A study on the Influence of submergence ratio on the transportation of suspended sediment in a partially vegetated channel flow

Riparian or aquatic vegetation thrives with seasons. The understanding of canopies’ Submergence-Ratio SR (stems’ height to water depth) influence on suspended sediments’ transportation is still limited. Thus, Large Eddy Simulations (LES) coupled with the Discrete Phase Method (DPM) are used to investigate the particles’ 3-dimensional distribution in a partially vegetated straight channel. The spanwise distribution of particles is quantified by the Probability Density Function (PDF), showing a non-uniformity of particles in time as quantified by the PDF variance. The findings and conclusions: (Ⅰ) With SR rising, the particles’ depletion effects exerted by the vegetation-side mixing layer are improved along the interface between vegetated and vegetation-side bare channel region. However, the SR has little effect on the variance of the particles’ PDF in the spanwise direction when the mixing layer is fully developed. (Ⅱ) During the developing stage of the over-canopy mixing layer, submerged vegetation with higher SR gain a stronger upwards (vertical) entrainment capability. The case (SR=60%) has a higher sediment concentration than other cases in the fully developed vertical mixing layer region above canopy. (III) The vertical suspension of particles in the vegetation-side bare channel region is analysed. Particles migrating from the vegetated region are entrained into the vegetation-side bare channel region by turbulent structures. Nevertheless, the vertical concentration profile is more uniform in the vegetated region than in the vegetation-side bare channel at the same streamwise location. The cases SR=40% and 60% still have higher sediment concentrations than other cases in the vegetation-side bare channel’s upper region.

Methods
The datasets are produced mainly based on the numerical simulations, some exprimental data is collected from published literatures.

河岸带与水生植被的生长节律随季节变化。目前学界对冠层淹没比（Submergence-Ratio，SR，即植被株高与水深之比）对悬浮泥沙输运的影响机制仍缺乏充分认知。为此，本研究采用耦合离散相模型（Discrete Phase Method，DPM）的大涡模拟（Large Eddy Simulations，LES）方法，探究部分植被覆盖直渠道内颗粒物的三维分布特征。通过概率密度函数（Probability Density Function，PDF）量化颗粒物的展向分布，并以PDF方差表征颗粒物随时间的非均匀分布特性。主要研究结论如下：
（Ⅰ）随着SR值升高，植被侧混合层对颗粒物的驱离效应在植被区与植被侧裸渠区域的交界面处显著增强；但当混合层充分发展后，SR值对颗粒物展向PDF方差几乎无影响。
（Ⅱ）在冠层上方混合层的发展阶段，较高SR值的淹没型植被具备更强的垂向卷吸能力；当冠层上方垂向混合层充分发展后，SR=60%工况下的泥沙浓度高于其余所有工况。
（Ⅲ）针对植被侧裸渠区域的颗粒物垂向悬浮过程开展分析：从植被区迁移而来的颗粒物通过湍流结构被卷吸至植被侧裸渠区域；但在相同流向位置处，植被区内的垂向浓度剖面相较于植被侧裸渠区域更为均匀；其中SR=40%与SR=60%工况下，植被侧裸渠上部区域的泥沙浓度仍高于其余工况。

研究方法
本数据集主要基于数值模拟实验生成，部分实验数据取自已发表的学术文献。