The temporal variation of flocs and fecal pellets in a tidal channel

Fine-grained sediment transported in suspension in a tidal channel consists of single grains, flocculated material and fecal pellets. The temporal variation during the tidal period in settling velocities of flocs, as well as the number and size of fecal pellets, is influenced by several parameters; current velocity and suspended-sediment concentration are shown to be the most important. The equivalent settling diameters of the suspended matter are almost constant close to the water surface, whereas at the bottom, they vary following the variation in suspended-sediment concentrations. The maximum number of fecal pellets are found around low water slack, when the tidal flats adjacent to the channel are being drained. After dispersion, the grain size distribution of both flocculated material and fecal pellets is almost identical, with a median diameter of 5 mu-m.