A silt fence, a type of sediment control, installed on a construction site. Photo Courtesy of U.S. Environmental Protection Agency (EPA).
Urban Erosion Control
Nitrogen, Phosphorus, Sediment
Erosion and sediment control practices protect water resources from sediment pollution and increases in runoff associated with land development activities that disturb the soil. Erosion and sediment control uses a suite of practices to divert surface runoff to treatment areas (e.g., using terraces, berms, or swales), reducing water velocity (e.g., using check dams), filtering runoff (e.g., using silt fences), and removing suspended particles via settling or infiltration. As a result, soil is retained on site and sediment and nutrients are prevented from leaving the disturbed area and polluting streams.2
Changes in factors relating to soil, vegetation, topography, or hydrologic conditions may alter the effectiveness of erosion and sediment control BMPs for removal of suspended solids or nutrients. For example, longer detention times behind silt fences may improve efficiency due to longer settling time. Efficiency can also be affected by the geomorphology of the unit; designs that maximize the area of contact between water and soil, vegetation, or microbial surfaces should in general increase efficiency. Increased vegetation density and biomass in swales or buffers is also likely to improve efficiency because of greater roughness, nutrient uptake, and more microbial surface area. While microbial removal processes that affect nitrogen removal are sustainable indefinitely under relatively constant environmental conditions, soil surfaces may become phosphorus-saturated, and further phosphorus sorption is therefore not possible. Capacity for sediment removal may also be impeded if high loading rates result in clogging or burial of vegetation. Additionally, high flow rates may lead to the formation of preferential flow pathways that reduce contact between water and microbes, soil, or vegetation.
Scalable to small farms?
1 "Documentation: Source Data, BMP Effectiveness Values." Chesapeake Assessment Scenario Tool. Web. 2013. http://casttool.org/Documentation.aspx .
2 Estimates of County-level Nitrogen and Phosphorus Data for Use in Modeling Pollutant Reduction Documentation for Scenario Builder Version 2.2." Chesapeake Bay. Dec. 2010. Web. May 2013. http://archive.chesapeakebay.net/pubs/SB_V22_Final_12_31_2010.pdf.