The John Mitchell Lecture 2023: Road Asset, Socioeconomic and Fatality Risk from Debris Flow

Fast-moving, rainfall-induced debris flow events are relatively common in the mountainous areas of the UK. The mechanisms of rainfall-induced, fast-moving debris flows are considered as they bridge between slow mass movements and flood phenomena. A series of case studies of debris flow impacts from Scotland and overseas will be described. The assessment of landslide hazards and risks is an essential precursor to landslide risk reduction. This is particularly the case when an authority is responsible for an infrastructure or building portfolio that may be affected by multiple hazards. A framework for risk acceptance is used to set the context, and the use of a semi-quantitative assessment to determine the sites of highest risk is described. These highest risk sites are subject to quantitative risk assessments for road user fatalities as a result of debris flows. A novel approach is taken to assess the socio-economic risks and the use of fragility curves to articulate the vulnerability of road infrastructure, including the newly-developed approach involving systems of assets, is also described. The effects of climate change are considered alongside likely social and/or demographic change. A strategic approach to landslide risk reduction is used to illustrate how a clear focus on the overall goal of risk reduction can be beneficial in developing an effective strategy before homing in on the desired outcomes and the generic approach to achieving those outcomes.