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6 BASE-FLOW DATA AVAILABLE The analyses in this report are based on records of streamflow that have been collected at 105 sites in Kansas and adjoining areas. For 84 of these sites, identified by solid triangles in figure 1, the streamflow records of at least 10 years duration have been used to define monthly values of base flow in order to develop base-flow probability curves at each site (fig. 12-95) and to develop regional base-flow relations for the State. For 21 sites, identified by open triangles in figure 1, streamflow records of less than 10 years duration have been analyzed to define the approximate base- flow relations shown in table 1, (p.lll). The total of 105 stations include all stations in Kansas with records long enough for analysis and with basins small enough (less than about 5,000 sq. mi.) for reliably separating the base-flow component from total flow. The basic information for these studies is contained in Technical report 6A, Base Flow Data (Busby and Armentrout, 1965). The report con- tains detailed information of the meaning of base flow, methods of compu- tations, and the following data for each of the 84 long-term gaging stations: (l) location of each site, (2) monthly and yearly mean base flow as com- puted from the records of total streamflow, and (3) two-thirds chance limits of likely values of monthly and yearly base flow during ungaged peri- ods, when these values are needed to extend the records to a long-term period common to all sites. The long-term period was selected by pro- cedures described in the following section. Selection of Base Period For statewide long-range water-planning purposes, base-flow rela- tions should be founded on the following criteria: (1) the period of record on which they are founded should be long enough to encompass a represen- tative sample of wet and dry periods; and (2) the relations should repre- sent the experience of the same standard period of years to permit un- biased comparison of basin characteristics. The available periods of streamflow records in Kansas are much too short to furnish an adequate sample of past experience for fully reliable prediction of future flows. But to obtain information now, it is necessary to select from the available records a long-term standard period, called a base period, that is as long and as representative as possible. Earlier low-.flow studies in this series of technical reports for Kan- sas had used the years 1921-56 as the base period, but for base-flow studies, daily streamflow records were collected at too few stations in 1921 and 1922