Multi - hazard modelling and risk estimation for transport systems along the eastern coast of Taiwan exposed to flooding, debris flows and seismic landslide events

Transport infrastructure is critical for societal functioning allowing for the movement of goods and services whilst facilitating societal connections between regions. Additionally, transport infrastructure is varied and geographically extensive; it includes roads, railways, and associated assets such as embankments, retaining walls and railway lines. These assets are vulnerable in different ways and are exposed to different  hazards with a varied spatial spread; for example, extreme precipitation and earthquakes can trigger landslide and slope failures in mountainous regions potentially leading to blockages of road networks. Whilst flooding may submerge roads and damage railway infrastructure leading to ballast scour causing delays and incurring large repair costs in both instances. Moreover, multiple hazards can occur at the same time with the potential to interact, such as landslides following flooding caused by heavy rainfall or earthquakes triggering landslides causing landslide dams.  Considering this, the goal of this work is to develop a multi hazard risk assessment framework for transport infrastructure exposed to multiple different and interacting natural hazards under future climate change. This provides a more holistic and accurate representation of multi hazard risk when compared to the study of single hazards, making a multi hazard risk assessment better able to take into consideration the full scope of risk threatening infrastructure systems. To conduct this research, Taiwan was selected as a case study as it represents a fascinating and dynamic landscape with advanced transport systems exposed to multiple different hazards, making it the perfect living lab to study multi hazards and their interactions. The work sought to determine the multi hazard risk of combined flooding, landslide and seismic landslides affecting transport systems on the eastern coast of Taiwan. This study simulated hazard events by integrating existing multi-hazard simulation software with new slope stability mapping software. A slope stability model employing the infinite slope model and factor of safety was generated to map slope stability under precipitation and earthquake conditions. Additionally, the Synxflow hazard modelling package was used to simulate the behaviours of landslide runouts and flooding under typhoon conditions to understand hazard behaviours. In tandem with this, GIS techniques were employed to map these combined risks within the catchment. To determine the risk to transport systems a segment-specific risk assessment was conducted, breaking down the transport systems into smaller segments to identify the area’s most at risk. Preliminary results of this show large swathes of transport systems vulnerable to multiple hazards threatening to block transport systems and cut of communities. Early results indicate that increased precipitation due to climate change is likely to exacerbate this threat, leading to more frequent road and rail closures and higher costs for repairs and rerouting.