Energy and momentum approaches can lead to different results in one dimensional analysis of flow through compound channels and therefore a choice between these two equations must be made to analyse the flow. This investigation is an effort to provide some insight into the validity of these two approaches for one dimensional analysis of steady gradually-varied flow through compound channels. To achieve this, at first the energy and momentum equations and a comprehensive form of steady gradually-varied flow governing equation (G.E.) are introduced. As the G.E. shows and it has been reported in the literature, the accuracy of the two approaches depend on two important factors, 1) correct evaluation of friction or energy slopes and 2) selection of a proper functional form for Froude number. It is a common practice to assume that energy and friction slopes are equal and can be estimated by typical resistance equations for corresponding steady uniform flow (conveyance estimation methods). This is a reasonable assumption and is justified because of the inexact empirical methods involved in evaluating the slopes. Then several computed water surface profiles corresponding to experimental data (M1, S1 and S2 types) are developed by combinations of different conveyance methods and Froude number definitions. Finally, experimental data collected in this study and those reported in the literature are used to compare different computed water surface profiles with laboratory measurements. The study indicates that the momentum principle is more consistent with corresponding steady uniform flow energy/friction slope for water surface profile computation in compound channels at least for the profile types considered in this study. Interestingly, this result is independent of the conveyance method used to estimate the corresponding steady uniform flow energy/friction slope.

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