Morphological changes in estuaries are typically discussed on decadal time scales, with reported changes often exceed several decimeters. In our study, we utilized refined in-situ data to investigate bed-level changes and rapid accretion-erosion transitions during tidal cycles off the Changjiang Estuary. A field study employing a high-resolution bottom tripod system was conducted, measuring various parameters such as water level, waves, velocity profiles, near-bottom suspended sediment concentration (SSC), and bed level changes over ten tidal cycles. Our findings reveal significant and intense bed level changes occurring at the scale of tidal cycles. The data suggests that downward sediment transport plays a dominant role in the overall accretion tendency throughout the study period. Additionally, our research introduces a dynamic critical bed shear stress that increases during tidal cycles, deviating from fixed values. We also present a new quadrant analysis method to elucidate the primary processes controlling near-bed sediment transport. The results highlight the importance of horizontal advective sediment transport in frequent accretion-erosion transitions at tidal-cycle timescales. This implies a frequent exchange of sediment between adjacent shoals and channels in the seaward region of the North Channel in the Changjiang Estuary, which holds significance for future navigation and construction management.

中文翻译：

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基于精细现场数据的复杂水动力环境中快速吸积-侵蚀转变机制

河口的形态变化通常在十年的时间尺度上讨论，报告的变化通常超过几分米。在我们的研究中，我们利用了精炼的原位数据来调查长江口潮汐周期期间的床位变化和快速吸积-侵蚀转变。采用高分辨率底部三脚架系统进行了实地研究，测量了各种参数，例如水位、波浪、速度剖面、近底部悬浮沉积物浓度（SSC）以及十个潮汐周期内的床位变化。我们的研究结果揭示了潮汐周期范围内发生的显着而剧烈的床位变化。数据表明，沉积物向下输送在整个研究期间的总体沉积趋势中起着主导作用。此外，我们的研究引入了动态临界床剪应力，该剪应力在潮汐周期期间增加，偏离固定值。我们还提出了一种新的象限分析方法来阐明控制近床沉积物输送的主要过程。结果强调了水平平流沉积物输送在潮汐周期时间尺度的频繁吸积-侵蚀转变中的重要性。这意味着长江口北航道临海区域相邻浅滩和航道之间泥沙交换频繁，对今后的通航和施工管理具有重要意义。