Bedload transport drives morphological changes in gravel-bed streams and sediment transfer in catchments. The large impact forces associated with bedload motion and its highly dynamic spatiotemporal nature make it difficult to monitor bedload transport in the field. In this study, we revise a physically-based model of bedload-induced seismic ground motion proposed by Tsai et al. (2012, htpps://doi.org/10.1029/2011GL050255) and apply it to invert bedload flux from seismic measurements alongside an Alpine stream. First, we constrain the seismic response of a braided river reach with a simple active experiment using a series of large-rock impacts. This allows the characterization of surface wave propagation and attenuation with distance from the impact source. Second, we distinguish bedload-generated ground vibrations from those caused by turbulent flow using frequency-based scaling relationships between seismic power and discharge. Finally, absolute bedload transport rates are quantified from seismic measurements using inverse modeling based on a simplified formulation of bedload particle motion. The results are verified with a large data set of bedload samples, demonstrating that seismic measurements can provide an indirect measure for bedload flux with uncertainties within a factor of 5 ±1 for instantaneous measurements (between 0.01 and 1 kg/m/s). Larger deviations may be caused by uncertainties in the contribution of turbulent flow effects, particle impact velocity, and especially particle size that may vary with sediment supply and flow conditions. When constraining these uncertainties, instream sediment transport measurements are no longer necessarily required and seismic monitoring may provide an accurate and continuous means to investigate bedload dynamics in gravel-bed streams.
Bedload transport is recognized as a key process in the development of river channel forms; however, most rivers suffer from an absence of data. Performing bedload measurements to document bedload transport rates is a challenge, as the deployment of traditional bedload samplers is time consuming and risky in floods. Consequently, bedload measurements are rarely executed. Alternative techniques are being developed to complement the use of traditional bedload measurements and to provide continuous monitoring. Passive acoustic measurements are made with hydrophones, measuring the underwater sounds naturally generated by bedload impacts in rivers. This paper proposes an innovative deployment of hydrophones to record bedload sounds at the scale of a cross section. The measured acoustic signals are interpreted with bedload samplings and with hydraulic and river bed parameters. Field experiments were done in 14 different sites, exploring a diversity of rivers. Bedload flux was observed to be the most consistent variable explaining the monitored acoustic power. Based on 25 experiments on 14 rivers, the cross‐section‐averaged acoustic power was related to the specific bedload flux and showed a good agreement (60% of bedload flux estimated within a factor of 2). The robustness of the obtained calibration curve remains to be tested. However, the potential of passive acoustic profiles to provide a continuous measurement of bedload sounds that could be used in the development of bedload gauging stations is shown.
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