Instructions / Assembly

ManualsBrandsEverbilt ManualsFencing3 ft. x 100 ft. Silt Fence

Design

The three principal aspects of silt fence design are: proper

placement of fencing, adequate amount of fencing, and

appropriate materials.

Proper Placement of Fencing

Placement is important because where a fence starts, runs,

and ends is critical to its effectiveness. Improper placement

can make the fence a complete waste of money. Analyze the

construction site’s contours to determine the proper placement.

Segment the site into

manageable sediment

storage areas for using

multiple silt fence runs.

The drainage area above

any fence should usually

not exceed a quarter of an

acre. Water ﬂowing over

the top of a fence during a

normal rainfall indicates the

drainage area is too large.

An equation for calculating

the maximum drainage area

length above a silt fence,

measured perpendicular to

the fence, is given in Fiﬁeld,

2011. Avoid long runs of

silt fence because they

concentrate the water in a

small area where it will easily

overﬂow the fence. The

lowest point of the fence in

Figure 4 is indicated by a

red arrow. Water is directed

to this low point by both

long runs of fence on either

side of the arrow. Most of

the water overﬂows the

fence at this low point and

little sediment is trapped for

such a long fence.

Purpose and Description

The purpose of a silt fence

is to retain the soil on

disturbed land (Figure 1),

such as a construction

site, until the activities

disturbing the land are

sufﬁciently completed to

allow revegetation and

permanent soil stabilization

to begin. Keeping the

soil on a construction site, rather than letting it be washed off

into natural water bodies (e.g., streams, rivers, ponds, lakes,

estuaries) prevents the degradation of aquatic habitats and

siltation of harbor channels. And not letting soil wash off onto

roads, which readily transport it to storm sewers, avoids having

sewers clogged with sediment. The cost of installing silt fences

on a watershed’s construction sites is considerably less than

the costs associated with losing aquatic species, dredging

navigation channels, and cleaning sediment out of municipal

storm sewers.

A silt fence is a temporary sediment barrier made of porous

fabric. It’s held up by wooden or metal posts driven into the

ground, so it’s inexpensive and relatively easy to remove.

The fabric ponds sediment-laden stormwater runoff, causing

sediment to be retained by the settling processes. A single

100 foot (ft) run of silt fence may hold 50 tons of sediment

in place. Most construction sites today do have silt fences.

But many do not work effectively because they are not well

designed, installed, or maintained. The focus of this fact sheet

is—how to make silt fences work.

Minimum Measure

Construction Site Stormwater Runoff Control

Subcategory

Sediment Control

Figure 1. Silt fence retaining sediment

Figure 2. Create manageable sediment

storage areas

Figure 3. Water should not ﬂow over the

ﬁlter fabric during a normal rainfall

Figure 4. Avoid long runs of silt fence

Ofﬁce of Water, 4203M

www.epa.gov/npdes/pubs/siltfences.pdf

www.epa.gov/npdes/stormwater/menuofbmps

Stormwater Best Management Practice

Silt Fences

EPA 833-F-11-008

April 2012

Summary of content (5 pages)

PAGE 1
Stormwater Best Management Practice Silt Fences Minimum Measure Construction Site Stormwater Runoff Control Subcategory Sediment Control Purpose and Description The purpose of a silt fence is to retain the soil on disturbed land (Figure 1), such as a construction site, until the activities disturbing the land are sufficiently completed to allow revegetation and permanent soil stabilization Figure 1. Silt fence retaining sediment to begin.
PAGE 2
Stormwater Best Management Practice: Silt Fences of a gentle slope, if large (Figure 10), can be more important than its slope in determining sediment loss. A silt fence should not be placed in a channel with continuous flow (channels in Figures 8 and 9 don’t Figure 10. Gentle slopes may require a have a continuous flow), nor silt fence across a narrow or steepsided channel. But when necessary a silt fence can be placed parallel to the channel to retain sediment before it enters the watercourse.
PAGE 3
Stormwater Best Management Practice: Silt Fences Appropriate Materials designed to slightly disrupt soil upward next to the slit and to minimize horizontal compaction, thereby creating an optimum condition for compacting the soil vertically on both sides of the fabric. Compaction is achieved by rolling a tractor wheel along both sides of the slit in the ground 2 to 4 times to achieve nearly the same or greater compaction as the original undisturbed soil.
PAGE 4
Stormwater Best Management Practice: Silt Fences damage a conventional silt fence. The bottom of the porous fabric is held firmly against both the ground and base of precast concrete, highway, barriers by light-colored stones. An alternative installation would Figure 18.
PAGE 5
Stormwater Best Management Practice: Silt Fences Permanent Soil Stabilization Lake shore example. The lake’s shoreline is being restored with plant plugs and seeded with native plant species. A plywood, perimeter, silt fence is used to trap sediment from a construction site on the Figure 21. Silt fence protecting a lake right-side of the picture, shore protect the lake shore from boat-wake erosion, and to prevent geese from eating the seeds and young plants.