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5 <br />sediment concentration in overland flow with increased slo a or, slo es <br />P P <br />i <br />less than 45 percent using simulated rainfall. Similarly, Barnett and <br />Rogers (1966) used simulated rainfall to conclude that the single best <br />predictive factor for soil loss was slope gradient to the 1.7 power. <br />They also found high clay or sand content to be associated with <br />decreased erosion while high silt is associated with increased erosion. <br />The principles of infiltration, particularly as they relate to <br />dynamic regraded surface mined land, are not perfectly understood. <br />Under natural or simulated rainfall at a constant intensity high enough <br />to produce overland flow, the infiltration capacity of a soil generally <br />decreased with time asymptotically, towards a final, constant infil- <br />tration capacity. The extremes of viewpoint (Horton, 1940} are: (1) the <br />infiltration rates are governed by the soil mass, with decreasing <br />capillary drive as the wetting front advances into the soil (Green and <br />Ampt, 1911; Phillip, 1957; Mein and Larson, 1971) or (2) soil surface <br />influences, which are dynamic as raindrops strike the surface and over- <br />land flow moves over the surface, Experimental evidence by Horton <br />supported the latter viewpoint for sails with considerable bare soil <br />exposed to direct impact by raindrops. The equations presented by Green <br />and Ampt, Phillip, and Mein and Larson apply for the most part only to <br />soils that are homogeneous and remain so throughout the time infil- <br />tration is occurring (Lehrsch, 1979). The equations also assume a <br />uniform initial water content in the sail. Nevertheless, decreased <br />capillary forces resulting from fine pores being filled with water <br />may contribute to decreased infiltration in some soils. Additionally, <br />