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table 4 because in the GIS it appears with 10 acres and in the model it has 18,624 acres. Structures <br />320772 (13,611 acres being modeled) is located in county/HUC Montezuma-14030002 which has a total <br />irrigated acreage in the GIS of 2,055. Structure 990707 (12,781 acres being modeled) is located in <br />county/HUC San Miguel-14030003 which has a total irrigated acreage in the GIS of 19,801. Including <br />these two structures would have put the percent modeled for these two areas well above 100%. Until <br />further refinement of the location of these structures is done they were not included in the pro-ration <br />values. <br />2.2 Crop Distribution for each Diversion Structure <br />The crop distribution of the irrigated areas served by each diversion structure is obtained using the DMI <br />demandts as shown in Table 3. In cases in which the crop distribution for a particular structure cannot be <br />identified, the crop distribution of the entire county-huc combination was adopted. <br />2.3 Irrigation Water Requirement Calculation <br />The Irrigation Water Requirement for each structure being modeled is estimated using the SCS Blaney- <br />Criddle method as implemented in the CRDSS-CU model. The CRDSS-CU Blaney-Criddle model has <br />the capability of using a soil moisture budget. For this phase of CRDSS, the State decided to use the SCS <br />Blaney-Criddle method without the soil moisture budget. <br />In addition to the soil moisture budget, the CRDSS-CU model has the capability of computing CU using <br />the Penman-Monteith equation. Some preliminary studies showed the potential for significant <br />differences in the CU values computed using the SCS Blaney-Criddle and the Penman-Monteith. The <br />State has a task force reviewing the results of the two equations. Based on extensive prior work by many <br />researchers, there is a well established body of knowledge that shows that as meteorological data <br />becomes available the Penman type equations can provide more accurate estimates of crop CU when <br />used properly. However, since this area did not have sufficient weather data or the quality of these data <br />was inconsistent, the SCS Blaney-Criddle was selected for this modeling effort. <br />The weather stations that were recommended to be used in the San Juan, Dolores, and San Miguel River <br />Basins as part of the CRDSS project (Task Memorandum 2.09-17) were adopted. The weather stations <br />and associated weights for the county-huc combinations are shown in Table 5. <br />For the San Juan, Dolores, and San Miguel River Basins the county-huc assigned to each structure is <br />based on the location of the areas served by that structure. This was done mainly because while <br />evaluating the Irrigation Water Requirement (IWR) for structure 322006 (Dove Creek Canal) it was <br />discovered that the location of this structure is far away from the lands it serves. Due to this fact the <br />structure was originally assigned a weather station with quite different characteristics than the land it <br />serves. <br />2.4 Water Supply results from STATEMOD <br />The average water supplied for all structures being modeled is 289,765 acre-ft, the average water supply <br />without including structures 990707 and 324675 is 237,365 acre-ft. The usable water supply is equal to <br />the estimated CU which is 232,568 acre-ft, and 213,215 acre-ft (Table 9) when structures 990707 and <br />324675 are not included. The average estimated Irrigation Water Requirement (IWR) is 289,599 acre-ft <br />for all structures, and 262,813 acre-ft (Table 7) when structures 990707 and 324675 are not included. <br />The average estimated shortage for all structures is 49,741 acre-ft and 42,303 acre-ft (Table 8) when <br />2 <br />12/16/96 2.09-08 CSU/IDS <br />