The Performance of Conventional Silt Fence Technology When Not Placed on the Contour

Studies were conducted of the effectiveness of silt fence installed on and off the contour at the Silt Fence Test Facilty (SFTF) at the USDA Hydraulics Laboratory laboratory in Stillwater, OK. Sediment laden flow from a source area was generated by a rainfall simulator using three different soil textures. This flow was directed to conventional silt fence erected on three different cross contour angles. Through use of special sampling apparatus, flow from the source area was sampled for flow rate, sediment concentration, and eroded size distribution. The same measurements were also made of flow along the toe of the fence and flow through the fence. Using these results, a model was developed of erosion of the toe trench to determine the point of failure by undercutting. The accuracy of the method was evaluated using the data collected. Background Under Phase II of the National Pollutant Discharge Elimination System (NPDES), disturbed construction sites 1 acre or larger will need to comply with the construction general permit applicable to their state or locality. A key element of the requirements is development of a stormwater pollution prevention plan (SWPPP) for