河口泥沙运动关键过程与滩槽格局转化研究

Estuaries and deltas play a profound role in land-ocean interactions, as on the one hand they are partially sediment sinks of river and on the other hand are sediment source to the shelf and ocean. As that sediment source to sink is an essential research question in estuary and coastal ocean studies. Nowadays river-supplied sediments to estuaries and deltas are decreasing world widely due reduced sediment yield and dam trapping in river basins, imposing severe threat on estuarine dynamics and associated erosion and deposition pattern. The Changjiang Estuary is such a system on the top of the risk list because of both dramatically reduced riverine sediment supply and intensive human activities in the estuary locally. The sediment transport dynamics and morphodynamics are disturbed by both natural processes and intensive human activities, whereas our understanding of their changing behavior and regime shift is poor. To that end in this project we aim to take the Changjiang Estuary as an example to explore 1) estuarine hydrodynamic adaptation to external changes with a focus on the nonlinear interactions between river-tidal dynamics and suspended sediment dynamics, 2) sediment transport regime changes in response to declined riverine sediment supply, and quantification of critical sediment transport parameters and sediment transport capacity, and 3) estuarine morphodynamic adaptation and the governing mechanisms. We also attempt to create models for examination of large scale estuarine morphodynamic evolution at varying time scales, in the aim to figure out how nature and human activities affect estuarine channel-shoal patterns, its regime shift threshold and the evolution in the future. The findings and outputs of this project will fill the knowledge gap regarding estuarine adaptation to external changes and provide insightful and scientific information needed for management purpose.

世界范围内的入海泥沙锐减，加剧了河口三角洲水沙输运变异和冲淤演变转化的进程，使得该区域人类生存环境面临严峻挑战，特别是我国大河河口三角洲已被列入高风险名单；在自然和高强度人类活动多重驱动下，以长江河口为代表的泥沙输运过程和滩槽演变格局，已呈现复杂的响应特征和明显的转变趋势，但我们对这些变化的定量表达及控制机理尚不清楚。据此，本重点基金旨在围绕河口泥沙输运的数量、变化及其归宿的关键过程，以“泥沙起动沉降参数化-输沙能力量化-滩槽格局转化”为主线，重点开展以下几个方面的研究工作：1）阐明泥沙运动与径潮流相互作用的非线性关系，探究减沙引发的动力场变化过程和机制；2）解析河口泥沙场对流域减沙的响应特征及变异过程，量化河口泥沙输运关键参数和输沙能力；3）揭示河口水沙变化及其滩槽格局的响应机制；4）研发河口冲淤演变的中长尺度模拟关键技术，诠释自然和人类驱动对河口滩槽格局的影响程度、转化阈值及演变趋势。

世界范围内的入海泥沙锐减，加速了河口三角洲水沙输运变异和冲淤演变转化的进程，使得该区域人类生存环境面临严峻挑战，特别是我国黄河、长江与珠江等大河三角洲已被列入全球高风险名单。在自然和高强度人类活动多重驱动下，以长江口为代表的大河河口泥沙输运过程和滩槽演变格局，已呈现复杂的响应特征和明显的转变趋势，但至今对上述变化的定量表达仍显匮乏，控制机理更未明晰。.本项目以“泥沙运动参数化-输沙能力量化-滩槽格局转化”为主线，聚焦河口泥沙输运和地貌演化的关键过程，开展多学科交叉与多技术融合的综合研究，取得了以下创新成果：1）阐明流域到河口的水沙变化过程和响应机制，揭示河口悬沙密度梯度对河口层化及环流结构的互馈机理；2）量化给出河口泥沙起动和侵蚀关键参数，发现细颗粒泥沙絮凝的物理-生物过程及藻类控制原理；3）揭示航道工程驱动下分汊河口环流结构转化和航道回淤机制；4）阐明河口滩槽系统“主槽窄深化、潮滩高淤低蚀、水下三角洲冲刷”的演变格局，厘清潮滩湿地“光滩-潮沟-盐沼”系统的相互作用；5）更新河口拦门沙对流域减沙的滞后响应认知，量化滞后时间尺度约为30年，预测了未来20年河口将呈现整体冲刷，其中减沙影响将显著大于海平面上升。.在长江、黄河与珠江河口三角洲开展了自主和联合观测共计16次，积累了丰富的水沙动力及地貌演变等现场资料。发表研究论文70余篇，其中SCI检索论文46篇。培养了一批优秀青年科技工作者及研究生，包括博士后5名，博、硕士研究生42名；广泛开展国内外学术合作交流，获批联合国海洋十年“大河三角洲”大科学计划，主持召开著名国际会议2次，项目团队成员在国际会议交流报告16次，中荷联合培养6名博士研究生；在科研成果、人才培养和国际交流等方面，推动了河口水沙动力及沉积地貌等学科发展。总的来说，本项目丰富了水沙运动及河床演变的理论，对河口的湿地保育、航运治理及水资源保护利用有重要科技支撑。