HEC-SSP — The Complete Guide: Free Flood Frequency Analysis from Gauge Records

HEC-SSP is Windows software from the Hydrologic Engineering Center (HEC) of the US Army Corps of Engineers for statistical analysis of hydrologic data. It is in the public domain and completely free, and its methods work on data from anywhere in the world, given a long enough record.

HEC-SSP

US Army Corps of Engineers (HEC)

Statistical analysis of hydrologic data: flood-flow frequency, volume-duration and coincident frequency, for deriving design floods from gauge records.

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What you get

Peak-flow frequency — fitting a distribution to annual peaks and computing the flow for a return period.
General frequency analysis — fitting various distributions to stages, rainfall or any other variable.
Volume-duration — frequency of flow volumes over different durations, important for reservoir design.
Coincident frequency — combining two variables, such as river flow and the water level at the outlet.
Plots and reports — frequency curves with confidence bands and the observed points.

What to know

Some of the methods follow the US federal guidelines for flood frequency analysis, but the mathematics does not depend on location: you enter a record from a local gauge and get the flow for a return period. The quality of the result depends on the length and quality of the record, so check outliers and missing years before running the analysis.

Related tools

For USGS flood frequency analysis — PeakFQ. To turn the design flow into a hydrograph from a catchment model — HEC-HMS. To compute flood levels in the channel — HEC-RAS.