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Numerical Modelling of Tsunami Propagation in Converging Channels

Author(s): Zhiwen Chen; Valentin Heller; Riccardo Briganti

Linked Author(s): Valentin Heller

Keywords: Converging channel; Solitary wave; SWASH; Tsunami propagation; Wave steepening

Abstract: Tsunamis have caused many severe natural disasters in human history, such as in 2018 at Palu City located at the end of a narrow bay resulting in over 4,340 fatalities. The tsunami characteristics are greatly affected by the water body geometry during propagation. This effect has not yet been fully investigated, especially for converging geometries such as fjords, bays and estuaries. This study focuses on the propagation of solitary waves in converging geometries. The numerical model SWASH was successfully validated with published laboratory experiments and analytical solutions for this purpose. Subsequently, the propagation of solitary waves was analysed for uniform-depth channels with side angles of 7.5˚, 15˚, 30˚ and 45˚ for curved wave sources (without sidewall reflection) and of 7.5˚ for straight wave sources (involving sidewall reflection). For a curved wave source, the wave heights closely followed Green's law and doubled as the channel width converged to 25% of the initial channel width. However, for the straight wave source, due to reflections from the converging walls, Green’s law is not well suited to predict the wave height. The observed stem wave height can be up to 11.2% larger than predicted by Green’s law for the geometry with a side angle of 7.5˚, and this discrepancy is likely to be larger for larger side angles. The straight wave source further reveals stem wave superposition and interaction, in addition to solitary wave steepening. The findings herein are aimed at enhancing the physical understanding of the effect of the water body geometry on tsunami propagation and improving tsunami prediction and hazard assessment.


Year: 2023

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