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Temnorarv Postmine Channels <br />• T-], T-2, T-3 (temporary) <br />Permanent Postmine Channel <br />Lower and Upper Refuse <br />Elk Creek Postmine Channel <br />IIW-1 <br />All diversion ditches aze designed to safely pass the peak flow from the 70-yeaz, 24-hour storm event. <br />The Elk Creek postmine channel is designed to safely pass the peak flow from the 100-yeaz, 24hour <br />storm event. All hydrologic and hydraulic inputs and results are shown on the SEDCAD computer <br />printouts in Sections 9 and 10. The locations of the ditches are shown on Maps 2.05-M4, Drainage <br />and Sediment Control Plan, and 2.05-M5 Postmining Topography. <br />The ]00-year, 24-hour peak flow for Elk Creek is ]07.Ocfs (using a conservative CN of 60). The <br />methodology and assumptions used to determine the peak flow are included in previously approved <br />• submittals (refer to Section 2). The existing, proposed, and postmine channel profiles for Elk Creek <br />aze shown on the Elk Creek Profiles (Map 2.05-M7). <br />A berm will be constructed to sepazate Ditches D3 and D4 and to separate Ditches DS and Dl. The <br />height of the berm will be at least 7 foot higher than the high flow mark of the ditches. A summary of <br />channel inputs and results are shown on the attached Figures. <br />Channel outlets have been designed for Ditches D4, D6, and D7. A conservative design flow of 4 cfs <br />was used in the designs. Channel downdrains to EIk Creek will be armored. Channel designs are <br />provided in Section 11. <br />Downdrains will be incorporated into the slope stabilization area. The downdrains will be field-fitted <br />as the slope area is graded. Atypical downdrain configuration is shown in Figure 7.1 and typical <br />locations are shown on Map 2.05-M4. <br />L <br />TR-43 Revised September 2003 <br />