35.35.140 Regulations – Geologically hazardous areas protection standards

35.35.140 Regulations – Geologically hazardous areas protection standards.

(1) New shoreline uses and developments shall be located, designed, constructed, and maintained to avoid impacts to geologically hazardous areas and their buffers. Impact avoidance measures shall include, but not be limited to, reducing the number, size or scale of buildings, driveways and other features; altering the configuration or layout of the proposed development; using environmentally favorable construction materials; implementing special drainage or runoff management practices; forgoing construction of accessory structures; preserving native vegetation; and other reasonable measures.

(2) New uses and developments may be allowed in geologically hazardous areas and/or their buffers only when specifically allowed by this Program and when all reasonable measures have been taken to avoid adverse impacts on slope stability and protect human health and safety.

(3) Critical facilities shall be prohibited in geologically hazardous areas and/or their buffers. Where linear critical facilities must cross geologically hazardous areas and/or their buffers, reasonable and practicable alternative alignments which minimize geologic hazard shall be considered and preferred; any necessary crossing for linear critical facilities shall be sited to minimize hazard and ecological impacts, and otherwise designed and maintained to minimize hazards based on a geotechnical report.

(4) No clearing, grading, filling, or other land disturbing activities will be permitted in landslide hazard areas, buffers, or adjacent to such areas during the typically wet winter months. When such activities are proposed between October 1st and April 30th, additional technical analysis shall be provided to ensure that no environmental harm, threat to adjacent properties, or safety issues would result, and include recommendations and plans for temporary erosion control and mitigation measures. The technical analysis shall be addressed in a geotechnical report.

(5) Development and alterations within erosion and landslide hazard areas (including channel migration zones) and any required buffers shall require a temporary erosion and sediment control plan and permanent drainage plan, consistent with Article IV of Chapter 35.25 CCC.

(6) Surface drainage shall not be directed across the face of a marine bluff, feeder bluff, or other landslide hazard area. The applicant must demonstrate that the stormwater discharge cannot be accommodated on site or upland by evidence of a geotechnical report. If there is no alternative to discharge across a landslide hazard area, stormwater runoff shall be collected above the face of the landslide hazard area and directed across the hazard area by tight line drain and provided with energy dissipating device at the outlet, above the OHWM.

(7) Geotechnical Report (Nonchannel Migration Zone). The Administrator’s approval of a new use, development, or land division creating a new lot for development in a landslide hazard area or buffer shall be contingent upon the findings of a geotechnical report prepared by either an engineering geologist, a geotechnical engineer, or a civil engineer licensed in the State of Washington, who is knowledgeable of regional geologic conditions and who has professional experience in landslide hazard evaluation. The geotechnical report shall certify that the proposed development will not adversely affect slope stability, be subject to risk of landslide, or impact adjacent properties or resources. Such certification shall be supported by clear documentation of all of the following:

(a) Site Plan. A site plan and/or engineered drawings drawn to an appropriate scale to clearly depict existing conditions and proposed development including:

(i) The type and extent of geologic hazard areas, any other critical areas, and buffers on, adjacent to, or that are likely to impact or influence the proposal or be influenced by the proposal, including properties and critical areas upslope and downslope of the subject site;

(ii) The location of existing and proposed structures, fill, access roads, storage of materials, drainage facilities, sewage facilities and other improvements;

(iii) The existing site topography and land cover; and

(iv) Proposed clearing and grading limits.

(b) Contents. The report shall include a description and analysis of:

(i) Geologic conditions, soils, hydrology, vegetation, topography, and critical areas in the vicinity of the site.

(ii) An analysis of bluff and slope erosion and recession rates shall be presented in those cases where stability is impacted or influenced by wave cutting, stream meandering, or other forces acting on the slope. For marine bluffs (including all feeder bluffs), this analysis shall include the medium and long-term quantitative erosion rates and description of the methods used to quantify the erosion rate (past erosion rates over a minimum of 40 years or as far back as earliest available aerial photos, and a projection of future rates over the next several decades).

(iii) Physical evidence of past erosion or landslide activity in the vicinity of the proposed development.

(iv) Available information and mapping related to the hazard areas including, but not limited to, the Clallam County Shoreline Inventory and Characterization Reports, Washington Coastal Atlas, and Washington Department of Natural Resources landslide hazard maps concerning stability of the site and land adjacent to the site.

(v) Analysis of slope stability for both the existing and developed condition and mechanisms for slope failure in the vicinity, including discussion of types, likely instigating factors, and general sizes of past landslides in the area. For marine bluffs (including all feeder bluffs), this analysis shall also include:

(A) Evidence of landslide activity such as: a mid-slope bench or low bank in an area of high banks, a slight seaward bow in an otherwise straight shoreline, a seaward bow of the cobble/boulder beach lag, lateral elevation changes (uplift) on the beach or subtidal, tilted silt or peat beds exposed among beach gravels, benches on which the vegetation is of a uniform age, areas with jack-strawed trees, groups of trees with kinked trunks – particularly conifers, a bowl-shaped indentation in the bluff edge or hummocky topography on the bluff face.

(B) Location of the intersection of the projected failure plane and the bluff top.

(D) Estimate of when the proposed new development (e.g., residence) or use would be undermined (to include allowance for bank recession equal to largest documented landslide in the vicinity).

(vi) Description of the run-out hazard of landslide debris to the proposed development that starts upslope (whether part of the subject property or on neighboring property) and/or the impacts of landslide run-out on downslope properties and critical areas.

(vii) The development will not significantly increase surface water discharge or sedimentation to adjacent properties beyond predevelopment conditions.

(viii) Conclusions regarding the effect of the proposed development on soil and geologic conditions.

(i) Recommendations on how to adequately protect the proposed development/use and minimize risk of erosion or landslides.

(ii) Methods and practices that avoid and/or reduce slope and shore impacts such as upland and slope drainage control, groundwater control, site vegetation retention and management, revegetation, clearing and grading limitations, and erosion control.

(iii) Identifying minimum buffer and building setback areas at the top or toe of slope based on geotechnical site constraints and the impacts of proposed construction methods on the erosion and landslide potential of the slope.

(iv) There is not significant risk of run-out hazard of landslide debris to the proposed development that starts upslope (whether part of the subject property or on a neighboring property) and/or the impacts of landslide run-out on downslope properties and critical areas.

(v) All newly created building sites will have a suitable building envelope and will be stable under normal geologic and hydrogeologic conditions.

(vi) Recommendations and conclusions on whether further analysis is necessary such as subsurface exploration and testing, additional slope stability or coastal process analysis, additional engineering design analysis, or other testing or analysis.

(d) Inspection. The County shall require a final inspection report stating that construction has or has not implemented the design recommendations of the geotechnical report, and evaluating of any deviation from the design recommendations. If the final inspection report is done by someone other than the qualified professional that prepared the geotechnical report, it must be done by a qualified professional. The Administrator may waive this requirement if the results of the geotechnical report concluded that there is no geologic hazard present on the site, nor will the project affect or be affected by any potential geologic hazards.

(e) Effectiveness of Geotechnical Report. A geotechnical report for a specific site may be valid for a period of up to five years when the proposed land use activity and site conditions affecting the site are unchanged. However, if any surface and subsurface conditions associated with the site change during the five-year period, the applicant may be required to submit an amendment to the geological assessment.

(f) Revisions to Geotechnical Report. Further recommendations shall be provided by the engineer of record should there be additions or exceptions to the original recommendations based on the plans, site conditions, or other supporting data. If the qualified professional who revises the plans and specifications is not the same engineer who prepared the geotechnical report, the new engineer shall, in a letter to the County, express his or her agreement or disagreement with the recommendations in the geotechnical report and state whether the plans and specifications conform to his or her recommendations.

(8) The Administrator may impose conditions on any new shoreline use and developments in geologically hazardous areas and their buffers as needed to:

(a) Protect slope stability and minimize erosion, seismic, and/or landslide hazard risks;

(b) Maintain natural sediment and erosion processes that are integral to the health and sustainability of freshwater and marine nearshore ecosystems;

(d) Protect human health and safety; and

(e) Reduce public liabilities for damages associated with seismic events, erosion and/or landslides.

(9) Seismic Hazard Protection Standards. Development may be allowed in seismic hazard areas when all of the following apply:

(a) Structures in seismic hazard areas shall conform to applicable analysis and design criteria of the Clallam County Building and Construction Code, CCC Title 21.

(b) Public roads, bridges, and utilities shall be allowed when there are no feasible alternative locations and geotechnical analysis and design by a qualified professional are provided that ensure the roadway, bridge and utility structures and facilities will not be susceptible to damage from seismically induced ground deformation. Mitigation measures shall be designed in accordance with the most recent version of the American Association of State Highway and Transportation Officials (AASHTO) Manual or other appropriate document.

(c) Construction of commercial, industrial or any publicly owned buildings within a seismic hazard area shall require a geotechnical report by a qualified geotechnical engineer or engineering geologist licensed in the State of Washington in accordance with this section. The results or conclusions of the evaluation shall be considered a condition of development approval.

(a) Channel Migration Zone (CMZ) Mapping. Clallam County shall make available to the public maps and supporting documents (e.g., methodology) of the potential CMZ based on best available information. These maps currently include the following:

(i) Delineation of the Dungeness River Channel Migration Zone – River Mouth to Canyon Creek; by Byron Rot and Pam Edens, Jamestown S’Klallam Tribe, October 1, 2008.

(ii) Final Washington Department of Ecology Channel Migration Assessments for Clallam County: Puget Sound WRIAs 18-19 (April 2018).

(iii) Final Washington State Department of Ecology Channel Migration Assessments for Clallam County: Pacific WRIA 20 (April 2018).

(iv) Washington State Department of Ecology Revised Channel Migration Assessment and Boundaries for Lower Morse Creek, Clallam County (January 2013).

These maps and supporting documentation shall be advisory and used by the Administrator to provide guidance in determining the applicability of the standards of this Program to a property. These maps shall be updated as new information becomes available.

(b) CMZ Checklist and Review. Applicants that propose new shoreline uses and development in the mapped potential CMZ within the shoreline jurisdiction shall submit a completed CMZ checklist available from the Administrator with their shoreline application. The Administrator will perform and document the results of the following steps to determine whether to require the applicant to prepare a CMZ assessment report:

(i) Review the submitted CMZ checklist and any other supporting information provided by the applicant;

(ii) Consult maps and related supporting databases and reports on the location and extent of the potential CMZ that are available to the public;

(iii) Review whether any significant channel movement has occurred between available County aerial photo series spanning at least 30 years where available;

(iv) Consult with State resource agencies of jurisdiction and/or expertise such as Department of Natural Resources, Department of Ecology and Department of Fish and Wildlife; and

(v) Conduct a site visit to observe and document (e.g., photos) current conditions and evidence of channel migration.

(c) CMZ Assessment Report. If required by the Administrator, the CMZ assessment report shall be prepared by a geologist, engineering geologist, professional engineer licensed in the State of Washington, or other qualified professional that demonstrates the following:

(i) The parcel on which the development or use is proposed is effectively protected (disconnected) from the channel movement due to the existence of permanent levees maintained by public agencies (not all roads and levees will be considered disconnection points); or

(ii) The proposed use or development site has minimal risk of channel migration as indicated by the existing channel type, land cover (and low likelihood of future alterations in land cover); surficial geology, low soil erosion potential; lack of evidence of likely avulsion pathways (including areas upstream of, but proximate to, the site); low inundation frequency(ies); whether channel movement has occurred between an aerial photo series spanning at least 30 years where available; and other available information. The assessment shall include a review of existing CMZ maps and studies; available data (e.g., aerial photos) regarding historical channel locations at the site; available topographic data (e.g., LiDAR, USGS topographic maps); identification of the site within a broader geomorphic reach of the river system, and the general characteristics of that reach; description of existing channel type, existing channel alterations and likelihood of future alterations with changes in land cover; surficial geology, soils and erosion potential; and geotechnical setbacks relating to erosion at the toe of adjacent slope(s). The approach to assessing local migration shall be generally equivalent to the methods detailed in “A Framework for Delineating Channel Migration Zones” (Ecology Publication No. 03-06-027), or similar method approved or sanctioned by Ecology.

The determination of minimal risk shall also consider the typical lifespan of the proposed use and development (e.g., 100 years for a single-family home); the ability and ease of moving the use or development (e.g., RV or mobile home); whether the use or development is temporary or permanent; and the likely effectiveness of applicable shoreline and critical area (e.g., wetlands) buffers between the stream and the proposed location of the use and development. The CMZ assessment shall also evaluate the risk of whether it would be reasonably foreseeable that the proposed use or development would require new shoreline stabilization or interrupt the process of channel migration.

(d) CMZ Field Determination. If a qualified professional determines that the proposed use or development is at risk to channel migration based on the CMZ assessment above, a field review is required to confirm the presence of a CMZ, and field observations shall be documented in the CMZ assessment report. Field observation finding shall include:

(i) Date of the site visit;

(ii) Who conducted the field review and their title/position;

(iii) Distance and location of channel walked;

(iv) Length and location of CMZ boundary delineated;

(v) Presence of avulsion hazard and/or erosion hazard areas;

(vi) Description of method(s) used to determine CMZ presence, CMZ outer edge delineation and marking (flagging, other);

(vii) Description and location of required shoreline and critical area buffers (e.g., wetlands) pursuant to Chapter 35.30 CCC and this chapter between the ordinary high water mark and the proposed use and development; and

(viii) Other applicable information.

(e) New Uses and Development Inside CMZ. Based on the results and recommendations of the channel migration zone assessment, the Administrator shall prohibit or limit use or development within a channel migration zone when such uses or development would likely be subject to channel migration or when it would be reasonably foreseeable that the use or development would require shoreline stabilization or interrupt the process of channel migration. In addition, based on the findings and recommendations of the CMZ assessment report, or a habitat management plan required by this Program, the Administrator may require a buffer of undisturbed natural vegetation from the edge of the channel migration zone to retain both a safety and habitat buffer if and when the channel migrates to the channel migration zone edge. The exception would be new uses and development that may be appropriate (e.g., water-dependent uses, restoration projects, etc.) and/or may be necessary (e.g., roads, utilities) within the CMZ that are otherwise authorized and consistent with this Program, including providing mitigation to address impacted ecological functions and processes.