Talk:Manning formula

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Is this right?[edit]

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[edit]

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[edit]

"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[edit]

"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 (talkcontribs) 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

Strickler[edit]

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)