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Water Resources of the United States


Flood Frequency Analysis Based on Bulletin 17C and recommendations of the Advisory Committee on Water Information (ACWI) Subcommittee on Hydrology (SOH) Hydrologic Frequency Analysis Work Group (HFAWG)

Program PeakFQ implements the Bulletin 17C procedures for flood-frequency analysis of streamflow records, providing estimates of flood magnitudes and their corresponding variance for a range of annual exceedance probabilities. The output also includes estimates of the parameters of the log-Pearson Type III frequency distribution, including the logarithmic mean, standard deviation, skew, and mean square error of the skew. The output graph includes the fitted frequency curve, systematic peaks, low outliers, censored peaks, interval peaks, historic peaks, thresholds, and confidence limits.

PeakFQ reads annual peaks in the standard peakfq (WATSTORE) text format available from NWISWeb at

NOTICE: Potential computational issues in the PeakFQ software continue to be investigated in collaboration with the U.S. Army Corps of Engineers (USACE). Refined user guidance and/or updated methodology documentation will be developed and made available, if needed. For detailed information, please visit this page.

To download the latest release, PeakFQv7.4, please see below.

Current Version: 7.4
Release Date: June 28, 2022
Version History (see below)
Veilleux, A.G., Cohn, T.A., Flynn, K.M., Mason, R.R., Jr., and Hummel, P.R., 2014, Estimating magnitude and frequency of floods using the PeakFQ 7.0 program: U.S. Geological Survey Fact Sheet 2013-3108, 2 p.,
Flynn, K.M., Kirby, W.H., and Hummel, P.R., 2006, User's manual for program PeakFQ, Annual Flood Frequency Analysis Using Bulletin 17B Guidelines: U.S. Geological Survey Techniques and Methods Book 4, Chapter B4, 42 pgs.
[ On-line | PDF | chm ]
Bulletin 17C:
England, J.F., Jr., Cohn, T.A., Faber, B.A., Stedinger, J.R., Thomas, W.O., Jr., Veilleux, A.G., Kiang, J.E., and Mason, R.R., Jr., 2018, Guidelines for determining flood flow frequency--Bulletin 17C: U.S. Geological Survey Techniques and Methods, book 4, chap. B5, 148 p.,
Software User Rights Notice
NOTE: Electronic and/or print versions of many U.S. Geological Survey reports can be found at the Publications Warehouse (
Contact: U.S.Geological Survey
Analysis and Prediction Branch
415 National Center
Reston, VA 20192

Distribution Files


Operating System

Download File




Windows 10

Readme.txt Installation and usage information, version history, and known bugs
PeakFQ.7.4.exe Self-installing executable (1.8 MB) Source code (747 KB)

The following software distributions have been superseded and are replaced by the newer version above.
These versions are provided online for historical reference only.
There is no support for installation or use of these versions.



Windows 10

Readme.txt Installation and usage information, version history, and known bugs
PeakFQ.7.3.exe Self-installing executable (2.6 MB) a> Source code (728 KB)



Windows 7/8/10

Readme.txt Installation and usage information
PeakFQ.7.2.exe Self-installing executable, includes executable program, sample data, and documentation (1.57MB) Source code (2.13MB)



Windows 7/8

readme.txt Installation and usage information
PeakFQ_7.1.exe Self-installing executable, includes executable program, sample data, and documentation (1.50MB) Source code (2.13MB)
release.pdf Version history through version 7.1



Windows XP

README.TXT and PKFQWin_5.2.exe (5.38MB)




README.TXT and peakfq4_1.exe (2.51MB)

Sun Solaris

README.TXT and peakfq4.1.Solaris.tar.gz (1.3MB)


README.TXT and peakfq4.1.source.tar.gz (705K)

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