Skip

Silt Fence

What is a Silt Fence?

This is a temporary barrier made of woven wire and fabric filter cloth (geotextile) that is used to catch sediment-laden runoff from small areas of disturbed soil to keep silt from getting in streams and homes.

When is a Silt Fence Used?

Silt fences are used for specific situations. Major considerations are slope, slope length, and the amount of drainage area from which the fence will catch runoff. Silt fences should be installed on the contour of a slope. Silt fences should not be installed across drainage ways, swales, gullies, ditches or other areas of concentrated water flow. Silt fences should be installed near homes, roads, ponds, and streams to divert debris flows away from these sites. Here are some design considerations:

Design Considerations for Silt Fence
Slope Steepness Maximum Slope Length
2:1�(50%) 50 feet
3:1�(33%) 75 feet
4:1�(25%) 125 feet
5:1�(20%) 175 feet
<5:1�(<20%) 200 feet

What Materials are Needed?

Fence Posts

Posts should be at least 36 inches long. Wood posts should be of hardwood with a minimum cross-section area of three inches. Steel posts should be standard “T” section and should weigh no less than one pound per linear foot.

Wire

Wire fence should be at least 14-gauge with openings no larger than six inches square.

Geotextile Fabric

Geotextile fabric should have the following minimum material properties to be suitable for this type of use.

Availability

These materials can be obtained from fencing contractors, ranch equipment suppliers, and home improvement stores.

Minimum Required Material Properties
Geotextile Property Minimum Acceptable Value Test Method
Grab Tensile Strength (lb) 90 ASTM D1682
Elongation at Failure (%) 50 ASTM D1682
Mullen Burst Strength (PSI) 190 ASTM D3786
Puncture Strength (lb) 40 ASTM D751 (mod)
Equivalent Opening Size 40-80 US standard sieve sizes
Ultraviolet Radiation Stability 90 ASTM G26

How is a Silt Fence Installed?

Prefabricated silt fence should be used whenever possible to minimize installation labor requirements. An eight-inch deep trench is dug along the silt fence alignment. The silt fence is unrolled and stretched tight while the posts are driven at least 16 inches below the ground surface. Sections of silt fence shall be joined at a post by overlapping the geotextile six inches and wrapping it around the post before the post is driven. The wire shall be overlapped and wired to the post. After the silt fence is erected, the trench is backfilled and the backfill is tamped by wheel rolling with small equipment or foot traffic.

What Maintenance is Needed?

Inspect the silt fence after every runoff event. Repair any damage immediately. Remove sediment and other debris from the upstream side of the fence when it accumulates to the extent that visible bulges develop in the silt fence. Remove the silt fence after vegetation or other permanent erosion control measures are installed and functional.

Silt Fence Illustrations

Illustration of how to install a siltfence. Illustration of how to install a siltfence.