You can enter Frequency Correction Factors, (a.k.a. Runoff Coefficient Saturation Factors), Cf, with your IDF Rainfall Curves. The Cf factors can be edited on the Known Equation Coefficients screen or the Computed Coefficients screens.
Cf factors are applied to the Runoff Coefficients when computing peak flows for the Rational Method. The intensities shown on your reports will not reflect this factor. The computed flows will, however. The product of C x Cf cannot exceed 1.0.
Correction Factors can be edited while you are setting up your IDF curves. Rather than clicking [Finish] just after entering or importing data, continue to click [Next] until you arrive at the Equation Coefficients screen shown below. There you can enter Cf values. Remember to click the [Apply] button.
Editing Correction Factors
If you need to edit existing Cfs, click on the [New…] button on the Rainfall Wizard window.
Then Click [Next]. Then [Next] again to reach the above screen. Then enter/edit the Cf values. Click [Apply]. Then [Finish].