弱动力浅海中的悬沙输运机制:以天津港附近海域为例

The suspended sediment transport associated with low flow patterns in shallow waters:a case study from the Tianjin subtidal area

根据在天津港附近海域获取的水动力和浊度数据,分析了悬沙输运特征和输运机制,结果表明:天津港附近海域受不规则半日潮控制呈低流态往复流特征,但涨潮流强于落潮流;涨潮期间底部悬沙浓度与垂线平均流速呈显著线性相关,存在显著的再悬浮作用;潮周期内的悬沙输运呈典型的不对称特征,形成向岸的净输运趋势。输运机制分析结果显示:潮泵效应(尤其是潮汐捕捉效应)是天津港附近海域悬沙输运的主要贡献项,其次是拉格朗日平流输运项,前者比后者高一个量级;垂向剪切作用最小。涨落潮期间流速与悬沙浓度的显著不对称是造成潮汐捕捉效应占主导的基本条件。在潮下带这种悬沙输运格局可能和潮间带发生的细颗粒沉积物捕集(堆积)作用有关。

The suspended sediment transport processes were analyzed on the basis of hydrodynamics and suspended sediment survey in the Tianjin subtidal waters of the Bohai Sea.The flow in the study area was characterized by the irregular semidiurnal tide and reciprocating flow.The current speed of flood was stronger than ebb.There is a significant linear relationship between the depth-averaged velocity and the suspended sediment concentration at the bottom layer during the flood period but not during the ebb,which indicates a strong resuspension event during the flood.The suspended sediment transported with strong asymmetric characteristics during tidal cycles,which results in the net sediment transportation onshore.The calculation of flux decomposition shows that the tidal pumping effect,especially the tidal trapping,is the main contribution in terms of the suspended sediment transport in the study area.It is followed by the Lagrangian advection transport,which as one order lower than the tidal pumping;the vertical shear contribution is minimum.In conclusion,the strong asymmetry of both the current velocity and suspended sediment concentration during the flood and ebb,were the main factor resulting in a strong tidal trapping.In addition,the suspended sediment transport patterns in the subtidal area may be related to the fine-grained sediment trapping over the intertidal area.