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r.'1..,..,,(, 9 AHEM. DlSTIUBUTIO"; OF B,\SE Fl.o\\. 1;'\ KA";SAS Although base flo\'.' avel'ages less thanone-foul'th of the total stream- ntH":, it is une of the most impol'tant reSOUI'cefi o~ Kansas. as many water users are dependent upon base flow fOl' their .supply. especiall,Y during lo\\'- fluw pel'iods. It is important to know how the magnitude of base flow var- ies thl'oughout the State. how it varies \vith the seaSGns and months, how dependable it i.s, and ho\.... its magnitude and expectancy can he l'elateJ to eel.tain factors. The areal distl'ibution of base flow and its celation to total flow, gl'ound-watcl' supplies, dil'ect runoff, and seasons of year is descl'ibed in this chaptcl'. The dependability of base flow and means 01 de- fining it at ungaged sites will be (H'esented in following chapters. \lap of 1\lean Base Flow \'alues of mean base flow for the standard haRe period 31'e listed in Technical 1'epol't 6A and in table J (p.lll ~ for the 105 gaging: stations shown in figuce 1. If basin boundaries ol'drainage uutlineswel'e ul'awnabove each uf these gaging stationf;, and if the streamline;; wel'c removed for clarity. a map would l'emain outlining the basins and sllh-basir.s he tween each gag- ing station such as shown in figlll'c 2. F'or instance, in the Beavel' Creek basin in nOI'thwcstern Kansas, the al'ea enclosed by lines t;outh\'vest of sta- tion 4 defines the basin of the most upstl'cam station. That area plus the area between stations -t and 5 outlines the total basin above station 5. Technical report fj!\ show.s that the mean hase flow of station -l fo)' the ex- tenJeu ha~e pedod b -t,2~) cfs. v.'hich from 1.-tfiQ sq, mi. of total area is equal to 0.0029 ds pel' sq. mi. This value is plotted at the ccntn..id of area above station 4, At station 5 the mean hase now is 7.18 cfs. But if -L2!l cfs is contdhllted by the portion of the basin above station 4 then 2.00 cfs must be contributed b.y the sub-basin between stations 4 and 5 where the intervening area is 1,710 minus 1.460 01' 250 sq. mi. Unit base flow pel' sqllal'e mile between stations 4 and 5 would thcI'efol'e he 0,012 cfs per' sq. mi. as plotted at the centl'oid of this sub-hasin. Unit hase no\',' pel' square mile has been detel'mined at 105 suhal'eas thl'oughout the State by the fore- going pl'ocedtll'e and is shown on figuI'e 2, Figure 2 ill11stl'ate~ that western Kansa~ basins ~-ield less mean base flow pel' square mile than eastern Kansas ba:-:ins. and that the most produc- tivC' basins al'e abcl\-e gaging stations "1''', "5" and "t" in :\lissouri and Oklahoma neal' the southeastel'n corner of Kansas (Spring Rh^er basin). These genel'al statements al'e partly suhstantiated by the increase in the progTessive eastward magnitude of avera~e annual rainfall which inc reases fnHn 16 inches pel' year in \":estern Kansas to -14 inches pel' yeal' in south- eastern Kansas, However. the cause for' lal>ge differences in mean base