Construction BMPs: Silt Fence

Silt Fence

Silt fence can be a very effective best management practice if it is used correctly. However, it is also one of the most misused and overused BMPs. Using silt fence incorrectly is not only ineffective, it can also be expensive. Here are some tips for using silt fence appropriately:

The slicing method of installing silt fence

Installation– Silt fence is designed to pool water on your site while sediment settles out of it. In order for your silt fence to be effective, the fabric must be trenched at least six inches into the ground so that it will contain stormwater on your site (see diagram below). There are also machines that will slice the fabric into the ground. The slicing method of installation is typically faster and more effective than trenching. While this may be a big investment initially, in the long run it can save a significant amount of time in both installation and maintenance.

Where to Place It– Silt fence should be used down slope of a disturbed area. It should be aligned parallel to the contours of the slope, with the ends of the silt fence curving uphill. Leave some room between the silt fence and the toe of the slope so there is more of an area for the water to pool.

An effective installation and placement of silt fence

Where NOT to Place It– Sit fence should not be used uphill of a disturbed area unless you are trying to keep stormwater from running on to your property. It should be used to control runoff, not to delineate property lines or work areas. Do not use silt fence in areas of concentrated flows; check dams are more appropriate for slowing the velocity of stormwater in channels. Silt fence should only be used for controlling sheet flow.
Maintenance– Silt fence must be maintained to be effective. Check your silt fence regularly to make sure it will hold water during a storm event. Additionally, if your silt fence is working properly, it will eventually fill up with sediment. When the sediment is halfway up the fence, it will need to be cleaned out so that there will be room for the water to pool.

 

An effective Silt Fence Diagram

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