The IDF Table Equation definition type calculates the storm data using the following equation:

Where

• i = rainfall intensity
• D = rainfall duration
• Rp = return period
• a, b, m, n = rainfall equation coefficients

When editing a definition of the IDF Table Equation type, the tabbed area of the dialog contains the following controls:

Storm Data Input Tab

Equation Duration Unit: Specify the unit to be used for duration (D) value in the equation.

Equation Intensity Unit: Specify the unit to be used for intensity (i) value in the equation.

a: Specify the value to be used for the a coefficient in the equation.

m: Specify the value to be used for the m coefficient in the equation.

b: Specify the value to be used for the b coefficient in the equation.

n: Specify the value to be used for the n coefficient in the equation.

Results Table: This table displays the calculated rainfall intensity values for the 2, 3, 5, 10, 25, 50, 100, 200, and 500 year return periods at durations of 5, 10, 15, 20, 30, 40, 50, 60, 80, 100, and 120 minutes.

Notes Tab

This tab contains a text field that allows you to enter descriptive notes that will be associated with the currently highlighted storm data definition.

Library Tab

This tab displays information about the storm data definition that is currently highlighted in the list pane. If the storm data definition is derived from an engineering library, the synchronization details can be found here. If the storm data definition was created manually for this model, the synchronization details will display the message Orphan (local), indicating that the storm data definition was not derived from a library entry.