海岸与内陆架细颗粒沉积物重力流输运过程

Coastal and inner shelf sedimentary bodies are often characterized by clinoforms. On top of these clinoforms, waves, tidal currents and wind-induced currents may induce hyperpycnal near-bed layers with high fine suspended sediment concentration. These layers move downslope driven by the gravity force. The gravity-driven sediment transport constitutes an important part of the total transport on clinoforms. In this project, we intend to couple the theory of gravity-driven sediment transport into numerical modelling system, and develop a novel 3D numerical module for gravity-driven transport. Thereafter, under the guidance of the model predictions, in situ observations are carried out at proper sites and times to catch the episodic events of gravity-driven transport and measure detailed characters. Using the integrated methods of numerical modeling and in-situ observation, the project investigates the initiation, formation, and transport processes of the gravity-driven hyperpycnal flow, including: (1) the probability, initiating factors, sediment provenance, maintenance processes of the gravity-driven hyperpycnal flow; and (2) the size, internal structure, and transport capability of the gravity-driven transport, and the relative contributions of different external factors. The observations are used to improve the original theory, and the interactions of theory, modelling, and observations will enhance our understanding of coastal and inner shelf fine sediment gravity-driven transport processes. Thus, a new transport model can be established to build the theoretical framework on shallow water gravity-driven transport.

海岸与内陆架细颗粒沉积体往往具有倾斜地层（Clinoform）的特征，在此之上，波浪、潮流、海流作用下产生的近底部高浓度浮泥层会在重力驱动下向下坡输移，这种重力流输运构成了倾斜地层沉积物输运的重要组成。本项研究计划将重力流理论融入数值模拟平台，发展重力流输运三维数值模块，在其指导下以海底三脚架系统为核心开展长周期现场沉积动力观测，高效捕捉偶发的重力流输运过程，提高其观测的效率性和分辨率，研究其诱发形成（重力流输运的可能性、诱发因素、物质来源、维持机制）和输运过程（重力流的规模、内部结构、输运能力、各因素贡献），进而修正改进原有理论。通过理论—模型—观测—理论的多次交互循环，最终深化海岸和内陆架细颗粒沉积物重力流输运过程和机制的认识，建立新的输运模式，为构筑浅海重力流输运的理论框架打下基础。

海岸与内陆架细颗粒沉积体往往具有倾斜地层的特征，在此之上，波浪、潮流、海流作用下产生的近底部高浓度浮泥层会在重力驱动下向下坡输移，这种重力流输运构成了倾斜地层沉积物输运的重要组成。本项目以江苏中部海岸内陆架为研究区域，在野外现场观测、室内分析实验和数值模拟三个主要方面针对这一问题开展工作。野外现场观测方面，共开展了5次海上观测，其中冬季3次、夏季2次，利用多个底基三脚架观测系统和船载观测系统，同步观测流速、波浪、湍流、悬沙浓度、温盐度等参数，并采集水样和底床沉积物样品，完成了计划预定工作量。室内分析实验方面，完成了沉积物和悬沙样品的粒度分析和沉积物样品室内分析。数值模拟方面，基于Delft3D开源数值模拟系统，建立以江苏陆架-潮滩沉积物输运和地貌演化数值模型，并建立了垂向一维紊动-水动力模型，研究了悬沙浓度分层效应和沉积物重力流输运过程。研究发现细颗粒沉积物被波浪和潮流作用悬浮起来并在观测点汇聚，形成了约10 - 20 cm厚的底部浮泥层，在距底床10 cm处的悬沙浓度约为8 kg/m3。浮泥层一旦形成后会使水流结构剧烈改变，梯度Richardson数维持在临界值0.25上下，因此由浪流联合作用形成足够的紊动以维持浮泥的再悬浮。这一近底部高浓度浮泥层在重力驱动下向下坡方向输运。本项目的取得了一系列研究成果，共发表论文13篇。其中，在国际SCI杂志上发表论文12篇，中文核心论文1篇。