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There is a cleanup tag but no talk to go with it. Any comments on what needs to be cleaned up? I added meander ratio as it seemed too small for its own article. Ruhrfisch 02:27, 19 April 2006 (UTC)
This article requires a heavy edit for a variety of scientific reasons - river meandering is a widely misunderstood phenomenon and getting to grips with current thinking (e.g., Seminara (2006), Journal of Fluid Mechanics, v.554, pp.271-297) requires a great deal of effort. The present article, however well-intentioned, perpetuates several misconceptions that do Wikipedia little credit. I can eventually take on the task if needed. -- Cstarknyc ( talk) 02:03, 15 April 2008 (UTC)
Erosion is greater on the outside of the bend where velocity is greatest. Deposition of sediment occurs on the inner edge because the river, moving slowly, cannot carry its sediment load, creating a slip-off slope called a point bar. The faster moving current on the outside bend has more erosive ability and the meander tends to grow in the direction of the outside bend. Point bar#Fallacy regarding formation of point bars calls this an enduring fallacy. I don't know which one is right, and neither statement has sources, but Wikipedia shouldn't contradict itself in such a blatant manner. -- 87.162.13.146 ( talk) 14:47, 9 July 2009 (UTC)
The following statement appears in Meander#Formation. The cited source is the Encyclopedia of Sediments and Sedimentary Rocks.
The helical flow is explained as a transfer of momentum from the inside of the bend to the outside. As soon as the flow enters the bend some of its momentum becomes angular, the conservation of which would require an increase of velocity on the inside and a decrease on the outside, exactly the opposite of what happens. Instead centrifugal force superelevates the surface on the outside, moving surface water transversely into it. This water moves down to replace the subsurface water pushed back at the end of the bend.
The words exactly the opposite of what happens suggest that in the vicinity of a meander the flow pattern is opposite to what is predicted by conservation of momentum. I don't have the Encyclopedia of Sediments and Sedimentary Rocks so I can't check exactly what is stated, but my sources all confirm that rivers, and water in general, do flow in accordance with the law of conservation of momentum. In particular, where rivers follow a curved path across the landscape (such as in a meander) they conform to vortex flow with the fastest primary flow towards the inside of the bend, and the slowest primary flow towards the outside of the bend. ( Secondary flow modifies this simple velocity profile.)
I suggest the offending text should be deleted unless it can be modified to make sense and match what is actually stated in the cited encyclopedia. Is anyone able to assist with this small task? Dolphin51 ( talk) 04:29, 10 July 2009 (UTC)
My emphasis.In the absence of secondary flow, bend flow seeks to conserve angular momentum so that it tends to conform to that of a free vortex with high velocity at the smaller radius of the inner bank and lower velocity at the outer bank where radial acceleration is lower. But secondary flow redistributes momentum in the bend to achieve a reversal of this relationship in the zone of fully developed bend flow.
On 15 & 16 May 2011 some text and an in-line citation were removed from Meander#Formation and replaced by the following new text. (See diff.):
I have now restored the original text as follows. (See diff.):
The end result is that some of the ideas are now duplicated. There is a need to rationalise what is there by removing any duplication, unsourced statements and unencyclopedic language.
My thoughts are that the new text is a bit too like a textbook for teenagers and not enough like an encyclopedia. Any other thoughts? Dolphin ( t) 03:07, 17 May 2011 (UTC)
I will try and think about it some more to try and make it easier to read, but the statement:"Flow of a fluid around a bend is vortex flow in order to conserve angular momentum. The speed of flow on the outside of the bend is fastest, and on the inside of the bend is slowest." is actually wrong and even the opposite of the cite they are quoting below which says "In the absence of secondary flow, bend flow seeks to conserve angular momentum so that it tends to conform to that of a free vortex with high velocity at the smaller radius of the inner bank and lower velocity at the outer bank where radial acceleration is lower." So, maybe switching the words outside and inside set it right, but I still feel it is a bit wrong. I actually have a friend who learned similar wrong ideas in a non fluid mechanics class and it was from a non-fluids textbook (like sedimentation). I feel like looking at the angular momentum is not the thing to do here, but I have to think about it a bit more. I remember that when dealing with an object like a spinning record (rigid body rotation) it makes sense to look at angular momentum (the outer edge has higher velocity than the inner), but here since the main flow is irrotational it does not make sense to explain it from such point of view. I think conservation of angular momentum here means there is no change in circulation in time so that if it starts irrotational it must stay that way (for the most part). Usually we talk in terms of pressure gradients due curvature and this cause a change in velocity or elevation due to Bernouli's equation. I will try and think of a better way of wording it. The .pdf file I cited seems to explain it nicely though.
MichaelScottRoberts (
talk) 06:12, 17 May 2011 (UTC)
Sorry to be so critical, but this text needs a thorough revision to reflect current thinking on how meander morphodynamics works. For example, it is incorrect to invoke secondary flow as the main mechanism for the evolution of a channel-transverse gradient (the slope of a point bar) and the work by Callander is known to contain a fundamental error. There is now an enormous body of work on meander theory by the likes of Parker, Seminara and many others, and yet the insights generated by their studies are entirely ignored here. cstarknyc 12:18, 11 August 2011 (EDT)
I notice that an attempt was made to expand and clarify what I had. I'm the most responsible for this article. I left an opening there through lack of thoroughness. However, the rewriting editors had terrible difficulty with it. First, the English was awful. It attempted to imitate the English of the sources. Well, the source English was bad to begin with but the digest was even worse. You have to know grammar, there is just no way around it. So, if you have been trying to avoid taking your required English, better cease and desist that. The editors reacted in a couple of different ways. First, they said everything three times as though pronouncing it three times gave it some kind of binding status. Second, they larded it up with references that said the same thing over and over, as though the more references the more authoritative. So, I condensed it. That involved some rewriting. I kept the references I thought were most relevant. I didn't see anything uncovered by references. What's being said there is relatively simple and does not need rocket science. Plain and simply the vortex flow around bends is caused by bottom drag. Big deal. One sentence. The rest of it does not appear to have changed much but I better check it. I appaud your intent, which was to fill a gap. Dave ( talk) 05:24, 17 August 2011 (UTC)
You didn't make any changes there. Per above you don't like my phraseology. I will change that to try to fit the quoted source. Feel free to change it yourself also. We aren't doing a technical treatise in a few paragraphs but it is important to get the right words. The source quotations do cover it so I will probably let them speak for themselves. Maybe they should be moved into the text. I'm not going to argue over whether the binding forces are relevant or what the pressure of centrifugal force is. YOU phrase it, YOU write it! Be brief, clear, to the point, technically correct, write in good English. At the moment I am going to start at the top. I have so many things to do, but I will work on this bit by bit. Dave ( talk) 10:50, 17 August 2011 (UTC)
Later. OK I see the restored paragraph. Whew, what a confusing array. I don't object to your language, it is basically the arrangement of ideas that is incomprehensible. There is no sense of how it fits together. The concept of sweeping the sediment is repeated three times! So, basically we are talking about the arrangement of ideas or logical flow in two paragraphs. There are some quoted sources in there so they should be used to establish the flow. This is a problem in logical flow. I need a little time to ponder this and come up with a flow that makes sense using your and the sources' language. No need to put a confusing tag on yet. Let's work on it. Dave ( talk) 11:32, 17 August 2011 (UTC)
I got a plan. The topic of those three paragraphs is the helical flow. So, we need to state
For this source a really unusual book publishing situation prevails. One and the same encyclopedia was published 2 or 3 times in 2003 as the branding changed. Same encyclopedia, different branding. This article cited 2 different brands. As it is the same book, I picked the last one of the year, which is previewable. The harvard ref system does not take into consideration this different branding. Rather than cite each brand separately I thought it better to pick one brand. Same book, same publisher, same pages, which changed names. The editor of this section cited Hickin 4 times. The harvard ref system permits brief reference to different pages of a single biblio item, a much more condensed technique than reciting the book multiple times. If you are interested you can find it on WP under template:harvnb. Dave ( talk) 01:25, 18 August 2011 (UTC)
Well really, I can't tell you how glad I am to see you both take such an interest. I don't think my role got across too clearly. The article was already about 80% written. As it happens the majority of the writing is mine, as I got it in almost a null state. However, that is neither here nor there. This one section we are working on was a very brief introduction to the subject. That is all I intended it to be. Some other editors wanted to expand it a bit to try and explain the spiral flow. I was not going to do that. I felt what they did needed a vigorous edit. I am acting as an editor here fixing what seems to be wrong. I'm primarily interested in the English composition and the format. Now, that being so, I noticed a certain paradoxical approach especially by you Dolphin. First, you seem only interested in this section, even though I wrote most of the rest of it. Second, whatever I write is always wrong, even though it is not. Third, although this is a collaborative effort, you make no contribution yourself even though I invite you to. Fourth, you seem to focus intensely on some detail but to not to be able to make sense of the whole flow.
Nevertheless if that is what it takes to get your participation, well, I welcome it. What we are trying to do with this introduction is give a few paragraphs introducing the formation of meanders, as that is the titled topic. I don't care who does it as long as it is done well. If you want to put everything back and start over that wouldn't bother me. If you want to rewrite it that would not bother me either. As far as what I wrote is concerned, I'm not especially attached to any of it. Delete it all if you wish. Here is the job requirement as I see it: one introduction to the topic of formation of meanders. It must be incisive but at the same time not so technical that the public cannot understand it. It must be written for the general interested public as an audience. It must be in correct formal English.
Now, I can't really tell you if something conforms to that standard until I see it. So far Dolphin you have avoided doing anything I can critique. What was wrong with the previous is as follows. Not correct formal English. Awkward and repetitios English. No logical flow. Larded with technical terms from Fluid Flows that mean nothing to the public. Overcited with repetitive sources. Too many sources of the same topic.
What would be best is if YOU wrote the intro. Go ahead. Write. What's holding you back? Nothing ventured, nothing gained. Second best is for me to discuss all your comments and keep rewriting until you are both happy. That would take a long time. If neither of those things happen the default is to put it back the way it was and not change it. I don't opt for that one. It already had a few tags on it. I would have a lot more to put on. The idea is to improve it. So, I'm most heartened by Siegmund's suggestion for collaborative action. Go ahead, Siegmund. Dolphin I appreciate your comments. I can answer some of those. I'm going to do that and also I am going to give the two of you a chance to make such changes as you see fit. A further rewrite is not warranted by me until I see where it is going. It can't go anywhere unless you make it go somewhere. Where do you want it to go? So, if I do not write anything immediately it is because I am waiting to see what you do. I may work on some of the formatting and finish editing the rest of it. I think I made two edits in the whole first part, which seemed good to me. Dave ( talk) 02:10, 18 August 2011 (UTC)
The section titled #Governing physics contains two statements that contradict statements in #Formation:
I have inserted the Citation needed tag on the two offending sentences. In addition to these offending sentences, I think the section Governing physics is sufficiently unencyclopaedic that it requires a clean-up, or even deletion. For example, it attempts to explain the secondary flow in terms of centrifugal force which is a fictitious force! It attempts to explain the commencement of a meander using the Coriolis force, citing a source that appears not to mention Coriolis force! Unfortunately, the whole of Governing physics was created on 23 December 2016 (see the diff) by User:Ariadne3s a new User who has not contributed since that date. Dolphin ( t) 13:24, 31 July 2019 (UTC)
There is an easily demonstrated (and fascinating) example of meandering that occurs without erosion or sedimentation being involved, which means, as Ricky Ricardo would say, "You have some 'splaining to do". (Full disclosure: I have not yet digested all of the article or all Talk sections.)
Hold a plate of glass (smooth, very flat) under a small steady stream of water, at about a 30-degree angle from horizontal. The water will run down the glass in a straight stream. Gradually level the plate toward horizontal. At some point the stream will suddenly break in meanders.
The suddenness and intensity of the meandering suggests some positive feedback is involved. But in any case, there is obviously no erosion or sedimentation involved; some 'splaining is called for.
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There is a cleanup tag but no talk to go with it. Any comments on what needs to be cleaned up? I added meander ratio as it seemed too small for its own article. Ruhrfisch 02:27, 19 April 2006 (UTC)
This article requires a heavy edit for a variety of scientific reasons - river meandering is a widely misunderstood phenomenon and getting to grips with current thinking (e.g., Seminara (2006), Journal of Fluid Mechanics, v.554, pp.271-297) requires a great deal of effort. The present article, however well-intentioned, perpetuates several misconceptions that do Wikipedia little credit. I can eventually take on the task if needed. -- Cstarknyc ( talk) 02:03, 15 April 2008 (UTC)
Erosion is greater on the outside of the bend where velocity is greatest. Deposition of sediment occurs on the inner edge because the river, moving slowly, cannot carry its sediment load, creating a slip-off slope called a point bar. The faster moving current on the outside bend has more erosive ability and the meander tends to grow in the direction of the outside bend. Point bar#Fallacy regarding formation of point bars calls this an enduring fallacy. I don't know which one is right, and neither statement has sources, but Wikipedia shouldn't contradict itself in such a blatant manner. -- 87.162.13.146 ( talk) 14:47, 9 July 2009 (UTC)
The following statement appears in Meander#Formation. The cited source is the Encyclopedia of Sediments and Sedimentary Rocks.
The helical flow is explained as a transfer of momentum from the inside of the bend to the outside. As soon as the flow enters the bend some of its momentum becomes angular, the conservation of which would require an increase of velocity on the inside and a decrease on the outside, exactly the opposite of what happens. Instead centrifugal force superelevates the surface on the outside, moving surface water transversely into it. This water moves down to replace the subsurface water pushed back at the end of the bend.
The words exactly the opposite of what happens suggest that in the vicinity of a meander the flow pattern is opposite to what is predicted by conservation of momentum. I don't have the Encyclopedia of Sediments and Sedimentary Rocks so I can't check exactly what is stated, but my sources all confirm that rivers, and water in general, do flow in accordance with the law of conservation of momentum. In particular, where rivers follow a curved path across the landscape (such as in a meander) they conform to vortex flow with the fastest primary flow towards the inside of the bend, and the slowest primary flow towards the outside of the bend. ( Secondary flow modifies this simple velocity profile.)
I suggest the offending text should be deleted unless it can be modified to make sense and match what is actually stated in the cited encyclopedia. Is anyone able to assist with this small task? Dolphin51 ( talk) 04:29, 10 July 2009 (UTC)
My emphasis.In the absence of secondary flow, bend flow seeks to conserve angular momentum so that it tends to conform to that of a free vortex with high velocity at the smaller radius of the inner bank and lower velocity at the outer bank where radial acceleration is lower. But secondary flow redistributes momentum in the bend to achieve a reversal of this relationship in the zone of fully developed bend flow.
On 15 & 16 May 2011 some text and an in-line citation were removed from Meander#Formation and replaced by the following new text. (See diff.):
I have now restored the original text as follows. (See diff.):
The end result is that some of the ideas are now duplicated. There is a need to rationalise what is there by removing any duplication, unsourced statements and unencyclopedic language.
My thoughts are that the new text is a bit too like a textbook for teenagers and not enough like an encyclopedia. Any other thoughts? Dolphin ( t) 03:07, 17 May 2011 (UTC)
I will try and think about it some more to try and make it easier to read, but the statement:"Flow of a fluid around a bend is vortex flow in order to conserve angular momentum. The speed of flow on the outside of the bend is fastest, and on the inside of the bend is slowest." is actually wrong and even the opposite of the cite they are quoting below which says "In the absence of secondary flow, bend flow seeks to conserve angular momentum so that it tends to conform to that of a free vortex with high velocity at the smaller radius of the inner bank and lower velocity at the outer bank where radial acceleration is lower." So, maybe switching the words outside and inside set it right, but I still feel it is a bit wrong. I actually have a friend who learned similar wrong ideas in a non fluid mechanics class and it was from a non-fluids textbook (like sedimentation). I feel like looking at the angular momentum is not the thing to do here, but I have to think about it a bit more. I remember that when dealing with an object like a spinning record (rigid body rotation) it makes sense to look at angular momentum (the outer edge has higher velocity than the inner), but here since the main flow is irrotational it does not make sense to explain it from such point of view. I think conservation of angular momentum here means there is no change in circulation in time so that if it starts irrotational it must stay that way (for the most part). Usually we talk in terms of pressure gradients due curvature and this cause a change in velocity or elevation due to Bernouli's equation. I will try and think of a better way of wording it. The .pdf file I cited seems to explain it nicely though.
MichaelScottRoberts (
talk) 06:12, 17 May 2011 (UTC)
Sorry to be so critical, but this text needs a thorough revision to reflect current thinking on how meander morphodynamics works. For example, it is incorrect to invoke secondary flow as the main mechanism for the evolution of a channel-transverse gradient (the slope of a point bar) and the work by Callander is known to contain a fundamental error. There is now an enormous body of work on meander theory by the likes of Parker, Seminara and many others, and yet the insights generated by their studies are entirely ignored here. cstarknyc 12:18, 11 August 2011 (EDT)
I notice that an attempt was made to expand and clarify what I had. I'm the most responsible for this article. I left an opening there through lack of thoroughness. However, the rewriting editors had terrible difficulty with it. First, the English was awful. It attempted to imitate the English of the sources. Well, the source English was bad to begin with but the digest was even worse. You have to know grammar, there is just no way around it. So, if you have been trying to avoid taking your required English, better cease and desist that. The editors reacted in a couple of different ways. First, they said everything three times as though pronouncing it three times gave it some kind of binding status. Second, they larded it up with references that said the same thing over and over, as though the more references the more authoritative. So, I condensed it. That involved some rewriting. I kept the references I thought were most relevant. I didn't see anything uncovered by references. What's being said there is relatively simple and does not need rocket science. Plain and simply the vortex flow around bends is caused by bottom drag. Big deal. One sentence. The rest of it does not appear to have changed much but I better check it. I appaud your intent, which was to fill a gap. Dave ( talk) 05:24, 17 August 2011 (UTC)
You didn't make any changes there. Per above you don't like my phraseology. I will change that to try to fit the quoted source. Feel free to change it yourself also. We aren't doing a technical treatise in a few paragraphs but it is important to get the right words. The source quotations do cover it so I will probably let them speak for themselves. Maybe they should be moved into the text. I'm not going to argue over whether the binding forces are relevant or what the pressure of centrifugal force is. YOU phrase it, YOU write it! Be brief, clear, to the point, technically correct, write in good English. At the moment I am going to start at the top. I have so many things to do, but I will work on this bit by bit. Dave ( talk) 10:50, 17 August 2011 (UTC)
Later. OK I see the restored paragraph. Whew, what a confusing array. I don't object to your language, it is basically the arrangement of ideas that is incomprehensible. There is no sense of how it fits together. The concept of sweeping the sediment is repeated three times! So, basically we are talking about the arrangement of ideas or logical flow in two paragraphs. There are some quoted sources in there so they should be used to establish the flow. This is a problem in logical flow. I need a little time to ponder this and come up with a flow that makes sense using your and the sources' language. No need to put a confusing tag on yet. Let's work on it. Dave ( talk) 11:32, 17 August 2011 (UTC)
I got a plan. The topic of those three paragraphs is the helical flow. So, we need to state
For this source a really unusual book publishing situation prevails. One and the same encyclopedia was published 2 or 3 times in 2003 as the branding changed. Same encyclopedia, different branding. This article cited 2 different brands. As it is the same book, I picked the last one of the year, which is previewable. The harvard ref system does not take into consideration this different branding. Rather than cite each brand separately I thought it better to pick one brand. Same book, same publisher, same pages, which changed names. The editor of this section cited Hickin 4 times. The harvard ref system permits brief reference to different pages of a single biblio item, a much more condensed technique than reciting the book multiple times. If you are interested you can find it on WP under template:harvnb. Dave ( talk) 01:25, 18 August 2011 (UTC)
Well really, I can't tell you how glad I am to see you both take such an interest. I don't think my role got across too clearly. The article was already about 80% written. As it happens the majority of the writing is mine, as I got it in almost a null state. However, that is neither here nor there. This one section we are working on was a very brief introduction to the subject. That is all I intended it to be. Some other editors wanted to expand it a bit to try and explain the spiral flow. I was not going to do that. I felt what they did needed a vigorous edit. I am acting as an editor here fixing what seems to be wrong. I'm primarily interested in the English composition and the format. Now, that being so, I noticed a certain paradoxical approach especially by you Dolphin. First, you seem only interested in this section, even though I wrote most of the rest of it. Second, whatever I write is always wrong, even though it is not. Third, although this is a collaborative effort, you make no contribution yourself even though I invite you to. Fourth, you seem to focus intensely on some detail but to not to be able to make sense of the whole flow.
Nevertheless if that is what it takes to get your participation, well, I welcome it. What we are trying to do with this introduction is give a few paragraphs introducing the formation of meanders, as that is the titled topic. I don't care who does it as long as it is done well. If you want to put everything back and start over that wouldn't bother me. If you want to rewrite it that would not bother me either. As far as what I wrote is concerned, I'm not especially attached to any of it. Delete it all if you wish. Here is the job requirement as I see it: one introduction to the topic of formation of meanders. It must be incisive but at the same time not so technical that the public cannot understand it. It must be written for the general interested public as an audience. It must be in correct formal English.
Now, I can't really tell you if something conforms to that standard until I see it. So far Dolphin you have avoided doing anything I can critique. What was wrong with the previous is as follows. Not correct formal English. Awkward and repetitios English. No logical flow. Larded with technical terms from Fluid Flows that mean nothing to the public. Overcited with repetitive sources. Too many sources of the same topic.
What would be best is if YOU wrote the intro. Go ahead. Write. What's holding you back? Nothing ventured, nothing gained. Second best is for me to discuss all your comments and keep rewriting until you are both happy. That would take a long time. If neither of those things happen the default is to put it back the way it was and not change it. I don't opt for that one. It already had a few tags on it. I would have a lot more to put on. The idea is to improve it. So, I'm most heartened by Siegmund's suggestion for collaborative action. Go ahead, Siegmund. Dolphin I appreciate your comments. I can answer some of those. I'm going to do that and also I am going to give the two of you a chance to make such changes as you see fit. A further rewrite is not warranted by me until I see where it is going. It can't go anywhere unless you make it go somewhere. Where do you want it to go? So, if I do not write anything immediately it is because I am waiting to see what you do. I may work on some of the formatting and finish editing the rest of it. I think I made two edits in the whole first part, which seemed good to me. Dave ( talk) 02:10, 18 August 2011 (UTC)
The section titled #Governing physics contains two statements that contradict statements in #Formation:
I have inserted the Citation needed tag on the two offending sentences. In addition to these offending sentences, I think the section Governing physics is sufficiently unencyclopaedic that it requires a clean-up, or even deletion. For example, it attempts to explain the secondary flow in terms of centrifugal force which is a fictitious force! It attempts to explain the commencement of a meander using the Coriolis force, citing a source that appears not to mention Coriolis force! Unfortunately, the whole of Governing physics was created on 23 December 2016 (see the diff) by User:Ariadne3s a new User who has not contributed since that date. Dolphin ( t) 13:24, 31 July 2019 (UTC)
There is an easily demonstrated (and fascinating) example of meandering that occurs without erosion or sedimentation being involved, which means, as Ricky Ricardo would say, "You have some 'splaining to do". (Full disclosure: I have not yet digested all of the article or all Talk sections.)
Hold a plate of glass (smooth, very flat) under a small steady stream of water, at about a 30-degree angle from horizontal. The water will run down the glass in a straight stream. Gradually level the plate toward horizontal. At some point the stream will suddenly break in meanders.
The suddenness and intensity of the meandering suggests some positive feedback is involved. But in any case, there is obviously no erosion or sedimentation involved; some 'splaining is called for.