Field testing a high-frequency acoustic attenuation system for measuring fine suspended sediments and algal movements

Authors: CARPENTER, BRIAN - University Of Mississippi; GOODWILLER, BRADLEY - University Of Mississippi; Wren, Daniel; Taylor, Jason; AUBUCHON, JONATHAN - Us Army Corp Of Engineers (USACE); BROWN, JEB - Us Geological Survey (USGS); POSNER, ARI - Us Bureau Of Reclamation

Submitted to: Applied Acoustics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/8/2022
Publication Date: 8/15/2022
Citation: Carpenter, B., Goodwiller, B., Wren, D.G., Taylor, J.M., Aubuchon, J., Brown, J., Posner, A. 2022. Field testing a high-frequency acoustic attenuation system for measuring fine suspended sediments and algal movements. Applied Acoustics. 198: 2022. 108980. https://doi.org/10.1016/j.apacoust.2022.108980.
DOI: https://doi.org/10.1016/j.apacoust.2022.108980

Interpretive Summary: Measurement of sediment concentrations is necessary for management of streams and rivers. Instrumentation that uses sound for sediment measurements is useful because it is inexpensive relative other measurement technology, it works in cloudy water, and it is typically not affected by algae growing the sensor surfaces. Acoustic instrumentation allows for continuous measurements, since they can work automatically with a computer controlling the instrument, reducing the need for personnel to be on site during potentially hazardous condition or at night. Fine sediments in rivers and streams, which can be seen in the brown-colored water present in many waterways, can be measured by comparing the amount of acoustic signal that travels between sensors in clear water to the signal through water with suspended sediment particles. This manuscript describes field testing of a device created at the National Center of Physical Acoustics, University of Mississippi, University, Mississippi for measuring fine particles in water. During the course of testing, it was found that signal levels from measurements in the Rio Grande River went up and down every day, in a way that did not make sense base on the flow rate in the river. This led to testing in the presence of algae populations in a controlled experiment and the conclusion that algae, moving in response to sunlight, likely caused the periodic changes in signal observed in Rio Grande River. Further field testing in Goodwin Creek, near Batesville, MS, showed that the acoustic device was able to measure sediment concentrations over a range of flow events, and the acoustic data agreed well with sediment concentrations based on physical samples collected at the same time as the acoustic data. The technology described in this manuscript is already being used by ARS to improve monitoring of sediment movement in Goodwin Creek, and, after continued development of the method, it is anticipated that monitoring agencies such as the U.S. Geological Survey will use the device for field measurements.

Technical Abstract: Acoustic measurements of suspended sediment have the potential to allow remote, autonomous monitoring of sediment movements at much higher temporal resolution than traditional manual sampling methods. While suspended sands present a challenging measurement problem due to their logarithmic distribution with depth, fine clay sediments are distributed evenly throughout a stream cross-section, making them amenable to point measurements. In order to improve measurement capabilities for fine sediments in stream channels, The National Center for Physical Acoustics (NCPA) at The University of Mississippi has developed a remote, autonomous acoustic system to monitor fine sediments transported in streams. The system was tested on the Middle Rio Grande near San Acacia, New Mexico, and in Goodwin Creek in Panola County, Mississippi. The acoustic instruments were compared to sediment concentrations from physical samples in both deployments. Diurnal patterns were found in the acoustic signals from the Middle Rio Grande, and a follow up experiment at The University of Mississippi Biological Field Station was used to investigate the potential effects of algal biomass on acoustic attenuation measurements. The results showed diurnal patterns in attenuation were associated with patterns in light, temperature and dissolved oxygen. These results combined with information from the literature suggest diel movement of algal colonies in the water column of slow moving water bodies may interfere with high-frequency acoustic measurements in natural environments and that acoustic methods have the potential to allow ecological researchers to evaluate algal biomass in the field. Results from Goodwin Creek demonstrate that the acoustic system is able to provide measurements of sediment concentration with high temporal resolution that track well with expected sediment transport patterns in response to flow hydrographs in higher gradient riverine environments.