Flow within road ditches, roof gutters, drainage conduits, wash-water trough flows in water and wastewater treatment plants, and side channel spillways are some practical examples of structures conveying spatially varied flow with increasing discharge. The water surface profile in such circumstances is an important factor in the design process. Accordingly, in order to decrease the water surface elevation along the channel, the bottom width of the channel is usually enlarged in the flow direction, this produces a non-prismatic channel. It has been mentioned that the presently available equations are applicable in prismatic as well as non-prismatic channels. The result of this study however, indicated that the presently available equations are sensitive to the position and the flow depth of the control section. This paper, based on the momentum principle, presents a new form of the governing equation for spatially varied flows with increasing discharge in non-prismatic channels. Also, the Newton Raphson method was utilized to solve the proposed equation and the results of the model were verified with experimental data.
Good agreements were observed between the computed values and the observed data,
which indicates the validity of the proposed model.
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