PeakFQ

PeakFQ is the USGS's reference implementation of Bulletin 17C — the US federal guideline for flood-frequency analysis. It fits the Log-Pearson Type III distribution to annual peak series using the Expected Moments Algorithm, handles historic and paleoflood information, censored data, Multiple Grubbs-Beck low-outlier screening and regional skew weighting.

If a US reviewer asks how your 1% AEP flow was computed, "PeakFQ per Bulletin 17C" ends the conversation. It reads USGS peak-flow files directly, so gauge-based frequency estimates take minutes. Outside the US the method still applies, though local guidance may prefer different distributions.