Signal Processing From Bedload Impact PLates Instrumented With an Accelerometer

Project ID: 4542
Principal Investigator: Robert Hilldale
Research Topic: Sediment Management and River Restoration
Funded Fiscal Years: 2015
Keywords: bedload impact plates, surrogate sediment mesurement, bedload

Research Question

A series of impact plates has been installed on the Elwha River to measure coarse bedload transport during and after the removal of Elwha and Glines Canyon Dams. The system consists of 72 steel impact plates that span the channel width, 46 of which are instrumented with a geophone and 26 are instrumented with an accelerometer. To date, physical bedload data have been collected for calibration of those plates instrumented with geophones (project #115)
The proposed research intends to determine the appropriate signal processing from the accelerometers so bedload can be measured on the Elwha using those plates instrumented with accelerometers, in addition to the geophone measurement.
Accelerometers possess a response across a broad frequency range, providing a very different signal response when compared to the geophone. Using impact plates instrumented with accelerometers to measure bedload may provide a more robust measurement through improved signal thresholding and measurement of the energy imparted to the bed by moving particles. There is also potential to obtain some information regarding particle size using accelerometers.
Answers to the following questions will be investigated: What frequency range is appropriate for processing particle impacts to measure bedload? Using a fast Fourier transform to process the accelerometer signal, what sample time and frequency is appropriate? What are the necessary post-processing algorithms to be incorporated into the existing LabView code? What is the minimum size detection for impact plates instrumented with an accelerometer? What is the appropriate field calibration for impact plates instrumented with an acelerometer?

Need and Benefit

There are two benefactors for this research, one is more immediate and narrow in scope, the other serves the broader interest of advancing the technology of bed load measurements. The immediate benefactor is the Elwha River Restoration Project, who will be monitoring sediment during and after dam removal. In a broader context, the sediment transport community will benefit from the advancement of a surrogate technology to continuously measure bed load. An advancement such as this would be a significant step forward in understanding the transport of bed material in a gravel bed river. We'll also gain a good understanding of the fate of the coarse reservoir deposits during and after dam removal, which will be the largest controlled release of sediment through dam removal in North America.
Accurate measurement of bed load is very difficult due to logistical issues related to the movement and capture of the coarsest fractions of coarse sediment constituting the bed material of a river. Generally, the coarsest fraction of a river's bed material is only mobilized during flood events, making it very difficult and potentially dangerous to place a sediment sampler on the bed of a river to collect a timed sample. Moreover, this methodology only results in a discrete sample occurring over approximately one or two minutes at each location across the river, providing an incomplete picture of the nature of bed load movement (< 1% of the total bed load is typically measured). This incomplete understanding of bed load has confounded researchers and has hindered the complete understanding and modeling of sediment transport.

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.

Registering Bed Load Impacts on the Riverbed for Surrogate Bed Load Measurement (final, PDF, 427KB)
By Robert C. Hilldale
Publication completed on September 30, 2015

This bulletin summarizes the research results and potential application to Reclamation's mission.

Signal Processing From Bedload Impact PLates Instrumented With an Accelerometer (final, PDF, 1.4MB)
By Robert Hilldale
Publication completed on September 30, 2015

Signal processing techniques than can yield estimates of total mass transported are being developed in collaboration with the USDA-ARS-NSL. It has been shown that the sum of peak voltages is well correlated with the total mass of particles passing over the plates. Future work will focus on refining the data processing techniques and incorporating estimates of particle size distribution based on peak height distribution.

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Last Updated: 6/22/20