Significance of Aggregation of Fine Sediment Particles in Their Deposition

The significance of aggregation processes, by which the properties of suspended fine sediment particles or flocs change during transport, is examined for the simple case of deposition of estuarine sediments in a flume. A multi-class model for aggregation processes is combined with a one-dimensional, unsteady, multi-class sediment transport model to calculate the deposition rate for two flume experiments—one with no recirculation of a medium-cohesion sediment, and the other in which a high-cohesion sediment was recirculated by pumping. The results show that while aggregation processes had a moderate effect on the rate of deposition of medium-cohesion sediment, they dominated high-cohesion sediment deposition. The results also suggest that multi-class fine sediment aggregation-plus-deposition calculations will produce more realistic results than single-class calculations in estuaries where sediment exhibits a high degree of cohesion and variability in flow-induced shearing.