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The Colorado Agricultural Statistics no longer reports the number of livestock by county. To get the <br />equivalent values for the adopted subarea, a methodology is developed and presented in Task <br />Memorandum 1.14-20. <br />Table 2 shows the number of livestock for each type in each subarea. The number of livestock by month <br />is assumed equal to the annual value. The consumptive use from this category is extremely small <br />compared to other categories, so monthly variations may not be significant. However, to preserve <br />consistency in the units, the values have to be provided per month. <br />Stock Ponds <br />There are approximately 1,268 individual stock ponds in the Gunnison River basin. Including each stock <br />pond as a separate field in the input file would involve too much detail. Instead, these stock ponds are <br />preprocessed by reducing them into two aggregate stock ponds for each subarea, one aggregate <br />representing all stock ponds located above 7,750 feet elevation and the other aggregate representing all <br />stock ponds below 7,750 feet. The elevation is chosen because, as described in the Colorado River <br />System Consumptive Uses and Losses Report, 1981-1985, all stock ponds located above 7,750 feet <br />elevation use a fullness factor equal to 0.87, while the rest use a fullness factor of 0.75. Thus, each <br />subarea should have, at most, two aggregate stock ponds. <br />The surface area of each stock pond is not available, therefore the storage capacity is used. Thus, the <br />aggregate stock pond will have an aggregate storage capacity. This capacity is converted to its <br />equivalent surface area using the following expression: <br />0.9 <br />SA = 0.1945 C <br />where SA = equivalent surface area (acres), and C = aggregate tank capacity (acre-ft). <br />The above equation was obtained from Arnold and Williams (1985). Table 3 shows the aggregate stock <br />pond capacity and surface area in each subarea. <br />The evaporation and rainfall data are obtained from a monthly weather file (the same file that is used for <br />computing consumptive use from evapotranspiration by SCS Blaney-Criddle). However, a separate set <br />of weather station weights is provided. The advantage of the aggregation is that instead of assigning a <br />weather station weight for each separate stock pond, the assignment can be made for each subarea <br />consistent with what is being done for the evapotranspiration category. Unfortunately, complete <br />evaporation data are rarely available from weather stations, and pan evaporation data are difficult to <br />obtain during the winter. Evaporation is then indirectly obtained from the monthly estimates of mean <br />temperature by a formula proposed by Blaney (1960): <br />e = 0.7k tp/100 <br />where e = evaporation, t = mean monthly temperature (deg F), p = percentage monthly daylight hours, <br />and k = Blaney monthly coefficients. <br />Reservoirs <br />There are approximately 125 reservoirs in the Gunnison River basin. Each reservoir is entered as a <br />separate field in the data file and is identified by county and HU. <br />2 <br />A275 01.09.9 5 1.14-23 Manguerra <br />