Integrated Bedload Monitoring for Mobility Threshold Analysis in an Alpine Stream

Monitoring bedload is challenging, particularly after extreme events, when the equilibrium state of mountain systems shifts, and the sediment dynamics changes. This study, conducted in the Rio Cordon (Dolomites, BL), aims at detect-ing the changes in bedload transport thresholds during minor events after the Vaia storm (October 2018). Three periods were analyzed during spring-summer 2023, adopting different field-based techniques: bedload tracing (95 Passive Integrated Transponders, PITs), and sediment trap (Bunte sampler). The three periods exhib-ited a Qp equal to 1.52, 0.21, and 0.35 m3s-1, respectively. Despite the recovery rates constantly > 85%, only the first period recorded grains displacements, with an average distance of 0.31 m (moved + not moved) and a transported Dmax of 92 mm. Regarding the data collected from the Bunte trap, transport rates of 0.29, 0.01, and 0.17 g s-1 were recorded for the first, second, and third period, respec-tively. The material transported during the first period registered a Dmax of 84 mm and a Dmedian of 57 mm. A Dmax of 16 mm and 42 mm with Dmedian of 8 mm and 24 mm were recorded in the second and third period, respectively. The integrated approach of both monitoring techniques enabled the identification of transport thresholds for each grain size class (i.e., D = 45.3 mm requires Qc ≥ 0.35 m3s-1; D = 128 mm requires Qc ≥ 1.52 m3s-1). These results underline the good performance of the Bunte approach as it overcomes the technical limitation of PITs forvalues<45.3mm.