Abstract

Fluvial flows carrying high sediment loads may plunge into reservoirs to form turbidity currents. However, the effects of tributary inflows on reservoir turbidity currents have remained poorly understood to date. Here a 2D double layer-averaged model is used to investigate a series of laboratory-scale numerical cases. By probing into the hydro-sediment-morphodynamic processes, we find that tributary location and inflow conditions have distinct effects on the formation and propagation of reservoir turbidity currents, and lead to complicated flow dynamics and bed deformation at the confluence. Two flow exchange patterns are generated at the confluence: turbidity current intrusion from the main channel into the tributary; and highly concentrated, sediment-laden flow plunging from the tributary into the turbidity current in the main channel. Tributary sediment-laden inflow may cause the stable plunge point to migrate downstream and is conducive to propagation of the turbidity current, whilst the opposite holds in the case of clear-water inflow from the tributary. Tributary inflow leads to a lower sediment flushing efficiency as compared to its counterpart without a tributary. Yet a high sediment concentration in the tributary may reinforce turbidity current in the reservoir, thereby increasing sediment flushing efficiency. Around the confluence, the planar distributions of velocity and bed shear stress of the turbidity current resemble their counterparts in confluence flows carrying low sediment loads or clear water. Yet, the bed exhibits aggradation near the confluence due to the turbidity current, in contrast to pure scour in a river confluence with a low sediment load. Appropriate account of tributary effects is required in studies of reservoir turbidity currents, and for devising strategies for long-term maintenance of reservoir capacity.

Article highlights

• Tributary inflow may cause the stable plunge point of reservoir turbidity current to migrate either upstream or downstream and modify its propagation.

• Tributary inflow may lead to lower sediment flushing efficiency by reservoir turbidity current.

• Tributary discharge and sediment concentration may lead to disparate bed deformation at confluence.

中文翻译：

---

支流流入对水库浊流的影响

摘要

携带高沉积物负荷的河流可能会冲入水库形成浊流。然而，迄今为止，支流流入对储层浊流的影响仍然知之甚少。这里使用二维双层平均模型来研究一系列实验室规模的数值案例。通过对水-沙-形态动力学过程的探讨，发现支流位置和入流条件对储层浑浊流的形成和传播具有明显的影响，并导致汇流处的水流动力学和河床变形复杂。汇流处产生两种流动交换模式：浊流从主通道侵入支流；以及从支流进入主河道的浊流中的高度集中的、富含沉积物的水流。含泥沙的支流流入可能导致稳定的下降点向下游迁移，有利于浊流的传播，而从支流流入的清水则相反。与没有支流的对应物相比，支流流入导致较低的沉积物冲洗效率。然而，支流中的高沉积物浓度可能会加强水库中的浊流，从而提高沉积物冲刷效率。在汇合处，浊流的速度和床层剪切应力的平面分布类似于它们在载有低沉积物负荷或清水的汇合流中的对应物。然而，由于浊流，河床在汇合处附近表现出积聚现象，这与低泥沙负荷的河流汇合处的纯冲刷形成对比。

文章重点

• 支流流入可能导致水库浊流的稳定下降点向上游或下游迁移并改变其传播。

• 支流流入可能导致水库浊流冲淤效率降低。

• 支流流量和泥沙浓度可能导致汇合处不同的河床变形。