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

Abstract

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