'wave' In A River.

[Khandro]

When on a rocky river-bed of a shallow-ish river, the current hits a large but submerged rock, the water folds back on itself above the surface and creates a continuing 'foaming wave' against the direction of the current.
Does this phenomenon have a name please?

[Octavius]

Do you mean like the riveer severn bore?

[Octavius]

http://www.severn-bore.co.uk/

[Baldric]

Try here,
whole page is quite interesting
http://en.wikipedia.org/wiki/Whitewater#Holes

[Octavius]

Oh I see you said against the current, probably a standing wave.

[jim360]

I'd need to see a clearer picture of what you are talking about but I think Octavius is on the right lines. Standing wave or some variation on that theme.

[Baldric]

From the link, thought this was what you meant,

Holes, or "hydraulics", (also known as "stoppers" or "souse-holes". See also Pillows), are formed when water pours over the top of a submerged object, or underwater ledges, causing the surface water to flow back upstream toward the object.

[Khandro]

'Standing Wave' sounds good. If you see a river like the Wye, it's the 'white bits'. The current is momentarily thrown back in itself.

[Khandro]

Octavius; Thanks, 'standing wave' led me to this; http://en.wikipedia.org/wiki/Standing_wave

[jomifl]

You got there at last Khandro, 6 months after I told you about standing waves and gave you a link you seem to have found one. You can see standing waves in water trickling from a tap too, if you look.

[jomifl]

By the way the current is not 'thrown back on itself', though it may sometimes appear to be the case. The current flows through the wave. A current 'thrown back on itself' is an eddy.

[Khandro]

jomifl; It's one thing disagreeing with you on other sites, and I have no wish to do so here but this is a subject I have never considered before and I have reason to search for an answer, (which I have) in what connection did you previously give me a link to an answer please.
Also if you look at baldric's link above there is a description of an eddy which sounds different from yours, in that it exists on the downside of the wave, though I may be misreading you.

http://en.wikipedia.org/wiki/Whitewater#Holes

[heathfield]

'Standing waves' yes, but if they are breaking, they can be called 'overfalls'.

[jomifl]

Khandro, perhaps you remember the thread where I gave you a link to a Dali painting depicting a woman sewing at an open window in Figueras. The painting shows a wave cloud over the pyrenees. This is caused by a a standing wave or waves in the air flowing over mountainous terrain. As the air ascends the moisture condenses to form a cloud , as it descends the moisture evaporates so that the cloud appears motionless relative to the ground. The cloud is continually being replenished at the upwind side and dissolved at the downwind side. Sometime there is a chain of wave clouds of diminishing size and constant intervals downwind from a mountain. Look up 'standing wave' in wiki and in youtube there are some good examples. Also set a tap at a slow trickle and with a bit of adjustment so that you get turbulent flow you will see standing waves starting at the tap and getting smaller but longer as the water accelerates under gravity. They are everywhere.

[Mojo-Jo-Jo]

That's a bit harsh Jomifl.
Most people would not associate water and the clouds together.
I know they are fluids and clearly so do you, but to pull up something like that just smacks of having a gratuitous dig.

[jomifl]

Well mojo, no dig was intended I can assure you. I'm sure Khandro can deal with the concept without having it dumbed down.

[jomifl]

The Severn Bore is not a standing wave, it is not a normal travelling wave, it is a mass of water travelling along a channel.

[Khandro]

In case it is of interest to anyone; I live by a river (the Neckar) on the upper reaches, and at the moment it is about 2 ft / 60 cm deep. When I stand on my bridge I look down on what I believe to be a lintel left from an earlier bridge, lying on the bed and 90 degrees to the river flow. This causes a constant wave backwards against the flow - which I now believe to be called a 'standing wave', it resembles a sea wave by the shore but remains in the same position and is continuously changing its shape which I find fascinating to watch and draw.
I happen to have recently read all of Leonardo's extensive notes on water, and I don't think there could be anything that would have escaped his attention, however when reading them I wasn't at that time particularly looking for this, and as they are so extensive I now cannot remember a reference, and it is anyway frequently difficult to follow his meaning as he was writing only for himself and in Renaissance period Tuscan, a cross between I think Latin and modern Italian, and my old translations are in 'Victorian English' which doesn't exactly help me to find it there.

[Peter Pedant]

Look at

Flow over a weir

If you are at all mathematical , v v interesting and well done course on waves and fluid flow at the OU

[Hypognosis]

I would use the term 'bow-wave' (as in bow of a ship). We're used to seeing this sort of thing, on the upstream side of a bridge pier, for instance, whilst the downstream side has whirls and eddies.

The extreme form would be 'bow-shock' as in ballistics or supersonic aircraft etc.

The key difference, in Khandro's case, is that it is a blunt object, facing across the direction of flow and obstructing it so it becomes a neat visual analogue of what happens at the front of an unaerodynamic car, except the effect is exaggerated because water is incompressible.

[Khandro]

Hypognosis; Does it make a difference that the obstruction is below the surface level of the river, creating the continuous wave above? and what would you describe then as a standing wave.
It's important to me not only scientifically but because I might use it in a title.