Chapter 19.18D
RESOURCE LANDS/CRITICAL AREAS—GEOLOGICALLY HAZARDOUS AREAS
Sections:
19.18D.010 Permitted uses and activities.
19.18D.040 Determination process—Geologically hazardous area.
19.18D.010 Permitted uses and activities.
Uses and activities allowed within designated geologically hazardous areas are those uses permitted by the zoning district, subject to the provisions of this chapter. (Ord. TLS 03-01-01B Exh. B (part): Ord. TLS 97-10-71B Exh. G (part))
19.18D.020 Classification.
A. All geologically hazardous areas shall be classified by Douglas County according to the level of risk associated with the hazardous area as established through an approved geologic hazard risk assessment and/or a geotechnical report submitted by the applicant in accordance with the DCC. Douglas County may use on-site inspections and the information sources identified in DCC Section 19.18.040 as guidance in identifying the presence of potential geologically hazardous areas.
B. Geologically hazardous areas in Douglas County shall be classified according to the following system:
1. Known or suspected risk;
2. No risk; and
3. Risk unknown.
C. Any land containing soils, geology or slopes that meet any of the following criteria shall be classified as having a known or suspected risk of being geologically hazardous areas:
1. Areas identified by the United States Department of Agriculture Natural Resources Conservation Service as having a “severe” rill and inter-rill erosion hazard;
2. Areas potentially subject to landslides based on a combination of geologic, topographic, and hydrologic factors. They include any areas susceptible because of any combination of bedrock, soil, slope (gradient), slope aspect, structure, hydrology, or other factors. Examples of these may include, but are not limited to, the following:
a. Areas of historic failures, such as:
i. Those areas delineated by the United States Department of Agriculture Natural Resources Conservation Service as having a “severe” limitation for building site development;
ii. Those areas mapped as class u (unstable), uos (unstable old slides), and urs (unstable recent slides) in the Department of Ecology coastal zone atlas; or
iii. Areas designated as quaternary slumps, earthflows, mudflows, lahars, or landslides on maps published as the United States Geological Survey or Department of Natural Resources division of geology and earth resources.
b. Areas with all three of the following characteristics:
i. Slopes steeper than fifteen percent;
ii. Hillsides intersecting geologic contacts with a relatively permeable sediment overlying a relatively impermeable sediment or bedrock; and
iii. Springs or ground water seepage;
c. Areas that have shown movement during the Holocene epoch or which are underlain or covered by mass wastage debris of that epoch;
d. Slopes that are parallel or sub-parallel to planes of weakness (such as bedding planes, joint systems, and fault planes) in subsurface materials;
e. Slopes having gradients steeper than eighty percent subject to rockfall during seismic shaking;
f. Areas potentially unstable as a result of rapid stream incision, stream bank erosion, and undercutting by wave action;
g. Areas that show evidence of, or are at risk from snow avalanches;
h. Areas located in a canyon or on an active alluvial fan, presently or potentially subject to inundation by debris flows or catastrophic flooding; and
i. Any area with a slope of forty-five percent or steeper and with a vertical relief of ten or more feet except areas composed of consolidated rock. A slope is delineated by establishing its toe and top and measured by averaging the inclination over at least ten feet of vertical relief.
3. Areas subject to severe risk of damage as a result of earthquake induced ground shaking, slope failure, settlement, soil liquefaction, or surface faulting. One indicator of potential for future earthquake damage is a record of earthquake damage in the past. Ground shaking is the primary cause of earthquake damage in Washington. The strength of ground shaking is primarily affected by:
a. The magnitude of an earthquake;
b. The distance from the source of an earthquake;
c. The type of thickness of geologic materials at the surface; and
d. The type of subsurface geologic structure.
4. Other geological events:
a. Volcanic hazard areas shall include areas subject to pyroclastic flows, lava flows, debris avalanche, inundation by debris flows, mudflows, or related flooding resulting from volcanic activity.
b. Mine hazard areas are those areas underlain by, adjacent to, or affected by mine workings such as adits, gangways, tunnels, drifts, or airshafts. Factors that should be considered include: Proximity to development, depth from ground surface to the mine working, and geologic material. (Ord. TLS 03-01-01B Exh. B (part): Ord. TLS 97-10-71B Exh. G (part))
19.18D.030 Designation.
All existing areas of unincorporated Douglas County classified as stated in DCC Section 19.18D.020, as determined by the review authority, are designated as geologically hazardous areas. (Ord. TLS 03-01-01B Exh. B (part): Ord. TLS 97-10-71B Exh. G (part))
19.18D.040 Determination process—Geologically hazardous area.
Douglas County shall review each development permit application to determine if the provisions of this chapter shall be initiated. In making the determination, the County may use any resources identified in DCC Section 19.18.040, as well as any previously completed special reports conducted in the vicinity of the subject proposal. The following progressive steps shall occur upon a determination by the County that a geologically hazardous area may exist on a site proposed for a development permit:
A. Step One. Douglas County staff shall determine if there is any possible geologically hazardous areas on-site designated by DCC Section 19.18D.030. This determination shall be made following a review of information available and a site inspection if appropriate. If no hazard area is determined to be present, this chapter shall not apply to the review of the proposed development.
B. Step Two. If it is determined that a geologically hazardous area may be present, the applicant shall submit a geologic hazard area risk assessment prepared by an engineer or a geologist. The risk assessment shall include a description of the geology of the site and the proposed development; an assessment of the potential impact the project may have on the geologic hazard; an assessment of what potential impact the geologic hazard may have on the project; appropriate mitigation measures, if any; and a conclusion as to whether further analysis is necessary. The assessment shall be signed by and bear the seal of the engineer or geologist that prepared it. No further analysis shall be required if the geologic hazard area risk assessment concludes that there is no geologic hazard present on the site, nor will the project affect or be affected by any potential geologic hazards that may be nearby.
C. Step Three. If the professional preparing the risk assessment in step two concludes that further analysis is necessary, the applicant shall submit a geotechnical report consistent with the provisions of DCC 19.18.120.
D. The geotechnical report shall include a certification from the engineer preparing the report, including the engineer’s professional stamp and signature, stating all of the following:
1. The risk of damage from the project, both on- and off-site is minimal;
2. The project will not materially increase the risk of occurrence of the hazard; and
3. The specific measures incorporated into the design and operational plan of the project to eliminate or reduce the risk of damage due to the hazard.
All mitigation measures, construction techniques, recommendations and technical specifications provided in the geotechnical report shall be applied during the implementation of the proposal. The engineer of record shall submit sealed verification at the conclusion of construction that development occurred in conformance with the approved plans.
E. A proposed development cannot be approved if it is determined by the geotechnical report that either the proposed development or adjacent properties will be at risk of damage from the geologic hazard, or that the project will increase the risk of occurrence of the hazard, and there are no adequate mitigation measures to alleviate the risks. (Ord. TLS 03-01-01B Exh. B (part): Ord. TLS 97-10-71B Exh. G (part))