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<br />T----- <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br />bank storage is given for any of the other Upper Basin reservoirs. <br /> <br />A number of different model runs were made to determine the amount of <br />storage that would be available during a critical drawdown period of the <br />Upper Colorado system. To get some idea of the stress placed on the system <br />under current modeling conditions, i.e. using the current demand schedule <br />that indicates development to 5.8 million acre-feet by the year 2040, an 81 <br />year (1986 to 2066), 8l-trace run was performed. Traces are modeling <br />simulation runs with a fixed sequence of hydrology. The initial trace <br />began with the initial hydrology year of 1906 set at the initial modeling <br />year of 1986. The hydrology was then shifted one year for each trace until <br />each of the 81 years of record had been used as the initial modeling year, <br />(see Table 1 for an alignment of hydrology and trace years). <br /> <br />This run indicated that the 5.8 MAF level of demands was not great enough <br />to completely utilize all of the system storage. Since sediment accumula- <br />tion continually changes reservoir characteristics, and because all up- <br />stream reservoirs in the CRSS model are forced down as Lake Powell empties, <br />the elevation of Lake Powell was used as an index to determine the storage <br />state of the system. The maximum drawdown in Lake Powell occurred in trace <br />75 in March 2065 with Powell elevation at 3530 or some 40 feet above <br />minimum power pool and corresponded to a total system storage remaining of <br />about 5.6 MAF. <br /> <br />Another 8l-trace run was performed that set the demands to a 6.3 MAF level <br />at the year 2040. At that level of demand, the system'is over stressed. <br />This is apparent in that not only is the entire upper Basin system storage <br />utilized, but the system remains drawn down to minimum levels for a <br />relatively high number of months. Of the 81 traces, there were 28 traces <br />in which Lake Powell was empty (at minimum power pool) from 3 to 31 months. <br />From Table 2 it can be seen that trace 75 is the critical trace in that it <br />reflects the greatest stress on the system. It should be noted that trace <br />75 not only produces the greatest number of months of complete drawdown, <br />but is also the trace in which the greatest amount of water in storage is <br />available and used. Because of this, additional analysis was focused on <br />trace 75. <br /> <br />30 <br />