Talk:Meander

message: 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)
replies: text: 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)
thread_title:  Why is there a clean up tag on this article? 

message: *Support; that article as an aspect of the processes described in this article. Please see Meander#Formation and Meander#Erosion_Mechanics. Walter Siegmund (talk) 18:19, 17 March 2010 (UTC)
thread_title:  Merge [[Bank erosion]] into this article 

message: 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.):
: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 CallanderCite 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)
replies: text: 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)

text: 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)

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

message: 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)
thread_title: Encyclopedia of Sediments

message: The section titled #Governing physics contains two statements that contradict statements in #Formation:
#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
#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)
replies: text: 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)
thread_title:  Contradictions 

message: 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)
thread_title:  Meandering without eorsion or sedimentation.