Manning's Roughness Coefficient

Written by Jerry Ratzlaff on . Posted in Fluid Dynamics

Manning's roughness coefficient, abbreviated as n, measures the frictional resistance exerted by a channel, culvert or pipe on the flow.

 

Formulas that use Manning's Roughness Coefficient

\(\large{ n =  \frac{1.49 \; r_h^{0.66} \; S^{0.5} }   {v}       }\)  (Manning Equation
\(\large{ n =  \frac  {  0.56 }  { Q } \; m_c^{5/3} \; m_l^{1/2} \; Q^{8/3} }\) (gutter flow rate)

Where:

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

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

\(\large{ m_c }\) = cross slope of pavement

\(\large{ m_l }\) = longitudinal slope of pavement

\(\large{ Q }\) = gutter flow rate

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

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

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

 

Tags: Equations for Coefficient Equations for Flow Equations for Hydraulic