摘要
The morphological changing trend of the Yangtze Estuary, the largest estuary of Asia, has become a focus of research in recent years. Based on a long series of topographic data from 1950 to 2015, this paper studied the erosion-deposition pattern of the entire Yangtze Estuary. An alternation between erosion and deposition was found during the past 65 years, which was in correspondence to the alternation between flood and dry periods identified by multi-year average duration days of high-level water flow (defined as discharge ≥ 60,000 m<sup>3</sup>/s, namely, D<sub>≥60,000</sub>) from the Yangtze River Basin. A quantitative relationship was further developed between the erosional/depositional rate of the Yangtze Estuary and the interpreting variables of yearly water discharge, D<sub>≥60,000</sub> and yearly river sediment load, with contributing rates of 1%, 59% and 40%, respectively. Mechanism behind the alternate erosion and deposition pattern was analyzed by examining residual water surface slope and the corresponding capacity of sediment transport in flood and dry periods. In flood periods, a larger discharge results in steeper slope of residual water level which permits a greater capacity of sediment transport. Therefore, more bed materials can be washed to the sea, leading to erosion of the estuary. In contrast, flatter slope of residual water level occurs in dry periods, and deposition dominates the estuarine area due to the decreased capacity of sediment transport and the increased backwater effect of flood-tide. Coastal dynamics and estuarine engineering projects alter the local morphological changes, but slightly affect the total erosional/depositional rate of the whole estuarine region. Heavy sedimentation within the Yangtze Estuary after the impoundment of the Three Gorges Dam can be attributed to the reduced occurrence frequency of flood years due to water regulation by the dam, and largely (at least 36%-52%) sourced from the sea. Deposition is still possible to occur in the Yangtze Estuary in the future, because the multi-year average D<sub>≥60,000</sub> is unlikely to exceed the critical value of 14 days/yr which corresponds to the future equilibrium state of the Yangtze Estuary, under the water regulation of the large cascade dams in the upper Yangtze. Nevertheless, the mean depositional rate will not surpass the peak value of the past years, since the total sediment load entering the Yangtze Estuary has presented a decreasing trend.
The morphological changing trend of the Yangtze Estuary,the largest estuary of Asia,has become a focus of research in recent years.Based on a long series of topographic data from 1950 to 2015,this paper studied the erosion-deposition pattern of the entire Yangtze Estuary.An alternation between erosion and deposition was found during the past 65 years,which was in correspondence to the alternation between flood and dry periods identified by multi-year average duration days of high-level water flow(defined as discharge≥60,000 m 3/s,namely,D≥60,000)from the Yangtze River Basin.A quantitative relationship was further developed between the erosional/depositional rate of the Yangtze Estuary and the interpreting variables of yearly water discharge,D≥60,000 and yearly river sediment load,with contributing rates of 1%,59%and 40%,respectively.Mechanism behind the alternate erosion and deposition pattern was analyzed by examining residual water surface slope and the corresponding capacity of sediment transport in flood and dry periods.In flood periods,a larger discharge results in steeper slope of residual water level which permits a greater capacity of sediment transport.Therefore,more bed materials can be washed to the sea,leading to erosion of the estuary.In contrast,flatter slope of residual water level occurs in dry periods,and deposition dominates the estuarine area due to the decreased capacity of sediment transport and the increased backwater effect of flood-tide.Coastal dynamics and estuarine engineering projects alter the local morphological changes,but slightly affect the total erosional/depositional rate of the whole estuarine region.Heavy sedimentation within the Yangtze Estuary after the impoundment of the Three Gorges Dam can be attributed to the reduced occurrence frequency of flood years due to water regulation by the dam,and largely(at least 36%-52%)sourced from the sea.Deposition is still possible to occur in the Yangtze Estuary in the future,because the multi-year average D≥60,000 is unlikely to exceed the critical value of 14 days/yr which corresponds to the future equilibrium state of the Yangtze Estuary,under the water regulation of the large cascade dams in the upper Yangtze.Nevertheless,the mean depositional rate will not surpass the peak value of the past years,since the total sediment load entering the Yangtze Estuary has presented a decreasing trend.
作者
ZHU Boyuan
LI Yitian
YUE Yao
YANG Yunping
LIANG Enhang
ZHANG Chuncai
BORTHWICK Alistair G.L.
朱博渊;李义天;岳遥;杨云平;梁恩航;张春财;BORTHWICK Alistair G.L.(School of Hydraulic Engineering,Changsha University of Science&Technology,Changsha 410114,China;Key Laboratory of Water-Sediment Sciences and Water Disaster Prevention of Hunan Province,Changsha 410114,China;School of Water Resources and Hydropower Engineering,State Key Laboratory of Water Resources and Hydropower Engineering Science,Wuhan University,Wuhan 430072,China;Key Laboratory of Engineering Sediment,Tianjin Research Institute for Water Transport Engineering,Ministry of Transport,Tianjin 300456,China;The Key Laboratory of Water and Sediment Sciences,Ministry of Education,College of Environmental Sciences and Engineering,Peking University,Beijing 100871,China;School of Engineering,The University of Edinburgh,The King’s Buildings,Edinburgh EH93JL,UK)
基金
Youth Project of National Natural Science Foundation of China,No.41601275
Open Research Fund of Key Laboratory of Water-Sediment Sciences and Water Disaster Prevention of Hunan Province,No.2019SS06
Scientific Research Key Project in Hunan Province Education Department,No.2014A006。
