14.15.180 Geologically hazardous areas.
(1) Classification. Geologically hazardous areas include areas susceptible to erosion, sliding, earthquake, or other geological event. They pose a threat to the health, and safety of the public. The following definitions shall be used in classifying geologically hazardous areas:
(a) Erosion Hazard Area. Erosion is a common occurrence due to hydrologic and geologic characteristics, vegetative conditions and human land use. Erosion hazard areas are sites designated by the USDA Soil Conservation Service as being highly erodible or having the potential to become highly erodible due to disturbance of ground cover.
(b) Seismic Hazard Areas. Seismic hazard areas are areas subject to a severe risk of earthquake damage as a result of seismically induced ground shaking, slope failure, deferential settlement, soil liquefaction, or surface faulting. For purposes of this classification, seismic hazardous areas are those areas that are underlain by alluvium as identified by United States Geologic Service (USGS) maps.
(c) Volcanic Hazard Areas. Volcanic hazard areas are areas which have potential risk to life and property by mud flows or flooding as a result of volcanic activity from Mt. St. Helens. All volcanic mudflow hazard areas shall be identified as flood hazards.
(d) Landslide Hazard Areas. Landslide hazard areas are areas within the town of Cathlamet that are subject to potential slope failure due to a combination of geologic, topographic and hydrological factors. These areas include:
(i) Areas identified by the town of Cathlamet Comprehensive Plan, 2002 (Figure 4-9, page 4-27).
(ii) Areas of historic failures or potentially unstable slopes, such as areas mapped current or future Soil Conservation Service Slide Hazard Area Studies; or marine bluffs, quaternary slumps, earthflows, mudflows, or landslides on maps published by the United States Geological Survey or Department of Natural Resources Division of Geology or as defined by the provisions of the Uniform Building Code (UBC) as adopted by the Town of Cathlamet. Hazard areas are identified on Sheet No. 163 of the Soil Survey of Wahkiakum County prepared by the Soil Conservation Service, 1986.
(2) Designation. Areas of the town of Cathlamet meeting the classification criteria for geologically hazardous areas are hereby designated as such under RCW 36.70A.170.
(3) Landslide and Erosion Hazard Area Standards. All development within designated landslide and steep slope hazard areas shall adhere to the following standards:
(a) An erosion control plan shall be submitted to the administrator for approval prior to any clearing, construction or other development in an erosion hazard area. The erosion control plan shall be designed so that the hazard is or mitigated such that the site is rendered as safe as an area without erosion hazards.
(b) For landslide hazard areas with a slope of 30 percent or steeper and with a vertical relief of 10 or more feet except areas of consolidated rock, a geological analysis and landslide control plan prepared by a qualified critical area professional shall be submitted to the administrator for approval prior to activity which would change the hydrologic characteristics of the site, such as filling, building, clearing construction, or other development in said area. The geological analysis shall indicate that:
(i) There is not significant risk to the development proposal or adjacent properties; or
(ii) The proposal is designed so that the hazard is significantly eliminated or mitigated such that the site and adjacent property are rendered as safe as an area without geologic hazards;
(iii) All proposed development on slopes greater than 50 percent over a vertical height of at least 10 feet shall be avoided if possible. Proposals for development shall include technical studies that evaluate the subsurface conditions and offer engineering solutions, including increased slope stabilization methods. (Ord. 433 § 18, 2002)