Power, W.L.; de Vilder, S.J.; Henderson, A.; Wang, X.; Lukovic, B.; Roger, J.H.M. 2024 Agent-based tsunami evacuation modelling of Eastbourne. Lower Hutt, NZ: GNS Science. GNS Science report 2024/29. 39 p.; doi: 10.21420/TR2N-WC12
Abstract
Eastbourne is a suburb of Lower Hutt that lies on the east side of Wellington Harbour. It consists of several communities distributed along the side of the harbour at the base of steep hills. For most of Eastbourne, there is only a single road connecting the suburbs with the rest of the country, and that road is at low elevation and next to the coast. Wellington Harbour is prone to tsunami, in particular those arising on the Hikurangi subduction zone and its associated crustal faults. Tsunami from the southern part of the Hikurangi subduction zone are expected to reach the entrance to Wellington Harbour in around 10 minutes, and then take a further 20 minutes to propagate to Petone at the north of the harbour. The time to arrive at Eastbourne communities is variable (from about 20 to 30 minutes) depending on proximity to the harbour mouth. Yet, in all cases, we are dependent on self-evacuation following the ‘Long or Strong, Get Gone’ advice to mitigate the risk to people. Our results indicate the importance of Eastbourne and Seaview residents starting to evacuate as soon as possible after the end of strong shaking, as this gives the maximum potential for reaching safety before a tsunami arrives. This is particularly important in Eastbourne due to the risk that a landslide might have blocked the nearest escape route and so allow time to reach an alternative route. Some of the potential evacuation routes around Eastbourne are only walking tracks, such as the Muritai Park and Bus Barn Tracks. These walking tracks are problematic because they do not provide shelter from the elements and leave evacuated people at risk from subsequent landslides caused by aftershocks. It should also be kept in mind that strong earthquakes are likely to occur more frequently than large tsunami. This study is unable to weigh the risks associated with the use of these tracks against the additional evacuation time required for some residents if they are not used. We suggest discussion of the options and risks with the local community – one option being that these walking tracks are only used as a ‘last resort’. Some locations along the Eastbourne coast, such as at Sunshine Bay, only have evacuation routes that involve first travelling along the coastal Marine Drive before it is possible to go to higher ground. We suggest investigating the provision of alternative options for these locations. Also worthy of additional attention are locations where there is only one feasible route to high ground and no reasonable alternatives if that route is blocked. There are fewer routes to high ground for workers in Seaview than was previously the case, due to some minor footpaths becoming overgrown and due to obstacles, such as gates and fences, preventing access through commercial properties at the base of the hills. Currently, there are only two obvious routes, either around the coast to Point Howard or north towards northern Gracefield. We encourage investigating the provision or re-instatement of other routes. Our modelling suggests that heading towards northern Gracefield is generally the better of the two main currently available options, as it leaves people less exposed to tsunami while en route. (auths)
