PERMFILE69474

• Permit No: C1994082A
• IBM Index Class Name: Permit File
• Doc Date: 9/27/2007
• Doc Name: Drainage and Sediment Control Plan
• Section_Exhibit Name: Tab 13 Attachment 13-12
• Media Type: D
• Archive: Yes

FeGruary 7999 Yoart Mine * 13-12 Draixage and SerGmext CaretrolPkn NB
•
TABLE ]3-12.6
Guide to Retatdance Class Selection
Stand Length of Vegetation
in. Retatdance 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-G 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. Retatdance 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 basel area and by laying over during high flows.
The higher the resistance, the higher elevation of flowing water in the channel. Retatdance 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 PARER (Pennsylvania
Department of Environmental Resources, Stover, 1990) method.
The minimum channel designs for the rock riprap lined channels are summarized on Figure 13-
12.3. Given the uncertainty in determining riprap Dso for steep slopes with the PARER Method,
SCC adds an additional 3-inches to the model recommended Dso size. SEDCAD4 demonstrations
are presented in Appendix 13-12.3.
6.3 Turf Reinforcement Mat Channel Design
Turf Reinforcement Mats (TRMs) allow vegetation to be used in areas where flow conditions
exceed the limits of natural vegetation (e.g., limiting velocities greater than 5 fps). They can be
used for steeper slopes (1.SH:1V, or flatter) and under medium to high flow conditions.
Montgomery Watron Mining Group * 765 S. Union Boulevard, Suite 460 * I~kewood, Colorado 80228 * [phone]
TR-30 Revised 03/07