Silt fence is a temporary sediment barrier made of geotextile fabric attached to stakes and buried at the bottom. It slows sheet flow from a disturbed area so sediment settles out behind the fence before water leaves the site. It's a perimeter control, and the EPA Construction General Permit lists silt fence among its examples.
Where silt fence works and where it doesn't
Use it for:
- Sheet flow from small drainage areas below graded areas, along the downslope perimeter of a site.
- Below stockpiles and around the toe of short slopes.
Don't use it for:
- Concentrated flow in ditches, swales or channels. It will overtop, undercut or blow out. Use check dams, sediment traps or channel linings.
- Large drainage areas or long, steep slopes above the fence.
- Across a stream or as the only control near a waterway.
- As inlet protection on paved streets, where purpose-made inlet devices work better.
Typical specifications
State and local BMP manuals set the exact specs. Common values:
| Item | Typical specification |
|---|---|
| Fabric | Woven or nonwoven geotextile meeting the manual's strength and flow specs, UV-stabilized |
| Height above ground | Usually about 18 to 36 inches |
| Toe-in (trench) | At least 6 inches deep, with the fabric buried and backfilled, or installed by static slicing |
| Posts | Wood (about 2 x 2 inch hardwood) or steel posts, driven firmly into the ground, often 12 to 18 inches deep |
| Post spacing | Commonly 6 to 8 feet apart, closer for heavier loads |
| Post side | Posts on the downslope side of the fabric |
| Drainage area | Often limited to about 1/4 acre per 100 feet of fence |
| Location | Along the contour, a few feet out from the toe of the slope to leave room for sediment storage |
Step-by-step installation
- Lay out the line on the contour, following the same elevation, not a straight line across changing grades.
- Turn the ends up slope. The EPA CGP requires perimeter controls to be installed on the contour with both ends extended up slope (for example, at 45 degrees), forming a crescent so water can't run around the ends. On long runs, add J-hooks or "smiles" so water can't travel along the fence to a low spot.
- Trench the toe, typically about 6 inches deep, on the upslope side, or install with a slicing machine.
- Drive the posts on the downslope side at the specified spacing.
- Attach the fabric to the posts on the upslope side, per the manufacturer (staples, ties or pockets).
- Bury the bottom of the fabric in the trench, backfill, and compact the soil firmly on both sides. The toe-in is what keeps water from flowing under the fence.
- Join sections by overlapping at a post and wrapping or splicing per the manual, never with a gap.
Inspection and maintenance
Inspect silt fence at every SWPPP inspection, after storms and when crews report problems. Look for:
- Sediment depth. The EPA CGP requires removing sediment before it reaches one-half of the above-ground height of the control. Some state manuals use a lower trigger, such as one-third.
- Undercutting or water flowing under the toe.
- Water running around the ends, which means the ends need to be extended up slope.
- Sagging, tears, loose fabric or leaning posts.
- Overtopping, a sign of too much drainage area or concentrated flow.
If the same section keeps failing, fix the cause. Under the CGP, needing the same routine fix three or more times at one location becomes a corrective action condition.
Super silt fence and alternatives
- Super silt fence (wire- or chain-link-backed silt fence) adds a steel fabric backing on heavier posts for higher loads and longer service.
- Compost filter socks and fiber rolls (wattles) can work on pavement or where trenching isn't possible.
- Sediment traps and basins for larger drainage areas.
Removal
Remove silt fence only after the area above it is stabilized. Remove the trapped sediment and spread it in a stable area, pull the fabric and posts, then seed and stabilize the disturbed strip. Biodegradable controls intended to stay can be left in place under the CGP.
Learn the full set of controls in the free sediment control lesson.
Sources and official references
Last reviewed: October 25, 2026 · Free general education based on the Clean Water Act, EPA NPDES rules and the EPA Construction General Permit. Your governing permit (EPA, state, tribal or local) controls. This is not legal advice, not EPA-approved, and not a California QSP/QSD or other state credential, and it does not issue a certificate. Nothing you enter on this page is saved or sent.