Although the Manning's Equation is most often used for calculating flow in open channels?, it can also be used to calculate flow in pipes.

Manning's Equation for Circular Pipes:

Q = \frac{1.49}{n}AR^{2/3}\sqrt{S}

where:

  • A = cross-sectional flow area (ft2)
  • R = hydraulic radius (ft)
  • S = slope of energy grade line or slope of channel bed for uniform flow
  • n = manning roughness factor (see Table of Manning's Roughness Coefficients)

Head Loss

h_F = \frac{4.637n^2L}{D^{5.333}}Q^2

where:


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