Flood‐Scale Bedload Transport Dynamics From Acoustic Monitoring Compared With 2D Hydro‐Sedimentary Modeling

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Abstract Accurate estimation of bedload fluxes is critical to understanding sediment transport processes and associated channel evolution in gravel‐bed rivers, however, traditional direct measurements using samplers are time‐consuming and complex. To overcome these limitations, new indirect methods have been developed to estimate fluxes from bedload self‐generated noise recorded by hydrophones, but results from acoustic monitoring have generally been compared with discrete bedload samples or long‐term sediment budgets, offering limited insight into their performance over short timescales. To address this gap, this study compares bedload discharge estimated from continuous acoustic monitoring with those derived from two‐dimensional hydro‐sedimentary modeling and evaluates the reliability of both approaches to improve understanding of sediment transport dynamics at the flood scale. Acoustic power was continuously recorded by a hydrophone fixed at the bank, related to cross‐sectional acoustic power using acoustic maps, and converted into bedload fluxes using a calibration curve. In parallel, a high‐resolution and well‐calibrated two‐dimensional hydro‐sedimentary model was used to compute grain shear stress and estimate fluxes using transport capacity formulas, parameterized with particle tracing and bedload measurements. Both methods provided reliable estimates of cross‐sectional bedload discharge when compared with in situ samples, and resulted in similar event‐integrated bedload discharge, but instantaneous values differed significantly: acoustic monitoring revealed a clockwise hysteresis, while the model exhibited a discharge‐dependent response. Comparison of both approaches revealed that acoustic measurement captured an early mobilization of recent local sediment deposits and a subsequent sediment‐limited regime due to insufficient upstream supply, which the model was intrinsically unable to reproduce.

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