Manning’s Roughness Coefficients for Culverts

Culvert

Manning’s n coefficients are used in culvert hydraulics calculations to determine friction losses within the pipe under outlet control flow conditions. Manning’s n values have been researched and provided by the culvert manufacturers. In this article we provide a tabulated list of Manning’s roughness coefficients for each type of corrugation profile and culvert size.

Concrete Pipe and other smooth walled pipe should be considered about 0.010.

The following table is for Corrugated Steel Pipe (metric)

Annular
68 x 13
All Diameters
Helical
38 x 6.5 mm 68 x 13 mm
200 250 300 400 500 600 900 1200 1400
&
larger
Unpaved 0.024 0.012 0.011 0.013 0.014 0.015 0.016 0.018 0.020 0.021
25% Paved 0.021 0.014 0.017 0.020 0.019
Fully Paved 0.012 0.012 0.012 0.012 0.012
Annular
76 x 25
All Diameters
Helical – 76 x 25 mm
1200 1400 1600 1800 2000 2200 &
larger
Unpaved 0.027 0.023 0.023 0.024 0.025 0.026 0.027
25% Paved 0.023 0.020 0.020 0.021 0.022 0.022 0.023
Fully Paved 0.012 0.012 0.012 0.012 0.012 0.012 0.012
Annular
125 x 25 mm
All Diameters
Helical – 125 x 25 mm
1400 1600 1800 2000 &
larger
Unpaved 0.025 0.022 0.023 0.024 0.025
25% Paved 0.022 0.019 0.020 0.021 0.022
Fully Paved 0.012 0.012 0.012 0.012 0.012

 

The following table is for Corrugated Steel Pipe (US units)

Annular
2-2/3″ x 1/2″
All Diameters
Helical
1-1/2″ x 1/4″ 2-2/3″ x 1/2″
8″ 10″ 12″ 15″ 18″ 24″ 36″ 48″ 54″
&
larger
Unpaved 0.024 0.012 0.014 0.011 0.012 0.013 0.015 0.018 0.020 0.021
25% Paved 0.021 0.014 0.017 0.020 0.019
Fully Paved 0.012 0.012 0.012 0.012 0.012
Annular
3″ x 1″
All Diameters
Helical – 3″ x 1″
48″ 54″ 63″ 72″ 78″ 86″
Unpaved 0.027 0.023 0.023 0.024 0.025 0.026 0.027
25% Paved 0.023 0.020 0.020 0.021 0.022 0.022 0.023
Fully Paved 0.012 0.012 0.012 0.012 0.012 0.012 0.012
Annular
5″ x 1″
All Diameters
Helical – 5″ x 1″
54″ 63″ 72″ 78″ &
larger
Unpaved 0.025 0.022 0.023 0.024 0.025
25% Paved 0.022 0.019 0.020 0.021 0.022
Fully Paved 0.012 0.012 0.012 0.012 0.012

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