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<br />0013JJ
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<br />CRDSS
<br />TASK MEMORANDUM 2.09-04
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<br />Consumptive Use Model
<br />Irrigation Water Requirements in the Dolores and San Juan River Basins
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<br />1.0 ISSUE
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<br />This task memorandum describes the computation of irrigation water requirement (IWR) in the
<br />Dolores and San Juan River Basins for years 1985 to 1990. The estimates are based on the
<br />computation of irrigation water requirements using the Soil Conservation Service (SCS) Blaney-
<br />Criddle method as implemented in the CRDSS-CU model using the CROSS recommended weather
<br />stations.
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<br />2.0 DISCUSSION/ANALYSIS
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<br />The estimation of the consumptive uses and losses from the entire Dolores and San Juan River
<br />Basins can be performed either by county (Archuleta, Hinsdale, La Plata, Mineral, and Montezuma)
<br />or by hydrologic unit (HU) (14080101, 14080102, 14080104. 14080105, 14080107 and 14080202).
<br />The U,S. Bureau of Reclamation (USBR) used the intersection of counties and HUs as the
<br />subdivisions for its Colorado River System Consumptive Uses and Losses Report, 1981-1985, To
<br />preserve consistency with these published reports, the Dolores and San Juan River Basins have been
<br />subdivided into 21 subareas that are the result of intersecting the counties and the HUs, These
<br />include subareas (I) Archuleta county HUI40801OI, (2) Archuleta in HU14080102, (3) Hinsdale in
<br />HUl4080102, (4) La Plata in HUl4080101, (5) La Plata in HUI4080104, (6) La Plata In
<br />HUl4080105, (7) Mineral in HUl4080101, (8) Mineral in HUl4080102, (9) Montezuma In
<br />HUl4080202, (10) Montezuma in HUl4080107, (II) Dolores in HUI4030002, (12) Mesa In
<br />HUl4030001, (13) Mesa in HUl4030004, (14) Montrose in HUl4030002, (15) Montrose in
<br />HUl4030002, (16) Montrose in HUl4030004, (17) Montezuma in HUI4030002, (18) San Miguel in
<br />HUI4030002, (19) San Miguel in HUl4030003, (20) Montezuma 14080203, and (21) Dolores
<br />14080203,
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<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 1985-1990, An alternative
<br />method that uses the 1985-1990 county statistics along with the 1993 acreage map to extrapolate the
<br />1985-1990 acreage data for the Gunnison River basin was presented in a CROSS consumptive use
<br />sub-committee meeting. Because of the large discrepancies in the Colorado Agricultural Statistics
<br />from year to year, direct use of the 1993 acreage data was suggested, (Task Memorandum 1.14-19
<br />details the issues and problems of using the Colorado Agricultural Statistics data,) The total irrigated
<br />acreage by crop in each subarea is shown in Table I along with the total irrigated area (230,897
<br />acres). Approximately 43 percent of the total area is located in La Plata county while Mineral county
<br />has the smallest area (approximately 0.5 percent), Approximately 85 percent of the irrigated area is
<br />devoted to pasture and 12 percent to alfalfa, In decreasing order of percentages, the remainder (3 %)
<br />is devoted to small grains, orchards, com, beans and vegetables.
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<br />11.26.96
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<br />2Jl9-04IDSlCSU
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