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0'" "'j O'7Q tJ n ....;.l ~ I 13. DEVELOPMENT OF FLOW DURATION RELATIONS A flow-duration curve is a cotlcise portrayal of the variations of discharge ata site. It shows the percentage of time various rates of stream discharge are equalledor exceeded, information that is not apparent from a chronolog- ical record of daily discharge. This section of the report describes how the streamflow records of Kansas have been used to define the flow-duration data actually experienced at each gaging-station site andhow they were regionally adjusted and extended to a common long-term base period to make them more useful for water resources investigations. Records Available The collection of streamflow records in Kansas began in 1895 but contin- ued only sporadically during the early years. A more consistent program of data collection was initiated about 1920 but statewide coverage remained poor until the 1940' s. An inventory of the records collected prior to October 1958 in Kansas and immediately adjoining areas is shown in table 1. Records at gaging stations consist of daily stages and discharges in at least part of each of the years indicated by a solid bar line, or they consist of stages and oc- casional discharge measurements in some earlier years as indicated by an open ba.r line. The gaging station.s are identified by numbers in the left col- umn of table 1 if operated by the Kansas district, or by letters if operated by districts of adjoining States. Locations of these sites are identified on figure 1. Records at sites other than gaging stations, which consist gene.r- ally of occasional low-flow discharge measurements, are unnumbered and .are identified by.X's on figure 1. Low-flow measurements are inadequate in themselves to define flow duration curves but methods described in subse- quent sections of this report show how the measurements are used for esti- mating the low portion of duration curves at ungaged sites. The inventory in table 1 includes all sites for which daily discharg.es and miscellaneous low-flow discharge measurements have been published in the water-supply papers of the Surface Water Branch, U. S. Geological Survey. Also included. are 63 .additional sites where periodic low-flow measurements have been obtained since October 1953 by the Division of Water Resources, Kansas State Board of Agriculture, as a cooperative investigation with the Geological Survey. All sites are listed in the downstream order used by the Survey since 1951. The years of record shown are water years, which end September 30 of the indicated year. Flow Duration for Period of Record The daily discharges of all complete years of record were punched on a special tape designed as the means of feeding the raw data into an electronic computer, For the purposes of this study the computer was programmed, or electronically instructed, to sort the data and determine the percent of time