Abstract
In China, the Lower Jingjiang Reach (LJR) of the Yangtze River could be one of the most complicated areas in terms of channel migration. The river had undergone many channel changes in the reach since the 18th century. Intensive human activities in recent decades, such as the construction of upstream dams and revetments, had directly affected the channel migration characteristics. The revetment would significantly diminish migration, whereas the reduced sediment caused by dams would increase bank erosion and bank failure risks. Satellite imageries of Landsat Multi Spectral Scanner (MSS), Thematic Mapper (TM), Enhanced Thematic Mapper Plus (ETM+) and Operational Land Imager (OLI) were employed to quantify the planform migration of the reach from 1983 to 2013 and to investigate the possible effect of human activities on the LJR channel evolution. Apart from the commonly used planform morphometric parameters, the migration direction was introduced to predict the future migration trends. Results showed that the LJR was gradually changing to a straighter channel, with sinuosity reducing from 2.09 to 1.9 and river length decreasing from 125.32 km to 113.31 km in the past 30 years. Planform morphometric parameters, such as migration rate of the channel centerline and erosion and deposition areas and rates, also decreased drastically in the past 30 years. The migration rate of the channel centerline decreased from 31.05 m·year−1 in 1983–1988 to 11.62 m·year−1 in 2009–2013. The lateral erosion and deposition areas decreased from 21.32 and 25.73 km2 in 1983–1988 to 4.83 and 5.83 km2 in 2009–2013. All of these findings indicate that the LJR tended to be in a steady state from 1983 to 2013 and was totally controlled by the bank revetments. However, the undercutting was strengthened because of the restrictive effect of revetments on lateral migration in the LJR. Moreover, the channel migrated to the left bank with a visible tendency as the total migration area to the left bank was approximately two times that of the right bank during the period. Consequently, the left bank of the LJR should be the focus of more attention in future migrations, and bank revetments of the left bank should be kept reinforced and adjusted with the change of water and sediment conditions.
Highlights
The dynamic change of river channels over time has been a major focus of study in geomorphology [1]
An evident restrictive effect of bank revetments on the bank lines was observed and the length of bank revetment in the left bank was similar to that of bank revetment in the right bank, the river channel still had a remarkable tendency to migrate to the left bank
The main conclusions derived from this study are as follows: (i) The planform morphometric parameters, including water surface area, river length, mean width and sinuosity, of the Lower Jingjiang Reach (LJR) during the period of 1983–2013 exhibited a generally decreasing trend
Summary
The dynamic change of river channels over time has been a major focus of study in geomorphology [1]. Cost-effective, multi-spectral and multi-temporal source of information, remote sensing has been extensively utilized to assess planform morphology change in many river basins Morphometric parameters, such as channel width [5,6], water surface area [7] and sinuosity [8], were calculated in several studies to evaluate the migration of channel planform morphology. Parameters of trajectory analysis to depict channel dynamics includes plan form characteristics (average width and length, water surface area, sinuosity) and channel migration parameters (channel migration area and rate, shift direction, lateral erosion and deposition area and rate) The former were directly measured parameters from the maps and the latter were derived parameters according to the migration analysis between two periods. The construction of the TGD (Figure 1), which is located in the upper stream approximately 300 km from the LJR, was often blamed for the increase in erosion
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