Mixing of fluid streams in rivers

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Discussion Overview

The discussion revolves around the observation of fluid dynamics at the confluence of a river and a side stream, specifically focusing on the visual separation of two distinct water types and the implications for flow behavior. The scope includes conceptual exploration of hydraulics theory and personal observations of river confluences.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant notes the clear boundary between the reddish-brown river water and the grey-green side stream, suggesting a lack of mixing.
  • Another participant shares a personal observation of a similar phenomenon at a different river confluence, expressing interest in the visual aspect.
  • A question is raised about the expected transition between the two water types, indicating some uncertainty about the nature of the observation.
  • There is a discussion about the flow of the side stream, with one participant asserting it has ceased while another counters that it is still flowing, despite appearances.
  • Participants acknowledge the difficulty of capturing true movement in still photos, with one asserting that the side stream was essentially still during the observation.
  • The main river's flow is described as very fast, with a reference to a nearby gauging station indicating high water levels.
  • One participant introduces the term "in spate" to describe the river's condition, suggesting it may be unfamiliar to others.

Areas of Agreement / Disagreement

Participants express differing views on the flow status of the side stream, with no consensus reached on whether it has ceased or is still flowing. The discussion remains unresolved regarding the dynamics of mixing at the confluence.

Contextual Notes

There are limitations in the observations due to the nature of still photography, which may not accurately represent fluid movement. Additionally, the discussion includes varying interpretations of flow behavior and terminology.

Who May Find This Useful

Individuals interested in fluid dynamics, river ecology, or those studying hydraulic phenomena may find the observations and discussions relevant.

Studiot
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Walking round a local amenity area today brought this photo of a side stream cut off by the local river in spate flowing past from left to right in the picture.

The river water is reddy brown and the side stream grey-green.
The two waters are not mixing as can be seen by the well defined boundary.
 

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This happens at many confluences, the most recent I've personally seen is at the confluence of the Monongahela and Allegheny rivers in Pittsburgh, PA. It's pretty neat to see.
 
What would you have expected it to look like?

The grey green needs to somehow transition to the reddish brown?

Maybe I don't get your question.
 
Maybe I don't get your question.

Obviously not since I didn't have one.

I just thought that some might be interested.

I can certainly see some features of hydraulics theory in play can you?

The most obvious is that the side stream flow has essentially ceased.
 
Studiot said:
Obviously not since I didn't have one.

I just thought that some might be interested.

Ah! Ok. My bad. Sorry.

The most obvious is that the side stream flow has essentially ceased.

No I don't think that's true. I think it is still flowing. The interface makes you think it isn't.
 
It is difficult to impossible to show true (as opposed to arty) movement in a still photo.

I can assure you that the water in the side stream was essentially still. Normally its level would not be that high and it would run out quite quickly into the river.
 
Studiot said:
It is difficult to impossible to show true (as opposed to arty) movement in a still photo.

I can assure you that the water in the side stream was essentially still. Normally its level would not be that high and it would run out quite quickly into the river.

The main stream was flowing very fast?
 
The main stream was flowing very fast?

That's what I said. The nearby river gauging station was running above the weir.

the local river in spate

Perhaps this English term is new to you?

Here are some typical flood pictures from November.

 
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