2013 Volume 19 Pages 147-152
We installed a pipe hydrophone and monitored bedload for two years at an upstream site of the Nunome Dam in Nara Prefecture. The data of acoustic energy and counts of different pulse amplitudes collected by the hydrophone were converted to volume of transported sediment (m3/s) based on equations obtained by sediment injection experiments at the site. Relationships between sediment size and acoustic energy or pulse counts suggested that bedload materials of >2mm were more likely measured by the hydrophone than finer materials.
Our estimation of annual sediment transport to the dam (7400-11000m3/year) was comparable to mean annual volume of sediment deposition in the dam (6400m3/year). Although 36-39 high-flow events occurred per year, more than 40% of the annual sediment transport was derived from a few large floods. Counts of different pulse amplitudes (16-, 4-, 2-fold) corresponded to bedload transport of different-sized materials (fine gravels, coarse gravels, pebbles, respectively).
