CRDSS_Task1_14-24_EvaluationOfUSBORProcedure_DeterminingWaterRequirementNotMet

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3) found that consumptive use was likely limited by the available water supply in 1987 through 1990. Similarly, for the Boles and Manney Ditch, the analysis indicated that in 1987, consumptive use was limited by the available water supply. The Boles and Manney Ditch diverts from the Uncompa hgre River; thus, it was assumed that the stream gaging station for determining cutoff dates should be the Uncompahgre River at Colona. In the USBR procedure, when the flow at the gage drops below 320 cfs, the consum ptive use for alfalfa-short acreage stops. In 1987, the alfalfa cutoff date in this HCU would have been June 22. The ratios of consumptive use to diversion for the Boles and Manney Ditch is shown in Table 3. These ratios indicate that the ditch was not water-short until August. Thus, it appears th at the USBR cutoff procedure would not accurately replicate the water-short period for this ditch. For Beach Nos. 1, 2, and 3, the consumptive use and diversion data were combined. The comparison of consumptive use to ditch diversion is shown in Tabl e 3. Since the cropping dist ribution under these ditches includes 20 percent alfalfa, when the water supply became limiting, the irrigation of alfalfa was probably cut back. According to the USBR de termination, it would be incorrectly assumed that these ditches had a full water supply. Comparing the wate r-short months shown in Table 3 to the cutoff dates in Table 2 shows that in the 6-year study period, only in 1990 was the USBR cutoff date a reasonable estimate of when the ditches became water-short. Thus, the procedure fo r estimating cutoff dates would be at most a rough estimate of when the water supply limits consumptive use in this ditch. In 1985 and 1986, the ditches were not water-short, but the USBR procedure would limit consumptive use after July in both years. H U 1 4 0 4 0 0 0 6 , M o n t r o s e C o u n t y Thirty-seven of the identified ditch st ructures were located in this HCU. Similar to the previous HCU, the USBR report indicates no pasture-short or alfalfa-short acreage in this HCU. However from this analysis, several ditches with irrigated crops including alfalfa and pasture grass were found to be water-short in this HCU. As can be observed in Table 3, the Spring Ditch was found to have a limited water supply in 1987 through 1990. The administration number (12503.00000) for Spring Ditch is relatively senior, based upon a review of priorities in this water district. The ditch diverts from Alkali Creek, a tributary stream; thus, it is possible that its water supply is cut back due to a limited phys ical supply. In only 1 year, 1989, does it appear that the USBR's cutoff dates would provide a reasonable estimate of when the water supply for this ditch becomes limiting. The Eagle Ditch was found to have a limited wate r supply in 1987, 1988, and 1990 (see Table 3). The irrigated area under this ditch is approximately 42 pe rcent alfalfa, and in times when the water supply is limited the irrigation on alfalfa is probably curta iled. The ditch has two water rights (17.85 cfs, Admin.number = 11729; and 15.96 cfs, Admin.number = 14198), and in reviewing records it is readily apparent when the more junior water right goes out of priority. Generally, in the months the ditch was water-short, the junior water right was partially or fully curtailed. The USBR cutoffs are not at all appropriate for this ditch. They generally occurred 1 month too soon. The JH Anderson Ditch No. 2 wa s found to be water-short in every year of the study period. Approximately 35 percent of the irrigated area under this ditch is alfalfa; thus, when the water supply is limited, a portion or all of the alfalfa was probably not irrigated. Because the comparison of consumptive use to diversion for this ditch (Table 3) shows that the shortage occurs in June of every year, it is suspected 5 A 275 01.09.95 1.14-24 Walter