珠江口洪季最大浑浊带的大小潮变化与机制分析

Spring-neap tidal variation and mechanism analysis of the maximum turbidity in the Pearl River Estuary during flood season

基于ROMS三维模型,模拟了珠江口洪季最大浑浊带的轴、侧向分布和大、小潮变化。模拟结果表明,珠江口伶仃洋最大浑浊带的轴向位置在22.3°—22.45°N之间,并随着潮流变化而周期性上下游迁移。控制最大浑浊带形成的主要因素是余流作用下的底层泥沙辐聚,决定最大浑浊带位置的主要因素是水平对流输沙,泥沙来源主要是上游浅滩沉积物的再悬浮。小潮期间堆积在浅滩的细颗粒沉积物在大潮期间被悬浮,搬运到下游的滞流点位置,在中滩南部和西滩外缘落淤。“潮泵”作用在大潮期间将泥沙向下游输运,在小潮期间向上游输运;垂向剪切作用则有利于悬浮泥沙的陆向输运;二者共同作用产生泥沙辐聚,形成最大浑浊带。大、小潮期间余流结构差异不大,主要由密度差和潮汐混合不对称共同导致,其中前者贡献更大。

The spring-neap tidal variation of the estuarine turbidity maximum(ETM)in the Pearl River Estuary(PRE)is studied,using the Regional Ocean Modeling System(ROMS).The longitudinal and lateral distribution of suspended sediment concentration(SSC)shows that the ETM is located between 22.3°–22.45°N and varies with flood and ebb tides.The main mechanism on the ETM formation is the bottom convergence generated by residual current.The location of the ETM is determined by horizontal advection.The sediment source is resuspended sediment on the shoal during spring tides.The fine sediment deposited on the shoal during neap tides is resuspended and transported downstream to the stagnation point during spring tides,and then trapped on the west shoal.The tidal pumping effect can transport suspended sediment seaward(landward)during spring(neap)tides,while the vertical shear always transports suspended sediment landward,both leading to the convergence of sediment in the ETM.The decomposition of residual current shows that the bottom landward residual flow is mainly induced by density difference,followed by asymmetric tidal-mixing.Moreover,there is little difference in residual currents between spring and neap tides.