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Executive Summary , , . " .-"'~ ..'.1 ',' J I I I I I I I I I I I I I I I I I I I rights. Existing demands with rights junior to the Juniper rights were served after existing reservoirs reached their capacity, Future demand increments, representing either year 20 IS or year 2040 demands, were met after all other demand were met. In Scenario I, the Juniper Project water rights were assumed not to exist; the same effect would obtain from the general subordination of those rights. Stagecoach Reservoir was operated to make winter releases for power generation; this also assisted in making room for spring inflows, Steamboat Lake was also operated with drawdown each year as a result of releases made to supplement flows in the Yampa River for purposes of fish habitat. In Scenario I, modeled demand shortages generally occurred only in the driest years and then demands were met through releases from existing reservoirs. Some shortages were due to capacity constraints of the reservoir outlet works. Other minor shortages occurred because the modeled demands were located where it, was impossible to increase the physical supply of water, for example on small tributaries with no storage reservoirs. Modeled shortages to future-level demands were also relatively small. Reservoir releases made to mitigate shortages resulted in slightly increased fluctuations in reservoir storage levels, Modeled shortages at the three levels of demand in Scenario I are summarized in Table S-5. Scenario II - Conversion of Juniper Rights Only In Scenario II, a Juniper Canyon instream flow water right equal in magnitude to the Juniper Project contemplated draft was modeled as existing with a 1954 priority date, The amount of the contemplated draft was defined in an earlier study (Wheeler, 1989) and averages 862,000 af per year, As specified in this scenario, the instream flow right could not callout the filling of existing reservoirs or the existing senior demands but could callout existing junior demands and all future demands. Modeled shortages to existing senior demands in Scenario II were identical to those predicted in Scenario I. This was as expected since the instream flow right is junior to most current level demands and should have no effect on them. Shortages to existing junior demands were large as a result of these demands being called out nearly every year by the Juniper instream flow right, Shortages to future demands under 2015 and 2040 demand conditions, were also large and frequent, When the Juniper right was subordinated to all junior demands, the previous shortages were reduced to Scenario I values. In model runs which represented future demand levels, the Juniper-based instream flow right frequently called out the junior future demand increments. This created a significant draft on existing storage accounts to which the future demands have access, Elkhead Reservoir (at its current capacity of 13,700 at) was drawn down to its minimum pool in most years. This created numerous shortages to certain Craig area demands which were assumed to have no access to storage in Stagecoach Reservoir. The modeled shortages at the three levels of demand in Scenario II are summarized in Table S-5, Scenario III - Enlargement of Elkhead Reservoir Scenario III was similar to Scenario II in that it included the instream flow right at Juniper Canyon, with a 1954 priority, but also included the simulation of an enlarged Elkhead Reservoir. The enlarged Elkhead Reservoir was initially modeled with a total capacity of 52,000 af, representing an enlargement of 38,300 af, The enlargement pool (38,300 at) was S-20