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IMPACT OF PLANNING OBJECTIVES Despite the facts that objectives of planning investigations have been shifting continuously for the past 30 years and that some of the shifts have been of major magnitude, the impact of the shifts on hydro- logic investigations of the first two types have been very small. In most cases the ultimate planning objectives are so far removed from basic analyses such as these, that extreme changes in objectives can be accommodated with little or no change in technology at this level. This is particularly true in the case of techniques for developing and analyzing basic hydrologic data. Most frequently changes in techniques for accomplishing this type of work result from advancements in the technology itself (such as methods for streamflow simulation) or from the availability of better "tools" for accomplishing the work (such as the availability of electronic computers). Nevertheless, even at this level there are sometimes instances where ~ change in planning objectives can demand changes in technology, even at a very basic level. For instance, the adoption of the comprehensive basin planning philosophy had a major impact on the hydrologic data requirements for planning studies. The , result was an increase in emphasis on regional correlation analyses and , the development of techniques that would provide coordinated estimates , of streamflow quantities at numerous points within a basin. Although there are situations in which the change in planning objectives stimulate new developments in hydrologic engineering methods at the basic data analysis level,it is not usually necessary for the hydrologic engineer to consult extensively with planners to ascertain the specific requirements Ifor the new techniques. A perceptive hydrologic engineer would probably discern the shift in emphasis and the resultant impact on requirements for hydrologic data, but he might find it necessary to consult with planners to establish the requirements for relative accuracy of the hydrologic data because of the large influence of the planning study objectives on data accuracy needs. , As the results of hydrologic engineering investigations become more the input into a planning analysis rather than the input into another hydro- logic analysis, there is an increase in the extent to which the hydrologic ~ngineer must coordinate modifications of existing techniques and development If new techniques. Hydrologic investigations which are closely associated ~ith important planning decisions can be greatly influenced by relatively 'inor changes in planning objectives, and the hydrologic engineer must oordinate closely with planners to insure that the hydrologic studies re relevant to and commensurate with the planning objectives. TRENDS FROM THE PAST Computer programs that incorporate many of the existing hydrologic gineering techniques have enabled the hydrologic engineer to provide 5