长江口门附近海域潮周期内悬沙质量浓度变化及其动力机制探讨

Study on the Change of Suspended Sediment Concentration During Tidal Cycle and Its Dynamic Mechanism Near the Changjiang Estuary

为了探讨潮周期内悬沙质量浓度变化的动力机制，于2010—04和2011—01（正常风况条件下）在长江口门附近海域3个测点（水深8～20m）进行了金潮（1次／h）动力泥沙观测，计算了流剪切应力（τc）、浪剪切应力（τw）、流-浪联合剪切应力（τcm）、底床沉积物临界侵蚀应力（τcr），并进行了悬沙质量浓度变化和动力因子变化的关联分析。结果表明：τc与τcm之比值大于0．81，说明在非风暴天气条件下研究区的水动力以流为主；τc在潮周期内存在1～2个数量级的波动，说明研究区的水流动力主要受到潮流控制；τcw既有大于τcr的时间段（约60％），也有小于τcr的时间段（40％），说明研究区底床和水体之间存在频繁的泥沙交换过程；τcw与悬沙质量浓度之间的统计相关性不显著，说明基于每小时观测的悬沙质量浓度变化主要反映平流作用而不是受局地动力条件变化引起的沉降一再悬浮过程的影响。

To understand the dynamic mechanism of the variation of suspended sediment concentration （SSC）, an in situ dual-tide observations of sediment dynamics （interval one hour） were conducted at three sites （8-20 m） near the mouth of the Changjiang Estuary in April, 2010 and January, 2011 （during calm weather）. The current shear stress （τc）, wave shear stress （τw） and shear stress due to combined currentwave action （τcw）, and critical bed shear stress for erosion （τcr） are calculated for each site, respectively. Meanwhile, the correlation between the SSC variation and the change of dynamic conditions is analyzed. The results show that the ratio of τc to τcw is greater than 0.81, indicating that the hydrodynamics in the studied area is dominated by current under the non-storm weather conditions; The τc can fluctuate 1 to 2 orders of magnitude during the period of tidal cycle, indicating that the hydrodynamics in the studied area is mainly controlled by tidal current; The τcw has periods of time either greater than τcr （60%） or less than τcr （40%）, indicating that frequent sediment exchange exist between the seabed and the overlying waters in the studied area. The correlation between the vcw and the suspended sediment concentration is not obvious, suggesting that the SSC variations observed hourly may chiefly reflect the influences of the function of advection rather than the affects of the sedimentation -resuspension processes caused by local hydrodynamic conditions.