18E.110.020 Erosion Hazard Areas.
A. Shoreline Erosion Hazard Indicators. Shoreline erosion hazard areas are areas potentially subject to land regression or retreat due to a combination of geologic, seismic, tidally influenced, and/or hydrologic or manmade factors. Shoreline erosion hazard areas can be identified by the presence of any of the following indicators:
1. Areas with active bluff retreat that exhibit continuing sloughing or calving of bluff sediments, resulting in a vertical or steep bluff face with little or no vegetation.
2. Areas with active land retreat as a result of wave action.
B. Erosion Hazard Area Categories.
1. Potential Erosion Hazard Areas. Potential erosion hazard areas, as depicted on the Critical Areas Atlas-Erosion Hazard Areas Map, are those areas where the suspected risk of erosion through either loss of soil, slope instability, or land regression is sufficient to require additional review to assess the potential for active erosion activity or apply additional standards. These potential erosion hazard areas are determined using the following criteria:
a. Shoreline Erosion Hazard Areas. Areas within 200 feet of a freshwater (lake or pond) or marine (Puget Sound, tidal marshes, and estuaries) shoreline, as measured landward perpendicularly from the edge of the ordinary high water mark. (See Figure 18E.110-1 in Chapter 18E.120 PCC.)
b. Riverine Erosion Hazard Areas. The rivers subject to regulation as a channel migration zone listed in Chapter 18E.70 PCC, Flood Hazard Areas, PCC 18E.70.020 B.4.
c. Soil Erosion Hazard Areas. Areas identified as having slopes of 20 percent or greater and that are classified as having severe, or very severe erosion potential by the Soil Conservation Service, United States Department of Agriculture (USDA).
2. Active Shoreline Erosion Hazard Areas. Land areas located directly adjacent to freshwater or marine waters that, through the geological assessment process, are identified as regressing, retreating, or potentially unstable as a result of undercutting by wave action or bluff erosion. The limits of the active shoreline erosion hazard area shall extend landward to include that land area that is calculated, based on the rate of regression, to be subject to erosion processes within the next ten year time period.
3. Stable Shoreline Erosion Hazard Areas. Areas that have been identified as potential erosion hazard areas, but, through the geological assessment process, meet one of the following conditions:
a. No indicators as set forth in 18E.110.020 A. actually exist that indicate the potential for future erosion activity to occur; or
b. Adequate engineering or structural measures have been provided through the submittal of a geological assessment – shoreline erosion geotechnical report that stabilizes the erosion hazard. Such engineering or structural measures must be completed, inspected and accepted for the area to be deemed stable.
4. Riverine Erosion Hazard Areas. Riverine erosion hazard areas are located within the lateral extent of likely watercourse channel movement due to bank destabilization and erosion, rapid incision, and shifts in location of watercourse channels. Riverine erosion hazard areas are also referred to as channel migration zones (CMZs). Rivers and streams subject to erosion are regulated as a CMZ as listed in PCC 18E.70.020 B.4.
5. Soil Erosion Hazard Areas. Soil erosion hazard areas are identified by the presence or absence of natural vegetative cover, soil texture condition, slope, and rainfall patterns, or man-induced changes to such characteristics that create site conditions which are vulnerable to erosion of the upper soil horizon. Soil erosion hazard areas are those areas with slopes of 20 percent or greater and that are classified as having severe, or very severe erosion potential by the Soil Conservation Service, United States Department of Agriculture (USDA).