Numerical modeling of tsunami inundation using upscaled urban roughness parameterization

This study develops and validates a numerical model of tsunami inundation using upscaled urban roughness parameterization and a Drag Force Model (DFM) to simulate the effect of structures as a drag force acting on flow. The DFM can deal with subgrid scale effects of structures using three upscaled parameters: the characteristic height of the structures, and the projected areas of the structures in the x- and y- directions. The validation is based on experimental results of the physical modeling of tsunami inundation conducted in the HyTOFU flume targeting the 2011 Tohoku Earthquake Tsunami; the physical model was a 1:250 scale idealization of the town of Onagawa in Japan. This study numerically simulated tsunami inundation by comparing the experimental results with numerical results reproduced by the DFM using roughness parameterizations. The validation of the DFM reveals that it can express the effect of the flow direction and inundation ratio, and it improves the estimation of inundated extent, maximum inundation depth, and arrival time when compared with other roughness parameterizations. This technique requires careful validation of inundation characteristics and mesh size dependency, and future work to improve estimates of the drag coefficient for the prototype scale and incident wave conditions is recommended.