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How It Works
The Chezy equation relates the mean velocity of steady, uniform open-channel flow to the channel's hydraulic radius, slope, and a roughness coefficient. Developed in the 18th century by Antoine de Chezy, it is one of the earliest formulas in hydraulic engineering. A higher Chezy coefficient means a smoother channel with less friction resistance.
Example Problem
A trapezoidal irrigation canal has a Chezy coefficient of 55 m0.5/s, a hydraulic radius of 0.8 m, and a bed slope of 0.002. What is the flow velocity?
- v = C × √(Rh × S)
- v = 55 × √(0.8 × 0.002) = 55 × √0.0016
- v = 55 × 0.04 = 2.2 m/s
Frequently Asked Questions
What is the Chezy equation?
The Chezy equation v = C√(RhS) calculates the average velocity of water in an open channel. It uses an empirical roughness coefficient (C) that depends on channel material and condition.
How is the Chezy coefficient related to Manning's n?
The two are related by C = (1/n) × Rh1/6. Manning's equation is more commonly used today because n values are well-tabulated for hundreds of channel materials.
What are typical Chezy coefficient values?
Values typically range from 30 m0.5/s for rough natural streams to 90 m0.5/s for smooth concrete channels. Most engineered channels fall between 50 and 70.
Related Calculators
- Manning Equation Calculator — the modern alternative for open-channel flow velocity.
- Hydraulic Radius Calculator — compute Rh from cross-sectional area and wetted perimeter.
- Hazen-Williams Calculator — empirical pipe flow velocity formula for water supply systems.
- Reynolds Number Calculator — determine whether flow is laminar or turbulent.
- Speed Converter — convert between m/s, ft/s, and other velocity units.