Towards an evaluation of bedload transport characteristics by using Doppler and backscatter outputs from ADCPs

Both the apparent bedload velocity and the backscattering strength measured by acoustic Doppler current profilers could assist bedload assessment in the field. To test this hypothesis, two ADCPs working at three frequencies (3 MHz and 1 MHz, M9; 2 MHz, StreamPro) were deployed simultaneously to measure seven different bedload transport conditions in a laboratory flume. The bedload transport was monitored by two high-speed cameras and a bedload trap. For some experiments 3 MHz and 1 MHz delivered spatially averaged apparent velocity, for others the velocity corresponded to the average velocity of particles. The 2 MHz severely underestimated the average particle velocity. The M9 backscattering strength decreased as the bedload concentration increased, independently of the size and velocity of transported particles. The 2 MHz resulted in almost constant backscattering strength. These findings demonstrate that further examination of the acoustic configurations and parameters could lead to a methodology for bedload quantification based solely on the acoustic outputs.