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Frbrnary 1999 Yaart Mine * 13J2 Drainage and Srdiment Control Plan •7A <br />• vegetated channel <br />• riptap channel <br />Channel sections with shallow slopes or low flows are typically vegetated. Channels with steeper <br />slopes or higher peak flows have traditionally been stabilized with rock riprap. In 2007 SCC <br />incorporated turf reinforcement matting (TRIM) as an alternative channel lining material. Channel <br />designs are summarized on Figure 13-12.1, Postmine Ditch Design Schedule. The actual design <br />demonstrations are presented in Appendix 13-]2.3, Postmining Channel Design SEDCAD4 Results. <br />6.1 Vegetated Channel Design <br />Inputs to the channel utility sub-routine fat vegetated channels include: <br />• Peak flow <br />• channel slope <br />• channel geometry (triangular or trapezoidal shape; bottom width [as appropriate]; side <br />slope) <br />• retardance class <br />• freeboard <br />Vegetated channels tend to become unstable when flow velocities exceed 5ve (5) feet per second <br />(fPs)• <br />Peak Flow <br />The 10-year, 24-hour peak flow value is calculated with the hydrology component of the SEDCAD4 <br />model. Appendix 13-12.1 presents the hydrology demonstrations. <br />Channel Slone <br />Channel slope is the most critical parameter. The steeper the slope, the lower the allowable <br />velocity. The channel slopes were determined by direct measurement from the mine permit maps. <br />Channel Geometry <br />Existing channels (constructed prior to 2007) were evaluated assuming a triangular, or V-shaped, <br />configuration, with a 3H:1V side slope. In certain situations, SCC designed atrapezoidal- shaped <br />channel with a bottom width of either three (3) or 10 feet and 4H:IV side slopes. <br />The design parameters for peak flow, channel slope and channel geometry are summarized on the <br />Figure 13-12.2. <br />Retardance Class <br />The reclamation seed mixture SCC uses to revegetate reclaimed areas results in a mixed grass <br />community. Consequently, the vegetation type selected as the model input is mixed grass. <br />The flow resistance varies by grasses type and length. Retardance classes have been divided into <br />five classes designated by A, B, C, D, and E. SCS (1979) developed guidance for selection of <br />vegetation retardance classes and they are outlined in Table 13-12.6, Guide to Retardance Class <br />Selection. <br />~~ <br />Montgomery Watron Mining Group * 165 S. Union Baulea~ard, Suite 4G0 * Lakevoad, Colorado 80228 * (303) 7G3-5140 <br />TR-30 Revised 03/07 <br />