Abstract This study explores the seasonal and tidal changes in flow and suspended matter dynamics in the tropical and macrotidal Van Uc River estuary (North Vietnam) and aims at understanding, among others, the sediment delivery to the ocean and the processes behind the estuarine siltation. Four campaigns took place during the contrasting high flow and low flow seasons, for each during neap and spring tides. Water and suspended matter fluxes, salinity, turbidity and particle size distribution (PSD) were measured for 24 h at three cross sections along the estuary. During the high-flow season, the estuary was mixed, with seaward sediment flux during neap tide and ephemeral up-estuary sediment flux at spring tides due to tidal distortion. During the low-flow season, the system transitioned from partially mixed to highly stratified with salty waters intrusions, salt wedge presence and up-estuary sediment flux varying with the tidal regime. The highest up-estuary sediment flow occurred during low-flow at spring tides and represented ⅔ of the outflow. The lower river discharge, the higher PSD variation. The increasing proportion of microflocs with increasing salinity as compared to primary particles and flocculi was observed at both seasons. Higher tidal variations of PSD at spring tides indicate the strong effect of turbulent shear. These findings also provide a new benchmark for hydro-sedimentary model calibration/validation.

中文翻译：

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越南红河 Van Uc 河口水文和悬浮颗粒物的季节性和潮汐变化

摘要 本研究探讨了热带和大潮汐 Van Uc 河河口（越南北部）的流量和悬浮物动力学的季节性和潮汐变化，旨在了解向海洋输送的沉积物以及河口淤积背后的过程等。在对比鲜明的高流量和低流量季节，分别在小潮和大潮期间进行了四次运动。在沿河口的三个横截面测量了 24 小时的水和悬浮物通量、盐度、浊度和粒度分布 (PSD)。在高流量季节，河口是混合的，由于潮汐畸变，小潮时向海的沉积物通量和大潮时的短暂性向上河口沉积物通量。在低流量季节，该系统从部分混合转变为高度分层，咸水入侵、盐楔存在和河口上游沉积物通量随潮汐情况而变化。最高的河口上游泥沙流量发生在大潮的低流量期间，代表流出量的 ⅔。河流流量越低，PSD 变化越大。在两个季节都观察到与初级颗粒和絮凝体相比，随着盐度增加，微絮体的比例增加。大潮时PSD的更高潮汐变化表明湍流剪切的强烈影响。这些发现还为水沉积模型校准/验证提供了新的基准。最高的河口上游泥沙流量发生在大潮的低流量期间，代表流出量的 ⅔。河流流量越低，PSD 变化越大。在两个季节都观察到与初级颗粒和絮凝体相比，随着盐度增加，微絮体的比例增加。大潮时PSD的更高潮汐变化表明湍流剪切的强烈影响。这些发现还为水沉积模型校准/验证提供了新的基准。最高的河口上游泥沙流量发生在大潮的低流量期间，代表流出量的 ⅔。河流流量越低，PSD 变化越大。在两个季节都观察到与初级颗粒和絮凝体相比，随着盐度增加，微絮体的比例增加。大潮时PSD的更高潮汐变化表明湍流剪切的强烈影响。这些发现还为水沉积模型校准/验证提供了新的基准。