Modeling the Dynamics of Small‐Scale River and Creek Plumes in Tidal Waters
Modeling the Dynamics of Small‐Scale River and Creek Plumes in Tidal Waters
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模拟潮汐水域中小规模河流和溪流羽流的动态
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发表时间：
2020
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通讯作者：
N. Nidzieko
中科院分区：
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作者：
N. B. Basdurak;J. Largier;N. Nidzieko
相对于大型河流羽流的动力学，对小型河流和山区溪流排放的命运研究很少。小流域的流动是间歇性的，形成短暂的低盐度表面羽流，由于浮力和环境潮流的流出惯性的相互作用，潮汐变化。区域海洋模拟系统（ROMS v3.0）是一个三维、自由表面、地形跟随的数值模型，应用于进入潮汐海洋的小河流流出（≤10 ms），在那里它们形成尺度约10 m或更小的小羽流。对动量平衡的分析指出了三个不同的区域：（i）惯性驱动的近场，其中平流、压力梯度和垂直应力发散控制羽流动力学，（ii）浮力驱动的中场，其中压力梯度、横向应力发散和旋转加速度占主导地位，以及（iii）平流远场，其中由环境潮流引起的局部加速度决定了河流/河口排放的命运。这些小的潮汐羽流的响应不同的浮力强迫和外流率进行了探讨。随着浮力的增加，羽流从狭窄/细长的底部附着流变为径向膨胀的表面层流。弱的外流促进了羽流层内的分层，并且随着较强的外流，羽流层变得更薄并且混合良好。当与科里奥利效应很重要的原型大河羽流相比时：（i）在这些小羽流中没有隆起，也没有沿岸浮力流，即，海岸接触大多是不存在的;和（二）羽强烈的影响，环境潮流，形成一个潮汐羽，是从河口偏上/下游。
The fate of discharges from small rivers and mountainous streams are little studied relative to the dynamics of large river plumes. Flows from small watersheds are episodic, forming transient low-salinity surface plumes that vary tidally due to interaction of outflow inertia with buoyancy and ambient tidal currents. An implementation of the Regional Ocean Modeling System (ROMS v3.0), a three-dimensional, free-surface, terrain-following numerical model is applied to small river outflows (≤10 ms) entering a tidal ocean, where they form small plumes of scale ~10 m or smaller. Analysis of the momentum balance points to three distinct zones: (i) an inertia-driven near-field, where advection, pressure gradient, and vertical stress divergence control the plume dynamics, (ii) a buoyancy-driven mid-field, where pressure gradient, lateral stress divergence, and rotational accelerations are dominant, and (iii) an advective far-field, where local accelerations induced by ambient tidal currents determine the fate of the river/estuarine discharge. The response of these small tidal plumes to different buoyancy forcing and outflow rate is explored. With increasing buoyancy, plumes change from narrow/elongated, bottom-attached flows to radially-expanding, surface-layer flows. Weak outflow promotes stratification within the plume layer, and with stronger outflow the plume layer becomes thinner and well-mixed. When compared with prototypical large-river plumes in which Coriolis effects are important: (i) in these small plumes there is no bulge and no coastal buoyancy current i.e., shore contact is mostly absent; and (ii) the plume is strongly influenced by ambient tidal currents, forming a tidal plume that is deflected upcoast/downcoast from the river mouth.