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ABOUT SILT FENCE

Definition: A silt fence is a temporary sediment barrier consisting of filter fabric entrenched into the soil and attached to supporting posts.  Silt fence installed with a trencher or by slicing is the most effective installation method to ensure against common silt fence failures. 

The slicing method for silt fence installation utilizes an implement towed behind a tractor to “plow” or slice the silt fence material into the soil.  The slicing method requires the “Tommy” silt fence machine or equivalent.  Silt fence machines install the silt fence by slicing through the soil, rather than excavating it.  Slicing minimally disrupts the soil upward and slightly displaces the soil, maintaining the soil’s profile and creating an optimal condition for future mechanical compaction.  Compacted soil resists water infiltration and moisture saturation, thus nearly eliminating washouts. 

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Purpose: Silt fence is a sediment control practice.  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.  Improperly applied or installed silt fence will increase erosion.  Reasons for the high failure rate of improperly designed and installed silt fence include:

 

 

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Improper installation on slopes causes gullies

  • Improper placement on the site;
  • Allowing excessive drainage area to the silt fence structure;
  • Shallow trenches with little or no soil compaction;
  • Inadequate attachment to posts;
  • Failure to maintain the silt fence after installation;
  • Installing silt fence along property boundaries producing “concentrated” runoff.

 

Silt fence must only be installed where water can pond.  When placed off contour, silt fence will effectively divert runoff if that is desired.

Silt fence can be used where:

  • sheet and rill erosion would occur;
  • protection of adjacent property or areas beyond the limits of grading is needed (perimeter control);
  • the size of the drainage area is no more than 1/4 acre per 100 linear feet of silt fence;
  • the maximum flow path length above the barrier is 100 feet (30.5 m);
  • the maximum slope gradient above the barrier is 2:1;
  • small swales are carrying silt, the slope is less than 2%, and the drainage area is less than 2 acres (0.8 ha);
  • no practice other than a silt fence is feasible.

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This silt fence was not keyed in and is improperly placed.

 

 

 


Post time: Mar-18-2019
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