Revisited sediment budget with latest bathymetric data in the highly altered Yangtze (Changjiang) Estuary
Revisited sediment budget with latest bathymetric data in the highly altered Yangtze (Changjiang) Estuary
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利用最新测深数据重新审视高度变化的长江口的沉积物预算
DOI：
10.1016/j.geomorph.2021.107873
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发表时间：
2021-07
期刊：
影响因子：
3.9
通讯作者：
Qin Changjie
中科院分区：
文献类型：
--
作者：
Guo Xingjie;Fan Daidu;Zheng Shuwei;Wang Hanmei;Zhao Baocheng;Qin Changjie
人类活动极大地改变了世界上大多数河流三角洲，其中可能发生了从净加积到净侵蚀的制度转变。利用2007 - 2019年每两年进行一次的水深调查的高分辨率DEM数据，详细分析了长江口潮下带地貌动力变化的因果关系，并根据年平均冲淤泥沙量更新了河口泥沙收支平衡。结果表明，潮下水道侵蚀几乎遍及整个黄海，研究期间的平均年侵蚀速率为-5.59 cm/yr。侵蚀高峰出现在南分支和三角洲前缘，平均年侵蚀速率分别为-12.64 cm/yr和-8.11 cm/yr。河口中部以桑迪浅滩为主，侵蚀减弱，仅崇明浅滩的净增长率为3.13 cm/a。河口侵蚀量与输沙量呈负相关关系，说明上游水利工程对河口地貌动力变化影响较大，但大型河口工程对局部地貌动力也有显著影响，工程附近存在深侵蚀带。2007-2019年期间，分流河道和三角洲前缘的年侵蚀泥沙量估计为1.66亿吨/年和2.06亿吨/年，前者几乎被近期来自分流河道的1.43亿吨/年的土地复垦采砂量所抵消。此外，大同-徐六井感潮河段的现代侵蚀泥沙量和采砂量分别为77 Mt/a和44 Mt/a。分析还表明，近几年来感潮河段大通站和徐六井站的输沙量分别为124 Mt/a和153 Mt/a，仅为90年代前的27.5%和37.7%。从河口进入外海的年泥沙量从20世纪90年代前的3.7亿吨/年减少到最近的1.4亿吨/年，减少了37.8%，导致最近在三角洲前缘严重的侵蚀。因此，强调河口系统响应自然和人为压力是非常动态的，在预测河口的形态动力响应时，应充分考虑各种工程项目在源-汇系统中的影响。
Most river-deltas of the world have been extremely altered by anthropic activities, where a regime shift from net accretion into net erosion may have occurred. In this study, subtidal morphodynamic variations in the Yangtze Estuary (YE) are elaborately analyzed for their causalities using high resolution DEM data from bathymetric surveys conducted every two years from 2007 to 2019; sediment budgetary balance in the estuary has been updated accordingly with mean annual depositional/erosional sediment amounts. The results show that subtidal channel erosion has occurred almost over the whole YE with a mean annual erosional rate of −5.59 cm/yr during the study period. Peak erosion occurred both in the South Branch and the delta front with mean annual erosional rates of −12.64 cm/yr and −8.11 cm/yr, respectively. The erosion lessened in the middle estuary where sandy shoals prevail, and a net accretive rate of 3.13 cm/yr was solely measured at the Chongming shoal. Negative correlation between estuarine erosional volume and riverine sediment discharge demonstrates the great impact of upstream hydro-engineering projects on estuarine morphodynamic change, but large-scale estuarine engineering projects also exert remarkable influence on local morphodynamics, evidenced by the presence of deep erosional belts near the projects. Annually eroded sediment amounts were estimated as 166 Mt/yr and 206 Mt/yr in the distributary channels and the delta front during the period 2007–2019, and the former was almost offset by recent sand mining amount of 143 Mt/yr from the distributary channels for land reclamation. Moreover, contemporary eroded sediment mass and sand mining amount from the tidal river reach between Datong and Xuliujing were reckoned as 77 Mt/yr and 44 Mt/yr, respectively. Our analysis further show that recently 124 Mt/yr and 153 Mt/yr of sediment discharge into the tidal river reach at Datong station and the YE at Xuliujing station account for merely 27.5% and 37.7% of their corresponding values before the 1990s, respectively. Annual sediment amount bypassing the estuary into the open sea has decreased by 37.8% from pre-1990s 370 Mt/yr to recent 140 Mt/yr, leading to recently severe erosion in the delta front. It is therefore highlighted that the estuarine system in response to natural and anthropogenic pressures is very dynamic, and the impacts of various engineering projects in the source-to-sink system should be fully taken into consideration when predicting its morphodynamic response in the estuary.
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