ADCP for suspended sediments and currents investigation at Lower Parana

The contribute presents some methods useful to investigate suspended sediments and velocity field patterns using Acoustic Doppler Current Profilers (ADCP) at big rivers such the lower Paranà. Two Teledyne-RDI ADCPs, working at different frequencies (600 and 1200 kHz), were used simultaneously on the same water column to investigate suspended sediments concentration and grain size pattern at four cross sections of lower Parana River bifurcation nearby San Martín city (Argentina). In the same campaign we also used the Sontek 1000 kHz ADCP formerly calibrated with water samples from Paranà reach and its secondary reach Colastine both nearby Santa Fe city, since it is wide accepted that the bed sediment and water characteristics are the same of San Martin site. The two frequencies method was calibrated on expected mean grain size and concentration. Preliminary results concerning concentration and grain size distribution are consistent with evidences coming from the in situ calibrated Sontek instrument. The ADCP velocities at river cross-section were analyzed in order to extract typical patters of depth averaged velocity and of its deviation from near bed velocity, that deviation was assumed as an index of secondary flow magnitude. Grain size and concentration patters were correlated to analyzed features of cross-section velocity field. Two different behaviors arouse depending on morphology length scales: the most of suspended coarse sand was transported at low depth areas, that correspond to bifurcation bar and reflected the primary flow variability along the cross-section. Whereas we found relative high concentration of relative fine sand at highest filtered depths (i.e. dune trough), that bears out significant correlation between observed dune morphology and suspended sediments.