Morphological evolution of the channel-shoal system in the South Channel of the Changjiang Estuary during 1958-2018: Causes and future trends |
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| Authors: | LUAN Hualong YAO Shiming QU Geng LEI Wentao |
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| Institution: | River Research Department, Changjiang River Scientific Research Institute, Wuhan 430010, China |
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| Abstract: | The stability of estuarine channel-shoal systems is important for port utilization, navigation maintenance, habitat protection and ecosystem service functions. This paper uses the South Channel of the Changjiang (Yangtze River) Estuary as a typical example to investigate the channel-shoal adjustment mechanism and its future trend. The combined approaches of bathymetric data analysis and process-based modeling (Delft3D) are applied. Quantitative analysis of morphological changes indicates that the South Channel experienced remarkable channel-shoal adjustment during 1958-2018. Periodic evolution was identified, including shoal migration, incision and emergence under natural conditions before the mid-1980s. Since then, fluvial sediment decline and local human intervention have interrupted the periodic processes. After 1986, as river sediment discharge started to decline, the South Channel converted to net erosion, and both the mid-channel shoal at the bifurcation node and the tail of the Ruifeng Shoal showed significant scour. Process-based hydrodynamic simulations revealed that the northern rotation of the mainstream downstream of Wusong triggered the erosion of the Ruifeng Shoal, while unordered sand mining at the shoal tail in approximately 2002 enhanced shoal shrinkage. In addition, the self-adjustment of the transverse section shape resulted in abnormal accretion in 2002-2007. Afterward, the South Channel underwent overall erosion as sediment discharge decreased to a low level (<150 Mt/a). Five stages of channel-shoal pattern adjustment and accretion/erosion status during the past 60 years were defined, i.e., the accretion stage (1958-1965), remarkable channel-shoal adjustment stage (1978-1986), slow erosion stage (1986-1997), shoal scour and shrinkage stage (1997-2007) and overall channel-shoal erosion stage (2007-2018). Model prediction of the evolutionary trend indicates that overall erosion within the South Channel is most likely to continue in 2015-2050. Further adjustment of the South Channel under extremely low sediment discharge may threaten the riverbed stability and the sustainable development of this large-scale estuary. Future work on adaptive strategies for varying conditions is recommended. |
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| Keywords: | channel-shoal pattern morphological evolution process-based modeling South Channel Changjiang Estuary |
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