Manning's Formula and Gravity Flow

Calculate cross-sectional average velocity flow in open channels using Manning's equation. This tool implements Manning's formula for gravity flow in circular pipes: v = (kn / n) * Rh^(2/3) * S^(1/2), where v is velocity, kn is the unit conversion factor, n is Manning's roughness coefficient, Rh is hydraulic radius, and S is the pipe slope.

Calculator

Inputs

Diameter of pipe (m)

Slope (m/m)

kn (unit conversion factor) (dimensionless)

Manning coefficient of roughness (n) (dimensionless)

Results

Cross-sectional area of flow-- m²

Wetted perimeter-- m

Hydraulic radius (Rh)-- m

Cross-sectional mean velocity (v)-- m/s

Volume flow rate (q)-- m³/s

Channel Type	Manning Coefficient (n)	Description
Clean and smooth	0.01	Clean, smooth channels
Concrete	0.012	Well-finished concrete
Earth	0.02	Natural earth channels
Gravel	0.025	Channels with gravel
Stones and debris	0.06	Stone and debris with 1/3 vegetation