The Role of Built Environment's Physical Urban Form in Supporting Rapid Tsunami Evacuations: Using Computer-Based Models and Real-World Data as Examination Tools

Abstract

Cities are increasingly becoming hot-spots for nature-originated disasters. While the role of the urban built environment in fostering disaster resilience has been recognized for some time, it has been difficult to translate this potential into practice. This is especially challenging in the case of rapid onset crises such as near-field tsunamis when appropriate urban forms must support the populations' ability to autonomously carry out safe and timely responses. In this respect, much of current research remains focused on large-scale elements of urban configuration (streets, squares, parks, etc.,) through which people move during an emergency. In contrast, the critical micro-scale of evacuees' experiences within the built environment is not commonly examined. This paper addresses this shortfall through a macro-and micro-scale analysis of a near-field tsunami scenario affecting the city of Viña del Mar, Chile, including a mixed-methods approach that combines computer-based models and fieldwork. The results show significant macro-scale tsunami vulnerability throughout major areas of the city, which nonetheless could be mitigated by existing nearby high ground and an urban form that allows short evacuation times. However, micro-scale outcomes show comparatively deficient spatial conditions that during an emergency might lead to dangerous outcomes including bottlenecks, falls and panic. Vertical evacuation, in turn, is confirmed as a suitable option for reducing vulnerability, but further examination of each shelter's characteristics is required.

Ex post analysis of engineered tsunami mitigation measures in the town of Dichato, Chile

“…The latter could be useful to improve the preparedness of Dichato against an event similar to the one that hit Chile in 2010. For example, if additional studies of potential evacuation are considered, restriction areas based on this information could be defined to ensure a prompt and safe evacuation (e.g., Imamura et al 2012;León et al 2019).…”

“…On the other hand, its horseshoe shape may induce long wave resonance (Gobierno Regional del Bío-Bío 2010). The 2.4-km-long beach of Dichato makes the area a touristic attraction, especially during summer, when the population can increase up to 5000 inhabitants (Koshimura et al 2010;Venegas San Martín 2012).…”

“…The epicenter was located off the Chilean coast, about 105 km northeast from the city of Concepción (Saito et al 2010;Yamazaki et al 2010) with a reported moment magnitude (Mw) of 8.8 (Pulido et al 2010;Saito et al 2010;Mas et al 2012;Robertson et al 2012). The tsunami generated free surface disturbances observed all around the Pacific Ocean basin, including the coast of Japan (Koshimura et al 2010;Robertson et al 2012). Five hundred and twenty-one people died as a direct result of either…”

“…Though most people were able to evacuate, there were 66 fatalities in Dichato, mostly tourists and elders who underestimated the intensity of the phenomenon (Mas et al 2012). More than 1200 families reported damages to their properties (Koshimura et al 2010), and approximately 80% of the exposed built structures were washed away (Gobierno Regional del Bío-Bío 2010), evidencing the high degree of destruction from the tsunami (Venegas San Martín 2012; Martínez et al 2016). This level of damage can be explained by the existence of wood houses, which were unable to uphold the large inundation depths and velocities.…”

“…Among the most damaged coastal towns in 2010 was Dichato, a relatively small settlement with three thousand inhabitants (according to the last census) (Koshimura et al 2010), located north of the epicenter, that suffered the destruction of houses and infrastructures near the beach and estuary (Koshimura et al 2010;Yamazaki et al 2010;Martínez et al 2016). After the event, the government proposed a tsunami mitigation plan, which included hard structural countermeasures to reduce the impact of tsunamis.…”