Elwha Impact Plate System - accelerometers
How can accelerometers be utilized as bed load impact sensors to measure bed load transport?
Can we improve the current impact plate system using accelerometers already installed? (See
The Elwha bed load impact plate system was installed in 2008 and 2009, consisting of 72
instrumented steel plates spanning the river at a concrete diversion. 46 of these plates are
instrumented with a geophone and the remaining 26 plates are instrumented with an
accelerometer. As a particle contacts an impact plate, it causes the plate to deflect and vibrate.
This movement is registered by the instrumentation and a voltage is sent to the host computer
In FY 2014 a prototype two-plate impact system was fabricated by the BOR - TSC shop (Dane
Cheek). This two plate system is full scale (matching the Elwha impact plate dimensions),
instrumented with an accelerometer attached to each plate and was tested for a week in early
April 2015 in a sediment and water recirculating flume at the National Sediment Lab in Oxford,
MS. This flume testing was carried out in cooperation with the Agricultural Research Service (Dr.
Roger Kuhnle) and the Univ. of Mississippi (Brian Carpenter and Bradley Goodwiller). The
purpose of this testing was to determine an appropriate measurement algorithm for the
accelerometers using a correlation between measured bed load and acoustic signals from the
During the 2015 lab experiments, were able to measure physical bed load transport for particles
larger than 4 mm, in terms of mass/time for each size class of sediment (0.5 phi sieve breaks).
This information will allow us to obtain a correlation between measured bed load and the
acoustic signals provided by the accelerometers, which will be used to provide an algorithm for
use in the Elwha impact plate system. Additionally, we will work toward a method for
determining the size of sediment crossing the impact plates instrumented with acceleromet
Need and Benefit
The ability to obtain continuous bed load measurements is a tremendous benefit to increase our
understanding of bed load transport in coarse bedded streams. Current methods can only
provide a very limited ability to obtain bed load measurement - limited spatially and temporally.
The limited ability to measure bed load is the primary reason for our lack of understanding
regarding the transport of bed material in fluvial systems. Coarse material in gravel bed rivers is
responsible for the river's morphology and a large part of its ecology. With continuous bed load
measurement more knowledge can be gained about sediment transport and deposition.
Because the Elwha impact plate system is downstream of two recently removed large dams,
much is to be learned about the transport of coarse delta sediment from a reservoir following
dam removal. A recently published paper in Geomorphology details the fluvial sediment loads
during the first two years following dam removal. This paper uses bed load data from the Elwha
impact plate system as well as acoustic suspended sediment data collected at the same location
by the USGS. This is important knowledge needed to inform future dam removals. Later this
calendar year we plan to present and then publish (maybe 2016) the first four years of fluvial
sediment loads following dam removal.
A complete and thorough calibration of the Elwha impact plate system is critical so that the bed
load measurements from this system are reliable. The proposed work will advance our ability to
confidently measure bed load on the Elwha river, and possibly determine particle size in
transport using the accelerometers. Additionally, the accelerometer plates are expected to
provide information on the transport of finer particles (perhaps 5.6 mm) than the geophone
plates (> 16 mm). This goes a long way toward filling a rather large data gap in the surrogate
sediment transport measurements on the Elwha River.
The technology developed for the Elwha impact plate system will be applicable to future efforts
to measure bed load in a similar fashion. Already there is a proposed Reclamation project on the
Rio Grande where ephemeral tributary sediment will be measured and impact plates are
expected to be a part of that system. The use of impact plate systems in North America is likely
to increase due to the need for better bed load data on rivers of concern and this knowledge
gained can be utilized in future efforts, regardless of the agency installing and operating a
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.
Field & laboratory calibration of impact plates to measure coarse bedload (final, PDF,
By Robert Hilldale
Publication completed on September 30, 2016