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<br />. <br /> <br />OG1452 <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />~ <br />~ <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />Fox and Olson show that the water requirement for cattle varies monthly and is generally <br />related to temperature. Included in the appendix is a table from their report showing daily <br />water intake and average mean temperature. It is recommended that the table be <br />incorporated into the USBR procedures. <br /> <br />RESERVOIR EVAPORATION <br /> <br />Reservoir evaporation accounts for about 4% of Colorado Consumptive Use and <br />Losses in the Colorado River basin. The Method Manual states that "the methodology <br />used for the 1985-1990 report will be different than that used in the 1981-1985 report." <br /> <br />USSR Procedure <br />In the 1985-1 990 report, two types of reservoirs are classified, measured and <br />unmeasured. Measured reservoirs include those reservoirs for which the evaporation is <br />already calculated by the operating entity. Unmeasured reservoirs include all others. <br /> <br />Reservoir evaporation of unmeasured reservoirs will be determined using NOAA <br />Technical Report NWS 33, "Evaporation Atlas for the Contiguous 48 United States," June <br />1982, Map 3 of 4., Map 3 shows the FWS (free water surface) average annual evaporation <br />rates. Net evaporation is calculated as FWS evaporation minus the,lesser of total annual <br />precipitation or salvage value. (Salvage value represents the pre-reservoir losses. The' <br />engineering used to determine pre-reservoir losses is also not available for review.) These <br />unit values are then multiplied by a maximum surface area times a fullness factor to <br />determine total evaporation. The fullness fact is a function of type of use and elevation. <br />For example, for irrigation reservoirs above 8,600 feet, the fullness factor is 87%, and for <br />those below 8,600 feet, the fullness factor is 75%. (The basis for the fullness factor is <br />unknown.) <br /> <br />Calibrate an Eouation for EstimatinG Pan Evaooration. Using the average annual <br />FWS evaporation to estimate pan evaporation is an improvement over the 1981-1985 <br />procedure but not a very accurate method. A procedure which would vary pan evaporation <br /> <br />16 <br />