source
USACE. (2013). Environmental Quality - Environmental Statistics.
Engineer Manual EM 200-1-16, 31 May 2013. Department of the Army,
U.S. Army Corps of Engineers, Washington, D.C. 20314-1000, p. M-10.
http://www.publications.usace.army.mil/Portals/76/Publications/EngineerManuals/EM_200-1-16.pdf.