水库下游弯曲河道水沙运动与滩槽演化互馈机制研究

In the research of river dynamics, water-sediment movement, evolution of shallow and chamfer in the curved river channel of the downstream reservoir is the key and difficult point. In traditional, many researchers consider that the discharge in drought period will increase and the mainstream will trend to be straight after the construction of dam Nevertheless, there is no unified understanding of the interaction mechanism between water-sediment movement and evolution of shallow and chamfer. A 50m×9m laboratory tank is used in this project. Firstly, the experiment of bed-forming process of curved rive is performed under typical curved river flow and sediment condition before storage of the three gorges project. An artificial curved river is formed in this procedure. Secondly, in the artificial curved river, the water and sediment movement characteristics of shallow and chamfer under the condition of equilibrium of sediment transport is studied, including flow resistance, distribution of secondary flow, momentum interaction of shallow and chamfer, distribution of sediment concentration and bed-load tracing experiment. Finally, on the basis of flow and sediment condition after the storage of the three gorges project, taking inlet run-off and different combination of sediment concentration into account, we study the impact of flow, sediment concentration distribution and water and sediment changes together successively. It will reveal the refactoring features of flow and sediment concentration distribution as the shallow and chamfer developing. The study of interaction mechanism between water-sediment movement and evolution of shallow and chamfer will provide some reference for the research on the curved river channel of the downstream reservoir.

水库下游弯曲河道水沙运动与滩槽演化是河流动力学的重要问题，长期以来一些学者认为水库修建后下游枯水期流量增加，主流趋直，是引起弯道滩槽变化（撇弯切滩）的主因，鉴于水沙和滩槽耦合影响的复杂性，水库下游弯道水沙运动与滩槽演化的互馈机制尚需进一步深入研究。本项目拟采用50m长×9m宽水槽，首先参考水库蓄水前水沙条件，开展弯曲河道造床过程试验，在室内形成自然弯曲小河；然后以此小河为对象，研究输沙平衡时滩槽水沙运动特性，包括水流阻力、二次流分布、滩槽动量交换、悬沙分布和推移质输移规律等；继而参考水库蓄水后水沙变化，考虑流量、含沙量不同组合，逐次开展流量、沙量和水沙共同变化对弯曲河道滩槽演化的影响研究，揭示水库下游弯道流速、挟沙力、含沙量和推移质输移随滩槽演化的重构特性和滩槽随水沙调整的变化趋势，阐释弯道水沙运动与滩槽演化的互馈机制，研究成果将丰富河床演变学相关内容，为水库下游弯曲河道深入研究提供依据。

弯曲河道具有迂回曲折的外形和蜿蜒蠕动的动态特征，其形成、发展和演变是受多种因素综合影响的复杂过程。弯曲河道独特的几何边界特征，使得弯曲河道的水沙运动特性和滩槽演变特性与其他类型河段显著不同。前人关于弯曲河道的水沙运动和滩槽演变规律做了大量的研究，也取得了丰富的成果。但前人的研究主要基于概化物理模型试验、原型观测资料分析和数值模拟，难以真实地反应边界条件相对自然的弯曲河道在整个形成和发展过程中的水沙运动特性和滩槽演变特性。本项目研究采用原型资料分析、概化水槽试验和理论研究相结合的方法，研究了弯曲河道造床过程、弯曲河道水沙运动特性以及水沙变化条件下弯曲河道滩槽演变特性。通过本项目研究，厘清了弯曲河道形成过程、平衡输沙与非平衡输沙（次饱和含沙水流）条件下弯曲河道水流运动、泥沙运动和滩槽演化规律，揭示了水库下游弯曲河道水沙运动随滩槽演化的重构特性，阐明了水库下游弯曲河道水沙运动与滩槽演化的互馈机制。本研究将为研究长江中下游弯曲河道滩槽演化互馈机制提供理论基础，为指导坝下游弯道的滩槽治理、航道保障、引水工程、堤防工程的建设提供技术支撑。