Experimental and theoretical tools for estimating bedload transport using a Japanese pipe hydrophone

Abstract

A Japanese pipe hydrophone is an acoustic sensor that is widely used in Japan to measure bedload transport. Here we report experimental and theoretical tools for calculating bedload transport using a Japanese pipe hydrophone, and discuss the limitations based on laboratory tests. We found a linear relationship between the momentum of colliding particles and the maximum amplitude of the acoustic wave, and found that the grain size can be calculated using this linear relationship. We determined the range over which this linear relationship holds, and found that it depended on the amplifier gain; we then used it to calculate the maximum flow depth. The median frequency and the form of the frequency distribution of the acoustic wave depended on the grain size, slightly on the flow discharge. The bedload transport rate can be calaculated using the velocity of the bedload and the sediment volume in the bedload layer using the linear relationship between the momentum of the colliding particles and the maximum amplitude of the acoustic wave.