Silt Fence, Turbidity Barrier, Silt Curtain, Turbidity Curtain, Silt Barrier

Turbidity Curtains Staked Silt Curtains Type 1 Turbidity Curtain Type 2 Turbidity Barrier Type 3 heavy Duty Silt Curtains Dredging Barge Turbidity Screen

SILT FENCE

Geotextile, Silt Barriers, Turbidity Curtain

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They are normally manufactured from woven geotextile filter fabric attached to wooden stakes spaced at regular intervals along the site perimeter. The filter fabric should be entrenched in the ground between the support stakes. When installed correctly and inspected frequently, these fences can be an economical effective barrier to sediment leaving the site. Staked Silt Barrier to control sheetflow, or Floating Turbidity Curtains if your project is in,on or next to a water resource.

Specification

This fence is generally used on construction sites with relatively small drainage areas. They are appropriate in areas where runoff will be low-level shallow flow, not to exceed 0.5 cfs.

Call +1-772-646-0597 or FAX +1-772-589-3343

The drainage area required for there use generally should not exceed 1/4 acre per 100-foot of fence length. Slope length above the fence should not exceed 100 feet (NAHB, 1995)as this can have a negative impact on performance.

Silt Fence Design Considerations:

Fabrics used for silt fences should be a pervious sheets of geotextile material such as polypropylene, nylon or polyester. These are chosen based on minimum synthetic fabric requirements, as shown below. Minimum requirements for silt fence construction (Sources: USEPA, 1992; VDCR, 1995)

Physical Property & Requirements

1) Filtering Efficiency of 75 - 85% (minimum)which is highly dependent on local conditions

2) Tensile Strength at 20% (maximum) should allow for Standard Strength of 30 lbs/linear inch (minimum)

3) Elongation effects should consider Extra Strength of 50 lbs/linear inch (minimum)

4) Ultraviolet Radiation allowance of 90% (minimum)

5) Slurry Flow Rate should be 0.3 gal/ft2/min (minimum)

Site Selection and Design use

If a standard strength geotextile is used, it can be reinforced with wire mesh behind the filter fabric. This can increase the effective life of the fence. The maximum life expectancy for synthetic fabric silt fences is approximately 6 months, depending on the local conditions. Burlap fences have a much shorter useful life span, usually only up to 2 months.

Wooden stakes should be at least 5 feet long and have a minimum diameter of 2 inches if oak is used. Softer woods such as pine should be at least 4 inches in diameter. When using metal post in place of wooden stakes, they should have a minimum weight of 1.00 to 1.33 lb/linear foot. If metal posts are used, attachment points such as hog rings are needed for fastening the filter fabric using wire ties.

A silt fence should be erected to eliminate unwanted gaps in the fence. If a continuous roll of fabric is not available, the fabric should overlap from both directions only at stakes or posts with a minimum overlap of 6 inches. A trench should be excavated to backfill the bottom of the fabric fence at least 6 inches below the ground surface. This minimizes entrainment of stormwater runoff.

The height of the fence posts should be between 16 and 34 inches above grade. If standard strength fabric is used in combination with wire mesh, the posts should be spaced no more than 10 feet apart. If extra-strength fabric is used without wire mesh reinforcement, the support posts should be spaced no more than 6 feet apart which is typical on most D.O.T. projects(VDCR, 1995).

The design should be able withstand the runoff from a 10-year peak storm event, and once installed should remain in place until all areas up-slope have been permanently stabilized.

Some Considerations when using a Silt fence;

Barriers like these have limitations and should not be installed along areas where rocks or other hard surfaces will prevent uniform anchoring of fence posts and entrenching of the fence fabric. This will greatly reduce the effectiveness of silt fencing and can create runoff channels leading off site and costly fines.

Staked silt barriers are not suitable for areas where large amounts of concentrated runoff are likely. If this may occure consider the use of other BMP's in conjunction with silt fence in order to direct water to settlings ponds. High winds may present a maintenance challenge, as high winds may damage the filter fabric.

When the pores of the fence filter fabric become clogged with sediment, pools of water are likely to form on the uphill side of fence. Siting and design of the silt fence should take this into consideration and care should be taken to avoid further erosion damage.

Our fences should be inspected frequently, as well as after each rainfall event, to ensure that they are intact. If gaps or tears are found, they should be repaired or the fabric should be replaced immediately.

Accumulated sediments should be removed from the fence base when the sediment reaches one-third to one-half the height of the fence to avoid failure. Sediment removal should occur more frequently if accumulated sediment is creating noticeable strain on the fabric. When the silt fence is removed, the accumulated sediment also should be removed.

Effectiveness

USEPA (1993) reports the following effectiveness ranges for silt fences constructed of filter fabric that are properly installed and well maintained: average total suspended solids removal of 70 percent, sand removal of 80 to 90 percent, silt-loam removal of 50 to 80 percent, and silt-clay-loam removal of 0 to 20 percent. Removal rates are highly dependent on local conditions and installation.

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