Hydraulic jump

A hydraulic jump is an abrupt rise in water depth as fast, shallow, supercritical flow changes to slower, deeper, subcritical flow. It dissipates substantial mechanical energy through turbulence and mixing.

Froude number: A dimensionless ratio comparing flow inertia with gravity-wave effects. It distinguishes the supercritical flow before a jump from the subcritical flow after it.
Open-channel flow: Liquid flow with a free surface exposed to atmospheric pressure. Hydraulic jumps are transitions within this kind of flow.
Stilling basin: A structure downstream of a dam or outlet designed to dissipate flow energy and reduce erosion. Its geometry holds a hydraulic jump in place to protect the channel downstream.
Rectangular channel: An open channel with a rectangular cross-section. Standard jump relations are commonly derived for this simple channel shape.
Hydraulic drop: A rapid fall in water depth as shallow, fast flow changes to deeper, slower flow downstream. It is the downstream counterpart to a hydraulic jump’s abrupt rise in depth.
Specific energy: The sum of flow depth and velocity head, measured relative to a channel bed. A jump reduces specific energy while conserving momentum across the transition.
Supercritical flow: Open-channel flow in which velocity exceeds the speed of small gravity waves. A hydraulic jump begins when this fast, shallow regime is forced to slow.
Spillway: A structure that safely conveys excess water from a dam or reservoir. Spillway discharge can enter a stilling basin at supercritical speed and form a jump.
Hydraulic jump in a rectangular channel: A hydraulic jump in a prismatic rectangular channel, with depth relations determined by the incoming Froude number. This canonical case gives a direct calculation of downstream conjugate depth.
Bore: A steep, moving wavefront that travels into shallower water, often producing an abrupt rise in depth. Unlike a typical channel jump, a bore propagates as a wave rather than remaining fixed by flow conditions.

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