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• The shape of the reclaimed channels was assumed to be trapezoidal with 3H:1V side slopes as a <br />worst case condition. The side slopes will be no steeper than 3H:1 V. <br />The channel bottom width was also calculated using SEDCAD 4. Attachment 13-12, Drainage and <br />Sediment Control Plan, shows all input and output information. All reclaimed stream channels will be <br />conservatively constructed to these measurements, Typical post mining channel profiles are shown on <br />Exhibit. 20-2, Post Mining Topography. The typical section will be used the entire length of the <br />reclaimed channel. Figure 13-12.3 presents is a summary of the post mining channel designs. <br />After the watershed has been graded and the location of the drainage channel determined, the channel <br />will be constructed to the required shape. All drainages will be inspected for stability according to the <br />rill and gully plan in Tab 22, Revegetation Ptan. Maintenance or monitoring that may be necessary as <br />a result of the inspections will be submitted to the Division for review and, if necessary, approval. The <br />side slopes of the meanders of the reclaimed drainage channels will he protected from erosion by <br />revegetation with drainage seed mix and shrub plantings according to Tab 22, Revegetation Plan. <br />Maintenance of reclaimed drainage channels will. be identified according to the Rill and Gully Plan. A <br />summary of the pre- and post mining drainage characteristics is shown on Table 20-2, Pre- and Post <br />• Mining Drainage Summary. <br />Runoff during the spring of 2003 caused significant erosion of approximately 2,450 feet of natural <br />channel that connects the eastern edge of the North Pit and Pond 011. In order to remediate the <br />damage, SCC wilt reconstruct the channel using a backhoe and other small equipment to minimize <br />additional disturbance. In general, the existing channel will be re-configured to have stable side slopes, <br />a 2 foot wide bottom, and a minimum of 0.3 feet of freeboard. <br />Re-construction activities will require temporary disturbance of surface area along side the actual <br />channel to allow access and construction. It is planned that the topsoil along side the existing channel <br />will be stripped back far enough to allow the channel side slopes to be reconfigured and stabilized. <br />Once a section of channel is reconstructed the topsoil will be re-spread and the backhoe w'dl proceed <br />working on the next section of channel. Equipment access will be via an existing road/trail that <br />currently exists along the drainage bottom, All disturbed areas, including the reconstructed channel, <br />will be re-seeded using the approved drainage seedmix. <br />As shown on Exhibit 20-26, Post-Mining Channel Profiles IYPM-121, grades along the length of the <br />channel range from around 9 percent to about 25 percent. The predicted flow in the reconstructed <br />• channel (after construction of Pond 011A) will be a maximum 6.0 cfs at velocities ranging from 3.8 to <br />4.99 fps on grades from 9 to 18 percent. It has been determined using SEDCAD analyses that <br />sections of the channel with less than 18 percent grade will be stable as a vegetated channel, while <br />sections over 18 percent grade will be vegetated and have wood or rock check dams installed in <br />TR-24 10 Revised 12103 <br />