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• <br />produced, such as probabilities determined using stability analysis or landslide movements. <br />The formula for Bayes' Rule is as follows: <br />P,~„:m = PP,;°, for outcome * Ps,~,~q,~°, for outcome <br />(PP,;o, * Psws~q~°,) for all outcomes <br />• <br />u <br />Bayes' Rule was used to revise and refine the probability of landslide outcomes found using stability <br />analysis and LVC ratings for 1999 as summarized in Table H4. <br />A7.2.4 Summary of Probability ABalysis <br />Table H4 indicates that based on updated slope stability analysis and taking into account 1999 conditions, <br />the probabilities of very slow to extremely slow movement have increased by 50% since 1997. Using LVC <br />data, the probabilities of very slow or extremely slow movement have increased 35% since 1997. Overall, <br />the predicted movement of the slide is expected to be very slow in the coming years with the chance of <br />rapid movement small. <br />7.3 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) will <br />provide a 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, say 95 percent. According <br />to Table H4, this level has no[ been reached at this time. Future monitoring should continue for a period of <br />at least four additional years, through several climatic conditions, with the probability of landslide <br />outcomes revised on an annual basis, afrer the spring seasons. The existing reclamation plan should be <br />adjusted accordingly to meet any changed conditions that may occur. <br />Barr Engineering Company <br />July 37, 1999 <br />2a Appendix H <br />7999 Addendum to <br />1997198 landslide Cortective Measures Report <br />