The application of bed load measurements to hydraulic model experiments using the hydrophones

Abstract

The estimation of grain size distribution has arisen as the subject of bed load measurements using hydrophones. Al-though field bed load measurements using hydrophones in some rivers have already begun, its application to hydraulic model experiments is still in its infancy. In this study, we investigated the estimation of the grain size distribution of mixed sand through a systematic experiment executed in a linear rectangular channel. We further show an exemplary hydraulic model experiment using a hydraulic model equipped with a hydrophone at both the cross-section of the downstream end of the model and the cross-section of the planned slit sabo dam installed in the middle of the model segment. The relationship between the non-dimensional grain size distribution and the sensitivity of the channel in this hydraulic measurement system for recording pulse numbers indicated good agreement, provided that the sensitivity of the channel for recording the number of pulses is ideal for the objective mixed sand. The applicable range of the channel sensitivity is, however, narrow, thereby lacking in general application. Therefore, in order to estimate the grain size distribution of mixed sand, it is necessary to adjust the channel sensitivity. From the hydraulic model experiment using hydrophones for measuring bed load, the reason that the peak of bed load sediment occurs at the downstream end of the hydraulic model could be explained by the changes of the number of pulses at the slit sabo dam. The result of our hydraulic model experiment suggests that a rational explanation of the phenomena of bed material transport is made possible by applying hydrophones to the hydraulic model experiments.