Acta Geographica Sinica ›› 2018, Vol. 73 ›› Issue (7): 1352-1364.doi: 10.11821/dlxb201807013

• Earth Surface Process • Previous Articles     Next Articles

Evolution characteristics of the gravel-bedded anastomosing river at the Qihama reach in the First Great Bend of the Yellow River since 1990

GAO Chao1,2(),WANG Suiji1,2()   

  1. 1. Key Laboratory of Water Cycle and Related Land Surface Processes, Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing 100101, China
    2. College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China
  • Received:2017-06-05 Online:2018-07-25 Published:2018-07-13
  • Supported by:
    National Natural Science Foundation of China, No.41571005, No.41271027

Abstract:

The anastomosing river located at the First Great Bend of the Yellow River is different from other sand-bedded anastomosing rivers because of its gravel-bedded materials. So, it needs to be revealed whether its specific characteristics have a similarity with the sand-bedded anastomosing river, in terms of erosion and deposition, the stability of channel and interchannel wetlands, and so on. Based on four remote sensing images in 1990, 2001, 2013, and 2016 and two Google earth images in 2011 and 2013, combined with field sampling and observations, the Qihama anastomosing river reach with a main channel length of about 12 km was selected to analyze the variations of channel planforms and sedimentary characteristics in the period 1990-2016. The results show that the gravel-bedded anastomosing river has a high stability as a whole, and there is no obvious bank erosion and deposition for varied channels and wetlands. During the past 26 years, the anastomosing belt area increased by 2.43%, and the ratio of land to water area was close to 1:1. The number of wetlands increased gradually with the highest increasing rate of 62.16% due to the fragmentization of some small interchannel wetlands. Talweg migrated to the left or the right alternately in a long period of time, and the migration rate was relatively stable. Due to the influence of talweg migration, the change of islands in the main channel is large and the bank shift rate of the main channel was about 5 m/a. The network composed of secondary channels is very stable and the channel average migration rate was only about 1 m/a. The sediments in the bank columnar sections are mainly composed of fine sands or silts, and the clay content is relatively high. Besides, the grain-size distribution presents a multi-peak curve, which is little different from the muddy sediments in bank columnar sections of sand-bedded anastomosing rivers. However, the dense vegetation on the riparian and interchannel wetlands protects the anastomosing channels in the study river reach from being eroded, and maintains the stability of the channels, which is also an important factor contributing to high stability of the gravel-bedded anastomosing river system.

Key words: gravel-bedded anastomosing river, anastomosing belt, wetlands, talweg, sediments, Yellow River