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<br />16 <br /> <br />Distribution of Base Flow in ~ummer' and Winter <br /> <br />Previously described maps show average yearly values. However, <br />the quantity of base flow varies during the year in a cyclic pattern. The <br />quantity during the pedact July through September, herein designated as <br />summer. is the mOl'e useful pOI"tion for agricultural pur'poses hecause it is <br />available in the stt'earn channels dUI'ing the primary irrigation season. <br />Figure 6 shows the variation in the average quantities of base flav.' fOl' the <br />summer period. The values are in cubic feet per second per squ2l'e mile <br />for the standard hase period (1923-62 in most areas) and are plotted at the <br />centroids of the hasin.s Qt' sub-basins for the 84 long-tel'm stations where <br />summer means are available. The summel' base flO\v diffel's mal'kedly be- <br />tween adjacent basins, as did yearly base now, but again yields 31'C gener- <br />ally highcr in eastern Kansas. <br /> <br />Figul'c 7 shows the ratio of the rate of summer base flow to that of <br />the complete year. Thus, a value of 1.00 indicates that the rate of summer' <br />base flow averages the same as for the complete yeaI'. I{atios scatter be- <br />tween adjacent stations but indicate some regional pattern. The highet' <br />z'atios in northwestern Kansas may he partly caused by gl'eater depen- <br />dence of base flow in this I'egion on rain storms which are most prevalent <br />in the summel'. <br /> <br />Figul'e 8 shows the l'ange in the avel'age quantities of base flow in the <br />winter period, .lanuary through i\lal'ch. These values may prove mOl'e <br />useful than those of summer base flow in futLll'c studies of the hydrologic <br />characteristics of base flow because the effects of evapotranspiration, <br />which are quantitatively unknown, arc at a minirnum. <br />