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en,-, 'l?" V..U . . 5. DEVELOPMENT OF LOW-FLOW FREQUENCY CURVES Most records of streamflow contain some information on drought expe- rience but the information is not in a form useful for future planning, This section of the report defines the records available, and describes how data such as the 30-day drought flows are abstracted from each year of record, arrayed in order of magnitude, and plotted on a frequency scale to depict the 30-day flow that might recur as an annual minimum at frequencies ranging from once in 2 years to once in 50 years, Records Available An inventory of the streamflow records and discharge measurements collected in Kansas and adjoining areas through September 1959 is shown in table 1. A solid bar indicates that gaging station records consist of daily stages and discharges in at least part of each of the water years indicated, and an open bar for some earlier years indicates that only records of stage and occasional discharge measurements are published. The inventory in- cludes all sites for which either daily discharges or miscellaneous low-flow discharge measurements have been published in U, S, Geological Survey re- ports on the surface water supply of the United States, Also included are 62 partial-record sites where periodic low-flow meas- urements have been obtained since October 1953 by the Division of Water Re- sources, Kansas State Board of Agriculture, as part of a cooperative inves- tigation with the Geological Survey. At 18 sites identified by cross-hatcheq open-bar lines, several measurements were obtained when the flow was largely from ground-water supplies, These measurements are analyzed in this report to extend the geographic coverage of low-flow frequency informa- tion. At the other partial-record sites, most of the measurements in recent years have been made at times of no flow or at times of direct runoff so that not enough data are available for analysis, All sites in table 1 are listed in the downstream order used by the Survey since 1951. The gaging stations are identified by numbers in the left column of table 1 if operated by the Kansas district and by letters if operated by offices of the U. S. Geological Survey in adjoining States, Numbers are also shown for the partial-record sites analyzed in this report, Complete low-flow frequen- cy curves have been developed for each gaging station that has six years or more of usable record prior to April 1957; the locations of these sites are identified by triangles on figure 1. Less complete low-flow frequency data have been estimated at short-term gaging stations and partial-record sites identified by x's on figure 1. Users who are interested in the location of the sites where records are not yet adequate, and which are not shown on figure 1 may consult figure 1 of Technical Report No, 1.