Tidal prediction and flow dynamics in Macao waters

Tidal dynamics is crucial in shaping marine ecosystems and the design of sustainable coastal infrastructure. With the increasing strategic importance of Macao as an innovation node in the Pearl River Estuary and newly acquired maritime jurisdiction rights, a more detailed study of the coastal flows in Macao's water is required. This study utilises extended harmonic analysis and a validated Finite Volume Community Ocean Model (FVCOM) to study two aspects of tidal dynamics in Macao respectively: (i) the impact of climate change and reclamation on the tidal constituents of Macao harbour; (ii) an elucdiation of the 3D tidal circulation in the shallow coastal waters. The results show that 40 tidal constituents are sufficient for accurate tidal prediction (with RMS error of 0.133 m). The primary harmonic constants are not affected by land reclamation and climate change over the past two decades; while the mean sea level has been increasing at an average of 3.4 mm per year. The tidal regime is predominantly mixed and mainly semi-diurnal, with a tidal range of approximately 2.4 m and 0.8 m during spring and neap tides respectively. During ebb the tidal flow splits into three main stream currents through the Macao Waterway, Shizimen Waterway, and the western beach of Lingdingyang, while flood tides follow similar routes. Maximum velocities in the main navigation channels in Macao, Shizimen, and eastern waterways are 0.32, 0.50 and 0.75 m/s, with coastal currents of around 0.35–0.50 m/s in the southern coastal waters near Coloane. Extensive tidal flats in Shizimen reveal maximum depths of around 0.8 m and surface velocities of around 0.31 m/s. The findings provide a basis for studying ecosystem dynamics in the coastal waters of ecological importance.