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structures 990707 and 324675 are not included. Although the annual water supply is close to the IWR, <br />the years 1989 and 1990 have by far the largest shortages as can be seen in Table 8. <br />2.5 Pro-ration of CU of modeled Structures to CU of County-HUC <br />At this time only a portion of the irrigated area is being modeled. Therefore, the CU for the area being <br />modeled is pro-rated (using GIS data) to estimate the total CU for each county-HUC. This is done by <br />generating a GIS report for all the structures in each county-huc and determining the percentage of <br />irrigated acreage modeled for each county-huc in the basin. The demand, supply and shortages can then <br />be pro-rated based on this percentage. <br />The total irrigated lands, lands being modeled, and percent of lands being modeled for each county-huc <br />are shown in Table 6. This information can be used to evaluate the validity of the pro-rated estimates of <br />CU and amount of water short in a county-huc (i.e. whether the county-huc combination is adequately <br />modeled by the structures). Sinc e a number of structures are not present on the GIS coverage (Table 4) <br />their areas were assumed to be part of the county-huc the structures was determined to be located at. <br />This is probably a good assumption for the small structures, however structures 320772 and 990707are <br />too large to be added to a single county-huc as explained in section 2.1. The average pro-rated estimate of <br />CU is 264,046 acre-ft (Table12). The average pro-rated estimate of shortage is 58,199 acre-ft (Table <br />11). The average pro-rated estimate of IWR is 322,245 acre-ft (Table 10). <br />Table 13 shows the water supply, average IWR, and water short for each structure. Table 14 shows the <br />same information by year. In Table 14 structures with water shortages greater than 50%, between 25% <br />and 50%, or between 10% and 25% are marked with an ***, **, or * respectively. Table 11 shows that <br />1989 and 1990 are by far the years with the greatest water shortages. The water supply for ditches <br />showing 25%-50% or more than 50% should be checked to make sure this shortages are correct. These <br />ditches can be identified using Table 14. <br />2.6 Issues for Review <br />The results presented here for the CU Model indicate a pattern of middle a nd late growing season <br />shortages. Some of the shortages might be caused by the fact that no soil moisture is being modeled. <br />These shortages could reflect the practice of having spring diversions in excess of what is needed to meet <br />the IWR in the Spring, in order to replenishing the soil profile from losses through the winter. This soil <br />moisture is used in the middle and late growing season when the diversions are less than the IWR. This <br />pattern of consumptive use shortages indicates that using a soil moisture budget might yield b etter results <br />in the future. <br />The weights assigned to each weather station serving a county-huc are based on the area of the county- <br />huc served by each weather station. This is probably a good assumption when modeling the whole <br />irrigated area, but could introduce some errors when modeling individual structures. The reason for this, <br />is that a structure might be located in an area of the county-huc that is represented by only one weather <br />station. Therefore, when modeling individual structures consideration should be given to further breaking <br />the county-huc areas by the zones where each weather station should be applied. <br />Structures such as 322006 (Dove Creek Canal) that are very large (19,312 acres) span several county- <br />huc?s. Structure 322006 spans three county-huc?s and is assigned only the weather stations from one <br />county-huc, which could introduce errors. In the future more detailed modeling of large structures should <br />3 <br />12/16/96 2.09-08 CSU/IDS <br />