Power, W.L.; Flores Henriquez, C.; Lukovic, B.; Nilsson, D.; Tan, M.; Hudson-Doyle, E.E.; Kuligowski, E.; Boersen, K.; Leonard, G.S.; Thomas, K-L.; Kaiser, L.H; Wilson, T.M; Khan, H. 2025 Tsunami Evacuation Modelling for Napier, Gisborne, and South New Brighton and Southshore. Lower Hutt, NZ: GNS Science. GNS Science report 2025/020. 75 p.; doi: 10.21420/YSA2-8731
Abstract
Tsunami evacuation is the single most effective way to mitigate the risks to life and limb posed by tsunami. Where the tsunami is generated close to Aotearoa New Zealand, this takes the form of self-evacuation following a long or strong earthquake. There are many challenges to achieving safe and timely evacuation, among them that our pedestrian and transport infrastructure was typically not designed with tsunami evacuations in mind, and does not always have the capacity required. Further, while we encourage those who can evacuate on foot to do so, there are some who cannot do this in the time required, and experience tells us that, even among the sufficiently able-bodied, some will use vehicles regardless. The challenges of tsunami evacuations can be most realistically simulated and identified using drills, but often it is not possible to run large-scale drills when the number of people required for a realistic exercise runs into the thousands. To fill this gap, the technique of agent-based evacuation modelling has been developed, to simulate large-scale evacuations. While these models are simplifications of very complicated situations, they can still be useful for identifying problems and proposing solutions. With this in mind, this report summarises agent-based tsunami evacuation models of three urban areas: Ahuriri Napier, Turanganui-a-Kiwa Gisborne, and Te Kai-a-Te-Karoro South New Brighton and Te Kai-a-Te Karoro Southshore in eastern Otautahi Christchurch. Different approaches were used for the three study sites, driven in part by the questions that were identified as important to our stakeholders, and in part by the research need to trial different methods. In Napier, we have taken a suburb-by-suburb approach, and looked into how the presence of large numbers of cruise ship tourists could affect evacuations. In Gisborne, we have focussed on the urban area and looked into the ways that our modelling could inform the location and design of Vertical Evacuation Structures (VES), an important form of mitigation when walking distances are too large. Finally, in South New Brighton and Southshore, we have studied the effect of the single bridge leading out of these suburbs as a bottleneck to both pedestrians and vehicles, and used this to trial ideas about how the two different modes of transport affect each other. Our results reinforce the primary importance of maximising timely participation in evacuations, the importance of heeding natural warnings and the “long or strong, get gone” advice, the need to encourage those who can make a safe and timely evacuation on foot to do so (especially in urban areas), and the potential value of VES as a last-resort option when evacuation distances are too large (auths)
