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<br />~~~'J <br /> <br />N <br />-.J <br />,a;" <br />Q <br /> <br />, <br />, <br /> <br />'i.,' ' <br /> <br />, <br />, '.I <br /> <br />Use of the CRSS hydrology data base with system storage results in a <br />critical drawdown period of 25 years beginning in 1953. This is contraste, <br />to the virgin flow data base used in previous hydrologic determinations <br />which produced a critical period of 34 years beginning in 1931. The virgil <br />flow data base was limited to annual flow values at Lee Ferry. The basis <br />of computing virgin flow was changed several times during the period of <br />record and for this reason, it is felt that the CRSS hydrology is more <br />consistent. <br /> <br />2. Use of The Colorado River Simulation System (CRSS) <br /> <br />The CRSS model was used to determine available system storage and was not <br />directly used to determine basin yield. However the hydrologic data from <br />the model were used for this purpose. The model provided an 81 year <br />sequence of hydrologic data based on historic records from 1906 to 1986. <br />These data were then used to create 81 possible hydrologic cycles for the <br />period from 1986 to 2066. Each of the 81 years functioned as the starting <br />point for a sequence with the preceding years added to the end of the <br />cycle. The same data were used in this investigation, as were employed in <br />verification runs for the 1984 hydrologic investigation. However using the <br />data in this way generated 81 possible permutations of the projected <br />hydrology to the year 2066 upon which current demands could be super- <br />imposed, (for a more complete explanation see Appendix II). When demands <br />were superimposed on these series of hydrologic projections, a critical <br />storage value of 24.762 MAF was derived for use in the mass balance <br />analysis. <br /> <br />5 <br />