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National Streamflow Statistics Program (NSS)

March 4, 2019

Overview of NSS

The U.S. Geological Survey (USGS) develops and publishes regression equations for estimating streamflow statistics 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 Streamflow Statistics (NSS) Program. The NSS program should be useful to engineers, hydrologists, and others for planning, management, and design applications. NSS is an easy-to-use interface that operates on computers with Microsoft Windows operating systems.

Screenshot of National Streamflow Statistics Program (NSS) data entry
Screenshot of National Streamflow Statistics Program (NSS) data entry

The regression equations included in NSS are used to transfer streamflow statistics from gaged to ungaged sites through the use of watershed and climatic characteristics as explanatory or predictor variables. Generally, the equations were developed on a statewide or metropolitan-area basis as part of cooperative study programs. Equations are available for estimating rural and urban flood-frequency statistics, such as the 100-year flood, for every state, for Puerto Rico, and for the island of Tutuila, American Samoa. Equations are available for estimating other statistics, such as the mean annual flow, monthly mean flows, flow-duration percentiles, and low-flow frequencies (such as the 7-day, 10-year low flow (7Q10)) for many of the states.

Each equation used in the NSS program is the result of considerable effort by USGS Hydrologists to study and document the behavior of streams in their State or region. As such, each equation has limitations that should be understood by the NSS user prior to applying results from NSS. This information can be found in the latest report listed on the NSS publications page. The NSS output provides indicators of the accuracy of the estimated streamflow statistics. The indicators may include any combination of the standard error of estimate, the standard error of prediction, the equivalent years of record, or 90-percent prediction intervals, depending on what was provided by the authors of the equations.


Installation Steps

  1. Download the NSS Program Installler and the NSS Database file.
  2. Verify that you have administrative privileges to install programs.
  3. Run the installer.  This will create an NSS directory in the Program Files (x86) folder.  The user will need full access rights to the NSS folder and subfolders to run NSS.
  4. Copy the NSS Database file to the NSS folder created in step 3.  It is NOT recommended to install the program or the database onto a network folder.  There is no need to open the database file directly.  The NSS Program knows the password for opening it.
  5. Run the program directly from the NSS.exe file in the NSS folder or using the shortcut created on the desktop.
  6. The first time the program runs, an window will pop up asking for the location of the NSS Database file.  Navigate to the location of the database from step 4, and the program should proceed to the main NSS window, ready to accept a new scenario.


Download Current Version of NSS

Note: The NSS program includes 2 components: an installable program and an accompanying database.  The first time the program is run after installation, it will ask for the location of the downloaded database.

NSS Program Installer: self-extracting executable of the NSS software (2,422,642 bytes, posted 2017-01-10). Please de-install any previous version of NSS and replace it with the most recent version before using the latest NSS database. Visit the version history page for information on changes to this program version.

NSS Database: needed by NSS software (19,103,744 bytes). Previous version of the database was dated 2017-09-27. Note: This file is password-protected and designed to be opened only by the NSS program. MS Access® is not required. Visit the version history page for information on changes to this database version.



NSS is a Windows 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 here and links to new documentation will be provided from the NSS publications page. Users should check often to determine if the database has been updated with new equations for their areas of interest.


Download the Region-of-Influence Data Files 

Regional-of-Influence (ROI) is a method of developing custom regression equations for estimating streamflow statistics for individual ungaged sites. The method is described in the documentation provided below. One or two additional files need to be downloaded for each state and placed in the directory in which users have installed the NSS software and database to allow NSS to run ROI regressions. 





Version History 

The NSS software has undergone numerous database and program updates.


Known Issues

NSS software has several known issues.


Data Requirement

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 Options

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.


System Requirements

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.



The NSS Web page 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 and known issues links on the main NSS Web page will document any changes made to the database or the software.



A brief description of NSS is provided in: Turnipseed, D.P., and Ries, K.G., III, 2007, The National Streamflow Statistics Program: Estimating high and low streamflow statistics for ungaged sites: U.S. Geological Survey Fact Sheet 2007-3010, 4 p.,

Complete documentation of the NSS, including program history, content, theory, application, and a user's manual, is contained in:

Ries, K.G., III, 2006, The National Streamflow Statistics Program: A computer program for estimating streamflow statistics for ungaged sites: U.S. Geological Survey Techniques and Methods Report TM Book 4, Chapter A6, 45 p.,

Note: The USGS publications listed above describe the NSS program up to version 4. For the most up-to-date documentation on the NSS program, please see the Help files associated with the downloaded NSS program.


Regional Regression Equation Publications by State or Territory

(Note: Regional regression equations may not be representative of the entire state.)


Citation Information

Publication Year 2019
Title National Streamflow Statistics Program (NSS)
Product Type Software Release
Record Source USGS Digital Object Identifier Catalog