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Purpose A silt fence is a temporary sediment barrier consisting of filter fabric entrenched into the soil and attached to supporting posts. Silt fence is intended to be installed where sediment-laden water can pond, thus allowing the sediment to fall out of suspension and separate from the runoff. It is not intended to be an erosion control practice. Design Considerations Silt fences have a useful life of one season. Their principal mode of action is to slow and pond the water and allow soil particles to settle. Silt fences are not designed to withstand high heads of water, and therefore should be located where only shallow pools can form. Their use is limited to situations in which sheet or overland flows are expected. Silt fences normally cannot filter the volumes generated by channel flows. When installed across a concentrated flow path, undercutting of the fence often occurs. Silt fences should not be designed to impound sediment or water more than 18 inches (0.5 m) high. Sediment shall be cleaned from behind the fence when it reaches 50% of the designed impoundment height (9 inch (0.2 m)). Some design considerations include:
- determine what kind of runoff, and how much, is coming onto the site; too much volume of water per silt fence area means failure will happen;
- determine where and how the total volume is going to exit; total drainage area is the prime consideration of silt fence quantity, not necessarily slope;
- soil type can play a role in the placement and quantity requirements; sandy soils might require more silt fence per area to contain the volume of potential sediment; clay soils might need fewer fences because the volume of potential sediment loss is less, although the volume of water might be greater because clay soils allow less rainfall infiltration;
- if all the elements of the silt fence installation are properly adhered to, the fabric does not make much difference; even lightweight non-woven fabric will hold 18 inches of sediment; wire supported fence is costly and ineffective.
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Reason for Failure Reasons for the high failure rate of improperly designed and installed silt fence include:
- Improper placement on the site;
- Water flow to great for silt fence structure;
- Shallow trenches with little or no soil compaction;
- Inadequate attachment to posts;
- Failure to maintain the silt fence after installation;
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| Roll Width |
Roll Length |
Product Type |
Post Spacing |
| .914m |
30m or 100' |
Woven |
1.8m or 6' |
| .914m |
30m or 100' |
Woven |
3.0m or 10' |
| .914m |
30m or 100' |
Non Woven |
1.5m or 5' |
| .914m |
15m or 50' |
Non Woven |
1.5m or 5' |
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Enviro-Pro Silt Fence Specifications |
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| Physical |
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MASS/UNIT
AREA |
ASTM |
MARV |
oz/y² |
min. 3.2 |
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g/m |
min. 110 |
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| GRAB TENSILE STRENGTH |
ASTM D-4632 |
MARV |
lb |
125 |
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N |
550 |
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GRAB
ELONGATION |
ASTM D-4632 |
MARV |
% |
15 |
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| Mechanical |
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PUNCTURE STRENGTH |
ASTM D-4833 |
MARV |
lb |
60 |
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N |
222 |
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MULLEN
BURST |
ASTM D-3786 |
MARV |
psi |
280 |
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kPa |
1930 |
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TRAPEZOIDAL
TEAR |
ASTM D-4533 |
MARV |
lb |
50 |
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N |
222 |
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| APPARENT OPENING SIZE (AOS) |
ASTM D-4751 |
MaxARV |
US Sieve |
30 |
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mm |
0.6 |
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| Hydraulic |
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PERMITTIVITY |
ASTM D-4491 |
MARV |
sec-¹ |
0.05 |
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WATER FLOW
RATE |
ASTM D-4491 |
MARV |
gpm/ft² |
10 |
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l/min/m² |
407 |
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| Endurance |
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UV RESISTANCE |
ASTM D-4355 |
MARV |
% Retained |
70 |
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@ 500 hours |
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