Hydraulic jump over a weir

River Geomorphology Video created by Little River Research and Design, with funding from the Missouri Department of Natural Resources. http://serc.carleton.edu/details/files/19076.html

This clip shows basic hydraulics over a weir with a small amount of plastic media in the flume. At the clip beginning dye is injected into flow upstream of the weir to show the transition from relatively deep, low velocity subcritical flow to critical and supercritical flow over the weir.

Downstream of the weir, supercritical flow is much faster and shallower. As the downstream gate is closed, stage rises and a submerged hydraulic jump appears downstream. Here we can also see the loss of energy due to the jump by comparing the elevation of the water surface below the weir with that above the weir. This energy loss is one of the things that make grade control structures work - they act to dissipate the energy of flow at a point of our choosing.

Note the turbulence and reverse roller (the sort that is very dangerous to be caught in) below the weir.

Category:

Science & Technology

Tags:

• hydraulic jump
• fluid mechanics
• physics
• science

[fwengsolutions]

You've mislabelled things a bit. It seems like you think that the hydraulic jump is the water diving down over the top of the weir. In fact the hydraulic jump is the turbulent jump in water surface elevation that you finally see moving up from downstream; that which you labelled a "submerged hydraulic jump". It's not a submerged hydraulic jump until it moves all the way up to the weir.

[argongemini]

question mate, how will you design a spillway to counter the submerged jump?

[gravelbar]

@fwengsolutions I'm the author of the video, and you're right. I was taught that a change in flow regime (e.g. subcritical to critical) was hydraulic jump, but I see that the definition is restrictied the way you describe, thanks for the correction.

[Cineenvenordquist]

@argongemini I guess I'd add a wetting surface (at the foot of the weir, unless there are more spillway rules) to create turbulence from the jump, or add cycloidal forms to throw pressure (merely) consistent with depth against what peeps call backwash; or, concentrate that submerged hydraulic jump/roller, add radial vanes and call it the observation pad. More love for the camera station crew.