Overview
Estimates of the magnitude and frequency of flood-peak discharges and flood hydrographs are used for a variety of purposes, such as the design of bridges, culverts, and flood-control structures, and for the management and regulation of flood plains. These estimates are often needed at ungaged sites where no observed flood data are available.Estimates of the magnitude and frequency of flood-peak discharges and flood hydrographs are used for a variety of purposes, such as the design of bridges, culverts, and flood-control structures, and for the management and regulation of flood plains. These estimates are often needed at ungaged sites where no observed flood data are available.
To provide simple methods of estimating flood-peak discharges, the U.S. Geological Survey (USGS) has developed and published regression equations for every State, the Commonwealth of Puerto Rico, and a number of metropolitan areas in the United States. In 1993, the USGS, in cooperation with the Federal Highway Administration and the Federal Emergency Management Agency, compiled all of the then-current statewide and metropolitan area regression equations into a micro-computer program titled the National Flood Frequency (NFF) Program (Jennings and others, 1994.)
New or updated regression equations have been developed for most States since the initial release of NFF. The new equations reflect the increased availability of flood-frequency data and advances in flood-regionalization methods since the previous equations were developed. As a result, the newer equations generally provide more precise flood-peak estimates than the equations they supersede.
NFF (version 3.2) is a Windows software program that can be used to:
- Obtain estimates of flood frequencies for sites in rural (non-regulated) ungaged basins.
- Obtain estimates of flood frequencies for sites in urbanized basins.
- Estimate maximum floods based on envelope curves developed by Crippen and Bue (1977).
- Create hydrographs of estimated floods for sites in rural or urban basins and manipulate the appearance of the graphs.
- Create flood-frequency curves for sites in rural or urban basins and manipulate the appearance of the curves.
- Obtain improved flood-frequency estimates for gaging stations by weighting estimates obtained from the systematic flood records for the stations with estimates obtained from regression equations.
- Obtain improved flood-frequency estimates for ungaged sites by weighting estimates obtained from the regression equations with estimates obtained by applying the flow per unit area for an upstream or downstream gaging station to the drainage area for the ungaged site.
- Save output from the program in text and graphic files.
- Obtain documentation and instruction for use of the program from help files.
Software
The NFF program, an accompanying data base, and documentation can be downloaded from the Web at http://water.usgs.gov/software/nff.html, or by anonymous File Transfer Protocal (FTP) from ftp://water.usgs.gov/ (directory: /pub/software/surface_water/nff). Documentation needed to solve the equations for individual States is provided through links from the main NFF Web page to reports, fact sheets, or pages from the previous NFF report, WRIR 94-4002.
The NFF Web and FTP sites and links will be updated as new equations
become available. It is recommended that users check these sites
periodically to determine whether changes in the software have
been made or new equations have been developed for areas of
interest that will require obtaining an updated version of the
database and new documentation. The version history link on the main NFF Web page will document any changes made to the data base or the software.
The database for NFF will be changed frequently to update and add new
equations. Please check this web site often to determine if a new
version of the data base is available. The version history link on the main NFF Web page will document any changes made to the data base or the software.
Contact
Problems with the NFF program, suggestions for improving the program,
questions about the hydrologic procedures, or requests for
additional information can be addressed to Kernell Ries (410-238-4317).
Documentation
A brief description of NFF is provided in:
- Perl, C.D., and Ries, K.G., III, 2002, The National Flood Frequency Program, Version 3: U.S. Geological Survey Fact Sheet 084-02, 4 p.
Complete documentation of NFF, including program history, content, theory, application, and a users manual, is contained in:
- Ries, K.G., III, and Crouse, M.Y., 2002, The National Flood Frequency Program, Version 3: A Computer Program for Estimating Magnitude and Frequency of Floods for Ungaged Sites, 2002: U.S. Geological Survey Water-Resources Investigations Report 02-4168, 41 p.
Documentation of the equations, maps, and other information needed to solve the regression equations for individual States is provided on line through links from the NFF web page (http://water.usgs.gov/software/nff.html) to the complete original State reports, fact sheets, or still-current pages from the report for the version 1.0 of NFF:
- Jennings, M.E., Thomas, Jr., W.O., Riggs, H.C., 1994, "Nationwide summary of U.S. Geological Survey regional regression equations for estimating magnitude and frequency of floods for ungaged sites, 1993": U.S. Geological Survey Water-Resources Investigations Report 94-4002, 196 p. (Superseded by WRIR 01-4168)
To see a table that indicates states with updated equations since release of NFF version 1.0 go to http://water.usgs.gov/osw/programs/nffpubs.html.
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