长江中游守护型控导工程改善航道条件的机理研究

After the impoundment of the Three Gorges Project, the sediment transport volume in the middle reach of the Yangtze River reduces sharply, and the water released from the reservoir is nearly sediment-free. The practices of waterway regulation in recent decades indicate that, through protecting and controlling some beneficial river regimes, the released clear water could scour the downstream channels, then the waterway would be improved under the condition of impoundment. However, well-interpreted expression is absent for the motivational and internal mechanisms of the regulation works improving the waterway. The method combining the prototype data analysis, generalized flume experiments and theoretical research was adopted in this study. Through the investigations of the temporal and spatial variations of the fluvial hydromorphology in the process of reconstructing balance and the couple effects of the transversal and longitudinal deformations in the process of bed-rebuilding for the middle reach of the Yangtze River, the preliminary results of previous theory research were extended with consideration of the temporal and spatial variations of the fluvial hydromorphology relation and regionally local variations, so as to reveal systematically the rationality of experienced knowledge, and propose explicitly the quantitative relationship between the expected waterway depth and the range of regulation works. It is expected the theoretical system about the mechanisms of the protective regulation works improving the waterway under the new water-sediment conditions in the middle reach of the Yangtze River would be formed. This research provides a theoretical basis for the laws and the tendency predictions of the riverbed evolution in the downstream navigation channel, a technical support for the parameter determines of the waterway regulation in the middle and lower reaches of the Yangtze River and a theoretical support for waterway upgrading in the constructions of the Yangtze Economic Zone.

三峡工程蓄水运用后，长江中游来沙量大幅减少，接近“清水下泄”。近十几年的航道整治实践表明，在三峡工程运行条件下，通过守护控制有利的洲滩形态，“清水下泄”就能较好的发挥其冲槽作用，改善航道条件，但控导工程改善航道条件的动力机制和内在机理缺乏理论上的完整表述。本研究拟采用原型资料分析、概化水槽试验和理论研究相结合的方法，通过对长江中游河道再重建平衡过程中河相关系时空变化特点、河道再造床过程中横向和纵向变形的耦合作用关系开展研究，将前期理论研究初步成果延伸考虑河相关系时空变化和区域性局部变化等因素，以达到系统揭示经验性认识的合理性，明确航道水深目标与控导工程范围的定量表达，预期形成新水沙条件下长江中游守护型控导工程改善航道条件机理的理论体系。本研究将为枢纽下游河道演变规律及趋势预测提供理论依据，为长江中下游航道整治参数确定提供技术支持，为长江经济带建设中航道等级的提升提供理论支撑。

本项目对长江中下游“清水下泄”条件下，守护型工程改善航道条件的机理进行了研究。采用原型资料分析、理论研究、模型试验和数值模拟相结合的方法，通过对长江中游河段宏观河相关系发展规律认识、河道再造床过程中横向和纵向变形耦合关系研究的基础上，运用河流动力学理论，研究了航道水深目标与守控工程范围的定量表达，其中对于横向限制性守护工程控制，探索了通过控制河床横向变形、减少洲塌滩冲横向补沙、加大浅区纵向清水冲刷、可实现航道条件的最大程度；对于纵向限制性守护工程，提出通过扩大丁坝护底形成一定范围内的免冲河床，以尽可能压缩无效冲刷的范围，使得航槽内的流速增加，提高丁坝的冲刷效率，赋予护底一定的整治功能的思路和方法，创新性地提出了基于提高航槽冲刷效率的丁坝护底范围确定方法。本研究将为枢纽下游河道演变规律及趋势预测提供理论依据，为长江中下游航道整治参数确定提供技术支持，为长江经济带建设中航道等级的提升提供理论支撑。

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