Laserfiche WebLink
<br />Based on the present ski area plan for deve10~ent, proposed <br />lift terminal structures, restaurants and the :majority of the <br />access roads and lift lines avoid rockfall ha1ard areas. <br /> <br />(3) Debris Flows I <br /> <br />Potential debris flow starting zones are shbwn on Map 10, <br />Chapter III. Debris flows would usually ~ caused by a <br />landslide resulting fran an increase in gro.undwater levels <br />within the slope. Groundwater level incr~ases may occur <br />following rapid snowrrelt or heavy precipitatiion. A gradual <br />rise in groundwater could also occur over se~'eral years as a <br />result of above-normal precipitation, t e removal of <br />vegetation or snOlllllaking. Once mobilized, a debris fleM <br />would generally be controlled by natural dra age channels to <br />sane degree, depending on the relative size of the flowing <br />mass and the channel capacity. Due to the ~ignificant area <br />of coverage on the site by potential debris geM start zones, <br />most of the site below the start areas is exPosed to risk of <br />debris flows. Map 10 shows estimated debris flow runout <br />zones based on preliminary modeling of possi~'le flow paths. <br /> <br />Most debris flows will probably be re1ativel small magnitude <br />events which will travel short distances, especially in <br />forested areas. Removal of trees on ski trails will <br />generally reduce flow path roughness th,reby increasing <br />debris flow travel distances. Larger magnitude debris flow <br />events can generally be anticipated to traVel farther from <br />their start areas. i <br />I <br />, <br />Potentially destructive debris flows star~ing on National <br />Forest ~stem land have in the past and pro~ly will in the <br />future reach U.S. Highway 160 and private ~and that may be <br />developed. Clearing of ski trails may incre~se the frequency <br />and size of debris flows reaching private 11and. While the <br />increased risk beyond that which is normal I for the area is <br />probably not great, it is, nevertheless, real and yet <br />difficult to quantify. Serious property d~ge and loss of <br />life is possible. I <br /> <br />The realigned portion U.S. Highway l60 WOU1~ be further fran <br />debris flow starting zones,. but removal ~f vegetation and <br />channelization would lengthen debris flow r,unout zones. The <br />probable net result, therefore, would be li~tle change in the <br />frequency of debris flows reaching the reapgned portion of <br />U.S. Highway 160, but an increase in the ri$k of debris flows <br />reaching other portions of the highway I below ski trail <br />development. ' <br /> <br />154 <br />