长江口横沙浅滩及邻近海域水动力特征分析

Analysis of hydrodynamics around the Hengsha Shoal of the Yangtze Estuary and its adjacent region

主控本海域泥沙运动和海床冲淤演变的水动力是水体中具有强周期性的潮汐运动和弱周期性的长江径流之耦合.潮汐运动主要由源潮波即半日潮波和日潮波叠加而成,因浅海非线性效应而衍生的浅水潮波也有相当贡献,从而形成具有以半日潮周期为主,且伴有日不等现象的水体流动.基本沿陆岸呈南北向传播的潮波,经长江口门在本海域顺势折向,入横沙浅滩南北的北槽和北港水槽,基本转成东西向的流动.本海域滩槽相间,且处在口门和滨坡交接段,复杂地势制约着潮流运动形式:顺河槽和沿横沙浅滩东侧分别为东西和南北主流向的往复流;而其间的海域基本呈南向流强于北向流的旋转流.正由于这种形式的旋转流存在,造成口外滨坡海床的冲刷以及挖入式港池的深水航道段会有较强的横流出现.长江径流顺河槽下泄东流,出口门后浮置于海外盐水之上,随不同季节,或东南或东北向汇入大海,由此往往造成上下水层流向不一致的垂向结构.

The dominant controlling dynamics for the Changjiang Estuary is the interaction be- tween the strongly periodic tide oscillation and the weakly periodic Changjiang River runoff. The astronomical tide in this region is the combination of the semidiurnal and diurnal tides, which produces the shallow tide wave due to the nonlinear interaction between these tide components. Therefore the tidal asymmetry in one period is subsequently induced. The tide wave mainly flow along the coasts with the northward direction, and turn to the northwestern direction into the North Passage and North Channel. The studied region, Hengsha Shoal, is characterized as theshallow shoals and deep channels, where is the buffering zone for river mouth and open ocean. This complex bathymetry produces the motions of the tide wave and runoff. The current in the channel and north region of Hengsha Shoal has the alternating pattern. And the significant rota ting current dominates the south area, which plays an important role on the stability of the local bathymetry and the strong cross-channel current. Since the Changjiang River＇s runoff flow east- ward, and float on the surface in this region, producing significant two-layer system in the verti- cal direction.