珠江西四口门盐水入侵数值模拟及分析

Numerical simulation and analysis of saltwater intrusion to four western watercourses of Pearl River estuary

采用非结构化三维近海及海洋有限体积模式(Finite Volume Coast and Ocean Model,FVCOM),对2003—2006年间的3个半月周期的珠江西四口门的盐水入侵现象进行了模拟计算。采用多个测站的水位和盐度的实测与模拟值的均方根、绝对平均误差和累积百分率对模型进行了检验。结果表明,其水位预测误差基本能控制在5%范围内,而盐度预测误差基本能控制在10%范围内;对磨刀门口门附近的涨、落潮流速与实测数据进行了对比,吻合较好。研究盐度空间分布发现,咸界的变化周期和潮汐运动规律相似,具有日周期和半月周期波动规律。垂向环流对小潮后盐度迅速上涨起到不可忽视的作用,且在垂向环流时盐水分层明显,盐度垂向梯度大;在小潮低潮位时磨刀门水道存在明显的盐水分层现象,而复杂的地形加剧盐水混合;盐通量变化规律与盐水的上溯规律一致,盐通量与潮通量呈正相关,相关性较好;盐通量与潮能通量呈负相关,且相关性较弱。

For better obtaining vast data and understanding the salt water movement to the estuary, the three-dimensional Finite-Volume Coastal Ocean Model （FVCOM） was used to simulate the salinity intru- sion to the four western watercourses of the Pearl River estuary under three semilunar conditions. The Root Mean Square Error （RMSE） and the mean absolute percentage error of simulated water level and salinity at multiple sites were verified by field observation data. The results show that the prediction error of the wa- ter level can be controlled within 5%, while the prediction error for salinity can be controlled within 10%. The numerical simulated flow velocity distribution near the entrance of Modaomen watercourse during rising and ebb tides were in good agreement with the measured data. It is acceptable and feasible to apply the FVCOM to simulate the salt water intrusion to the west four watercourses of the Pearl River. The results show that the salinity contour has the phenomenon of one high and one low values of salinity. The vertical circulating current promotes the salinity increasing quickly after neap tide. The salinity stratification is more obvious in the period of ebb tide than in the rising tide whether in the spring or neap tides because the complicated topography intensifies the salinity mixing. Salt fluxes reflect changes of salt into estuary, the change rules are close to the rules of salinity intrusion. In addition, the tidal energy flux is small in neap tides and large in spring tides. The salinity flux is in positive correlated to tidal flux; however, the salini- ty flux is negative related to tidal energy flux and the correlation is weak.