What phenomenon occurs in an open channel when a rapidly flowing stream changes to a slower stream?

A hydraulic jump refers to a specific phenomenon that occurs in open channel flow when the flow regime changes from supercritical (rapid and shallow) to subcritical (slower and deeper). This transition is characterized by a sudden increase in water depth and a corresponding decrease in velocity. The hydraulic jump is an important feature in fluid mechanics and hydraulic engineering since it signifies a change in flow conditions that impacts energy and momentum in the system.

When water flows rapidly and has high kinetic energy, it is in a supercritical state. Upon encountering a change in channel geometry or friction, the flow may slow down significantly, resulting in a hydraulic jump. The jump is marked by a turbulent mixing region where the flow transitions from a state of lower depth and higher velocity to a state of higher depth and lower velocity.

Understanding hydraulic jumps is crucial for engineers when designing channels, spillways, and other hydraulic structures, as they can significantly affect flow characteristics and energy dissipation.