Experimental measurements suggest that the frictional resistance experienced by a uniform flow is approximately proportional to the square of the volumetric flow rate, provided the velocity of the flow is not too small. If u defines the mean velocity and m the mean hydraulic depth, the Chezy formula gives:

where i is the gradient of the total head line and C is the Chezy coefficient. In the context of open channel flow, the Chezy formula may be written as:

where the bed slope (s) is equivalent to i for steady uniform flows.

Although the Chezy formula was originally defined empirically, it is directly related to the *friction factor* (f). The Chezy coefficient is thus dependent upon surface roughness, the Reynolds number, and the hydraulic mean depth. Tabulated values of C and the related coefficient n (usually referred to as *Mannings coefficient*) are given by Chow (1959).

#### REFERENCES

Chow, V. T. (1959) *Open-Channel Hydraulics*. McGraw-Hill Inc., New York.