Recent bathymetric changes in the Changjiang Estuary under the influence of artificial regulation engineerings and basin reservoirs have been analyzed based on the maritime charts since 1997 and recent fieldworks. The...Recent bathymetric changes in the Changjiang Estuary under the influence of artificial regulation engineerings and basin reservoirs have been analyzed based on the maritime charts since 1997 and recent fieldworks. The results indicate a slight erosion of the channels in the upper and middle estuary, continuing deposition and seaward move of the mouth bar crest and intensifying erosion at the nearshore seabed. It is noteworthy that the morphological evolution caused by intensive human activities dominates over the changes from nature process. First, the riverbes are eroded overall in the South Branch （SB）, the South Channel （SC） and the upper and middle reaches of the North Channel （NC）. The nearshore seabed outside the river mouth is being eroded slightly, which is attributed to the declining sediment supply from the Changjiang Basin due to the construction of the Three Gorges Dam upstream. The sediment above the seabed is very active and coarsened, meanwhile, sand waves are becoming more distinct. Second, a deposition occurs in the North Brach （NB）, the mouth of the NC, the mouth bars of the North Passage （NP） and the South Passage （SP） and especially the main channel of the NP, where it shows a massive siltation after the deep waterway project. The reasons for the recent changes are not only the dynamic structure in estuarine mouth bars, but also the supply of sediment resuspension in a local and offshore area. Meanwhile, the severe erosion and siltation in some reaches is related to the construction of estuarine engineerings. It is indicated that the Changjiang Estuary is gradually self-adjusted and adapting to the varying natural factors and intensive human activities. The study on the mechanism of self-regulation of the recent bathymetric changes in the Changjiang Estuary has important and practical significance.展开更多
The mouth bar in the Yangtze estuarine waterways has a significant influence on navigational transport within the estuary, flood discharge and construction of the Shanghai Port. In this paper the morphological evoluti...The mouth bar in the Yangtze estuarine waterways has a significant influence on navigational transport within the estuary, flood discharge and construction of the Shanghai Port. In this paper the morphological evolution and mechanisms of mouth bar formation of the Yangtze estuarine waterways are studied by analyzing hundreds of years of historical data and the latest profile maps of some or the main mouth bar channels in the Yangtze Estuary. The results are shown as follows： The mouth bars in the North Branch have moved gradually from outside the mouth to the inside and formed a huge sand bar. In the North Channel, the head of the mouth bar has migrated about 30 kilometers downstream, and a channel bar has been developing since 2001. Two mouth bar tops, which always existed in the North Passage disappeared in 2010. The head of the mouth bar in the South Passage has migrated downstream about 14 km and the number of tops increased at first but is reduced to only one now. According to the results, we can conclude that the evolution of the mouth bars differs depending on their location. In the North Branch it is directly related to large-scale reclamation in Chongming Island, but in the North Passage it has a close relationship with regulation of the Yangtze Estuary Deepwater Channel. However, the evolution of mouth bars in the North Channel and South Passage is not only connected with the Yangtze Estuary Deepwater Channel Regulation Project, but also with the reclamation in the East Hengsha Shoal and the closure of the Qingcaosha Reservoir.展开更多
Observation data of along-estuary and lateral current velocities over a transect located at the South Channel of the Yangtze estuary was obtained during a spring tide in August 2011.Harmonic analysis was done on the c...Observation data of along-estuary and lateral current velocities over a transect located at the South Channel of the Yangtze estuary was obtained during a spring tide in August 2011.Harmonic analysis was done on the current velocities to get a mean component and a semi-diurnal component.Based on these two components,the driving mechanisms of mean lateral flow and M2 lateral tidal flow are shown and analyzed respectively.The dominant driving force of mean lateral flow is nonlinear advection and that of lateral M2 tidal flow is Coriolis force.The friction plays an important role near the bottom and surface for both lateral mean flow and M2 tidal flow.展开更多
The construction of channel regulation projects,reservoirs,and other human activities have led to significant changes in channel geometry and hydrodynamic conditions in mountainous macrotidal estuaries.However,their i...The construction of channel regulation projects,reservoirs,and other human activities have led to significant changes in channel geometry and hydrodynamic conditions in mountainous macrotidal estuaries.However,their impact on the long-term evolution of the turbidity maximum zone(TMZ)in these estuaries is still unclear.Therefore,the Minjiang Estuary(ME)was selected as the study area and using the Gabor filter and surface suspended sediment concentration(SSSC)data retrieved from GF PMS/WFV and Landsat-TM/ETM+/OLI images in the flood season from 1986 to 2020,the flow direction of Chuanshi Waterway,the spatiotemporal evolution characteristics of TMZ in the ME,and the influence of human activities on these were analyzed.The results indicate that during flood tides in the past 35 years,the TMZ was mainly distributed in sections from the Changmen to the Chuanshi and Meihua waterways.The construction of the Shuikou Reservoir caused the SSSC to decrease by 65 mg/L at the Chuanshi Tidal Gauge Station in the ME.The TMZ in the ME waterway channel notably migrated toward the sea due to the waterway regulation project,with the landward and seaward boundaries moving by 2.5 km and 3 km seaward,respectively.The main distribution area moved from Jinpaimen to the section from Chuanshi Waterway to the mouth of the ME.These variation characteristics were basically consistent with the annual average TMZ in the flood season.Through the interactions between nature and human interventions,the flow regime of the ME tended to converge in the flood season.Therefore,human activities have significantly impacted the long-term evolution of the TMZ in the ME.展开更多
基金The National Natural Science Foundation of China under contract Nos 51479074 and 41340044the Special Key Program of the Ministry of Science and Technology of China under contract No.2013FY112000
文摘Recent bathymetric changes in the Changjiang Estuary under the influence of artificial regulation engineerings and basin reservoirs have been analyzed based on the maritime charts since 1997 and recent fieldworks. The results indicate a slight erosion of the channels in the upper and middle estuary, continuing deposition and seaward move of the mouth bar crest and intensifying erosion at the nearshore seabed. It is noteworthy that the morphological evolution caused by intensive human activities dominates over the changes from nature process. First, the riverbes are eroded overall in the South Branch （SB）, the South Channel （SC） and the upper and middle reaches of the North Channel （NC）. The nearshore seabed outside the river mouth is being eroded slightly, which is attributed to the declining sediment supply from the Changjiang Basin due to the construction of the Three Gorges Dam upstream. The sediment above the seabed is very active and coarsened, meanwhile, sand waves are becoming more distinct. Second, a deposition occurs in the North Brach （NB）, the mouth of the NC, the mouth bars of the North Passage （NP） and the South Passage （SP） and especially the main channel of the NP, where it shows a massive siltation after the deep waterway project. The reasons for the recent changes are not only the dynamic structure in estuarine mouth bars, but also the supply of sediment resuspension in a local and offshore area. Meanwhile, the severe erosion and siltation in some reaches is related to the construction of estuarine engineerings. It is indicated that the Changjiang Estuary is gradually self-adjusted and adapting to the varying natural factors and intensive human activities. The study on the mechanism of self-regulation of the recent bathymetric changes in the Changjiang Estuary has important and practical significance.
基金National Natural Science Foundation of China,No.40776056Research Subject of Shanghai Association for Science ＆ Technology,No.10dzl210600Fund from the Ministry of Science and Technology of China for the State Key Laboratory of Esmarine and Coastal Research.No.2008KYYW01 Acknowledgements I am heartily grateful to Jiang Hong, Wang Dongmei, Yang Zhongyong, Ni Yizhuo and Tana for their help during the process of writing the article.
文摘The mouth bar in the Yangtze estuarine waterways has a significant influence on navigational transport within the estuary, flood discharge and construction of the Shanghai Port. In this paper the morphological evolution and mechanisms of mouth bar formation of the Yangtze estuarine waterways are studied by analyzing hundreds of years of historical data and the latest profile maps of some or the main mouth bar channels in the Yangtze Estuary. The results are shown as follows： The mouth bars in the North Branch have moved gradually from outside the mouth to the inside and formed a huge sand bar. In the North Channel, the head of the mouth bar has migrated about 30 kilometers downstream, and a channel bar has been developing since 2001. Two mouth bar tops, which always existed in the North Passage disappeared in 2010. The head of the mouth bar in the South Passage has migrated downstream about 14 km and the number of tops increased at first but is reduced to only one now. According to the results, we can conclude that the evolution of the mouth bars differs depending on their location. In the North Branch it is directly related to large-scale reclamation in Chongming Island, but in the North Passage it has a close relationship with regulation of the Yangtze Estuary Deepwater Channel. However, the evolution of mouth bars in the North Channel and South Passage is not only connected with the Yangtze Estuary Deepwater Channel Regulation Project, but also with the reclamation in the East Hengsha Shoal and the closure of the Qingcaosha Reservoir.
基金supported by the National Natural Science Foundation of China(Grant Nos.41340044,50939003)Joint Research Projects of Netherlands Organization for Scientific Research and the National Natural Science Foundation of China(Grant No.51061130544)
文摘Observation data of along-estuary and lateral current velocities over a transect located at the South Channel of the Yangtze estuary was obtained during a spring tide in August 2011.Harmonic analysis was done on the current velocities to get a mean component and a semi-diurnal component.Based on these two components,the driving mechanisms of mean lateral flow and M2 lateral tidal flow are shown and analyzed respectively.The dominant driving force of mean lateral flow is nonlinear advection and that of lateral M2 tidal flow is Coriolis force.The friction plays an important role near the bottom and surface for both lateral mean flow and M2 tidal flow.
基金National Natural Science Foundation of China–The Netherlands Organization for Scientific Research-Engineering and Physical Sciences Research Council(NSFC-NWO-EPSRC)No.51761135023。
文摘The construction of channel regulation projects,reservoirs,and other human activities have led to significant changes in channel geometry and hydrodynamic conditions in mountainous macrotidal estuaries.However,their impact on the long-term evolution of the turbidity maximum zone(TMZ)in these estuaries is still unclear.Therefore,the Minjiang Estuary(ME)was selected as the study area and using the Gabor filter and surface suspended sediment concentration(SSSC)data retrieved from GF PMS/WFV and Landsat-TM/ETM+/OLI images in the flood season from 1986 to 2020,the flow direction of Chuanshi Waterway,the spatiotemporal evolution characteristics of TMZ in the ME,and the influence of human activities on these were analyzed.The results indicate that during flood tides in the past 35 years,the TMZ was mainly distributed in sections from the Changmen to the Chuanshi and Meihua waterways.The construction of the Shuikou Reservoir caused the SSSC to decrease by 65 mg/L at the Chuanshi Tidal Gauge Station in the ME.The TMZ in the ME waterway channel notably migrated toward the sea due to the waterway regulation project,with the landward and seaward boundaries moving by 2.5 km and 3 km seaward,respectively.The main distribution area moved from Jinpaimen to the section from Chuanshi Waterway to the mouth of the ME.These variation characteristics were basically consistent with the annual average TMZ in the flood season.Through the interactions between nature and human interventions,the flow regime of the ME tended to converge in the flood season.Therefore,human activities have significantly impacted the long-term evolution of the TMZ in the ME.
