Laserfiche WebLink
CRDSS <br />TASK MEMORANDUM 1.14-22 <br />Consumptive Use Model <br />Irrigation Consumptive Uses and Losses in the Gunnison River Basin <br />1.0 ISSUE <br />This task memorandum formalizes the verification/implementation of the CRDSS consumptive use (CU) <br />model for the Gunnison River basin as a prototype. It includes only the evapotranspiration (ET) <br />categories of consumptive use. The non-evapotranspiration or other uses categories are covered in Task <br />Memorandum 1.14-23. The verification that is required for 1 year (1985), as specified in Phase I, is done <br />for 6 years (1985-90). <br />2.0 DISCUSSION/ANALYSIS <br />The estimation of the consumptive use and losses from the entire Gunnison River basin can be performed <br />piecewise either by county (Delta, Gunnison, Hinsdale, Mesa, Montrose, Ouray, and Saguache) or by <br />hydrologic unit (HU) (14020001, 14020002, 14020003, 14020004, 14020005, 14020006). The U. S. <br />Bureau of Reclamation (USBR) uses the intersection of counties and HUs as the subdivisions for its <br />Colorado River System Consumptive Uses and Losses Report, 1981-1985 . Thus, the Gunnison River <br />basin has been subdivided into 15 subareas that are the result of intersecting the counties and the HUs. <br />These subareas include: (1) Delta County in HU14020002, (2) Delta in HU14020004, (3) Delta in <br />HU14020005, (4) Delta in HU14020006, (5) Gunnison in HU14020001, (6) Gunnison in HU14020002, <br />(7) Gunnison in HU14020003, (8) Gunnison in HU14020004, (9) Hinsdale in HU14020002, (10) Mesa <br />in HU14020005, (11) Montrose in HU14020002, (12) Montrose in HU14020005, (13) Montrose in <br />HU14020006, (14) Ouray in HU14020006, and (15) Saguache in HU14020003. The subarea in county <br />Delta and HU 14020002 will be referred to by the county and the last digit of the HU, for example, <br />Delta2. This convention is used in the rest of the document. <br />The irrigated acreage, including the type of crop cover for each subarea, is obtained through a geographic <br />information system (GIS) using a 1993 irrigated acreage map developed by the State Engineer's Office <br />and the USBR. Because of the lack of a better methodology for estimating the 1985-90 acreage data, it <br />has been decided that the 1993 acreage data be used directly for 1985-90. An alternative method, which <br />uses the 1985-90 Colorado Agricultural Statistics along with the 1993 acreage map to extrapolate the <br />1985-90 acreage data, was presented in a CRDSS consumptive use sub-committee meeting. Because of <br />large discrepancies in the Colorado Agricultural Statistics from year to year, direct use of the 1993 <br />acreage data was suggested. Task Memorandum 1.14-19 details the issues and problems associated with <br />using the Colorado Agricultural Statistics. The total irrigated acreage by crop in each subarea is shown <br />in Table 1 along with the total irrigated area (253,653 acres). Approximately 23 percent of the total area <br />is located in subarea Montrose6, and 32 percent is located in Delta County. Hinsdale2 has the smallest <br />area (approximately 0.5 percent). Approximately 69 percent of the irrigated area is devoted to pasture, <br />and 12 percent to alfalfa. The remaining 19 percent is devoted to corn, beans, small grains, orchard, <br />vegetables, and tree farms, in decreasing order. The entire irrigated area in Gunnison County is basically <br />devoted to pasture. <br />1 <br />A275 01.0995 1.14-22 Manguerra <br />