Modulation of residual current and water flux by the construction of Yangshan deep-water harbour, Shanghai, China

Extensive coastal and offshore engineering is conducted primarily for economic development or safety. Understanding of the induced modulations in hydrodynamics is an important foundation for engineering benefits and environmental safety. Construction of the Yangshan Deepwater Harbour (YDH) has intensively altered local geometry and topography, and induced significant changes in tidal dynamics. In this study, the modulations of currents, especially the residual currents and water fluxes, along with its four-phase construction are carefully examined through application of a high-resolution unstructured-grid numerical model. Results show that the YDH’s construction significantly weakened local tidal currents, especially those in the Inner Harbour Area (IHA), but strengthened currents in narrow passages. The constructions significantly adjust Eulerian residual current, especially around islands, thus modulations in the Eulerian residual transport current. A stagnant zone is developed by the first phase construction and shifted by the following constructions. It is pushed westward by the Stokes residual current. Tidal fluxes in most of the remaining passages are increased by the YDH’s construction, mainly relating to the deeper topography and stronger currents, but the net tidal fluxes are reduced. The residual momentum balance is controlled by a quasi-Bernoulli equilibrium between barotropic pressure gradient and advection terms, the relative contributions of the pressure term and the convective term have changed. Although this is a site-specific study, the findings may be applicable to engineering influence analysis in other coasts. • Construction of Yangshan Deepwater Harbour significantly weakens local tidal currents. • Harbour alters Eulerian residual current via tidal rectification, minimally affecting Stokes residual current. • Constructions create a stagnant zone in Eulerian residual current, shifted floodward by Stokes residual current. • Tidal fluxes increased in most passages, while net tidal fluxes were overall reduced.