长江口南北支分流口江心洲动力地貌变化过程研究

Study on morphodynamic change process of mid-channel bar atdistributary mouth of North and South branches of the Changjiang Estuary

中文关键词:  江心洲  动力地貌演变  长江口北支  人类活动

英文关键词:mid-channel bar  dynamic morphodynamic evolution  North Branch of Changjiang Estuary  human activities

中文摘要:

      地处径潮流汇合处的河口分流口江心洲在河口河势变迁中扮演着重要作用。本文利用1959－2022年长江北支入口段实测地形数据、长江入海水沙以及南北支分水分沙比等数据，对北支入口段新生江心洲动力地貌变化过程进行分析。研究结果表明：1959－2022 年期间新生江心洲地貌演变经历了 4 个阶段：第一阶段（1959－1997年） 北支主流位于崇头一侧，新生江心洲向海门港侧迁移；第二阶段 （1997－2008年） 崇头侧泥沙淤积，新生江心洲重新迁移至崇头侧；第三阶段 （2008－2017年） 新生江心洲形状与位置基本达到稳定状态，变化较小，但体积趋于增长态势；第四阶段 （2017－2022年） 新生江心洲经历冲刷且高程大幅降低，但形状位置没有明显改变。其中新生江心洲位置与形态的变化受白茆沙分流比以及北支主流变化影响较大，但沙洲的高程因洪水事件而出现强冲刷。

英文摘要:

      Mid-channel bar at the distributary mouth of the estuary, which located at the confluence of river currents and tidal flows, plays a significant role in the changes in river regime at the estuary. Based on the measured topographic data of the entrance section of the North Branch, Changjiang River from 1959 to 2022, as well as the records of fluvial water and sediment discharge,water and sediment diversion ratios, this paper analyzed the morphodynamic evolution processes of the newly formed midchannel bar at the entrance section of the North Branch. The results show that: The morphodynamic evolution of the newly formed mid-channel bar can be divided into four stages during 1959－2022: In the first stage (1959－1997), the main stream of the North Branch was at Chongtou side, and the newly formed mid-channel bar migrated to Haimen Port; In the second stage (1997－2008), sediment deposition occurred at Chongtou, and the newly formed mid-channel bar migrated back to Chongtou side; In the third stage (2008－2017), the shape and position of the newly formed mid-channel bar basically reached a stable state with little change, but its volume trended towards growth. In the fourth stage (2017－2022), the newly formed mid-channel bar experienced erosion, with its elevation decreasing significantly, while its shape and position changing slightly. The change of discharge diversion ratio at Baimao Shoal Channel and movement of main stream of the North Branch were responsible for position and shape change of the newly formed mid-channel bar. However, the elevation of the bar was strongly eroded due to river floods