长江口浅滩对河流来沙减少和大型河口工程的动力地貌响应

在河流输沙锐减和大型河口工程的影响下，长江口浅滩的动力地貌演化机理发生显著变化。本项目以长江口横沙浅滩为典型研究区，研究其地貌机理，关注不同时空尺度的两类人类活动影响，一是流域尺度（>50年的长时间尺度）的人类活动改变沉积物供给（系统边界条件），二是河口工程尺度（<30年的中短时间尺度）的人类活动改变局地水动力条件（系统内驱动力）。分析泥沙起动、悬浮、输运和沉降过程，探讨水下三角洲侵蚀为河口湿地淤涨提供沙源的可能。在时间尺度上注重横沙浅滩在河流高、低输沙率期、河口工程建设期和建成期的冲淤对比，在空间尺度上注重横沙浅滩与水下三角洲前缘（纵向上）以及九段沙（横向上）的冲淤对比，进而从物质和能量角度揭示河流输沙减少和大型河口工程对地貌演化影响的耦合机制，验证“水下三角洲侵蚀反哺湿地淤涨”的工作假说，为长江口的陆海统筹管理提供理论依据和技术支撑。

The morphodynamic evolution mechanism of shoals in the Yangtze Delta has changed much under the combined impacts of riverine sediment decline and major estuarine projects. This project will take the Hengsha Shallow Shoal in the Yangtze Delta as a typical research object to study the evolution mechanism. It will focus on two kinds of human activities in both temporal and spatial scales. The first is change in riverine sediment supply (system boundary condition) by human activities in the drainage basin (>50 years over a long time scale), and the second is change in local hydrodynamic conditions (system internal drive) by human activities of estuarine projects in the delta (<30 years over a short to medium time scale). The processes of sediment initiation, suspension, transport and settling will be analyzed to investigate the potential of sediment supply from subaqueous delta front to wetlands. In temporal scales, much attention will be paid on the comparisons of the Hengsha Shallow Shoal between the periods of high sediment flux, low sediment flux, estuarine projects’ construction, and post estuarine projects’ construction. In spatial scales, much attention will be paid on the comparisons between the Hengsha Shallow Shoal with the outer delta front (longitudinally) and with the Jiuduansha Shoal (transversely). Studies will be conducted from the view of material and energy, in order to reveal the coupling mechanism of riverine sediment decline and major estuarine projects on geomorphic evolution, verify the hypothesis that ‘erosion of subaqueous deltas can support wetlands’ expansion’, and provide theoretical reference and technical support for coordinated land and maritime management of the Yangtze Delta.