Experimental study on the settling of irregularly shaped sediment particles from the source region of the Yangtze River

IF 3.5 2区 环境科学与生态学 Q2 ENVIRONMENTAL SCIENCES
Xiaoyong Cheng , Zhijing Li , Yujiao Liu , Zhongwu Jin , Yinjun Zhou , Yisen Wang , Guiqiao Wang , Junfeng Han , Zhixian Cao
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Abstract

Settling plays a pivotal role in sediment transport and morphological evolution of alluvial rivers. Sediment particles in the source regions of large rivers are more likely to feature irregular shapes due to less abrasion than in lower reaches of the rivers. However, the settling of irregularly shaped sediment particles from the source region of a river has to date remained poorly understood. Here, sediment particles were sampled from the Tuotuo River basin in the source region of the Yangtze River. A total of 28 experimental runs were done in a purpose-built settling cylinder to investigate the settling of the sediment particles, with particle Reynolds number, Rep, defined using terminal settling velocity, ranging from 0.22 to 5,939. The results demonstrate that large Rep and irregular particle shape favor unstable settling behavior with wobbling motion and intense velocity fluctuations. An irregular particle experiences larger drag, and, thus, attains a lower terminal velocity than an equivalent sphere, and the shape effect which reduces terminal velocity tends to become significant with increasing Rep and decreasing Corey shape factor. The measured terminal velocities are compared with five empirical formulas. It is shown that the formulas of Dietrich, Haider and Levenspiel, and Wu and Wang are favorable to use (within the range ±20% of the measured data), whereas Zhang's formula and van Rijn's formula may considerably overestimate the terminal velocity, as no shape descriptor is incorporated to account for irregular shape effects. The current study facilitates a new experimental dataset that may be utilized to further investigate sediment settling dynamics. Also, it has direct implications for enhancing the understanding of morpho-dynamics in the source region of the Yangtze River, which may experience significant changes in response to climate change and anthropogenic activities.
长江源区不规则泥沙颗粒沉降试验研究
沉积在冲积河的输沙和形态演化中起着关键作用。大河源区泥沙颗粒由于较少的磨蚀作用,较下游泥沙颗粒更有可能呈现不规则形状。然而,迄今为止,人们对河流源区不规则形状沉积物颗粒的沉降仍然知之甚少。本文对长江源区沱沱河流域的泥沙颗粒进行了采样。在一个专门建造的沉降筒中,共进行了28次实验,以研究沉积物颗粒的沉降情况,颗粒雷诺数Rep由终端沉降速度定义,范围为0.22至5,939。结果表明,大的Rep和不规则的颗粒形状有利于不稳定沉降行为,具有摆动运动和强烈的速度波动。不规则颗粒受到较大的阻力,因而获得较低的终端速度,并且随着Rep的增大和Corey形状因子的减小,降低终端速度的形状效应趋于显著。实测的终端速度与五个经验公式进行了比较。结果表明,Dietrich、Haider和Levenspiel以及Wu和Wang的公式(在测量数据的±20%范围内)是有利的,而Zhang的公式和van Rijn的公式可能大大高估了终端速度,因为没有纳入形状描述符来考虑不规则形状效应。本研究为进一步研究泥沙沉降动力学提供了新的实验数据集。此外,这对进一步认识长江源区在气候变化和人类活动的影响下可能发生的重大变化具有直接意义。
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来源期刊
International Journal of Sediment Research
International Journal of Sediment Research 环境科学-环境科学
CiteScore
6.90
自引率
5.60%
发文量
88
审稿时长
74 days
期刊介绍: International Journal of Sediment Research, the Official Journal of The International Research and Training Center on Erosion and Sedimentation and The World Association for Sedimentation and Erosion Research, publishes scientific and technical papers on all aspects of erosion and sedimentation interpreted in its widest sense. The subject matter is to include not only the mechanics of sediment transport and fluvial processes, but also what is related to geography, geomorphology, soil erosion, watershed management, sedimentology, environmental and ecological impacts of sedimentation, social and economical effects of sedimentation and its assessment, etc. Special attention is paid to engineering problems related to sedimentation and erosion.
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