Suspended sediment flux at the Rhone river mouth (France) based on ADCP measurements during flood events.

Abstract : Suspended sediment distribution and fluxes were estimated within the dominant channel at the mouth of the Rhone River for two annual flood events. The estimates were based on ADCP acoustic backscatter intensity and using calibration and post-processing methods to account for the grain-size distribution (GSDs). The fluxes were very similar to those obtained from suspended sediment measurements based on surface sampling at an automated station located 35 km upstream. Suspended Sediment Concentrations (SSC) and GSDs showed little variation along the channel cross section, except for a graduate suspension that appeared at the maximum of discharge, corresponding to velocities lower than 1 m.s-1 near the bottom. However, without post processing to account for the GSD, an under-estimation of 10% was observed during the two floods periods. The two flood events, separated by only two weeks, had clear differences in suspended fluxes and SSC, with twice more flux during the first event.