Silt fence top of the structure; requiring another silt fence above or below it (creating a new ponding area), or for the silt fence to be removed, the sediment removed or spread out, and a new fence installed. The fence is not designed to concentrate or channel stormwater. The fence is installed on a site before soil disturbance begins, and is placed down-slope from the disturbance area. Sediment is captured by silt fences primarily through ponding of water and settling, rather than filtration by the fabric. Sand and silt tends to clog the fabric, and then the sediments settle in the temporary
Soil mechanics may be given the classification symbol "GW" (well-graded gravel), "GP" (poorly graded gravel), "GM" (gravel with a large amount of silt), or "GC" (gravel with a large amount of clay). Likewise sands may be classified as being "SW", "SP", "SM" or "SC". Sands and gravels with a small but non-negligible amount of fines (5–12%) may be given a dual classification such as "SW-SC". Clays and Silts, often called 'fine-grained soils', are classified according to their Atterberg limits; the most commonly used Atterberg limits are the Liquid Limit (denoted by "LL" or formula_39), Plastic Limit (denoted by "PL" or formula_40), and