_PERMIT FILE - C1981008A ‎(13)‎

• Permit No: C1981008A
• IBM Index Class Name: PERMIT FILE
• Doc Name: Sedimentation Pond 004
• Section_Exhibit Name: Tab 13 Attachment D
• Media Type: D
• Archive: Yes

TABLE 1 (Cont. )
DESCRIPTION 10 r-24hr 25 r-24hr 100 r-24hr
Peak Inflow Rate 2. 7-cfs 3.36-cfs 5.95-c s
Peak Discharge Rate 0.20-cfs 0.02-cfs 2.54-cfs
Basin Trap Efficiency 100% ---
Detention of Flow (Sediment) 49.85-hrs --- ---
Detention of Hydrograph Centers 16.48-hrs --- ---
Input consists of precipitation amount (inches) , watershed area (acres) ,
time of concentration (hours) , runoff curve number (CN) , representative
particle-size distributions of soils in the area, sedimentology
information, spillway information, etc. The drainage area for Sediment
Pond 004 was determined from a 1" = 400' topographic map (see Exhibit
13-4) .
In some instances, the mining will cause the drainage area to change
during the life of the sediment structure. When the pit moves into the
watershed, runoff will be intercepted by the pit and diverted away from
the structure. In these cases, a conservative procedure was used; the
structure was analyzed for the largest anticipated drainage area that
will contribute runoff to the structure. This condition usually occurs
at the start of mining and again during the reclamation period.
SCS Curve Numbers (CN) and "k" Factor
SCS curve numbers were estimated for each subwatershed based on the
cover type, percent vegetation cover, hydrologic conditions, and
hydrologic soil type. Several sources were used to obtain this data:
1. Cover Type - Aerial photographs of the mine site were used to
identify the existing cover type. Maps delineating the
proposed mining plan were used to identify areas that will be
disturbed by mining. Three general categories of cover type
were used: undisturbed, disturbed, and reclaimed. Further
sub-classifications were made in each category as shown in
Table 2.
The cover type (and the tributary drainage area) for some
structures will vary throughout the life of the structure as
mining and subsequent reclamation occurs. For these cases,
the anticipated worst condition is assumed for the hydrologic
analysis.
3