UG_210_21_9 - UG 210-21-9 ENG – PeakFQ, Version 7.3, Computer Program and Documentation
UG 210-21-9 ENG – PeakFQ, Version 7.3, Computer Program and Documentation
User Guide: 210-21-9 Date: May 28, 2021
Subject: ENG – PeakFQ, Version 7.3, Computer Program and Documentation

Purpose.   This user guide announces the availability of the U.S. Geological Survey (USGS) frequency analysis software, PeakFQ, version 7.3, and explains how to obtain the software and program documentation.
Effective Date.   Effective Upon Receipt
Background.   PeakFQ is a statistical software package developed by USGS to implement Bulletin 17C procedures for flood-frequency analysis of streamflow records. PeakFQ provides 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. The USGS Techniques and Methods, Book 4, Chapter B5, “Guidelines for Determining Flood Flow Frequency – Bulletin 17C”, developed by the Advisory Committee on Water Information (ACWI) Subcommittee on Hydrology (SOH) Hydrologic Frequency Analysis Work Group (HFAWG) form the basis for the flood frequency analysis in PeakFQ.

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

USGS makes USGS-developed software and related material available for use in the public interest and advancement of science. USGS is not under obligation to provide support, consultation, training, or assistance of any kind with regard to use, operation, or performance of this software. Users assume all risk for using the software. For more information, see the USGS Software User Rights Notice website at
Distribution.   NRCS tested and CCE (common computing environment) certified PeakFQ, version 7.3, for deployment to NRCS Information Technology Service (ITS) supported workstations on May 20, 2021. The project reference number is RFC: CRQ3973024.

NRCS users are to obtain the PeakFQ, version 7.3, software through their ITS managers.

PeakFQ program documentation is available through the PeakFQ website at

PeakFQ, version 7.3, replaces all previous versions of PeakFQ. This user guide updates and replaces User Guide 210-19-3: ENG - PeakFQ 7.2 Computer Program and Documentation, dated March 11, 2019.

Filing Instructions. Users wishing to retain paper copies of any of the PeakFQ documentation should place it in a three-ring binder adjacent to other technical directives.
Contact.   NRCS users with statistical analysis related technical questions may contact agency hydrology and hydraulics personnel at the East, Central, and West National Technology Support Centers, the National Design Construction and Soil Mechanics Center, and the National Water Management Center.

Direct questions and comments regarding software operation to appropriate State-level staff or to Jacob Dieguez, Hydraulic Engineer, West National Technical Support Center, at or (443) 699-5226.

Contact Claudia C. Hoeft, National Hydraulic Engineer, Conservation Engineering Division, at or (202) 720-0772 with questions regarding this directive.


Deputy Chief for Science and Technology 
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