[clarification needed] The analogous condition in gas dynamics is supersonic speed.
This is the velocity at which waves travel outwards from a pebble thrown into a lake.
It is only in supercritical flows that hydraulic jumps (bores) can occur.
In fluid dynamics, the change from one behaviour to the other is often described by a dimensionless quantity, where the transition occurs whenever this number becomes less or more than one.
The Hydraulics of Open Channel Flow: An Introduction.