Author(s): Massimo Guerrero; Slaven Conevski; Sandor Baranya; Nils Ruther
Keywords: Coustic backscatter; Sound attenuation; Suspended sediment concentration; Danube River
Abstract: The complexity of fluvial hydromorphological monitoring and the man ever-increasing data needs make an essential point of involving faster and modern measurement techniques as a common practice among engineers. In particular, suspended sediment real-time measurement remains challenging and prone to physical sampling difficulties encountered in the field. Therefore, the indirect methods thrived, which enable more frequent measurements with a moderate effort. However, these methods usually require a solid background in the field of optics and acoustics and experimental validations eventually proving their accuracy. The focus of this study is aimed towards evaluating the possibility and advantages of combining the acoustic backscattering strength (BS) and attenuation. The recently developed Sequoia’s Acoustic Backscatter Sensor, LISST-ABS provides BS measurement at 8MHz which is particularly sensitive to particles coarse than 30 microns, whereas a low frequency acoustic Doppler current profiler (ADCP) may be used to effectively evaluate sound attenuation that is mainly produced by clay-silt particles. The first venture of measurements was done in a reach of the river Danube, near Budapest where the LISST-ABS was applied with US P-61-A1 point-integrating sampler. Later on, the physical samples collected were analyzed in Laboratory, evaluating LISST-ABS sensitivity to fine sediment BS. While this first test confirmed a decreasing sensitivity of 8MHz probe for clay-silt particles, the proposed integration of a 600 k Hz ADCP will be tested in the future eventually extending the concentration measurement sensitivity towards very fine sediment.