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Data Set 3 - Alfalfa-short and Pasture-short Crops Considered <br />Using the crop-aggregated soil combinations of the second data set, parts of alfalfa and pasture areas are <br />assigned water short. These areas are calculated using a ratio (water short area/total area) that the USBR <br />adopted in the Colorado River System Consumptive Uses and Losses Report, 1981-85. The ratio is <br />constant for each subarea for each crop (alfalfa, pasture) as shown in Table 4, and is applied to all years <br />in the report. <br />The length of the growing seasons for alfalfa-short and pasture-short are assumed to be equal to the <br />average of the values that are reported in the USBR Colorado River System Consumptive Uses and <br />Losses Report, 1981-85. Similarly, the specified planting and cutoff dates in the report are averaged in <br />each subarea to obtain equivalent numbers for the 1985-90 report. Thus, each crop combination is <br />assigned a single planting and cutoff date for all years, though these numbers can be varied in each year. <br />Figure 5 shows the total annual IWR for the whole Gunnison River basin computed using the two forms <br />of the SCS Blaney-Criddle ET estimation method (with and without enhancements). As expected, the 6- <br />year average annual IWR is lower than the previous data set runs, i.e. 326,140 acre-ft (8.3 percent lower) <br />and 371,150 acre-ft (7.4 percent lower) for SCS Blaney-Criddle with and without enhancements, <br />respectively. <br />The estimated IWR of the first two runs can be viewed as the total IWR in the Gunnison River basin <br />without any water supply limitations. The third data run considered the short areas, and therefore the <br />IWR might be closer to the actual water use. <br />Figure 6 shows the 6-year average annual consumptive use by subarea. The highest volumetric water use <br />by subarea, by county, and by HU is in Montrose6 (99,840 and 109,240 acre-ft), Delta (132,940 and <br />147,770 acre-ft), and HU14020006 (116,030 and 129,500 acre-ft). <br />In the USBR Colorado River System Consumptive Uses and Losses Report, 1981-85 , the determination <br />of alfalfa-short and pasture-short areas has become a prerequisite of consumptive use calculation. This is <br />because the XCONS2 program does not automatically account for water supply information in the <br />calculations. With the CRDSS enhancements, o ne of which is the incorporation of the water supply <br />information, the determination of alfalfa-short and pasture-short areas is a product rather than a <br />prerequisite of the consumptive use calculations. <br />A more detailed tabular result is included in Section 4.0 <br />Data Set 4 - New Set of Weather Station Weights <br />The first three data sets were run using the USBR recommended set of weather station weights. The <br />fourth scenario uses all the data from the third data set except the set of weather stations and weights. <br />Modification of the weather stations used by the USBR are proposed in Task Memorandum 1.14-18, and <br />the new weights are computed using GIS. <br />Figure 7 shows the annual IWR for the whole Gunnison River basin computed using the two forms of the <br />SCS Blaney-Criddle ET estimation method (with and without enhancements). The 6-year average <br />annual IWR is higher than the previous data set run, i.e. 335,710 acre-ft (2.9 percent higher) and 380,500 <br />acre-ft (2.5 percent higher) for SCS Blaney-Criddle with and without enhancements, respectively. <br />Figure 8 shows the 6-year average annual IWR by subarea. The change in the set of weights affected <br />4 <br />A275 01.0995 1.14-22 Manguerra <br />