Author(s): Riccardo Bonomelli; Gabriele Farina; Marco Pilotti
Linked Author(s): Marco Pilotti
Keywords: Tsunami propagation Shallow Water Equations Vulnerability
Abstract: In the spring of 2021 the sudden acceleration of a 2 million cubic meters landslide along the shores of Lake Iseo (Italy) created the condition for the generation of a subaerial landslide-generated wave. Nobody was ready to manage a sudden tsunami-like emergency in an area characterized by a high density of population and large economic exposure. On the other hand, experts were aware that in 1934, in Tafjord (Norway), a similar event had caused waves with a runup larger than 20 m which destroyed the fjord coastline. Accordingly, the potential risk was huge. This dramatic event highlighted the need for an effective procedure to manage this type of emergency that, although rare, is possible in all the lakes of the pre-alpine and alpine area. Considering that, despite the large body of knowledge that has been presented in the international literature over the last decades, no specific emergency plan exists in Italy to deal with the occurrence of subaerial landslide-generated waves in lakes, in this contribution a modelling chain is presented to quantify the impacts of such an event on the towns located on the lake shores. The final goal is to support community decision-makers in a situation of uncertainty, to enable robust and aware decisions. The fall of a landslide in a lake generates a 3D free-surface flow whose accurate simulation is extremely challenging. Today the state-of-the-art technique to model landslide tsunami generation is provided by the Smoothed Particle Hydrodynamics method, whose main problem is the high computational cost, that can be limited with suitable parallelization. However, its use is still restricted and it can’t be suggested as a procedure to be used in emergency. In this contribution we simplify the description of the near field by modelling the landslide as a granular material which suddenly detaches from the slope above the lake, using a custom shock-capturing finite volume solver of the Shallow Water Equations with an ad-hoc friction law, used to describe the motion of the landslide. Once the landslide reaches the lake surface, the same solver is then used with a Newtonian friction law to model the wave propagation and to compute the maximum water elevation in the impact zone along the coast, as well as the wave runup and overland flow. Finally, vulnerability of human life to inundation in the affected towns is assessed using a physically based state-of-the-art approach that considers people stability impacted by a flood.
Year: 2025