Lin, S.-L.; Wolter, A.; Rosser, B.J.; Henderson, A.; Lukovic, B. 2024 It’s Our Fault; No Matou Te Hapa (IOF): natural hazards impacts on Maori communities and key facilities, Takapuwahia, Porirua, case study. Lower Hutt, N.Z.: GNS Science. GNS Science report 2024/40. 29 p.; doi: 10.21420/6XFB-X221
Abstract
This report summarises a detailed impact assessment for people and assets (i.e. buildings, infrastructure) in Takapuwahia, Porirua, for the It’s Our Fault Programme, supported by tangata whenua and the local community. The assessment was carried out using hazard and asset datasets developed (updated or collated) for the study area. Several community engagement hui were carried out to co-design the project scope and tasks, collect data and provide progress updates, as well as produce useful outputs (e.g. poster-size maps). Assessment results were discussed to support the Takapuwahia community to weigh the risks of decisions (e.g. planning) or to invest in new development. Findings from the assessment are: • All people and assets in the study area are exposed to earthquake shaking, although in different shaking intensities depending on earthquake scenarios (475-, 975- and 2475-year return periods). However, the impact could vary due to different shaking intensity, and building/infrastructure condition and vulnerable populations (e.g. kaumatua, tamariki, those with disabilities). • Tsunami impact to the Takapuwahia community is expected to be low when caused by earthquakes with a 475- or 975-year return period. However, some people (particularly the most vulnerable community members), buildings and infrastructure are exposed to tsunami hazard (i.e. with 1 m or higher inundation water) during the most extreme event considered (i.e. tsunami caused by a 2475-year return period earthquake). • For liquefaction hazard (susceptibility) impact, the modelled outputs show that ~10%of the population and buildings in Takapuwahia are located in high liquefaction hazard zones, and ~20% are exposed to low liquefaction hazard. For infrastructure, ~20% of the assets are in high liquefaction hazard zones, while another ~20% are exposed to low liquefaction hazard. • For landslide impact, the study area is expected to have a low landslide impact caused by earthquakes with 475- or 975-year return periods or rainfall with 50-, 100-or 250-year ARI. However, some people, buildings and infrastructure are exposed to landslide hazard during the most extreme event (i.e. landslides caused by a 2475-year return period earthquake). Considering a slope-angle-only susceptibility model, ~3% of the assets are located in high to very high slope hazard zones, and less than 10% are exposed to moderate slope hazard. A desktop review of hazards uphill of the community was also conducted. The review indicates that exposure to landslide hazard would increase, while exposure to tsunami and liquefaction hazard would decrease (depending on where relocation occurred). De-vegetation of the slopes above the current township might increase landslide susceptibility. We recommend further site-specific investigations, including sea-level-change evaluation, to be completed. Lastly, the complete exposure analysis results accompany this report as a digital appendix, containing maps (A1 poster size) of impact results (auths)
