Bedload regime transition detected with seismic measurements during flood events in a morphodynamically active Alpine river

Abstract Sediment transport is a key process that strongly influences river morphology but remains difficult to measure and understand, especially during floods in mountainous regions. The paper aims to detect and interpret changes in bedload transport regimes during high‐magnitude flood events in an Alpine braided reach (La Séveraisse, French Alps) using continuous seismic monitoring. For the seven investigated floods identified over the 5 years of record, we observe a consistent break in the scaling relationship between the low‐frequency seismic power and the high‐frequency seismic power, suggesting a change in bedload transport regime linked to sediment mobility. Using time‐lapse cameras and hydrological conditions, we find this breakpoint is associated with significant morphological changes occurring at Shields stress ratios approaching a critical value of 2. Based on these results and existing literature, we suggest the break in seismic power corresponds to a transition in bedload regime associated with the disruption of the bed armour layer and particle dynamics being highly influenced by grain–grain interactions. This study demonstrates that changes in sediment transport regime can be accurately identified from seismic observations near rivers, furthering our understanding of the links between sediment transport and channel morphology dynamics.