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<br />----U0589 <br /> <br />EFFECTS ON DILLO~ RESERVOIR <br /> <br />This analysis assumed that Dillon Reservoir had been in <br />operation since 1963 and diverting water through the Roberts Tunnel <br />at the rate of 131,000 acre-feet per year for use on the eastern <br />slope whenever storage was available. Senior water rights on the <br />west slope were met first, hor/ever; and when insufficient water <br />'remained, transmountain diversions were shorted. <br /> <br />The top curves in Figure 2 show the maximum quantities reached <br />in each year. Storage was not allowed to exceed the spillway crest <br />elevation of g017 m.s.l. The lower curves show the minimum guantities <br />reached in each year. Active storage in the pool (254,000 acre-feet) <br />is available to the Roberts Tunnel~ below that lie some 4,000 acre- <br />feet with 500 surface acres which are above the minimum reservoir <br />elevation of about 8831 m.s.l. This elevation is the lowest from <br />which releases can be made to the Blue River. <br /> <br />The plots indicate that with a targeted yearly depletion of <br />131,000 acre-feet the reservoir would fall more than 100 feet below <br />full pool on seven occasions; of these, six were in the "Drought of <br />the . 60' s. " However, there woul d also be 27 years duri ng wh i ch the <br />reservoir spilled. In non-drought years, the typical cycle (the <br />difference between top and bottom lines, i.e. between maximum and <br />minimum pool) would be about 40 feet. This-lis considerably more <br />fluctuation than the average annual drawdown of 10.2 feet which <br />actually occurred during the 1966-1973 period as reported in the <br />Final Environmental Statement. That document predicted such an <br />increase, without quantifyina it, in a statement on paoe 2-85, "As <br />additional waters are diverted from Dillon Reservoir through the <br />Roberts Tunnel, the annual drawdown of the reservoir will increase <br />until the annual dependable water supply is fully utilized." <br /> <br />SAME EFFECTS WITI10UT ~ PRnJFCT <br /> <br />The significance of the quotation cited above is that it was <br />taken from a section of the Environmental Statement entitled FUTURE <br />ENV IROMENT I,ITHOUT THE PROPOSED ACTION. vJhether Stronti a Springs Dam <br />and the Foothills Treatment plant are built, whether some alternative <br />structures are developed, or whether an al,ternative relying on con- <br />servation measures is selected, Dillon Reservoir will be worked harder <br />each year as Denver's water consumption grows. Estimates of when the <br />dependable water supply will be fully util ized rann,e from DHB's <br />projection of 1988 to predicted effects of conservation effurts which <br />could extend the present supply to 2000 or somewhat beyond. <br /> <br />10 <br />