This article applies to all regulated uses within or adjacent to areas designated as geologically hazardous.
(Ord. 342 § 510, 1992)
The following development shall be exempt from grading plan or geotechnical report requirements of this article:
(1)
Grading which exposes less than 5,000 square feet of earth and presents no danger for any development proposal within an erosion or land-slide hazard area or buffer;
(2)
An excavation below finished grade for basements and footings of a building, retaining wall or other structure authorized by a valid building permit. This shall not exempt any fill made with the material from such excavation nor exempt any excavation having an unsupported height greater than five feet after the completion of such structure;
(3)
Exploratory excavations under the direction of soil engineers or engineering geologists;
(4)
An excavation which (a) is less than two feet in depth, or (b) which does not create a cut slope greater than five feet in height and steeper than one and one-half horizontal to one vertical; and
(5)
A fill less than one foot in depth and placed on natural terrain with a slope flatter than five horizontal to one vertical, or less than three feet in depth, not intended to support structures, which does not exceed 50 cubic yards on any one lot and does not obstruct a drainage course.
(Ord. 342 § 520, 1992)
Developments permitted on properties designated as geologically hazardous shall be the same as those permitted in the underlying zoning classification subject to the standards of this chapter and article.
(Ord. 342 § 530, 1992)
(1)
Classification. The following definitions and terms shall be used in classifying geologically hazardous areas:
(a)
Erosion Hazard Area. Any area containing soils which meet one of the following conditions:
(i)
Soils or soil complexes described and mapped within the soil survey of Clallam County as having a moderate, severe or very severe erosion hazard potential, and soils of the Elwha, Clallam and Yeary series when occurring on slopes 15 percent or greater.
(ii)
Any soil sloping greater than or equal to 40 percent.
(b)
Landslide Hazard Area. Any area potentially subject to mass movement due to a combination of geologic, topographic, and hydrologic factors. The following areas are considered to be subject to landslide hazards:
(i)
Areas of historic failures or potentially unstable slopes, such as areas mapped within the Soils Conservation Service slide hazard area studies; marine bluffs; and areas designated as quaternary slumps, earthflows, mudflows, or land-slides on maps published by the United States Geological Survey or Department of Natural Resources Division of Geology and Earth Resources.
(iii)
Any slope 40 percent or steeper and with a vertical relief of 10 or more feet except areas composed of consolidated rock.
(iv)
Slopes greater than 80 percent subject to rockfall during seismic shaking.
(v)
Any area potentially unstable as a result of rapid stream incision (e.g., ravine side walls), stream bank erosion or undercutting by wave action (e.g., marine bluffs).
(vi)
Any area located on an active alluvial fan, presently or potentially subject to inundation by debris flows or deposition of stream-transported sediments.
(vii)
Slopes that are parallel or subparallel to planes of weakness, such as bedding planes, joint systems and fault planes in subsurface materials.
(c)
Seismic Hazard Areas. Any area subject to severe risk of damage as a result of earthquake induced ground shaking, slope failure, settlement, soil liquefaction, or surface faulting. These conditions occur in areas of loose sand or gravel, peat, artificial fill and landslide materials, poorly drained soils with greater than 50 percent silt and very little coarse material, soil units with high organic content, unconsolidated, recent (post-glacial), fine-grained alluvium in low areas subject to frequent saturation, and areas of artificial fill. These areas are considered likely to experience some sort of surficial disturbance under anticipated earthquake loads.
(2)
Designation. Lands classified as erosion, landslide or seismic hazards are hereby designated as geologically hazardous areas and are subject to the procedures and standards of this chapter and article. Geologically hazardous areas shall be mapped whenever possible. These maps shall be advisory and used by the administrator to provide guidance in determining applicability of the standards to a property. Sites which include geologically hazardous areas which are not mapped shall be subject to the provisions of this article and chapter. The administrator shall use, but is not limited to, the following information sources as guidance in identifying the presence of geologically hazardous areas:
(Ord. 342 § 540, 1992)
All development within designated erosion hazard areas or adjacent to such areas shall adhere to the following standards:
(1)
Drainage and Erosion Control. All development which exposes 5,000 square feet of earth or more shall submit and have approved a drainage and erosion control plan as specified in Article VIII of this chapter.
(2)
Clearing and Grading.
(a)
All development which exposes 5,000 square feet of earth or more shall submit and have approved a grading plan as specified in Article VIII of this chapter.
(b)
Excavation, grading and earthwork construction shall only be allowed from April 1st to October 15th, or outside this date range if weather conditions do not cause any erosion problems. The following projects are also allowed throughout the year:
(3)
Utilities. Construction of public and private utility corridors may be allowed in erosion hazard areas when no practicable alternative exists; and provided, that a geotechnical report (Article VIII) indicates that such alteration will not subject the area and development to the risk of erosion.
(4)
Land Divisions. No new lot or parcel shall be created in a known erosion hazard area without meeting the following requirements:
(a)
A drainage and erosion/sediment control plan shall be submitted and approved which concludes that division of property will not increase erosion or sedimentation of adjacent properties or watercourses; and
(b)
Any contiguous erosion hazard areas greater than one acre in area within a proposed land division development proposal site shall require the submission of a geotechnical report (Article VIII). All areas which are determined to be unbuildable shall be dedicated as an open space tract, easement or covenant which assures the ownership and protection of the area.
(5)
Trails. Trail construction may be allowed; provided, that such trails are not constructed of concrete, asphalt or other impervious surface which would contribute to surface water runoff unless such construction is necessary for soil stabilization or soil erosion prevention.
(Ord. 342 § 550, 1992)
All development within designated landslide hazard areas or adjacent to such areas shall adhere to the following standards:
(1)
Drainage and Erosion Control. All development which exposes 5,000 square feet of earth or more shall submit and have approved a drainage and erosion control plan as specified in Article VIII of this chapter. Surface drainage shall not be directed across the face of a marine bluff, landslide hazard or ravine. If drainage must be discharged from the bluff into adjacent waters, it shall be collected above the face of the bluff and directed to the water by tight line drain and provided with an energy dissipating device at the shoreline.
(2)
Grading and Clearing.
(a)
All development which exposes 5,000 square feet of earth or more shall submit and have approved a grading plan as specified in Article VIII of this chapter. There shall be minimum disturbance of trees and vegetation on landslide hazard areas in order to minimize erosion and stabilize bluffs.
(b)
Excavation, grading and earthwork construction shall only be allowed from April 1st to October 15th, or outside this date range if weather conditions do not cause any landslide problems. The following projects are also allowed throughout the year:
(3)
Buffers. A minimum buffer of 30 feet shall be established from the top, toe and all edges of landslide hazard areas. Existing native vegetation within the buffer area shall be maintained. The buffer may be reduced to a minimum of 10 feet when an applicant demonstrates to the satisfaction of the review authority that the reduction will adequately protect the proposed development and the landslide hazard area. The buffer may be increased by the review authority for development adjacent to a marine bluff or ravine which is unstable. Normal nondestructive pruning and trimming of vegetation for maintenance purposes, or thinning of limbs of individual trees to provide for a view corridor, shall not be subject to these buffer requirements.
Alterations of the buffer for landslide hazard area, or the hazard area itself, may occur for development meeting the following criteria:
(a)
There will be no increase in surface water discharge or sedimentation to adjacent properties;
(b)
There will be no decrease in slope stability on adjacent properties;
(c)
No reasonable alternative exists; and
(d)
A geotechnical report (Article VIII) is submitted and demonstrates that:
(i)
There is no hazard as proven by evidence of no landslide activity in the past in the vicinity of the proposed development and a quantitative analysis of slope stability indicates no significant risk to the development proposal and adjacent properties; and
(ii)
The landslide hazard area can be modified or the development proposal can be designed so that the landslide hazard is eliminated or mitigated so that the site is as safe as a site without a landslide hazard.
(4)
Land Divisions. No new lot or parcel shall be created in a lawn landslide hazard area without meeting the following requirements:
(a)
No lot or parcel shall be created in a landslide hazard area or its required buffer unless a geotechnical report (Article VIII) of the property indicates that proposed building sites will be safe; and
(b)
Any contiguous landslide hazard areas greater than one acre in area within a proposed land division development proposal site shall require the submission of a geotechnical report (Article VIII). All areas which are determined to be unbuildable shall be dedicated as an open space tract, easement or covenant which assures the ownership and protection of the area.
(5)
Utilities.
(a)
Construction of public and private utility corridors may be allowed in landslide hazard areas; provided, that a geotechnical report (Article VIII) indicates that such alteration will not subject the area and development to the risk of landslide.
(b)
Septic system drainfields shall be located outside of landslide hazard areas and their associated buffers, except for the toe of slope, unless otherwise justified by a qualified geotechnical engineer.
(c)
Stormwater retention and detention systems, including percolation systems and curtain drains utilizing buried pipe or french drain, are prohibited in landslide and steep slope hazard areas and their buffers unless a geotechnical report indicates such a system shall not affect slope stability. The city of Forks city council may require that a licensed civil engineer shall design the systems and certify that the systems have been installed as designed.
(6)
Trails. Trail construction may be allowed; provided, that such trails are not constructed of concrete, asphalt or other impervious surface which would contribute to surface water runoff unless such construction is necessary for soil stabilization or soil erosion prevention.
(7)
Critical Facilities. Critical facilities shall not be sited within landslide hazard areas unless such facilities meet the following criteria:
(Ord. 342 § 560, 1992)
All development within designated seismic hazard areas shall adhere to the following standards:
(1)
Land Divisions. No new lot or parcel shall be created in a seismic hazard area without placing a note on the face of the plat which indicates the presence of a potential hazard and encourages the builder to have any structure designed by a civil engineer to withstand potential seismic activity.
(2)
Utilities. Construction of public and private utility corridors may be allowed in seismic hazard areas; provided, that a geotechnical report (Article VIII) indicates that such alteration will not subject the area and development to the risk of earthquake. Utility corridors which carry oil, gas or any other hazardous substance transmission facility shall be prohibited in seismic hazard areas.
(3)
Critical Facilities. Critical facilities shall not be sited within seismic hazard areas unless such facilities meet the following criteria:
(4)
Construction on Artificial Fills. The city of Forks city council may require that construction on artificial fills shall be certified by a geotechnical report (Article VIII) as safe from earthquake damage. This provision shall not apply to normal maintenance or repair of existing legal structures not exceeding 50 percent of the fair market value of the existing structure.
(5)
Public Buildings (Commercial, Industrial, Publicly Owned). Construction of commercial, industrial or any publicly owned building which allows public access shall prepare a preliminary or shallow geotechnical report (Article VIII) evaluation prior to the granting of development permits. The evaluation shall demonstrate that the proposed design will adequately protect the public which has access to the proposed development. The results or conclusions of the evaluation shall be considered a condition of development approval. For the purposes of this section, public access does not include employees of the company or authorized salespeople.
(Ord. 342 § 570, 1992)