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The channel bottom width is also calculated using SEDCAD 4. Attachment 13-12, Drainage and . <br />Sediment Control Plan, shows all input and output information. All reclaimed stream channels are <br />conservatively constructed to these measurements. Typical post mining channel profiles are shown on <br />Exhibit 20-2, Post Mining Topography. Figure 13-12.3 presents is a summary of the post mining <br />channel designs. <br />After the watershed has been graded and the location of the drainage channel determined, the channel <br />is constructed to the required shape. All drainages are inspected for stability according to the rill and <br />gully plan in Tab 22, Revegetation Plan. Maintenance or monitoring that may be necessary as a result <br />of the inspections are submitted to the Division for review emd, if necessary, approval. The side slopes <br />of the meanders of the reclaimed drainage channels are protected from erosion by revegetation with <br />drainage seed mix and shrub plantings according to Tab 22, Revegetation Plan. Maintenance of <br />reclaimed drainage channels will be identified according to the Rill and Gully Plan. A summary of the <br />pre- and post mining drainage characteristics is shown on Table 20-2, Pre- and Post Mining Drainage <br />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 will 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 will 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 (YPM-12), 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 011A1 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 beers determined using SEDCAD analyses that <br />sections of the channel with less than 18 percent grade uvill 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 />PR-02 10 Revised 03/05 <br />