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<br />CYCC has modified the repair plan for the drainage in Area 41. <br />Presently, the plan calls for excavating approximately 70,000 CY of <br />material from the drainage and hauling this material to Area 51 for <br />disposal. This will reduce the drainage gradient from over 40~ to less <br />than 24%. This is the maximum gradient that would occur in this short <br />segment of drainage, the overall gradient is approximately 18%. <br />CYCC is planning to riprap the drainage bottom after the drainage has <br />been reconstructed. A review of Table 3.2 in Appendix II of the permit <br />revision demonstrates that the approved channel would have required <br />riprap. <br />A point that should be brought out is riprap is a channel armoring <br />which requires no maintenance if sound and durable rock is used. As <br />per the attached report, which can be inserted into Appendix I, Channel <br />Design, CYCC will riprap the drainage bottom with suitable material. <br />It is anticipated that after several growing seasons vegetation will <br />become established in the drainage bottom, and it will then blend in <br />with the surrounding vegetation. Coarse-grained rivers develop a <br />material armoring similar to riprap which maintains short steep <br />segments (riffles) in the profile, between flat segments (pools). <br />Therefore, riprap is a natural appearing means of stabilizing a channel <br />that should not interfere with the postmining land use. When properly <br />designed and placed riprap can provide for long term stability. <br />MLRD COMMENT: <br />Erosional Stability of Reclaimed Drainages (other than Area 41) <br />The plan presented in the application for stabilizing oversteepened, erosive <br />channel segments consists primarily of structural control (rock riprap). <br />While we have some specific concerns which are detailed below, the riprap <br />specifications are fundamentally sound, from an engineering perspective. <br />However, the Division does not find acceptable the use of structural <br />controls as a substitute for lower channel gradients or as a remedial action <br />to be employed when reclamation plans are not adhered to. <br />