Definition of critical, sub-critical and SuperCritical flow

Critical flow

The flow at depth equal to the critical depth is known as critical flow.

Sub-critical Flow

The flow at which depth of the channel is greater than critical depth, velocity of flow is less than critical velocity and slope of the channel is also less than the critical slope is known as sub-critical flow.

1. The channel is called as deep channel for sub-critical flow.
2. Sub critical flow is also called as slow or tranquil flow.

SuperCritical flow

The flow at which depth of the channel is less than critical depth, velocity of flow is greater than critical velocity and slope of the channel is also greater than the critical slope is known as supercritical flow.

1. The channel is called as shallow channel for supercritical flow.
2. Supercritical flow is also called as rapid or fast flow.