三门湾海域污染物扩散数值研究

Numerical simulation of pollutants diffusion in the Sanmen Bay

本文基于Delft3D建立了二维水动力数值模型和污染物输运扩散模型,分析了三门湾海域的三种主要污染物即化学需氧量(COD)、总氮(TN)、总磷(TP)的输运扩散规律。水动力计算结果与实测结果基本吻合,能够较好重构三门湾海域的水动力环境特征。根据物质输运特征,将三门湾划分为7个动力单元,即健跳-浦坝、海游-蛇蟠南、青山、沥洋、乐井洋-石浦、混合区域、口门区域。Lagrange运动轨迹表明,各动力单元的物质输运基本控制在本单元范围内;污染物整体浓度分布符合湾顶较高、养殖区附近较高、混合区与口门区附近较低的特征;各污染因子中,相同水域的TN浓度最大,COD浓度稍小,而TP浓度则小于前两者约一个量级;落潮时,浓度等值线移向湾口,各单元区块污染物分布范围较涨潮时扩大,其中沥洋单元、青山单元和乐井洋单元的变化最显著;各污染因子中COD的变化最为明显,TN次之,TP的变化最小。

Based on Delft 3D,a two-dimensional hydrodynamic model and a pollutant diffusion model were established to compute the concentration of three major pollutants,including Chemical Oxygen Demand(COD),total concentration of nitrogen(TN),and total concentration of phosphorus(TP),in the Sanman Bay.Hydrodynamic results agreed well with the in-situ measurement.Therefore,the model well represented the hydrodynamic characteristics in the Sanmen Bay.According to the material transport characteristics,the Sanmen Bay was divided into 7 hydraulic units,including the Jiantiao-puba,Haiyoushepannan,Qingshan,Liyang,Lejingyang-shipu,mixing area and entrance area.Lagrangian tracer suggested that the material transport in each hydraulic unit was basically limited in its own unit.The distribution of pollutants concentration showed that there was high concentration near the top of the bay and cultivation area,while concentration in the mixing unit and entrance unit was comparably lower.Among all the pollution components,the concentration of TN was the largest,and that of COD was slightly smaller,while the concentration of TP was about one order of magnitude smaller than that of TN and COD in the same unit.During ebb tide,compared with spring tide,the concentration isoline moved to the bay mouth,and the distribution of pollutants concentration in each unit was enlarged,in which Liyang unit,Qingshan unit and Lejingyang unit showed the most significant change.Among the three main pollutants,the variability of COD concentration is the most obvious,followed by TN,while TP is the least.