Why is Manning’s formula more often used than Chezy formula in open channel flows?

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Manning’s formula was proposed by Robert Manning (an Irish engineer) to calculate uniform flow in open channel. It is probably the most widely used uniform-flow formula around the world. Its extensive usage is due to the following reasons:

(i) The majority of open channel flows lies in rough turbulent region;
(ii) It is simple in form and the formula is well proven by much practical

Manning’s formula shall not be applied in situations where Reynolds number effect is predominant. For Chezy formula, it is less commonly used owing to insufficient information to find out equivalent roughness and it is not backed by sufficient experimental and field data. However, in smooth boundaries, Chezy formula shall be adopted instead of Manning’s formula.


This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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