| 摘要: |
| 三峡工程的运用引起坝下游分汊段冲淤调整，进而改变分流分沙格局，对防洪、航运和生态等带来深远影响。本文选取监利~石矶头河段内三种不同类型分汊河段为研究对象，分析持续冲刷条件下的汊道演变特点，并基于二维水沙模型对比计算了三峡工程运用前后不同流量级下的分流分沙比，最后阐明了分流格局调整的驱动成因。结果表明：三峡运用后，研究河段内顺直分汊段两汊有冲有淤，弯曲及鹅头分汊两汊均冲，且冲刷主要发生于枯水河槽，整治工程阻止了江心洲两缘高滩崩退且促进了洲头低滩淤积；冲刷强度大的汊道发展为主汊，造成部分分汊段主支汊易位，南门洲及陆溪口右汊枯水流量下分流比分别由0.42、0.40提升至0.95、0.81，增幅均超100%；汊道不平衡冲淤是分流分沙格局调整的主要成因，且影响随流量增大而减小，主汊相对支汊冲刷厚度每增加1.0m，主汊分流比增加约7.6~15.8%，分沙比增加约8.2~11.8%；平面形态改变进一步影响了分流格局，南阳洲左汊口门处低滩淤积不利于入流，且高滩崩退后左移降低了左汊洪中流量下的分流比。 |
| 关键词: 分流分沙比 汊道演变 分汊河型 整治工程 长江中游 |
| DOI： |
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| 基金项目:国家自然科学基金项目（面上项目，重点项目，重大项目） |
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| Variation characteristics and causes of flow and sediment diversion ratios in the typical bifurcated reaches of the Middle Yangtze River after the Three Gorges Project operation |
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Zhu Heng, Xia Junqiang, Deng Shanshan, Zhou Meirong
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State Key Laboratory of Water Resources Engineering and Management
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| Abstract: |
| The operation of the Three Gorges Project led to significant channel adjustments in the downstream reaches, and thus changed the diversion patterns of flow and sediment in bifurcated reaches, which had a significant impact on flood control, navigation, water diversion, and ecology. This study investigated the variation characteristics of four distinct bifurcated reaches in the reach between Jianli and Shijitou of the Middle Yangtze River. Using a two-dimensional flow-sediment transport model, this study compared the flow and sediment diversion ratios before and after the reservoir operation under different flow regimes, and consequently identified the drivers behind the variation in diversion patterns. The results demonstrate that during the post-operation period, the straight bifurcated reach underwent erosion and deposition, while both the main and second branches of the curved bifurcated reach underwent erosion, primarily occurring in the low-water channels. River regulation projects prevented the retreat of high floodplain of the mid-channel bar (MCB) and caused the deposition of low floodplain of the MCB. The channels with higher erosion intensity evolved into the main branches, causing the shift in the main and second branches of some bifurcated reaches. The low-discharge diversion ratios in the right branch of the bifurcated reaches of Nanmenzhou and Luxikou increased from 0.42 and 0.40 to 0.95 and 0.81, respectively, with both showing an increase of over 100%. The imbalanced erosion in the bifurcated reaches is the primary cause for the variation in flow and sediment diversion patterns, with the impact decreasing for a higher discharge. For every 1.0 m increase in the relative scour depth between the main and secondary branch, the flow diversion ratio of the main branch would increase by approximately 7.6–15.8%, and the sediment diversion ratio would increase by approximately 8.2–11.8%. Changes in the mid-channel bar planform would further influence the flow diversion patterns. Sediment deposition on the low floodplain was adverse to the inflow entering the left branch of the Nanyangzhou reach, while the retreat of the high floodplain in the left branch further decreased the flow diversion ratio under the medium to high discharge conditions. |
| Key words: Flow and sediment diversion Channel evolution Bifurcated channel pattern River regulation engineering Middle Yangtze River |
