PeakFQ — The Complete Guide: Flood-Frequency Analysis and Design Floods from Gauge Data
PeakFQ is the USGS tool for flood-frequency analysis. You supply a series of annual peak flows from a gauging station and it fits a log-Pearson Type III distribution following the US Bulletin 17C procedures. It is in the public domain, free for commercial work too, and comes as a browser application and as an R package.
PeakFQ
U.S. Geological Survey (USGS)
Flood-frequency analysis of annual peak flows following Bulletin 17C.
Get it from the vendorWhat you get
- Frequency curve — a log-Pearson Type III fit to the peak-flow record.
- Return-period discharges — values for the 10-, 50-, 100-year floods and more.
- Confidence limits — the uncertainty band around each discharge.
- NWIS retrieval — pulling USGS gauge data directly.
- R package — running the analysis inside scripts and batch workflows.
What to keep in mind
The method follows US guidance rather than any local standard, so outside the United States check that the approving authority accepts it. Automatic retrieval only works for US gauges; data from other sources must be prepared in the format the tool expects. Older desktop versions are kept in the USGS legacy-software archive.
Related tools
To estimate flows at an ungauged US stream — StreamStats. To turn the resulting discharge into water levels — HEC-RAS. For flexible statistical work of your own — R.
StreamStats
U.S. Geological Survey (USGS)
Browser-based GIS application for delineating watersheds and estimating streamflow statistics in the United States.
Get it from the vendor
HEC-RAS
US Army Corps of Engineers
1D/2D hydraulic model for rivers, bridges and culverts, with floodplain mapping. The world standard.
Get it from the vendor
HEC-HMS
US Army Corps of Engineers
Rainfall-runoff hydrological model — infiltration, unit hydrograph and routing. Pairs with HEC-RAS.
Get it from the vendor
R
R Foundation
The leading language for statistics and data analysis — quality control, experiment analysis, reliability and forecasting.
Get it from the vendorThe bottom line
PeakFQ is the standard tool for Bulletin 17C flood analysis — free, transparent and especially convenient for anyone working with USGS data.