The movement of grain sediment within the bottom boundary layer is influenced by complicated

multi-scale dynamic processes. Dynamic characteristics of turbulence and small-scale sediment exchange process within the bottom boundary layer at modaomen channel are discussed based on bottom boundary layer observation data over various tide levels by using ADV and OBS in winter of 2010. The result shows that: ① The ranges of sediment settling velocity

bottom stress and bed erodibility increase with tidal range.②Bed erodibility changes are similar to mean velocity. When velocity is less than 0.3m/s

the bed erodibility remains at about 0.002 kg/m

2

. If velocity is larger than 0.3 m/s

sediment will resuspend. ③ Suspended sediment and bed sediment exchange process is enhanced with increasing tidal range

and it is stronger during ebb tide than during flood tide.