2012-06-20_PERMIT FILE - C2010089A (29)

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The first portion of Table 7 shows the CU analysis for 74 acres irrigated by 27 shares. The monthly field delivery to the crop is the monthly averages shown in Table 2 minus 15% transit loss. This amount is 235.74 acre -feet, and when compared to 337.16 acre -feet needed by the crop, shows that the crop is not being delivered a full water supply. Because the water is used and reused several times in a ditch system such as the CC Ditch, an efficiency coefficient of 45% is reasonable to use. The 45% coefficient is often used as a standard by the CO DWR in this region. The resulting CU for 27 shares and 74 acres is 106.08 acre -feet that can be changed and fully consumed. The other 55 %, 129.66 acre -feet, must be released back to the appropriate drainage to replace historic return flows. The second portion of Table 7 shows the CU analysis for 34 shares that irrigates 71.14 acres. Using the same method described above, the resulting CU for the 34 shares and 71.14 acres is 133.59 acre -feet that can be changed and fully consumed and 163.27 acre -feet that must be returned to the drainages to replace return flows. However, as discussed in the following sections of this report, this acreage has not been irrigated for the entire period of study, therefore the available CU has been discounted by 8.9% to account for this. The corrected resulting CU available for full consumption is 121.68 acre -feet. COMPARISON OF CU RESULTS WITH 88CW55 AND 1988 REPORT The 1988 Report used a 17 -year period from 1970 to 1986 to report historical diversions. It was all the information available at that time that had monthly totals of water diverted into the Highline Canal. Records prior to 1970 showed only periodic daily readings of flows and were not usable. When the annual totals were compared to current diversion records from CO DWR, there are slight differences in most years. The source of these differences is unknown. There is only a small difference between the new 277.9 acre - feet /year of historical diversions associated with Western Fuels' 27 shares as contrasted to the 273.3 acre - feet/year in the 1988 Report. There are transit losses in the canal that the 1988 Report did not expressly address. Paragraph 5C of the 88CW55 decree states that the CC Ditch Company determined that 28% of the water delivered into the Highline Canal has historically been lost to ditch losses. However, the decree also states that "these losses will not be charged against applicant's historical consumptive uses." The transit losses should have been used in the consumptive use analysis in the 1988 Report to determine the quantity of water that arrived at the crop, however recent information indicates that 28% is excessive and 15% is a more reasonable estimate of the actual transit losses. For temperature and precipitation data, the 1988 Report also used an average between the Nucla and Uravan stations. After analyzing the updated climate data, there does not appear to be a significant difference between the two data sets. The CU calculations in the 1988 Report were done on an annual basis, but today's standards require the analysis to be monthly. The 88CW55 decree mentions a mixture of grass and alfalfa. Alfalfa has a higher CU, so to be more conservative and realistic with what has been observed in the Nucla area, this new analysis is based only on grass crop coefficients. The 1988 Report used a smaller efficiency of 36% in the CU analysis. Current practice indicated that 45% is an appropriate number for this area and type of system. 4