冲积性河流河槽迁移改道演化机制及临界条件

Alluvial river channel suddenly migration and avulsion has ever brought unexpectedly disasters for human being. To the Yellow River as an example, constant supersaturating sediment make channel to be continuously silt. The secondary suspended river is growing seriously year by year nearly twenty years, which leads to a discussion whether the Lower Yellow River channel should be shifted. Although some researches in different levels have been done, it is still in dispute. What’s more, with the development of society and rising of wealth, the loss due to alluvial river channel suddenly migration becomes more and more, even beyond measure. So, it’s necessary to carry out a research on alluvial river channel evolution mechanism and critical indicators. Firstly, the general law of river channel evolution will be analyzed including length, slope, gradient and sinuosity etc. Secondly, alluvial river channel evolution experiment will be conducted, and then the river development evolution mechanism will be revealed. Finally, based on data from observation and test data, the critical state of channel migration will be defined. This project not only helps to understand the alluvial river natural evolution rule and adjustment mechanism deeply, but also has important theoretical significance and practical value to carry out river regulation and make rivers management strategy.

冲积性河流迁移改道曾经给人类造成灾难性后果。以黄河为例，持续的过饱和输沙使黄河下游河道不断淤积抬升，特别是近二十年日益严峻的二级悬河，再次引起人们对黄河下游河道改道与否的大讨论。对此，不少学者开展了不同层面的研究和有益探索，但至今仍无定论。更值得一提的是，随着生产力的快速发展和社会财富的不断积累，河流迁移改道所付出的代价和可能造成的经济损失无法估量。本项目拟在深入研究河道迁移改道的河长、河道纵比降、弯曲度等指标自然演化规律的基础上；通过理论研究，结合冲积性河流精细自塑模型试验，揭示河道发展演化机制和河槽迁移改道机理；结合原型实测资料和已有大型河工模型试验资料，界定河槽迁移改道的临界状态，建立冲积性河流迁移改道的临界条件。研究不但有助于加深对冲积性河流演化规律和河道调整机理的认识、丰富学科研究内容，而且对于河流治理方略的制定也具有重要的理论意义和实用价值。

冲积性河流河道的演化规律及调整机制是河流动力学界关注的焦点问题。冲积性河流河槽迁移改道是河流舍弃原来的部分或整个河道，形成新河道的过程。本项目以冲积性河流河槽迁移改道为研究对象，开展冲积性河流精细化自塑模型试验，引入突变理论，重点研究迁移改道过程中河道纵横比降和几何形态等参数的变化规律，提出河槽迁移改道的演化机理和临界条件。结果表明：（1）冲积性河流河槽经历了散流-归股-淤积-延伸-出汊-改道等一系列演化过程。历史时期黄河下游河道尤其是北宋河道和明清故道时期表现十分明显。现代黄河三角洲上河道也经历了类似的过程。（2）明晰了960-1938年黄河下游河患的时空变化特征，揭示了黄河下游河道的淤积过程存在着自上而下和自下而上两种形式。（3）分别构建了二维和三维河道不稳定性表达式，基于尖点突变模式和燕尾突变模式构建河道状态判别式，探寻冲积性河流河槽迁移改道的临界状态和条件。 当河流的弯曲系数大大超过或达到平衡曲面的取值，有改道的可能。研究成果为正确深入认识冲积性河流河槽的演化规律和调整机理提供了支撑，为制定河流长远治理方略提供了科学依据。.项目发表论文9篇，其中SCI/EI2篇，授权国家发明和实用新型专利2项；参加国际国内学术会议18人次，培养研究生3名，青年科技骨干人才3名，形成了一支从事河床演变的高水平研究团队。