浮泥作用下淤泥质潮滩动力演变机制研究

Tidal flats in the interface zone between land and sea are important nesting areas for biological communities and valuable potential land resources for coastal cities. The tidal flat profile and its evolution have attracted lots of attentions from the academia and among the engineers. Fluid mud, a characteristic feature near the bottom of mudflats, has strong interactions with flow and waves. It can switch the sediment exchange patterns in the water column and affect sedimentary processes of mudflats. However, the life cycle of the fluid mud and their quantitative influence on mudflat evolution are still not clarified. This study will employ physical experiments to investigate the interaction of fluid mud with flow and waves. By analyzing the movement and entrainment of fluid mud with water depth, flow velocity and wave parameters, the key factors controlling the movement and entrainment of fluid mud will be revealed, as well as the characters of wave damping and flow drag reduction. Fluid mud processes will be added in a morphodynamic model and two-way coupled with modules for wave, flow, sediment transport and bed evolution. The impact of fluid mud on the morphodynamics of tidal flat will be illuminated by analysis of the simulated wave attenuation, flow structure changes and sediment transport features. Extensive comparison of fluid mud life cycle and tidal flat changes under different scenarios of wave, flow, grain size and sediment concentration will be carried out for extracting a general evolution mode of mudflat under fluid mud. This study will supplement our knowledge of tidal flat evolution under fluid mud effects, and provide scientific support for comprehensive understanding the morphodynamics of tidal flat and improving the accuracy of morphological evolution modelling.

潮滩位于陆海相互作用的敏感地带，不仅是生物宝贵的栖息地，也是重要的土地储备资源，潮滩形态及其演变规律受到科学界和工程界的共同关注。浮泥是淤泥质潮滩近底层常见的一种泥沙运动形态，可与水动力相互作用、改变水体泥沙交换、影响潮滩沉积过程，但浮泥的生成-消亡及对潮滩演变的定量影响尚不明晰。本项目拟通过开展浮泥与波流动力相互作用的物理模型实验，研究浮泥运动及破坏与水深、流速、波浪要素的相关关系，揭示浮泥运动及消亡的关键控制因子，阐明浮泥削波和减阻规律；耦合浮泥模块与动力地貌模型，模拟分析波浪衰减、水流结构变化、泥沙输运特点，厘清浮泥对潮滩动力演变的调控机制；同时探明波浪、潮流、泥沙粒径、悬沙浓度等对浮泥生成-消亡周期和潮滩剖面变化的影响，最终提出浮泥作用下潮滩动力演变模式。本项目将补充浮泥作用下潮滩演变的基础知识，为全面了解潮滩演变规律、实现潮滩演变精准预测、保护潮滩抵御环境变化提供基础科学支持。

潮滩作为生物宝贵的栖息地和重要的土地储备资源，其形态和演变规律受到科学界和工程界的共同关注。浮泥是淤泥质潮滩近底层常见的一种泥沙运动形态，可与水动力相互作用、改变水体泥沙交换、影响潮滩沉积过程，但浮泥的生成-消亡及对潮滩演变的定量影响尚不明晰。本项目通过物理模型实验和数值模拟研究了浮泥生成-消亡与水动力间的相互作用，继而阐明了浮泥对潮滩动力演变的调控机制。主要结果如下：（1）浮泥界面运动导致波高衰减，水体紊动强度垂向分布最大值位置上移；浮泥被破坏后削波作用消失，高浊度水体紊动强度和流速呈垂向对称。（2）浮泥粘度是影响波浪衰减的主控因子，波浪在浮泥上的衰减速率也因水深和波浪环境变化而不同。由于浮泥对不同频率波浪吸收能力不同，波浪谱由外海传至近岸发生“频移”。（3）丰富的泥沙供给和弱动力环境是浮泥生成的必要条件，潮汐动力和泥沙沉降速度影响潮滩浮泥赋存位置。浮泥在自身重力影响下具有周期性流动和跨岸分布不均匀的特点。（4）波浪-水沙-浮泥运动耦合模型揭示了波浪引起的底部切应力增强是浮泥消亡的主要因素，但小浪通过增强水体紊动抑制潮滩浮泥持续淤积，可一定程度上降低潮滩浮泥流动性，维持其稳定。（5）由于浮泥的削波减阻作用，泥沙输入与地貌演变间正反馈关系增强，使潮滩在波浪环境中仍能处于淤涨状态，并加快了凸形剖面的形成。项目丰富了浮泥对淤泥质潮滩动力演变影响的知识，为保护潮滩抵御环境变化提供了基础科学支持。