Abstract
Understanding and predicting bedload transport is an important element
of watershed management. Yet, predictions of bedload remain uncertain up
to several order(s) of magnitude. In this contribution, we use a
five-year continuous time-series of streamflow and bedload transport
monitoring in a 13.4 km2 snow-dominated Alpine
watershed in the Western Swiss Alps to investigate the hydrological
drivers of bedload transport. Following a calibration of the bedload
sensors, and a quantification of the hydraulic forcing of streamflow
upon bedload, a hydrological analysis is performed to identify daily
flow hydrographs influenced by different hydrological drivers: rainfall,
snow-melt, and mixed rain and snow-melt events. We then quantify their
respective contribution to bedload transport. Results emphasize the
importance of mixed rainfall and snow-melt events, for both annual
bedload volumes (77% in average) and peaks in bedload transport rate.
Results further show that a substantial amount of bedload transport may
occur during late summer and autumn storms, once the snow-melt
contribution and baseflow have significantly decreased (9% of the
annual volume in average). Although rainfall-driven changes in flow
hydrograph are responsible for a large majority of the annual bedload
volumes (86% in average), the identified melt-only events also
represents a non-negligible contribution (14 % in average). Through a
better understanding of the bedload magnitude-frequency under different
hydrological conditions, the results of this study may help to improve
current predictions of bedload transport, and we further discuss how
bedload could evolve under a changing climate through its effects on
Alpine watershed hydrology.