At-a-site and between-site variability of bedload transport, inferred from continuous surrogate monitoring, and comparison to predictive equations

Abstract. This study investigates spatial and temporal variability of bedload transport in four Swiss mountain streams using continuous Swiss Plate Geophone (SPG) monitoring. This surrogate measuring system had been calibrated in previous studies to produce reliable estimates of bedload transport rates. The measurements were analysed at two different time scales: short-term transport events typically covering a duration of a few weeks and multi-year annual transport totals. Power-law relations between dimensionless transport intensity and shear stress were derived to evaluate the temporal variability in the steepness of transport relations and in the reference shear stress. Results were compared with predictive equations developed for mountain streams. Findings show substantial variability both within and across sites, likely reflecting the influence of sediment availability, stream slope, streambed texture and flow history. Overall, continuous monitoring highlights the strong role of temporal spatial variability on bedload transport levels, possibly due to changing sediment availability and bed surface composition, and with implications for predictive modelling and river management.