Manning’s Equation
Note: Manning’s roughness coefficients are the same as the roughness coefficients used in Kutter’s equation.
Manning’s equation, which is based on Chezy’s equation, is one of the most popular methods in use today for free surface flow. For Manning’s equation, the roughness coefficient in Chezy’s equation is calculated as:
| C | = | Chezy’s roughness coefficient (m 1/2 /s, ft. 1/2 /sec.) | |
| R | = | Hydraulic radius (m, ft.) | |
| n | = | Manning’s roughness (s/m 1/3 ) | |
| k | = | Constant (1.00 m 1/3 /m 1/3 , 1.49 ft. 1/3 /ft. 1/3 ) |
Substituting this roughness into Chezy’s equation, you obtain the well-known Manning’s equation:
