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I'I>;'!"''''*N U,,, "_I ~-,,-11' ADAPTATION TO DROUGHT 21 notable exception was the extremely low runoff forecast that was made early in March 1977 for the Yakima River in Washington. The early forecast was revised upward in mid-May to predict runoff of 50 percent or more. The larger than anticipated and previously unquan- tified return flow from irrigation was the main reason for the big change in the forecast. In the meantime, some farmers did not plant crops or reduced the acreage planted, and some made sizeable investments in wells which may not have been needed. Ground-water use -A recent development that was made possible by large electronic computers is the digital modelling of ground- water basins. The output from the model is a forecast but in a different sense than forecasts of weather and runoff. Once the model is calibrated, it can be operated to show what will happen to the ground-water resource in the area modeled if different water manage- ment plans are implemented. Some models will indicate what will happen to water levels, to the volume of water, and to the water quality in one or more aquifers. The digital model can be a powerfUl tool to improve the operational efficiency of aquifer systems par- ticularly during a drought period when unusual stresses are applied to aquifers by increased pumping from existing wells and from proposed wells. Base flow projections -The natural reces- sion of streamflow after a storm follows a regular pattern. Previous records at gaging stations on streams are used to define reces- sion characteristics. Then when a drought occurs, streamflow data obtained early in the season are the bases for a projection of the recession relations from which stream dis- charges and stages can be estimated for various dates later in the season. This was done for nearly 100 sites in Idaho so that any- one diverting water from a stream could determine if enough water would be available and if the intake would be low enough to divert the flow. Long-term Planning Public and private agencies have always made long-term plans for water developments because the location of a source of water, the feasibility and design studies, the financing, and the construction take many years to accomplish. Now that a drought has occurred, new data are available that might affect the operation of existing water-supply systems and the design of proposed developments. Anal- yses of the new data and implementation of the results of the analyses will take awhile. Now that longer records of streamflow provide a good data base and new statistical techniques and computer capabilities have been developed, more long range plans are based in part on probabilities of occurrence and the risk involved. One example was given earlier in this report (see p. 6 and fig. 2). It is a frequency analysis of low flows which indicates how the flows in 1977 relate to the flows over the long-term record and docu- ments that such low flows are truly rare events. Whether or not a new development would be designed to prevent such low flows in the future depends upon many other factors also, but extreme events are frequently used as the bases for designs. The large reductions in the amounts of water stored in reservoirs have been described previously. If the drought had continued in 1978, water supplies in many areas would have been reduced drastically, because only small amounts of stored water would have been available. The low reserves for carryover to 1978 led one agency representative to state that they would never let the carryover stor- age get that low again. To prevent this will take a reassessment and a change of operating rules and in some cases legal actions will be necessary. The latter at least will be a long- term effort. Research is continuing to develop better techniques and models to forecast water sup- ply conditions not only more accurately but more frequently so that more efficient manage- ment and use of water can be accomplished. Development of better sensors to measure factors upon which forecasts are made and better means of transmitting the data to cen- tral locations are being pursued. The use of satellites and meteor bursts to transmit signals is becoming common. Water rights, water law, the general lack of law relating to certain aspects of the water resource, particularly ground water, and econ- omic, social, and bureaucratic factors are intrically interwoven. Solutions to water related problems, both with respect to