近20 a长江中游分汊河段的江心洲经历了冲刷并发生蚀退,但对微弯河段和顺直河段的江心洲差异化冲刷尚未有清晰认识。选取长江中游武汉河段的白沙洲和天兴洲作为研究对象,采用遥感影像、水文资料及野外调查,分析了白沙洲与天兴洲形态变化及差异化冲刷的原因。结果表明:1989—2020年,白沙洲洲体萎缩将近43.83%,天兴洲洲头浅滩变化较大,整体出露面积相对稳定;白沙洲与天兴洲的归一化植被指数(NDVI)整体较小,洲体植被覆盖空间差异性减小;这2个江心洲枯水期出露面积的变化主要体现在洲头浅滩;位于顺直河段的白沙洲洲头及侧向洲体遭遇冲刷,左侧洲体出现窝崩现象,其主要原因是白沙洲大桥桥墩的壅水与阻流作用;位于微弯河段的天兴洲自三峡工程蓄水后洲头遭受冲刷,2004年洲头守护工程实施和人工抛石有效地抑制了冲刷并实现了促淤作用。因此,江心洲的冲刷差异性主要体现在河段形态、主支汊相对位置和有无守护工程。
Abstract
Over the past two decades, mid-channel bars in the branching sections of the Middle Yangtze River have experienced substantial scouring or even retreating, yet the specific variances in scouring between slightly meandering and straight channels remain unclear. Baishazhou Sandbar and Tianxingzhou Sandbar, located in the Wuhan reach of the Middle Yangtze River, were selected as study sites to investigate the causes of morphological changes and differential scouring. This investigation utilized a combination of multi-source remote sensing imagery, hydrological data, and field surveys. The findings reveal significant alterations in the morphology of Baishazhou Sandbar, shrinking in size by approximately 43.83% between 1989 and 2020. Meanwhile, the head of Tianxingzhou sandbar underwent notable changes, although the overall exposed area remained relatively stable. Analysis of the normalized vegetation index (NDVI) indicates generally low vegetation cover on both sandbars, with diminished spatial discrepancies. During dry season, variations in exposed area primarily correlate with the bar head region. Specifically, on the Baishazhou Sandbar which is located in straight channel, scouring was observed on the head and lateral side, while local collapse on the left side, both due to the obstruction of Baishazhou Bridge piers. Similarly, on Tianxingzhou Sandbar which is located in slightly meandering channel, the bar head has experienced scouring following the impoundment of the Three Gorges Project. However, the implementation of protection measures, including artificial rock rip-rap in 2004, effectively mitigated scouring and facilitated deposition. In conclusion, differential scour of mid-channel bars manifests in several aspects, including channel planform, the relative positioning of mainstream and branches, and the presence or absence of protective infrastructure.
关键词
江心洲 /
微弯河段 /
顺直河段 /
差异化冲刷 /
水沙变化 /
长江中游 /
武汉河段
Key words
mid-channel bar /
slightly meandering reach /
straight reach /
differential scour /
water-sediment change /
Middle Yangtze River /
Wuhan Reach
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基金
国家重点研发计划项目(2023YFC3209502); 湖北省技术创新重点研发计划项目(2023BCB110)
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