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'OO? 3 ') 'I.: < LDM: lk . . As the Upper Basin develops there will arrive a time when its water will no longer be available for further uses on the lower river. The question is when will that time arrive. To forecast this, studies have been made using various assumed rates of depletion in the Upper Basin and various assumed rates of releases from Lake Powell. All of the studies indicate that sub- stantial shortages, amounting to more than 1.0 maf per year before the end of the present century, will exist in the supplies required to meet total uses of 7.5 maf by Arizona, California and Nevada and to meet a delivery of 1.5 maf of water per year to Mexico. The period would be extended somewhat if Lake Mead were depleted to absolute dead storage, during long periods of drawdown. A period of low water supply in the Colorado River Basin, such as existed from 1930 to 1964, will occur again at some time, or one which might be more severe could occur. Under such conditions, minimum releases from Lake Powell would be necessary. Simple arithmetic indicates that there will not be enough water on the lower river to sustain a delivery of 7.5 maf for the states of Arizona, California and Nevada, and to take care of the Mexican burden. The obvious conclusion is that a firm water supply is not available in the Colorado River to satisfy a basic beneficial consumptive-use requirement of 7.5 maf from the main stem by Arizona, California and Nevada, plus delivery of 1.5 maf of water to Mexico. If these require- ments as well as upper Basin requirements are to be satisfied, projects must be authorized and constructed to import major amounts of water into the Colorado River Basin from sources of surplus. Such importation is im- portant to both the Upper and Lower Basins." - 3 - 8/26/65 ,~,.,'-