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003099 Water Supply , and Apportionment Considerations SUllunary Within the Colorado River Basin, present mainstrea::! '1later uses, losses, and required deliveries to Mexico are less than long-ter::! ?'rerage annual supplies. However, by the late 1980s, upon the com- pletion and full use of the Central Arizona Project, demands are ,,::pected to be approxi:nately equal to the total average annual supplies. Thereafter, as uses increase in the Upper Basin, demands ::lay be sustained for many years by gradual drawdown of the large 'rolumes of water that are currently stored in the Basin's reservoirs. At some time after the year 2000,water require::lents within the Colorado River basin will no longer be able to be met by annual run- eff and storage withdrawals. At that time, diversions will have to oe reduced and increases in diversions will have to be limited. The reduction in diversions will occur to the Central Arizena Project and, to some extent, to the Southern Nevada Water Project, and Upper Basin. diversions ,rill be limited and will not be permitted to expand beyond that which would be in compliance with the terms of the Colorado River Compact. However, through au;;mentation of the Colorado River so as to enable the United States to assume the responsibility, as defined by the Congress, for delivery to Mexico of Colorado River water pursuant to the Mexican Water Treaty, much of these reductions and limitations will be overcome. At this time, the possibility of augmenting the Colorado River by transbasin diversion appears to be infeasible, and the only t'fO alternatives that currently appear to be viable are cloud seeding to increase precipitation and vege- tative management to increase the proportion of snowfall t~4t ends up as runoff. Preliminary studies indicate that these t'dQ alter- rs"ives could together augment tl:.e '.vater s'lpply available in the COlorado River by the quantity specified by CQngress. Water Supply and Requirements The future water supply of a river that fluctuates in flow as widely as the Colorado cannot be predicted with complete confidence. Whhin that limitation, however, and considering all available in- formation, it appears that the dependable long-term average annual C-17 ~ "