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4 <br />! • by limiting soil detachment, shortening the distance the sediment <br />travels, or providing more opportunity for the sediment to be deposited. <br />The shape and length of slopes, and slope gradients of the regraded <br />surface mined land all influence infiltration, overland flow and <br />erosion. Zingg (1940) observed overland flow and soil loss on steep <br />slopes during a short rain whereas more moderate slopes produced no <br />overland flow. He attributed this difference to greater opportunity for <br />depression storage on more moderate slopes. He found that doubling the <br />degree of slope increased the total soil loss 2.8 times, while doubling <br />the horizontal length of slope increased the total soil loss 3.03 <br />times. Mosley (1973) found that on a 5 degree slope, about 60 percent <br />of the soil detached by raindrop impact moved downslope and 40 percent <br />. moved upslope. The proportion of soil moved downhill increased with <br />increased slope until on a 25 degree slope about 95 percent of the <br />soil detached by raindrop impact moved downhill. A concave slope will <br />probably deliver less sediment and be less susceptible to erosion by <br />overland flow than a straight or convex slope (Schumm, 1477, p. 7l ). <br />Nassif and Wilson (1475) demonstrated that the greater the slope, the <br />lower the infiltration capacity. So, on steeper slopes, not only will <br />a greater proportion of precipitation result in overland flow but the <br />velocity of the overland flow will also be greater, as shown by Manning's <br />equation: <br />V = 1.44 d 213 S 1/2 <br />n <br />where V is the flaw velocity, n is a roughness coefficient, d is the <br />depth of flow, and S is the slope. Not surprisingly, Kilinc and <br />Richardson (1973) experimentally demonstrated a dramatic increase in <br />