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2.2 Stockpond <br />There are about 1336 individual stockponds in the Yampa River Basin. The (storage) tank <br />capacity for each stockpond was obtained from a Dbase file provided by the State Engineer?s <br />Office. Individual stockpond tank capacities were summed into two aggregates (stockponds <br />located above 7750 ft. and stockponds below 7750 ft in elevation). This elevation is chosen <br />because, all stockponds located above 7750 ft. elevation use a fullness factor equal to 0.87, while <br />the rest use a factor of 0.75 (USBR, 1991). <br />Tank capacity is converted to its equivalent surface area for both aggregates by using the <br />following expression: <br />= <br />0 . 9 <br />SAC 01945 . <br />where SA = equivalent surface area (acres), and C = aggregate tank capacity (acre-ft). The above <br />equation is obtained from Arnold and Williams (1985). Table 4 shows the aggregate stockpond <br />capacity and surface area in each sub-basin. <br />Climate data used to determine evaporation are retrieved from monthly weather files using <br />CRDSS weather stations and weights. The advantage of the aggregation is that instead of <br />assigning a weather station weight for each separate stockpond, the assignment can be made for <br />each sub-basin consistent with what is being done for the irrigation category. Unfortunately, <br />complete evaporation data are rarely available from weather stations and pan evaporation data <br />are difficult to obtain during the winter. Evaporation is then indirectly obtained from the monthly <br />estimates of mean temperature by a formula proposed by Blaney (1960) when data are <br />unavailable: <br />= <br />ektp 07100 ./ <br />where t = mean monthly temperature (deg F), p = percentage monthly daylight hours, k = Blaney <br />monthly coefficients. Table 5 shows the summary of the stockpond evaporation values as <br />calculated with the CRDSS CU Model. <br />2.3 Reservoir <br />Reservoir surface area and evaporation are reported by the United States Geological Survey for <br />1990 by Hydrologic Unit, but not for 1985. Values reported for surface area and evaporation by <br />the USGS are shown in Table 6, these data can be obtained from the USGS world wide web page <br />at http://h2o.er.usgs.gov/public/watuse. The program has the option of calculating evaporation <br />based on weather data if the surface areas of the reservoirs are provided. <br />2.4 Municipal <br />Population data were obtained from the 1980 census (Bureau of the Census, 1981) and 1990 <br />census (Bureau of the Census, 1991). Values for the years 1985-1989 were obtained by linear <br />interpolation for county and municipality populations. The total municipal population located in <br />the basin (Table 7) was subtracted from the basin-wide population to obtain a rural population <br />for each county. The percentage of each county in the basin (determined by GIS) was multiplied <br />by the rural population and summed to achieve a basin-wide rural population for each year <br />(Table 8). <br />01.21.96 2 02.09-12 IDS/CSU <br />