Chezy’s Resistance Coefficient in a Circular Conduit

Bachir Achour*
Research Laboratory in Subterranean and Surface Hydraulics University of Biskra, PO Box 145 RP, 07000, Biskra, Algeria.

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© 2015 Bachir Achour;

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the Research Laboratory in Subterranean and Surface Hydraulics University of Biskra, PO Box 145 RP, 07000, Biskra, Algeria; Tel: 0021333522315; Fax: 0021333522315; E-mail:


In the literature, there is no explicit method for calculating the resistance coefficient of Chezy, especially for a circular conduit. Existing relationships are either implicit or do not take into account all parameters influencing the flow such as kinematic viscosity or the slope of the conduit. In many practical cases, one affects arbitrarily a constant value for Chezy’s coefficient. It is a physically unjustified approach, because Chezy’s coefficient varies with flow parameters, especially the filling rate of the conduit and the absolute roughness. In this paper, simple and explicit relationships are presented for the calculation of Chezy’s resistance coefficient in a circular conduit. These relationships have been established based on the rough model method. The Chezy’s resistance coefficient is expressed in terms of known hydraulic parameters of the flow in a referential rough model. For fast calculation of Chezy’s coefficient, the simplified method is the most appropriate since it requires only four parameters which are the discharge, the absolute roughness, the slope and the kinematic viscosity. The study also shows that the Chezy’s resistance coefficient reaches a maximum whose expression is well defined. Some examples are presented showing how to calculate Chezy's coefficient in a circular conduit with a minimum practical data.

Keywords: Chezy’s coefficient, circular conduit, discharge, energy slope, hydraulic radius, rough model method.