弱潮河口强波潮作用下潮滩演化过程和机制研究

Storm-induced strong current-wave activities are well known to cause drastic morphological changes in estuarine tidal flats particularly for microtidal estuaries, thus playing an important role in the morphological revolution of river deltas. Dense vegetation and muddy environment make it difficult to obtain high-solution tidal flat morphology data and the morphological impacts of storms on tidal flats are insufficiently studied. Moreover, the internal relationship between storm (strong hydrodynamics) and tidal flat evolution (significant erosion/deposition) is not completely understood. Attempt is made by a case study of tidal flats in the Yellow River Estuary (YRE), which is a typical microtidal environment and experiences several cold-wave storms every year. This work aims to: (a) accurately obtain large-scale and high-resolution morphological data in tidal flats by using terrestrial laser scanner and developing effective vegetation filtering methods. The filtering method is based on mathematical morphology, which validly filter vegetation by increasing window sizes of morphological filters and thresholds progressively; (b) unveil spatial and temporal morphological response of tidal flats to storm-induced hydrodynamics and quantify its role in tidal flat evolution; and (c) investigate storm-induced hydrodynamics and sediment transport in the “mudflat-creek-marsh” system based on field measurements, thus identifying the relationship between hydrodynamics and morphological change and unveiling the controlling mechanisms of morphodynamics in microtidal flats during storms. This work will contribute to high-resolution quantification of tidal flat morphological changes, advance the understanding of tidal flat morphodynamics in microtidal environments, and provide scientific supports for river delta management and coastal protection.

风暴引起的强波潮作用是河口潮滩尤其是弱潮河口潮滩演化的主要影响因素，对河口三角洲发育演变具有重要意义。由于潮滩宽广泥泞、植被密布，高精度潮滩地形数据难以获取，对风暴作用下潮滩如何演化尚缺乏定量认识；同时风暴（强波潮作用）和潮滩演变（显著冲淤）之间的内在联系仍存许多未知。本项目将以典型弱潮河口黄河口潮滩为例，重点研究：1）基于数学形态原理，采用过滤窗口与阈值同步增大算法，解决三维激光数据中矮小密集植被难以滤除问题，实现大面积高精度地形数据获取；2）基于高精度地形数据，量化风暴所致强波潮作用对黄河口潮滩演化的贡献；3）基于同步水沙动力数据，厘清强波潮作用下“光滩-潮沟-盐沼”系统内的泥沙起动、输移与沉降过程，量化波潮作用与潮滩演化之间关系，探明风暴影响下弱潮潮滩演化动力机制。本项目有助于推动潮滩演化高精度定量化研究，深化对弱潮河口潮滩演化规律与机理的认识，并为河口三角洲保护提供科学依据。

本项目聚焦河口海岸这一陆海相互作用关键区域，系统研究风暴过程在河口潮滩冲淤平衡、失衡及再平衡过程中的作用。结合高精度水沙动力过程、潮滩地形变化同步野外实测数据，揭示了不同类型河口潮滩尤其是弱潮河口潮滩演变对极端风暴天气响应特征与时间尺度，此外还量化了植被对潮滩演变的影响，完善了对河口潮滩生物-物理-地貌过程的认识。本项目以典型弱潮河口黄河口潮滩为例，采用野外现场观测、理论分析及室内试验等综合研究方法，主要研究成果包括：1）基于高精度潮滩地形数据与同步水沙动力过程数据，量化风暴所致强波潮作用对黄河口潮滩演化的贡献，探明了风暴影响下弱潮潮滩演化动力机制，并通过与长江口等其它类型河口潮滩进行对比，得出风暴对潮滩演变影响及其控制机制的普适性结论, 泥沙供给充沛与否是潮滩淤积或冲刷的决定因素，风暴则是潮滩泥沙重分配的重要动力因子；2）基于数学形态原理，采用过滤窗口与阈值同步增大算法，解决三维激光数据中矮小密集植被难以分类等问题，构建高精度潮滩数字高程与植被分布模型，揭示植被、流域来沙等季节性变化因子对河口潮滩演变的影响；3）基于现场观测数据探究了黄河口潮滩泥沙絮凝特征，发现水体紊动强度阈值是控制潮滩泥沙絮凝的关键因子，高于阈值促进泥沙絮凝，反之则抑制，补充了对弱潮河口潮滩泥沙絮凝特性及冲淤演变机制的认识。本项目有助于完善对风暴影响下河口潮滩系统演变过程及其控制机制的认识，为风暴影响下海岸带安全与社会经济发展提供科技支撑。