Use the Pressure Head node to specify the pressure head (instead of the pressure) on a boundary. It adds this boundary condition for the pressure head
Hp = Hp0, where
Hp0 is a known pressure head given as a number, a distribution, or an expression involving time,
t, for example. The dimension of the pressure head is length (SI unit: m).
Enter a value or expression for the Pressure head Hp0 (SI unit: m). The default is 0 m.
) and select Advanced Physics Options in the Show More Options dialog box.