Seismic Monitoring of Bedload Transport in Large Gravel-bed Rivers
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.
Contact the Principal Investigator for information about partners.
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