2008-12-04_PERMIT FILE - C1994082A ‎(4)‎

• Permit No: C1994082A
• IBM Index Class Name: Permit File
• Doc Date: 12/4/2008
• Doc Name: Drainage and Sediment Control Plan
• Section_Exhibit Name: Tab 13 Attachment 13-12
• Media Type: D
• Archive: Yes

~~ FeGruary 1999 I'oart Mine * 13-12 Drainage and Sediment Control Plan • f0
6.0 POSTMINING CHANNELS
The channel utility sub-routine contained within SEDCAD4 was used to design the postmine
channels. The design methodology used in SEDCAD4 is based on the limiting permissible velocity
method. If the actual design velocity is less than the permissible velocity, the channel is stable.
Seneca Coal Company (SCC) uses two types of channel designs at the Yoast Mine:
• vegetated channel
• riprap channel
Channel sections with shallow slopes or low flows are typically vegetated. Channels with steeper
slopes or higher peak flows have traditionally been stabilized with rock riprap. In 2007 SCC
incorporated turf reinforcement matting (TRM) as an alternative channel lining material. Channel
designs are summarized on Figure 13-12.3, Postmining Channel Design. The actual design
demonstrations are presented in Appendix 13-12.3, Postmining Channel Design SEDCAD4 Results.
6.1 VEGETATED CHANNEL DESIGN
Inputs to the channel utility sub-routine for vegetated channels include:
• Peak flow
• channel slope
• channel geometry (triangular or trapezoidal shape; bottom width [as appropriate]; side
slope)
• retardance class
• freeboard
Vegetated channels tend to become unstable when flow velocities exceed five (5) feet per second
(fPs)•
Peak Flow
The 10-year, 24-hour peak flow value is calculated with the hydrology component of the SEDCAD4
model.
Channel Slone
Channel slope is the most critical parameter. The steeper the slope, the lower the allowable
velocity. The channel slopes were determined by direct measurement from the mine permit maps.
Channel Geometry
Existing channels (constructed prior to 2007) were evaluated assuming a triangular, or V-shaped,
configuration, with a 3H:1V side slope. In certain situations, SCC designed atrapezoidal- shaped
channel with a bottom width of either three (3) or 10 feet and 4H:1V side slopes.
The design parameters for peak flow, channel slope and channel geometry are summarized on the
Figure 13-12.3.
Montgomery lYlatron Mining Group * 16S S. Union Baulevarrl, Suite 460 * Lakemoatl, Colorado 80228 * [phone]
TR-30 Revised 05/07