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长江中游沙质河段床沙级配调整过程计算
李林林, 夏军强, 周美蓉, 邓珊珊, 王洪杨
武汉大学水资源与水电工程科学国家重点实验室
摘要:
三峡工程运用后,长江中游荆江河段持续冲刷,床沙与推移质、悬移质泥沙不断交换,从而造成该河段床沙发生不同程度的调整,对长江中下游河床演变及非平衡输沙机理的研究具有重要影响。在新水沙条件下,总结分析了沙波运动特性及床沙交换方式,引入Markov三态转移概率及非均匀沙隐暴系数,得到基于状态转移概率的沙质河段床沙级配调整的计算模型。研究结果表明:(1) 2009~2014年,沙市站年内床沙中值粒径(d50)有先增大后减小的趋势,而监利站年内床沙中值粒径则先减小后增大,且荆江河段年际床沙中值粒径(d50)总体呈上升趋势,粗化程度约为6.9%~9.3%;(2) 2009~2014年,沙市站床沙组成中d < 0.062mm的泥沙所占比重不变,0.062 < d < 0.25mm的泥沙所占比重逐年减少(累计减少11.4%),d > 0.25mm的泥沙所占比重逐年增加(累计增加11.4%),而监利站床沙组成均存在波动性变化;(3) 荆江河段床沙转换为推移质的概率随着泥沙粒径的增大而增大,床沙转换为悬移质的概率随着泥沙粒径的增大而减小,而推移质和悬移质转换为床沙的概率均随着泥沙粒径的增大而增大,河床发生冲刷粗化时泥沙输移的主要形式为悬移质(概率为81%~87%),而淤积细化时床沙补给主要来源于推移质(概率为8%~12%)。通过验证,本文概率模型的计算结果与实测资料符合较好,能够应用于长江中游沙质河段年际床沙粗化及年内床沙级配调整过程预报,为进一步开展三峡工程下游非均匀悬移质泥沙沿程恢复机理的研究提供理论基础。。
关键词:  床面冲淤  床沙调整  起动概率  沙波运动  荆江河段  长江中游
DOI:
分类号:
基金项目:国家自然科学基金项目(51725902; 51579186)
Adjustment of bed material composition in a sand-bed reach of the Middle Yangtze River
LI Linlin, XIA Junqiang, ZHOU Meirong, DENG Shanshan, WANG Hongyang
State Key Laboratory of Water Resources and Hydropower Engineering Science,Wuhan University
Abstract:
After the operation of the Three Gorges Project, the bed material in the Jingjiang Reach has suffered from adjustment in different degrees, and the bed material continuously exchanged with bed load and suspended load, which has a significant influence on the bed evolution and non-equilibrium sediment transport in local subreaches. In this study, the exchange of bed material and the movement of sand waves are firstly analyzed and improved, with the hiding-exposure effect and three-state transition probability of nonuniform sediment being considered; Finally, the equilibrium equation for calculating the grain size distribution in sand-bed reaches is proposed based on the threshold probability. These calculated results show that: (1) In 2009-2014, the annual process of median grain size d50 at Shashi firstly increased and then decreased, while the median grain size d50 at Jianli increased after decreasing; The composition of surface bed material in the Jingjiang Reach showed an upward increasing trend, and the coarsening degree was about 6.9%-9.3%; (2) The percentage of fine sand in bed material remained unchanged, and the medium sand decreased while the coarse sand increased from 2009 to 2014 at Shashi (the variation was about ±11.4%); There was a slight change in the composition of bed material at Jianli; (3) The transition probability from bed material to bed load increased with an increase of d, while the probability to suspended load decreased with it, and the probability from bed load and suspended load to bed material increased with an increase of d; The main form of sediment transport was the suspended load when riverbed scouring occurred (the probability was 81%-87%), and the supply of bed material mainly came from bed load when riverbed deposition occurred (the probability was 8%-12%). The probabilistic model developed in this study show reasonable agreement against the field observations at the Shashi and Jianli stations from 2009 to 2014, and it can also provide a theoretical basis for further studies on the mechanism of non-uniform suspended sediment recovery in the reach downstream of the Three Gorges Dam.
Key words:  bed evolution  adjustment of bed material  threshold probability  movement of sand waves  Jingjiang Reach  Middle Yangtze River
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