The ADCP's bottom track capability for bedload prediction: Evidence on method reliability from sandy river applications

River processes understanding requires the investigation of sediment transported by the streamflow. To this aim, the use of physical samplers is particularly challenging in large sandy rivers, which pushed the thriving of surrogate methods. The acoustic Doppler current profiler (ADCP) has been recently used to quantify the suspended-load as well as the bed-load. The latter is related to the apparent velocity of particles at the bedload layer as resulting by comparing the ADCP's velocity from its capability to acoustically track the bottom and from accurate GPS recordings. The reliability of this technique depends on instrument frequency, acoustic pulse length used and site-specific properties, such as riverbed composition and bedforms presence that eventually require further research. This work presents ADCP-DGPS measurements in the large sandy Parana River in Argentina, performed with ADCPs operating at 600 and 1200 kHz frequencies and using different acoustic pulse lengths to eventually assess the bedload rate. Combining theoretical parameters and apparent velocity of bed-particles from ADCP, assessed values agree on bedload rate values obtained with the dune tracking method with a discrepancy of 29% on average. The measurements obtained with 1200 kHz and longer pulse lengths deliver better agreements, although variation with longest pulse length was 15% off at most.