Comparison of tsunami simulation using diffusive and fully-dynamic shallow water equations models using Hec-Ras 6.1

Abstract

This study highlights a comparison between the diffusive and fully-dynamic shallow water equations (SWE) for tsunami simulations using HEC-RAS 6.1. The case study used is the 2011 Japan Tohoku Tsunami recorded in the Hilo Bay, Hawaii. For the numerical simulations, three grid sizes of 10, 20, and 30 meters are used. The numerical results, i.e., velocity and water surface elevation, are compared with the benchmark data to ensure the model accuracy produced by the software. The results show a significant delay in the wave arrival time for both equations employed. However, using the fully-dynamic SWE results in a longer delay than the diffusive SWE. The fully-dynamic SWE compute the wave amplitude more accurately than do the diffusive SWE, although both approaches are not still in agreement with the benchmark data. The significant difference in both equations lies in the location of the maximum velocity value. Changing the grid sizes for both equations only increase the computational cost without giving any significant difference. It can be concluded that using both equations does not produce any accurate results compared to the benchmark data, although the differences between each equation are significant for some parameters. The inaccuracy of the results is hypothetically because HEC-RAS 6.1 uses the sub-grid bathymetry approach, by which the mesh calculation takes place at the sub-grid level. This approach is possibly not suitable to be applied to shock wave cases, which in this report is the tsunami wave.