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modeled by the diversion structures). Table 9, 10 and 11 show the IWR, the amount of water short, and <br />the estimated crop CU, respectively, by county-huc combination. <br />Table 12 shows the average water supply, IWR, and water short for each structure. Table 13 shows the <br />same information by year. In Table 13 structures with water shortages greater than 50%, between 25% <br />and 50%, and between 10% and 25% are marked with an ***, **, or * respectively. Table 7 shows that <br />1988, 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 13. <br />2.6 Issues for Review <br />In the Yampa River Basins it appears that some shortages occur later in the growing season (Jun. Jul, <br />Aug, and Sep), this can be seen in ditches such as 440593 (DENNISON A MARTIN D) and 440573 <br />(CATARACT DITCH). This might be caused by the fact that no soil moisture is being modeled. The <br />reason being that historical spring diversions might o ccur in excess of what is needed to meet the IWR, <br />most likely for replenishing the soil profile. This soil moisture is used in the middle and late growing <br />season when the diversions are less than the IWR. This pattern of consumptive use shortages indicates <br />that using a soil moisture budget might yield better results in the future. <br />The set of weather station weights was assigned based on the location of the structure (i.e. county-huc <br />where the structure is located) and not the location of the area being served. It may be useful in the future <br />to assign weights based on the location of the majority land-area served by each structure. <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 diversion structures. The reason <br />for this, is that a structure might be located in an area of the county-huc that is represented by only one <br />weather station. Therefore, when modeling individual diversion structures consideration should be given <br />to further breaking the county-huc areas by the zones where each weather station could be applied. <br />If any ditches are considerably water short but historically divert small volumes of wa ter compared to <br />Head Gate Requirements (which are computed based on the IWR values and the efficiency), the <br />diversion records and the area assigned to these ditches should be considered for future review to <br />determine the cause of these discrepancies. <br />If any ditches serving irrigated areas have a large discrepancy between the historical diversion and the <br />calculated Head Gate Requirement, the diversion records and the area assigned to these ditches should be <br />considered for future review to determine the cause of the discrepancy. <br />If any ditches historically divert considerably more water compared to the HGR, the diversion records <br />and the area assigned to these ditches should be considered for future review to determine the cause of <br />the discrepancy. These cases are more difficult to detect from the CU model because STATEMOD only <br />diverts the amount required by the crop. They would be detected by comparing the historical diversions <br />with the calculated diversions. <br />3 <br />12/16/96 2.09-07 CSU/IDS <br />