Debris-flow risk-to-life: Upper-bound preliminary screening

Where the potential for future debris-flow occurrence is unrecognised, developments can be unknowingly exposed to debris-flow impact, with corresponding risks to lives. Debris-flow modelling is unsuited to routine local office use, so a simple screening procedure is proposed to enable local officials to identify locations where debris flow risk-to-life may be unacceptable, and prioritise where expert modelling and risk analysis are most urgently required for risk-management decision-making . This procedure calculates catchment Melton ratio R from topographic data, uses a linear upper bound of field data relating R to the annual probability of debris-flow occurrence, and matches a model-based debris-flow risk-to-life analysis for Matata, New Zealand. Our data suggest that any development exposed to debris flows will require a detailed risk assessment to ensure that risk-to-life does not exceed acceptable levels.