Weather & Calamities
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Manning’s Equation (Channel Flow)

Average velocity of water flowing in an open channel or river.

Formula

V=1n R2/3 S1/2V = \frac{1}{n}\,R^{2/3}\,S^{1/2}

Variables

VFlow velocity (m/s)
nManning roughness coefficient
RHydraulic radius (m)
SChannel slope

Example

Smooth concrete (n=0.013) carries water faster than a rocky bed

Did You Know?

Manning’s formula, from 1889, still sizes storm drains and rivers worldwide.

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