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<br />001359 <br /> <br />Shortages <br />The next step in this analysis was to identify irrigated lands which did not receive a full water supply <br />in any year. Shortage acreage for each Unit and crop was computed using the acreage identified in <br />the Type I Study. The same stations and cutoff flows presented in the 1981-85 CRSCU&L Report <br />were used. A listing of cutoff flows and dates by unit are presented in Table 2-5. It should be noted <br />that the Type I Study was conducted on only a few gages in the Basin. Cutoff dates at other locations <br />were obtaining by associating a location with an appropriate Type I Study gage. Irrigation shortages <br />were applied in Colorado and Utah. Colorado Units 5B (Spring Creek) and 6B (Upstream of <br />Durango) were not shorted in this analysis to be consistent with state of Colorado CRDSS model. In <br />addition, Dolores Project lands, both full service and supplemental, were not shorted after availability <br />of project water. <br /> <br />Estimated irrigated crop acreage, Type I shortage acreage, and meteorologic data were input to the <br />XCONS program for each Unit. In addition, the application depth for computation of effective <br />precipitation, monthly percentage of daylight hours, planting and harvest dates, mean air temperature <br />of earliest and latest moisture use, and length of growing season for each crop type were input to the <br />XCONS program for each Unit. All crop growth parameters are tabulated in Appendix A.iv. <br /> <br />The next step of irrigation depletion analysis is computation of unit depletions. This is a simple <br />equation stated as: <br /> <br />Unit Volumetric Depletion <br /> <br />= Unit monthly crop water requirement * acres (year) <br />* (1.0 + incidental loss rate (HUC)) <br /> <br />Sprinkler Evaporation <br />Sprinkler evaporation is usually computed as 7.0 percent of headgate diversions. This rate was <br />applied to Dove Creek lands (Units 3, lIB, and 12). A higher rate of 10.0 percent was applied to <br />pre-project lands in Unit llA, assuming that higher losses have occurred in older systems. Sprinkler <br />evaporation rate of NIIP was reduced slightly to 6.7 percent of the headgate diversion to account for <br />measured spillage. Recorded headgate diversions were available for these lands. However, <br />adjustments were made to MVIC lands (Units IIA, liB, and 12) to account for reservoir storage. <br />Sprinkler evaporation was computed as a function of adjusted diversions rather than the recorded <br />transbasin diversions. <br /> <br />Proportioning Unit Irrigation Depletions to Gauging Stations <br />Determination of irrigated acres above each gage was estimated utilizing a GIS coverage of irrigated <br />acreage overlaid by a coverage representing delineated subbasins and Units, Delineated subbasins <br />represent lands located between a reach (between upper and lower gage, the gain area). Each <br />subbasin is referenced based on a subbasin id number. For example: Station 09342500, San Juan <br />River At Pagosa Springs, CO (Figure 2-2, Map Ref I): <br /> <br />Subbasin id numbers associated with gage: 7 (See Figure 2-6, Subbasin Id Map) <br /> <br />DRAFT - SJRIP Hydrology Model Documentation <br />June 18, 1999 <br /> <br />20 <br />