Manning, A.J.; Martens, C.; De Mulder, T.; Vanlede, J.; Winterwerp, J. C.; Ganderton, P. and Graham G. W., 2007. Mud Floc Observations in the Turbidity Maximum Zone of the Scheldt Estuary During Neap Tides. Journal of Coastal Research, SI 50 (Proceedings of the 9th International Coastal Symposium), 832 – 836. Gold Coast, Australia, ISSN 0749.0208

Significant changes of sediment concentration and shear stress can occur within an estuarine turbidity maximum. Prediction of mud transport depends on a good specification of the settling velocity and the mass settling flux. This can only be achieved by using field measurements of floc settling dynamics that can be implemented in sediment transport models. This paper describes flocculation observations conducted during a neap tide in the Lower Scheldt Estuary. The data forms part of the Deurganckdok tidal dock field survey commissioned by the Flemish government. The findings showed that within the turbidity maximum zone the suspended sediment concentration reached 277 mg l^-1 and the floc mass distribution was bi-modal, with 46% of the population comprising macroflocs up to 507 µm in diameter. These macroflocs had individual settling velocities ranging from 1 to 11 mm s^-1. In the turbidity maximum the macroflocs represented 88% of the floc mass, had a Ws_macro = 3.9 mm s^-1 and contributed to 97% to the total settling flux. In contrast, at peak turbulence, the floc mass distribution was now weighted 58%:42% in favor of the smaller microflocs.