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Appendix Exh7-14N -North Tributary, East Pit Ditch <br />The North Tributary of the East Pit Ditch is located in Section 15 of T3N, R93W. The alignment <br />of this ditch is shown on Map 41. This channel was designed following a revision to the <br />postmining topography approved under TR-63. <br />The ditch is designed to meet the requirements of Rule 4.05.3 for drainages less than one square <br />mile. The drainage area of this basin is about 76 acres. This requires that the channel be capable <br />of handling flows from a 10 year, 24 hour event. The steepest portions have a slope of about <br />12.5 percent. The overall length of the channel is about 3,500 feet. <br />As shown on the attached SEDCAD printout, the design storm produces a peak discharge of <br />about 0.09 cfs and a total runoff volume of about 0.04 acre-feet at Station 0. This design event is <br />based on a Curve Number of 56 and assumes that the entire drainage area is contributory to the <br />channel. <br />For ease of construction, a trapezoidal channel cross-section 12 feet in width will be employed. <br />Channel side slopes will be 3H:1 V slopes and a minimum depth of 4.0 feet will be used. For <br />design consistency, an average riprap diameter of 18 inches will be used. Using Figure 3 of <br />Exhibit 7, Item 14H, it can be determined that this size is more than adequate for the peak flow <br />and channel slope involved. <br />• <br /> <br />Exh. 7-14N-2 Revision Date: 7/25/06 <br />Revision No.: TR-63 <br />