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<br /> <br />26 <br /> <br />"In-stream structure" is a human-made structure placed within a stream or river waterward of the <br />ordinary high water mark that either causes or has the potential to cause water impoundment, or the <br />diversion, obstruction, or modification of water flow. In-stream structures may include those for <br />hydroelectric generation, irrigation, water supply, flood control, transportation, utility service <br />transmission, fish habitat enhancement, or other purpose. <br />17A.02.470 Landslide Hazard Areas. <br />“Landslide hazard areas” are areas potentially subject to landslides based on a combination of <br />geologic, topographic, and hydrologic factors. They include any areas susceptible because of any <br />combination of bedrock, soil, slope (gradient), slope aspect, structure, hydrology, or other factors. A <br />slope is delineated by establishing its toe and top and measured by averaging the inclination over at <br />least ten (10) feet of vertical relief. Potential landslide hazard areas include but are not limited to the <br />following areas: <br />1. Areas designated as quaternary slumps, earth-flows, mudflows, or landslides on maps <br />published by the U.S. Geological Survey or Washington State Department of Natural <br />Resources. <br />2. Areas with all three (3) of the following characteristics: <br />a. Slopes steeper than fifteen percent (15%); <br />b. Hillsides intersecting geologic contacts with a relatively permeable sediment <br />overlying a relatively impermeable sediment or bedrock; and <br />c. Springs or groundwater seepage. <br />3. Areas that have shown movement and/or are underlain or covered by mass wastage debris; <br />4. Slopes that are parallel or sub-parallel to planes of weakness (which may include but not be <br />limited to bedding planes, soft clay layers, joint systems, and fault planes) in subsurface <br />materials; <br />5. Slopes having gradients steeper than eighty percent (80%) subject to rock fall during seismic <br />shaking; <br />6. Areas that show evidence of, or are at risk from snow avalanches; and <br />7. Any area with a slope of forty percent (40%) or steeper and with a vertical relief of ten (10) or <br />more feet except areas composed of competent bedrock. <br />8. Potentially unstable slopes resulting from river erosion or undercutting. <br />9. Areas that show past sloughing or calving of sediment or rocks resulting in a steep slope that <br />is poorly vegetated. <br />10. Deep-seated landslide areas characterized by one or more of the following features, which <br />may be evident in aerial images, topographic maps, LiDAR imagery or on the ground: <br />a. scalloped ridge crests at the top of the slope, <br />b. crescent shaped depressions, <br />c. head scarps, <br />d. side scarps, <br />e. ponds or sag areas on mid slopes, <br />f. benches and scarps on mid slope areas, <br />g. hummocky ground, <br />h. linear fractures in the ground. <br />11. Areas below unstable slopes or that have been identified as landslide hazard areas that <br />could be impacted by landslide run out. <br />12. Areas above or adjacent to unstable slopes that could be impacted if the landslide area <br />expands. <br /> <br />17A.02.480 Mine Hazard Areas.