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首页> 外文期刊>Estuarine Coastal and Shelf Science >A simulation study on effects of suspended sediment through high riverine discharge on surface river plume and vertical water exchange
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A simulation study on effects of suspended sediment through high riverine discharge on surface river plume and vertical water exchange

机译：河道高排沙量对地表河羽和垂直水交换影响的模拟研究

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Rivers transport freshwater and suspended sediment matter (SSM) from land to coastal seas. In coastal seas termed as regions of freshwater influence (ROFIs), SSM is not only passively transported but also changes the density of ambient water and influences the physical characteristics especially in flood events, when a lot of SSM is supplied to the sea. Although the influence of SSM on the physical field in ROFIs would be significant, interactive physical processes, such as dynamics of river plumes and estuarine circulations, have hardly been investigated for hypopycnal plumes (i.e., the riverine sediment-freshwater is not denser than the seawater). In order to quantitatively estimate the interactive effects of SSM, we employ a non-hydrostatic ocean model with Lagrangian particles, which represents SSM and affects the density and buoyancy of ambient water. We use two experimental settings: (1) realistic simulations of the Tango Bay, Japan under the flooding of September 2013 and (2) idealized simulations for an open-bay ROFI. The former is conducted to assess whether the simulations could reproduce an actual event to some extent. The realistic simulations demonstrate that the choice of parameters such as SSM-particle size and composition is important for coastal simulations of flood events. The latter is conducted to understand the basic physics and to study the quantitative sensitivities of the physical processes to the riverine flux, composition, and particle size of SSM. The idealized simulations demonstrate that a large amount of riverine SSM affects the physical field in ROFIs through the following process: 1) horizontal density differences between nearshore and offshore waters are reduced as apparent density is increased close to the river mouth by riverine SSM, 2) the strength of vertical circulation is weakened by the reduced horizontal density difference, and 3) vertical water exchange between the surface and the subsurface layers decreases. The process in the control case of this study increases the relative amounts of surface freshwater in the river plume by 0.8% of the total riverine freshwater input. Sensitivity experiments with changing the parameters of SSM flux into the river, SSM composition, and SSM-particle diameter show that the percentage can be raised up to 2%. Meanwhile, the above-mentioned processes do not apply to extreme cases of small particle size and enormous SSM input wherein homopycnal (i.e., a similar density between the riverine sediment-freshwater and the ambient seawater) and hyperpycnal (i.e., the density of the riverine sediment-freshwater mixture exceeds the ambient seawater) plumes take place.
机译：河流将淡水和悬浮沉积物（SSM）从陆地运输到沿海海域。在被称为淡水影响（ROFI）区域的沿海海域中，SSM不仅是被动运输的方式，而且还会改变周围水的密度并影响物理特性，特别是在洪水事件中，因为向海中供应了许多SSM。尽管SSM对ROFIs的物理场的影响是巨大的，但对于洋状羽状流，很少研究交互的物理过程（例如河羽和河口环流的动力学）（即，河底沉积物-淡水并不比海水浓密） ）。为了定量评估SSM的交互作用，我们采用了具有拉格朗日粒子的非静水海洋模型，该模型代表SSM，并影响环境水的密度和浮力。我们使用两个实验设置：（1）在2013年9月的洪水下对日本探戈湾进行的真实模拟，以及（2）对开放式ROFI进行理想化的模拟。进行前者是为了评估模拟是否可以在一定程度上重现实际事件。真实的模拟表明，诸如SSM颗粒大小和成分之类的参数的选择对于洪水事件的海岸模拟非常重要。进行后者是为了了解基本物理原理，并研究物理过程对SSM的河流通量，组成和粒径的定量敏感性。理想化的模拟表明，通过以下过程，大量的河流SSM通过以下过程影响ROFI的物理场：1）随着河流SSM增大靠近河口的表观密度，近岸和近岸水域之间的水平密度差异减小了，2）水平密度差的减小会削弱垂直循环的强度，并且3）表层与地下层之间的垂直水交换减少。在本研究的控制案例中，该过程使河羽中地表淡水的相对量增加了河道淡水总输入量的0.8％。通过更改进入河流的SSM流量参数，SSM组成和SSM粒径的敏感性实验表明，该百分比可以提高到2％。同时，上述过程不适用于小颗粒尺寸和大量SSM输入的极端情况，其中高纯（即河流沉积物-淡水和周围海水之间的密度相似）和高纯（即河流的密度）之间沉积物与淡水的混合物超过了周围的海水）。

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