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water use are synonomous for other functional water uses, this is not true for irrigation water use in the Missouri Basin, In the water supply calculations, the MCC used the average irrigation water requirements modified by estimated water shortages most likely to occur, Thus, for 1975 the total estimated irri9ation water consumptive requirement for the Missouri River Basin of 13,243.4 MGD (14,832.5 acre-feet) is reduced to a total actual consumptive use estimate of 10,172 MGD (11,392.6 acre-feet), Similar estimates of actual water use for the 1985 and 2000 projections were not made, Livestock The U.S. Soil Conservation Service estimated current water use and projected water requirements for livestock from agricultural statistical reports and trend demand levels printed in the 1972 OBERS. Although not stated in the SCS publication on "Livestock Water Use," dated July 1975, SCS officials have stated that 20 percent of small pond evaporation losses were included in the estimates for livestock water use. Steam Electric The Bureau of Power of the Federal Power Commission provided estimates of current and projected power generation and water requirements. The assump- tions and methodologies used are described in the following paragraphs: Currently, about 80 percent of the electric energy produced in the United States is generated by steam-electric plants. For the foreseeable future, the bulk of electric generation is expected to depend on nuclear and fossil-fueled steam-electric plants. In steam-electric plants small amounts of extremely pure water are required for boiler use, and larger amounts of relatively untreated water are used for condenser cooling purposes. Eventually all waste heat produced in the cooling process is dissipated to the atmosphere through evaporation, radiation and conduction in the natural water bodies (once through cooling), in cooling ponds, lakes or channels; or through evapo- ration in wet cooling towers; or through conductive cooling in dry cooling towers. In some cases a combination of systems may be used. Hydroelectric plants, which now account for about 15 percent of the total electric generation, are expected to provide smaller percentages in future years. Projections of electric power requirements were made by the five FPC Re- gional Offices in the Bureau of Power. Each of these offices is familiar with the nature of the region under its jurisdiction and the unique combination of factors affecting the electric power requirements therein. They make periodic regional surveys of the electric power industry and continually evaluate the many factors affecting that industry. They also make projections of future electric power requirements for each FPC power supply area (PSA) in their regions. The PSA's have been established to disaggregate the United States into 50 subareas for electric power studies, Each power market area selected for this study consists of one or more of these PSA's. For the 1975 estimates, load data for each PSA were updated to include expected changes, The most current historical monthly and annual electric energy consumption data were used for each identifiable load segment in the industrial, commercial, residential, agricultural, municipal and government load classes. The expected changes reflected schedules of major load changes, II 1-8 I I I I I I I I I I I I I I I I I I I