AZ vs. CA:17 California Exhibits, Vol. XVII; Nos. 2701-2724; 2800; 2901-2905; 3001-3050

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-14- the total period of sixty years of records used in this study, or, for two-thirds of the time. On the other hand, for thirty years in this period or half the time, the average flow would be 15,000,000 acre feet or more. The first figure, 13,000,000 acre feet, is more conservative than necessary for conditions we are now facing in the Upper Basin. The second average rate, 15,000,000, might not be practical if maximum use of the water supply were contemplated, because much less water would then be available for the necessary longtime carry-over storage to equalize stream flow and fulfill Compact obligations. The mean of these two quantities, or 14,000,000 acre feet, is suggested as a more practical "safe yield" figure. This quantity was exceeded sixty percent of the time and this is believed to be a very reasonable figure. Conclusions 1) On the basis of all the data now available, the present "safe yield" of the Upper Colorado River at Lee Ferry appears to be from 13,000,000 to 14,000,000 acre feet annually. This yield is more than ample for the projects now proposed if sufficient carry-over storage is provided on the main stem and larger tributaries to properly regulate the flow to the Lower Basin. 2) Continuous records for the next 25 years will show whether or not a larger safe yield may be justified in future designs for additional projects. 3) On the basis of study of available data, a total period of record for 85 years will not change materially the present approximate long-time average of 15,000,000 acre feet.