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• Following Phase II release and reclamation of the sediment control system, permanent drainage <br />installations were designed and installed for two sites at Chimney Rock to carry water off steep <br />slopes. Ditch 2 takes water from approximately 19 acres of the reclaimed East Pit which has <br />collected at the Facilities area and safely carries it off the fill slope into the AVF. Culvert CS <br />takes water from approximately 1.88 acres of Barren Ridge and drops it off the bank into <br />Stollsteimer Creek. The 10-year 24-hour storm of 2.1 inches was used for the sizing of these <br />permanent structures (Rule 4.05.3(3)). <br />The size of Ditch 2 was developed by using baseflow inputs from the peak discharges calculated <br />in Table 7-7-1 for ditches 2S1 and 2S2A (9.09 cfs + 5.21 cfs = 14.3 cfs), and adding it to the <br />drainage from 4.85 acres from the Facilities area and the cut slope to the south. A curve number <br />of 84 was used for the cut slope, reflecting fair rangeland on D soils. A curve number of 91 was <br />used for the Facilities area pad. Ditch 2 is designed as a trapezoidal rip-rap (D~o = 12") ditch <br />with an 8-foot bottom width, 0.44 feet deep. <br />The sizing of Culvert 5 was developed using a curve number of 83 for the reclaimed surface, <br />reflecting a cover of 64.3 percent (page 7-3). Culvert 5 is a corrugated polyethylene pipe with a <br />design Manning's n of 0.019. <br />SEDCAD design runs for the ditch and culvert are attached. <br />• <br />• <br />Rev. 12/19/97 <br />