2023-02-21_PERMIT FILE - C1981019A

• Permit No: C1981019A
• IBM Index Class Name: Permit File
• Doc Date: 2/21/2023
• Doc Name: Prospect Pond
• Section_Exhibit Name: Exhibit 07 Item 14 Appendix Exh 7-14PP
• Media Type: D
• Archive: Yes

Exh. 7-14PP-3 Revision Date: 1/30/23
Revision No.: TR-158

By Rule these channels are required to be designed in accordance with Rule 4.05.4(2)(b) for the
10-year, 24-hour storm event as the watershed reporting to the Prospect Pond is less than one
square mile. However, for built in conservatism, all these channels have been designed to the
25-year, 24-hour storm event.

A road traverses across the Section 16 Fill Ditch near station 1+85, which provides access to
maintain power line infrastructure in the area. A culvert is installed and maintained in the
Section 16 Fill Ditch, but it is not a Colowyo mining related structure. Please see Volume 1,
Section 4.12 for a further discussion. The culvert is modeled even though it is not a Colowyo
culvert, to ensure it is sized appropriately. Given that, the peak storm discharge of 0.13 cfs
requires a minimum of one 4” culvert is necessary in the Section 16 Fill Ditch. However, one
24” culvert is installed, which will more than suffice for the flows generated by the Section 16
Fill Ditch.

For the Final East Pit Ditch, Reach 2, structures will be placed approximately every 200 feet to
create a stability wall to ensure riprap lining is

A SEDCADTM model has been included which evaluates the peak flow and total runoff volume
for each of the channel segments for the 25 year, 24-hour storm event. The channel
configurations are summarized below.

Prospect Ditch
Station Peak Flow
(CFS)
Average
Slope (%) Channel Type Side Slopes Erosion
Protection
Reach 1 3.93 23.6 Trapezoidal 12’
bottom 2H:1V Riprap,
D50 = 6”
Reach 2 1.45 13.0 Trapezoidal 12’
bottom 2H:1V Vegetation
Reach 3 1.23 12.4 Trapezoidal 15’
bottom 2H:1V Vegetation

North Tributary East Pit Ditch
Station Peak Flow
(CFS)
Average
Slope (%) Channel Type Side Slopes Erosion
Protection
Reach 1 Station
0+00 to 6.1+00 1.48 21.5 Trapezoidal 12’
bottom 2H:1V Riprap,
D50 = 6”
Reach 1 Station
6.1+00 to 10+41 0.88 7.2 Trapezoidal 12’
bottom 2H:1V Riprap,
D50 = 3”
Reach 2 1.28 12.2 Trapezoidal 12’
bottom 2H:1V Riprap,
D50 = 3”

EP3 Inlet and Outlet Ditches
Station Peak Flow
(CFS)
Average
Slope (%) Channel Type Side Slopes Erosion
Protection