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The (storage) tank capacity for each stockpond was obtained from a Dbase file provided by the <br />State Engineer?s Office. Individual stockpond tank capacities were summed into two aggregates <br />(stockponds located above 7750 ft. and stockponds be low 7750 ft in elevation). This elevation is <br />chosen because, all stockponds located above 7750 ft . elevation use a fullness factor equal to 0.87, <br />while the rest use a f actor of 0.75 (USBR, 1991). <br />Tank capacity is converted to its equivalent surface area for both aggregates by using the following <br />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 ar e retrieved from monthly weather files using CRDSS <br />weather stations and weights. The advantage of the aggregation is that instead of assigning a <br />weather station weight for each separate stockpond, the assignment can be made for each sub-basin <br />consistent with what is being done for the irriga tion category. Unfortunately, complete evaporation <br />data are rarely available from weather stations and pan evaporation data are difficult to obtain <br />during the winter. Evaporation is then indirectly obtained from the monthly estimates of mean <br />temperature by a formula proposed by Bl aney (1960) when data are 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 calculated <br />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 the <br />USGS are shown in Table 6, these data can be obtained from the USGS wo rld wide web page at <br />http://h2o.er.usgs.gov/public/watuse. The program has the option of calculating evaporation based <br />on weather data if the surface areas of the reservoirs are provided. <br />2.4 Municipal <br />Population data were obtained from the 1980 censu s (Bureau of the Census, 1981) and 1990 census <br />(Bureau of the Census, 1991). Values for the y ears 1985-1989 were obtained by linear interpolation <br />for county and municipality populations. The total municipal population located in the basin (Table <br />7) was subtracted from the basin-wide population to obtain a rural population for each county. The <br />percentage of each county in the basin (determi ned by GIS) was multiplied by the rural population <br />and summed to achieve a basin-wide rural population for each year (Table 8). <br />The per capita gross usage for each type of us e (urban, rural, commercial and public) can be <br />provided by the user (and thus, allowed to vary ) for each sub-basin, also a different consumptive <br />use ratio can be used for urban and rural consumptive use. The values used for this task memo were <br />obtained from USBR, 1991, as shown in Table 9. <br />2 <br />01.21.97 2.09-10 IDS/CSU <br />