珠江磨刀门河波型河口细颗粒泥沙絮凝动力机制

Flocculation of fine sediment is important process and key linkage for sediment transportation and dispersion processes in an estuary, and is controlled by estuarine dynamic structure. A river and wave dominated estuary has special dynamic structure with the combined influences of river, tide and wave. The wave-current interaction and salinity stratification control the flocculation processes in a river and wave dominated estuary, but their influencing mechanisms require further research. Therefore, the flocculation of fine sediment in a river and wave dominated estuary is an important scientific issue about research on estuarine sediment movement. The Modaomen Estuary of the Pearl River, a typical river and wave dominated estuary, is selected as an ideal site to investigate the flocculation process of fine sediment. The simultaneous shipboard survey and instrumented bottom tripod measurement are continuously conducted to obtain data of floc properties and dynamic structure over a spring-neap cycle in the flood and dry seasons at a fixed mooring site outside of the sediment bar in the Modaomen Estuary, respectively. The processes of floc growth and floc settling are investigated. Effects of combined influence of river, tide and wave on flocculation process are examined, and the key factors influencing the flocculation of fine sediment are explored. And then the estimation method of floc settling velocity and flocculation mode of fine sediment are proposed to reveal the dynamic mechanism for flocculation of fine sediment in a river and wave dominated estuary. This study not only has important scientific implications for exploring the sediment dispersion and diffusion mechanisms in the river and wave dominated estuary, but also supplies guidelines for the comprehensive regulation and exploitation of navigation channel in the Modaomen Estuary.

细颗粒泥沙絮凝是河口泥沙输移扩散的重要过程和关键环节，河口动力结构是直接控制其过程的关键因子。河流波浪型（河波型）河口独特的动力结构以“径流-潮流-波浪”（径-潮-波）耦合为典型特征，其波流耦合、盐度层化等对絮凝过程起关键控制作用，但作用机制尚待研究。因此，河波型河口细颗粒泥沙絮凝是河口泥沙运动研究的重要科学问题。本项目选取珠江磨刀门河波型河口为研究区域，在拦门沙外侧布设一个固定观测点，同步采用船载和座底三脚架仪器观测方式，于洪枯季各进行大中小潮连续观测获取絮凝体及动力结构数据，研究细颗粒泥沙絮凝发育和絮凝沉降过程，分析“径-潮-波”耦合动力结构对絮凝过程的影响作用，确定关键影响因子，进而建立絮凝体沉速估算方法，构建河波型河口絮凝模型，揭示河波型河口细颗粒泥沙絮凝动力机制。该研究不仅对阐明河波型河口泥沙输移扩散机制具重要理论意义，而且为磨刀门河口整治规划及航道开发维护提供科学依据。

细颗粒泥沙絮凝是河口泥沙输移扩散的重要过程和关键环节，河口动力结构是直接控制其过程的关键因子。河流波浪型（河波型）河口独特的动力结构以“径流-潮流-波浪”（径-潮-波）耦合为典型特征，其波流耦合、盐度层化等对絮凝过程起关键控制作用，但作用机制尚待研究。项目以珠江磨刀门河波型河口为研究靶区，在了解珠江河口泥沙性质（源汇格局）变化基础上，基于多次磨刀门河口定点船载、三脚架及走航等方式获取的原型观测数据，揭示了河口絮凝体粒径、体积浓度和沉速等特性垂向和平面分布以及不同时间尺度（季节和潮周期）变化特征，通过分析不同因素对絮凝体特性的影响作用，揭示了波流耦合动力是控制河波型河口细颗粒泥沙絮凝体发育和絮凝沉降的主要因素，盐度层化可以抑制絮凝体垂向运动；在此基础上，构建表征水体紊动的指标，建立其与絮凝体粒径、沉速等参数间关系，建立了细颗粒泥沙絮凝模型和沉速估算方法，阐明了磨刀门河波型河口细颗粒泥沙絮凝动力机制。本项目执行期间，发表8篇高水平学术论文，其中SCI学术论文6篇，协助培养2名毕业研究生；研究成果针对河波型河口“径-潮-波”耦合的典型动力特征，揭示了该类河口细颗粒泥沙絮凝过程及动力机制，这不仅对阐明河波型河口泥沙输移扩散机制具重要理论意义，还可为磨刀门河口整治规划及航道开发维护提供科学依据。