Erosion hazard areas are those areas that have severe or very severe erosion potential and could lead to sediment transfer into wetland areas, aquatic priority habitats, or waters of the state, as detailed in the soil descriptions contained in the Web Soil Survey for Lewis County, Washington, Soil Survey Staff, Natural Resources Conservation Service, United States Department of Agriculture. Available online at:
https://websoilsurvey.sc.egov.usda.gov/
Accessed December 1, 2016.
(Ord. 1284 § 4, 2018; Ord. 1370 (Exh. B), 2025)
(1) 
Classification of Steep Slope Hazard Areas. Steep slope hazard areas are areas where there is not a mapped or designated landslide hazard, but where there are steep slopes equal to or greater than a 35 percent slope with a vertical relief of 10 or more feet. Steep slopes which are less than 10 feet in vertical height and are not part of a larger steep slope system, and steep slopes created through previous legal grading activity, are not regulated steep slope hazard areas. Presence of a steep slope suggests potential slope stability problems.
(2) 
Classification of Landslide Hazard Areas. Landslide hazard areas are those areas meeting any of the following criteria:
(a) 
Areas subject to previous slope failures, including areas of unstable old or recent landslides;
(b) 
Areas with all of the following characteristics:
(i) 
A slope greater than 15 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) 
Slopes that are parallel or sub-parallel to planes of weakness (such as bedding planes, joint systems, and fault planes) in subsurface materials;
(d) 
Slopes having gradients greater than 80 percent subject to rockfall during seismic shaking;
(e) 
Areas potentially unstable as a result of rapid stream incision and streambank erosion or undercutting;
(f) 
Areas located in a canyon, on an alluvial fan, or presently or potentially subject to inundation by debris flows or catastrophic flooding.
(3) 
Mapped Landslide Hazard Areas. Landslide hazard areas include the following mapped sources:
(a) 
Areas mapped as "unstable," "landslides," and "old landslides" in the Slope Stability Study of the Centralia-Chehalis Area, Lewis County, Washington, by Allen J. Fiksdal, Department of Natural Resources, Division of Geology and Earth Resources, 1978.
(b) 
Areas included in the Landslides and Landforms maps available from the Washington Department of Natural Resources Division of Geology and Earth Resources, dated July 2016 or as amended. Available data was accessed from:
http://www.dnr.wa.gov/programs-and-services/geology/publications-and-data/gis-data-and-databases
on December 22, 2016.
(Ord. 1284 § 4, 2018; Ord. 1370 (Exh. B), 2025)
(1) 
Classification of Seismic Hazard Areas. Seismic hazard areas are locations subject to severe risk of damage as a result of earthquake-induced soil liquefaction, ground shaking amplification, slope failure, settlement, or surface faulting.
(a) 
All structures that require a building permit within Lewis County are required to be consistent with the D1 seismic zone (as specified in the International Building Code).
(b) 
Active faults or trenches are considered seismic hazards.
(c) 
Areas of known faults and soil liquefaction hazards are depicted in Ground Response Geographic Information System data dated June 2010 and Seismogenic Features data dated April 2016 and retrieved from the Washington Department of Natural Resources Division of Geology and Earth Resources. Available data was accessed from:
http://www.dnr.wa.gov/programs-and-services/geology/publications-and-data/gis-data-and-databases
on December 22, 2016.
(Ord. 1284 § 4, 2018; Ord. 1370 (Exh. B), 2025)
(1) 
Classification of Volcanic Hazard Areas. Volcanic hazard areas are locations where the risk to life and property by a large volcanic event is high. For the purpose of these regulations, damage from lahars and near volcano hazards constitute the primary volcanic hazards. Volcanic tephra (ash), while disruptive and potentially dangerous, is not considered a volcanic hazard that is subject to these regulations.
(a) 
Volcanic hazard areas are shown on maps available from the United States Geological Service (USGS) Volcano Hazards Program. Data was accessed from:
https://www.usgs.gov/natural-hazards/volcano-hazards/
on January 3, 2017. Maps for Mount Rainier, Mount Saint Helens and Mount Adams are dated March 2014.
(Ord. 1284 § 4, 2018; Ord. 1370 (Exh. B), 2025)
(1) 
Classification of Mine Hazard Areas. Mine hazard areas are those areas within 100 horizontal feet of a mine opening at the surface or which are underlain at a depth of 300 feet or less by mine workings. Known locations of historic mines are identified in the Washington State Department of Natural Resources, Division of Geology and Earth Resources, Open File Report 94-7; The Washington State Coal Mines Map Collection: A Catalog, Index, and User's Guide, by H.W. Schaase, M. Lorraine Koler, Nancy A. Eberle, and Rebecca A. Christie, 1994, 107 pages; Open File Report 84-6, Inventory of Abandoned Coal Mines in the State of Washington, by F.V. LaSalata, M.C. Meard, T.J. Walsh, and H.W. Schaase, 1985, 42 pages; and specific maps and surveys of mine workings on file with the Division of Geology and Earth Resources.
(Ord. 1284 § 4, 2018; Ord. 1370 (Exh. B), 2025)
(1) 
Classification of Channel Migration Zones. Channel migration zones are areas within which a river channel can be expected to migrate over time due to hydrologically and geomorphologically related processes.
(2) 
Mapped channel migration zones are based on:
(a) 
The location of severe and moderate channel migration areas as identified within the report: Channel Migration and Avulsion Potential Analyses: Upper Nisqually River, Pierce County, Washington, produced by GeoEngineers for Pierce County public works and utilities, water programs division, 2007, 59 pages; or as revised.
(b) 
The location of severe and moderate channel migration areas identified within the report: Geomorphic Evaluation and Channel Migration Zone Analysis Addendum: Cowlitz River, near Packwood and Randle, Lewis County, Washington, produced by GeoEngineers for the Lewis County public works department, 2009, 76 pages; or as revised.
(c) 
The location of historical migration zones (HMZ), avulsion hazard zones (AHZ), and erosion hazard areas (EHA) within the report Reach Analysis and Erosion Hazard Management Plan: Cispus River from River Mile 12.3 (Greenhorn Creek) to River Mile 17.6 (Cispus Road Bridge), prepared by Herrera Environmental Consultants, Inc. for the Lewis County public works department, 2004, 105 pages; or as revised.
(d) 
The location of the channel migration area identified for Rainey Creek within the report: Geomorphic Evaluation and Channel Migration Zone Analysis, Lewis County, Washington, produced by GeoEngineers for the Lewis County public works department, 2003, 52 pages; or as revised.
(e) 
The location of a channel migration zone may be modified by the administrator based on a study provided by an applicant and prepared by a qualified professional that demonstrates there are specific geologic, landform, hydraulic, sediment transport, or other factors that demonstrate that a specific area is not in the channel migration zone. Such a study shall be developed in accordance with best available science and investigate areas upstream and downstream of the review site that could influence the migration of the channel and the channel migration corridor.
(Ord. 1284 § 4, 2018; Ord. 1370 (Exh. B), 2025)
(1) 
Classification of Alluvial Fan Hazards. Alluvial fan hazard areas are low, outspread, relatively flat to gently sloping deposits of sediments and organic debris, shaped like an open fan or segment of a cone, deposited by streams or debris flows where they issue from narrow, steep valleys upon a plain or broad valley or wherever the gradient of the stream suddenly decreases.
(2) 
A single mapped alluvial fan hazard area is depicted in Geomorphic Evaluation and Channel Migration Zone Analysis Addendum: Cowlitz River, near Packwood and Randle, Lewis County, Washington, produced by GeoEngineers for the Lewis County public works department, 2009, 76 pages. Additional research is necessary to identify the location, presence, and potential risk of other alluvial fan hazards.
(Ord. 1284 § 4, 2018; Ord. 1370 (Exh. B), 2025)