Passive Acoustic Monitoring of Bed Load with Drifted Hydrophone

Recent studies have shown that bed load can be monitored with passive acoustic techniques, which consist of measuring the noise generated by the particles impacting the riverbed and converting this measured noise into a sediment flux. The technique still faces the difficulty that each environment has its own acoustic properties and that calibration is needed when operating from a river bank. However, recent work with an extensive field campaign in a large variety of rivers has shown that when measuring as close as possible to the noise sources by attaching a hydrophone to a floating board, the relation between acoustic power and local bed load flux can be described by a unique intersite power function. In this paper, we present the measurement protocol and validation based on a new field campaign comprising 17 measurements on eight rivers. The validation results show that the acoustic method successfully predicts bed load flux within a factor of 3 for more than 70% of the measurements.