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<br /> <br />50 <br /> <br />A slope is delineated by establishing its toe and top and measured by <br />averaging the inclination over at least ten (10) feet of vertical relief; <br />ix. Potentially unstable slopes resulting from river erosion or undercutting; <br />x. Areas that show past sloughing or calving of sediment or rocks resulting in a <br />steep slope that is poorly vegetated; <br />xi. Deep-seated landslide areas characterized by one or more of the following <br />features: scalloped ridge crests at the top of the slope, crescent shaped <br />depressions, head scarps, side scarps, ponds or sag areas on mid slopes, <br />benches and scarps on mid slope areas, hummocky ground, linear fractures <br />in the ground. These features may be evident in aerial images, topographic <br />maps, LiDAR imagery or on the ground; <br />xii. Areas below unstable slopes or that have been identified as landslide hazard <br />areas that could be impacted by landslide run out; and <br />xiii. Areas above or adjacent to unstable slopes that could be impacted if the <br />landslide area expands. <br />b. Potential Erosion Hazard Areas. Erosion hazard areas shall include areas <br />containing soils that may experience significant erosion, including: <br />i. Soil areas identified by the Natural Resources Conservation Service as <br />having “severe” or “very severe” erosion hazard. <br />ii. Slopes forty percent (40%) or steeper with a vertical relief of ten (10) or more <br />feet, except areas composed of consolidated rock. <br />iii. Concave slope forms equal to or greater than fifteen percent (15%) with a <br />vertical relief of ten (10) or more feet, except areas composed of <br />consolidated rock. <br />iv. Channel migration zones, which are defined as the areas along a river or <br />stream within which the channel(s) can be reasonably predicted to migrate <br />over time as a result of natural and normally occurring hydrological and <br />related processes when considered with the characteristics of the river and <br />its surroundings. <br />c. Alluvial Fan Hazard Areas. Alluvial fan hazard areas shall include those areas on <br />alluvial fans where debris flows, debris floods, or clear water floods have the <br />potential to significantly damage or harm the health or welfare of the community. <br />They include the area generally corresponding to the path of potential flooding, <br />channel changes, sediment and debris deposition, or debris flow paths as <br />determined by analysis of watershed hydrology and slope conditions, topography, <br />valley bottom and channel conditions, potential for channel changes, and surface <br />and subsurface geology. <br />i. If the approval authority determines that a proposed use along a Type S or F <br />stream is within a historic channel migration zone, based on field conditions, <br />historic information, LIDAR imagery or aerial photography, and the one- <br />hundred-year channel migration hazard area has not been mapped, the <br />approval authority shall require the applicant to determine if a one-hundred- <br />year channel migration hazard area is present on the site and, if so, delineate <br />its location and extent. <br />ii. The determination as to whether the one-hundred-year channel migration <br />hazard area affects the subject property shall be based on the findings of a <br />qualified professional proficient in fluvial geomorphology using a reliable <br />methodology to determine channel migration accepted by the department <br />(e.g., as described in the Washington Department of Natural Resources' <br />Forest Practices Board Manual, Standard Methods for identifying Channel <br />Migration Zones and Bankfull Channel Features, dated 8/2001, as amended; <br />or in "A Framework for Delineating Channel Migration Zones," Washington <br />Department of Ecology, 2003, as amended). Maps delineating the one-