珠江口伶仃洋的Kelvin潮波利用二维分析模型和三维数值模拟的研究

KELVIN WAVES IN THE LINGDINGYANG REGION, PEARL RIVER ESTUARY, SOUTH CHINA, BY ANALYTICAL MODEL AND 3-D NUMERICAL MODELLING

伶仃洋的研究是整治珠江口的关键课题之一,也是河口学研究方面极有意义的。其地形复杂:浅滩和深槽互相交替,潮间带在低潮时露出;径流从四个口门流入,洪季和枯季相差几倍;又有大、小潮的变化;除了纵向盐度梯度外,又有横向的盐度梯度。利用分析模型和三维斜压式数值模拟两种方法,认为河口宽度较大因而科氏力起一定作用,加之虎门附近的反射作用,形成具有部分反射的Kelvin潮波系统。斜压作用和漏斗状地形的修正,可以解释主要的水文特征。例如东部潮差较大,水位较低。潮流是往复流,超前于潮波的相位越向南越大,盐度的空间分布是东南较高,时间变化滞后于潮波。含沙量的空间分布是东南较低。揭示出:东部涨潮流大于落潮流,西部则相反,以至形成了海水由东部流入,河水由西部流出的余流循环。这些结果提示:选择航道在东槽较好,东岸排污污染将随余流循环而影响到整个伶仃洋,等等。对经济建设及总体长远规划提供重要的依据。

The investigation of the Lingdingyang region is not only important for the economical development of the Pearl River estuary, South China but also interesting for estuarine studies. Its topography is complicated with channels, shoals and tidal flats situated alternatively. Fresh water discharges from the four river branches are subjected to seasonal variations against the unequal semi-diurnal tides. The special transversal salinity gradient exists together with the longitudinal salinity gradient in ordinary estuaries. By means of an analytical model and 3-D numerical modelling, it can be concluded that incident and reflected Kelvin tidal waves are formed as the estuary is wide enough to induce significant Coriollis effect. With corrections by the baroclinic effect and funnel shape topography, the essential hydrological characteristics can be explained. Tidal ranges are larger and water levels lower in the east. Currents are mainly alternative, instead of rotationary, and lead the tidal waves with larger phase angles in the south while salinity is higher in the southeast and pertaining larger phase lag in the south. The sand contents, as a negative correlation of the salinity, are lower in the southeast and reach the maximum soon after the low water. Further, counter—clockwise residual currents result from stronger flood currents in the east and stronger ebb currents in the west. These suggest that: The east channel should be chosen for navigation. The polluted discharges in the east will influence the whole area following the residual currents, etc.