Manning’s Equation

Water flows in a sloping drainage channel because of the force of gravity. Flow is resisted by the friction between the water and wetted surface of the channel. The quantity of water flowing (Q), the depth of flow (y), and the velocity of flow (V) depend upon the channel shape, roughness (n), and slope (S). […]

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Manning’s n For Riprap-Lined Channels

HEC-15 Section 6.1 – MANNING’S ROUGHNESS Manning’s roughness is a key parameter needed for determining the relationships between depth, velocity, and slope in a channel. However, for gravel and riprap linings, roughness has been shown to be a function of a variety of factors including flow depth, D50, D84, and friction slope, Sf. A partial […]

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Trapezoidal Channel: Manning’s n

Caltrans Highway Design Manual Commonly accepted values for Manning’s roughness coefficient are provided in Table 866.3A. The tabulated values take into account deterioration of the channel lining surface, distortion of the grade line due to unequal settlement, construction joints and normal surface irregularities. These average values should be modified to satisfy any foreseeable abnormal conditions […]

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Circular Pipe: Manning’s n

Caltrans HDM Table 851.2 Suggested values for Manning’s Roughness coefficient (n) for design purposes are given in the tabe below. Manning “n” Value for Alternative Pipe Materials(1) Type of Conduit Recommended Design Value “n” Value Range Corrugated Metal Pipe(2) (Annular and Helical)(3) 2⅔” x ½” corrugation 0.025 0.022 – 0.027 3″ x 1″ “ 0.028 […]

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