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• Particle Size Distribution. SEDCAD+ provides a default particle size <br />distribution for both undisturbed and disturbed soils. These default distributions <br />were derived using a number of gradation curves from around the United States <br />for disturbed and undisturbed soils. They are intended to be typical <br />representative curves. <br />The default distribution representing undisturbed soils was utilized for <br />undisturbed and reclaimed areas. <br />Runoff Volume, V. Runoff volume is calculated by SEDCAD+ as previously <br />described in the SEDCAD+ Calculations portion of the Hydrology section, and <br />is considered to be an internal input. <br />Peak Discharge, Q,, Peak discharge is calculated internally within the <br />SEDCAD+ program as previously described, and is considered to be an internal <br />• input. <br />Soil Erodibility Factor, K. The majority of the soil types in the Grassy Creek <br />mine area are described as fine sandy loam, therefore from Barfield, et. al,, <br />(1981), Figure 5.5, page 330: <br />K = 0.24 <br />Representative Slope Length. The slope length is representative of the typical <br />slope length found on the subwatershed and the distance from the point of <br />origin of overland flow until the point that the slope decreases such that <br />significant deposition occurs or until flow enters a defined channel. A length of <br />250 feet was used for all subwatersheds. <br />Average Slope. The average slope is entered in percent and is the typical or <br />representative slope for overland flow for each subwatershed. Average slope <br />8 <br />