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Granular landslides impacting reservoirs may generate large waves and cause active sediment transport, and an increased understanding of these processes is important for public safety and effective reservoir management. This study investigates the waves and sediment transport caused by landslides impacting reservoirs using a two-dimensional coupled double-layer-averaged shallow water hydro-sediment-morphodynamic model. In contrast to existing models, which cannot fully account for sediment transport, the model makes a physical step forward. The model is benchmarked against laboratory experiments of landslide-generated waves in both two and three dimensions. Based on extended numerical cases, the capability of the model is further demonstrated by comparisons with empirical relationships of waves in 2-D. In addition, sediment transport is resolved in terms of the sediment concentration and bed deformation. The results show that the wave types and amplitudes in 2-D are dictated by the sediment transport speed, which also governs the landslide-to-wave momentum transfer and the landslide efficiency, which is defined as the ratio of the horizontal runout distance to the vertical fall height. With increasing sediment transport speed, landslide-generated waves in 2-D vary gradually from smaller nonlinear oscillatory waves to larger waves with solitary-like wave characteristics, including nonlinear transition waves, solitary waves, and dissipative transient bores. In contrast to the momentum transfer ratio, the landslide efficiency increases with the sediment transport speed and decreases with the reservoir water depth and the lateral spreading in 3-D cases.

Plain Language Summary The waves and sediment transport due to granular landslides impacting reservoirs are numerically solved by a double-layer-averaged shallow water hydro-sediment-morphodynamic model. It is shown that wave type and amplitude in 2-D are dictated by sediment transport speed relying on initial landslide volume and velocity, slope angle, and reservoir water depth. Contrary to the landslide-to-wave momentum transfer ratio, landslide efficiency increases with initial landslide volume and velocity as well as slope angle and is constrained by reservoir water depth and lateral spreading in 3-D.