"National Flood Frequency program (NFF)" means a regression equation program developed by US Geological Survey that estimates flood-peak discharges for every state, which can be downloaded for free at http://water.usgs.gov/software/nff.html [File Link Not Available].
N.H. Admin. Code § Env-Wq 1502.41
(See Revision Note #1 at chapter heading for Env-Wq 1500) #9343, eff 1-1-09