This dissertation focuses on sedimentary processes (erosion, flocculation, and deposition) in intertidal flats to comprehensively understand sediment dynamics. Considering topographic connectivity of the intertidal flats with tidal channel and salt marshes, the sedimentary processes were revealed by in-situ measurements using acoustic Doppler current profiler (ADCP), acoustic Doppler velocimeter (ADV), submergible digital holographic camera (LISST-Holo), and Gust erosion microcosm system (GEMS). Each chapter includes specific sedimentary processes as follows: erosion and deposition in intertidal flats (Chapter II), erosion and flocculation in intertidal flats (Chapter III), and the difference of sedimentary processes between salt marshes and intertidal flats (Chapter IV).
Chapter II dealt with the contribution of erosion in intertidal flats to the sediment transport compared to horizontal advection from tidal channel. Under strong winds, erosion type of sediment bed was shifted from floc erosion to surface erosion with increasing erosion rate. It resulted in high contribution (up to 87 %) of eroded sediments to total suspended sediments and decreased the bed elevation with enhanced seaward sediment transport. In Chapter III, it was revealed that the eroded sediments by the surface erosion had different floc structures from those of advected sediments. The macrotidal conditions allowed flocs to have spring-neap and flood-ebb variations in their size and structures. In general, the flocs in intertidal flats grew during spring tides and broke up during neap tides, but the strong winds caused the surface erosion supplied smaller and denser flocs into the water column compared to those by horizontal advection. Chapter IV covered interactions between erosion and flocculation in intertidal flats and salt marshes. The presence of vegetation entirely changed physical conditions with decreasing current speed and turbulence. Under the strong winds, however, the stems and leaves of vegetation generated stem wakes enhancing the erosion within the vegetated area. Unlike the intertidal flats, the vegetation trapped the eroded sediments inside of vegetated area. The presence of vegetation, which enhanced turbulence under winds and trapped sediments, caused the repetitive erosion and deposition resulting in highly erodible sediment bed. The bed elevation in vegetated area rapidly decreased as soon as the vegetation was cut-off artificially. Moreover, the flocs within vegetated area highly depended on the stem wakes, showing the similar size and structure regardless of winds.