Graphical frequency functions may be used for flows or for stages.
Where Can I Find Data for Graphical Frequency Functions
The data required for a graphical frequency function can be obtained from statistical analysis of annual peak flows or annual peak stages in HEC-SSP, or using hydrologic and hydraulic modeling in HEC-HMS and HEC-RAS, respectively.
Working with Graphical Frequency Functions in HEC-FDA
Graphical frequency functions should be provided as paired data with an equivalent record length. The paired data consists of a column of standard frequencies and a column of stages or flows. If retrieving a stage-frequency relationship from the hydraulics modeling, be sure to enter a 9th coordinate for the 0.99 AEP event.
Differences Between HEC-FDA Versions 1 and 2
Graphical flow- and stage- frequency functions are entered and used the same way in both versions.
Steps to Configure a Graphical Frequency Function
Right-click on frequency function and select Create New Frequency Function...
Enter a useful name, a description, the equivalent record length, and select graphical
Select flow or stage, and enter flows or stages and the probabilities of exceedance
Compute confidence limits to view the graphical frequency function uncertainty (not required for a simulation - confidence limits are calculated automatically).
Click Save and Close. See below image for completed Graphical Flow Frequency Function.
