Bronwyn Matthews , Mark Naylor, Hugh Sinclair, Andrew Black, Richard David Williams, Calum Cuthill, Matthew Gervais, Michael Dietze, Anna Smith

Seismological observations provide a non-invasive and continuous means of indirect measurement of fluvial bedload transport (i.e. the transport of coarse granular material, as a function of water depth, in rivers). However, a significant challenge remains in independently characterising the seismic signature of bedload transport from other sources, such as turbulence. Previous research suggested using the hysteresis relationship between water level and frequency-filtered seismic power spectrum as a diagnostic tool for identifying bedload transport. We present a unique dataset from an alluvial Scottish river, including seismic and hydroacoustic measurements, to analyse bedload transport during the three successive high flow events within a year. Examining data from successive events enabled us to evaluate the consistency of bedload transport thresholds and the influence of past transport events. Our findings reveal that bedload transport was observed in all three events, with the threshold for entrainment influenced by antecedent events. Following the largest of the three events the entrainment water level dropped by 20\%, meaning it was easier to mobilise sediment. We also found that while hysteresis patterns observed in the seismic observations were linked to the size and timing of high flow events, they were not a necessary observation for bedload transport to have occurred. In fact, despite bedload transport occurring in all three events, hysteresis was only observed in the largest event suggesting that hysteresis alone is insufficient for identifying bedload transport. Our work suggests that there is a greater richness in the seismic data than has previously been identified and exploited, providing crucial information for effective river and land-use management in a changing climate with potentially impacted high flow events.