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I I I I I I I I I I I I .1 I I !I I I I B-6 Case 2 - 100yr rainfall (24hr) occurring after a snow- melt peak and with the reservoir full at ele- vation 8279.7. We selected the base snow melt flows under this situation to be 75% of the 100yr peak snow melt inflow. The reser- voir level is set at 79.7 since this seems to represent the normal operating mode after the reservoir is filled. Case 3 - 25yr snow melt peak and 25yr rainfall peak entering the reservoir simultaneously at a level of 79.5. Theoretically this has a probability of 1 in 625, excluding considera- tion of the need for a full reservoir. E. SUMMARY OF RESULTS The reservoir routing calculation summaries are pre- sented on the attached Figures 1, 2, and 3. Each peak reservoir discharge was reduced by 300cfs to reflect ir- rigation diversions upstream of Phase 2; 1983 & 1984 records indicate a range of 200-400cfs for this effect. The discharge ranges are shown to depict the impact of variance in the operator's selection of reservoir re- leases. As listed above, a summary of the results is as follows: PEAK PEAK PEAK PEAK SNOW MELT RAINFALL DI5- FLOW AT INFLOW INFLOW CHARGE YMCA SITE Case 1 - 100yr Snow melt 4500cfs -0- 3800-4000cfs 3500-3700cfs Case 2 - 100yr Rainfall 3200cfs 6480cfs 4800-5000cfs 4500-4700cfs Case 3 - 25yr Snow melt/25yr Rainfall 3600cfs 5l00cfs 5000-5200cfs 4700-4900cfs The 25yr Snow melt/25yr Rainfall simultaneous occur- rence seems to be unnecessarily restrictive. As stated above, the theoretical probability of this occurrence is 1 in 625, not counting the need for a full reservoir at the time. The theoretical probability of simultaneous occurrence of 10yr events would be 1 in 100; based on the above work we would estimate the reservoir discharge to be on the order of 4400cfs. The probability of a looyr rainfall occurring around July 1, with a full reservoir and continuing snow melt flows of the 3200cfs range is a reasonable condition and provided the second highest estimated discharges. We therefore recommend a 100yr event flow of 4600cfs at the Phase 2 site, based on Case 2 conditions.