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CRDSS <br />TASK MEMORANDUM 1.14-20 <br />Consumptive Use Model <br />Estimating Livestock in the Gunnison River Basin <br />1.0 ISSUE <br />The objectives of this task memorandum are to develop, describe, and use a method for estimating the <br />number of livestock per hydrologic unit in the Gunnison River basin. This method will use yearly State <br />livestock records given in the Colorado Agricultural Statistics (CAS), and the geographic information <br />system (GIS) 1993 data for areas computed using the maps generated as part of the spatial database for <br />the CRDSS. <br />2.0 DISCUSSION/ANALYSIS <br />Introduction <br />The livestock consumptive use is the daily amount of water consumed by each animal type in the basin <br />expressed in gallons/head/day. This amount depends directly on the number and types of livestock in a <br />given region. The consumptive use (CU) model uses three types of animals in computing livestock <br />consumptive water use. These types are cattle-calves, sheep-lambs, and hogs-pigs. After reviewing the <br />CAS data, the CRDSS CU team found that the CAS no longer provided a record of the number of <br />livestock per county similar to the years 1981-1985. For the years 1985-1990 and after, the number of <br />livestock is recorded for the whole state. To use the State data, a method for subdividing it into counties <br />and hydrologic units was developed using the historical 1981-1985 CAS data a nd the CRDSS spatial <br />database. <br />Estimating Livestock Per County <br />To convert the Colorado State livestock reported in the CAS 1985-1990 to per county data, the weighted <br />average for animal types is needed. The weighted average for livestock distribution in the county was <br />computed from CAS data for the years 1979 to 1983. The percentage for livestock type in the county <br />was estimated by dividing the weighted average by the total State livestock number. Table 1 in section <br />4.0 shows the CAS 1979 to 1983 county livestock number, the computed weighted averages, and the <br />percentage of county to total state livestock ratio. <br />To compute the CAS livestock per county, the percentage of county to state livestock numbers from table <br />1 were multiplied by the CAS total Colorado State livestock number for each of the years from 1985 to <br />1990. Table 2 shows the estimated number of livestock per county for each livestock type for the years <br />1985 to 1990. Figure 1 shows the livestock comparison between the calculated weighted average from <br />1979 to 1983, and the estimated livestock number for 1985. <br />Area Percentages for Each Hydrologic Unit <br />Since just some portions of counties fall inside the Gunnison River basin, a method to convert the <br />livestock number to the hydrologic unit and the percentage of the total area of the county falling within <br />1 <br />A 275 .01.09.95 1.14-20 Al-azzawe <br />