In ARR 1987 there was a provision to increase the coefficient of runoff (cy) to account for the storm ARI - this is knowns as the Frequency Factor.
By default, Civil Site Design doesn't factor up or down the coefficent of runoff (C) factor, however users can enable this factoring by creating a file named CfactorFreqAdjust.txt in the CSD Settings Folder (use the command General Tab > Settings Panel > Open Settings folder to open to the current location of the CSD Settings).
The file does not need any contents inside - the software just looks for the file to be located in the settings folder and, if present, makes the adjustment to C factors based on storm ARI (or equivalent AEP). The file is also attached if users would prefer to copy a file into the CSD Settings.
Here is some information found regarding this adjustment:
Table 2.2 will be applied if this file is included in the CSD Settings folder.
