Velio Coviello

and 9 more

In mountain rivers, long-term observations of water and sediment fluxes are crucial for understanding the dynamics of bedload fluctuations at multiple temporal scales. Here we analyze 7 years of data gathered at a bedload monitoring station in the glacier-fed Sulden/Solda River (South Tyrol, Italy). Continuous seismic data gathered from 8 geophone plates are analyzed to estimate the bedload flux at 1 minute scale. Sixty-five direct bedload sampling were carried out to derive the calibration equations adopted to quantify the transported bedload mass. The signal power is proposed as a more effective metric for calculating bedload mass than threshold-based impulses. Results show: (i) a remarkable variability of bedload rate for the same value of flow discharge; (ii) the joint effect of storm-driven flood events and seasonal changes in sediment supply on bedload rates; and (iii) the strong impact of climatic factors (i.e., temperature and snow cover) on bedload fluxes. Moderate bedload rates occurring in late spring/early summer are likely related to the mobilization of riverbed sediments, while higher bedload peak rates observed in July-August are associated with the activation of glacial and proglacial sediment sources. The dataset shows a complex climatic control on bedload transport at the basin scale, where precipitation, air temperature and snow cover determine flow and glacier melting dynamics. These findings suggest how the effects of the ongoing climatic change (e.g., higher frequency of intense rainfall events and prolonged heat waves) can result in a marked increase in bedload transport in glacier-fed rivers of the Alps.