Beat-the-wave evacuation mapping for tsunami hazards in Seaside, Oregon, USA

Abstract

Previous pedestrian evacuation modeling for tsunamis has not considered variable wave arrival times or critical junctures (e.g., bridges), and did not effectively communicate multiple evacuee travel speeds. We summarize an approach that identifies evacuation corridors, recognizes variable wave arrival times, and produces a map of minimum pedestrian travel speeds to reach safety, termed a ''beat-the-wave'' (BTW) evacuation analysis. We demonstrate the improved approach by evaluating difficulty of pedestrian evacuation of Seaside, Oregon, for a local tsunami generated by a Cascadia subduction zone earthquake. We establish evacuation paths by calculating the least-cost distance (LCD) to safety for every grid cell in a tsunami hazard zone using geospatial, anisotropic path distance algorithms. Minimum BTW speed to safety on LCD paths is calculated for every grid cell by dividing surface distance from that cell to safety by the tsunami arrival time at safety. We evaluated three scenarios of evacuation difficulty: (1) all bridges are intact with a 5-min evacuation delay from the start of earthquake, (2) only retrofitted bridges are considered intact with a 5-min delay, and (3) only retrofitted bridges are considered intact with a 10-min delay. BTW maps also take into account critical evacuation points along complex shorelines (e.g., peninsulas, bridges over shore-parallel estuaries) where evacuees could be caught by tsunami waves. The BTW map is able to communicate multiple pedestrian travel speeds, which are typically visualized by multiple maps with current LCD-based mapping practices. Results demonstrate that evacuation of Seaside is problematic seaward of the shore-parallel waterways for those with any limitations on mobility. Tsunami vertical evacuation refuges or additional pedestrian bridges may be effective ways of reducing loss of life seaward of these waterways.

Households’ Intended Evacuation Transportation Behavior in Response to Earthquake and Tsunami Hazard in a Cascadia Subduction Zone City

“…This knowledge gap is especially large for CSZ earthquake and tsunami events. Wood et al used least-cost-distance with consideration to critical retrofit bridges after an earthquake to create a beat-the-wave (BTW) map illustrating the minimum pedestrian travel speed to evacuate safely for each census cell ( 26 ). This analysis, with its applied approach, can help locals to identify effective evacuation strategies.…”

“…The evacuation of Seaside faces difficulty from the problematic seaward off-shore-parallel waterways, especially for those with mobility issue. However, the authors mentioned that this method is based on case scenarios, so there is no universal answer for all communities ( 26 ).…”

Comparison of inundation depth and momentum flux based fragilities for probabilistic tsunami damage assessment and uncertainty analysis

“…The vulnerability of this city to possible tsunami hazards, including estimates of damage (Dominey-Howes et al, 2010;Wiebe and Cox, 2014) and life safety (Wang et al, 2015;Priest et al, 2016) have been widely studied by various research groups. Recent studies on life safety and tsunami evacuation at Seaside indicate the problems of existing evacuation routes and the necessity of evacuation shelters to minimize the casualties in the city (Wang et al, 2015).…”

Using Evacuation Drills to Improve Tsunami Evacuation Preparedness and Resilience

“…Research demonstrated different approaches for effective evacuation strategies such as evacuation modeling (Mas et al, 2012(Mas et al, , 2015Wang et al, 2016;Takabatake et al, 2017;Mostafizi et al, 2019), evacuation planning (Scheer et al, 2012;Lindell et al, 2019b) shelter optimization (Raskin et al, 2011;Fraser et al, 2012;Park et al, 2012;Raskin and Wang, 2017;Wang et al, 2016;Mostafizi et al, 2019;Mas et al, 2012), route optimization and allocation (Kitamura et al, 2020;Wood et al, 2014), and spatial evacuation mapping (Priest et al, 2016;Wood et al, 2014;Fraser et al, 2014). Such studies could help local authorities identify critical infrastructure, create tailored evacuation plans, and optimize shelter locations and evacuation routes.…”

“…The THF had a significant contribution to the Anisotropic path modeling (Wood and Schmidtlein, 2012;Fraser et al, 2014;Priest et al, 2016). It was used to estimate the evacuees' walking speed and also the minimum "beat-the-wave" speed depending on the path cost with the change in slope.…”