人类活动影响下的长江水下三角洲地貌动力系统状态转换

人新世地球科学研究的重点和难点之一是人类活动的定量化。过去几十年里，由于相对海面上升和长江入海沉积物减少，长江水下三角洲正在发生由淤涨向蚀退的系统状态转化，人类活动成为影响长江水下三角洲地貌动力系统状态的活跃且重要的因素。现代长江口的人类活动形式多样、规模可观，但是其作用强度和沉积与地貌效应等问题尚不明确。本项目运用现场观测、数值模拟和情景预测等方法，对河口整治工程、深水航道疏浚和潮滩围垦所反映的边界条件与地貌格局调整、沉积物再分配与捕获效应进行参数化，在此基础上分析沉积物活动时间与活动层物质总量、滞留系数与滞留时间，从沉积物供应量、沉积量与逸出量的角度全面了解长江水下三角洲的源汇格局，了解长江水下三角洲地貌动力系统的状态并预测其演化。开展此项研究，对于回答人类营力的作用强度和效应等科学问题，丰富地貌动力学和沉积动力学的研究内容，辅助长江三角洲可持续发展战略的决策，具有理论和实践价值。

Quantification of anthropogenic activities is one of the important and difficult problems faced by earth science researchers. In the latest decades, anthropogenic activities in Changjiang drainage basin (such as dam construction) and Changjiang Delta (such as urbanization and groundwater pumping), along with global warming,have led to a significant decrease in sediment flux into the estuary as well as accelerating relative sea-level rise. As a consequence, these activities and changes brought about regime shift in the Changjiang subaqueous delta.morphodynamic system from progradation to retreat. Moreover, the cumulative effects of human activities in Changjiang Subaqueous Delta become much more active and comparable to natural dynamic process in terms of magnitude. Therefore, sedimentary and geomorphological effects caused by anthropogenic activities could be identified unprecedentedly. This project focus on human activities and their environmental impacts, including sedimdent partition caused by dredging along deep-water channel, sediment trap caused by sea dyke construction and reclamation over tidal flat, and mophological pattern changes caused by estuarine regulation projects. In-situ observations, physical process-based numerical modelling and state-behavior-based conceptual modelling will be adopted in this research, and the stability and mobility of sediment and sediment retention index, the overall pattern of source-sink, the balance and budget of sediment, as well as the future geomorphological state of Changjiang subaqueous delta, will be evaluated and predicted. With large river deltas being the important base of human civilization in Anthropocene, this study attempts to quantify the strength of anthropogenic effects, to enrich research content of geomorphodynamics and sediment dynamics, and further to support scientific decision-making concerning a sustainable development of the Changjiang Delta.