Free Manning Equation Calculator
Calculate open-channel flow velocity and discharge using the Manning equation.
m
m/m
m^2
Flow Velocity
2.167 m/s
Discharge (Q)3.251 m^3/s
Flow Velocity vs Manning's Roughness (n)
Manning's Equation for Open Channels
The Manning equation is the most widely used formula for computing uniform open-channel flow.
Formula
V = (1/n) R^(2/3) S^(1/2)
Q = A V
where n is Manning's roughness coefficient, R is the hydraulic radius (A/P, area divided by wetted perimeter), and S is the slope of the energy grade line (equal to channel slope for uniform flow).
Example Calculation
A concrete-lined channel with n=0.013, R=0.5 m, slope 0.2%, area 1.5 m^2.
- 01R^(2/3) = 0.5^0.667 = 0.630
- 02S^(1/2) = 0.002^0.5 = 0.04472
- 03V = (1/0.013) x 0.630 x 0.04472 = 76.92 x 0.02817 = 2.168 m/s
- 04Q = 1.5 x 2.168 = 3.252 m^3/s
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