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24. flow duration relations, differences in concurrent experiences will result in a preponderance of discharges in different class intervals that will be re- flected as minor irregularities in correlation when one station is compared with another. The technique of combining the experience of several streams has been used to regionalize the flow-duration curve at each gage site. I[ In the area covered by this report there are 21 gaging station records of sufficient length to define flow-duration curves for the base period 1921-56. Some of these lacked a few months of record to complete this period and es- timates were therefore made for the miss ing periods by correlation with oth- er stations for the number of days of flow in each ra.nge of discharge. These 21 stations are referred.to as "pivot stations, "and are identified in the sub- sequent list of gaging-station descripti.ons. They are fairly well distributed throughout the State and those of comparable drainage area were compared with each other. Figure 2 illustrates the relation of three pivot stations in the northeastern region. In preparation of this figure, adjusted flow-duration data were pre- pared for each of the three pivot stations for the base period 1921-56. Data for each station were plotted as shown by dots on figure 64 for Delaware River at Valley Falls. Although not shown, in order to avoid a confusion of lines, the dots were connected by straight lines to avoid biased interpreta- tion of data. Values of discharge were read from these lines at selected values of percent of time. From similar plots for the other two pi.vot sta- tions, values of discharge were read for the same values of percent of time. Then on figure 2 discharges of'Valley Falls were plotted a,gainst the discharge of the same percent of time for the other two statLons. Smooth curves were drawn based on the plotted points. These curves were drawn with care so that the departures from the plotted points represent an averaging of experi- ence rather than distortion.of individual basic characteristics. The varia- tions in curvature are to be expected. They reflect the differences in bas in characteristics. The straight lines on figure 2 indicate the relations which would exist if the bas ins had identical yield characteristics. The combined experience of the three basins was then defined by averaging the curve val- ues of discharge from figure 2 at each indicated percent of time for Valley Falls as defined .by each of the other twopiVCit stations with the correspond- ing original discharges for Valley Falls. These avera,ged values provided the points for plotting the regionally adjusted flow duration curve for Valley Falls. The curve is shown as a heavy line on figure 64. Regional flow dura- tion curves for the other two pivot stations were then defined by the applica- tion of values from the regional curve for Valley Falls to the appr.opri"ate correlation curve on figure 2. The pivot stations .in Kansas on the main stems of the Republican, Kansas, and Arkansas Rivers were treated as separate groups. With one exception the remaining pivot stations were regionalized .not as simple groups of three but as an unbroken, multiple-connected network of stations across the State. This treatment sometimes required a second minor adjustment of a region- alized relation but the end result was considered more truly representative.