Experimental Study on the Effects of a Vertical Jet Impinging on Soft Bottom Sediments
Experimental Study on the Effects of a Vertical Jet Impinging on Soft Bottom Sediments
复制标题
DOI：
10.3390/su12093775
复制
发表时间：
2020-05
期刊：
影响因子：
3.9
通讯作者：
W. Fan;Weichen Bao;Yong Cai;Canbo Xiao;Zhujun Zhang;Yiwen Pan;Ying Chen;Shuo Liu
中科院分区：
文献类型：
--
作者：
W. Fan;Weichen Bao;Yong Cai;Canbo Xiao;Zhujun Zhang;Yiwen Pan;Ying Chen;Shuo Liu
人工下降流是一种生态工程方法，它通过将富氧的表层水引入到密度跃层之下来潜在地缓解海底缺氧。然而，向下的水流到达底部时可能会扰动沉积物（或引起沉积物再悬浮），然后对当地生态系统产生不利的副作用。为了评估这一点，我们提出了一个理论模型和实验数据的人工下降流引起的沉积物再悬浮。理论模型考虑了泥沙再悬浮的临界条件和下沉流扰动泥沙时的冲刷量。在水槽中进行了改变下降流流速、排放位置和沉积物粒径的实验，结果与我们的理论模型一致。结果表明，泥沙再悬浮的临界弗劳德数（Fr）为0.5。为了防止泥沙再悬浮，需要调整下降流流速和下泄位置，使Fr < 0.5，否则有一部分泥沙释放到水中，其体积可由基于Shields理论的推导公式预测。此外，沉积物再悬浮的副作用，如水浊度增加和磷的释放，其幅度进行了讨论，相对于工程参数。今后的研究重点将放在人工下降流的现场试验及其环境影响上。
Artificial downwelling, which is an ecological engineering method, potentially alleviates bottom hypoxia by bringing oxygen-rich surface water down below the pycnocline. However, the downward flow is likely to disturb sediments (or induce sediment resuspension) when reaching the bottom and then have unwanted side effects on the local ecosystem. To evaluate this, our paper presents a theoretical model and experimental data for the sediment resuspension caused by artificial downwelling. The theoretical model considers the critical conditions for sediment resuspension and the scour volume with the downwelling flow disturbing sediment. Experiments with altered downwelling flow speeds, discharge positions relative to the bottom, and particle sizes of sediment were conducted in a water tank, and the results were consistent with our theoretical model. The results show that the critical Froude number (hereinafter Fr) for sediment resuspension is 0.5. The prevention of sediment resuspension requires the downwelling flow speed and the discharge position to be adjusted so that Fr < 0.5; otherwise a portion of sediment is released into the water and its volume can be predicted by the derived formulation based on the Shields theory. Furthermore, sediment resuspension has side effects, such as a water turbidity increase and phosphorus release, the magnitudes of which are discussed with respect to engineering parameters. Further study will focus on field experiments of artificial downwelling and its environmental impacts.