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Road Drainage Ditch 6 <br />Design Parameters: <br />Precipitation: <br />Use 10-year, 24-hour storm precipitation depth = 1.8 in <br />Land Use: <br />Undisturbed area = 19.51 ac with CN = 63 (Sagebrush - Hyd. Soil Gp. C) <br />Road surface (gravel) = 0.80 ac with CN = 89 <br />Maximum road grade = 3.0 <br />Ditch length = 1,395 feet <br />Ditch design =triangular ditch with 3:1 side slopes (see Figure 2) <br />Ditch surface material is alluvial silts colloidal <br />Limiting ditch velocity = 3.75 fps <br />Results: <br />Peak flow = 0.74 cfs <br />Peak velocity = 2.43 fps <br />Culvert 6 <br />Use same design parameters as Road Drainage Ditch 6 <br />Peak flow = 0.74 cfs <br />Diameter required = 18-inch CMP minimum, with a minimum of 2 feet <br />compacted cover, and riprap protection at the inlet and outlet <br />• CERTIFICATION <br />I, Richard Spotts, state that the information presented in the Access Road Drainage <br />Ditch and Culvert Design Report for Twentymile Coal Company was prepared by <br />me or by persons under my supervision and is correct to the best of my knowledge <br />and information. <br />Water & Earth Technologies, [nc. <br />Richard Spotts, P.E. <br />President <br />Principal Engineer/Hydrologist <br />• <br />