水沙锐减条件下游荡型河道迁移率及调整机理研究

The migration of wandering river is extremely sensitive and complicated. The river planform will change significantly due to altered incoming water-sediment conditions and boundaries. The mechanism of channel morphology adjustment is still not clear, particularly in wandering reach in Lower Yellow River. Quantitative research about the migration rates is relatively scarce, and there is no suitable model to make a prediction. So, based on the Topologically Constrained Transect Method (TCTM) within the GIS developed in 2003, the parameters of channel migration was messured. Firstly the river planform features in different period were analyzed, particularly about the migration rates after the operation of Xiaolangdi Resovior. And then the migration pattern and mechanism in sediment-laden river will be discovered. Furthermore, the project will develop an empirical model for predicting bend migration rates in wandering river in Lower Yellow River. The resulting equations will be test to predict maximum migration distance. Knowledge of migration rates is fundamental to the understanding of river landscape, especially in the development of floodplains. So, the output of the research results not only enrich the migration theory in sediment-laden stream, but also provide technical support for regulation of Lower Yellow River. The research has important academic meaning and practical value.

游荡型河道迁移摆动是极其敏感和复杂的，即当水沙条件乃至边界条件发生改变时，可能使得河道平面形态发生一些趋势性的变化。尤其是小浪底水库运用以来，黄河下游游荡型河段演变机理认识仍不清晰，河湾迁移的定量研究仍较少，也没有合适的经验模型进行预测。因此，本项目拟以基于GIS的TCTM技术为基础，精确提取黄河下游游荡型河道主流线迁移摆动参数，分析不同时期黄河下游游荡型河段河道迁移特征值，重点研究小浪底水库运用以来河道迁移规律。同时，以冲积性河流平衡理论为基础，深入揭示多沙河流河道迁移模式及调整机理，进而建立黄河下游游荡型河段河道迁移率模型，并进行检验。河道迁移率是研究河流地貌的基础，特别是河漫滩研究的基础。因此，本项目研究成果可丰富多沙河流河道迁移理论，并为黄河下游河道治理提供技术支撑，具有重要的学术意义和实用价值。

游荡型河道的河床演变是比较复杂，尤其是含沙量较高的黄河下游，受水库调控，下游两岸大堤和河道整治工程的影响，其演变更为复杂。本文即针对黄河下游游荡型河道的河道平面形态变化，尤其是主流线的迁移率开展了详尽的研究工作。研究结果表明，游荡型河道由于水沙和边界条件的改变，黄河下游游荡性河段的从60年代的心滩边滩遍布，且面积大，水面宽广的典型游荡性河道外型，转化为2016年，拥有弯曲型河道的外型，且弯曲系数增大，河湾半径减小，心滩边滩大幅消失，主流归顺统一的平面形态。发现河道河道能态越低，不平衡程度越强，河道实际比降越小于输沙平衡所需比降，即Jmin/Jc越大，则河道心滩边滩面积越大，弯曲系数越小，辫状强度越大。最后建立了黄河下游游荡型河段迁移率模型，建立了各河湾的迁移率M与汛期平均平流量之间的关系，并预测了小浪底转入正常运用期，主流线迁移率的可能变化范围。经对比，发现黄河下游与加拿大，等美国部分河流的迁移率模型有较大差异。后者是天然河道，且含沙量较低，主流线迁移率较小，因此，主流线迁移率M主要与河岸粘性含量和漫滩洪水发生次数有关。而黄河下游在完善的两岸工程约束下，汛期平均流量对其影响最大。本项目的研究成果，可为黄河下游河治理提供科技支撑，也丰富了多沙河流迁移率演变的理论成果。