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An abrupt increase of depth in a free-surface liquid flow. A hydraulic jump is characterized by rapid flow and small depths on the upstream side, and by larger depths and smaller velocities on the downstream side. A jump can form only when the upstream flow is supercritical, that is, when the fluid velocity is greater than the propagation velocity c of a small, shallow-water gravity wave (c = gh, where g is the acceleration of gravity and h is the depth). A considerable amount of energy is dissipated in the conversion from supercritical to subcritical flow. See Open channel
an abrupt turbulent rise in water level in an open channel during a change in flow from a so-called turbulent condition to a calm condition. Hydraulic jump is accompanied by the formation of a surface “roller,” within which the heavily air-saturated fluid is in compound rotary motion.
Hydraulic jump usually occurs during the passage of a flow through the openings of hydraulic structures, such as spillways and floodgates. Channel degradations can occur as a result of high flow rates along the bottom in the hydraulic jump zone. The theory of hydraulic jumps is treated in hydraulics.