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Ghapter 17A.06 <br />GEOLOGICALLY HAZARDOUS AREAS <br />Sections: <br />17A.06.010 Purpose and lntent <br />174.06.020 Desiqnation.Classification.andMappino <br />174.06.030 General Protection Standards <br />17A.06.040 Landslide Hazard Area Standards <br />17A.06.050 Erosion Hazard Area Standards <br />174.06.060 Alluvial Fan Hazard Standards <br />17A.06.070 SeismicHazardStandards <br />174.06.080 Volcanic Hazard Areas <br />174.06.090 Mine Hazard Areas <br />174.06.100 Reportinq <br />17A.06.010 Purpose and lntent <br />The purpose of this Chapter is to protect human life and safety. prevent damage to <br />structures and propertv, and minimize impacts to water qualitv and fish and wildlife caused <br />bv qeoloqic hazards. <br />17A.06.020 Desiqnation. Classification. and Mappinq <br />1. Desiqnation. Lands classified as landslide. erosion (includinq channel miqration zones), <br />alluvialfan. seismic. and mine hazard areas. are herebv designated as geologically <br />hazardous areas.2. Classification. <br />a. Potential Landslide Hazard Areas. Landslide hazard areas shall include areas <br />potentially subject to landslides based on a combination of qeoloqic. topoqraphic. <br />and hvdrolosic factors. They include any areas susceptible because of anv <br />combination of bedrock. soil. slope (qradient), slooe aspect. structure. hvdroloqy. or <br />other factors. Potential landslide hazard areas include but are not limited to the <br />followinq areas:i. Areas of historic failures: <br />ii. Areas desiqnated as quaternary slumps. earth-flows. mudflows. or landslides <br />on maps published bv the U.S. Geoloqical Survev or Washinqton State <br />Department of Natural Resources; <br />iii. Areas with all three (3) of the followino characteristics: <br />1. Slopes steeper than fifteen percent (15%): <br />2. Hillsides intersectinq qeoloqic contacts with a relatively permeable <br />sediment overlyinq a relatively impermeable sediment or bedrock: <br />and <br />3. Sprinqs or groundwater seepaqe; <br />iv. Areas that have shown movement and/or are underlain or covered bv mass <br />wastaqe debris: <br />v. Slopes that are parallel or sub-parallel to planes of weakness (which may <br />include but not be limited to bedding planes. soft clay lavers. joint systems. <br />and fault planes) in subsurface materials: <br />vi. Slopes havino qradients steeper than eiqhty percent (80%) subject to rock <br />fall during seismic shakino: <br />vii. Areas that show evidence of, or are at risk from snow avalanches: and <br />viii. Any area with a slope of fortv oercent (40%) or steeper and with a vertical <br />relief of ten (10) or more feet exceot areas composed of competent bedrock. <br />49