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Geologically Hazardous Areas? Past/Historic Failure Or Instability

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Geologically Hazardous Areas? Past/Historic Failure Or Instability H Geologically A N D Hazardous Areas O U Critical Areas Ordinance T DD22 What is the purpose of reviewing • Areas showing evidence of active or Geologically Hazardous Areas? past/historic failure or instability. The purpose of this review is to minimize • Areas parallel or subparallel to planes of hazards to the public and to reduce the risk of weakness in subsurface geologic materials. property damage from development activities • Slopes steeper than 80% that are subject to on or adjacent to geologically hazardous areas. rock fall during seismic shaking. In addition, this review is intended regulate • Areas at risk of mass wasting due to land use to protect existing and new seismic forces. development while avoiding the need for construction of flood control devices and Seismic Hazard Areas maintaining natural geologic and hydrologic Seismic hazard areas are subject to a severe processes. risk of earthquake damage as a result of: • Seismically induced ground shaking What are Geologically Hazardous • Differential settlement, or soil liquefaction, Areas? such as: Landslide Hazard Areas o areas of man-made fill Landslide hazards are areas throughout the o partially decomposed organic materials county where there is potential for slope failure at least 5-feet thick due to any combination of geologic, o filled wetlands topographic, and hydrologic features. These o alluvial deposits subject to liquefaction areas include, but are not limited to: • Slope failure or mass wasting • Areas with all three of the following characteristics: • Lateral spreading 1. slopes between 15% and 35%; and • Surface faulting 2. a relatively permeable sediment Alluvial Fan Hazard Areas overlying a relatively impermeable Alluvial fan hazard areas are those areas on sediment or bedrock; and alluvial fans that have the potential to damage 3. springs or ground water seepage. or harm the community health or welfare. They • Slopes greater than 35%. include the area that generally corresponds to the path of potential stream flooding, channel • Potentially unstable slopes resulting from changes, sediment and debris deposition, or rapid river or stream incision, river or debris flow paths as determined by stream bank erosion, or undercutting wave topography, hydrology, geology, potential for action. channel changes, and depositional history. THE PLANNING AND DEVELOPMENT SERVICES HANDOUT SERIES Whatcom County Planning & Development Services 5280 Northwest Drive, Bellingham, WA 98226 Phone (360) 676-6907 Fax (360) 738-2525 Inspections (360) 738-2520 Updated: 2/20/07 Volcanic Hazard Areas Regulatory requirements Volcanic hazard areas are areas that are The following requirements apply to all subject to lava flows, pyroclastic flows, development activities within geologically pyroclastic surges, mud flows, lahars, debris hazardous areas: flows, debris avalanche, ash clouds or ash fall, lateral blast, ballistic debris, or flooding 1. Projects are to be directed toward areas resulting from volcanic activity. of parcels or parcels under contiguous ownership that are not subject to, or at Erosion Hazard Areas risk from, geologic hazards and/or are Erosion hazard areas include surface erosion outside associated buffers. areas, which include slopes greater than 15% 2. Division of land may not create buildable with “severe” or “very severe” rill and inter-rill parcels that are entirely within a hazard erosion hazard, and coastal and riverine area. Land may be divided if each erosion areas, which include areas subject to resulting lot has sufficient buildable area impacts from lateral erosion due to moving outside of the hazard area. water such as river channel migration and 3. Projects shall be engineered and/or shoreline retreat. constructed to minimize risk to health and safety, protect buildings and Tsunami and Seiche Hazard Areas occupants from the hazard, and to avoid Tsunami and seiche hazard areas include or compensate for impacts to other coastal areas and lake shoreline areas that are critical areas. susceptible to flooding, inundation, debris 4. A qualified professional, licensed in the impact, and/or mass wasting resulting from State of Washington, shall review coastal or inland wave action generated by projects in accordance with the critical seismic events. areas assessment report process (WCC 16.16.255). Mine Hazard Areas Mine hazard areas are lands in proximity to 5. All reasonable measures must be taken abandoned coal mines and associated to minimize risks and other adverse underground mine workings such as adits effects associated with geologically (mine entrances), tunnels, rooms and chutes, hazardous areas, and the amount and pillars, and air shafts. Potential mine hazards degree of alteration shall be limited to include: the minimum necessary. • Subsidence of the ground surface. 6. Structures in seismic hazard areas shall • Ground and surface water contamination conform to the applicable provisions of from tailings and underground workings. the International Building Code (IBC). • Concentrations of lethal or noxious gases. Geologic Assessment Report • Underground mine fires. When County critical area maps or other sources of credible information indicate that a Critical Area Ordinance: Geologically Hazardous Area Reviews Page 2 of 3 site proposed for development or alteration is, o the proposed development and or may be, located within an active or potential development alternatives geologically hazardous area, the Technical o proposed mitigation measures Administrator may require a geologic • Landslide hazard areas: assessment report. o assessment of slope stability for existing In addition to general critical areas assessment and developed conditions report requirements, a geologic assessment o analysis of slope recession rate report must include the following site-specific o description of landslide debris run-out and proposal-related information unless the hazard to proposed development, down- Technical Administrator determines that any of slope and up-slope properties, and these requirements is unnecessary due the critical areas scope and/or scale of the proposal: • Seismic hazard areas: a detailed A scaled site plan showing: • engineering evaluation of expected ground o type and extent of geologic hazard displacement, liquefaction, and/or other areas, other critical areas, and buffers dynamic settlement effects, and proposed on or adjacent to the site mitigation measures location of existing and proposed o • Mine hazard areas: description of historical structures, fill, access roads, materials data and remnant mine conditions (dates of storage, and drainage facilities showing operation, years of abandonment, strength distance to floodplain (as applicable) of overlying rock, etc.) o existing site topography o clearing limits Fees • Descriptions of: Please refer to the current Whatcom County Unified Fee Schedule. o areas on the site, surrounding areas that influence or could be influenced by the site, or areas within 300 feet that meet Information the criteria for geologic hazard areas Due to the administrative complexity of these o site features including geology, past or regulations, it is usually best to contact the potential channel migration, hydrology, County Geologist to answer any additional soils and vegetation questions. o processes affecting the property or Planning and Development Services affected by development of the property 5280 Northwest Drive vulnerability of the site to seismic and o Bellingham, Washington 98226 USA other geologic processes E-mail: [email protected] o potential hazards that could be created or exacerbated by development Staff Contact: County Geologist • Description and analysis of risk associated Phone: (360) 676-6907 with: Critical Area Ordinance: Geologically Hazardous Area Reviews Page 3 of 3 .
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