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: Forecasts of 1980 river basin water use presented in the reports of the 1960 Senate Select Committee on National Water Resources and in the Water Resources Council's First National Water Assessment of 1968 were compared to estimates of actual use in 1980 to assess the accuracy of efforts to forecast future water use. Results show that the majority of the forecasts were substantially in error. In general, the First National Assessment forecasts erred by a smaller margin, but tended to repeat the regional patterns of overestimation (underestimation) exhibited in the Senate Select Committee forecasts. Moreover, forecasts of the two groups that came within 20 percent of the 1980 withdrawals, in general were accurate, not because of superior prediction, but because of offsetting errors in forecast components. This performance leads us to conclude that water use forecasts, regardless of the time‐frame or the forecast method employed, are likely to always be highly inaccurate. Accordingly, if such forecasting efforts are to be of value in contemporary water resources planning, forecasters should direct their attention toward methods which will illuminate the determinants of the demand for water.

The High Plains aquifer, which underlies about 174,000 square miles (1 square mile = 2.59 km2) in the Great Plains, is the principal source of water in one of the nation's major agricultural areas. This paper examines relationships between the scale of management areas and physical factors, resulting from the lateral movement of groundwater, that limit the ability of irrigators in the High Plains to reduce their own future pumping lifts. At the scale of individual farms, irrigators have very limited ability to “bank” water in order to obtain reduced future pumping lifts. On the other hand, at the scales typical of regional management, reductions in pumpage will result primarily in reductions in water level declines within the management area.

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__________________________________________ Introduction _______________________________________ Nature of the problem ____________________________ Buford Dam _______________________. Relationship of flow and dissolved oxygen ______. Managing the dissolved-oxygen concentration _____. The range of alternatives _______________. The alternatives considered _____________________ Study overview _______________________, The dissolved-oxygen model ___________________________ Results from the dissolved-oxygen model _________ The hydrologic simulation model ________________________ Operation of the Buford Dam hydroelectric generating facility: assumptions and definitions ___________ 9 Description of the hydrologic simulation model ______ IQ Results from the hydrologic simulation model _______ H Page Fici'KKs 13,14. Diagrams illustrating: 13. The method of determining the least-cost combination of the percentage of waste flow receiving nitrification and the minimum flow at Atlanta, Ga., required to produce a minimum dissolved-oxygen concentration of 4 mg/L, in 1990 ______________________________________________________ 14. The solution for least-cost combinations of percentage of wastes receiving nitrification and minimum flow at Atlanta, Ga., necessary to produce a minimum dissolved-oxygen concentration of 5 mg/L, for 1980, 1990, and 2000 _________________________________________________ 21 15. Graph showing the costs (benefits foregone plus added waste-treatment cost) of attaining various minimum dissolvedoxygen concentrations under different policies for 1990 _______________________________-___ 16. Diagram illustrating the relationship between estimated annual dependable-peaking-capacity benefits and minimum flow at Atlanta, Ga., with and without reregulation, for 1980, 1990, and 2000 __________________________ TABLES Fagv TAHLK 1. The expected average daily flow from waste-treatment plants discharging to the Chattahoochee River between Atlanta,