基于河段尺度的坝下游河床演变分析方法及其应用

With the reservoir operation in an alluvial river, the downstream river below a dam usually experiences a long process of channel evolution in a long-distance reach. Previous analytical methods for fluvial processes mostly apply to river reaches under equilibrium or specified hydrometric sections in an alluvial river. Therefore, it is necessary to propose a reach-scale approach to investigating the fluvial processes of a river downstream of a dam. In this project, two typical downstream rivers are taken as study reaches, including the Middle Yangtze River and the Lower Yellow River, with the research methods of field inspection, analysis of observed data, and derivation of basic theory for fluvial processes being adopted, and a reach-scale analytical method for the downstream channel evolution is proposed, with its application in the typical downstream reaches also being conducted. A method is first proposed for calculating characteristic parameters for channel evolution at reach-scale, which can describe the downstream channel geometry as a whole, and the key morphological factor influencing the fluvial processes is then revealed, with the concept of reach-scale sediment transport capacity and the corresponding expression being presented. Based on the basic principle of fluvial processes, a conceptual model is developed for predicting the reach-scale channel evolution, and it will be used to quantitatively investigate the processes of macro channel adjustment in the downstream reaches below the dams of Xiaolangdi and Three Gorges, with the long trends of channel evolution of these reaches being predicted. Therefore, anticipated results obtained from this project not only can help to develop the basic theory of fluvial processes subject, and but also can provide the related reference to river regulation and flood control planning for downstream rivers.

冲积河流上修建水库后，必然会引起坝下游河床发生长距离、长时间的调整过程。以往河床演变分析方法多适用于平衡态河流或仅适用于特定的断面，因此需要采用基于河段尺度的分析方法来研究坝下游河床的调整规律。本项目拟以典型坝下游河流（黄河下游及长江中游）为研究对象，采用河道现场查勘、实测资料分析及河床演变基本理论推导相结合的研究方法，开展基于河段尺度的坝下游河床演变分析方法及其应用的研究。首先提出基于河段尺度的河床演变特征参数的计算方法，用于从整体上描述坝下游的河床形态特征；揭示影响坝下游河床冲淤的关键水沙因子，提出河段挟沙力的概念及相应表达式；从河床自动调整原理出发，建立基于河段尺度的河床演变概化模型，用于定量分析近期小浪底及三峡水库坝下游河床的宏观调整过程，并预测这些坝下游河段的长期演变趋势。因此预期成果不仅能发展河床演变学的基本理论，而且也能为坝下游河道整治及防洪规划等提供科技支撑。

冲积河流上修建水库后，改变了进入下游河道的水沙条件，必然会引起坝下游河流的再造床过程。这些坝下游河流的演变特点，将对防洪、航运、滩区土地利用等多方面带来一系列的影响。因此，研究并掌握坝下游河床的演变规律，具有十分重要的科学意义。本项目以典型坝下游河流（黄河下游及长江中游）为研究对象，采用河道现场查勘、实测资料分析及河床演变基本理论推导相结合的研究方法，开展了基于河段尺度的坝下游河床演变分析方法及其应用的研究。首先提出了基于河段尺度的坝下游河床演变特征参数的计算方法，计算了河段平均的河床特征参数，用于从整体上描述坝下游的河床形态特征；同时揭示了影响坝下游河床冲淤的关键水沙因子，并建立了河段挟沙力的计算方法和河段平均冲淤强度指标，该指标可以较好地反映河段在一定水沙及地形条件下的冲淤趋势，为河段冲淤过程预测提供了依据；然后从河床自动调整原理出发，建立了基于河段尺度的坝下游河床演变概化模型，用于定量分析近期小浪底及三峡工程下游河床的宏观调整过程，可较好地反映各河床演变特征参数随进、出口及河床边界条件改变的调整趋势。项目负责人于2017年获批国家杰出青年科学基金资助；2018年获得科技部“中青年科技创新领军人才”称号；2018年获得国务院政府特殊津贴。此外还获省部级一、二等科技奖励3项（1项二等奖排名第1；2项一等奖排名第2、4）及第13届钱宁泥沙科学技术奖。共培养水力学及河流动力学方向的硕博研究生11名，其中博士研究生5名，硕士研究生6名；出版和待出版(已交稿)专著各1部；取得软件著作权3项；获批国家发明专利3项；发表相关学术论文47篇，其中SCI收录19篇，EI收录17篇。本项研究成果不仅丰富了河床演变学的基础理论，而且还能为坝下游河流的河道整治及防洪规划等提供科技支撑。