Chapter 20 A study of in situ floc size in turbidity maximum, Yangtze estuary, China

In this study, changes in the spectrum of floc diameter of suspended fine sediment were measured in the turbidity maximum of the Yangtze estuary using the in situ instrument LISST-100 without disturbing the natural flocs. At the same time, both salinity and current velocity were measured with OBS-3A and ADP, respectively. The results indicate that there is obvious flocculation occurring in the turbidity maximum of the Yangtze estuary. The formation and break-up of flocs are evident. Large current velocity breaks large flocs into small flocs, while salinity causes small flocs to form larger ones. The variation in current and salinity results in quarter-diurnal and semidiurnal variations in floc diameter, respectively. The critical diameter for the flocculation of fine cohesive sediment is about 32.5 μm in the turbidity maximum of the Yangtze estuary.