Tidal processes • Waves • Sediments • Flocculation

Flocculation

The process by which clay particles stick together is known as flocculation. Each clay platelet contains attractive and repulsive forces, known as van der Waals Forces and Coulombic Repulsive Forces, respectively. In fresh water, the attractive forces equal the repulsive forces and there is no net effect in terms of particles being attracted to each other or repelled from each other. However, in saline fluids, such as sea water, the repulsive forces reduce and the attractive forces become dominant. The strength of the attractive forces is increased as the clay particles get closer together, the net result being they stick together, or flocculate.

Flocculation is an important process in areas where fresh water and saline water mix, such as estuaries. For example, clay particles being transported down a river and into an estuary are brought close together during the mixing process and at the same time are introduced to saline water, where they flocculate. The zone of high suspended sediment concentration is known as the turbidity maximum.

This process is relevant to the settling velocity of particles, which is dependent on the particle diameter, with larger diameters settling faster. That is, the process of flocculation will result in larger particles which will settle faster. Indeed, since individual particle settling rates are in many cases so slow as to prevent their deposition within a tidal period, flocculation is essential for the formation of intertidal mudflats and, ultimately, saltmarshes.