IN-SITU SIZE DISTRIBUTION OF SUSPENDED MATTER DURING THE TIDAL CYCLE IN THE ELBE ESTUARY

In situ size of suspended particles was measured with an underwater ph otographic system in the Elbe estuary. The data from the measurements at a stationary position indicate that the formation of large flocs to ok place at low current velocities and that the size distributions var ied with the tidal cycle as a consequence of flocculation, deposition and resuspension processes. Flocculation of suspended particles in the estuary is interpreted as a dynamic process: the size of flocs change s with time and their distribution depends on the rates of aggregation and disaggregation of the particles. This is related to physical fact ors of which turbulence and differential particle settling play key ro les in producing large flocs. Fluid shear is responsible for disaggreg ation of large flocs. Salinity and the organic content of particles ma y affect flocculation processes with respect to the particle cohesive interaction, but they have no critical effect on the variation of floc size during the tidal cycle in the estuary.