Manning Equation

Written by Jerry Ratzlaff on . Posted in Fluid Dynamics

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

Manning Equation Formula

(Eq. 1)  \(\large{ v =  \frac{1.49 \; r_h^{0.66} \; S^{0.5} }{n}   }\)

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

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)

Solve for:

\(\large{ S =  \left(   \frac{v n}{1.49 \; r_h^{0.66} }   \right)^2   }\)

\(\large{ r_h =  \left(   \frac{v n}{1.49 \; S^{0.5} }   \right)^{\frac{1}{0.66}}   }\)

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

 

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