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Summary of NFF

NAME

NFF - The National Flood Frequency Program

ABSTRACT

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. These equations have been compiled into the National Flood Frequency (NFF) Program.

METHOD

NFF is a Visual Basic 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.

DATABASE

NFF works in concert with a Microsoft Access database, NFFv3.mdb, which contains the information needed to solve the regression equations for each State. As new equations become available, the NFF database will be updated and links to new documentation will be provided from the NFF web site. Users should check often to determine if the database has been updated with new equations for their areas of interest.

HISTORY

Version history can be obtained at https://water.usgs.gov/software/NFF/history/.

DATA REQUIREMENT

NFF requires user input of physical and climatic characteristics used as independent variables in the equations. Manual or automated methods for measuring the input parameters are described in documentation provided for each state.

OUTPUT OPTIONS

Output is provided in the NFF user interface, and includes input parameters, peak-flow estimates, standard errors, and equivalent years of record. This output can be saved to a text file or printed. Hydrographs and frequency plots are presented in separate windows. The graphs and data used to create them can be saved to bitmap files or printed.

SYSTEM REQUIREMENTS

NFF requires a computer running Windows 98 (or newer) or Windows NT Version 4.0 with service pack 5 (or higher). Adobe Acrobat Reader is required to display or print the User Manual in PDF format; however, the User Manual is available in other formats in addition to PDF. Microsoft Internet Explorer version 5.0 or newer is required to invoke the on-line help section. The amount of free disk space that is required varies greatly depending on the amount of station data stored in database files. For optimal performance, a processor running at 400 megahertz or faster with at least 128 megabytes of memory is recommended.

DOCUMENTATION

Documentation of the program history, content, theory, and application, including 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: U.S. Geological Survey Water-Resources Investigations Report 02-4168, 42 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 (https://water.usgs.gov/software/NFF) to the complete original State reports, fact sheets, or still-current pages from the report for the previous version of NFF:
• Jennings, M.E., Thomas, W.O., Jr., and 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.

CONTACTS

Inquiries about this software should be directed to: