Numerical study of the tidal waves in the Gulf of Tonkin

A high resolution numerical model for the tides and tidal currents in the Gulf of Tonkin (GT, also known as Beibu Gulf) and its adjacent waters is developed on the basis of Princeton Ocean Model (POM08),and is used to numerically simulate the four principal tidal constituents, K₁, O₁, M₂ and S₂. The main tidal characteristics are presented in detail, followed by an analysis of the influences of Qiongzhou Strait (QzS) on the tidal wave system in the GT from the point of tidal energy dissipation.Diurnal tides are dominant in the GT.For either K₁ or O₁ constituent, there is a half rotary tidal system near the southern mouth of GT, with the amphidromic points located almost on the coast near Thuan An, Vietnam.The residual current is westward in the QzS, resulting in a water volume transport of 0.034 Sv; after flowing out of the western mouth of QzS, it first turns northward and then southward, forming a anticlockwise curve in the GT.Strong tidal currents are found in two regions: the QzS and the waters off the west coast of Hainan Island, where the tidal energy dissipation rates are the highest in the modal domain.The tidal motion in the GT is maintained by the energy flux from the South China Sea through the southern mouth of the GT.Tidal energy fluxes into the QzS from the western mouth, and nearly all the energy of diurnal tides dissipates away within the strait.The energy dissipation of the four constituents amounts to 3.33 GW in the QzS, accounting for 35% of that consumed in the GT, though the area of QzS is only 2% of that of the GT.The Qiongzhou Strait, as an important area of energy dissipation, plays a significant role in the formation of the tidal waves in the GT.Calculation shows that the bottom boundary dissipation of tidal energy accounts for 83% and 80% of the total dissipation in the GT and QzS, respectively.