To create an graphical frequency function, from the Study Tree right-click on Frequency Functions and select the create new option. Enter the name for the function and a description (optional, but recommended). Select Graphical, select either Flow or Stage. Provide at least eight coordinates of exceedance probability and flow (or stage), and an equivalent record length. Click on Compute Confidence Limits to view the 0.025 and 0.975 confidence limits. Click Save and Close to create the new function.

Graphical Frequency Function Example for Flow-frequency

To edit the created frequency function, from the Study Tree right-click on the created function and click Edit Frequency Function.

Frequency Function FDA icon Computed confidence limits are for viewing purposes only, there is no need to compute confidence limits to use the frequency function in an expected annual damage compute. The computational engine calculates the uncertainty when the entered frequency function is used in a compute. Once created, users will need to re-compute the confidence limits if opened in the Editor.

Retrieve Graphical Frequency Function

Users may retrieve graphical stage-frequency curves from the imported hydraulic data (review the Add Graphical Frequency Function section for instructions). Recall that index points must also be imported in the FDA study to use this option (review the Index Points section for import instructions). Don't forget to edit the equivalent record length for each function after generation. 

  1. To create an graphical stage-frequency function, from the Study Tree right-click on Frequency Functions and select the Retrieve Graphical Frequency Function option.
  2. Select the appropriate Hydraulic Dataset and Index Point Set to retrieve from, and click the GenerateFrequencyCurves button.
    Retrieve graphical frequency functions option requires the hydraulic dataset and index point set.
  3. The generated frequency curves are added to the Study Tree under the Frequency Functions element and is automatically named based on the name of the imported index point(s) (e.g., 3347000) and hydraulic dataset (e.g., WOP-BaseYear).
    Example retrieved graphical stage-frequency function.
  4. Provide the correct equivalent record length for each generated stage-frequency function. To edit the generated frequency function, from the Study Tree right-click on the created function and click Edit Frequency Function.