Signature of bedload particle transport mode in the acoustic signal of a geophone

ABSTRACT

The purpose of this study is to develop a relationship for predicting the bedload rate from the acoustic signal of a geophone, under the rolling and saltating bedload transport modes. Controlled experiments corresponding to near-incipient, marginal, and general bedload motion were conducted. The geophone recorded impacts and resulting acoustic signal impulses at the lower “Frequency 1” (100–200 kHz) and the higher “Frequency 4” (380–480 kHz) ranges. Rolling particles produced stronger responses in Frequency 1 and weaker in Frequency 4 due to rotational vibrations. Instead, saltating particles generated stronger responses in Frequency 4 and weaker in Frequency 1 because of spheroid vibrations. The impulse in both Frequency 1 and 4 was related to bedload transport, as it accounts for the number and magnitude of the signal spikes due to the particle impacts. This study complements efforts for quantifying bedload transport using geophones by relating bedload to impulse for rolling and saltation.

Keywords:

• Acoustic
• bedload particle
• geophone
• mode of transport
• rolling
• saltation

Acknowledgements

The authors wish to acknowledge the support by D. Caldwell and Dr C. Pecorari with ClampOn Inc., who kindly provided us with the custom version of the ClampOn software for the geophone sensor, the acoustic frequency ranges and very helpful discussions. Thanks are also due to Kenneth Wacha for helping conduct the experiments, and to the staff of the machine shop of IIHR-Hydroscience and Engineering for their technical assistance. The authors would like to acknowledge the numerous discussions with researcher Robert Hilldale from USBR, Sedimentation and River Hydraulics, Technical Service Center that helped improving this work. Also, the second author would like to thank several members of the BRIC community such as Professor Jonathan Laronne Ben-Gurion University and Dr John Gray USGS who have helped stimulate interesting discussions. Finally, the feedback provided by three anonymous reviewers is gratefully acknowledged. Partial support for completing this project was provided by the U.S. NSF CBET 1033732.