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<br />i-.~I <br /> <br />J7.2.3 Probability Based Upon Bayes' Rule. <br />For a detailed discussion of probability based upon Bayes' Rule, refer to the 1999 Addendum. Bayes' <br />Rule was used to revise and refine the probability of landslide outcomes found using stability analysis and <br />LVC ratings for 2000-2001 as summarized in Table J4. In general based on 2000-2001 movements and <br />stability analysis, the probability of furore very slow and extremely slow movement has increased and the <br />probability of rapid or slow movement has decreased. <br />J7.2.4 Summary of Probability Analysis <br />Table ]4 indicates that based on updated slope stability analysis and taking into account 2001 conditions <br />the probabilities of very slow to extremely slow movement have increased by 12% since 1997. Using LVC <br />data, the prot•~bilities of very slow or extremely slow movement have increased 49% since 1997. Overall, <br />the predicted movement of the slide is expected to be extremely slow to suspended in the coming years <br />with only a small chance of rapid movement. <br />J7.3 Future Monitoring <br />The measured movements and pore pressure changes within the landslide provide the most accurate <br />estimate of the landslide's performance. Long-term monitoring, together with risk and probability analysis <br />performed in the previous section and other methods (i.e., climatological, FLAC, and judgement) provide a <br />basis for estimating long-term stability. <br />The period of monitoring should continue until a level of confidence has been reached that the predicted <br />probability of a desired landslide outcome is within a specified tolerance level, usually about 95 percent. <br />Looking at Table J4, based on the probability analysis performed and the criteria that very slow to <br />extremely slow movement is acceptable, the present confidence level lies between 80% and 96%, very <br />close to the specified tolerance of 95%. Future monitoring should continue for a period of at least one <br />additional year, with the probability of landslide outcomes revised in the coming year to determine if the <br />specified criteria are reached. The existing reclamation plan should be adjusted accordingly to meet any <br />changed conditions that may occur. <br />Barr Englneering Company <br />December 75, 2000 <br />16 Appendlz J <br />2001 Addendum to <br />1997A8 Landsllda Corrsctlve Measures Report <br />