Talk:Manning formula

Physical mathematical demonstration:

Consider a particle ∂m of fluid subjected to a differential force and torque: Linear acceleration is conceivable, but the angular acceleration is infinite. Then, as the observation indicates that there is rotation in the fluids, the acceleration and torque must have disappeared by the time they were observed, and the angular velocity became constant. Then, for an incompressible and Newtonian fluid, due to Helmholtz theorem , we can determine v.

The demonstration is here:

https://www.academia.edu/37329704/MANNING_EQUATION_DEMONSTRATION

We believe that the universe of scientists, colleagues, teachers and students, we appreciate your comments. --Osmand Charpentier (talk) 15:04, 30 August 2018 (UTC)

The demonstration section in the article just promotes a broken link without adding any useful information to the article. I propose deleting it.--Pere prlpz (talk) 19:22, 23 June 2019 (UTC)

@Osmand Charpentier: I suggest participating in the discussion instead of (or in addition to) reverting.--Pere prlpz (talk) 19:55, 10 December 2019 (UTC)

The two links ([1] or [2]) are broken, so I also recommend deleting this section. Content should be on Wikipedia (viewable and editable), and not locked in a private business' website. Furthermore, content should be supported by primary references. As I cannot see the linked content, I cannot say much on this aspect. +mt 00:06, 11 December 2019 (UTC)

It is true that the links you mention are broken, I have already changed them.190.219.183.165 (talk) 23:30, 28 December 2020 (UTC)

Is this right?

I'm no expert by a long way, but the sentence "The discharge formula can be used to manipulate Manning's equation to compute flow knowing limiting or actual flow velocity" seems wrong to me. Shouldn't that be "...without knowing limiting or actual flow velocity"? • TheBendster (talk) 2 May 2008, 17:01 (UTC)

I have now fixed it and clarified a little. My apologies if there is any mistake. • TheBendster (talk) 7 May 2008, 06:21 (UTC)

Empirical wrong on many levels

There are TWO errors in the first paragraph:

"The Manning formula, known also as the Gauckler-Strickler formula in Europe, is an empirical formula for open channel flow, or flow driven by gravity. It was developed by the Irish engineer Robert Manning. For more than a hundred years, this formula lacked a theoretical derivation. Recently this formula was derived theoretically[1],[2] using the phenomenological theory of turbulence."

1) The link for empirical formula links to the definition for chemistry rather than physics. The physics definition for an empirical equation is an equation that can predict results but can't be proven theoretically.

Be bold! Change it. Awickert (talk) 18:42, 20 December 2008 (UTC)

OK - I did it. Awickert (talk) 04:34, 21 December 2008 (UTC)

2) The forum ala is called "empirical" and then in the next line it is said to be derived theoretically. These two statements contradict each other.• Mbaboy (talk) 13 Sep 2008, 02:25 (UTC)

I don't think so - it was originally created as an empirical relationship, and then shown to be theoretically true. Awickert (talk) 18:42, 20 December 2008 (UTC)

Suggested edits

"Error rates of ±30% or more are common using the Gauckler-Manning Formula while error rates within ±10% are possible with properly constructed weirs or flumes." -- This claim should certainly be cited.

The use of the term "river-" should be removed throughout. Neither Mannings 'n' nor Rh are limited to natural channels. Manning's equation is routinely used (in the USA anyway) to analyze and design pipes and other manmade conduits.

Likewise, in the second paragraph under G-M Section, "Values vary greatly in natural stream..." should be rewritten as "In natural streams, values vary greatly..."

"...which is dependent on many factors, including river-bottom roughness and sinuosity" -- Please double check. I don't think sinuosity affects Manning's n. I 2nd that. Sinuosity is not a factor in determining "n". >Sediment size(clay, silt, sand, cobble, boulder)/vegetation characteristics and slope affect "n" (Jarret's (sp) Equation) (+ others)

"Most friction coefficients (except perhaps the Darcy–Weisbach friction factor) are estimated 100% empirically and they apply only to fully-rough turbulent water flows under steady flow conditions." -- This claim should certainly be cited.

Steventodd (talk) 03:33, 24 November 2009 (UTC)

Units of Gauckler–Manning coefficient

"n is the Gauckler–Manning coefficient (independent of units)" It is NOT true that the manning coefficient n is dimensionless! This is a severe drawback of this formula and it is one of the reasons why it should be used carefully.

n has the units: s / m^(1/3) — Preceding unsigned comment added by Schneemann77 (talk • contribs) 13:50, 20 July 2011 (UTC)

I did see a note later on in the article, but you are correct and I've made some edits. I added a dimensional analysis of units to the formulas to be clear. +mt 20:52, 20 July 2011 (UTC)

    Disagree :n is unitless/ or dimensionless. The apparent inconsistency in units in the Manning equation are handled through the conversion factor k.

Units of k are 1 m(^1/3)/s converting to US customary units = 1.4859 ft^3/s

The inclusion of English units, s/[ft^1/3], in the description of the Gauckler–Manning coefficient, commonly known as Manning's n-value, is incorrect. The value of the coefficient is specific to the channel or pipe being examined and does not change if velocity or flow is computed in either English or metric units. Instead the conversion coefficient, 1 or ~1.486, compensates for the measurement system used to define the units of the result and other input values. The conversion coefficient of 1 used for metric computations implies that Manning's n-value has metric units. Note that V has units for L/T; to obtain this output, (1/n) must have units of L^1/3/T to balance the the R_h^2/3 term where R_h has units of L. — Preceding unsigned comment added by 166.137.19.54 (talk) 19:49, 15 May 2023 (UTC)

While the usage of the term "Manning's n-value" is common in the US engineering literature, a more appropriate citation would "Kutter's n-value" as noted in the biography of Robert Manning (engineer). 166.137.19.54 (talk) 20:03, 15 May 2023 (UTC)

Strickler

What has Strickleer got to do with this? There is no mention in the article about him nor why his name ios attched in Europe. Does anyone know? — Preceding unsigned comment added by 141.244.66.102 (talk) 07:37, 8 October 2012 (UTC)

Albert Strickler published a paper in 1923 that examined various formulas for predicting velocity and flow in open channels. The paper validated the Manning formula for a broad range of conditions and demonstrated that Manning's n-value could be characterized as a function of surface roughness (at least for simple cases). MississippiRiverRat (talk) 22:25, 5 August 2023 (UTC)

See Draft:Albert_Strickler MississippiRiverRat (talk) 23:51, 29 August 2023 (UTC)

Seems implausible...

"...The greater the hydraulic radius, the greater the efficiency of the channel and the more volume it can carry..." . This suggests that a square open top channel that is 3 wide by 3 deep can carry more volume than an open top rectangular channel 2 wide by 1000 deep. . If true that is highly counterintuitive and might be worth mentioning. If not true, the text should be clarified. BGriffin (talk) 02:05, 29 April 2017 (UTC)BGriffin

Think you might have this wrong. According to the given equation, the hydraulic radius of the 3x3 channel is 9/(3+3+3) = 1, but the hydraulic radius of the wide channel is 2000/(2+1000+2) ~ 2. So The wider channel is, in fact, more competent. But in general, yes, you can get some kind of counterintuitive results where channels are not wide. I'll take a quick look at text for clarity. DanHobley (talk) 16:18, 29 April 2017 (UTC)

I was referring to a channel 2 wide and 1000 deep so Hr= 2000/(1000+1000+2)= <1 I don't think the formula is wrong. I believe the descriptions of what the hydrolic radius tells us are wrong. At least two things in the article are incorrect in this respec (AFAICT). Th first is the explanation that a canal with higher hydrolic radius can carry a larger volume of water. This is incorrect for the example given above but might more easily be seen by comparing a channel to another similar channel that differs from the first only by the addition of a much smaller attached side channel (which on its own would have a smalled hydrolic radius). The combined channels would be capable of greater flow yet the addition of the high perimeter to cross section area added channel would bring the overall hydraulic radius down. The second error is in the statement that a deeper channel has a larger hydraulic radius. This is not the case for deep channels.

BGriffin (talk) 18:13, 2 November 2018 (UTC)BGriffin

New section

A single editor with two accounts? You are so scientific that you erase such an important contribution for all the hydraulics students of the world, why is it not yours? This is more important than things about your jealousy or my possible vanity. And therefore you are violating Wikipedia's principle of good faith. Your human capacity is such that you would erase Cristrobal Colón having discovered America. What is your problem? The proof of Manning's equation is exact. If wrong, contribute what. If there are errors about wikipedia rules, help correct them. Avoid fanatism. And write clearly, my language is Spanish. — Preceding unsigned comment added by Osmand Charpentier (talk • contribs) 17:29, 14 April 2021 (UTC)