PERMFILE46806

• Permit No: C1980006
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: Exhibit 42 Part 3
• Media Type: D
• Archive: No

•
design event is 31.1 hours. See Figure 23-27, Typical
Sedimentation Pond Cross-Section, for a diagram of the
primary spillway outlet.
(b) To prevent surface film (which contains coal dust) from
discharging and to prevent short circuiting, a 6-inch
trash collector/skimmer device is mounted over the riser
as shown in Figure 23-27, Typical Sedimentation Pond
Cross-Section.
(c) As shown on the Loadout Area Hydrology Map, (Map 19). the
maximum possible distance separates the inlet and outlet
to prevent short circuiting.
Emergency Spillway Design
Drainage area
• 25-year, 24-hour event
_ Runoff - Curve /90
Peak Flow - Curve /90
Flat Slope
Type II Storm
Western Colorado
Channel Type
Sfde Slopes
Channel Gradient
7.445 acres
2.0 inches
1.09 inches
7.6 cfs/inch runoff or
8.28 cfs
Trapezoidal
2:1
less than lY
By trial and error, using U.S. Department of Transportation, 'Design
Charts for Open Channel Flow". the appropriate channel width to carry
the peak flow at less than the critical curve velocity is three (3) feet
with riprap bottom.
Channel Width 3.0 feet
Depth of Flow 0.78 feet
Yelocity of Flow 3.1 feet per second
Criticai Yelocity 3.8 feet per second
23-I66