Yes / Based on the method of characteristics, an analytical solution for the one-dimensional shallow-water equations is developed to simulate the instantaneous dam-break flows propagating down a triangular wet bed channel in this study. The internal relationships between the hydraulic properties associated with the dam-break flow are investigated through the comparisons with the well-known analytical solutions for rectangular channels. Meanwhile, laboratory experiments are conducted in a prismatic, horizontal and smooth flume with a triangular cross-section. The non-intrusive digital image processing is applied for obtaining water surface profiles and stage hydrographs. Results show that the dam-break flow propagation depends on the dimensionless parameter defined as the ratio of initial tailwater depth over reservoir head. has significant effect on the dam-break wave in the downstream flooded area. For , the water surface profiles in the reservoir for different at a given time remains similar. For ≥ 0.5, extra negative waves occur in the reservoir, leading to the water surface undulations. Undular bores are generated at the dam site and propagate downstream. Time evolution of dam-break flows under three different reservoir heads is similar for the same . The inception of water surface profile change is earlier when the reservoir head is larger. The analytical model shows satisfactory agreement with the experimental results though some errors exist between the analytical solution and measurements due to the formation of extra negative waves, jet and undular bores. The similarities and discrepancies between the hydraulics in the triangular and rectangular channels are identified analytically in terms of the profiles of water depth, velocity, discharge, bore height and wave-front celerity with . The presented solution could be applied to predict the effect of wet bed condition on the dam-break wave in triangular channels, while laboratory measurement data could be used for validating analytical and numerical models. / National Natural Science Foundation of China (Grant No: 51879179), Sichuan Science and Technology Program (No. 2019JDTD0007) and Open Fund from the State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University (SKHL1809)

Yes / The existing analytical solutions of dam-break flow do not consider simultaneously the effects of wet downstream bottom and bed slope on the dam-break wave propagation. In this study, a new analytical solution for the shallow-water equations (SWE) is developed to remove this limitation to simulate the wave caused by an instantaneous dam-break. The approach adopts the method of characteristics and has been applied to simulate the dam-break flows with different downstream water depths and slopes. The analytical solutions have been compared with predictions by the lattice Boltzmann method and the agreement is good. Although the proposed analytical solution treats an idealized case, it is nonetheless suitable for assessing the robustness and accuracy of numerical models based on the SWE without the frictional slope. / The National Key Research and Development Program of China (Grant No: 2018YFC1505000), National Natural Science Foundation of China (Grant Nos: 51879179; 51579166) and Sichuan Science and Technology Program (No. 2019JDTD0007); Open Fund from the State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University (SKHL1809). .

Yes / A sudden dam failure is usually simulated by the rapid removal of a gate in laboratory tests and numerical simulations. The gate-opening time is often determined according to the Lauber and Hager instantaneous collapse criterion (referred to as Lauber-Hager criterion) established for a rectangular open channel with a dry bed. However, this criterion is not suitable for non-rectangular channels or initial wet-bed conditions. In this study, the effect of the gate-opening time on the wave evolution is investigated by using the large eddy simulation (LES) model. The instantaneous dam break, namely the dam break without a gate, is simulated for comparison. A gate-opening criterion for generating dam-break flow in non-rectangular wet bed channel is proposed in this study, which can be used as an extension of the Lauber-Hager criterion and provides a more comprehensive and reasonable estimate of the gate opening time. / National Natural Science Foundation of China (Grant No: 51879179), the Open Fund from the State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University (SKHL1809) and Sichuan Science and Technology Program (No. 2019JDTD0007).

Yes / The bed slope and the tailwater depth are two important ones among the factors that affect the propagation of the dam-break flood and Favre waves. Most previous studies have only focused on the macroscopic characteristics of the dam-break flows or Favre waves under the condition of horizontal bed, rather than the internal movement characteristics in sloped channel. The present study applies two numerical models, namely, large eddy simulation (LES) and shallow water equations (SWEs) models embedded in the CFD software package FLOW-3D to analyze the internal movement characteristics of the dam-break flows and Favre waves, such as water level, the velocity distribution, the fluid particles acceleration and the bed shear stress, under the different bed slopes and water depth ratios. The results under the conditions considered in this study show that there is a flow state transition in the flow evolution for the steep bed slope even in water depth ratio α = 0.1 (α is the ratio of the tailwater depth to the reservoir water depth). The flow state transition shows that the wavefront changes from a breaking state to undular. Such flow transition is not observed for the horizontal slope and mild bed slope. The existence of the Favre waves leads to a significant increase of the vertical velocity and the vertical acceleration. In this situation, the SWEs model has poor prediction. Analysis reveals that the variation of the maximum bed shear stress is affected by both the bed slope and tailwater depth. Under the same bed slope (e.g., S0 = 0.02), the maximum bed shear stress position develops downstream of the dam when α = 0.1, while it develops towards the end of the reservoir when α = 0.7. For the same water depth ratio (e.g., α = 0.7), the maximum bed shear stress position always locates within the reservoir at S0 = 0.02, while it appears in the downstream of the dam for S0 = 0 and 0.003 after the flow evolves for a while. The comparison between the numerical simulation and experimental measurements shows that the LES model can predict the internal movement characteristics with satisfactory accuracy. This study improves the understanding of the effect of both the bed slope and the tailwater depth on the internal movement characteristics of the dam-break flows and Favre waves, which also provides a valuable reference for determining the flood embankment height and designing the channel bed anti-scouring facility. / National Natural Science Foundation of China (Grant No: 51879179, 52079081), the Open Fund from the State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University (SKHL1809) and the Sichuan Science and Technology Program (No. 2019JDTD0007)