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comparison. Table 3 shows the average basin consumptive use estimates and the consumptive <br />use estimates for the explicit and aggregate structures for the period 1976 through 1996. <br />Table 3 <br />Average Annual Crop Consumptive Use Comparison (1976-1996) <br /> StateCU Previous CRDSS StateMod Enhanced StateMod <br />Comparison Results Results % Difference Results % Difference <br />Ex licit Structures 55,825 51,366 8 % 53,631 4 <br />Aggregate Structures 26,986 29,808 -10 % 29,792 -10 % <br />Total Basin 82,811 81,174 2 % 83,423 -1 <br />Difference = (StateCU Results- StateMod Results)/StateCU Results <br />The Enhanced StateMod with variable efficiency and soil moisture accounting estimates <br />consumptive use of explicit structures that is much closer to the StateCU results than the <br />Previous CRDSS StateMod estimates. Because the diversion records for the explicit modeled <br />structures are relatively complete for this time period, the StateCU consumptive use results for <br />these structures is considered to be very good. The Enhanced analysis predicts consumptive use <br />that averages less than StateCU because, as discussed above, the model is unable to divert the <br />full headgate demand during simulation for every structure. <br />Although the Enhanced StateMod analysis predicts total basin consumptive use that is very close <br />to the StateCU results, there is a large difference in consumptive use of the aggregate structures. <br />In the StateCU analysis, aggregate structures are estimated to experience shortages equal to the <br />average of the shortages seen by other structure within the same water district. For both <br />StateMod analyses (Previous CRDSS and Enhanced), the aggregate structure headgate demands <br />are determined by dividing the irrigation water requirement by the basin-wide average monthly <br />efficiency. Therefore, the historic "estimated" headgate diversions used during the StateMod <br />analysis are not the same as the headgate supply calculated by StateCU. The StateMod analysis <br />predicts aggregate structure consumptive use based on irrigation water requirement and water <br />available in priority, therefore is likely a more accurate method. <br />Dry-Year Crop Consumptive Use Comparison <br />Table 4 shows the total basin consumptive use estimates and the consumptive use estimates for <br />the explicit and aggregate structures for the representative dry year 1977. Focusing on explicit <br />structures, the Enhanced StateMod estimates consumptive use of explicit structures in dry years <br />that is much closer to the StateCU results than the Previous CRDSS StateMod estimates. This <br />occurs because both the Enhanced StateMod and StateCU models use a variable efficiency <br />approach that allows more consumptive use to occur in a dry year than the Previous CRDSS <br />approach that using an average efficiency. <br />Table 4 <br />Cro Consum tive Use Com arison Re resentative Dr Year - 1977 <br /> StateCU Previous CRDSS StateMod Enhanced StateMod <br />Comparison Results Results % Difference Results % Difference <br />Ex licit Structures 58,166 48,386 17 % 54,264 7 <br />Aggregate Structures 29,283 31,263 -7 % 31,951 -9 % <br />VariableEff Taskl-5 14 of 17 November 5, 2001 <br />