AbstractThe present paper attempts to study the flood wave propagation at a right-angled combining open channel junction utilizing the three-dimensional (3D) transient Reynolds-averaged Navier-Stokes (RANS) equations. The present study advocates using the 3D model over the depth-averaged two-dimensional (2D) model by comparing simulations obtained from 3D and 2D models for steady flows. The 3D model is validated against the experimental results of the flood routing in a single reach channel, available in the literature. The flood wave at the channel inlet is generated by a half-cycle of the sinusoidal function. Three different cases (Cases 1, 2, and 3) are considered by applying the flood wave at the inlet of the main channel, tributary channel, and both the channels, respectively. The steady-state junction flow with equal discharge in both the upstream channels is considered as the initial condition for the flood wave simulations. The rising flood flow of the main channel offers huge flow blockage to the tributary channel flow in Case 1, while vice versa in Case 2. The blockage causes significant flow accumulation leading to the stage rise. In Case 2, the flow reversal occurs as the flow in the main channel is entirely blocked by the rising flood flow of the tributary channel. The interplay of the flow blockage by the main channel to the tributary channel and vice versa results in water accumulation and release, alternatively. The maximum stage rise occurs in Case 3 due to the combined effects of the rising flood wave and flow blockage, simultaneously.Practical ApplicationsThe previous flood routing studies at the channel junction have disregarded the momentum equation. This may not be accurate as momentum exchange occurs between the main and tributary channel flow. Considering the dynamic interaction between the approaching flows, the present paper attempts to study the flood wave propagation at a right-angled combining open channel junction utilizing the fully three-dimensional numerical model. Three different simulation cases considered for investigating the flood wave propagation demonstrate the impact of the main channel flood wave on the tributary flow and vice versa. The alternate amplification and attenuation of the flow discharge in both the upstream channels continue to happen due to the interplay of the blockage offered by the main channel to the tributary channel and vice versa before the junction flow attains the base flow condition. The results of the present study improve the understanding of flood wave propagation at the channel junction.