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In 2004 SCC observed erosional instability in the watershed drained by Channel SIIPM-8. <br />. Hydrologic modeling using the approved curve number value for reclaimed conditions <br />(CN=62) indicates there would be no runoff associated with a 10-year, 24-hour storm event. <br />However, the erosional instability indicated that precipitation falling in the area does cause <br />runoff. Vegetation monitoring in the area of the reclaimed Wadge Pit indicates that the <br />vegetation cover condition is "fair" (30% to 70%) rather than "good" (>70%). Consequently, <br />a curve number value of 71 better describes the hydrologic conditions for the reclaimed <br />Wadge Pit area. <br />2.2 Channel Designs <br />The channel utility sub-routine contained within SEDCAD+ was used to design the postmine <br />channels. As part of the TR-36 technical revision the postmine channel design modeling was <br />converted to the 4`n generation of the SEDCAD+ model - SEDCAD4. The design methodology <br />used in SEDCAD4 is based on the limiting permissible velocity method. If the actual design <br />velocity is less than the permissible velocity, the channel is stable. <br />Seneca Coal Company (SCC) uses three types of channel designs at the Seneca H Mine: <br />• vegetated channel <br />• • riprap channel <br />• vegetated channels with a turf reinforcement mat <br />Channel sections with shallow slopes or low flows are typically vegetated. Channels with <br />steeper slopes or higher peak flows have traditionally been stabilized with rock riprap. In <br />2007 SCC incorporated vegetated channels with turf reinforcement matting (TRM) as an <br />alternative channel lining material. Channel designs are summarized on the Postmine <br />Channel Schedule table found at the start of Appendix B. The actual design demonstrations <br />are presented in Appendix B. <br />2.2.1 Vegetated Channel Design <br />Inputs to the channel utility sub-routine for vegetated channels include: <br />• peak flow <br />• channel slope <br />• channel geometry (triangular or trapezoidal shape; bottom width [as appropriate]; <br />side slope) <br />• retardance class <br />• freeboard <br />Vegetated channels tend to become unstabte when flow velocities exceed five (5) feet per <br />second (fps). <br />TR-41 7-12-5 Revised 04/07 <br />