长江口北支上段岸滩侵蚀及保护实施效果分析

受上下游工程、来水来沙影响，长江口北支上段近期岸滩侵蚀后退严重。为揭示北支上段近期演变机理，控制河势变化和保护生态基底，收集2001年以来长江口北支全河道水下地形资料，并开展了2017—2020年工程区段水下地形精细实测，基于水动力数学模型研究了岸滩保护措施合理性，以分形理论评价了保护措施实施后效果。结果表明：①长江口北支进口江心洲发育，导致上段“S”形主轴弯曲度加大，加剧了暗沙、江心洲和岸滩动荡；②在冲刷最严重的岸滩采用丁坝群加护坎可有效阻止岸滩侵蚀后退；③多年水下地形实测和分形理论计算评价，岸滩趋于稳定，生态基底得以恢复。鉴于新江心沙洲发育和岸滩、深槽变化加剧了北支上段演变的复杂性，建议尽快成立综合协调部门，统筹提出满足水利、防洪、供水、航运、生态等多目标需求的综合整治方案。

Beach erosion and protection effect analysis on the upstream of the North Branch of the Changjiang (Yangtze) Estuary

Abstracts: Duo to frequent construction activities in the upstream and downstream of Changjiang (Yangtze) River, and water and sediment flows from the South Branch and North Branch in the Changjiang River mouth, the upstream of the North Branch has suffered from severe erosion and recession in recent years. To reveal the evolution mechanism of the upstream of the North Branch, control the river regime change, and protect the ecological background, the underwater terrain data of the whole river course of the North Branch since 2001 were collected, and the fine measurement of underwater terrain in the construction area from 2017 to 2020 was carried out. Based on the hydrodynamic mathematical model, the beach protection measures were studied and demonstrated, and the effect of the protection measures after implementation was evaluated in fractal theory. Results show that: ① the sandbar development at the entrance of upstream of the Northern Branch leads to the increase of the curvature of the upper S-shaped principal axis, which aggravates the instability of shoal, sandbar, and beach; ② the spur-dike and berm combination can effectively prevent the erosion and retreat of the most severely scoured beach; ③ the beach tends to be stablized and the ecological base has been restored as shown by after many-year underwater topography measurement according to fractal theory calculation and evaluation. Finally, the complexity of the evolution was aggravated by the changes of shoal, sandbar and deep channel in the upstream of the North Branch, it is suggested to establish a comprehensive coordination department as soon as possible to put forward a comprehensive improvement plan to meet the multi-objective needs of water conservancy, flood control, water supply, navigation, ecology, etc.