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The channel bottom width is also calculated using SEDCAD 4. Attachment 13-12, Drainage and Sediment <br />Control Plan, shows all input and output information. All reclaimed stream channels are conservatively <br />constructed to these measurements. Typical post mining channel profiles are shown on Exhibit 20-2, Post <br />Mining Topography. Figure 13-12.3 presents 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 is <br />constructed to the required shape. All drainages are inspected for stability according to the rill and gully <br />plan in Tab 22, Revegetation Plan. Maintenance or monitoring that may be necessary as a result of the <br />inspections are submitted to the Division for review and, if necessary, approval. The side slopes of the <br />meanders of the reclaimed drainage channels are protected from erosion by revegetation with drainage <br />seed mix and shrub plantings according to Tab 22, Revegetation Plan. Maintenance of reclaimed drainage <br />channels will be identified according to the Rill and Gully Plan. A summary of the pre- and post mining <br />drainage characteristics is shown on Table 20-2, Pre- and Post Mining Drainage Summary. <br />Runoff during the spring of 2003 caused significant erosion of approximately 2,450 feet of natural channel <br />that connects the eastern edge of the North Pit and Pond 011. In order to remediate the damage, SCC will <br />reconstruct the channel using a backhoe and other small equipment to minimize additional disturbance. In <br />general, the existing channel will be re-configured to have stable side slopes, a 2 foot wide bottom, and a <br />minimum of 0.3 feet of freeboard. <br />Re-construction activities will require temporary disturbance of surface area along side the actual channel <br />to allow access and construction. It is planned that the topsoil along side the existing channel will be <br />stripped back far enough to allow the channel side slopes to be reconfigured and stabilized. Once a section <br />of channel is reconstructed the topsoil will be re-spread and the backhoe will proceed working on the next <br />section of channel. Equipment access will be via an existing road/trail that currently exists along the <br />drainage bottom. All disturbed areas, including the reconstructed channel, will be re-seeded using the <br />approved drainage seedmix. <br />As shown on Exhibit 20-2B, Post-Mining Channel Profiles (YPM-12), grades along the length of the channel <br />range from around 9 percent to about 25 percent. The predicted flow in the reconstructed channel (after <br />construction of Pond 011A) will be a maximum 6.0 cfs at velocities ranging from 3.8 to 4.99 fps on grades <br />from 9 to 18 percent. It has been determined using SEDCAD analyses that sections of the channel with <br />less than 18 percent grade will be stable as a vegetated channel, while sections over 18 percent grade will <br />be vegetated and have wood or rock check dams installed in <br />• <br />PR-02 10 Revised 03/05 <br />