Talk:Meander

Why is there a clean up tag on this article?
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)


 * Removed the tag. It was added last Dec. and some fixin' was done, but nobody thought to take the ugly tag away :-). Thanks for bringing it to my attention. Vsmith 03:17, 19 April 2006 (UTC)

Revision required
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 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)


 * I agree that this is a contradiction, and Wikipedia shouldn't contradict itself. I believe the contradiction should be resolved as follows.


 * When liquids or gases follow a curved path (such as a river bend) the primary flow must conform to vortex flow. That is why the primary flow in tropical cyclones is vortex flow.  In vortex flow, the speed is fastest at the center of the vortex, getting progressively slower as the distance from the center increases.  Consequently, as a river flows around a bend the primary flow is fastest on the inside of the bend and slowest on the outside of the bend.


 * This simple model is complicated a little by the secondary flow. In the case of a flowing river the secondary flow is a slower moving carpet of water along the river bed and alongside the banks of the river.  This slower moving carpet is partly the boundary layer caused by viscous forces at the liquid boundary, and partly due to loss of momentum due to contact with irregularities in the river bed, exposed rocks, vegetation etc.


 * There is a pressure gradient laterally across the river and it causes the secondary flow to be partly across the river towards the inside of the bend. This sweeps sand and other submerged objects towards the inside of the bend, reducing the depth of the water and eventually forming a point bar (or sand bar.)  The shallow depth over the point bar causes the water to flow more slowly there than in the main stream.  This observation entices observers to conclude that the river is flowing fastest on the outside of the bend.  If that were true, the river would not be conforming to vortex flow and it would prove the laws of physics are untrue.


 * The primary flow of any vortex, or partial vortex such as a river bend, is fastest where the radius is smallest and slowest where the radius is greatest. In the case of a river, the secondary flow is most significant in the slow-moving flow on the inside of a bend but this does not mean the fastest flow is on the outside of the bend where the radius is greatest.


 * The enduring fallacy is the notion that a river carries in suspension a load of rocks, sand and other submerged objects, and then as the river slows while it passes over the point bar it drops this load of rocks, sand and submerged objects! No matter how fast a river is moving it cannot carry rocks in suspension.  The reason sand bars are made of sand, rocks and submerged objects is because this debris has been swept into those positions very slowly, across the river bed over thousands of years.  The sand and rocks are not carried in suspension, at high speed, by the river and then miraculously dropped out of suspension as the river flows over a convenient sand bar.  (If that were true, they would be dropped near the outside of the bend where the flow is slowest.  Tropical cyclones conform to vortex flow - why wouldn't rivers as they flow around a bend?)  A river bend is not the only place that the water in a river slows down.  A river also slows wherever the bed falls away and the depth increases, and where the river becomes wider.  If it were true that a slowing river drops its suspended load of sand and rocks, extensive deposits of sand and rocks would also be found wherever the river slows down due to greater depth or width.  It doesn't happen!  Point bars form on points at river bends, but they don't form in mid-stream where the river widens or becomes deeper.


 * Try the experiment with a circular bowl of water. Drop some sand or rice or tea leaves into the bowl and set the water circulating in a circular pattern.  The secondary flow will sweep the heavy particles into the center of the bowl.  The heavy particles will not be swept to the perimeter of the bowl by the primary flow.


 * I don't have any suitable references in front of me at present, but have a look at Secondary flow in a region of flow curvature which is cited in Secondary flow.


 * The words you have quoted above are inconsistent with the laws of physics, and with vortex flow in particular. I have corrected the offending paragraph and cited the website quoted above. Dolphin51 (talk) 00:31, 10 July 2009 (UTC)

Do meanders defy the law of conservation of momentum?
The following statement appears in Meander. 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)

"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."My emphasis.
 * I have now located a copy of the Encyclopedia of Sediments and Sedimentary Rocks and read Meandering Channels by Hickin. The text on which the above quotation about exactly the opposite of what happens is based appears to be the following:


 * This text does not support the statement that presently exists in Meander indicating that an increase of velocity on the inside and a decrease on the outside is exactly the opposite of what happens. I will amend the statement to something consistent with what Hickin has written in Meandering Channels.  Dolphin51 (talk) 12:02, 18 August 2009 (UTC)


 * I haven't analyzed this section completely yet, but I have to make one comment: Explaining a phenomenon by invoking centrifugal force (as in the quotation from the Encyclopedia of Sediments and Sedimentary Rocks) is in general not a good idea because it generally has cause and effect reversed.  (Example: If you spin a rock around on a string, the tension on the string is not created by centrifugal force from the circular path; rather, the circular path is caused by the centripetal force you exert on the string.)  BMJ-pdx (talk) 18:24, 17 February 2021 (UTC)

Merge Bank erosion into this article

 * Support; that article as an aspect of the processes described in this article. Please see Meander and Meander. Walter Siegmund (talk) 18:19, 17 March 2010 (UTC)
 * Strong oppose and being bold and closing. Bank erosion occurs in non-meandering rivers as well. Therefore it can not in its entirety be a subsection of this article. Awickert (talk) 05:23, 10 May 2010 (UTC)

Formation
On 15 & 16 May 2011 some text and an in-line citation were removed from Meander and replaced by the following new text. (See diff.):


 * In order for a flow to have a curved path there must be a centripetal force inward that is present (this is similar to spinning a bucket on a string, but here we do not have solid body rotation ie. a spinning record). The force presents itself as a pressure gradient outwards (larger pressure on the outside of the bend then inside) or from a change in elevation at the free surface (larger elevation on the outside of the bend).  At the free surface of the river the pressure must be constant, equal to atmospheric pressure, so the elevation must change to maintain the curved flow.  In the middle (in the vertical) of the river a pressure gradient is present to maintain the curved flow.  At the floor of the river, the no slip condition requires no velocity.  This sets up a situation that has lower velocity at the floor which is not enough to overcome the pressure gradient and a secondary cross flow develops (into the bend at the floor).  The secondary flow into the bend at the floor due to the pressure gradient must eventually go up due to conservation of mass and the flow is outward above the floor.  This entire situation is very similar to the Tea leaf paradox. This secondary flow caries sediment from the outside of the bend to the inside making the river more meandering. Cite Callander  Cite Falcon


 * It is a misconception that the flow at the outside is faster then the inside (which would be true for solid body rotation which we don't have here), it is actually the opposite. We consider the flow to be irrotational for the most part here, which requires the flow outside to be slower than the flow inside (otherwise the flow would not be irrotational.) Cite Lewalle

I have now restored the original text as follows. (See diff.):
 * Flow of a fluid around a bend is vortex flow in order to conserve angular momentum. The speed of flow on the inside of the bend is fastest, and on the outside of the bend is slowest. Cite Hickin The water surface is also super-elevated towards the outside of the bend, so on the floor of the channel the water pressure is greater on the outside of the bend than on the inside of the bend. This pressure gradient drives a cross-current towards the inside of the bend. Cite Hickin

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)
 * In restoring the original text I inadvertently restored an incorrect version saying the flow on the outside of the bend is fastest. I have now corrected it.  Dolphin  ( t ) 11:55, 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)
 * I agree that conserving angular momentum conveys little meaning. I find the idea of uniform angular momentum to be more meaningful.  In a free vortex the angular momentum per unit of mass is uniform throughout the vortex - close to the center of rotation the velocity is high but the radius is small; conversely, remote from the center of rotation the velocity is low but the radius is large.  A free vortex can be characterized by the fact that velocity times radius is a constant, and velocity times radius (times mass) is angular momentum.  Dolphin  ( t ) 07:34, 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)


 * Please feel free to improve the article. Richard New Forest (talk) 19:35, 11 August 2011 (UTC)

Formation reformed
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)


 * Thanks for taking an interest in this article. I have a few difficulties with some of your edits - eg. addition of original research and elimination of properly sourced material.  I deleted the following:
 * The centrifugal force depends on the linear momentum. Where does that idea come from?  Original research so I deleted.
 * In a spinning solid, the centrifugal force is balanced by centripetal forces supplied by the rigid bonds between molecules. A spinning fluid, which has no such bonds, transfers mass to the outside, where building up against the far bank it increases the pressure and super-elevates the outside surface. A pressure gradient forms between inside and outside, which balances the centrifugal force. This might be appropriate in an article on mechanics but not in our article on meander.  Wikipedia is not a textbook or a guidebook.
 * The following material is technically sound and cites a reliable published source. Recent edits eliminated it so I have replaced it: The cross-current along the floor of the channel is part of the secondary flow and sweeps dense eroded material towards the inside of the bend. The cross-current then rises to the surface near the inside of the bend and, moving near the surface, flows towards the outside of the bend, forming a helical flow. The greater the curvature of the bend, and the faster the flow, the stronger is the cross-current and the stronger the sweeping of dense eroded material along the floor of the channel towards the inside bank.
 * You have also made use of the expression centrifugal pressure. What is that?
 * Seeing there are at least two of us interested in this article, I suggest that some discussion on this Talk page about shortcomings would be better than wholesale re-writes. Dolphin  ( t ) 07:50, 17 August 2011 (UTC)
 * Well hello there. I didn't think I would make these changes without discussion. We really are talking about one introductory section, which I originally wrote. It was short and to the point but it summarized and left the mechanism unexplained. When I looked at it again it was long, awkward, badly written and incomprehensible. Now, I don't care who writes it or what phraseology. And, we can argue over the appropriate content for quite a long time. There is no original research there. What I wrote is clear. But, that is not the direction in which the argument should go. That is just butting heads. This is original research. No it isn't. Yes it is. No it isn't. And so on. That's not the way I operate. I take what is there and try to fix it. Write it, rewrite it any way you like. If it makes sense and is in reasonable English I leave it. So, I don't mind working with you. Do as you like. What I will do is keep checking it. For the references, well WP does not like chains of numbers. What I noticed is that they came after statements that did not seem to need references because a reference had already been given or the statement was too simple. References support specific points. You don't need a whole bibiography to support a point. One good ref will do. Moreover, it was not clear to me what point was being supported. So, according to my method I now will look at what is currently there. I don't know what you mean by wholesale rewrite. Only those 3 or 4 paragraphs were in question, and there already were some tags on them. They had already been rewritten but they did not improve the article. This article is fairly well along. What I usually do is edit. I'm going to give it a light edit. That means I look for things that are wrong. These article's are not anyone's property. One more point. You won't be seeing me too intensely as my time is limited. No doubt it will take a long time to get through here. I'm amenable to most any reasonable argument. I give in a lot or give in with minor changes. Hey, if you don't like my fixes, provide you own! I emphasize English a lot. Oh, there is one more general criticism. The authors of these source articles often use scientific jargon that is not comprehensible to the general public. The way WP often handles that is to put in blue links to other articles. On the whole WP is trying to create articles comprehensible to the general public. Admittedtly that is the most difficult part of the task. We could all improve on that. With these general comments then, on with the edit. I'll be keeping you posted. I'm interested in fixes. If that is not on your agenda, we can always put the text back, tags and all, but I would probably have to add more tags. On with the edit! But not very fast. Don't hang on me, I move very slowly.Dave (talk) 10:35, 17 August 2011 (UTC)


 * Most of us can live with any standard of written English but we can't live with statements like the following, especially when they are inserted without citation or reference:
 * The centrifugal force depends on the linear momentum.
 * The vortex motion is a result of the removal of momentum from the bottom layers of the flow by the drag exerted by the bottom.
 * In a spinning solid, the centrifugal force is balanced by centripetal forces supplied by the rigid bonds between molecules. A spinning fluid, which has no such bonds, transfers mass to the outside, where building up against the far bank it increases the pressure and super-elevates the outside surface. (Technically correct but not appropriate in an article dedicated to meanders.)
 * Using this Talk page to let people know what you consider are the problems is a good idea. Alternatively you might find it easier to work on your changes using your Sandbox.  When you have it looking the way you want it to go you could use this Talk page to let interested Users know, and those interested Users can then comment on your proposed re-write.  Dolphin  ( t ) 13:07, 17 August 2011 (UTC)

More on the formation
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
 * What it is
 * What causes it. Here we have the article of the tea leaf paragraph which does explain it in a comprehensible way. Before I started sections of that were hacked out and doctored up for here, but here they did not fly. I suggest we make brief mention of the causes and let the blue link to the tea leaves do its work.Dave (talk) 12:16, 17 August 2011 (UTC)


 * @Dave: You added the following paragraph - Water flows primarily downstream. If the channel were straight, the flow would be mainly primary. Around a bend, however, a rotational component develops, which added to the irrotational component moves the flow in a spiral direction. Looking downstream, the rotation is from inside to outside along the top and vice versa on the bottom. The paragraph is unsourced.  I can make the following comments:
 * Water flows primarily downstream. While this is undoubtedly true, I don't see that it adds anything to the article, or is necessary for understanding of any of the sentences that follow.
 * The article talks about primary and secondary flow. What this adds to the article is a definition of primary flow. It is a lead-in to what follows. The public cannot be expected to know what primary and secondary flow are. So, it adds: definition of primary flow, transition to technical discussion of secondary flow. Naturally the professot of fluid dynamics or any of his students will not find this information relevant, as they already take it for granted. You have to keep the audience in mind. We are not dazzling with our technical jargon or abtruseness but are trying to explain. Our goal is not to turn out a fine paper for the geological society but to write an article for the general public, being careful to define our terms. If you have a blue link here that would be good too.
 * If the channel were straight, the flow would be mainly primary. In any open channel the flow is always mainly primary.  That is what primary flow means.  Even in a curved channel the flow is mainly primary.  The secondary flow is that part of the flow that deviates from the primary flow for reasons associated with viscous forces, loss of momentum due to interference from weeds, tree trunks, submerged objects etc.
 * Great! Just what we're looking for in my view. That should go in earlier I think just about as you have written it. You wrote it for me with some disdain no doubt. Don't write it for me, write it for the public. I have in the past taken impromptu writing just like that and thrown it into the article. These are your own words. They make better sense than the doctored up stuff.
 * Around a bend, however, a rotational component develops, In fluid dynamics, rotational flow and irrotational flow have precise meanings.  Your use of the expression rotational component doesn't conform to the precise meaning usually given to rotational flow.  (Rotational flow doesn't mean the flow is going around a corner, it means a region where vorticity is non-zero.)
 * Right. That is how I meant it. Didn't that come across? If not, more explanation - probably your own words right here will suffice, made more objective.
 * Looking downstream, the rotation is from inside to outside along the top and vice versa on the bottom. The rotation is from inside to outside along the top and vice versa on the bottom regardless of whether one looks downstream, upstream, down from on top or up from the bottom!  Dolphin  ( t ) 23:23, 17 August 2011 (UTC)
 * You know, your right! Why didn't you change it? You seem to want to confront, man. What I want you to do is collaborate. Your words are probably more to the point than mine, or at least that is the impression you give. You're coming up with some great definitions. Oh, if the spiral flow is going to get more extensive, as it seems as though it may, perhaps we should have a distinct section for it instead of making it the intro to meander formation.Dave (talk) 02:48, 18 August 2011 (UTC)


 * Hi Dave; I think you deleted an important point in your edits. "At the floor of the river, the no slip condition requires no velocity. This sets up a situation that has lower velocity at the floor which is not enough to overcome the pressure gradient and a secondary cross flow develops (into the bend at the floor). The secondary flow into the bend at the floor due to the pressure gradient must eventually go up due to conservation of mass and the flow is outward above the floor." These words explain why cross-channel flow occurs. I think it would be helpful if this point were restored and moved to near the beginning of the section (but after the explanation of the change in elevation at the free surface, which seems also to have been removed). Much of the rest of the discussion may be abbreviated or deleted, I think. Best wishes, Walter Siegmund (talk) 01:21, 18 August 2011 (UTC)
 * Oh, OK, go right ahead. You know what seems best to you. No one has your idea in his head as clearly as you do. Give it a shot! Throw your hat in the ring. I think we may have to have a distinct section on this spiral flow business instead of trying to use it as an intro.Dave (talk) 02:48, 18 August 2011 (UTC)

Encyclopedia of Sediments
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)

Siegmund and Dolphin
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)


 * I think the greatest contribution I can make to the article is to convince all participants of three things:
 * If you can't cite a reliable published source for your statements, don't add them to the article.
 * This is a scientific topic - don't add material for which you doubt your own expertise. (Measure your expertise against the sources you will be citing.)
 * Don't remove material that cites a reliable published source.
 * Once these three things are understood by all participants I am willing to get serious about adding to, and repairing, the article. Dolphin  ( t ) 07:55, 18 August 2011 (UTC)
 * I support these principles. I note that they are a restatement of long established Wikipedia policies and guidelines, for the most part. We encourage all editors to contribute, but those edits must be consistent with WP:RS. Often those with little scientific knowledge and expertise can nonetheless play a valuable role in identifying text that is opaque, jargon-ladened, or inappropriately technical. We don't remove well-sourced content except in accordance with WP:UNDUE, a narrow exception that may have little relevance to this topic. Best wishes, --Walter Siegmund (talk) 19:08, 18 August 2011 (UTC)
 * Well thank you, Walter. There are a few parts I think you are leaving out. It isn't quite as narrow as all that. There is a question of what is "well-sourced." There may not be agreement on that point, don't you agree? Since we are citing authoritative parts of the code, I recommend WP:INTEGRITY and WP:CITEBUNDLE. Most of my questions usually fall into that area. My removals in this case fell into that area. Of course one can negotiate "well-sourced." You may not agree and I may agree with your not agreeing. However Dolphin has volunteered to do this. I agreed to his application of these rules to his volunteer work. I don't necessarily agree to your "narrow" interpetation of WP policy, as I just pointed out. You can't possibly "legislate" every case that comes up and claim that your legislation is the authoritative one. Trying to be the fundamentalist of WP I think is not a good idea. Placing refs is more of an art than a science. If they fit, if they work, no one questions them. If questions arise, they have to be negotiated. I think we can probably trust Dolphin's judgement. Things that have bothered me are the things mentioned in the two articles I just cited. The mere presence of a ref does not make it a good one. A chain of refs at the end without any indication of what they are supposed to cover is not recommended. To me they look like several refs on the last thing said, which typically is not very significant. Often they appear not to cover anything, as they have been moved around. I like to see refs distributed to where they belong. If you don't distribute them then you are supposed to explain where they apply. I do not wish to trouble Dolphin with these matters while he is trying to write. There is nothing more frustrating than trying to write something and having someone constantly butt in. At the end I doubt if there will be any problems. If is isn't broken, don't fix it. Well, since you are putting yourself in the position of "we" on WP and using the term "narrow" I thought some clarification of what "we" are supposed to be doing was relevant to you. It might avoid confusion later. I'm giving a Dolphin a totally free hand here after having explained what I thought we are trying to do. If any issues come up I certainly will bring them up in discussion. He can restore what I removed or not just as he pleases. I don't see how I could be more collaborative. The two of you brought up your issues and we have worked them out. Let's not anticipate problems that probably will not occur.Ciao.Dave (talk) 02:57, 20 August 2011 (UTC)
 * If you mean me, Dolphin, I agree, no problem. That transitional paragraph that you said was uncited I actually had a source for. I was using one of the sources in this section. I have not put it in because we are going to rewrite. I want you to do the rewriting so I am not going to throw obstacles in your path. If I put the cite in you might feel you had to keep it. I make myself almost a court of last resort - if no one else is going to fix it I will undertake it. The court of last resort is the administrators. I think I'm a reviewer so I try to be one when I can. I generally don't get involved with good articles. This one is not quite good yet. I'm intermediate in expertise. WP does not require expertise. However I join the general sentiment that you shouldn't be making pronouncements on topics you know nothing about. For example, I discourage people with no Latin from working on Latin language articles. In theory, however, anyone can work on any articles. If you want to present yourself as an expert that it fine with me. This is too much work for nothing not to take you seriously. I feel I will have a role in the English and the formatting but as I say I can't look at anything until I have something to look at. My concerns will be logical flow and correctness. it is a tough job I admit to write something that is sufficiently technical and is correct but does not confuse the reader with unexplained terms. You won't be seeing me seriously on this for a while. I do have a few minor items on the layout and formatting, but that will not take long. There's another one also of interest to me, Braided river, if you should care to waste even more time on public education. I think I'm your main opponent so there is no reason why you should not get started. Anything I wrote as I say is fair game. I cede it. Well I'm off to Greece where I am trying to improve a few articles there. Later, as long as you need or want.Dave (talk) 19:28, 18 August 2011 (UTC)

Contradictions
The section titled contains two statements that contradict statements in :


 * 1) In Governing physics it says “Ultimately, the downstream velocity of the fluid is convectively transported to the outside bend, resulting in higher velocities at the outside bend.” This statement and all that goes before it is unsourced. In contrast, in Formation it says: “Due to the conservation of angular momentum the speed on the inside of the bend is faster than on the outside.” This statement is sourced from Hickin, Edward J. (2003) Meandering Channels, p.432
 * 2) In Governing physics it says “In real meandering rivers, we observe higher downstream fluid velocities at the outside bends.” This statement and all that goes before it is unsourced. In contrast, in Formation it says “Since the flow velocity is diminished, so is the centrifugal pressure. The pressure of the super-elevated column prevails, developing an unbalanced gradient that moves water back across the bottom from the outside to the inside.” The cited source is Hickin p.432. Later in the same paragraph it says “This entire situation is very similar to the Tea leaf paradox” and the cited source is Albert Einstein’s explanation of meandering rivers.

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)


 * More than 5 months have passed since I inserted the "Citation needed" tag on those two offending sentences. In that time no attempt has been made to supply a citation to support the sentences. The User who inserted this material on 23 December 2016, User:Ariadne3s has not contributed to Wikipedia since that date. I have now removed the two offending sentences - see my diff. Dolphin ( t ) 04:40, 10 January 2020 (UTC)

Meandering without eorsion or sedimentation.
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.

BMJ-pdx (talk) 18:46, 17 February 2021 (UTC)