# Manning Equation

Manning equation, expressed in numerous ways, is a commonly used equation for the uniform flow in open channels.

### Manning Equation Formula

\(\large{ v = \frac{1.49 \; r_h^{0.66} \; S^{0.5} }{n} }\)

\(\large{ v = \frac{1.49 \; r_h^{2/3} \; S^{1/2} }{n} }\)

Where:

\(\large{ v }\) = flow velocity in a channel, culvert, or pipe

\(\large{ S }\) = channel slope or energy slope line

\(\large{ r_h }\) = hydraulic radius

\(\large{ n }\) = Manning roughness coefficient

\(\large{ k }\) = unit conversion factor (\(k = 1.49\) English units ft/sec) (\(k = 1.0\) SI units m/sec)

Tags: Equations for Flow Equations for Hydraulic Equations for Open Channel