Abstract
AbstractBedload 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) 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 (between 0.01 and 1 kg/m/s), demonstrating that seismic measurements can provide an indirect measure for bedload flux with an uncertainty of less than one order of magnitude. Larger deviations may be due to the contribution of turbulent flow effects and remaining uncertainties in particle impact mechanics (elasticity and velocity). When constraining these uncertainties, seismic monitoring may provide an accurate and continuous means to investigate bedload dynamics in gravel‐bed streams.
Highlights
Sediment transport in gravel‐bed rivers is characterized by highly dynamic bedload processes that lead to largely fluctuating transport rates (Gomez et al, 1989; Hoey, 1992)
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
To complement punctual bedload measurements, we show that a scaling approach of seismic power with continuous discharge measurements allows the frequency range dominated by bedload to be clearly constrained (Figure 8), which is crucial for the accuracy of subsequent bedload transport inversions
Summary
Sediment transport in gravel‐bed rivers is characterized by highly dynamic bedload processes that lead to largely fluctuating transport rates (Gomez et al, 1989; Hoey, 1992). Quantifying bedload transport rates in both space and time is critical for the understanding of sediment transfer and coupled morphodynamics in river systems (Ashmore, 1991; Ashmore & Church, 1998; Williams et al, 2015), in Alpine environments with high energy and sediment availability (e.g., Lane et al, 1996). In order to acquire the necessary field data and to overcome practical limitations of direct measurements, seismic techniques have been proposed to provide an indirect measure of bedload transport
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