三峡工程运用后坝下游弯曲河道演变规律研究

Under the influnce of highly non-saturated sandy water, new characteristics are shown on the evolution of bending reach in downstream reservoir, such as beach continuous degradation, the movement to convex bank of the talweg and main channel, even the appearance of bend bypassing and shoal cutting, which results in a large adjustment of river regime and affects the control of basin flood, shipping security and the utilization of shoreline. This project adopts prototype observation, data analysis, theoretical explanation and physical model experiment to study a series of scientific problems, such as the water and sediment movement of bending river under the effect of highly non-saturated sandy water, the mechanism of convex beach degradation and the coupling mechanism of trough evolution. The complete data based on factors, such as water surface gradient, velocity, sediment concentration, bed load transport rate, bed composition and river terrain, can be obtained by prototype observation and physical model test of various water and sediment process combinations on Laijiapu bending reach, which is located in downstream reservoir, during flood, normal-water, low-water period. The research results will show the change law of velocity of curved river, re-distribution characteristics of sediment concentration with the adjustment of trough siltation and bedload transport in downstream reservoir, interpret dynamic factor of convex beach erosion and the coupling mechanism of the vertical and horizontal curve deformation, predict the evolution trend of Laijiapu bend with variation of water and sediment. These research findings not only enrich the theory of river evolvement but also give a basis for regulating the meandering river in downstream reservoir.

在严重次饱和含沙水流作用下，三峡水库下游弯曲河道的演变呈现新特点，边滩冲刷难以恢复，主河槽及深泓向凸岸侧偏移，严重会出现“切滩撇弯”现象，致使河势出现较大调整，影响其防洪、航运及岸线利用等。本项目拟通过原型观测、资料分析、理论阐释与实体模型试验相结合的研究方法，研究严重次饱和含沙水流作用下弯曲河道的水沙运动规律、边滩冲刷机理及滩槽演变的耦合机制等科学问题。通过三峡水库下游调关来家铺弯曲河段洪、中、枯水期的系统原型观测与多种水沙过程组合的实体模型试验，获取研究所需的水面比降、流速、含沙量、推移质输沙率、河床组成、河道地形等为分析要素的完整的基础数据；揭示水库下游弯道流速、含沙量随滩槽冲淤调整后的重分布特性及推移质输移规律，阐释凸岸边滩冲刷动力要素与弯道纵横向变形的耦合机制，预测水沙变化条件下调关来家铺河段的演变趋势。研究成果将丰富河床演变学的学科内容，也可为水库下游弯曲河道的治理提供依据。

在低含沙水流作用下，三峡水库下游弯曲河道演变呈现新特点，边滩冲刷不易恢复，主河槽及深泓向凸岸侧偏移，严重会出现切滩撇弯，致使河势出现较大调整，影响其防洪、航运及岸线利用等。本项目通过系统的原型观测获取调关莱家铺弯曲河段较完整的水沙运动及断面地形的基础数据，以实测资料与理论分析、数模计算与实体模型试验相结合的研究方法，综合研究了低含沙水流作用下弯曲河段的水沙运动规律、边滩冲刷机理及纵横向演变的耦合机制等科学问题，阐明了研究河段来水来沙变化特性，三峡水库下游典型弯曲河段流速、含沙量分布，推移质输沙率、水流动力轴线等随流量的变化规律与纵横向变形的耦合机制，揭示了弯道局部凸岸边滩冲刷凹岸深槽淤积的机理，预测了水沙变化条件下调关来家铺河段的演变趋势，提出了相应的河势控制方案。研究成果丰富了河床演变学的学科内容，可为三峡水库下游弯曲河道的治理提供参考依据。