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<br />~~ <br />• <br />4.4 Control Pracfice Factor <br /> <br />The SEDCAD+ Model considers the sediment loss from an area with a given cover and conservation pratxice, <br />az compared to tha[ of a field in continuous fallow, by introduction of a Control Practice (CP) Factor. The <br />CP is a function of Canopy Cover and Percent Ground Cover. The CPs used in this analysis were selected <br />from the SEDCAD+ guidelines. <br />CP Factors <br />Condition CP Value and Reference <br />Asphalt Paved Areaz 0.003' <br />Mulched and Undisturbed Oak Brush/Grass Areas 0.013r <br />Coal Product 0.05' <br />Rock Outcrop 0.05` <br />Gravel Paved Areas 0.08r <br />Industrial Areas 1' <br />' Estimate <br />Z Mulched areas equaled to a CP Factor for Permanent Pasture, Rangeland, Idle Land, and Grazed <br />Woodland, no appreciable vege[a[ion canopy, grass cover <br />~ CP Factors for Rock Cover, 80% Rock Cover <br />' Typical Factor for Bare Soil Condi[ions, compac[ed <br />5. DITCH AND CULVERT DESIGN PARAMETERS <br />The ditch design is the West Elk Mine standard triangular-shaped ditch with 2-horizontal to 1-vettipl <br />sideslopes, with three exceptions. D3-4B is a vertical sided mnaete ditch. D3-lA is an earthen Swale with <br />3.5:1 side slopes. D3-2A is a shotcreted triangular shaped ditch. A freeboard of 0.3 fool waz used- The <br />channel bottom matrix of erodible ditches was described az a noncolloidal coarse gravel with a Manning's "n" <br />of 0.025. The maximum allowable velocity of water over such erodible soils is 6 feet per second (fps). All <br />culverts are circular. The intake ends of all culveru are mitered into the fill slope. <br />6. LIMITATIONS OF, AND EXCEPTIONS TO, THE <br />SEDCAD+ MODEL <br />No limitations of the SEDCAD+ model were encountered in this analysis. Although the SEDCAD+ <br />demonstration provides design information for culverts, alternative designs were provided for culverts using <br />the nomography from the Hnndbook of Sree! Drninage & Highway Consrrucrion Products, American Iron and <br />Sree! Institute. <br />7. SEDCAD+ ANALYSIS INFORMATION <br />Enclosure 1 is a SEDCAD+ demonstration of the drainage system. <br />6 <br />