Aggregation Rate of Fine Sediment

Abstract

A dynamical description of estuarial fine sediment aggregation has been developed. The spectrum of fine particle or agglomerate size is represented by a discrete number of classes based on particle mass. Aggregation and disaggregation, respectively, move mass up and down through the classes. The frequency of two- and three-body particle collisions due to Brownian motion, shearing and differential settling is expressed by simple statistical relationships, using a new form of the collision efficiency parameter. This parameter is defined by nondimensional terms accounting for the physical and chemical forces that determine whether close encounters result in collisions. Calculations of the rate of change of sediment mass for each class as the aggregation process approaches equilibrium, when compared with previously obtained data in a Couette chamber, highlight the need to characterize the sediment as to particle density and strength. Near equilibrium, three-body collisions seem to play a major role by disaggregating particles that have been aggregated by the more numerous but less forceful two-body collisions.