2010-05-07_PERMIT FILE - C2009087A ‎(28)‎

• Permit No: C2009087A
• IBM Index Class Name: Permit File
• Doc Date: 5/7/2010
• Doc Name: DRAINAGE AND SEDIMENT CONTROL PLAN
• Section_Exhibit Name: Exhibit 2.05.3-E2 Drainage and Sediment Control Plan
• Media Type: D
• Archive: Yes

Peabody Sage Creek Mine — Drainage and Sediment Control Plan
The flow resistance varies by grass type and length. Retardance classes have been divided into five
• classes designated by A, B, C, D, and E. SCS (1979) developed guidance for selection of vegetation
retardance classes and they are outlined in Table 2.05.3 -E2 -8, Guide to Retardance Class Selection.
Under short grass conditions, the channel is more prone to being eroded than with tall grass
conditions. Consequently, stability is evaluated under short grass conditions. Retardance classes of
D and E are typically used for stability analysis of vegetated channels.
Tall grass conditions are used to determine channel capacity. The tall grass affords a great deal of
resistance to channel flow as a function of stem basal area and by laying over during high flows. The
higher the resistance, the higher the elevation of flowing water in the channel. Retardance classes of
A through C (especially A and B) are used for capacity analysis. SCCC used retardance values of
Class D for stability and Class B for capacity.
U
TABLE 2.05.3 -E2 -8
Guide to Retardance Class Selection
Stand
Length of Vegetation
in.
Retardance Class
Good
>30
A
11-24
B
6 -10
C
2 -6
D
<2
E
Fair
>30
B
11-24
C
6 -10
D
2 -6
D
<2
E
The minimum design configuration for the vegetated channels are summarized on Table 2.05.3 -E2 -5
(Operational Runoff Ditch Design Schedule) and Table 2.05.3 -E2 -6 (Postmine Channel Design
Schedule).
4.3.2 Rock Riprap Design
Prior to 2007, all unstable channel reaches (e.g., flow velocities greater than 5 fps) were armored
with rock riprap. Riprap size was determined using the SEDCAD riprap lined channel sub - routine,
utilizing either the Simons /OSM (Simons, et al., 1982) or PADER (Pennsylvania Department of
Environmental Resources, Stover, 1990) method.
The minimum channel designs for the rock riprap lined channels are summarized on Table 2.05.3 -
E2-5 and Table 2.05.3 -E2 -6. Given the uncertainty in determining riprap D50 for steep slopes with
• the PADER Method, SCCC adds an additional 3- inches to the model recommended D5o size.
2.05.3 -E2.18