USDA Agricultural Non-Point Source Pollution Model (AGNPS):

  HYPERLINK
"http://www.wsi.nrcs.usda.gov/products/w2q/h&h/tools_models/agnps/index.
html" 
http://www.wsi.nrcs.usda.gov/products/w2q/h&h/tools_models/agnps/index.h
tml 

