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SCC used retardance values of Class D for stability and Class B for capacity. <br />Freeboard <br />In accordance with Rule 4-05.3, SCC designed all postmine channels with a minimum freeboard <br />of 0.3 feet. <br />The minimum channel designs for the vegetated channels are summarized on Figure 20.1.2, <br />SEDCAD demonstrations are presented in Appendix 13-5, <br />Rock Riprap Channel Design <br />Prior to 2007, all unstable channel reaches (e.g., flow velocities greater than five (5.0) fps were <br />armored with rip rap. Riprap size was determined using the SEDCAD4 riprap lined channel sub- <br />routine, utilizing either the Simons/OSM (Simons, et al., 1982) or PADER "Pennsylvania Department <br />of Environmental Resources, Stover, 1993) method. <br />The minimum channel designs for rock rip rap lined channels are summarized on Figure 20-1.2. <br />Given the uncertainty in determining riprap D5o for steep slopes with the PADER method, SCC adds <br />an additional 3-inches to the model recommended size D5o size. SEDCAD4 demonstrations are <br />presented in Attachment 20-1. <br />i n <br />Turf Reinforcement Mat Channel Des q <br />Turf reinforcement mats (TRMs) allow vegetation to be used in areas where flow conditions exceed <br />the limits of natural vegetation (e.g., limiting velocities greater than 5 fps). They can be used for <br />steeper slopes (1.5H:1V, or flatter) and under medium to high flow conditions. <br />In select situations SCC may use TRMs as an alternative channel lining. Typical matting <br />construction consists of a three-dimensional corrugated matrix (with either coconutlstraw or <br />polypropylene fiber) that will anchor and reinforce roots and stems for long-term stability. In <br />addition, the TRM deflects flowing water away from the soil surface and increases surface <br />roughness. <br />TRM products that SCC may use at the II-W Mine are manufactured by the following companies (this <br />is not an all inclusive list; if other products are available they may be utilized if they meet the <br />minimum design characteristics): <br />• American Excelsior Company <br />• Colbond Geosynthetics <br />• Greenfix America <br />• North American Green <br />• Propex Geosynthetics <br />TR-59 16 Revised 05/07 <br />