大河三角洲河口海岸演化机理模型研究:(II)模型构建与实证

Researches on dynamics model and numerical simulation of the large-scale estuarine shoreline evolution: (II) numerical modeling and a case study

本文以z坐标下的三维斜压海洋动力学数值模式为基本模式原型 ,在整理渤海基本数据并诊断计算风生环流和热盐环流作为背景环流场基础上 ,初步建立了渤海海域动力环境数值模式。模式采用了经校正的Bagnold型方程来计算渤海底移质沉积物输运 ,悬移质计算则是取二维深度平均悬移质输运方程和河床变形方程 ,计算含沙量分布以及由悬移物引起的冲淤厚度。利用这种方法建立的沉积物输运模式 ,定量模拟了渤海沿岸和海底的沉积物输运方向和冲淤分布。模拟结果与通过多年实测水深估算获得的渤海海底沉积物的冲淤变化分布相比较 。

Based on a z coordinate 3D baroclinic numerical modeling (ZOM) developed by Fang & Yu (1998), currents (include tidal current) of the Bohai Sea are diagnostically simulated considering the wind driven circulation and thermohaline circulation. The splitting mode technique is used in model discretization and forward elimination and back substitution is employed in solving water elevation equation. The advection, bottom friction, buoyancy, and vertical eddy viscosity are elaboratedly treated in order to keep numerical stabilization. The horizontal resolution is 10′. There are 5 layers in vertical. The numerical results coincide with observation data quite well when comparison between the calculated current and observation data in an oil rig of the Bohai Sea during Dec. 1995 to Sep. 1996. The deviation of current direction between the calculation and observation is smaller than 14.8°,while that of current speed is 8.8cm/s(23%). A modified Bagnold load sediment formulas is used in mass transport model. The suspend sediment transport is calculated according to formular given by Dou et al. (1995). The numerical sediment transport model shows that the head of the Bohai Bay and Liaodong Bay are alluvial sea areas. In the rest sea area of the Bohai Sea, especially in the Bohai Strait, appears erosion area. In order to calibrate the numerical results, a comparison between the numerical output and secular changes of the depth of the Bohai Sea during recent 50 years is achieved, and the result illustrates the consistent change pattern. Of course, this paper is only a preliminary research on connection of the physical process and sediment process. In next step, the function of ocean wave, fresh water dilute, cohesive sediment transport, sediment entrainment and near shore process will be considered in the model.