This study used 3D numerical simulations to model the potential risk of impulse waves originating from concurrent landslides in Çetin Dam reservoir in Southeast Turkey, which is near an active orogenic belt and related uplift system. A volume of fluid (VOF) model based on the Reynolds averaged Navier–Stokes equations was used to accurately simulate the free-surface/solid interaction, landslide deformation, and wave propagation. A renormalization group (RNG)-based k-ε turbulence model was used to create a fluid coupled model, and a drift-flux model was selected to simulate the potential landslide. A partially submerged landslide located 4900 m from the dam and another subaerial landslide located 800 m from dam were first modelled separately. 3D numerical models show that the impulse wave triggered by the subaerial landslide reaches 4 m in height at 34 seconds right in front of the dam, whereas the wave induced by the partially submerged landslide reaches 4.2 m in height at 205 seconds. After the effects of both landslides were modelled separately, the cumulative effect of impulse waves was evaluated in the case of the two landslides occurring simultaneously. As predicted, the highest wave reaching the dam body occurred 15 seconds later due to the interference of the two waves. However, contrary to expectations, the height of the new wave increased, which was probably due to the constructive interference of the original waves, and it reached 5.6 meters at the dam body. Numerical analysis shows that when more than one landslide occurs simultaneously in the reservoir, the resulting interference affects the wave properties considerably.