Bioswale, Photo Courtsey of Natural Resources Conservation Service Iowa.
Nitrogen, Phosphorus, Sediment
Vegetative open channels are practices that convey stormwater runoff and provide treatment as the water is conveyed. Runoff passes through either vegetation in the channel, subsoil matrix, and/or is infiltrated into the underlying soils. Typically, channels are constructed for conveyance with treatment occurring as water is conveyed. Channels designed for infiltration are known as bioswales.2
Design calculations must be done by a qualified engineer familiar with hydrology and hydraulics. This practice will have detailed design standards for slope, velocity, infiltration rates, width, residence time, manning n value, maintenance, pipe placement, soil amendments, and various other design elements.
Scalable to small farms?
1 "Documentation: Source Data, BMP Effectiveness Values." Chesapeake Assessment Scenario Tool. Web. 2013. http://casttool.org/Documentation.aspx .
2 Simpson, Thomas, and Sarah Weammert. "Developing Best Management Practice Definitions and Effectiveness Estimates for Nitrogen, Phosphorus and Sediment in the Chesapeake Bay Watershed." Chesapeake Bay Program. Dec. 2009. Web. June 2013. http://archive.chesapeakebay.net/pubs/BMP_ASSESSMENT_REPORT.pdf.