Landslide-triggered tsunami modelling in alpine lakes

Abstract

The Alps are the location of potentially catastrophic landslide-generated tsunami. Numerical modelling based on shallow water equations represents a valuable tool able to provide prediction in order to assess this threat. However, some inherent numerical problems (e.g. artefacts development when applied to real cases, difficulty for wet to dry bed transition) are well known, but not resolved yet. Our main objective is to find a method that is relevant for landslide-triggered tsunami modelling, as accurate as possible in order to use it as predictive tool. Thus, we investigated numerical models, based on shallow water equations, which could run on high resolution bathymetry. Accordingly, four Godunov-type solvers are confronted to the exact solution. Interestingly, at high resolution, which is needed for bathymetry, the difference between monotonous first-order methods gradually disappears. The simplest Lax-Friedrichs scheme is suggested as the method of choice. The experiment of a 2D circular dam break, solved using Lax-Friedrichs scheme, is presented and the resolution at which results are converging is reported. Performance of high resolution 2D runs on CPU and GPU are reported, documenting 50 fold speedup on GPU. As result of this speedup, the high resolution run take less than an hour on GPU card that cost less than 1000 SFr.