长江中下游平滩流量对水沙条件变化的滞后响应

As an important integrated parameter to describe the morphological characteristic of channel form and evaluate flood carrying and sediment transport capacity of river channel, the bankfull discharge is one of the most important contents in fluvial processes research.Due to the altered flow and sediment regimes, the bankfull discharge in the middle and lower reaches of Yangtze River was noticeably adjusted in recent years, and resulted in negative influence to the navigation and river channel stability. However, the phenomenon of delayed response that existed in the bankfull discharge variation was neglected in the previous studies, and it is difficult to grasp the mechanism of bankfull discharge adjustment. In this study, combining the basic theory and measured data analysis, the middle and lower alluvial reaches of Yangtze River will be selected as sample and its processes and characteristics of bankfull discharge variation delayed response to the altered flow and sediment regimes will be illustrated. The delayed response model for bankfull discharge in the middle and lower reaches of Yangtze River will be established to describe the process of bankfull discharge adjustment due to the constantly altered flow and sediment regimes, and the calculation methods for key parameters of the model will be determinated. Afterwards, the bankfull discharge evolution process in recent years will be simulated, and the adjustment trend will be predicted as well for the middle and lower reaches of Yangtze River. This study not only has important academic significance to reveal the delayed response mechanism in fluvial processes, but also has great value of accurate grasp the bankfull discharge variation in the middle and lower reaches of Yangtze River.

平滩流量作为反映冲积河流河道形态和过流能力的重要参数，是河床演变学研究的重要内容之一。受水沙条件变化的影响，近年来长江中下游河道的平滩流量发生了较大变化，对河道的稳定性和航运等带来不利影响，但由于以往研究中没有考虑平滩流量变化过程中存在的滞后现象，很难把握平滩流量的变化规律。因此，本项目以长江中下游冲积河段为对象，通过实测资料分析和理论研究，阐明近年来长江中下游平滩流量变化对水沙条件变化的滞后响应过程和特点；分析水沙条件不断变化情况下平滩流量的调整模式，建立长江中下游平滩流量的滞后响应模型及其关键参数的计算方法；模拟计算长江中下游平滩流量演化过程，预测平滩流量的调整变化趋势。本研究不仅对揭示河床演变的滞后响应过程具有重要的学术意义，而且对准确把握长江中下游平滩流量的变化规律具有重要的实用价值。

冲积河流的水位与新生河漫滩相平时对应的流量称为平滩流量，相应的河道断面面积称为平滩面积，一般情况下，冲积河流的平滩流量与平滩面积具有很好的相关关系。由于平滩水位对应的水流流速大,输沙能力高,造床作用强，平滩流量和平滩面积是反映冲积河流河道形态特征的重要参数，也是反映水流造床能力和河道排洪输沙能力大小的重要指标，在河道治理和河流生态修复的工程实践中得到了广泛的应用。. 众所周知，河床演变是由水流与河床相互作用中的输沙不平衡所引起的，在水流与河床这对矛盾的两个方面中，来水来沙条件起着决定性作用。所以，平滩流量和平滩面积作为重要的河道形态特征和河槽过流能力指标，必然与上游来水来沙条件密切相关；此外，由于河床的冲淤需要一个时间过程，河床演变一般滞后于来水来沙条件的变化，滞后响应是冲积河流河床调整过程中的一种普遍现象。以往关于长江中下游河道河道横断面调整等河床演变的研究，多是侧重于河道的平衡状态，如造床流量与河相关系等，对于河床演变过程中的滞后现象认识不够，没有考虑滞后现象对平滩流量的影响，因此难以准确把握平滩流量的调整规律。. 本项目以长江中下游典型冲积河段为研究对象，广泛收集了系列水沙及断面资料，以冲积河流中的滞后响应现象为主线，分析了长江中下游河道断面调整对水沙变化的响应过程和特点，结果表明长江中下游河道断面调整不仅与当年的水沙条件有关，而且与前期一定时期内的水沙条件有关，是一定时期内的水沙条件累积作用的结果，考虑滞后现象建立了适合长江中下游的滞后响应模型，模拟了长江中下游典型水文断面在水沙变化后的演化过程，并预测了河道的调整变化趋势。本研究不仅对揭示河床演变的滞后响应过程具有重要的学术意义，也为研究长江中下游河床演变提供新的思路和方法，对准确把握长江中下游河道断面调整的变化规律具有重要的实用价值。