Sediment availability and connectivity: a geomorphological framework for debris-flow hazard assessment

The occurrence and magnitude of debris flows largely depend on the amount of sediment stored within a catchment and the effectiveness of its connection to the channel network. Quantifying both sediment availability and its connectivity is therefore a critical requirement for constraining numerical simulations used to delineate debris-flow inundation areas. To support more reliable hazard assessments in alpine regions, an integrated geomorphological framework was developed and implemented in the Camonica Valley (Italian Alps) to characterise potential debris flow behaviour. The approach places particular emphasis on sediment connectivity as a key link between sediment sources and downstream propagation, reinforcing the role of geomorphological and geomorphometric analyses as a foundation for numerical modelling. Field observations, historical records of past events, and morphometric indicators are jointly used to discriminate between dominant flow processes and to estimate the volumes of sediment that may be mobilised during extreme events. The workflow combines GIS-based regional screening of debris-flow susceptibility along the drainage network with the identification of sediment source areas derived from orthophotos and terrain analysis, followed by an explicit evaluation of sediment connectivity and field-based verification of sediment thickness. Overall, the methodology provides a coherent and transferable basis for debris-flow hazard zonation and land-use planning in mountain environments, with sediment connectivity explicitly embedded in the assessment process.