The effect of turbulence and particle size on suspended sediment concentration measurements in the intertidal zone

Reliable measurements of sediment transport are crucial to understand beach morphodynamics. However, acoustic measurements of sediment transport are influenced by turbulence and variations in particle size. The aim of this study is to investigate this influence. Suspended sediment concentrations were measured in the intertidal zone of a macro-tidal, sandy beach with both optical and acoustic sensors. Simultaneously, particle size was measured with a LISST (Laser In-Situ Scattering and Transmissometry). The results indicate that acoustic backscatter is sensitive to both turbulence when flow velocity exceeds 0.35 m/s and variations in particle size for particles larger than 50 μm. As a result, suspended sediment concentrations based on acoustic backscatter highly deviated from the optical results. These estimates greatly improved when corrected for both particle size and to a lesser extent for turbulence. More research remains necessary to evaluate the influence of turbulence and variations in particle size on optical and acoustic measurements.