Numerical Simulation of Impulse Waves Generated by Sliding Masses

Landslide-generated impulse waves are a significant hazard in coastal areas. They could be generated by a number of natural mass-movement processes including landslides, avalanches, debris and lava flows. One example is the famous 1958 tsunami in Lituya Bay, Alaska, that had an amplitude of more than 500 meters and was generated by a huge rock avalanche. These impulse waves are the result of a dynamic interplay of several highly unstable processes where three interacting phases (air, fluid and solid material) are involved. The sliding solid material has complicated rheological behavior characterized by the interaction between solid and fluid phases. In addition, there is the overall three-dimensional turbulent flow behavior and the interfacial flow structure. Recent modeling activities operate in the frame of depth-averaged Navier-Stokes equations and hence are restricted to applications where the relation between horizontal (H) and the vertical length scales (V) is V/H<<1. In order to avoid this limitation, and to better understand the generation and runup of these waves, we are in the process of developing a new numerical model. It operates on the basis of three-dimensional incompressible Navier-Stokes equations for the water and the moving solid material. In order to account for the turbulent flow behavior, we use the large-eddy simulation approach. Together with standard numerical methods like the Chorin type scheme, which solves these equations in the finite volume context, the model realizes a level-set algorithm for tracking the interface between the ambient air and the two other phases. As a first test case, we numerically modeled the interaction of water with a solid, sliding wedge as a simplified subaerial landslide and investigated the characteristics of the induced water waves.