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~J <br />CHAPTER VI <br />PHYSICAL AND HYDROLOGIC CHARACTERISTICS <br />Soil erosion is, in part, a function of infiltration capacity. <br />Lower infiltration capacity results in greater overland flow and an <br />increased opportunity for surface soil loss. Since one of the objec- <br />tives of this study was to determine the physical and hydrologic <br />characteristics of regraded coal spoils, infiltration measurements were <br />made at each site and soil and site characteristics were determined. <br />Infiltration Rates <br />~~H+i x; <br />Hortan's Equation <br />Horton (1940) developed a versatile model far describing infil- <br /> <br />tration rate against time from an infiltrometer experiment with constant <br />rainfall application. Horton's equation is: <br />f = fc + (fo-fc)e-kt <br />where: <br />f is infiltration rate at any time, t <br />fc is final infiltration capacity <br />fo is initial (t=o) infiltration rate <br />k is decay coefficient. <br />The versatility of Horton's equation comes from the flexibility of <br />the decay coefficient which incorporates all soil features, static or <br />dynamic, contributing to the decrease of infiltration rate with time. <br />For this study the equation was fit to the replicated data collected <br /> <br />at each sampling site by using the simplified method developed by Norton <br />49 <br />