Title: Subtidal hydrodynamics in Hong Kong waters: links of Pearl River Estuary, Mirs Bay with continental shelf off Hong Kong
PI: Jianping Gan; CI: Joseph Lee
Hong Kong is surrounded by the waters of Pearl River Estuary (PRE) to the west, Mirs Bay (MIB) to the east and continental shelf (COS) to the south and they jointly form Hong Kong Seawaters (HKW). These three water entities have their own inherent hydrodynamics that is mainly governed by flow-topography (effect) interaction forced by monsoon wind stress, tides and buoyancy from Pearl River. Their respective hydrodynamics are mixed coastal-estuarine circulation in the broad PRE, topography-following flow in MIB and monsoon driven upwelling/downwelling shelf circulation in COS. Unlike tidal currents that reverse direction within semi-diurnal or diurnal time scales, subtidal forcing is well known to be the major driver that shapes overall transport (flow) field in the coastal embayment such as HKW, for a time scale beyond tidal periods. Subtidal hydrodynamics is essential for understanding, modeling, and managing seawater properties from shelf offshore to near shore in HKW. COS is tightly linked with PRE and MIB geographically and dynamically, and the underlying hypothesis in this proposed study is that integrated hydrodynamics in the subtidal time scale among PRE, MIB and COS, not each individual itself, governs the dynamic environment of HKW. This scientific subject has rarely been studied in HKW. Based on the dynamic evidence derived from HKW and from the other parts of the world’s oceans, it is hypothesized that: (H1) Monsoon-driven upwelling/downwelling shelf circulation in COS and its associated hydrodynamic response in HKW largely controls the subtidal circulation in HKW. (H2) The shelf circulation in COS is time and space dependent subject to the control of monsoon winds, tides and buoyancy from Pearl River discharge. (H3) Shelf circulation in COS strongly regulates the subtidal hydrodynamics in PRE/MIB, which is modulated by the variable coastline and shelf topography in HKW. Unlike previous studies that have mainly focused on tidal hydrodynamics in PRE, this proposed project, for the first time, integrates the study of hydrodynamics in COS with ones in PRE and MIB to provide comprehensive understanding of hydrodynamics in HKW. The strategy of the study is to combine field measurements of repeat horizontal mappings and mooring arrays with an enhanced spatial resolution of advanced down-scale modeling system to identify the time dependent, three-dimensional integrated hydrodynamics in HKW. As the fundamental theory that governs the water motion and associated properties/materials transport, the study of subtidal hydrodynamics will help advance our understanding of overall marine environmental conditions in the HKW.