Bedload Monitoring by means of Hydro - Acoustic Techniques

This study provides an evaluation of a hydro-acoustic technique for efficient quantification of the bedload transport in riverine environments. Stationary bedload measurements/experiments were conducted simultaneously at different field study sites and laboratories, using different acoustic Doppler current profilers (ADCP) working at four different frequencies. A post-processing procedure for the ADCP outputs was developed and the data was compared with other bedload transport measuring techniques (e.g., imagery data, physical samples). The 3 MHz delivered spatially averaged apparent velocity, as well as the 1 MHz for the sand experiments only. The apparent velocity for the 1MHz gravel corresponded to the true mean particle velocities. The 2 MHz severely underestimated the true particle velocities. The backscattering strength measured by the M9 decreased as the bedload concentration increased, independently of the particle's velocities and size; the backscattering strength registered by the StreamPro resulted in almost constant values. Each ADCP yielded different results because of the different frequency backscatter sensitivity and acoustic penetration in the active bedload layer. In addition to the frequency, other acoustic parameters such as the percentage of the filtered data, transducers width, beam opening angle, beam-grazing angle and the pulse length, contributed to the acoustic bedload sampling. The results permitted quantification of the bedload transport characteristic and development of a new updated methodology for continuous non-intrusive bedload transport measurements. An extensive examination of the internal processing algorithms is necessary to clarify the best processing configuration, in addition to collecting more data and performing a detailed uncertainty analysis.