Abstract As river flow debouches into the sea, it is affected by the tidal fluctuation at the estuary mouth, which results in a backwater zone, where the rising residual water level (averaged over a lunar day) in the landward direction is changing periodically. This is known as backwater hydrodynamics, especially the variation of the residual water levels that are controlled by the interplay between tide and river flows, while these hydrodynamics follow the traditional stage-river discharge relation in the upstream river-dominated region. However, the tidal asymmetry contributions to the residual water level that are caused by secondary tidal species (e.g., diurnal tide D1), overtide generation (e.g., the quarter-diurnal tide D4) and their interplay with river flow are poorly understood. In this study, we aim to understand the impacts of secondary and quarter-diurnal tidal species on the increase in residual water level in tidal rivers. To quantify the contributions made by different components, we decomposed the numerically computed subtidal friction into different components representing the contributions made by the river flow alone, the tide-river interaction, and tidal asymmetry due to the nonlinear interaction between different tidal species. The results show that the contribution by tidal asymmetry to the residual water level is minor, while the contributions by river flow and tide-river interaction are dominant, accounting for more than 90% and 80% at the upstream and downstream end of the estuary, respectively. The contribution made by river flow increases, while the tide-river interaction decreases in the landward direction. The semidiurnal tidal species (D2) predominantly control the residual water level induced by the tide-river interaction along the Yangtze estuary, which accounts for 70%, while the contributions made by the diurnal and quarter-diurnal tidal species are minor and comparable in magnitude in the seaward reach where tide-river interactions are important. The method proposed in this study to quantify the contributions of river flow and different tidal species to the residual water level will enhance our understanding of riverine and tidal impacts on estuarine backwater hydrodynamics and can be used to guide effective and sustainable water management in the Yangtze estuary and other tidal rivers with substantial river flow.

中文翻译：

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次生和四分之一日潮汐物种对潮汐河流回水水动力的影响

摘要 河流入海时，受河口处潮汐波动的影响，形成回水带，向陆方向上升的剩余水位（一个农历日的平均值）呈周期性变化。这被称为回水水动力，特别是受潮汐和河流相互作用控制的残余水位的变化，而这些水动力遵循上游河流主导区域的传统阶段河流流量关系。然而，潮汐不对称对残余水位的贡献是由次要潮汐物种（例如，日潮 D1）、大潮的产生（例如，四分之一日潮 D4）及其与河流流量的相互作用引起的。在这项研究中，我们的目标是了解次生和四分之一昼夜潮汐物种对潮汐河流剩余水位增加的影响。为了量化不同分量的贡献，我们将数值计算的潮下摩擦分解为不同的分量，分别代表单独的河流流量、潮汐河流相互作用以及由于不同潮汐物种之间的非线性相互作用引起的潮汐不对称性。结果表明，潮汐不对称对剩余水位的贡献较小，而河流流量和潮河相互作用的贡献占主导地位，分别占河口上下游端的90%以上和80%。分别。河流流量的贡献增加，而潮汐河流相互作用在向陆方向减少。半日潮物种（D2）主要控制长江口潮河相互作用引起的残余水位，占70%，而昼夜潮汐物种（D2）的贡献较小，幅度相当在潮汐河流相互作用很重要的向海区域。本研究提出的量化河流流量和不同潮汐物种对剩余水位贡献的方法将增强我们对河流和潮汐对河口回水水动力影响的理解，并可用于指导长江口有效和可持续的水资源管理和其他有大量河流的潮汐河流。