Flume Experiment on Bedload Measurement with a Plate Microphone

Abstract

Measuring sediment transport is essential for a better maintenance of sediment bypass tunnels. Hydrophone, a metal pipe with a microphone, has been installed in some Japanese rivers, and has measured based on counts of pulse caused by hitting sound of gravels. Geophone, thick steel plate, is also indirect measurement technique mainly used in Switzerland by converting plate movement into voltage. However, the hydrophone often underestimate bedload when the pulses are successive and overlap. Although the geophone is robust for measuring coarse sediment, it cannot detect fine sediment. To improve weak points of these two techniques while leaving their advantages, we developed a method to measure bedload transport by a plate microphone. The plate microphone uses a thick plate instead of a pipe, which is expected to record hitting sounds of fine sediment and also to be robust against hitting by coarse sediment. We examined bedload transport measured by the plate microphone using an artificial flume. The output data is calibrated by number or volume of bedload particles under two conditions (flow velocity and grain size) to understand the effect of these conditions on the bedload estimation.