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Postmining Drainage Channels in the South Area <br />within SEDCAD4 was used to design the postmine <br />The channel utility sub-routine contained <br />channels in the II-W South Area. The design methodology is based on the limiting permissible <br />velocity as noted above. If the actual design velocity is less than the permissible velocity, the <br />channel is stable. <br />SCC utilized three types of channel designs for the South Area: <br />• vegetated channel <br />•riprap channel <br />• vegetated channel with a turf reinforcement mat ` <br />Channel sections with shallow slopes or low flows are typically vegetated. Channels with steeper <br />slopes or higher peak flows have traditionally been stabilized with rock riprap. In 2007, SCC <br />incorporated vegetated channels with turf reinforcement matting (TRM) as an alternative channel <br />lining material. Channel designs are summarized on Figure 20-1.2, Postmine Channel Designs for <br />South Area. The design demonstrations are presented in Attachment 20-1, Postmining Channel <br />Designs. <br />Vegetated Channel Designs <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]; side slope) <br />• retardance class <br />• freeboard <br />Vegetated channels tend to become unstable when flow velocities exceed five (5) feet per second. <br />Peak Flow <br />The 10-year, 24-hour peak flow value is calculated with the hydrology component of the <br />SEDCAD4 model. <br />Channel Slope <br />Channel slope is another critical input parameter. The steeper the slope, the lower the <br />allowable velocity. The channel slopes were determined by direct measurement from mine <br />permit maps. <br />TR-59 14 Revised 05/07 <br />