Manning Equation

Written by Jerry Ratzlaff on . Posted in Fluid Dynamics

Manning Equation

Manning equation applies to uniform flow in open channels.

Manning Equation Formula

\( Q =  v_aA  \)          \( discharge \; flow \; rate  \;=\;  average \; velocity   \;\;x\;\;  average \; area  \)

\( Q =  \frac  { k }  { n }    \left( \frac {A}  {P} \right) ^{2/3}   S^{1/2} \)          \( discharge \; flow \; rate  \;=\;    \frac  { unit \; conversion \; factor }  { Manning \; roughness \; coefficient }  \;  \left( \frac { average \; area}  { wetted \; perimeter} \right) ^{2/3}   channel \; slope^{1/2} \)

Where:

\( Q \) = discharge flow rate

\( v_a \) = average velocity in a channel, culvert, or pipe

\( A \) = average area in a channel, culvert, or pipe

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

\( n \) = Manning roughness coefficient

\( P \) = wetted perimeter

\( S \) = channel slope

 

Tags: Equations for Flow