Seismic Monitoring of Bedload Transport in Large Gravel-bed Rivers

Project ID: 5561
Principal Investigator: David Gaeuman
Research Topic: Sediment Management and River Restoration
Funded Fiscal Years: 2015
Keywords: bedload transport, sediment transport, monitoring

Research Question

The goal of this project is to advance seismic monitoring of bedload transport to a practical level. It builds on results from a prior study that collected riverside seismic and infrasound data during a dam-controlled flood in the Grand Canyon [Schmandt et al. 2013]. That study demonstrated that seismometers outside the channel can discriminate and quantitatively track the intensity of wave energy generated by bed-load transport and fluid transport processes.

Although seismic measurements have great promise as a useful method for monitoring of bedload transport, a thorough calibration study in a setting where established methods are currently being employed is needed, as are better constraints on the spatial averaging function that is implicit in measurements of seismic power at a riverside station. The proposed research addresses the need for calibration data by leveraging an existing bedload sampling program in the Trinity River of Northern California. The Trinity River Restoration Program (TRRP) has been operating four sediment sampling stations on the Trinity River since 2004. Bedload and suspended load transport rates are measured over the course of annual high-flow releases from Lewiston Dam to compute annual sediment loads and long-term sediment budgets. Sediment sampling is performed by a contractor (Graham Matthews and Associates) that has established itself as a leading expert in managing the logistical challenges associated with sediment sampling in large, swift rivers. In addition to sediment monitoring, TRRP also collect annual bathymetric data using multi-transducer or multibeam sonar. TRRP can therefore provide pre- and post-release bathymetry that can be used to explore the relationship between the reach-scale spatial variability in the fluvial seismic signals and local geomorphic change. These existing TRRP data collection programs offer a tremendous logistical advantage and cost savings for research into this sediment surrogate technology.

Need and Benefit

Traditional physical sampling of bedload in large rivers is both difficult and dangerous. As a result, various portable surrogate technologies for measuring bedload transport rates have been investigated over the years, including active acoustic measurements [Rennie et al. 2002; Gaeuman and Pittman 2010] and passive acoustics [e.g., Hilldale S&T project].

As with these other surrogate technologies, seismic measurements offer the potential to provide long-term continuous monitoring of bedload transport at a minimal cost, while also avoiding the logistical challenges and risks associated with the collection of physical bedload samples during high discharge events. The capacity for continuous monitoring makes it possible to acquire data during transient or unexpected events that conventional sampling would be unlikely to capture.

However, seismic methods offer several advantages over other portable surrogate technologies. Inexpensive seismic sensors can be deployed outside the channel in reach-scale arrays that make it possible to localize the sources of the seismic energy received, thereby distiguishing between target signals and background noise. This capacity also allows for spatially-explicit data acquisition, such that spatial variability in bedload transport rates can be resolved at the reach scale, thereby opening a new avenue for exploring bedload dynamics. And recent work [Schmandt et al. 2013] indicates that seismic monitoring is sensitive to bedload transport even in near-critical shear stress conditions.

Once fully developed, seismic monitoring of bedload transport in rivers could have a broad range of applications relevant to the Bureau of Reclamation. As is the case for the Trinity River, estimates of bedload fluxes are needed to inform management decisions such as designing release hydrographs and guiding gravel augmentation in dam-controlled rivers. Seismic detection of bedload entrainment could prove useful for defining flow thresholds for flushing flow releases or evaluating risks to infrastructure. Empirical bedload transport data is also needed to calibrate and/or validate computational bedload equations used in numberical models to predict future channel evolution.

Contributing Partners

Contact the Principal Investigator for information about partners.

Research Products

Bureau of Reclamation Review

The following documents were reviewed by experts in fields relating to this project's study and findings. The results were determined to be achieved using valid means.

Seismic Monitoring of Bedload Transport in Large Gravel-bed Rivers (final, PDF, 1.9MB)
By David Gaeuman
Publication completed on September 30, 2016

Several recent studies have shown that seismic energy generated by bedload transport in rivers can be detected by seismometers deployed outside the channel. This report presents the results of a comparison between seismic observations, changes in streambed topography, and measured bedload transport rates obtained during a damcontrolled flood in the Trinity River of Northern California. Seismic data were collected using an array of 77 seismometers spanning both sides of a reach of river nearly half a mile long. Seismic amplitudes reached maxima shortly after gravel augmentations at the upstream end of the study reach, followed by amplitude decay lasting 7 to 10 hours. The frequencies of the bedload-generated signals were found to be in the range of 20 to 100 Hz. Seismic amplitudes were greatest in the section of channel immediately downstream from the gravel augmentation location, where migrating bedforms were detected and net gravel deposition was greatest. These results demonstrate the potential for out-of-stream seismic monitoring to detect spatial and temporal variations in coarse sediment transport at the sub-reach scale. Potential applications include sediment transport monitoring in remote watersheds and exploration of how coarse sediment slugs produced by hillslope failures or other abrupt changes in sediment supply are propagated downstream.

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Last Updated: 4/4/17