In-situ observation of aggregate dynamics in a tidal channel using acoustics, laser diffraction and optics

To describe the dynamics of aggregates in a tidal channel, in situ measurements of current velocity, turbulence, backscatter intensity, particle size distribution and suspended matter concentration have been carried out throughout half a tidal cycle. The dynamics of suspended particle matter are shown: distinct turbidity clouds due to temporal increases in total concentration are detected by all sensors but acoustic methods seem to underestimate the amount of SPM when large aggregates are present. This study compares two different approaches for the in-situ analysis of particle size distributions: a laser diffraction method (Sequoia LISST 100) and image analysis of in-situ photography. Both instruments are limited due to their resolution and technical properties. Applied in combination, the two methods reveal the broad range of particle sizes ranging from a few microns to millimetre size.