Abstract
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.