Submergence is a parameter used to determine the amount of liquid needed above a pipe supply from a tank or reservoir to ensure smooth flow and avoid vortexing. AFT Fathom offers a pipe output parameter for submergence and also submergence margin, which is the difference between the submergence and the actual pipe depth.

Note: Pipe output parameters for submergence include options for Submergence Inlet and Submergence Outlet. Like all pipe output parameters, the Inlet and Outlet reference the inlet and outlet of the pipe. They do not describe if flow is entering or exiting the tank.

The equation used in AFT Fathom for submergence is given by ANSI/HI Standard 9.8.7 1998ANSI/HI Standard 9.8-1998, American National Standard for Pump Intake Design, 1998, published by Hydraulic Institute, 6 Campus Drive, Parsippany, New Jersey, USA, p. 32:

Where S is the submergence and Fr is the Froude number. Note that the required submergence can be modified by using devices such as baffles in which case the above equation would not apply.