# Roughness Coefficient

Written by Jerry Ratzlaff on . Posted in Fluid Dynamics

Roughness coefficient, abbreviated as n, also called Manning coefficient or Manning roughness coefficient, measures the roughness of the flow against the ground surface in an open channel.  The Manning roughness coefficient is one of the most important ways to describe the water flow over the ground surface.

The roughness coefficient is used to calculate the friction factor using a Moody Diagram and the Reynolds number.

## roughness Coefficient formula

 $$\large{ n = \frac {1} {C} \; r_h^{1/6} }$$

### Where:

$$\large{ n }$$ = roughness coefficient

$$\large{ C }$$ = Chezy coefficient

$$\large{ r_h }$$ = hydraulic radius