Acta Geographica Sinica ›› 2017, Vol. 72 ›› Issue (5): 817-829.doi: 10.11821/dlxb201705005

• Climate Change and Surface Processes • Previous Articles     Next Articles

Mechanism of barrier river reaches in the middle and lower reaches of the Yangtze River

Xingying YOU1,2(), Jinwu TANG3, Xiaofeng ZHANG1, Yunping YANG4, Zhaohui WENG2, Zhaohua SUN1   

  1. 1. State Key Laboratory of Water Resource and Hydropower Engineering Science, Wuhan University, Wuhan 430072, China
    2. Hubei Provincial Water Resources and Hydropower Planning Survey and Design Institute, Wuhan 430064, China
    3. Changjiang Institute of Survey Planning Design and Research, Wuhan 430012, China
    4. Key Laboratory of Engineering Sediment, Tianjin Research Institute for Water Transport Engineering, Ministry of Transport, Tianjin 300456, China
  • Received:2016-08-15 Revised:2016-12-07 Online:2017-05-20 Published:2017-05-20
  • Supported by:
    The Key Program of National Natural Science Foundation of China, No.51379155;The National Key Technology R&D Program, No.2013BAB12B02-02;National Program on Key Research Project of China, No.2016YFC 0402306, No.2016YFC0402106;Fundamental Research Funds for Central Welfare Research Institutes, No.TKS160103

Abstract:

The channel in the middle and lower reaches of the Yangtze River is characterized by staggered distribution of the bifurcated channel and the single-thread channel. The amplitude of change of river regime is stronger in a bifurcated channel than in a single-thread channel. The adjustment of the river regime in the upper reaches usually propagates to the lower reaches through the migration of the main stream line and causes the riverbed evolution of the lower reaches. Whether the adjustment of the river regime in the bifurcated channel can pass through a single-thread channel and propagate to the lower reaches will affect the stability of the overall river regime. Studies show that the barrier river reach can block the upstream channel adjustment from propagating to the lower reaches; therefore, it plays a key role in stabilizing the river regime. This study investigates 34 single-thread channel reaches in the middle and lower reaches of the Yangtze River. On the basis of the systematic summary of the regularities of riverbed evolution in the middle and lower Yangtze River, the control factors of barrier river reach are summarized and extracted: the planar morphology of single-thread and meandering; no flow deflecting node in the upper or middle part of the river reach; the hydraulic geometric coefficient is less than 4; the longitudinal gradient is greater than 1.2?; the clay content of the concave bank is greater than 9.5%; the median diameter of the bed sediment is greater than 0.158 mm. Derived from the Navier-Stokes equation, the calculation formula of the bending radius of flow dynamic axis is deduced, and then the roles of these control factors in restricting the migration of the flow dynamic axis and shaping the barrier river reach are analyzed. The barrier river reach is considered as such when the ratio of the migration force of the flow dynamic axis to the constraining force of the channel boundary is less than 1 at different flow levels. The mechanism of the barrier river reach is such that even when the upstream river regime is adjusted, the channel boundary of this reach can constrain the migratory amplitude of the main stream line and centralize the planar position of the main stream line under different upstream river regime conditions, providing relatively stable incoming flow conditions for the lower reaches, thereby blocking the adjustment of upstream river regime from propagating to the lower reaches.

Key words: barrier river reaches, flow dynamic axis, channel boundary, the middle and lower reaches of the Yangtze River