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February 1999 Yoart Mine * 13-12 Drainage and Sediment Control Plan • 12 <br />The minimum channel designs for the rock riprap lined channels are summarized on Figure 13- <br />12.3. Given the uncertainty in determining riprap D;o for steep slopes with the PADER Method, <br />SCC adds an additional 3-inches to the model recommended D;o size. SEDCAD4 demonstrations <br />are presented in Appendix 13-12.3. <br />6.3 TURF REINFORCEMENT MAT CHANNEL DESIGN <br />Turf Reinforcement Mats (TRMs) allow vegetation to be used in areas where flow conditions <br />exceed the limits of natural vegetation (e.g., limiting velocities greater than 5 fps). They can be <br />used for steeper slopes (1.SH: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 athree-dimensional corrugated matrix (with either coconut/straw 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 />TR1bI products that SCC may use at the Yoast Mine are manufactured by the following companies <br />(this 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 />Channel stability was analyzed using the erodible channel sub-routine. The designs assume the <br />TRM is installed over bare soil. The channel roughness coefficient (i.e., Manning's n) and the <br />limiting velocity values were hand entered. Examples of manufacturer's published performance <br />values for select TRM products under bare soil conditions are summarized in Table 13-12.7, Turf <br />Reinforcement Mat Performance Guide. Manufacturer's performance specifications for these <br />products are found in Appendix 13-12.A, Tutf Reinforcement Mat Design and Installation <br />Information. To calculate the greatest potential instability (i.e., the highest velocity) SCC selected <br />a roughness coefficient value of 0.023, which is less than any of the manufacturer's published <br />values. SCC selected 9.0 feet per second as the limiting velocity value. <br />Channel capacity was analyzed using the vegetated channel sub-routine. The channel toughness <br />coefficient is automatically calculated by the model. The limiting velocity values were hand <br />entered (manufacturer's published limiting velocity values for select TRM products are <br />summarized in Table 13-12.7. The designs assume a mixed grass community 11 - 24" tall, which <br />corresponds to a "B" retardance class, and results in a higher surface water elevation. <br />The postmine channels at Yoast Mine lined with TRMs will be either three (3) or ten (10) feet wide. <br />The minimum channel designs for the TRM lined channels also are summarized on the Figure 13- <br />12.3. SEDCAD4 demonstrations are presented in Appendix 13-12.3. <br />TRM installation will be in accordance with recommendations developed by the Erosion Control <br />Technical Council (ECTC, 2006) or the individual manufacturer's recommendations. <br />General installation steps are as follows: <br />Montgomery Watson Mining Grosrp * 165 S. Union Bouleyar~ Suite 460 * Ivkewoad, Colorado 80228 * (303) 763-Sf40 <br />TR-30 Revised 05/07 <br />