Estimating suspended sediment concentrations using a broadband ADCP in Mahshahr tidal channel

Abstract

Abstract. Data sets of Acoustic Doppler Current Profiler (ADCP) backscatter intensities (ABS) were used to evaluate suspended sediment concentrations (SSC) in the Mahshahr Channel (MC) of the Persian Gulf. Since the echo intensity is closely related to turbidity in water, the ADCP may be a promising tool to monitor the sediment transport. The low susceptibility of the acoustic backscatter to bio-fouling and the ADCP provision of current profiles as well as sediment time series makes this monitoring method more advantageous compared with the traditional methods. Time series of ADCP backscatter intensity profiles were used for improving temporal resolution of SSC estimates. Backscatter and traditional observational data were separated into two segments. The first part was utilized for calibrating the backscatter data and attributing the intensity to suspended particle concentrations and using the second part acoustic intensities were validated. Acoustic based SSC estimates are slightly underestimated in comparison with traditional water sample based SSC values, but still there is good agreement between acoustic SSC and traditional observations. Results illustrate a rather high correlation between lab based and acoustic based particles in suspension (R2 = 88 %). Additionally measurements reveal the domination of a semidiurnal ebb asymmetric system in the MC. Tidal currents provide the main energy source for particle resuspension and transport. Maximum suspended load concentrations are evident in ebb tides, while the currents strengths are enough to refloat loads from the bed. In general spring tides show higher SSC values compared with neap tides in the study area.