Aspects of the relationship between flocs in suspension and those held in a cohesive sediment bed were investigated experimentally using an erosion rig with kaolinite as the sample material under different medium conditions. The critical shear-stress, tau(c), required to initiate the erosion were measured, and the floc sizes of the eroded products (d(E)) were analysed in situ using macro-photography. Factors such as age, density, pH and ionic strength were investigated. Separate experiments were performed to measure the floc size in the settling zone (d(A)). The results show that the floc sizes from the above two different measurements show the same variance with respect to physico-chemical (pH and ionic strength) changes in the environment. This work has been very successful in showing the relationship between the flocs in suspension and those eroded from a bed of sediment, so one property can be predicted from knowledge of another. (C) 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.