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minor, with the separation of the two occurring at a drainage area of 500 sq mi in eastern Kansas and 1,000 sq mi in western Kansas. The need for each type of data and the methods of obtaining the data are described in the following sections. Current-Purpose Streamflow Data Current-purpose streamflow data are needed at many sites on a day-to- day basis for the management of water, for the assessment of current water availability, for the management of water quality, for the forecast of water hazards, and for the surveillance necessary to comply with legal requirements. This classification represents the need for information on the actual flow at any moment, or during any specific day, week, month, or year. Furthermore, these data are used currently for a particular purpose, and the interest is in flows as they occur, as well as in the historical record. Streamflow data obtained for current use are of significant value. A current knowledge of the rate of flow and storage at different points in the system provides a basis for water-management decisions that govern the economic efficiency of the operation. Current-purpose-data stations are considered separately in this study because (1) justification can be related to specific needs, (2) the loca- tion of the stations and periods of operation are usually specified with- out regard to possible transfer value of the hydrologic data, and (3) the financing is usually provided by the user of the data. Current-purpose data are obtained by the operation of gaging stations to meet the specific requirements of the particular water-management system. Data for Planning and Design of Water Projects Designers and planners of water-related faci lities increasingly utilize the statistical characteristics of streamflow rather than flow at specific times. The probability that the historical sequence of flow observed at a given site will occur again is remote, and predictions of future flows needed in design and planning must consider al I probable flows and sequences of flow. This information enables prediction of future streamflows, not in terms of specific events, but in terms of probability of occurrence over a span of years. For example, many highway bridges are designed on the basis of the flood that will be equaled or exceeded once in 50 years on the average; storage reservoirs can be designed on the basis of the probability of deficiency of storage for a given draft rate; the water available for irrigation, dilution of ' waste, or other purposes may be stated in terms of the mean flow or probability of flow magnitudes for periods of a year, season, month, week or day. In addition, there Is a 10