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Table 4 shows the annual irrigation water requi rement (IWR) for 1985-1990 for the entire Colorado <br />River basin as estimated by using the SCS Blaney-Criddle method. The 6-year average annual IWR <br />is 419,413 acre-ft. The peak IWR is in 1989 (445,125 acre-ft) while the lowest IWR occurred in <br />1986 (381,167 acre-ft). A more detailed tabular result is shown in Table 5, showing the 6-year <br />average annual IWR by subarea. The highest six year average IWR by subarea, by county, and by <br />HU is in Mesa 14010005 (197,767 acre-ft), Mesa (198,779 acre-ft), and HU14010005 (280,056 acre- <br />ft), respectively. <br />Table 6 shows the 6-year average annual IWR in terms of unit depth for each subarea. The average <br />value for the Upper Colorado River basin is 1.54 feet. The highest per unit depth IWR by subarea <br />and county, is in Mesa 14010005 (1.97 feet), and the smallest unit dept h IWR is in Gunnison <br />14010004 (0.81 feet). <br />3.0 CONCLUSIONS/RECOMMENDATIONS <br />The 6-year average IWR for the Upper Colorado River basin is estimated to be 419,413 acre-ft. The <br />water supply information should be considered directly when estimating the actual consumptive use. <br />The CRDSS consumptive use (CRDSS-CU) program has this capability. By linking CRDSS-CU to <br />the Water Resource Planning Model (STATEMOD), estimates of consumptive use are subject to the <br />actual availability of water supply. The results of this process are presented in Task Memoranda <br />2.09-05 - 2.09-08. Other uses (non-irrigation CU) are presented in Task Memoranda 2.09-10 - 2.09- <br />13 and total values for the basins of the Colorado River Basin modeled in phase IIB are presented in <br />Task Memorandum 2.09-20. <br />Depending on the level of detail desired, several different data sets can be prepared for estimating <br />IWR in the Upper Colorado River basin. Smaller subareas may be chosen to increase the <br />representativeness of the consumptive use data. For example, the growing season of a particular crop <br />may not be uniform across a subarea defined by HU and county combination, thus, breaking the <br />subarea into smaller areas would allow assigning a more representative growing season for each <br />smaller area. Similarly, when the weather parameters in a HU-county subarea are derived by <br />weighting two or more weather stations, it may be better to break the subarea into smaller areas such <br />that each smaller area is associated with a single weather station. <br />4.0 OTHER ESTIMATES OF CONSUMPTIVE USE <br />The CRDSS-CU model incorporates an enhanced version of the SCS Blaney-Criddle methodology <br />which includes a monthly soil moisture budget. This allows soil (i.e., water holding capacity, and <br />AWC) and management (i.e., management allowed depletion, MAD) characteristics as well as winter <br />soil moisture carry-over to be incorporated in the estimation of IWR. Using the enhanced version of <br />the CU model, new estimates can be obtained. <br /> 2 <br />11.26.96 12.09-01- IDS/CSU <br />