河口泥沙输运在自然和人类驱动下的响应和源汇转化研究

The aims of the project are to study the sediment transport processes and source-sink transformation in response to interactions of natural processes and human activities in the Changjiang Estuary. The research uses innovative observation system and combines long-term observations and numerical modeling to answer questions of driven mechanisms for current and future sediment dynamics and potential morphdynamic adjustment in the estuary. The proposed studies include 1) evaluate sediment influxes into and out of the estuary based on long-term observations; quantify the spatial and temporal sediment division among the branches in the Changjiang Estuary using field observations and numerical modeling. Emphasis is placed on the change of sediment transport processes and estuarine adjustment in response to reducing sediment inflow and change of morphology due to local hydraulic engineering modifications. 2) understand the role of competitions between river flow and tidal currents interacting with estuarine bathymetry in controlling the dynamic field and sediment transport and its impact on source-sink transformation; study the influences of natural processes and human interventions on change of sediment dynamics and regime shifting between source and sink. 3) apply advanced in-situ instrument to study large-scale spatial sediment transport processes and sedimentation mechanisms for representative tidal flats with high accretion rate and active sedimentation regions with high sediment exchange rate. 4) use coupled hydrodynamic-sediment transport and estuary-morphdynamic models to study the individual roles of the natural processes and human interferences resulting in source-sink transformation. Diagnose correlations between change of upstream sediment sources and downstream source-sink transformation and determine dominant controlling factors; predict the future changes in the estuarine hydrodynamics and sediment transport in response to decrease of upstream sediment flux and increase of downstream human activities.

河口泥沙输运和源汇转化是陆海相互作用的核心科学问题。观察研究发现，长江河口在自然和高强度人类活动双重驱动下，河口段水沙交换敏感区含沙量明显降低，中值粒径减小，分布特征也有相应调整；而我们对自然、流域和河口工程导致水沙变化的主控机制尚未深入研究，对动力场变化与泥沙源汇转化的关系及演变趋势尚不明确。所以，本课题主要研究内容包括：1）还原进入河口的实有水沙通量；给出分汊河口控制断面水沙交换和泥沙场的变化量及其对大型水利工程的响应特征；2）揭示径流和潮流对河口水沙输运及源汇转化的主控机制和特征参数；辨析自然和人类驱动在水沙平衡格局变化中的作用权重；3）选取河口高交换潮滩和高交换水域，借助新技术，实施水沙输运和源汇转化敏感区观测研究；4）采用数值模型进行案例诊断分析，诠释河口泥沙场的源汇转化途径和机制；尝试量化自然和人类驱动的影响程度；预测河口泥沙输运过程演变和源汇转化趋势。

河口泥沙输运和源汇转化是陆海相互作用的核心科学问题。观察研究发现，长江河口在自然和高强度人类活动双重驱动下，河口段水沙交换敏感区含沙量明显降低，中值粒径减小，分布特征也有相应调整；而我们对自然、流域和河口工程导致水沙变化的主控机制尚未深入研究，对动力场变化与泥沙源汇转化的关系及演变趋势尚不明确。通过本课题研究工作，我们在1）河口水沙通量变化与泥沙场响应研究；2）分汊河口控制断面水沙变化及水动力场格局研究；3）河口高交换潮滩水沙输运及其人类活动响应案例研究和4）河口水沙运动的工程响应及源汇转化研究等方面取得进展。主要包括分析研究进入河口的实有水沙通量及其变化；给出分汊河口控制断面水沙变化量及其对大型水利工程的响应；揭示河口水沙输运及源汇转化的主控机制；选取河口高交换潮滩和高交换水域，借助新技术实施了水沙输运敏感区观测研究；采用数值模型进行案例诊断分析，诠释河口泥沙场的源汇转化途径和机制；量化了以深水航道工程为案例的人类驱动的影响程度。