Open Channel Flow (Manning)

Calculate flow rate, velocity and Froude number in a rectangular or trapezoidal open channel with Manning's equation, free online.

Bottom width (m)

Flow depth (m)

Side slope z (horizontal : 1 vertical; 0 for rectangular)

Bed slope (m/m)

Manning's n

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Manning: Q = (1/n)·A·R^(2/3)·S^(1/2) where A is the flow area, R = A ÷ wetted perimeter, S the bed slope and n the roughness (0.012 smooth concrete, 0.030 earth channel, 0.035 natural stream). Froude number Fr = v ÷ √(g·A/T): below 1 is subcritical (tranquil) flow.