What can be learnt from the catastrophic failure of a check dam system? A forensic analysis of a cascading natural-anthropogenic hazard

Check dams can be effective in reducing debris-flow hazards, however their failure could have serious consequences for people and infrastructures and should be avoided. The examination of these failures embracing a forensic engineering analysis, still rather poorly represented in the scientific literature, would lead to important improvements in how residual risk is planned and managed. In this study, we developed a framework for the forensic analysis of check dam systems failures in terms of cascading natural-anthropogenic hazards, and we applied such framework to a catastrophic event that occurred in October 2018 in the Rotian creek catchment (Eastern Italian Alps). The post-event survey and analysis gathered observations about rainfall, peak discharges, morphological impacts, and damaged check dams. Based on these data, we applied a newly developed coupled hydrologic-hydraulic debris flow model and we assessed the failure mode of the check dam system. Our results highlight important practical implications for improving residual risk management, namely: (i) the development of debris flow models capable of simulating the role of check dams and their failure in the debris flow dynamics, (ii) the call for extensive datasets of check dam system failures, and (iii) the necessity to develop methodologies for the prioritisation of field inspection and maintenance of existing check dam systems.