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'.. of avoidance of a flood control mandated release. Shortage threshold set at elevation 1120 feet. RESERVOIR STARTING CONDmONS An analysis was also developed to examine the effect of starting runs at full reservoir conditions versus existing reservoir conditions. ADDmONAL MODEL RUN OBSERVATIONS During the study, hydrologic and water use changes occurred that forced Reclamation to revise and rerun the model studies. The most significant change was the most recent CAP projected water delivery schedule which extended the time frame when Arizona would be fully diverting their apportionment until year 2035, and which extended out the year that the lower basin would be using less than full projections of 7.5 maf apportionment until year 2009. CRSS-EZ MODEL RUN OBSERVATIONS Recognizing that the change in CAP schedule altered the effects and results of the model runs, and recognizing that Basin States had not reached consensus on a methodology, Reclamation was asked to, redevelop the runs and make a proposal to the States as to an appropriate surplus methodology. After changing the starting conditions and the depletion schedules numerous CRSS-EZ runs were made to increase the understanding of the system, and of the effect of alternate surplus and shortage provisions. Initially the runs focused on modeling the system under full development conditions. Under full development the governing principal that appeared to dominate the water supply of the lower basin is the recognition that within the lower basin the total of uses and losses exceed the total average supply. The upper basin objective minimum release is to supply 8.23 maf to the lower basin. To 'is';ure that this supply can be provided a critical period of record was established for the upper basin. The critical period assumed is that period of hydrologic record in which Lake Powell would experience the greatest reduction in storage over the entire hydrologic record under specific release conditions. The critical period of record is a function of the hydrology, and demands. The upper basin in theory maintains sufficient storage in upper basin reservoirs (602(a) requirement) such that an average 8.23 maf of minimum flow can be provided to the lower basin through the critical period of record without impairment to upper basin uses or without impacting the minimum power pool. In addition the 602(a) restricts the equalization provision such that equalization is not required if upper basin reservoir storage is below the 602(a) storage level. 18