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National Streamflow Statistics Program

Summary of NSS


NSS - The National Streamflow Statistics Program


Estimates of streamflow statistics are used for a variety of water-resources and emergency planning, management, and regulatory purposes, and for design of structures such as bridges and culverts. These estimates are often needed at ungaged sites where no observed flow data are available.

To provide simple methods of estimating streamflow statistics, the U.S. Geological Survey (USGS) has developed and published regression equations estimating the magnitude and frequency of floods for every State, the Commonwealth of Puerto Rico, and a number of metropolitan areas in the United States, and regression equations for estimating other streamflow statistics are available for many states. These equations have been compiled into the National Streamflow Statistics (NSS) Program.


NSS is a Visual Basic program that can be used to:

  1. Obtain estimates of various streamflow statistics for sites in rural (non-regulated) ungaged basins.
  2. Obtain estimates of flood frequencies for sites in urbanized basins.
  3. Obtain indicators of the errors associated with the estimated streamflow statistics, which may include any combination of the standard errors of estimate or prediction, the equivalent years of record, or 90-percent prediction intervals.
  4. Obtain estimates for ungaged sites by use of the Region-of-Influence method, which generates a custom regression equation for each ungaged site, in areas where the method has been implemented.
  5. Estimate maximum floods based on envelope curves developed by Crippen and Bue (1977).
  6. Create hydrographs of estimated floods for sites in rural or urban basins and manipulate the appearance of the graphs.
  7. Create flood-frequency curves for sites in rural or urban basins and manipulate the appearance of the curves.
  8. 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.
  9. 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.
  10. Save output from the program in text and graphic files.
  11. Obtain documentation and instruction for use of the program from help files.

Note: References to commercial vendors of software products or services is for informational purposes only and does not imply endorsement by the U.S. Government.


NSS works in concert with a Microsoft Access database, NSSv6_MM-DD-YYYY.mdb, where MM is the month, DD is the day, and YYYY is the year, of the most recent release. The database contains the information needed to solve the regression equations for each State. To protect the integrity of the database, it is password protected and not intended to be opened directly by users.

As new equations become available, the NSS database will be updated and links to new documentation will be provided from the NSS web site. Users should check often to determine if the database has been updated with new equations for their areas of interest. In addition, users wishing to use region-of-influence regression for states where is has been implemented need to download additional file from the NSS web page and place in the directory in which the software and database are installed.


Version history can be obtained at


NSS 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 is provided in the NSS user interface, and includes input parameters, 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.


NSS requires a computer running a 32-bit or 64-bit version of Microsoft Windows. 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.


A brief description of NSS is provided in: Turnipseed, D.P., and Ries, K.G., III, 2006, The National Streamflow Information Program: Estimating High and Low Streamflow Statistics for Ungaged Sites: U.S. Geological Survey Fact Sheet 2007-3010, 4p.

Documentation of the program history, content, theory, and application, including a users manual, is contained in: Ries, K.G. and others, 2007, The National Streamflow Statistics Program: A computer program for estimating streamflow statistics for ungaged sites: U.S. Geological Survey Techniques and Methods Report, Chapter 6 of Book 4

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 NSS web page (


Inquiries about this software should be directed to:

Todd Koenig
U.S. Geological Survey
1400 Independence Road
Mail Stop 100
Rolla, MO 65401

Electronic mail:
Phone: 573-308-3924