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<br />U018SJ <br /> <br />Soil <br /> <br />Soil effects' on the amount Of runoff expected from anarea can <br /> <br />be quite striking: Differences in the amount of infiltration between <br />. <br />two soil types under identical conditions of vegetation cover may be <br /> <br />as great as a factor of 10 (ASeE, 1949. p. 48). In general, sandy <br /> <br />soils and soils .of open structure, such as S01'lle fdable silt lqams. <br /> <br />may have 'infiltration capacities from 0.5 to 1 inch per hour; s.oils <br /> <br />. <br /> <br />in the in.termediate range of infiltrations typical of many loam soils <br /> <br />in agricultural r~gions, ;h~ve iqfiltrationcapacities of 0.1 to 0.5 <br /> <br />inch per hour; and soils of the low infiltration group, characteristic' <br /> <br />of heavy loams- and clay soils, may have infiltration rates as low as <br /> <br />0.01 to 0.10 inch per hour. <br /> <br />More specific information may be avail- <br />, . , <br /> <br />able from' local soil ill_filtration and permeability measurements. <br /> <br />When infiltration capacity is determined .from local. infiltrometer <br /> <br />. <br /> <br />measurements rather than hydx;ograph analyses, the quantities must <br /> <br />be used with caution since, in general, iqfiltr,ome'tersgive relative <br /> <br />rather than exact quantitative measures of infiltration. <br /> <br />Diebold (1954) reports relationship of permeability of 4.1llsoil <br /> <br />series in the Southwest to the silt coutent of those soils and gives a <br /> <br />Oasis for estimating permeability of a series., Relative infiltration <br /> <br />and permeability are given in the description of soil-series. More <br /> <br />than 1,2.00 soil series have been desccribed in the Southwest (U. S. <br /> <br />34 <br /> <br />~ <br /> <br />