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9. n" rJn.~)'" tli.lt,}., KANSAS STREAMFLOW CHARACTERISTICS PART 1 FLOW DURATION by L.. W. Furness ABSTRACT Flow duration curves have been developed from daily records of stream- flow at 122 sites in Kansas and adjoining areas. These curves show the per- centage of time various rates of discharge have been equalled or exceeded. Thus, the general availability of flow at each site is depicted and such stream characteristics as dependability of low flows in times of drought or persis- tence of high flows in times of flpod a-re defined. Insofar as the limited pe- riod of observed data at a given site may be considered a representative sam- ple of long-term experience, the duration curve may be used to estimate the future general availability of streamflow at that site. The flow-duration data observed at individual sites have, by correlation with selected long-term records, been extended in time to reflect the 36-year period 1921-56 and ex- panded in areal coverage to reflect regional rather than local experience. The period 1921-1956 is one in which bothwe:t .ana.dry per'iodsare we11rep- resented a.nd therefore is a reasonable hasefor prediction purposes. The mean flows or yields of streams are readily determined irom their flow duration curves. Using duration data developed in this report the yields of Kansas streams in general are delineated on a map (fig. 130) by use of values of mean flow for the drainage areas above the farthest upstream gag- ingstations on each stream and its tributaries and the successive interven- ing drainage areas for th.e .gag,ing stations lying downstream therefrom. For convenience these areas are termed "sub-basins." This map reveals that mean flow decreases quite uniformlyacro.ss the State from a maximum of 0.8 cubic feet per second per square mile in southeastern Kansas to a hun- dredth of. that amount in some portions of western Kansas. To the extent that available records are criteria, the natural mean flow of most Kansas streams may be quite reliably estimated from this map. Mean flows for the base period 1921-1956 are compared with mean annual precipitation 101' es- sentiallythe same period. It is shown that for areas where mean annualpre- cipitation is in excess of 28 inches, or roughly the eastern half of the State, mean flow and mean annual precipitation are directly related within 16 per- cent, twe-thirds of the time. Methods for synthesis of flow-duration curves .for ungaged areas are de- veloped. . Curves and maps are presented from which may be derived five points and an average slope factor of the synthetic curve. The expected ac- curacy of the derived curve at th.es.e points is shown to vary from 7 to 27 per- cent, two-thirds of the time. Measurements of low flow at the site under consideration will improve the accuracy of the lower portion of the curve.