The processes of aggregation and disaggregation in fresh water and estuaries have long been considered to be determinants of waterway siltation rates. The aggregation of inorganic and organic particles suspended in water has manifold significance for the transport and fate of sediments, particulate food supplies to aquatic organisms, and the distribution of contaminants. A number of theoretical treatments based on the collision equations have appeared in the marine literature. The collision functions described above for physical mechanisms are based on the assumption that particle motion is unaffected by the proximity of other particles. The term “disaggregation” describes the breakup of aggregates, producing either primary particles or fragments containing assemblages of primary particles. The horizontal flux of any substance, dissolved or particulate, is taken as the mass transported through a unit area per unit time, which is dimensionally equivalent to the product of concentration and velocity.