枯季长江口南槽悬沙输运过程和机制研究

开展枯季河口悬沙输运机理研究对于揭示弱径流条件下的陆海相互作用、河口季节性冲淤和水沙关系等具有重要的科学意义.本文根据2018年12月18-25日长江口南槽3个站位连续13个潮周期的同步流速、流向和悬沙浓度等观测资料,运用通量机制分解法研究了各输沙项的特征、贡献和输运机理.结果 表明,从小潮至大潮流速和悬沙浓度不断增加,由南槽上部至下部流速和悬沙浓度逐渐降低.观测期间平均流速与平均悬沙浓度存在明显的正线性关系,但受底质空间差异影响,悬沙浓度对流速的响应强度存在显著的空间变化.枯季期间南槽存在着中上部向陆净输沙、下部向海净输沙的空间输运格局.平流输沙和潮泵输沙是影响和控制净输沙的关键因素,二者的强度和贡献存在明显的潮周期变化和空间变化,垂向环流输沙的强度很弱,对净输沙贡献很小.南槽涨落潮输沙不对称现象明显,流速、悬沙浓度和历时都具有一定的涨落潮不对称性,这些不对称现象共同调节和控制着潮周期净输沙强度和方向的时空变化.

Suspended sediment transports and mechanism in the South Passage of the Changjiang Estuary during the dry season

The research on the characteristics of estuary suspended sediment and its transport mechanism is of great significance for revealing the interaction between land and sea, the evolution of erosion and deposition of estuary topography, and suspended sediment process to the sharply decreasing suspended sediment in the drainage basin. Based on the field observation data of current velocity and suspended sediment concentration (SSC) over 13 consecutive tidal cycles at three anchor stations in the South Passage of the Changjiang River Estuary from December 18th to 25th, 2018, characteristics of sediment transport are analyzed by using the mechanism decomposition method. The results show that the current velocity and SSC continued to increase from neap tide to spring tide, and they gradually decreased from the upper reach to the lower reach in the South Passage. During survey period, there are positive linear relationships between averaged current velocity and averaged SSC, and affected by difference in bed sediment properties, the response of SSC to the strength of current velocity exhibits remarkable spatial variation. During dry season, the net suspended sediment transport directed landward in the middle and upper reach while seaward in the lower reach. The advection and tidal pumping terms dominated the net sediment transport, and the strength and contribution of them displayed notable tidal and spatial variation. The contribution of vertical circulation transport term was slight. The flood-ebb asymmetries in current velocity, current duration and SSC were obvious, and these asymmetries jointly regulate and control the temporal and spatial variation of net suspended sediment transport.