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12 TECHNIQUE OF SEPARATION Base-flow amounts were determined by analyses of discharge hydro- graphs. These hydrographs form a chronological graphic picture of the total flow of a stream and can be used for separation of the flow into its various components, as shown schematically in figure 2. The upper line on figure 2 is a representation of a stream hydrograph plotted on semi- logarithmic paper. The area in solid black immediately below the top line represents the portion of total flow derived directly from precipitation on the channel. The dark-shaded area represents the surface runoff. The light-shaded area represents the interflow, and the widely dotted portion represents the ground-water flow. Bank storage, consisting of water tem- porarily seeping into the banks from the channel during a flood rise, has not been designated in figure 2, and is not considered a separate compo- nent of flow. In Kansas, the dependable supply of flow exclusive of that directly con- tributed by storm rainfall must be determined. This can be done by sepa- rating the total flow into two parts as shown by the heavy dashed line on figure 2. The area above the dashed line represents direct runoff and the area below represents base flow. The background and techniques for sepa- ration are described in the following paragraphs. The accompanying illus- trations (fig. 3-7) delineate each of the successive steps. Separation of total flow into base flow and direct runoff is inexact, particularly during periods of recurrent precipitation. However, certain facts are available to reduce the possible uncertainties: the entire flow is base flow toward the end of periods of no precipitation; adjacent recessions on the hydro graph have similar shapes; and direct runoff ends about the same number of days after the peak for all rises. Because these facts are clearest on the discharge hydro graph, the hydrograph is used as a tool for separation. The first step is to draw hydrographs of daily discharge on semi-log- arithmic paper for each year of record for each station. A bar graph of daily precipitation at a nearby station is added at the bottom of each hydro- graph to identify periods of excess precipitation and periods of no precipi- tation. Figure 3 is an example of such a hydrograph for Neosho River at Strawn, Kans. and of the daily precipitation at Cottonwood Falls, Kans. during the period January to July 1961. Little or no precipitation occurred in ,January and in the last half of June and early July. The hydrograph for each of these periods shows es- sentially a continuous recession. The total flow probably consisted only of