2022-07-12_PERMIT FILE - C1981019A ‎(17)‎

• Permit No: C1981019A
• IBM Index Class Name: Permit File
• Doc Date: 7/12/2022
• Doc Name: Sediment Control System Analysis at End of Mining
• Section_Exhibit Name: Volume 18 Exhibit 7 Item 23 Part I
• Media Type: D
• Archive: Yes

Exh. 7-23I-4 Revision Date: 4/28/22
Revision No.: TR-154
Station 10+00
to 25+00
(LCG-2)
62.39 4.9 Trapezoidal
10’ bottom 3H:1V 4.0 Riprap,
D50 = 9”
Station 25+00
to 55+00
(LCG-3)
88.39 4.7 Trapezoidal
12’ bottom 3H:1V 4.0 Riprap,
D50 = 9”
Station 55+00
to 85+00
(LCG-4)
93.23 7.8 Trapezoidal
10’ bottom 3H:1V 4.0 Riprap,
D50 = 9”
Station 85+00
to 102+79 43.19 7.4 Trapezoidal
10’ bottom 3H:1V 4.0 Riprap,
D50 = 6”

Sage Draw, Grouse Draw, Sharpie Draw, Lower, Middle, and Upper Bobcat Draws

Sage Draw, Grouse Draw, Sharpie Draw are tributary drainages to the reconstructed portion of
Little Collom Gulch, while Lower, Middle, and Upper Bobcat Draws are tributary to natural
portion of Little Collom Gulch. Contributory areas to these ditches are less than one square mile
which would make the required modeled storm event the 10-year 24-hour storm event. For ease
and conservatism, all six channels have been modeled against the 100-year 24-hour storm event.

Lower and Middle Bobcat Draw will be constructed inside the reclaimed footprint of the Section
36 and Middle Ponds. Therefore, in the 100-Year 24-Hour model, it is assumed the entire
watersheds reporting to both ponds have been approved for Phase II bond release and both ponds
are no longer necessary for sediment control. In lieu of the two sediments ponds post mine channel
configurations have been added to the model.

A SEDCADTM model (100 Year 24 Hour Channel Demonstration model) has been included which
evaluates the peak flow for each of the channel. The minimum channel configurations for Little
Collom Gulch are summarized below

Name
Peak
Flow
(CFS)
Average
Slope
(%)
Channel
Type Side Slopes
Minimum
Depth
(Feet)
Erosion
Protection
Sage Draw 21.46 2.1 Trapezoidal
5’ bottom 3H:1V 4.0 Riprap,
D50 = 9”
Grouse Draw 36.89 16.8 Trapezoidal
10’ bottom 3H:1V 4.0 Riprap,
D50 = 9”
Sharpie Draw 6.51 22.0 Trapezoidal
10’ bottom 3H:1V 4.0 Riprap,
D50 = 6”
Lower Bobcat
Draw 64.62 6.4 Trapezoidal
10’ bottom 3H:1V 4.0 Riprap,
D50 = 9”
Middle
Bobcat Draw 64.62 5.0 Trapezoidal
10’ bottom 3H:1V 4.0 Riprap,
D50 = 9”
Upper Bobcat
Draw 59.37 8.3 Trapezoidal
10’ bottom 3H:1V 4.0 Riprap,
D50 = 9”