长江口北支小潮至大潮水沙输运机制研究

Mechanism of water and suspended sediment transport from neap tide to spring tide in North Branch of Changjiang Estuary

根据2010年4月23日至30日在长江口北支主槽内获得的流速和悬沙观测资料,运用机制分解法分析了从小潮到大潮连续变化过程中北支的水沙输运特征。研究结果表明:从小潮到大潮余流和单宽输水量不断增加,输水方向向海。单宽输沙量从小潮到大潮趋于增加,但输沙方向具有小潮和大潮向海、中潮向陆的特点。在各输沙项中,平流输沙占主要地位,其输沙方向向海,输沙量从小潮到大潮显著增加,大潮输沙量约为小潮的46倍;潮泵输沙占次要地位,其输沙强度和输沙方向随潮周期变化频繁;垂向净环流的输沙强度很小,输沙方向向陆。此外,从小潮到大潮的过程中,一些重要输沙项的贡献率随潮周期变化显著,这表明各潮周期的悬沙输运机制有时存在较大差异。

Based on the data of current velocity and suspended sediment concentration measured in the main channel of North Branch of the Changjiang Estuary from April 23 to 30 in 2010,the transport mechanism of water and suspended sediment during a neap-spring tidal cycle is analyzed by using the mechanism decomposition method.The results show that the residual current velocity and the magnitude of water transport at the measurement station are increased gradually from neap tide to spring tide.The direction of net suspended sediment transport is landward in the neap tides and in the spring tides,and is seaward in the medium tides.The magnitude of absolute suspended sediment transport is increased significantly from neap tide to spring tide.The advection transport term is the principal constituent of the suspended sediment transport,which is enhanced remarkably from neap tide to spring tide with the magnitude in spring tide 46 times bigger than that in neap tide.The tidal pumping transport term is the secondary constituent of the suspended sediment transport,its magnitude and direction change frequently with the tidal cycle.The magnitude of net vertical circulation transport term is very small and the transport direction is landward.During the measurement period,the contribution of some important transport terms had significant variation within the neap-spring tidal cycle,which means that the difference of suspended sediment transport mechanism between these tidal cycles sometimes is remarkable.