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Manning's coeff to absolute roughness

  1. Dec 1, 2008 #1
    Does anyone have the equation that the absolute roughness is expressed in terms of Manning coefficient, with the reference included?

    I have found one from Webber 1971.

    n = k1/6/26

    n = applicable Manning roughness coefficient,
    k = absolute roughness (mm)

    Reference :Webber, N.B. (1971) Fluid Mechanics for Civil Engineers. Chapman & Hall.

    when I apply this equation to Manning coefficient of 0.011 (epoxy lined Ductile Iron Pipe)

    I get an sbsolute roughness (k) = 0.000001795477 ft.

    I need some confermation on the value and equation
  2. jcsd
  3. Dec 2, 2008 #2


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    Science Advisor

    The one you have from Webber is the only one I know of. The value you calculated for the roughness (k) seems reasonable. A commercial steel pipe has a roughness of about 0.00015-ft, so I imagine an epoxy lined one would be even less like you have determined.

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