GGU-2D-TRANSIENT: "Special 1" menu item
This menu item is only available for vertical-plane and axis-symmetrical systems. You will see the following information:

You can thus restrict the occurrence of boundary conditions This can be useful in order to avoid a negative pressure in the system.
For example, this can apply to the water side of an embankment if a potential is initially defined at the top of the embankment and then the water level lowered to the base.