We discussed basic characteristics of seasonal variation of sediment compositions in the previous report. In this paper we deal with the rapidity and extent of the variation of sediment composition.
The main results are as follows. When the surface sediment size became finer, the fresh water inflow to the estuary was about 100m³/s (5.6m³/s/100km²) and the change was completed in about 10 days. On the other hand, the change becoming coarser was completed in a day. In this case the fresh water inflow was over 400m³/s (22m³/s/100km²). Judging from the change of longitudinal distributions of sediment size, finer particles always exist from the river mouth to the bay, and the extent to which finer particles are dominant expands upstream from spring to summer. When finer particles in the surface sediment were dominant, the thickness of the sediment layer where the finer particles were dominant was several centimeters in the middle reaches of the estuary. The time lag between the variation of the concentrations of the sediment constituents and the sediment size was not found due to the observation at intervals of 2 days.