Measuring the variations of the apparent settling velocity for fine particles

This note establishes the fact that the settling velocity for fine flocculent particles in flowing aquatic systems vary considerably and the settling velocity should therefore be understood as a variable which varies temporally and spatially in the flow field. In the mathematical formulation the settling velocity of a suspension appears in the actual and local mass conservation equation as an apparent settling velocity. A new approach to measuring this variable settling velocity is mentioned and its relation to well-known principles, e.g. settling columns, is discussed.