2009-09-29_PERMIT FILE - C1994082

• Permit No: C1994082
• IBM Index Class Name: Permit File
• Doc Date: 9/29/2009
• Doc Name: Drainage and Sediment Control Plan
• Section_Exhibit Name: Tab 13 Attachment 13-12
• Media Type: D
• Archive: No

February 1999
Yoast Il~fine * 13-12 Drainare and Sediment Control Plan • 11
Retardance Class
The reclamation seed mixture SCC uses to revegetate reclaimed areas results in a mixed grass
The flow resistance varies by grasses 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 13-12.6, Guide to Retardance Class
Selection.
TABLE 13-12.6 -
Guide. to Refardarice Class Selection
Stand Length of Vegetation
~m•) Retardance Class
Good
>30 A
it - 24 B
6-10 C
2-6 D
<2 E
Fair
>30 B
11-24 C
6-10 D
2-6 D
<2 E
Under short grass conditions, the channel is more prone to being eroded than during 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.
community. Consequently, the vegetation type selected as the model input is mixed grass.
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 Basel area and by laying over during high flows.
The higher the resistance, the higher elevation of flowing water in the channel. Retardance classes
of A through C (especially A and B) are used for capacity analysis.
SCC used retardance values of Class D for stability and Class B for capacity.
•
Freeboard
In accordance with Rule 4.05.3, SCC designed all postmine channels with a minimum freeboard of
0.3 feet.
The minimum channel designs for the vegetated channels are summarized on the Figure 13-12.3.
SEDCAD4 demonstrations are presented in Appendix 13-12.3.
6.2 ROCK RIPRAP CHANNEL 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 SEDCAD4 riprap lined channel sub-
routine, utilizing either the Simons/OSM (Simons, et al., 1982) or PADER (Pennsylvania
Department of Environmental Resources, Stover, 1990) method.
Montgomery Watson Mining Group * 165 S. Union Bauleyar~ Suite 460 * Iakewood, Colorado 80228 * [phone]
TR-30 Revised 05/07