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<br />- 3.7, <br /> <br /> <br />0318~)S <br /> <br />witho.nly half as much channel. Thus, in a local. area. the relative <br /> <br />length of visible channels may be a helpful index to the expected <br /> <br />runoff in aTeas6f similar watershed conditions. <br /> <br />Effect of area <br /> <br />Area effects. on the runoff can be quite important in estimating <br /> <br />the total yield of ephll,mer,a.l .streams. The runoff in small local <br /> <br />storms.te'nds,to be absorj:led in t;he channel and ca'u.cause a marked <br /> <br />. reduction in the runoff per u.nit ",rea a$ the areas become lax:ger. <br /> <br />l.nAl1:~upper Cheyenne River basin runoff from a 50-acre watershed <br />. ,- r ' " <br /> <br />was appro<,imately 3 acre feet; ):lowever, runoff was only double <br /> <br />this from a 2.00-acre watersheCij,(~~$itley:an.dSc):lumm, 1961). <br /> <br />Kepple (1961) reports losses of 2.5-.acre foot per mile of dry chan- <br /> <br />nel in Arizona and estimates the maximum to. be much higher. <br />, - ~.,' , <br /> <br />Merely increasing the drainage area is therefore probably not the <br /> <br />. most efficient way of increasing the supply; this point is suggested <br /> <br />by data in table 3; wherein in general, although not always, the <br /> <br />larger drainage basins have tJ:le lowest unit area runoff (Cull.er, 1961). <br /> <br />Geology <br /> <br />Geologic rock type and the character of individual formations <br /> <br />can caus.e consid,erable variation in rUtloff wit):lin short distances. <br /> <br />Large expanses of alluvium of varying .porosity within a drainage <br /> <br />basin can have a notable effect on the runoff.. With consolidated <br />