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# Manning’s Equation For Open Channels

### Manning’s Equation For Open Channels

One of the more popular of the numerous equations developed for determination of flow in an open channel is Manning’s variation of the Chezy formula:

V=C ?RS

where
R= hydraulic radius, ft (m)

V =mean velocity of flow, ft/s (m/s)

S= slope of energy grade line or loss of head due to friction, ft/linear ft (m/m), of channel

C =Chezy roughness coefficient

Manning proposed:

C=(1.4861/6)/n

where
n= is the coefficient of roughness in the Ganguillet–Kutter formula.
When Manning’s C is used in the Chezy formula, the Manning equation for flow velocity in an open channel results:

V=(1.486R2/3S1/2)/n

Because the discharge Q=VA, this equation may be written:

Q=(1.486AR2/3S1/2)/n

where A =area of flow, ft2 (m2)
and Q= quantity of flow, ft3/s (m3/s).

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Kanwarjot Singh is the founder of Civil Engineering Portal, a leading civil engineering website which has been awarded as the best online publication by CIDC. He did his BE civil from Thapar University, Patiala and has been working on this website with his team of Civil Engineers.