A hydrograph can be computed from any of the supported hydrologic models. A hydrograph can also be defined/imported using the New command in the Hydrograph menu. This option allows you to copy a hydrograph from the clipboard, or open a text file using the text import wizard and define it for a selected basin or outlet node.
The hydrograph should be selected prior to bringing up the detention basin calculator.
Related Topics:
Detention Basin Calculator
Displaying Hydrographs