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<br />002~59 . <br /> <br />Wyoming Depletions <br /> <br />The average annual water yield from the Little Snake River Basin is about 428,000 AF near its <br />confluence with the Yampa River, roughly 27% of the combined flow of these two rivers, <br />Streamflow data indicate that an average annual discharge of 372.600 AF passes the gage near <br />Dixon, Wyoming. Below the Dixon gage, two significant tributaries, Muddy Creek and Willow <br />Creek, annually contribute an average of about 10,690 AF and 7,440 AF, respectively, for a total <br />of 390,730 AF/year. These gaged flows already reflect losses due to depletions from the Little <br />Snake River Basin upstream in both Colorado and Wyoming. <br /> <br />Sources of depletions in Wyoming include irrigated agriculture, environmental use, municipal in- <br />basin use and trans-basin diversions for the City of Cheyenne. As in Colorado, irrigation is the <br />largest water consumer in the Little Snake River Basin of Wyoming. Irrigation consumption in <br />Wyoming was estimated by multiplying the number of acres devoted to each type of crop by a crop- <br />specific Consumptive Irrigation Requirement (CIR). The CIR is the amount of irrigation needed <br />in excess of rainfall to produce a crop. However, the maximwn consumptive use of any crop is <br />achieved only with an adequate water supply (States West Water Resources 2000). <br /> <br />The CIR at Dixon has been estimated to be about 1.9 feet for alfalfa and 1.75 feet for pasture grass <br />or grass hay. For the Green River Basin Water Plan, these numbers were modified to include <br />mountain meadow hay, for which irrigated lands above Baggs have been estimated to experience <br />1.63 feet of annual CIR (States West Water Resources 2000). There are 11,571 acres under <br />irrigation above Baggs, 10,298 acres in meadow hay and 1,272 acres in alfalfa; below Baggs there <br />are 4,358 irrigated acres, 3,879 acres in pasture grass/grass hay and 479 acres in alfalfa (Table 10). <br /> <br />Table 10. Calculation ofConswnptive Irrigation Requirement, Little Snake River Basin, Wyoming <br /> <br /> GrassIMeadow Alfalfa Totals <br /> Irrigated acreage 10,298 1,273 11,571 <br />Above CIR (feet/year) 1.63 1.90 <br /> - <br />Baggs <br /> CIR (AF/vear) 16,786 2.419 19205 <br /> Irrigated acreage 3,879 479 4,358 <br />Below CIR (feet/year) 1.75 1.90 <br />Baggs - <br /> CIR (AF/vear) 6788 910 7698 <br /> Total irrigated acreage 14,194 1,755 15,929 <br /> Total CIR (AF/year) 23,574 3,329 26,903 <br /> <br />A review of irrigation diversion records show actual depletions less than CIR would predict, which <br />is to be expected. Estimates of agricultural depletions, based on studies for the Little Snake <br />Supplemental Irrigation Water Supply (High Savery) Project (Bums and McDonnell 1999), indicate <br />the basin currently receives about 75% of its needs, with average annual irrigation depletions <br />estimated to be 20,050 AF. Nevertheless, full CIR provides a reasonable estimate of the needs and <br />aggregate consumptive demands for irrigation in the basin. <br /> <br />Management Plan for Endangered Fishes in the Yampa River Basin <br /> <br />25 <br />