufficient to structurally support the weight of the larger rock required on the face of the structure.
g. Structures shall incorporate the installation of native aquatic plants, such as hardstem bulrush (Scirpus acutus), below the ordinary high water mark to mitigate the effects of introduced structures on wave action and erosion.
7. Shoreline protective structures within shorelines and other water bodies used by or that have the potential to be used by salmonids shall provide for adequate upstream and downstream salmonid migration.
8. Shoreline protective structures shall not interfere with the public's right of navigation. Where shoreline protective structures located on the Sammamish River or Lake Sammamish are wholly or partially publicly funded, such structures shall provide public access if none exists, or enhance existing public access, commensurate with the scale of the project's impacts to public access.
9. Shoreline protective structures shall be designed to minimize aesthetic impacts to the shoreline.
10. Protection of Vegetation. Removal of shoreline, riparian, and aquatic vegetation shall be limited to the minimum extent necessary to construct the project. Significant trees and other shoreline or riparian vegetation shall be protected and replaced adjacent to the water body, pursuant to RZC 21.68.110, Tree Protection, Landscaping, and Screening Within Shorelines. All upland and aquatic areas disturbed by construction shall be replanted and restored pursuant to RZC 21.64.030.D, Wetlands Performance/Design Standards, and RZC 21.64.020.F, Riparian Stream Corridor Performance Standards.
11. Proposals for bioengineered or other nonstructural methods involving erosion-control plantings shall include a five-year maintenance plan to ensure the long-term survival of vegetation.
12. All proposals for shoreline protective structures shall mitigate adverse impacts to fisheries, aquatic and wildlife resources, shoreline vegetation, and impacts to other natural shoreline systems. Mitigation may include, but is not limited to, relocation of threatened structures, use of natural vegetation for bank stabilization, replacement of native vegetation, installation of in-water habitat features, replacement of gravel substrate, or restoration of shallow water habitat. At a minimum, mitigation shall meet the requirements of RZC 21.64.030.D, Wetlands Performance/Design Standards, and 21.64.020.F, Riparian Stream Corridor Performance Standards.
13. All proposals for shoreline protective structures shall include provisions for adequate erosion control, emergency erosion control, and protection of water quality, fisheries, and aquatic life during construction.
14. All material resulting from excavation or dredging during construction shall be disposed of in a manner that prevents the material entering into a water body through erosion or floodwaters.
15. Maintenance corridors and service roads accessory to a shoreline protective structure shall be the minimum size necessary to safely accomplish maintenance and repair; and shall be located, where possible, in areas already disturbed or away from significant trees, and where siltation and erosion impacts will be minimal.