Use of Flood, Loss, and Evacuation Models to Assess Exposure and Improve a Community Tsunami Response Plan: Vancouver Island

Abstract

Communities developing plans for response to tsunami require site-specific estimates of the hazard, elements at risk, and potential losses, and an assessment of the effectiveness of mitigations and protective actions. Citizens want to know whether they can reach safe havens in sufficient time and whether recommended safe haven locations can offer sufficient protection. This paper investigates how flood, loss, and evacuation predictive models can be used to develop baseline estimates of potential losses without mitigations in place, with the goal of helping communities assess and improve response plans. A case study is presented for the District of Ucluelet, British Columbia, which is susceptible to the Cascadia Subduction Zone (CSZ) earthquake and tsunami hazard. Approximately 58% of the community’s buildings and key elements of the critical infrastructure are in a tsunami hazard zone. Depending upon the time of day and year, between one-half and two-thirds of the resident and tourist population are at risk, and depending on the evacuation strategy, between one-fifth and one-third of the population-at-risk could be lost. These mortality rates are comparable to observed rates for a rapid-onset, high-intensity tsunami. Alternative emergency response plans are simulated and assessed for their effectiveness in terms of the potential for loss reduction and for increases in evacuation rates. The importance of self-activation and rapid protective action is confirmed, and pedestrian-based evacuation to an expanded set of proximal safe havens is recommended. Tourists form a large proportion of the population-at-risk during high season and could experience significant proportional losses. Future research is needed to assess the community’s understanding of tsunami risk and whether community preparedness has actually improved. This study also confirms the need for broader initiatives to estimate populations at risk, to conduct evacuation modeling studies, and to assess whether evacuation on foot, in vehicles, or in combination is most effective.