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CRDSS <br />TASK MEMORANDUM 2.09-02 <br />Consumptive Use Model <br />Irrigation Water Requirements in the White River Basin <br />1.0 ISSUE <br />This task memorandum describes the computation of irrigation water requirement (IWR) in the <br />White River Basin for years 1985 to 1990. The estimates are based on the computation of irrigation <br />water requirements using the Soil Conservation Service (SCS) Blaney-Criddle method as <br />implemented in the CRDSS-CU model using the CRDSS recommended weather stations. <br />2.0 DISCUSSION/ANALYSIS <br />The estimation of the consumptive uses and losses from the entire White River basin can be <br />performed either by county (Garfield, Moffat and Rio Blanco) or by hydrologic unit, HU (14050005, <br />14050006, and 14050007). The U.S. Burea u of Reclamation (USBR) used the intersection of <br />counties and HUs as the subdivisions for its Colorado River System Consumptive Uses and Losses <br />Report, 1981-1985. To maintain consistency with these published reports, the White River basin has <br />been subdivided into eight subareas that are the result of intersecting the counties and the HUs. <br />These include subareas (1) Garfield in HU14050007, (2) Moffat in HU14050007, (3) Rio Blanco in <br />HU14050005, (4) Rio Blanco in HU14050006, and (5) Rio Blanco in HU14010007. <br />The irrigated acreage, including the type of crop cover for each subarea, is obtained through a <br />Geographic Information System (GIS) using a 1993 irrigated acreage map developed by the State <br />Engineer's Office and the USBR. Because of the lack of a better methodology for estimating the <br />1985-1990 acreage data, the 1993 acreage data was used directly for the years 1985-1990. An <br />alternative method that uses the 1985-1990 county statistics along with the 1993 acreage map to <br />extrapolate the 1985-1990 acreage data for the Gunnison River basin was presented in a CRDSS <br />consumptive use sub-committee meeting. Because of the large discrepancies in the Colorado <br />Agricultural Statistics from year to year, direct use of the 1993 acreage data was suggested. (Task <br />Memorandum 1.14-19 details the issues and problems of using the Colorado Agricultural Statistics <br />data.) The total irrigated acreage by crop in each subarea is shown in Table 1 along with the total <br />irrigated area (25,493 acres). Approximately 99 percent of the total area is located in Rio Blanco <br />county. Approximately 86 percent of the irrigated area is devoted to pasture and 12 percent to <br />alfalfa. In decreasing order of percentages, the remainder (2 %) is devoted to corn and small grains. <br />Orchards, beans and vegetables are not grown in the White River basin. <br />The weather stations recommended by CRDSS (shown in Table 2 and 3). The data sets are prepared <br />to support the input requirements for estimating evapotranspiration by the SCS Blaney-Criddle <br />method. The data set for Penman-Monteith calculations was not prepared, mainly because of a lack <br />of representative daily weather data for the entire White River Basin. <br />Table 4 shows the annual irrigation water requiremen t (IWR) for 1985-1990 for the entire White <br />River basin as estimated by using the SCS Blaney-Criddle method. The 6-year average annual IWR <br />is 32,502 acre-ft. The peak IWR is in 1990 (36,170 acre-ft) while the lowest IWR occurred in 1986 <br />(29,159 acre-ft). A more detailed tabular result is shown in Table 5, showing the 6-year average <br />annual IWR by subarea. The highest IWR by subarea, by county, and by HU is in Rio Blanco <br /> 1 <br />11.26.96 12.09-02- IDS/CSU <br />