Acta Geographica Sinica ›› 2017, Vol. 72 ›› Issue (3): 420-431.doi: 10.11821/dlxb201703005

• Climate Change and Surface Processes • Previous Articles     Next Articles

The typical meandering river evolution adjustment and its driving mechanism in the downstream reach of TGR

Yongyang FAN1(), Wei ZHANG1(), Jianqiao HAN1,2, Mengqing YU1   

  1. 1. State Key Laboratory of Water Sources and Hydropower Engineering Sciences, Wuhan University,Wuhan 430072, China
    2. Northwest A & F University, Yangling 712100, Shaanxi, China
  • Received:2016-11-03 Revised:2017-01-25 Online:2017-03-15 Published:2017-03-15
  • Supported by:
    National Natural Science Foundation of China, No.51479146, No.51609096

Abstract:

The impoundment of huge reservoirs deeply changes the water and sediment process in the downstream reaches and then influences the evolution of the downstream rivers. The meandering rivers sensitively responded to the variation of water and sediment process. That is why the meandering rivers are the important survey regions of river evolution, channels regulation and flood control projects. Based on the measured hydrological and morphological data from 1996 to 2016, the evolution law and its driving mechanism of the typical meandering river in the downstream reaches of Three Gorges Reservoir (TGR) are studied. By building the relationship between the cross-sections variation and the influencing factors, the mechanism is well examined. The results show that (1) before the establishment of the Three Gorges Reservoir, the meandering rivers have two types of evolution laws named "Convex banks deposition and concave banks erosion" and "Convex banks erosion and concave banks deposition". After the impoundment of the great project, the meandering rivers are featured only by the latter type. (2) After the retaining of water and sediment of TGR since 2003, the low flow channel and bankfull channel in Lower Jingjiang River have been continually eroded and the erosed areas are found in the low shoal of convex banks. The phenomenon is mainly resulted from the variation of water flow and sediment transportation and also influenced by the upstream river region, riverbed boundaries and branches. (3) The growing process of flow discharge from low water to bankfull discharge can lead to the increase of sediment transport capacity. When no big flood of discharge over 35000 m3/s is observed after the impoundment of TGR, the duration of bankfull discharge (22000-25000 m3/s) decides the erosion or deposition of convex banks after the impoundment. When the number of lasting days of bankfull discharge (22000-25000 m3/s) exceeds 20, the convex banks will be eroded. The concentration of coarse sand decrease contributes to the improvement of strength of water.

Key words: downstream reaches of reservoirs, meandering river, evolution adjustment, driving mechanism, Lower Jingjiang River