The exchange flow structure was examined in the North Passage of Changjiang River Estuary, where a deep waterway project (DWP) was carried out to improve the navigability. Before the construction of the DWP, the friction effect played a significant role in shaping the transverse structure of the exchange flow. The turbulent eddy viscosity generated near the seabed can be transferred to the upper water column, which facilitated vertical momentum exchange. As a result, the landward inflow extended to −2 m below the water surface and the seaward outflow was concentrated on the shallow shoal on the southern side of the cross section. After the construction of the DWP, the turbulent mixing was suppressed as a result of density stratification. The friction felt by the water was constrained in the lower half of the water column and the vertical momentum exchange was reduced. Meanwhile, the channel became dynamically narrowed with a Kelvin number of 0.52. Therefore, the Coriolis played a minor role in shaping the transverse structure of the exchange flow. As a consequence, the exchange flow featured a vertically-sheared pattern, with outflow at the surface and inflow underneath. Additionally, the gravitational circulation was enhanced due to increase in along-channel density gradient and stratification. The exchange flow components associated with the lateral processes (residual currents induced by eddy viscosity-shear covariance and lateral advective acceleration) were reduced, which suggests that lateral processes played a minor role in modifying the along-channel dynamics when the estuary becomes dynamically-narrowed.

在长江口北通道检查了水流的交换结构，并进行了深水航道工程（DWP）以改善通航性。在DWP建造之前，摩擦效应在形成交换流的横向结构方面起着重要作用。在海床附近产生的湍流涡流粘度可以转移到上水柱，这有利于垂直动量交换。结果，陆上流入流扩展到水面以下-2m，而海流出流集中在横截面南侧的浅滩上。在构造DWP之后，由于密度分层而抑制了湍流混合。水所感觉到的摩擦被限制在水柱的下半部分，垂直动量交换减少了。同时，通道的开尔文数变为0.52，从而动态变窄。因此，科里奥利（Coriolis）在形成交换流的横向结构中起次要作用。结果，交换流具有垂直剪切的模式，在表面有流出，在下面有流入。另外，由于沿通道密度梯度和分层的增加，重力循环得到了增强。减少了与横向过程相关的交换流量分量（由涡流粘度-剪切协方差和横向对流加速度引起的残余电流），