Technical note: Effects of free-surface on design charts for open channels

  • M Rahimpour
Keywords: Open-channel flow, normal depth, free-surface effect


Normal depth is an important parameter for the design of channels and canals. For rectangular, trapezoidal, and circular channel sections it is possible to express normal depth by a trial-and-error procedure or analytically. However, the effects of free-surface on the design charts for determination of the normal depth are not investigated. In this paper, graphical solutions of normal depth for the rectangular, trapezoidal, and circular cross-sections have been obtained in the non-dimensional form. To evaluate the resistance effects of the free-surface in the calculation of the normal depth, the dimensionless-form of Manning’s equation with free-surface weight factor is introduced herein. The design charts reported previously were modified.

Keywords: Open-channel flow; normal depth; free-surface effect


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eISSN: 0378-4738