A numerical investigation of the dynamics and structure of hyperpycnal river plumes on sloping continental shelves
A numerical investigation of the dynamics and structure of hyperpycnal river plumes on sloping continental shelves
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DOI：
10.1002/jgrc.20209
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发表时间：
2013-05-01
影响因子：
3.6
通讯作者：
Hsu, Tian-Jian
中科院分区：
文献类型：
--
作者：
Chen, Shih-Nan;Geyer, W. Rockwell;Hsu, Tian-Jian
利用三维水动力模式（区域海洋模拟系统）研究了倾斜大陆架上高密度河流羽流的动力学和结构。重点是羽流的变化的斜率和沉降速度（w（s））的响应。理想化的模型被配置为代表小型山区河流系统在洪水事件。河口的高密度沉积物浓度规定为60克/升，因此沉积物-淡水混合物的密度比海水大，导致羽流作为暗流穿过大陆架。选择了0.001-0.03的陆棚坡度的实际范围。根据河流的承载能力，沉降速度是变化的。模型推导出的速度分布和夹带率与之前的实验室实验相比具有优势。横岸和沿岸动量平衡主要是在重力强迫和底部摩擦之间。但是，科里奥利偏转在沿岸动量预算中的羽流核心处是显著的（即，Ekman天平）。随着坡度的增加和沉降速度的降低，高密度羽流从沉积状态过渡到自悬浮状态。由无量纲参数ws 3/q B（q（B）是浮力输入）控制的临界斜率估计值合理地捕获了状态转变。在沉积制度，羽流的跳动（跨岸渗透）尺度与平流距离：增加坡度和流量增强重力强迫和羽流速度，导致跳动增加。相反，增加沉降速度缩短了垂直沉降时间，从而减少了羽流的水平足迹。对于所考虑的参数范围，沉积羽流的流出被限制在距离口15公里以内，而自悬浮羽流的穿透基本上是无限的。
A 3-D hydrodynamic model (Regional Ocean Modeling System) is used to investigate the dynamics and structure of hyperpycnal river plumes over sloping continental shelves. The focus is on the plume's response to varying slopes and settling velocities (w(s)). The idealized model is configured to represent small mountainous river systems during a flood event. A hyperpycnal sediment concentration of 60 g/L is specified at the river mouth such that the sediment-freshwater mixture is denser than the seawater, causing the plumes to traverse the shelves as undercurrents. A realistic range of shelf slope of 0.001-0.03 is chosen. The settling velocity is varied based on river's carrying capacity. The model-derived velocity profiles and the entrainment rate compare favorably against prior laboratory experiments. Both cross-shore and alongshore momentum balances are primarily between gravitational forcing and bottom friction. But, the Coriolis deflection is significant at the plume core in the alongshore momentum budget (i.e., Ekman balance). As the slope increases and settling velocity decreases, hyperpycnal plumes transition from depositional to autosuspending regime. An estimate of critical slope governed by a dimensionless parameter ws3/qb (q(b) is buoyancy input) reasonably captures the regime transition. In the depositional regime, the plume's runout (cross-shore penetration) scales with advective distance: increasing slopes and discharge enhance the gravitational forcing and plume velocity, leading to an increase in runout. In contrast, increasing settling velocity shortens the vertical settling time, thereby reducing the plume's horizontal footprint. For the range of parameters considered, the runout of depositional plumes is confined within 15 km from the mouth, whereas the penetration of autosuspending plumes is essentially unlimited.