Dynamical Control of Asymmetrically Oblique Tidal Currents to the Sedimentary Characteristics and Development of Linear Sand Ridges in the Liaodong Shoal, East Bohai Sea

The Liaodong Shoal is a group of linear sand ridges located in the east Bohai Sea of China.In this study,54 surface sediment samples have been collected,current measurements at 4 stations have been carried out and bathymetric data were obtained.The current directions are rightward deflected relative to the strikes of the sand ridges.Affected by the narrowing effect of the ridge,the current velocities exhibited an anti-‘C’type vertical profile.The velocities of the lower currents linearly correlate with the water depths.The near-bed current velocities over the troughs are estimated to be higher than those over the ridges,and this feature could be explained by the loss of kinetic energy together with the conversion between kinetic energy and gravitational potential energy.The sedimentary characteristics that are compatible with the tidal dynamics are developed across the ridges and troughs,including grain size compositions,grain size parameters,mineral compositions and Dhm indexes.The existence of the angles between the current directions and the strikes of the sand ridges is the key factor for the growth of the sand ridges.The asymmetric hydrodynamic features between the flood and ebb currents lead to the differences in the topographical and sedimentary characteristics on both sides of a sand ridge.Insufficient material supply led to the degradation of the sand ridges,and the reduction of the tidal current intensity has led to the development of the subordinate sand ridges in the troughs.Sand ridges are migrating.

Characteristics of modern sedimentation in Qingdao bays

With available survey data and 237surface sediment samples,the modern sedimentation in Qingdao bays is studied.The research result shows that the east area is shallower(16.4 m) than that in the west(45.8 m).The geography was formed by a symmetric wave in a sequence of bank-offshore depression-platform-tidal channel-platform-offshore depression-foreshore from south to north.Flood sedimentary systems were formed from inlet of the Jiaozhou Bay in the west to the barrier bar in the east.Lateral sedimentation includes mainly tidal current ridges in two tidal channels.Gravel sandy sediments formed by wave lie in midland of from seashore to wave base.Dynamic functions are mainly tide and wave.Tidal current moves sediment in vertical and horizontal directions,sorting sediments and providing materials for coastwise beaches.The sources of sediment are mainly from eroded headland rocks.In general,grain sizes in this area from the inlet of the Jiaozhou Bay in the west(120°17') to the barrier bar outside in the east(120°35') are coarse-fine-coarse,forming gravel-gravelly sand(G-S),sand(S),gravel clay silt(G-YT),clay silt(YT),gravelly silty sand(G-TS),silty sand(TS),gravelly sandy silt(G-ST),and sandy silt(ST) in turn.