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(.l fl. rl 'J" "i q un ! 'j 11. of converting the basic streamflow records to such useful forms has long been an insurmountable hurdle. But with electronic computers, this obstacle has now been minimized. More than 900,000 values of daily discharge have been electronically sorted, arrayed in order of magnitude and averaged by groups to supply the initial data for the studies in this repo rt. A flow duration curve is a useful device for analyzing the availability and variability of streamflow. Such a curve is developed by arraying all of the daily discharges at a selected site in order of magnitude, computing the per- cent of time the various rates of discharge are equalled or exceeded and then plotting the discharge rates against the corresponding percentages of time. Such a curve defines the frequency of occurrence of various rates of flow without regard to chronological sequence., Flow duraFon curves have had wide-spread use among engineers for many years. The curves are applicable for determining the probability of occur- rence of various future rates of flow. 2 and used for investigating problems dealing with water supply, power developments, sediment production, dilu- tionand disposal of sewage or industrial wastes. The shape of the flow dura- tion curves may be indicative of ground-water contribution to the stream, geologic structure, topography, soils, vegetation and other factors in the basin, 3 and provides a convenient and approp:t'iate means .of relating the char- acteristics of different streams. The area under the duration curve is a tunc..,. tion of the mean yield. This report undertakes to provide water-use planners of Kansas with di- rectly usable flow durati..on relations. It presents observed flow duration data at 122 gaging-station sit,,\! in Kansas and adjoining areas as experienc-eddur- ing their respective periods of record. Some of these records may reflect a preponderance of either the floods or droughts of a small basin that is not typical of the experience in that region. For future planning purposes,re- gional experience should be more representative of future expectancy and would be best defined if records for a long-term period common to all sites were available. Accordingly an effort has been made to develop flow dura- tion curves, adjusted by correlation techniques, to reflect regional influences and to be uniformly representative of the hydrologic experience of a 36-year base per iod 192:1 -56. As flow duration data are frequently needed at sites where no gaging- station records are available, this report also gives meth- ods for synthesizing data at these sites. A step in. the analyses included the development of a map (fig. 130) showing the variation of mean flow in Kansas which will prove useful in further studies. 2 Foster, H. A., 1924, Theoretical frequency curves and their application to engineering problems: Trans. Amer. Soc. Civ. Engr., vol. 87. 3 Lane, E. W., and Lei, Kai, 1950, Streamflow variability: Trans. Amer. Soc. Civ. Eng., vol. lIS, pp. 1084-1134.