How Does a Silt Fence Work?

Silt fence is typically used for 2 different reasons: as an outer perimeter for construction sites, or to control water flow and erosion. Additionally, it can be used to provide slope control, catching material that has been eroded from another area onto a slope or incline. Silt fence works as a filter to trap soil and sediments, but allow water through at a reduced speed.

What is Silt Fence?

Most silt fence is a weave of synthetic materials. The surface of silt fence is porous enough to allow water to flow through it, but prevents as much as 80 percent of water-borne particles from escaping. Rolls are available in 50 and 100-foot sections. Silt fence is typically held in place with thick stakes that are driven into the ground on the back sides of the fence and attached with tacks or staples.

Prevent Erosion

To prevent erosion, silt fence acts as a water break. Placing it at the top of a slope can protect the slope by halting or slowing the flow of water down it. This method is often used on slopes where sod will be laid, to protect the slope until the grass has had a chance to take root. Silt fence is often used in clay soils with high potential for erosion.

Soil collected by the silt fence can be loaded into a wheelbarrow or truck and redistributed where it belongs.

Slope Control

To use silt fencing for slope control, install more than one line of fencing along a slope or incline. The closer the lines of silt fence, the less water flow allowed to take place between them. Additionally, any erosion that does occur gets trapped at the silt fence, adding material onto the slope, building it up. Most application of this type keep the lines of silt fence 5 to 10 feet apart, but the same process is sometimes used on large tracts of land with the fencing placed anywhere from 20 to 50 feet apart.

Site Contaminants

As a construction fence, silt fencing prevents the site from contaminating surrounding waterways or wetlands. The fencing is partially buried around the perimeter of the job site, facing towards the construction area. This prevents accidental spills or other contaminants from escaping the job site, making the eventual cleanup easier. 

Additionally, most construction sites have a great deal of loose soil, and a silt fence help retains that soil so that it can be used once the construction is completed.

Flow Control

Another use for silt fence is to control the flow of water in a specific area. This can be useful for temporarily redirecting a stream or for moving flowing water from one location to another. Keep in mind that a silt fence will not contain all water flow, and as much as 1/3 of the water will escape through the material.