Manning's coeff to absolute roughness

[Danger86514]

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 = k^1/6/26

where:
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

 

[stewartcs]

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 = k^1/6/26

where:
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

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.

CS

 

[oswaler]

It is important to note that the Manning's coefficient and absolute roughness are two separate parameters that are related but not interchangeable. The Manning's coefficient is a dimensionless constant that represents the roughness of a surface, while absolute roughness is a physical quantity that represents the height of the surface irregularities.

The equation provided by Webber (1971) relates the Manning's coefficient to the absolute roughness in terms of millimeters. It is not clear from the provided information what units are being used for the Manning's coefficient of 0.011, but assuming it is in millimeters, the calculated absolute roughness of 0.000001795477 ft seems reasonable.

However, it is important to note that this equation is just one of many empirical relationships that have been developed to estimate the Manning's coefficient based on various factors such as surface material and flow conditions. It is always best to use equations and values from reputable sources and to verify with experimental data when possible.