How is critical flow characterized?

Critical flow is specifically characterized by a Froude number of one. The Froude number is a dimensionless parameter that compares inertial forces to gravitational forces in a flowing fluid. When the Froude number equals one, it indicates that the flow velocity is equal to the wave velocity, which is a key condition for determining critical flow. In practical terms, this means that the flow is at a transition point between subcritical (calm, slower-moving water) and supercritical (fast, turbulent water) conditions.

Achieving a Froude number of one indicates a state of flow in which the kinetic energy of the water is balanced with the potential energy available due to gravity. This critical state is quite important in various hydraulic applications, such as designing channels, spillways, and understanding flow behavior around structures.

Other conditions, such as turbulent flow, high sediment concentration, or stagnant water, do not properly define critical flow and reflect different flow regimes or characteristics distinct from this specific point of balance illustrated by a Froude number of one.