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c. Tributary Apportionments: Four Scenarios The above tables illustrate a middle scenario of tributary apportionments. The following Table 8 puts these apportionments into perspective with three other sce- narios. This table shows how differing assumptions as to the Colorado River's virgin flows at Lee Ferry, the resolution of 1922 Compact issues, and the implementation of the 1968 Act may cascade through the Upper Basin. The first column in Table 8 assumes: (1) that virgin flows at Lee Ferry will average 13.5 MAP/yr.; (2) that these virgin flows will go unaugmented; (3) that the 1922 Compact issues will be resolved against the Upper Basin; and (4) that the cur- tailment scheme in the 1968 Act will not be enforced against the Lower Basin. The second column makes all of the same assumptions, except that virgin flows at Lee Ferry are assumed to average 15.0 MAF/yr. The third and fourth columns again illustrate this variation between 13.5 and 15.0 million acre-feet of average virgin flows, while assuming that the 1968 Act will be enforced against the Lower Basin. The assumptions as to flow augmentation and the 1922 Compact remain the same for both of these last two columns. Column three is the middle scenario illustrated above in Tables 4 through 8. With one exception, the same methodology is applied to derive the tributary apportionments for the other columns. The exception is column 1 for Colorado. In this case, Colorado's statewide apportionment of 1.893 MAF/yr. is not enough to cover Colorado's existing depletions plus its share of mainstem reservoir evaportion, and the problem is one of allocating curtailments of existing depletions rather than remaining compact shares. In this case, the allocations are based on the proportions which each tributary's existing depletions bear to Colorado's total existing depletions. Since 23% of all of Colorado's Colorado River depletions occur on the Gunnison, for example, 23% of the curtailment necessary to bring Colorado within its 1948 Compact entitle~ ment in this case is borne by the Gunnison. In this extreme case, such an approach to tributary apportionment may be inappropriate, and some alternative method of making the necessary curtailment, such as the intergration of all W priorities on all Colorado River tributaries as suggested below, may have to be explored. The application of this methodology across the board for every scenario may also have one other weakness. In the more extreme cases, it is likely that the drawdown of mainstem reservoirs may increase sharply, with a corresponding decrease in evaporation losses. On the other hand, the con- verse will probably apply in the more optimistic scenarios. The tables do not account for this relationship, but instead show a constant 10% discount on the mainstem reservoir eva- poration charge. -35-