How do floc characteristics change once they have deposited to a bed, and how, if at all, are they modified during re-entrainment?

In many environments, recently deposited flocs (< 1 day) can be re-entrained by increases in stress at the bed, e.g., during the ebb or flood. Being able to properly characterize this re-entrainment process is important for adequately modeling mud transport. This research examines whether or not floc characteristics modified during the re-suspension process. Two hypotheses were tested are that: (1) flocs grow in size once deposited on a bed; and (2) that re-entrainment efficiency plays a crucial role in dictating re-suspension concentration which in turn influences the flow growth rate and equilibrium floc sizes after resuspension. These hypotheses are explored through a series of laboratory experiments in which the natural tide cycle in an estuarine zone was mimicked by applying shear rate cycles of high shear (G = 40s-1) and low shear (G = 0 and 10s-1) to a suspension in a mixing chamber. Floc size evolution was obtained from images of flocs in the water column and on the bed. The experiments examine three different consolidation time scenarios - the low shear period (6 hours, 6 days, and 12 days). The experiments used mixture of clay (80% Kaolinite and 20% Montmorillonite) with concentrations of 25, 100 and 400 mg/L, along with two bed conditions, i.e., smooth and rough bed. The results show three primary conclusions: (1) during the low shear period the bed-flocs grow and have larger sizes compare to that of the re-suspended flocs. Yet, during high shear period, re-entrained flocs reached to its equilibrium size in the order of 1-20 minutes; (2) bed-floc size is a function of the consolidation time. For 12 day experiments, the bed-floc size was approximate 8-16 times larger than the freshly deposited floc. In 6 hour and 6 day experiments, there was unnoticeable difference between freshly deposited flocs and re-suspended flocs; and (3) the data showed that all the deposited floc re-suspended, albeit at different rates depending on concentration.