2024 – 1929 Failure of Briseis Dam – Lessons for Dam Break Modelling Using Contemporary Methods

Karl Velasco, Kosta Tsourdalakis, Tim Rhodes, Josh Clark

The 1929 Briseis Dam disaster offers valuable lessons to dam break modellers and decision makers through the examination of individual testimonies detailing the tragic event. Cascade Dam was constructed in the same location of the failed dam and was recently reassessed using contemporary numerical modelling and procedures. Subsequently, the consequence category was revisited in the context of the revitalised township of Derby. Observed flood behaviours were compared with the modelled results which provided some confidence in the outcomes. However, certain limitations were identified that cannot currently be replicated in standard dam break modelling practices. The sensitivity to breach parameters were tested following the standard approach, but it was not the primary factor influencing the consequence category. Instead, careful deliberation should focus on the assumed population at risk and itinerants in the township of Derby and its surroundings areas, as these are the critical factors determining the outcome. The coroner’s inquest provided valuable insight to the realities of a dam breach disaster, in particular the human behaviour aspect during a catastrophic event. The tragic lessons of the 14 lives lost have been revisited to allow a considered approach to the assessment of the Cascade Dam. While the circumstances may be rare, and not necessarily transferable to other dams, the history of Briseis Dam and its unfortunate victims is nonetheless compelling and serves as a reminder of the human element in dam break practices and consequence assessments.