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'I '. Hydrology Model runs were performed on a calendar year basis over the study period of years 1995 through 2050 or 56 years. Initial conditions of beginning reservoir contents correspond with the projected storage conditions for January 1, 1995. The hydrology used for the upper basin was the Colorado River natural flow for the years 1906 through 1990. The hydrology used for the lower basin was the Colorado River natural tributary flow and reach gains for the years 1906 through 1990. Eighty-five traces were run beginning with the 1906 through 1963 trace and ending with the 1990 plus 1906 through 1962 trace. (Historical Index Sequential Method) Upper and Lower Division Depletion Schedules All runs assumed the Modified Upper Division depletion schedule where Upper Division use without evaporation losses equaled 5,060 thousand acre-feet (kat) in year 2050. (See Figure 1). The assumed depletion or diversion schedules for the Upper Division, Lower Division and Southern Nevada Water System (SNWS), Metropolitan Water District of Southern California (MWD), and CAP are shown on Table 1. MODEL CRITERIA The following general operating criteria were used on all scenarios. Model Runs used the yearly model CRSS-EZ, with 85 traces, projected out to year 2050 (56 years) Upper basin depletion schedule with 5.060 maf of use in year 2050 + upper basin reservoir evaporation Lower basin depletion schedule with the new lower CAP schedule with full 7.5 maf of use starting in year 2009. Both MWD and SNWS divert unused Lower Division unused apportionment. ANTICIPATED FWOD CONTROL SURPLUS At the beginning of each year, the amount of system flood control space was determined to protect against an unanticipated flood control release. The required flood control space was then checked against the projected runoff adjusted by depletion. If the projected runoff was 10