Chézy formula

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In fluid dynamics, the Chézy formula describes the mean flow velocity of steady, turbulent open channel flow:


  • is average velocity [m/s],
  • is Chezy's coefficient [m½/s],
  • is the hydraulic radius (~ water depth) [m], and
  • is the bottom slope [m/m].

The formula is named after Antoine de Chézy, the French hydraulics engineer who devised it in 1775.

Usage with Manning coefficient[edit]

This formula can also be used with Manning's Roughness Coefficient, instead of Chézy's coefficient. Manning derived[1] the following relation to C based upon experiments:


  • is the Chézy coefficient [m½/s],
  • is the hydraulic radius (~ water depth) [m], and
  • is Manning's roughness coefficient.

Unlike the Manning equation, which is empirical, the Chézy equation is derived from hydrodynamics theory.[2]

See also[edit]


  1. ^ Manning, R., "On the flow of Water in Open Channels and Pipes." Transactions Institute of Civil Engineers of Ireland, vol. 20, pp 161-209, Dublin, 1891, Supplement, vol 24, pp. 179-207, 1895
  2. ^ Martin & McCutcheon, 1999, Hydrodynamics and Transport, Lewis

External links[edit]