Article III. Geologically Hazardous Areas
18.65.250 Applicability and designation – Geologically hazardous areas.
(1) This article regulates development activities on or within 50 feet of a geologically hazardous area.
(2) Geologically hazardous areas include areas susceptible to erosion, landsliding, seismic, or other geological events. The following areas are designated as geologically hazardous areas:
(a) Erosion hazard areas, defined as those areas underlain by soils that are subject to severe erosion when disturbed, including areas likely to become unstable, such as bluffs, steep slopes, and areas with unconsolidated soils. The soils subject to severe erosion include, but are not limited to, those classified as having a severe to very severe erosion hazard according to the United States Department of Agriculture Natural Resources Conservation Service, the 1973 King County Soils Survey, or any subsequent revisions or addition by or to these sources, such as any occurrence of river wash (“Rh”) and any of the following when the soils occur on slopes inclined at 15 percent or more:
(i) The Alderwood gravelly sandy loam (“AgD”);
(ii) The Alderwood and Kitsap soils (“AkF”);
(iii) The Beausite gravelly sandy loam (“BeD” and “BeF”);
(iv) The Kitsap silt loam (“KpD”);
(v) The Ovall gravelly loam (“OvD” and “OvF”);
(vi) The Ragnar fine sandy loam (“RaD”); and
(vii) The Ragnar-Indianola association (“RdE”);
(b) Landslide hazard areas, defined as those areas subject to severe risk of landslide, based on a combination of geologic, topographic, and hydrologic factors. They include any areas susceptible to landslide because of any combination of bedrock, soil, slope (gradient), slope aspect, structure hydrology, or other factors, and include, at a minimum, the following:
(i) An area with a combination of:
(A) Slopes steeper than 15 percent of inclination;
(B) Impermeable soils, such as silt and clay, interbedded with granular soils, such as sand and gravel; and
(C) Springs or seasonal ground water seepage;
(ii) Areas of historic failures such as:
(A) An area that has shown movement during the Holocene epoch, which is from 10,000 years ago to the present, or that is underlain by mass wastage debris from that epoch;
(B) Those areas delineated by the United States Department of Agriculture Natural Resources Conservation Service as having a significant limitation for building site development;
(C) Areas designated as quaternary slumps, earthflows, mudflows, lahars, or landslides on maps published by the United States Geological Survey or Washington Department of Natural Resources;
(iii) An area potentially unstable as a result of rapid stream incision, stream bank erosion or undercutting by wave action including stream channel migration zones;
(iv) An area that shows evidence of or is at risk from snow avalanches;
(v) An area located in a canyon or on an active alluvial fan, presently or potentially subject to inundation by debris flows, or catastrophic flooding, or deposition of stream-transported sediments;
(vi) Any area with a slope of 40 percent or steeper and with a vertical relief of 10 or more feet except areas composed of bedrock;
(vii) Slopes having gradients steeper than 80 percent subject to rockfall during seismic shaking; and
(viii) Slopes that are parallel or subparallel to planes of weakness (such as bedding planes, joint systems, and fault planes) in subsurface materials;
(c) Steep slope hazard areas, defined as those areas on a slope of 40 percent inclination or more within a vertical elevation change of at least 20 feet. For the purpose of this definition, a slope is delineated by establishing its toe and top, as defined in CMC 18.20.046, and is measured by averaging the inclination over at least 10 feet of vertical relief; and
(d) Seismic hazard areas, defined as those areas in the City of Covington subject to severe risk of earthquake damage as a result of ground movement, ground displacement, or soil liquefaction in areas underlain by cohesionless soils of low density and usually in association with a shallow ground water table or other seismically induced settlement.
(3) Alterations within geological hazard areas are allowed pursuant to CMC 18.65.050.
(4) The critical area report shall include a geotechnical evaluation prepared by a geotechnical engineer or engineering geologist licensed in the State of Washington.
(5) The Director may approve a permit for development activities within 50 feet, but not less than 15 feet, of a steep slope area or a landslide hazard area, based on the findings of critical area report that the development will not be at risk of damage due to the geologic hazard and will not lead to nor create any increased slide, seismic or erosion hazard.
(6) Allowed alteration within a steep slope, erosion, or landslide hazard area shall minimize alterations to the natural contour of the slope and foundations shall be tiered where possible to conform to existing topography in accordance with Chapter 14.60 CMC. Freestanding retaining devices are only permitted when they cannot be designed as structural elements of the building foundation. Structures and improvement shall be located to preserve the most critical portions of the site and its natural landforms and vegetation. (Ord. 08-21 § 4 (Exh. C); Ord. 09-19 § 9 (Exh. D); Ord. 06-17 § 4 (Exh. B))