长江口浑浊带北槽悬沙输运研究

Study on transport of suspended sediment in the Turbidity Maximum Zone in the North Passage of the Yangtze Estuary

2012年8月和2014年7月在长江口北槽浑浊带进行了大小潮水文泥沙定点连续观测,分析了水沙分布特征,计算了悬沙输运量,并且运用机制分解法,分析各输沙项的作用。结果表明,北槽浑浊带垂向平均含沙量空间分布差异明显,北槽下部最高,中部次之,上部最低。垂向平均含沙量大小潮均值北槽下部为0.72 kg/m^3,中部为0.51 kg/m^3,上部为0.23 kg/m^3;平流输沙在大小潮均起主要作用,大潮平流输沙显著强于小潮。北槽下部小潮期间垂向净环流输沙作用显著,占净输沙的-278.3%;小潮期间,北槽中部和上部平流输沙起主要作用,底层悬沙输运向海。而北槽下部底层悬沙输运受“潮泵效应”影响显著,方向向陆。悬沙输运方式的差异导致小潮期间北槽中下部底层悬沙不能下泄入海。

Based on the observation over spring and neap tide in the Turbidity Maximum Zone in the North Passage of the Yangtze Estuary in August 2012 and July 2014,the current speed and sediment characteristic were studied,and the suspended sediment flux was calculated.It was found that: ( 1) The depth-averaged suspended sediment concentration in the North Passage differed significantly in space.The depth-averaged suspended sediment concentration in spring and neap tide was 0. 72 kg /m3 in the lower part,0. 51 kg /m3 in the middle part,and 0. 23 kg /m3 in the upper part.( 2) Lagrangian transport dominated in this area,the magnitude was larger during spring tide than during neap tide.In the lower part of the North Passage,the net vertical circulation played a significant role in neap tide which account for -278. 3% of the residual sediment flux.( 3) During the neap tide,the advective sediment flux accounted for the seaward residual sediment flux in the bottom layers in the upper and middle part of the North Passage,but the tidal pumping flux contributed to the landward residual sediment flux in the bottom layers in the lower part of the North Passage,which was responsible for the convergent residual sediment transport between this two areas,and might suppress the seaward transport of near-bottom suspended sediment.