A. Erosion Hazard Areas. Erosion shall meet the following requirements:
1. Buffer Not Required for Erosion Hazard Areas. No buffer is required from an area categorized as only an erosion hazard area.
2. Best Management Practices. Best management practices for sediment and erosion control shall be implemented in an erosion hazard area.
3. Vegetation Shall Be Retained. Unless otherwise provided or as part of an approved alteration, removal of vegetation from an erosion hazard area shall be prohibited.
4. Seasonal Restriction. Site development work shall be allowed only from May 1st to October 1st of each year; provided, that the city manager may extend or shorten the dry season on a case-by-case basis depending on actual weather conditions, except that timber harvest, not including brush clearing or stump removal, may be allowed pursuant to an approved forest practice permit issued by the City or the Department of Natural Resources.
5. Utility Lines and Pipes. Utility lines and pipes shall be permitted in erosion hazard areas only when the applicant demonstrates that no other practical alternative is available. Such utilities shall be designed by qualified professionals to resist ground movement and erosion.
6. Point Discharges. Point discharges from surface water facilities and roof drains onto or upstream from an erosion hazard area shall be prohibited except as follows:
a. Conveyed via continuous storm pipe downslope to a point where there are no erosion hazard areas downstream or downslope from the discharge; or
b. Discharged at flow durations matching predeveloped conditions, with adequate energy dissipation, into existing channels that previously conveyed stormwater runoff in the predeveloped state.
7. Alterations. In addition to meeting the requirements in KMC §
18.55.640,
alterations of an
erosion hazard area may only occur for activities for which a special study is submitted demonstrating that the
alteration will not increase surface water discharge or sedimentation to adjacent properties beyond predevelopment conditions.
B. Landslide Hazard Areas. In addition to meeting the requirements in KMC §
18.55.640, activities on
sites containing
landslide hazards shall meet the following requirements:
1. General Standards. The following standards shall apply in all landslide hazard areas:
a. Buffer Required for Landslide Hazard Areas. A buffer shall be established from all edges of landslide hazard areas. The size of the buffer shall be determined by the city manager to eliminate or minimize the risk of property damage, death or injury resulting from landslides caused in whole or part by the development, based upon review of and concurrence with a critical area report prepared by a qualified professional.
(1) Minimum Buffer. The minimum buffer shall be equal to the height of the slope, as measured from the toe to the top, or 50 feet, whichever is greater.
(2) Buffer Reduction. The buffer may be reduced to a minimum of 25 feet when a qualified professional demonstrates to the city manager’s satisfaction based upon review of a special study that the reduction will adequately protect the proposed development, adjacent developments and uses and the subject critical area through slope stability improvements or structural means.
(3) Increased Buffer. The buffer may be increased where the city manager determines a larger buffer is necessary to prevent risk of damage to proposed and existing development.
b. Vegetation Shall Be Retained. Unless otherwise provided or as part of an approved alteration, removal of vegetation from a landslide hazard area or related buffer shall be prohibited.
c. Point Discharges. Point discharges from surface water facilities and roof drains onto or upstream from a landslide hazard area shall be prohibited except as follows:
(1) Conveyed via continuous storm pipe downslope to a point where there are no landslide hazard areas downstream or downslope from the discharge;
(2) Discharged at flow durations matching predeveloped conditions, with adequate energy dissipation, into existing channels that previously conveyed stormwater runoff in the predeveloped state; or
(3) Dispersed discharge upslope of the steep slope onto a low-gradient undisturbed buffer having a width of at least 50 feet and demonstrated to be adequate to infiltrate all surface and stormwater runoff, and where it can be demonstrated that such discharge will not increase the saturation of the slope.
d. Utility Lines and Pipes.
(1) Utility lines and pipes shall be permitted in landslide hazard areas only when the applicant demonstrates that no other practical alternative is available. The line or pipe shall be located aboveground and properly anchored and/or designed so that it will continue to function in the event of an underlying landslide. It must be demonstrated by the applicant that a utility line within the landslide hazard area has been designed in a manner that does not negatively impact the stability of the slope, minimizes or eliminates the potential for rupture or failure, and ensures that in the event of failure there will not be a life/safety risk. Stormwater conveyance shall be allowed only through a high-density polyethylene pipe with fuse-welded joints, or similar product that is technically equal or superior. Automatic shutoff valves shall be provided on petroleum or natural gas lines to isolate the landslide area.
(2) Access roads to serve utilities may be permitted within a landslide hazard area and associated buffer if the City determines that no other feasible alternative exists, and the road is designed so as not to lower the stability of the slope. Such a road shall not be used for general ingress/egress to the property unless otherwise approved as part of a development proposal.
e. Seasonal Restriction. Permitted site development work shall be allowed only from May 1st to October 1st of each year; provided, that the city manager may extend or shorten the dry season on a case-by-case basis depending on actual weather conditions, except that timber harvest, not including brush clearing or stump removal, may be allowed pursuant to an approved forest practice permit issued by the City or the Washington Department of Natural Resources. An exception may be granted by the city manager for emergency repair of structures or landslides when waiting for the clearing window will (1) create a life-threatening risk; (2) do additional damage to the structure; or (3) damage adjacent property or structures.
f. Trails. Trails shall be permitted when all of the following conditions have been met:
(1) The proposed trail shall not decrease the existing factor of safety within the landslide hazard area or any required buffer;
(2) The proposed trail is for pedestrian use only, and is a maximum of four feet wide;
(3) The trail shall not be sited within a landslide hazard area or associated buffer when there is such a high risk of landslide activity that the use of the trail would be hazardous; and
(4) The trail shall be designed and constructed using an engineered drainage system or other methods to prevent the trail surface from becoming a drainage course.
g. Subdivisions. The division of land in landslide hazard areas and associated buffers is subject to the following:
(1) Land that is located wholly within a landslide hazard area or its minimum buffer as required by subsection (B)(1)(a) of this section shall not be subdivided.
(2) Land that is located partially within a
landslide hazard area or its minimum
buffer may be divided; provided, that each resulting
lot has sufficient buildable area outside of, and will not affect, or be affected by, the
landslide hazard area or its
buffer. For single-family residential subdivisions and short subdivisions on
sites in the R-4 zone located partially within a
landslide hazard area and its minimum
buffer, minimum
lot size in the area outside of the
landslide hazard area and its
buffer may be reduced to 5,400 square feet with no limitation on the percentage of smaller
lots, regardless of KMC §
18.21.030, Footnote 16. These smaller
lots shall be located so as to have the least impact on surrounding properties in terms of consistency of
street frontages and privacy of abutting properties and the
lot area shall exclude access easements and access panhandles.
(3) Access roads shall be allowed within a landslide hazard area and associated buffer only if the City determines that no other feasible alternative exists, and the road is designed so as not to lower the stability of the slope.
h. Prohibited Development. On-site sewage disposal systems, including drain fields, shall be prohibited within landslide hazard areas and related buffers.
2. High Landslide Hazard Areas – Additional Standards.
a. No new
alteration shall be permitted in a high
landslide hazard area unless approved as a
reasonable use exception, KMC §
18.55.180.
b. Modifications to a previously approved alteration, including remodeling of an existing residence, in a high landslide hazard area may be permitted only if a critical areas report is submitted demonstrating that the proposal is determined to be safe as sited and designed and under anticipated conditions by a qualified engineer, or engineering geologist, as appropriate, licensed in the State of Washington.
3. Moderate Landslide Hazard Areas – Additional Standards.
a. Design Standards. Alterations of a moderate landslide hazard area and/or its buffer may only occur for activities for which a critical areas report is submitted. Alterations shall be designed to meet the following basic requirements unless it can be demonstrated that an alternative design that deviates from one or more of these standards provides greater long-term slope stability while meeting all other provisions of this article. The requirement for long-term slope stability shall exclude designs that require regular and periodic maintenance to maintain their level of function. The basic development design standards are:
(1) The proposed development shall not decrease the factor of safety for landslide occurrences below the limits of 1.5 for static conditions and 1.2 for dynamic conditions. Analysis of dynamic conditions shall be based on a minimum horizontal acceleration as established by the current version of the International Building Code;
(2) Structures and improvements shall minimize alterations to the natural contour of the slope and foundations shall be tiered where possible to conform to existing topography;
(3) Structures and improvements shall be located to preserve the most critical portion of the site and its natural landforms and vegetation;
(4) The proposed development shall not decrease slope stability on adjacent properties or result in greater risk or a need for increased buffers on neighboring properties;
(5) The use of retaining walls that allow the maintenance of existing natural slope area is preferred over graded artificial slopes; and
(6) Development shall be designed to minimize impervious lot coverage.
C. Slopes Created by Previous Grading. Artificial slopes meeting the criteria of a landslide hazard area based on slope steepness and height that were created through previous permitted grading or are legally nonconforming may be further altered or graded, provided the applicant provides information from a qualified professional demonstrating that the naturally occurring slope, as it existed prior to the permitted grading, did not meet any of the criteria for a landslide hazard area and that a new hazard will not be created. Previously graded slopes meeting the criteria of a landslide hazard area that were not permitted or were illegally created are considered to be landslide hazard areas.
D. Seismic Hazard Areas. Activities proposed to be located in
seismic hazard areas shall meet the standards of KMC §
18.55.640, Performance standards – General requirements, and the International Building Code.
Development or renovation of property in designated tsunami or seiche zones, when identified by the USGS or Washington State Department of Natural Resources, may be allowed if taking into account
Designing for Tsunamis, Seven Principles for Planning and Designing for Tsunami Hazards (National Tsunami Hazard Mitigation Program, 2001) and following the regulations for floodways.
E. Other
Hazard Areas. Activities on
sites adjacent to
geologically hazardous areas shall meet the standards of KMC §
18.55.640, Performance standards – General requirements.
(Ord. 11-0329 § 3 (Exh. 1); Ord. 19-0488 § 2 (Exh. 1); Ord. 24-0624 § 5 (Exh. C))