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Hazen Williams formulation

Hazen-Williams formulation

The Hazen-Williams equation is an empirical formula which relates the flow of water in a reach with the physical properties of the reach and the pressure drop caused by resistance. It is used in the design of water pipe systems such as fire sprinkler systems, water supply networks, and irrigation systems. The Hazen-Williams equation has the advantage that the resistance number C is not a function of the Reynolds number, but it has the disadvantage that it is only valid for water and it is not able to account for temperature or viscosity.

\[ Q = k \cdot C \cdot A \cdot R^{0.63} \cdot S^{0.54} \]

Equation: Hazen-Williams discharge formula for pressure pipe flow with resistance coefficient C.

where:

  • k — is a conversion factor for the unit system (k = 1.318) for US customary units, k = 0.849 for SI units)
  • C — is the roughness coefficient
  • R — is the hydraulic radius
  • S — is slope of the energy line (head loss per length of pipe) The slope of the energy line S is used as the friction slope \(I_f\).