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<br />I <br />I <br />I <br />I <br />I <br />'I <br />'. <br />. <br />I <br />I <br />'. <br />I <br />,. <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />"'I"i~" r:, <br />U:..Jv.V..L. <br /> <br />If the demand exceeded the total available supply in any month (including <br /> <br /> <br />storage), the shortage was recorded as a "deficit" and that month was <br /> <br />identified as a "failure", i.e., a failure to meet the specified demand. <br /> <br />The reliability of the system was measured by the probability of failure. <br /> <br />For example, if in 200 of the 1000 years examined the system failed in one <br /> <br />or more months, then the probability of annual failure is 20 percent (i.e., <br /> <br />200 failures + 1000 possible failures = 20 percent). The "recurrence <br /> <br />interval" for failure is the inverse of the probability of failure and <br /> <br /> <br />would be equal to five years in this example (i.e., 1000 divided by 200). <br /> <br />The recur~ence interval represents the expected number of years between <br /> <br />events of similar magnitude. For this example, similar events will occur <br /> <br />approximately once every five years. The five year recurrence interval <br /> <br />does not imply that an event will occur exactly once every five years, but <br /> <br />that the event will, over a specified number of years, occur in <br /> <br />approximately 20 percent of the years specified. <br /> <br />In addition to calculating the probability of failure or recurrence <br /> <br />interval for any combination of demand and supply, the following <br /> <br />information was computed to characterize the severity of the failure(s): <br /> <br />1. Average duration in months of all defici ts encountered <br />2. Average monthly defici t in acre-feet <br />3. Maximum monthly defici t in acre-feet <br />4. Average cumulative deficit in acre-feet <br /> <br />This information is presented in Table 9-1 of this report. <br /> <br />2-7 <br />