Mannings Value for Slotted PVC Pipe

[1467]

Any Ideas?

I can not find any sources.

 

[Highway2Heel]

What size pipe are you using? This will, of course, affect the "n" you use.

I've typically seen something in the neighborhood of 0.01-0.016 used for 3"-8" pipe; 0.016-0.018 for 10"-12" pipe and 0.019-0.021 used for larger than 12".

Maybe some others can shed more light on this for you in the way of actual sources, of specific values, for varying cases.

H2H

 

[1467]

Concrete is 0.013, so how can PVC be higher than that. And the pipes are 8-10 inches.

 

[1467]

The slots only account for 5% of the total area within on linear foot. So the slots will make a slight impact but not alot.

 

[1467]

The rest of the area is smoother then a babies butt

 

[SlideRuleEra]

Manning number of 0.009 is often used for typical PVC pipe, see question/answer #7 at this link

http://www.uni-bell.org/faq.html#top

Here is a reference (see page 14 of 19) to an assumed manning number of 0.02 for perforated pvc pipe

http://www.brisbane.qld.gov.au/bccwr/lib78/wsud_chapt5.6.1_to_5.8_bioretention_basins.pdf

More than double the unperforated value. Like you, I doubt if the manning number is that high.

http://www.SlideRuleEra.net

 

[ccor]

I agree with Uni-Bell that the n=0.009 is probably accurate for PVC flowing full. Many suggest using 0.011 because Camp (circa 1950) found that n-values vary with depth. According to his findings the max n/n0 = 1.2. Which 0.009 * 1.2 = 0.011. Whether Camp's study is applicable to smooth pipes is conjectural. I tend to use n = 0.011. For perf. or slotted pipe I might be temped to use n=0.012.