Numerical assessment of coastal multihazard vulnerability in Tokyo Bay

Many bays worldwide are susceptible to coastal hazards such as storm surges, river floods, and tsunamis. Because most previous studies have focused on one or two of the above-mentioned hazards, in this study, we assess coastal vulnerability based on all three hazards. To accommodate the increase in the number of cases in multihazard analysis, an efficient method based on an estimated overflow volume without computing for inundation is proposed. Subsequently, the method is validated via a comparison with inundation simulation. It is shown that when the free overflow is dominant, the result yielded by the method is consistent with that of the inundation simulation. Using Tokyo Bay as the study area, an efficient method is applied to multihazard vulnerability assessment. By comparing the overflow volume maps and maximum anomaly distribution along the coast for four types of hazards, we investigate the characteristics of different types of hazards and identify the differences between single and multiple hazards. Furthermore, we compare the differences between superposing and concurrent computation methods for multiple hazards. It is discovered that the linear superposing method tends to overestimate the total water elevation in coastal regions; however, in the coast, where the superposing method underestimates multihazard anomalies, dike upgrades must be considered.