2013-10-30_PERMIT FILE - C1981038A ‎(2)‎

• Permit No: C1981038A
• IBM Index Class Name: Permit File
• Doc Date: 10/30/2013
• Section_Exhibit Name: Volume 8 Surface Drainage - Drainage - Design & Location
• Media Type: D
• Archive: Yes

Straw Log substitute for Silt Fences
The following pages (SAE -31 through SAE -57) provide silt fence designs for
three separate drill hole configurations. The information on this page provides
the design basis for substituting straw logs for silt fences. The straw log
substitution can be used anywhere a silt fence is required.
The following table summarizes the peak water stage, trap efficiency and silt
fence length for various configurations of gob vent drill pads.
Volume 8
Description
Peak
Trap
Length
Drainage
Drill Pad
Water
Efficiency %
Feet
Design &
Stage
Location
Feet
Tab
SAE -31 -39
100'X 100' on 10:1 Slopes
0.09
60.05
100
SAE -40 -48
100'X 100' on 5:1 Slopes
0.10
59.92
110
SAE -49 -57
100'X 100' on 3:1 Slopes
0.08
59.92
200
The design flow rate for all of the silt fences is 10 gallons per minute per square
foot. The maximum peak water stage is 0.10 feet or 1.2 ".
The key factor in sediment control is the trap efficiency. According to data
published by American Excelsior Company, its 12" Curlex sediment log has a
trap efficiency (% Soil Retained) of 70.3% and a flow rate of 37.5 gallons per
minute per square foot. Its 6 and 9 inch sediment logs have a trap efficiency of
53.9% at 42.5 gallons per minute per square foot.
The high flow rates of the sediment logs in relation to the silt fence design would
indicate run -off will not overtop the straw logs. The straw logs will filter the run-
off faster than the sediment fences. The favorable trap efficiency of the straw
logs indicate they are as good as or better than the designed silt fences. The 6
and 9 inch straw logs have a slightly lower trap efficiency that is not considered
significant.
Straw logs will be keyed into the natural soil below the gob vent hole drill pads
and other small area exemption areas. The total length of the straw logs will be
comparable to the length indicated in the approved silt fence designs including tie
back distances. The straw logs will be overlapped to prevent flow bypas �, ' ',
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pieces are joined to achieve the a ppropriate total linear foota ge. 0
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MR -132 SAE -30 10/13
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