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<br />. <br /> <br />. <br /> <br />Small Reservoir Feasibility Study <br /> <br />5-7 <br /> <br />j <br /> <br />~ <br /> <br />dry years. It should be noted that Dillon lake levels are very sensitive to assumptions about <br />Robens Tunnel diversion rates and patterns and may not be as near to the target values in the <br />absence of new East Slope storage for Denver, <br /> <br />Water Exoorts <br /> <br />~ <br /> <br />Transmountain diversions from the basin are the same under the two baseline demand <br />scenarios. Denver takes an average of 162,000 AF per year through the RobertS Tunnel while <br />Colorado Springs takes an average of 13,900 AF per year through the Hoosier Tunnel. The high <br />level of Denver diversion reflects development of the Straight Creek Project and full utilization <br />of Blue River exchange potential from Williams Fork and Muddy Creek reservoirs. The Vidler <br />and Englewood (Boreas Pass) systems annually divert an average of 700 AF and 500 AF, <br />respectively. <br /> <br />~ <br /> <br />- <br /> <br />... <br /> <br />~ <br />- <br /> <br />Additional Scenarios <br /> <br />... <br /> <br />Based on the results of the baseline scenarios, two additional scenarios were <br />constructed to evaluate new water facilities and management measures. The first of these, <br />designated Scenario III, depicted a new 4650 AF storage facility on Peru Creek to mitigate Snake <br />River flow deficiencies resulting in minor snowmaking curtailments. Variations on Scenario III <br />also evaluated the reliability of the Laskey Gulch infi1tration gallery as an emergency water <br />source and the yield of a rehabilitated Old Dillon Reservoir system. <br /> <br />.- <br /> <br />... <br /> <br />~ <br /> <br />~ <br /> <br />Scenario IV depicted the same water facilities and measures as Scenario III. However, in <br />Scenario IV the Peru Creek reservoir was operated to maintain a minimum Snake River flow of 6 <br />cfs instead of the 2 cfs curtailment flow presently mandated by instream flow agreements. This <br />higher instream flow target reflects the fact that the 2 cfs level is intended only to insure skier <br />safety; any snowmaking diversion bringing streamflows below 6 cfs requires Forest Service <br />approval, In both scenarios, the Peru Creek reservoir was assumed to store out-of-priority <br />ahead of Dillon under protection of the Summit County Agreement and, possibly, additional <br />agreements with Denver. The net depletion to Dillon Reservoir associated with the Peru Creek <br />Reservoir would be evaporation of not more than 70 AF per year. <br /> <br />~ <br /> <br />"" <br /> <br />Water Deliveries <br /> <br />. <br />.. <br /> <br />. <br />. <br /> <br />Because ma."lY of the shortages to in-basin water users have institutional rather than <br />physical causes, development of the Peru Creek Reservoir has only limited impact on water <br />delivery shortages identified in the baseline scenarios. In all the variations of Scenario III, only <br />four water users were affected by the measures Simulated; these impacts are summarized in <br />Table 5-6. <br /> <br />I <br /> <br />Keystone snowmaking shortages associated with curtailment for instream flow are <br />eliminated by releases from Peru Creek Reservoir, but shortages associated with Green <br />Mountain operating targets are not. The increase in shortages to Mesa Cortina are the result of <br />the senior call on Salt lick Gulch exerted by the Old Dillon Reservoir system; if the Old Dillon <br />system is operated to its decree limits, there may be periods when competition for the limited <br />physical supply could jeopardize recharge to the alluvial aquifer supplying the Mesa Cortina <br />wells. <br /> <br />. <br />. <br /> <br />. <br />