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Executive Summar April 23, 2003 <br />Page iv <br />Similarly, at full use of the existing system the average Moffat Tunnel diversions will <br />increase by about 6% from 63,000 acre-feet of existing demand to 67,400 acre-feet. <br />Again, this increase will occur as demand increases without building any new facilities. <br />If the next project on line is a North System supply with a firm yield of 15,000 acre-feet, <br />diversions would increase from Grand County by 9% to 73,600 acre-feet, while a South <br />System supply would increase diversions by 8% to 72,600 acre-feet. <br />Northern Colorado Water Conservancy District Water Needs <br />The Colorado-Big Thompson/Windy Gap system is designed to collect up to an average <br />of 310,000 acre-feet of water from the Upper Colorado River for conveyance through the <br />Alva B. Adams Tunnel to the East Slope for supplemental irrigation and municipal water <br />supply purposes. Under existing demands CB-T and Windy Gap diversions from the <br />West Slope average about 247,800 acre-feet per year. Under future demands, average <br />annual diversions are expected to increase by about 10% up to 271,700 acre-feet. <br />lll. Study Results <br />Phase II of the UPCO study represents the most comprehensive water planning and <br />hydrologic evaluation to-date for the headwaters of the Colorado River. The primary <br />results of this phase of the UPCO study are detailed quantifications of water supplies, <br />stream flows, and reservoir levels for various locations in Grand and Summit Counties. <br />The results of the modeling are voluminous, containing daily data for 45 years at nearly <br />401ocations for several separate model "runs." <br />The data display tool provides a means to compare various water supply and planning <br />options. Four water supply and demand "scenarios" were modeled: <br />l. Existing Demand with Existing Supply <br />2. Full Use Demand of Existing Supply <br />3. Full Use with 15,000 acre-feet of New North System Supply including full use of <br />Windy Gap <br />4. Full Use with 15,000 acre-feet of New South System Supply including full use of <br />Windy Gap <br />The evaluation entailed reviewing the model output for locations of interest and <br />comparing the current conditions with future conditions to discern where and when water <br />shortages are likely to occur. The table below summarizes the estimated water supply <br />shortages for water providers in Grand and Summit Counties. <br />Hydrosphere, 1002 Walnut Suite 200, Boulder, CO 80302