Measuring bed load with hydrophones
Using the knowledge gained from previous hydrophone deployment and concurrent bed load
measurement on Halfmoon Cr. (CO) and Walnut Gulch (AZ), how can we progress the
measurement system into larger rivers? Due to the widely varying acoustic environments in
rivers of different depth and width, transferring specific relationships from small rivers (e.g.
Halfmoon Cr.) to larger river (e.g. Trinity R., Elwha R.) is not necessarily direct. We need to
investigate correlations of measured bed load to acoustic energy on a larger river to answer such
things as: How many hydrophones are necessary to provide a complete measurement without
overlapping? How does the relationship between measured bed load and acoustic energy change
with river size? What is the appropriate depth to deploy the hydrophone? How significant is flow
noise and can we do something to minimize its effect? What frequency ranges are available for
evaluation in larger rivers that are not well propagated in smaller rivers due to shallow depths?
Hydrophones measure bed load by recording the self generated noise (SGN) when moving gravel
collides with other particles that are on the bed or in motion. Prior research has shown that
there is a range of frequencies generated from moving gravel. Much of this research has been
conducted in the lab or in coastal environments, both offering different acoustic environments
than a river. The research currently being conducted by the team included in this proposal is
the most comprehensive effort known to determine acoustic parameters and metrics for
quantification of bed load with hydrophones.
Need and Benefit
The primary benefits of a hydrophone system to measure bed load are; reduced cost, the
opportunity to collect continuous bed load data, and portability. Classic means of bed load
measurement are costly, possess inherent risks, and can only be collected at discrete locations
and times, providing an incomplete understanding of bed load transport. Using hydrophones to
measure bed load will provide concrete data that can only be loosely predicted at this time. In
addition, bed load data from hydrophones is an affordable means to collect the necessary
information to vastly improve numerical models of sediment transport, allowing for more
accurate long term predictions. Reliable and continuous bed load data is needed to make more
informed decisions regarding our efforts in fluvial environments, including improvement in and
around infrastructure and improvements for aquatic habitat.
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.
Development of a portable passive-acoustic bedload monitoring system (final, PDF, 603KB)
By Robert Hilldale
Publication completed on September 30, 2016