2009-01-07_PERMIT FILE - C1981022 ‎(11)‎

• Permit No: C1981022
• IBM Index Class Name: Permit File
• Doc Date: 1/7/2009
• Doc Name: Revised and New Channel Designs
• Section_Exhibit Name: Exhibit 2.05-E3 Section 7
• Media Type: D
• Archive: No

Substation 3 Channels
SS-1, SS-2, SS-3, & SS-4
Temporary Post Mine Channels
T-1, T-2, T-3 (temporary)
Permanent Post Mine Channel
Lower and Upper Refuse
Elk Creek Postmine Channel
Bear Creek Main Postmine Channel
Bear Creek Side Postmine Channel
All diversion ditches are designed to safely pass the peak flow from the 10-year, 24-hour storm event. Calculations
for the Bear Creek Steep Channel (BCCD-2) were evaluated using a conservative design flow of 2.0 cfs. The Elk
Creek postmine channel, Bear Creek Main postmine channel, and Bear Creek Side postmine channel are designed
to safely pass the peak flow from the 100-year, 24-hour storm event. All hydrologic and hydraulic inputs and
results are shown on the SEDCAD computer printouts in Sections 9 and 10. The locations of the ditches are
shown on Maps 2.05-M4, Drainage and Sediment Control Plan, and 2.05-M5 Postmining Topography.
The 100-year, 24-hour peak flow for Elk Creek is 107.Ocfs (using a conservative CN of GO). The 100-yr, 24-hr peak
flow for Bear Creek is 155.0 cfs (using a CN of 57). The methodology and assumptions used to determine the peak
flow are included in previously approved submittals (refer to Section 2). The existing, proposed, and postmine
channel profiles for Elk Creek are shown on the Elk Creek Profiles (Map 2.05-M7). Furthermore, the postmine
channel profiles for Bear Creek are shown on the Bear Creek Profiles (Map 2.05-M6)
A berm will be constructed to separate Ditches D3 and D4 and to separate Ditches DS and D1. The height of the
berm will be at least 1 foot higher than the high flow mark of the ditches. A summary of channel inputs and results
are shown on the attached Figures.
Channel outlets have been designed for Ditches D4, D6, and D7. A conservative design flow of 4 cfs was used in
the designs. Channel downdrains to Elk Creek will be armored and the designs are shown in Section 11.
Downdrains will be incorporated into the slope stabilization area. The downdrains will be field fitted as the slope
area is graded. Atypical downdrain configuration is shown in Figure 7.1 and typical locations are shown on Map
2.05-M4. Small area exclusions for the Bear Creek fan site are identified on Map 2.05-E1-BCA2.
Designs for HCD-1, 1-iCD-2, and I-ICD-4 are shown on Map 2.05-MSJ.
Designs for BCCD-1 and BCCD-2 are shown on Map 2.05-E1-BCA2.
Designs for BCPCD-M andBCPCD-S are shown on Map 2.05-IvI6.