Laserfiche WebLink
<br />"')1 .,.. <br />OU".uJ <br /> <br />judged to have a relatively high risk include existing slopes <br />in surficial deposits exceeding approximately 3:1 (horizontal <br />to vertical) and steep cliffs. <br /> <br />Future slope failures may occur as a result of natural <br />changes in the surface or sub-surface conditions or may <br />result from construction activities such as grading or <br />removal of trees. Based on observation of existing slide <br />paths in the area, an induced landslide could be large (one <br />hundred feet wide and run one-half mile or more as a debris <br />flow) or small (25 feet wide and run 100 feet). The adverse <br />effects of a large slide would include the destruction of <br />surface vegetation and topsoil in the slide path, the <br />possible deposition of thousands of cubic yards of rrnld on <br />lower slopes or in stream channels and possible damage to <br />on-mountain facilities. <br /> <br />Road construction may cause cut and fill failures, especially <br />where switchbacks are necessary on steep slopes and where <br />roads must cross oversteepened slopes adjacent to actively <br />eroding streams. The IlPst significant problem areas for <br />access roads generally occur on the steeper slopes near the <br />main ridge line. Slides from road construction are usually <br />small (perhaps 50 feet wide but may run up to several hundred <br />feet) and can be stabilized after they occur. Should such a <br />slide occur adjacent to a live stream there would be a large <br />but short term increase in sediment. These type of events <br />are not uncommon to natural stream environments. <br /> <br />Clearing of ski trails on unstable slopes will increase the <br />risk of slope failures and associated debris flows. Loss of <br />root strength in the upper soils and higher groundwater <br />levels from reduced evapo-transpiration and increased snow <br />accumulation are all factors which result from clearing and <br />reduced slope stability. Snownaking equipment will probably <br />be used on the lower slopes. This may increase ground water <br />levels even more. <br /> <br />More detailed data collection and analysis of the sub-soil, <br />bedrock and groundwater conditions on the steep slopes will <br />be required to estimate the existing and potential future <br />slope stability of the proposed ski trails. As a result of <br />this more detailed site specific study (generally described <br />in Appendix A) some of the areas proposed for development may <br />be denied. <br /> <br />(2) Rockfall <br /> <br />The severity of the rockfall hazard is highest adjacent to <br />cliffs of greater height along Bootjack Ridge (see Map 9, <br />Chapter nIl. Elsewhere, the deSignated rockfall zones <br />present medium to relatively low degrees of risk. <br /> <br />I <br />,I <br /> <br />153 <br />