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I I I I I I I I II I I I I I I I I I I I Small Reservoir Feasibility Study S-8 Table S-6 Annual Water Delivery Shortages to In-basin Users (values in acre-feet) Scenario III Scenario IV Water User Number Average Maximum Number Average Maximum Keystone Snowmaking1 2 353 390 2 353 390 Mesa Cortina2,3 31 46 94 31 46 94 Dillon/Dillon Valley4 31 372 510 31 372 510 Notes: 1. Green Mountain contents at or below minimum target. 2, Historic User Pool (HUP) releases at maximum annual limit, 3. Insufficient supply due to competition from Old Dillon system, 4. Demands combined, Laskey Gulch assumed to be sole source of supply, Dillon and Dillon Valley would experience severe wintertime shortages under ultimate demand conditions if they were forced to depend on Laskey Gulch alone as an emergency water source, Conservation measures would have to reduce average monthly demand more than 50% to rely solely on Laskey Gulch. However, allocations of Summit County subordination water and Dillon storage water to the two municipalities under the Summit County Agreement would be adequate to make up the difference if the emergency lasted no more than a month, Instream Flows The same critical reaches were reviewed for Scenarios III and IV as were reviewed in the baseline scenarios. Snake River minimum flows are unaffected by Peru Creek releases in Scenario III since the target flow is already met in Scenario II by curtailing snowmaking diversions, In Scenario IV, Snake River minimum flows are raised to decreed 6 cfs level. Flows below Dillon are unaffected by Peru Creek operations, since those releases are stored in Dillon. However, a separate computation was performed to determine the quantity of water needed to eliminate periodic below-Dillon flow deficiencies (flows less than 50 cfs). This augmentation would be required in 5 years of the 31-year study period; the average water requirement for this purpose would be 370 AF and the maximum requirement would be 852 AF, Under suitable institutional arrangements, releases for this purpose could be made from a number of sources including: 1) unused portions of Dillon storage water (Summit County Agreement), 2) unused portions of Summit County subordination water, 3) Peru Creek Reservoir, 4) Goose Pasture Tarn, 5) Clinton Gulch Reservoir, and 6) a rehabilitated Old Dillon system, Because the Summit County Agreement does not appear to subordinate to instream flow maintenance, options 1 and 2 may require additional agreements with Denver,