盐水楔河口絮凝体分布规律及控制因素——以珠江磨刀门为例

Distribution pattern of flocsand and its controlling factors in a saltwater-wedge estuary:A case study of the Modaomen Estuary of the Pearl(Zhujiang)River

细颗粒泥沙絮凝是影响河口泥沙输移扩散的关键过程,受控于河口复杂动力结构,其中河口水体层化环境下絮凝体空间分布规律亟待探究。针对该问题,本文基于2020年珠江磨刀门河口枯季大面积走航原型观测数据,分析磨刀门河口絮凝体时空分布特征,探究不同动力对其影响作用,揭示水体层化下絮凝体分布规律。结果表明,观测期间磨刀门河口絮凝体中值粒径介于1.87~395.53μm,体积浓度介于20.29~1 495.67μL/L;垂向上,中表层水体中值粒径多大于底层,平面上最大值多位于中心拦门沙和西侧。采用多峰分解方法可将磨刀门河口絮凝体分解为基本颗粒和絮凝核(统称微絮团)、小絮团、大絮团等组分,大絮团占比最大;总体来讲,中表层水体微絮团和小絮团体积浓度小于底层,底层大絮团体积浓度小于中表层。这与盐水楔河口动力结构密切相关,强盐度层化抑制絮凝体在各水层间的交换,导致表层水体大絮团占比远高于中底层,而底层絮凝体受湍流剪切强度影响,以解絮为主,小絮团和微絮团占比高。本研究不仅有助阐明复杂动力结构下细颗粒泥沙絮凝机制,也能为磨刀门河口拦门沙治理、水沙调控及航道疏浚等提供技术支撑。

Flocculation of fine sediments is a key process affecting sediment transport and dispersion in estuaries,which is controlled by complex dynamic structure of estuaries,and spatial distribution of flocs in a stratification condition needs to be explored.To solve this problem,in this study,based on the hydrology and sediment cruising observation in the Modaomen Estuary of the Pearl River during the dry season in 2020,spatial and temporal distri-bution of flocs in the Modaomen Estuary was analyzed,impacts of dynamics factors were investigated,and distribu-tion pattern of flocs in a stratification condition was uncovered.The results show that median floc size in the Modaomen Estuary during the observation period ranged from 1.87μm to 395.53μm,and volumetric concentration of flocs ranged from 20.29μL/L to 1495.67μL/L.Vertically,median floc size in the middle and surface layers was generally larger than that in the bottom layer.The plane distribution characteristic of the median floc size is that the maximum values generally occurred at the central bar and the west side.Decomposition of multimodal floc size dis-tributions indicates that the flocs in the Modaomen Estuary were composed of primary particles(Pp)and Flocculi(collectively known as Pico-flocs),microflocs(Micro),macroflocs(Macro),among which Macro was dominant.In view of vertical distribution,the volumetric concentration of Pico-flocs and Micro in the bottom layer tended to be larger than that in the surface and middle layers,while volumetric concentration of Macro in the surface and middle layers was generally larger than that in the bottom layer,which is closely related to dynamic structure in the salt wa-ter wedge estuary.Strong salinity stratification inhibited the exchange of flocs between different water layers,res-ulting in a relatively higher percentage of Macro in the surface layer than that in the middle and bottom layers.In the bottom layer flocs were affected by intensity of turbulent shear and deflocculation process was dominant.As a result,the percentage of Pico-flocs and Micro was higher than the surface and middle layers.This study is not only helpful to elucidate the flocculation mechanism of fine sediment under complex dynamics,but also provides tech-nical support for regulation of mouth bar,goverment of water and sediment,and channel dredging in the Modao-men Estuary.