三峡运行后坝下游弯曲分汊河道演变规律研究

This research aims to investigate flow structures,sediment transport, and channel bed deformation in the bending braided rivers, with focus on the evolution of the diverging area，the interchange between bar and island , and the alteration between main-tributary channles. The research adopts a comprehensive method incorporating data mining, theoretical analysis, physical model, and numerical simulation. A series of parameters are used for analysis of the flow characteristics and channel evolution, including morphological index(plane form and cross section),velocity distribution, sediment concentration, grain size of suspended and bed material loads, and topographical features A new approach is proposed for physicl model design,which uses the gradient scale to quantify vertical scale with other scales being determined through test according to Qian Ning's physical model principle in which the resistance similarity of sand save is considered.An integrated system enables simultaneous,real-time measurement of velocity profile and sediment concentration, and the dynamic processes of river bed can also be monitored to construct 3-D topographical map. For typical sections in the bending braided river, the measurements provide basic data of velocity distribution,sediment concentration,and scour/deposition processes. Several key issues are then discussed for the Three Gorges Project after its impounding such as the variation of the main flow and sediment concentration distribution. Prediction is made of the developing trend of the Jianli braided river reach under changing flow and sediment discharges. The research will provide technical support for training, utilization and preservation of braided rivers and enrich our knowledge in fluvial process.

本项目将以实测资料分析和基础理论阐释为基础、以概化模型试验为主线、以数学模型计算为拓展的研究方法，以河道平面与断面形态指标、水沙过程与持续时间、流速、含沙量、悬移质与床沙级配及地形变化等为分析要素，研究弯曲分汊河段的水沙运动规律、分流区冲淤演变机理及滩槽演变的相互制约机制、主支汊变化过程及突变--缓变交替的临界条件等科学问题。提出了根据钱宁的模型设计原理，考虑沙波阻力相似，以比降比尺计算垂直比尺，进行探索性试验确定其它比尺的概化模型设计的新思路。测量和重构重点河段河床三维地形的动态变化过程，实现流速和含沙浓度垂线分布的同步实时测量。获取弯曲分汊河段典型断面的流速、含沙量、河床冲淤过程等基础数据；揭示三峡水库运行后弯曲分汊河段主流流路、含沙量分布随流量的变化规律，预测水沙变化条件下监利河段的演变趋势。研究成果将丰富河床演变学的学科内容，也可为弯曲分汊河道的治理开发与岸线保护提供技术支撑。

本项目采用原型观测资料分析、理论阐释、数学模型计算与概化模型试验相结合的技术手段，开展了三峡水库下游弯曲分汊河道水沙运动特性、水沙运动与滩槽演变的耦合机制及演变趋势研究，揭示了弯曲分汊河道水面比降、断面平均流速沿程变化、横断面流速分布、水流动力轴线、水流紊动强度及紊动能的变化规律，阐明了不同水沙条件下弯曲分汊河道悬移质泥沙与推移质泥沙运动特性，揭示了水沙与河道边界变化条件下弯曲分汊河道滩槽演变特性，以及水沙运动与滩槽演变的耦合机制，探讨了分流区悬移质含沙量分布与主流分布的异位现象与主支汊易位的演变模式，预测了来沙减少条件下弯曲分汊河道的演变趋势。研究成果不仅丰富了河床演变学中变化水沙条件下弯曲分汊河道水沙运动与演变规律等方面的内容，而且可为弯曲分汊河道的治理与保护提供科技支撑，具有重要的科学意义与实际应用价值。