分汊河段滩槽调整对水沙条件变化的响应机理研究

In numerous catchments throughout the world human intervention has strongly altered natural river dynamics, especially in recent decades. Dams and reservoirs constructed to generate hydroelectric power and flow diversions constitute the most common forms of intervention in fluvial systems, and each causes substantial changes to the flow and sediment regimes. Process-response may generate remarkable downstream anabranching channel changes, the different phenomenon of the main branch development and the secondary branch development appeared in many downstream anabranching channel. The most research have focused on the formation and development of anabranching channel, which cannot provide useful guidance for explain the catastrophic phenomenon appeared in the anabranching channel.Insufficient consideration of mechanical mechanism of hydrograph and boundary control factors to shape the configuration of channel and bar are the main limitations in previous research, the response mode of channel and bar configuration to the change of flow and sediment based on the energy balance cannot built. In this research project, using anabranching channel in the middle of the Yangtze River as example, with intensive investigation of data gained both from prototype, numerical simulation and generalized model. The main factor to cause the atastrophic phenomenon appeared in the anabranching channel is revealed by the progressive way of from macroscopic law and mechanical mechanism to energy balance. The response mode of channel and bar configuration to the change of flow and sediment is built. The result will not only help to develop the fluvial process theory, but also provide useful guidance for anabranching channel regulation.

随着人类对河流开发利用程度增强，众多大型水利枢纽的修建使得工程下游的水沙过程发生了较大变化，造成下游冲积型分汊河段滩槽演变出现了“主长支消”和“主消支长”的差异化调整现象。已有研究主要是针对天然分汊河道的形成原因及发育过程，对分汊河道滩槽调整差异化现象的主要原因尚无法解释。其关键原因在于各种水沙过程和边界形态因子塑造滩槽形态的力学机理未能得到系统揭示，基于能量平衡的滩槽形态特征对水沙条件变化响应模式未能建立。本项目拟以长江中游分汊河段为背景，在充分吸收河流地貌、河流动力学及河床演变学已有成果和研究手段基础上，以宏观规律-局部动力学机制-能量平衡关系这种层层递进的方式来确定造成分汊河段滩槽形态调整差异化的主控因素，构建能够全面描述分汊河段滩槽形态调整对水沙条件变化的响应模式，预期成果可以促进河床演变理论的发展，为分汊河道的治理提供理论依据和技术支撑。

大型水利枢纽的修建使得下游水沙过程发生了较大变化，造成下游冲积型分汊河段滩槽演变出现了“主长支消”和“主消支长”的差异化调整现象。已有研究主要是针对分汊河道的形成原因及发育过程，对分汊河道滩槽调整差异化现象的主要原因尚无法解释。本项目以长江中游典型分汊河段为背景，通过实测资料统计、理论分析、数学模型计算和概化模型试验等相结合的技术手段，进行了分汊河段滩槽冲淤调整规律、水沙过程和边界形态因子塑造滩槽形态的动力学机制研究以及能量耗散状态和滩槽稳定形态的关系研究。主要成果有：.(1)提出了一种基于水流动力横向分布的汊河属性分类方法：以水动力条件将汊道划分为枯水主流倾向汊道（第I类）、洪水主流倾向汊道（第II类），尽管三峡水库蓄水后长江中游分汊河道内“主长支消”、“主消支长”的演变现象并存，但都呈现了枯水倾向汊河发展速率大于洪水倾向汊河的调整过程。.(2)改进了综合阻力计算公式和分流比计算式，进而构建了物理机制更加完善的分汊河段水沙数学模型。.(3)明确了影响分汊河段滩槽调整的新水沙条件要素主要是不同径流过程离散度、来流挟沙饱和度条件、临界流量等：径流过程离散度的减小，来流挟沙饱和度的降低一般有利于弯曲分汊段主汊的冲刷发展；基于不同流量下的流速、切应力等水动力要素分布规律，提出存在两个临界流量，使低滩冲淤性质发生转换；漫滩洪水持续时间越长，越有利于洪水主流倾向汊河的发展，中小水持续时间越长，越有利于枯水主流倾向汊河的发展。.(4)建立了适用于描述分汊段能耗过程的计算模式；基于能耗指标变化特征，揭示了三峡水库蓄水后不同类型汊道调整机制，并明确了江心洲滩的存使得分汊河段整体的能量变化幅度较小，从而有利于分汊河段的滩槽格局保持相对稳定。.研究成果揭示了新水沙条件下分汊河道滩槽发生差异化调整的机理，促进了河床演变理论的发展，同时还为分汊河段趋势的预测及治理提供判断依据和技术支撑。