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()"'" c") ~ ^ \.Ju ~:iD 47. Duration Curves Flow duration curves of 115 of the stat ions in this section represent natu- ral unregulated conditions of flow, Other investigators may deem it neces- sary to apply definitive criteria for the identification of natural flow, but,for: this report it was arbitrarily decided that essentially natural flow-duration relations could be developed from,all years of record at all stations except as follows: (1) For station e, South Fork Republican River near Benkelman, records were used only prior to closure of Bonny Reservoir. (2) For lower RepublicanRiver stations 8, 13, and 14, all records were used prior to clo- sure of Harlan County Reservoir in November 1952, thus not evaluating the possible effect of older reservpirs and diversions in the headwaters. (3) For_' stations on Smoky Hill and Solomon Rivers, records were used only for the years prior to respective closure upstrea:m of Ced.ar Bluff, Kanopolis, Kir- win and Webster Reservoirs. The possible effect of these reservoirs and those on Republican River was not evaluated for the cmaIn-stem stations on Kansas River below Republican River. (4) On the main stem of Arkansas River, the stations from near Wichita to Arkansas City were considered not to have been significantly affected by irrigation developments during the pe- riod, and by John Martin Reservoir. However, duration curves for natural flow conditions were not prepared for the seven stations upstream, because the period of natural flow conditions was too short. (5) For stations below Fall River Reservoir on Fall River and Verdigris River, only records prior to 1949 were used. Flow-durat ion curves of natural flow may be used to de- fine the rate of flow per unit area of their drainage basins. For the 115 sta- tions in this group, the discharge scale is shown as cubic feet per second (abbreviated to second-feet or ds) per square mile. Flow-duration curves for established regulated.conditions are included for three Smoky Hill River stations below Kanopolis Reservoir, seven upper Ar- kansas River stations and two Fall River stations below Fall River Reservoir. The discharge scale for these curves is shown in cubic feet per second be- cause these data are applicable onlyat one pointon the river. Users of these curves should fully understand their limitations. Althbugh their periods of regulated records have been extended to the base period 1921-56 by the same methods used for extending records of natural flow; the curves define only the extension of the observed short pattern of experience. If the man-controlled operational plan of the reservoirs should change in future years, the regu- lated flow-duration curves would also change accordingly. The following factors are applicable to all figures in th.is section. The sta- tions are arranged in downstream order. Open circles on each figure show the flow-duration relations for the period of observed ,data. This period is defined in the explanatory box and is either for the complete periodof record if cons idered unregulated or for the period either before or after regulation. Solid-line curves on each.iigure show the regional flow duration curve adjust- ed to the base period 1921-56. The significance of the shape and other prop- erties of these flow duration curves will be described in subsequent sections of this report.