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• APPENDIX IV-4 <br />CULVERT SIZING - X34 <br />Culvert #34 will pass water under the rock ramp at the base of the key cut <br />in the 5A highwall <br />Peak Flow: (from peak rates of discharge for small watersheds 24 hr, type <br />II storm distribution tables) <br />Area = 9.0 Acres <br />CN = 90 (rock outcrop, gravel yard, overburden piles, soil <br />class D) <br />Grade = steep (16%) <br />Peak flow = 17 cfs/inch of runoff (Figure S-lA) <br />• 10 yr. 24 hr. precipitation = 1.7 in. <br />Runoff = 0.84 in. for 1.7 in. rainfall and CN = 90 <br />Peak Discharge = 14.3 cfs <br />24" Culvert: <br />Slope = 0.089 ft/ft <br />N = 0.0255 for corrugated, galvanized steel culvert <br />Q = 1.486 AR 2/3 S 1/2 <br />N <br />AR 2/3 for 24" Culvert = 1.979 <br />Q = 34.4 cfs, OK for flow. <br /> <br />(REV. 4/29/86) <br />