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Mannings Roughness Coefficient (n) for Woods (Light Underbrush vs. Dense Underbrush)

  • 1.  Mannings Roughness Coefficient (n) for Woods (Light Underbrush vs. Dense Underbrush)

    Posted 10-08-2020 07:06 PM
    Table 3-1 of NRCS TR-55 provides Manning's n values for sheet flow.  Can anyone provide photograph examples of what the surface descriptions might look like for for Woods, light underbrush (n=0.4) vs. dense underbrush (n=0.8)?  I am trying to make a decision on what is best for a time of concentration calculation for a wooded site.

    Thank you!

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    Christopher Cloutet P.E., M.ASCE
    Civil Engineer
    Slidell LA
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  • 2.  RE: Mannings Roughness Coefficient (n) for Woods (Light Underbrush vs. Dense Underbrush)

    Posted 10-09-2020 10:05 AM
    Try: https://pubs.er.usgs.gov/publication/wsp2339

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    Andrew Scott P.E., M.ASCE
    Virginia Departement of Transportation
    Suffolk VA
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  • 3.  RE: Mannings Roughness Coefficient (n) for Woods (Light Underbrush vs. Dense Underbrush)

    Posted 10-09-2020 10:40 AM
    That's an excellent resource!

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    Maria Price P.E., M.ASCE
    Engineering Manager
    City of Chattanooga
    Chattanooga TN
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  • 4.  RE: Mannings Roughness Coefficient (n) for Woods (Light Underbrush vs. Dense Underbrush)

    Posted 10-09-2020 02:32 PM

    In addition to the excellent USGS source, there is a paper in the Encyclopedia of Coastal Science. The Seabed Roughness discusses roughness in current, wave and wave-current environments, and presents equivalence of different coefficients – Manning, Chezy and others. It does not specifically address woody waterways, typical of your case – but you may find it useful, have a look.

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    Dilip

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    Dr. Dilip Barua, Ph.D, P.Eng, M. ASCE
    Vancouver, BC, Canada
    https://widecanvas.weebly.com
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  • 5.  RE: Mannings Roughness Coefficient (n) for Woods (Light Underbrush vs. Dense Underbrush)

    Posted 10-10-2020 12:17 PM
    Thank you for these excellent references, but I am still looking for simply just a couple of pictures to show the differences between light underbrush vs dense underbrush. Any help is greatly appreciated.

    Thanks again.

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    Christopher Cloutet P.E., M.ASCE
    Civil Engineer
    Slidell LA
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  • 6.  RE: Mannings Roughness Coefficient (n) for Woods (Light Underbrush vs. Dense Underbrush)

    Posted 10-10-2020 09:10 PM

    Chris: if you have not used it already, perhaps the 1991/1994 USACE manual: EM 1110-2-1601 (Hydraulic Design of Flood Control Channels) may help your specific need. In Chapter 5, it details methods to estimate/predict 'n'.

    Among others, it indicates values and methods for vegetative channel areas. If you do not have the manual, it is freely downloadable from USACE EM website: https://www.publications.usace.army.mil

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    Dilip

    Website

    ORCID ID

    Google Scholar



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    Dr. Dilip Barua, Ph.D, P.Eng, M. ASCE
    Vancouver, BC, Canada
    https://widecanvas.weebly.com
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  • 7.  RE: Mannings Roughness Coefficient (n) for Woods (Light Underbrush vs. Dense Underbrush)

    Posted 10-12-2020 04:00 PM
    Thank you. I am adding these resources to my personal library.

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    Christopher Cloutet P.E., M.ASCE
    Civil Engineer
    Slidell LA
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  • 8.  RE: Mannings Roughness Coefficient (n) for Woods (Light Underbrush vs. Dense Underbrush)

    Posted 8 days ago
    Hi Chris, the USGS publication has several photos with measured n values. Therese
    https://pubs.er.usgs.gov/publication/wsp2339



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    Therese Baer P.E., M.ASCE
    President
    Baer Engineering and Enviro Consulting
    Austin TX
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