A silt fence is a temporary barrier designed to retain sediment and control erosion on a construction site. The fence is made of woven, synthetic filtration fabric that is supported by wood or steel posts. The fence prevents the downhill flow of sediment while letting water runoff pass through the fabric.
Type A vs. Type B Silt Fence
Most of the specifications for type A and type B silt fences are the same. The difference between a type A and type B silt fence is that a type A silt fence has 36-inch wide filter fabric and a type B silt fence has 22-inch wide filter fabric. Type A silt fences are recommended for use on construction projects that will take six months or more, while type B silt fences are recommended for use on small construction projects that will take less than six months.
Type C Silt Fence
For high runoff flows or velocities, a type C silt fence is the best choice. Like a type A, the type C is 36 inches wide but it also has wire reinforcement that permits almost three times the runoff flow rate of a type A. Type C silt fences are also recommended when the downhill slope has a vertical height of more than ten feet.
According to Mountain Empire Community College, silt fences are often installed incorrectly. To make the fence the most effective, the fabric needs to be buried at least eight inches deep, but most people don't bury the fabric. According to the U.S. Forest Service, you should not install silt fences across streams, waterways, ditches or other areas of concentrated flow.