乐清湾悬沙输移机制分析

Study on the transport mechanism of suspended sediment in Yueqing Bay

以乐清湾海区特征测站实测资料为据,运用机制分解法将悬沙净输移通量分解成多个动力项并讨论不同区域悬沙输移的时空分布特征,认为潮泵输沙在湾内贡献均较大,在浅滩附近占明显优势,垂向净环流输沙在小潮期中、内湾作用显著,平流输沙在开阔水域及中湾深槽起主要作用。从余流分布、流速与含沙量的相位关系、垂向余流结构与悬沙浓度垂向梯度变化等方面探讨了主要输沙项的动力机制,结果表明:(1)欧拉余流输沙与潮动力强弱呈正相关;(2)潮汐捕集输沙与悬沙再悬浮、潮流不对称性及涨、落潮背景含沙量密切相关;(3)垂向净环流输沙与垂向拉格朗日余环流发育及悬沙浓度垂向梯度相关。

According to the measured field data in Yueqing Bay,the transport flux of suspended sediment in observed stations is divided into several dynamic items using the mechanism decomposition method,and the space-time distributional characteristics of suspended sediment transport is examined.It is indicated that the tidal pumping effect plays an important role in the bay and especially has a clear superiority in shallow regions.The vertical circulation causes prominent sediment transport in middle and inner bay during neap season,and the advection is the primary factor for sediment transport in deeper channels and open regions.Meanwhile,the dynamic mechanism of main items is discussed in terms of residual current distribution,the phase relationship between velocity and sediment concentration,the vertical residual current structure and the vertical gradient of sediment concentration.The conclusions could be made as following：（1） The Euler residual current effect is correlated positively with tidal power.（2） The tidal trapping effect has close linked with tidal dissymmetry,bottom sediment resuspended and the background concentration difference between spring and ebb tide.（3） The development of Lagrange vertical residual current and the vertical gradient of suspend sediment concentration are responsible for the net vertical circulation transport.