淤泥质海岸泥滩潮沟演变动力机制

Tidal flats and tidal creeks are geomorphic cells of tidal flat system. Mudflat creeks, developing in the middle and lower parts of most muddy flats, play key roles on flow and sediment exchange on tidal flats. The development and evolution of mudflat creeks have great influences on tidal flat geomorphology. It is significant for studying the evolution dynamic mechanisms of mudflat creeks to enrich the subjects of coastal dynamics and morphodynamics, and practically worthful to the flood drainage of sea-entering rivers, the construction of offshore navigation channels, especially the reclamation activities on intertidal flats as well. In this study, such methods as Remote Sensing analysis, observations in situ, flume experiments and numerical simulations are synthetically applied, and the temporal and spatial variations of current and sediment conditions are explored, as well as the primary dynamic factors and their contributions to mudflat creek incision. The correlations are built between upward infiltration flow and flood/ebb tide duration, water depth of high water level, sediment characteristics, as well as the correlations of pore water pressure. The erosion process and the stability of mudflat creek bank are discussed. The coupling model is built synthetically considering the erosion of mudflat creek bank, tidal current, sediment transport and seabed evolution. Based on the coupling model, the erosion and instability processes of mudflat creek bank are reproduced, as well as the evolution of mudflat creeks. The evolution dynamic mechanisms of mudflat creeks are brought forward.

潮面和潮沟是潮滩系统的两大重要地貌单元。泥滩潮沟普遍存在于淤泥质海岸潮滩的中下部，在潮滩上发挥着重要的输水、输沙作用，其发育及演变对于潮滩形态有重要的影响。泥滩潮沟演变动力机制研究，对于丰富海岸动力学、地貌动力学等学科内容具有重要的学科意义，同时，对于入海河道泄洪、外海航运通道建设，特别是滩涂围垦工程建设，具有重要的实用价值。本项目综合运用遥感分析、现场观测、水槽试验和数值模拟等手段，研究潮沟水沙动力时空变化特性，探明潮沟下切的关键动力因素及其对于潮沟下切的贡献，建立滩面反渗水量、孔隙水压力与涨落潮历时、高潮位时滩面水深、土壤特性间的定量关系，探究潮沟壁冲刷稳定机理，建立潮沟壁冲刷稳定、潮沟“水-沙-地貌演变”耦合模型，复演潮沟壁冲刷、失稳等演变过程，揭示泥滩潮沟演变动力机制。

潮滩滩面和潮沟是潮滩系统的两大重要地貌单元，其演变机制是海岸工程领域的重要内容。本项目通过逐月的滩面高程现场观测，揭示了潮滩横剖面的演变规律，全剖面自岸向海呈现出“稳定-淤积-稳定-淤积-冲刷”的双峰特征，各分带地貌演变过程具有明显的季节性差异；开发了潮滩一维剖面模型，探究了地下过程、植被对潮滩剖面形态演变的影响；建立了平面二维水动力、泥沙输运及潮滩地貌演变概化模型，探究了潮流、波浪、泥沙供给等因素及其季节性变化对潮滩演变过程的贡献机制。开展同步水沙过程观测，发现了潮滩上的极浅水过程包括涨潮初期和落潮后期两个阶段；在这两个阶段，滩面水深在10 cm量级，但此时流速梯度很大，含沙量很高，涨潮初期和落潮后期的流速、含沙量均存在显著的“脉冲”现象，前者是涨潮前锋带来的强烈悬沙效应，后者则是极浅水环境下薄层水流输沙的证据，这两个极浅水阶段的水动力特征对潮滩的微地貌形态的形成和塑造起到关键作用。开展潮沟下切水槽试验，研究潮沟下切的关键动力因素及潮差、涨落潮历时不对称、海平面上升其对于潮沟形成、发展的影响；建立潮沟壁冲刷稳定、潮沟“水-坍塌-地貌演变”耦合模型，复演了潮沟壁冲刷、失稳、塌落过程，阐明了潮沟边壁坍塌的机理，评估了潮沟边壁坍塌在潮沟边壁后退中的贡献率。本研究对于预测潮滩的演变趋势、提高海岸防护能力、促进海岸带资源开发与安全等具有重要理论意义和现实价值。