In Reply Refer To:
Mail Stop 415

August 25, 2008


SUBJECT: Availability of the National Streamflow Statistics (NSS) program (version 4.0) and accompanying documentation.

The purpose of this memorandum is to announce the availability of the National Streamflow Statistics (NSS) program, version 4.0, and accompanying documentation (/osw/programs/nss/). The NSS Program is a computer program that replaces the National Flood Frequency Program (NFF; /osw/programs/nffp.html) to provide simple methods of estimating flood-peak discharges and low flow frequency/duration discharges. This computer program is a significant enhancement to the NFF program. It compiles the most current USGS regression equations that can be used to estimate the magnitude and frequency of flood-peak discharges for rural and urban ungaged sites in the 50 States, Puerto Rico, and the Island of Tutuila, American Samoa, and also includes regionalization studies of low flow frequency and duration for 29 States and Puerto Rico. The report and program should be of interest to those individuals involved in flood-frequency analysis as well as those interested in low-flow duration and frequency analysis.

The NSS program includes over 3,000 regression equations in hundreds of regions throughout the country. Procedures for plotting frequency curves and flood hydrographs for selected recurrence-interval peak discharges are also available in NSS.
A brief description of the 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 5, Chapter A6, 45 p.


The software program and accompanying MS-Access data base (NSS 2008_01_18.mdb), the Techniques and Methods Report and the Fact Sheet can be downloaded from the Web at /software/NSS/. The web page also contains links to documentation for solving the regression equations for individual States.

The Office of Surface Water plans to update the NSS data base quickly when new regression equations are published for various States; therefore, NSS users should check the Web site often to ensure that they have the latest version of the data base.
Comments or suggestions about the NSS program should be addressed to Robert Holmes, Office of Surface Water, 573-308-3581, or

Stephen F. Blanchard /signed/
Chief, Office of Surface Water
U.S. Geological Survey
National Center, MS 415
12201 Sunrise Valley Drive
Reston VA 20192-0002
571-216-1423 (cell)
703-648-6693 (fax)