Applying ADCPs for long term monitoring of SSC in rivers

Abstract

The flow rate and the suspended sediment concentration (SSC) of two different rivers draining into the Adriatic Sea basin, the Secchia in Italy and the Devoll in Albania, were analysed by processing the data collected in a 245-days period at monitoring stations equipped with side-looking acoustic Doppler current pro lers (H-ADCPs). SSC was determined as a by-product of the echo profi les along the horizontal aligned acoustic beams emitted by H-ADCPs. For the first time, the effect of organic matter other than a change of inorganic particles size distribution was evaluated as a possible reason for backscatter and attenuation variations during hydrological events. This reduced average deviations between acoustically inferred and sampled concentrations from one order of magnitude to 20% of actual values. The improvement required the measuring of attenuation to backscatter ratio (ABR) in addition to sound attenuation. The validation interval covered three order of magnitudes from 10-1 gl-1 to 10 gl-1 . In this paper the potential of the ABR-method using H-ADCP to continuously monitor suspended sediment fluxes is tested in two different rivers, enabling single peak flood analysis and reliable assessment of sediment budget across a river cross-section. The advantages and disadvantages of this method are presented and discussed.