The devastating consequences of past events, such as the 2004 Indian Ocean and 2011 Tōhoku tsunamis, emphasise the need for continued improvement in resilience measures. Given that 80% of magnitude 8+ earthquakes occur on the Pacific Rim, New Zealand's tsunami risk is significant. This research develops a novel tsunami inundation model. The proposed model applies equations based on hydraulic principles, including energy conservation (friction loss). While it does not fully replicate hydrodynamic models, it maintains a two-dimensional approach and offers significant improvements over currently implemented simplified methods. It retains excellent computational efficiency (seconds to minutes) while achieving a significant increase in accuracy that is comparable to traditional hydrodynamic models, which typically take hours to days. Calibration of the roughness input variables to hydrodynamic modelling at Gisborne and Christchurch, New Zealand, optimised the model to achieve similarity index values of above 84% for inundation extent, while 77% of inundation depths were within ±1 m and over 93% within ±2 m. This research then produces the first nationally consistent tsunami exposure assessment for New Zealand using a physics-based modelling method. Using probabilistic shoreline wave amplitude data, the study generates high-resolution (10 m) inundation maps for seven return periods (50th and 84th percentiles). These maps are integrated with land cover and infrastructure data to quantify exposure and identify the most vulnerable locations. The results highlight exposure not only to the commonly studied cities but also to several provincial areas. The identification of exposure is the foremost step towards practical resilience efforts; however, understanding specific infrastructure impacts ensures that countermeasures and risk reduction practices are implemented. Therefore, a detailed evaluation of the NZTA Bridge Manual is conducted. Comparisons are made between the NZTA methodology and the rapid model developed in this research. The results reveal a significant overestimation of bridge and culvert exposure by NZTA methods. The study further highlights critical exposure locations for bridge and culvert assets. Flow depths calculated at bridge locations are significantly overestimated using the NZTA method compared to results derived from hydrodynamic modelling and the rapid model. This research then conducts component-level modelling of culvert assets, due to their identified vulnerability in the transportation network. At a 1:15 geometrical scale, laboratory experiments evaluated the response of different culvert set-ups to tsunami bores. The findings provide a detailed description into overtopping, flow regimes and pressure distributions and give laboratory experiments as validation studies for future numerical modelling and design improvements. Overall, this research performs a multi-modal tsunami inundation assessment, uniting macro-level exposure modelling with micro-level component responses by integrating modelling, exposure analysis, and experimental validation. The findings support refining current tsunami guidelines, improving infrastructure planning, and enhancing community preparedness. Overall, the study’s multi-model approach strengthens many elements of New Zealand’s ability to mitigate and respond to future tsunami events
Surface-rupturing earthquakes can trigger the sudden avulsion of river channels, causing rapid and persistent coseismic flooding of previously unaffected areas. This phenomenon, known as fault-rupture-induced river avulsion (FIRA), occurs when fault displacement significantly alters river channel topography. The importance of understanding FIRA as a secondary seismic hazard was highlighted by events during the 2010 Darfield and 2016 Kaikoura earthquakes in New Zealand. This thesis develops a national model to identify and quantify FIRA susceptibility across New Zealand by integrating hydrological datasets (NIWA RiverMaps and Flood Statistics) with active fault information (NZ Active Faults Database and RSQSim earthquake simulations). The methodology applies the F-index framework proposed by McEwan et al. (2023), which quantifies FIRA potential based on the ratio of fault throw plus discharge-dependent depth to bank full depth at each fault-river intersection. The model successfully identified 3,796 potential FIRA-susceptible fault-river intersections nationwide, with 451 involving waterways equal to or larger than the Hororata River. Regional analysis revealed higher concentrations of FIRA-susceptible sites in the Bay of Plenty, Canterbury, and Marlborough regions. Validation against historical events showed the model effectively located known FIRA occurrences from the Kaikoura and Darfield earthquakes, though with some limitations in accurately predicting F-index values due to complex fault displacement patterns and challenges in modelling bank full depths of large, braided rivers. This research establishes New Zealand's first nationwide assessment of fault-induced river avulsion susceptibility. The approach creates a structured methodology for identifying high-risk fault-river intersections and determining which sites require thorough localised examination. The methodology developed offers a template for similar assessments in other tectonically active regions and contributes to improving earthquake hazard assessment and disaster preparedness planning.
The North Canterbury and Marlborough regions of Aotearoa | New Zealand were severely impacted by almost 30,000 landslides triggered during the 2016 Kaikōura Earthquake. Of these landslides approximately 200 dammed rivers. In the study area near Waiau, rupture of The Humps and Leader faults (and associated ground motions) initiated at least 42 co-seismic landslides. The Leader Landslide is the largest of these landslides, with an area of approximately 600,000 m2 and a volume of 6-8 million m3. The landslide buried approximately 980 m of active Leader River bed length and dammed the river. The dam produced four lakes, with two remaining today and two having been breached by partial landslide collapse and knickpoint migration in the year following the earthquake. As of 2025, the landslide dam has not been completely breached and Lake Rebekah remains. The Leader Landslide dam presents a unique opportunity to chart the evolution of the active riverbed pre- and post-earthquake, for up to 2 km downstream of Lake Rebekah. The river’s evolutionary timeline was observed using LiDAR, satellite aerial imagery, and drone surveys from 2001 to 2024 to develop maps and topographic difference models. Key timeframes for riverbed change events were also constrained with information and dated photography gathered from previous communications with the landowners at Woodchester Station, where the landslide is located. Finally, Schmidt Hammer testing of the Pliocene-Miocene Greta Siltstone Formation was conducted to investigate the role of bedrock strength on the rate of riverbed erosion. I present the history of evolution of the Leader River, pre- and post-earthquake, and consider factors impacting riverbed morphology changes. Despite the stability of Lake Rebekah, these data show that the position and morphology of the Leader River has changed significantly in response to the landslide, with the formation of two knickpoint waterfalls up to 14 m-high, four waterbodies, and diversion of the river around the landslide toe. Evolution of the river is characterised by longer periods of stasis (e.g., months to years) punctuated by rapid changes in riverbed morphology (e.g., hours to weeks) associated with incision and aggradation. In particular, the knickpoints migrated upstream at variable spatial and temporal rates. Factors controlling the rates of processes include; rain-storm events, partial lake outburst flooding, spatial changes in Pliocene-Miocene siltstone bed induration and landowner intervention to stabilise the landslide dam. An overarching conclusion of this thesis is that landforms can develop rapidly (i.e., hours to weeks) and in the absence of historical accounts, could be interpreted to have formed over hundreds to thousands of years.
