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<br />002627 <br /> <br />August 23. 2000 <br /> <br />page 2 <br /> <br />Municipal Depletions <br /> <br />According to Purcell (2000), municipal demands in the Little Snake River Basin are created by uses in <br />the towns of Baggs and Dixon. Between the two, a total of 76 acre-feet of water is currently depleted. <br />Bums and McDonnell (ibid.) provide a higher current municipal depletion of 106.8 acre-feet. Current <br />population estimates are 375, 300 for Baggs and 75 for Dixon, for a current use rate of 0.20 acre- <br />feeVperson-year using Purcell's numbers. To project these depletions to year 2045, population <br />projections outlined by Watts (2000) are used. While Watts proposes three growth scenarios, only the <br />moderate growth scenario is used herein. This scenario is based. on U.S. Census Bureau projections. <br /> <br />According to Watts, Baggs and Dixon, together, would experience total growth of 10.8 percent from <br />2000 to 2030. Projected to 2045, or another 15 years beyond the 2030 horizon looked at by Watts, gives <br />a growth total of 16.2 percent. This projection is performed by linear extrapolation, which is <br />satisfactory in this case because the moderate growth curve is linear in later years. <br /> <br />Therefore, projecting municipal demands consists of taking existing use and increasing it by the <br />expected percentage population increase. A current depletion of 76 acre-feet annually, increased by <br />16.2 percent, gives a 2045 municipal depletion of 88 acre-feet per year. <br /> <br />City of Cheyenne Depletions <br /> <br />Part of the City of Cheyenne's water supply system is comprised of the Stage I and Stage II Projects. <br />These projects consist of collection and transmission systems in the Little Snake River Drainage. Water <br />is collected from several tributaries of the Little Snake River and delivered to a tunnel that transports the <br />water under the continental divide to Hog Park Reservoir in the North Platte River Basin. Storage in <br />Hog Park Reservoir is released to replace water diverted to Cheyenne through the Rob Roy supply <br />components of the Stage I and II Projects, which transport water from the North Platte River Basin to <br />the South Platte River Basin. The current amount of water diverted from the Little Snake Basin, based <br />on the 1995-1997 usage period, is 14,400 acre-feet per year. <br /> <br />Maximum annual capacity of the Stage 1111 system is dictated by the larger of the potential yield of this <br />system (21,000 acre-feet, Black and Veatch, 1994) versus the one-fill limitation on Hog Park Reservoir <br />(22,656 acre-feet). In this case, maximum potential depletion allowed to the Little Snake River Basin is <br />therefore 22,656 acre-feet. The City of Cheyenne has no current plan to enlarge the Stage VII system, <br />however, its capacity will be reached in the 2040-2050 time frame under current growth estimates. <br />Agricultural Depletions <br /> <br />Agricultural depletions arise from the consumptive use of water by irrigated crops and pasture. <br />Determination of this depletion requires estimates of the current irrigated acreage in the basin and of <br />actual crop consumptive requirements. <br /> <br />~ <br />f' <br />r <br /> <br />O'Grady, et ai, (2000) calculated the amount of irrigated lands in the Little Snake Basin using 1983- <br />1984 aerial photography corrected by 1997-1999 infrared satellite imagery. This work resulted in an <br />estimate of current irrigation of Wyoming lands totaling 15,929 acres. Crop distribution in the basin <br />was previously estimated to be 75 percent grass hay, I I percent alfalfa and 14 percent irrigated pasture <br />(Western Water Consultants, 1992). <br /> <br />Appendix C - Technical Memoranda from Colorado and Wyoming <br /> <br />C-6 <br />