2012-05-11_PERMIT FILE - C1981033 ‎(4)‎

• Permit No: C1981033
• IBM Index Class Name: Permit File
• Doc Date: 5/11/2012
• Section_Exhibit Name: EXHIBIT 11 DRAINAGE AND SEDIMENT CONTROL PLAN
• Media Type: D
• Archive: No

Sediment Pond Operations
A 12" CMP will handle 2.1 cfs with no head. Therefore the
• calculated 5.4 cfs flow may be to high. The pond contains
170,000 gallons within the 1.7 feet (H2 -H1). At a flow of
2.1 cfs the pond would dewater to the top of the outlet pipe
in 3 hours (170,000/(2.1 *7.48 *60). Use 3 hours for the time
it takes to dewater the pond to the top of the CMP.
Therefore the water level in the pond can be lowered 1.7 feet in
in 3.0 hours. According to the stage diagram, the water storage
capacity between elevations 6005.9 and 6004.2 is 0.54 AF.
Once the water level in the pond reaches the top of the 12" CMP
at elevation 6003.9, the flow though the outlet pipe will reduce.
Use the open channel flow equation to determine the time it takes
to dewater the remaining 0.21 AF (0.75 AF - 0.54 AF).
The water level in the pond must be reduced to elevation 6003.5 to
provide for 0.75 AF capacity. The invert elevation of the outlet end
of the outlet pipe is 6003.2. Therefore use a minimum flow depth of
0.3 feet (6003.5 - 6003.2). The slope or head on the pipe varies
from it ((6003.9 - 6003.5)/37) to 04. Use the average slope 0.54.
FLOW IN A CIRCULAR CHANNEL
DEPTH OF FLAW
3.6
RADIUS OF PIPE
6
SLOPE OF PIPE
0.005
• MANNINGS "N"
0.024
INCLUDED ANGLE
AREA
WETTED PERIMETER
R= AREA /WETTED PERMITER
V= (1.49 /N) *(R ^.667) *(S ^.5)
=
INCHES
INCHES
EXPRESS AS DECIMAL
EXPRESS AS DECIMAL
132.84
0.198168 FEET ^2
1.16 FEET
0.17
1.35 FEET /SEC
Q - A X V - 0.2680 CFS
Time required to dewater 0.21 AF 9.5 Hours
Therefore the total time required to dewater the pond is 12.5
hours (3.0 + 9.5).
Sediment Removal
The sediment storage for the pond is provided for between elevations
6000.0 and 6002.9. The required sediment capacity is 0.15 AF.
According to the stage filling diagram, there is 0.15 AF of sediment
storage between elevations 6002.0 and 6002.9. At 604 sediment
storage capacity, the elevation of the sediment would be 6002.6.
Therefore, the sediment does not need to be removed from the pond
until it reaches elevation 6002.6 which is 0.3 feet below the invert
of the inlet end of the outlet pipe.
• 11 -13 New August 4, 1993