Spatiotemporal distribution pattern and transport mechanism of suspended sediments in Longkou offshore under the action of tidal current

Based on the data collected from tidal current observation and suspended sediment sampling at the coastal Longkou Bay, which had lasted for a total of 27 hours in January, and May 2017, the characteristics of tidal current field and the transport mechanism of suspended sediments were studied with the method of Morlet Wavelet Transform and flux mechanism analysis. The results show that the concentration of suspended sediments is lower within the bay, but relatively higher at the mouth and outside areas of the bay. Vertically, the concentration of suspended matters gradually decreases from the bottom to top. The peak of suspended sediment concentration has a half to two hour time lag behind the peak of current velocity, and the variation in suspended sediment concentration shows a cycle of 12～16 h variation. The net sediment transport rate ranges from 1.21 to 239.77 g·s⁻¹·m⁻¹. In general, the suspended sediment flux outside the bay is higher than that inside. In terms of seasonal variation, the suspended matters are far higher in January than that in May, indicating the seasonal transport characteristics: storage in summer and transport in winter. Suspended sediments move towards SW and S in offshore waters, while in the water to the north of the Qimu Island follow a W and SW path to the head of the island. When it comes into the bay, the transport of suspended sediment is separated into two branches along the north and west sides of the artificial island respectively. Under the joint effect of ocean current, topography and so on, the net sediment transport is mainly from the Bohai Sea to Laizhou Bay in the study area.