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ARS Home » Southeast Area » Oxford, Mississippi » National Sedimentation Laboratory » Watershed Physical Processes Research » Research » Publications at this Location » Publication #358714

Research Project: Managing Water and Sediment Movement in Agricultural Watersheds

Location: Watershed Physical Processes Research

Title: Acoustic wave propagation in rivers: an experimental study

item GEAY, THOMAS - Universite Grenoble Alpes
item LUDOVIC, MICHEL - Universite Grenoble Alpes
item ZANKER, SEBASTIEN - Electricite De France (EDF)
item Rigby Jr, James

Submitted to: Earth Surface Dynamics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/2019
Publication Date: 6/12/2019
Citation: Geay, T., Ludovic, M., Zanker, S., Rigby Jr, J.R. 2019. Acoustic wave propagation in rivers: an experimental study. Earth Surface Dynamics. 7(2):537-548.

Interpretive Summary: Gravel transport along the beds of rivers and streams is a major component of the sediment load in rivers and one difficult to measure. Direct measurements typically involve capturing samples of bed load for a specified time at a point on the river bed. Such methods are difficult, expensive, and produce highly variable results with uncertain implications for the overall transport of the river. Acoustic methods are being developed as an indirect method of measuring gravel movement by recording the sound of colliding gravel particles and estimating the quantity of moving gravel from the sound generated. Such methods have the advantages of being relatively inexpensive and also accounting for a large area of the river bed. In order to relate the recorded sound to a quantity of gravel, the dynamics of sound propagation in rivers must be accounted for. This work characterizes sound propagation in a number of natural rivers for the purposes of developing acoustic measurements of bed load.

Technical Abstract: This research has been conducted to develop the use of Passive Acoustic Monitoring (PAM) in rivers, a surrogate method for bedload monitoring. PAM consists in measuring the underwater noise naturally generated by bedload particles when impacting the river bed. Monitored bedload acoustic signals depends on bedload characteristics (e.g. grain size distribution, fluxes) but are also affected by the environment in which these acoustic waves are propagated. This study focuses on the determination of propagation effects in rivers. An experimental approach has been conducted in several streams to estimate acoustic propagation laws in field conditions. It is found that acoustic waves are differently propagated according to their frequency. As reported in other studies, acoustic waves are affected by the existence of a cutoff frequency in the kHz region. This cutoff frequency is inversely proportional to the water depth: larger water depth enables a better propagation of the acoustic waves at low frequency. Above the cutoff frequency, attenuation coefficients are found to increase linearly with frequency. The power of bedload sounds is more attenuated at higher frequencies than at low frequencies which means that, above the cutoff frequency, sounds of big particles are better propagated than sounds of small particles. Finally, it is observed that attenuation coefficients are variable within 2 orders of magnitude from one river to another. Attenuation coefficients are compared to several characteristics of the river (e.g. bed slope, bed rugosity). It is found that acoustic waves are better propagated in rivers characterised by smaller bed slopes. Bed rugosity and the presence of air bubbles in the water column are suspected to constrain the attenuation of acoustic wave in rivers.