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Under short grass conditions, the channel is more prone to erosion than during tall grass <br />conditions. Consequently, stability is evaluated under short grass conditions. Retardance classes <br />of D and E are typically used for stability analysis of vegetated channels (Warner, et. al., 1998). <br />Tall grass conditions are used to determine channel capacity. The tall grass affords a great deal <br />of resistance to channel flow as a function of stem base) area and by laying over during high <br />flows. The higher the resistance, the higher elevation of flowing water in the channel. <br />Retardance classes of A through C (especially A and B) are used for the capacity analysis <br />(Warner, et. al., 1998). <br />SCC assumed Eaix vegetated conditions for the Old Wolf Creek area, and used retaxdance values <br />of Class E for stability and Class C Eor capacity. <br />Freeboard <br />SCC designed all postmine channels with a minimum freeboard of 0.3 Eeet. <br />3.2 Turf Reinforcement Mat Channel Design <br />Turf reinforcement matting (TRM) allows 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, ox Elattex) and under medium to high flow conditions. <br />SCC plans to use TRM as a channel lining material, were appropriate. Typical matting <br />construction consists of athree-dimensional corrugated matrix (with either coconut/straw ox <br />polypropylene fiber) that wilt 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 (these products have been approved by CDRMS as channel <br />lining materials at other SCC mines) in constructing the Old Wolf Creek Area channel are <br />manufactured by the following companies (this is not an all inclusive list; if other products are <br />available they may be utilized if [hey meet the minimum design characteristics): <br />• American Excelsior Company <br />• Colbond Geosynthetics <br />• Greenfix America <br />• North American Green <br />• Proper 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 toughness coefficient (i. e., Manning's n) and the <br />limiting relociry values were hand entered. Examples of manufacturer's published performance <br />values for select TRM products under bare soil conditions are summarizes in Table 3, Turf <br />Reinforcemenl~Mat Performance Guide. Manufacturer's performance specifications for these products <br />are found in Attachment B, Turf $einfor~ement Mad DeriBn and Inrtalladion Information. To calculate <br />the greatest potential instability (i. e., the highest velocity) SCC selected a roughness coefficient <br />value of 0.023, which is less than any of the manufacturer's published values. SCC selected 9.0 <br />Old Wolf Creek Axen Remediation Plan S Revised 06/07 <br />