The Acoustic Properties of Suspended Sediment in Large Rivers: Consequences on ADCP Methods Applicability

GUERRERO, MASSIMO; RUTHER, NEIL; SZUPIANY, RICARDO N.; STEFAN HAUN; SANDOR BARANYA; LATOSINSKI, FRANCISCO

Water

MDPI

Año: 2016 vol. 8 p. 1 - 22

The use of echo-levels fromAcoustic Doppler Current Profiler (ADCP) recordings has become more and morecommon for estimating suspended bed-material and wash loads in rivers over thelast decade. Empirical, semi-empirical and physical-based acoustic methods havebeen applied in different case studies, which provided relationships betweenscattering particles features derived from samples (i.e., concentration andgrain size) and corresponding backscattering strength and sound attenuation.These methods entail different assumptions regarding sediment heterogeneity inthe ensonified volume (e.g., particle size distribution (PSD) and spatialconcentration gradient). Our work was to compare acoustic backscatter andattenuation properties of suspended sediments, sampled in the rivers Parana andDanube that represented rather different hydro-sedimentological conditionsduring the surveys. The Parana represents a large sandy river, characterizedthrough a huge watershed and the typical bimodal PSD of sediment in suspension,while the Danube represents in the investigated reach an exposed sand-gravelbed and clay-silt particles transported in the water column in suspension. Sandand clay-silt concentrations clearly dominate the analyzed backscattering strengthin the rivers Parana and Danube, respectively, with an effect of PSD level ofsorting in the latter case. This comparison clarifies the extent of assumptionsmade, eventually advising on the actual possibility of applying certain ADCPmethods, depending on the expected concentration gradients and PSD of suspendedsediment to be investigated.